Wafer-level hermetic micro-device packages
A hermetically sealed micro-device package encapsulating a micro-device and including a transparent window allowing light to pass into and out of a cavity containing the micro-device comprises a semiconductor substrate having a micro-device operably disposed thereupon. The substrate has a first frame-attachment area formed thereupon having a plan that circumscribes the micro-device. A sheet of transparent material has a window aperture portion defined thereupon, the sheet having a second frame-attachment area formed thereupon having a plan that circumscribes the window aperture portion. A frame/spacer is positioned between, and hermetically bonded to, the semiconductor substrate and the transparent sheet, the frame/spacer including a continuous sidewall having a plan on one side substantially corresponding to, and substantially in register with, the plan of the first frame-attachment area, having a plan on the opposite side substantially corresponding to, and substantially in register with, the plan of the second frame-attachment area, and having a height that exceeds the height of the micro-device.
This application is a Divisional of U.S. patent application Ser. No. 10/713,475 filed Nov. 14, 2003, which is a Continuation-In-Part of U.S. patent application Ser. No. 10/133,049 filed Apr. 26, 2002, now U.S. Pat. No. 6,723,379, which is a Continuation-In-Part of U.S. patent application Ser. No. 10/104,315 filed Mar. 22, 2002, now U.S. Pat. No. 6,627,814.
TECHNICAL FIELD OF THE INVENTIONThe current invention relates to packages for photonic devices, optical devices, micro-mechanical devices, micro-electromechanical systems (MEMS) devices or micro-optoelectromechanical systems (MOEMS) devices, and more particularly, to manufacturing hermetic packages having a transparent window at the wafer level or substrate level of device fabrication.
BACKGROUND OF THE INVENTIONPhotonic, photovoltaic, optical and micro-mechanical devices are typically packaged such that the active elements (i.e., the emitters, receivers, micro-mirrors, etc.) are disposed within a sealed chamber to protect them from handling and other environmental hazards. In many cases, it is preferred that the chamber be hermetically sealed to prevent the influx, egress or exchange of gasses between the chamber and the environment. Of course, a window must be provided to allow light or other electromagnetic energy of the desired wavelength to enter and/or leave the package. In some cases, the window will be visibly transparent, e.g. if visible light is involved, but in other cases the window may be visibly opaque while still being “optically” transparent to electromagnetic energy of the desired wavelengths. In many cases, the window is given certain optical properties to enhance the performance of the device. For example, a glass window may be ground and polished to achieve certain curve or flatness specifications in order to disperse in a particular pattern and/or avoid distorting the light passing therethrough. In other cases, anti-reflective or anti-refractive coatings may be applied to the window to improve light transmission therethrough.
Hermetically sealed micro-device packages with windows have heretofore typically been produced using cover assemblies with metal frames and glass window panes. To achieve the required hermetic seal, the glass window pane (or other transparent window material) has heretofore been fused to its metallic frame by one of several methods. A first of these methods is heating it in a furnace at a temperature exceeding the window's glass transition temperature, TG and/or the window's softening temperature TS (typically at or above 900° C.). However, because the fusing temperature is above TG or TS, the original surface finish of the glass pane is typically ruined, making it necessary to finish or re-finish (e.g., grinding and polishing) both surfaces of the window pane after fusing in order to obtain the necessary optical characteristics. This polishing of the window panes requires additional process steps during manufacture of the cover assemblies, which steps tend to be relatively time and labor intensive, thus adding significantly to the cost of the cover assembly, and hence to the cost of the overall package. In addition, the need to polish both sides of the glass after fusing requires the glass to project both above and below the attached frame. This restricts the design options for the cover assembly with respect to glass thickness, dimensions, etc., which can also result in increased material costs.
A second method to hermetically attach a transparent window to a frame is to solder the two items together using a separate preform made of a metal or metal-alloy solder material. The solder preform is placed between a pre-metallized window and a metal or metallized frame, and the soldering is performed in a furnace. During soldering, no significant pressure is applied, i.e., the parts are held together with only enough force to keep them in place. For this type of soldering, the most common solder preform material is eutectic gold-tin.
Eutectic gold-tin solder melts and solidifies at 280° C. Its CTE at 20° is 16 ppm/° C. These two characteristics cause three drawbacks to the reliability of the assembled window. First, the CTE of Mil-Spec kovar from 280° C. to ambient is approximately 5.15 +/−0.2 ppm/0 C., while most window glasses intended for sealing to kovar have higher average CTEs over the same temperature range. During cooling from the set point of 280° down to ambient, the glass is shrinking at a greater rate than the kovar frame it's attached to. The cooled glass will be in tension, which is why it is prone to cracking. To avoid cracking, the glass should have an identical or slightly lower average CTE than the kovar so as to be stress neutral or in slight compression after cooling. Using solders with lower liquidus/solidus temperatures puts the kovar at a higher average CTE, more closely matching the average CTE of the glass. However, this worsens the second drawback of metal-allow solder seals.
The second drawback to soldering the glass to the kovar frame is that the window assembly will delaminate at temperatures above the liquidus temperature of the employed solder. Using lower liquidus/solidus temperature solders, while reducing the CTE mismatch between the kovar and glass, further limits the applications for the window assembly. Most lead-free solders have higher liquidus/solidus temperatures than the 183° C. of eutectic Sn/Pb. Surface-Mount Technology (SMT) reflow ovens are profiled to heat Printed-Wiring Board (PWB) assemblies 15-20 degrees above the solder's liquidus/solidus temperature. So the SMT reflow-soldering attachment to a PWB of a MOEMS device whose window was manufactured using lower melting-point solder preforms might have the unfortunate effect of reflowing the window assembly's solder, causing window delamination.
The third drawback is that the solder, which is the intermediate layer between the glass and the kovar frame, has a CTE up to three times greater than the two materials it's joining. An intermediate joining material would ideally have a compensating CTE in-between the two materials it's bonding.
A third method to hermetically attach a glass window to a frame is to solder the two items together using a solder-glass material. Solder-glasses are special glasses with a particularly low softening point. They are used to join glass to other glasses, ceramics, or metals without thermally damaging the materials to be joined. Soldering is carried out in the viscosity range h where h is the range from 104 to 106 dPa s (poise) for the solder-glass; this corresponds generally to a temperature range T (for the glass solder or solder-glass) within the range from 350° C. to 700° C.
Once a cover assembly with a hermetically sealed window is prepared, it is typically seam welded to the device base (i.e., substrate) in order to produce the finished hermetically sealed package. Seam welding uses a precisely applied AC current to produce localized temperatures of about 1,100° C. at the frame/base junction, thereby welding the metallic cover assembly to the package base and forming a hermetic seal. To prevent distortion of the glass windowpane or package, the metal frame of the cover assembly should be fabricated from metal or metal alloy having a CTE (i.e., coefficient of thermal expansion) that is similar to that of the transparent window material and to the CTE of the package base.
While the methods described above have heretofore produced useable window assemblies for hermetically sealed micro-device packages, the relatively high cost of these window assemblies is a significant obstacle to their widespread application. A need therefore exists, for package and component designs and assembly methods which reduce the labor costs associated with producing each package.
A need still further exists for package and component designs and assembly methods that will minimize the manufacturing cycle time required to produce a completed package.
A need still further exists for package and component designs and assembly methods that reduce the number of process steps required for the production of each package. It will be appreciated that reducing the number of process steps will reduce the overhead/floor space required in the production facility, the amount of capital equipment necessary for manufacturing, and handling costs associated with transferring the work pieces between various steps in the process. A reduction in the cost of labor may also result. Such reductions would, of course, further reduce the cost of producing these hermetic packages.
A need still further exists for package and component designs and assembly methods that will reduce the overall materials costs associated with each package, either by reducing the initial material cost, by reducing the amount of wastage or loss during production, or both.
SUMMARY OF THE INVENTIONThe present invention disclosed and claimed herein comprises, in one aspect thereof, a hermetically sealed micro-device package encapsulating a micro-device. The package includes a transparent window allowing light to pass into and out of a cavity containing the micro-device. The micro-device package comprises a semiconductor substrate, a sheet of transparent material and a frame/spacer. The semiconductor substrate has a micro-device operably disposed thereupon, and also a first frame-attachment area is formed thereupon having a plan that circumscribes the micro-device. The sheet of transparent material has a window aperture portion defined thereupon, and also has a second frame-attachment area formed thereupon having a plan that circumscribes the window aperture portion. The frame/spacer is positioned between, and hermetically bonded to, the semiconductor substrate and the transparent sheet. The frame/spacer includes a continuous sidewall having a plan on one side substantially corresponding to, and substantially in register with, the plan of the first frame-attachment area, a plan on the opposite side substantially corresponding to, and substantially in register with, the plan of the second frame-attachment area, and a height that exceeds the height of the micro-device.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring now to
Referring now to
The sheet 304 has a window portion 312 defined thereupon, i.e., this is the portion of the sheet 302 which must remain transparent to allow for the proper functioning of the encapsulated, i.e., packaged, micro-device 112. The window portion 312 of the sheet has top and bottom surfaces 314 and 316, respectively, that are optically finished in the preferred embodiment. The sheet 304 is preferably obtained with the top and bottom surfaces 314 and 316 of the window portion 312 in ready to use form, however, if necessary the material may be ground and polished or otherwise shaped to the desired surface contour and finish as a preliminary step of the manufacturing process. While in many cases the window portion 312 will have top and bottom surfaces of 314 and 316 that are optically flat and parallel to one another, it will be appreciated that in other embodiments at least one of the finished surfaces of the window portion will be contoured. A sheet seal-ring area 318 (denoted with cross-hatching) circumscribes the window portion 312 of the sheet 304, and provides a suitable surface for joining to the front seal-ring area 310.
Referring now to
In many applications, it is desirable that window portion 312 of the sheet 304 have enhanced optical or physical properties. To achieve these properties, surface treatments or coatings maybe applied to the sheet 304 prior to or during the assembly process. For example, the sheet 304 maybe treated with siliconoxynitride (SiOn) to provide a harder surface on the window material. Whether or not treated with SiOn, the sheet 304 may be coated with a scratch resistant/abrasion resistant material such as amorphous diamond-like carbon (DLC) such as that sold by Diamonex, Inc., under the name Diamond Shield®. Other coatings which may be applied in addition to, or instead of, the SiOn or diamond-like carbon include, but are not limited to, optical coatings, anti-reflective coatings, refractive coatings, achromatic coatings, optical filters, solar energy filters or reflectors, electromagnetic interference (EMI) and radio frequency (RF) filters of the type known for use on lenses, windows and other optical elements. It will be appreciated that the optical coatings and/or surface treatments can be applied either on the top surface 314 or the bottom surface 316, or in combination on both surfaces, of the window portion 312. It will be further appreciated, that the optical coatings and treatments just described are not illustrated in the figures due to their transparent nature.
In some applications, a visible aperture is formed around the window portion 312 of the sheet 304 by first depositing a layer of non-transparent material, e.g., chromium (Cr), sometimes coating the material over the entire surface of the sheet and then etching the non-transparent material from the desired aperture area. This procedure provides a sharply defined border to the window portion 312 which is desirable in some applications. This operation may be performed prior to or after the application of other treatments depending on the compatibility and processing economics.
The next step of the process of manufacturing the cover assembly 300 is to prepare the sheet seal-ring area 318 for metallization. The sheet seal-ring area 318 circumscribes the window portion 312 of the sheet 304, and for single aperture covers is typically disposed about the perimeter of the bottom surface 316. It will be appreciated, however, that in some embodiments the sheet seal-ring area 318 can be located in the interior portion of a sheet, for example where the sheet will be diced to form multiple cover assemblies (i.e., as described later herein). The sheet seal-ring area 318 generally has a configuration which closely matches the configuration of the frame seal-ring area 310 to which it will eventually be joined. Preparing the sheet seal-ring area 318 may involve a thorough cleaning to remove any greases, oils or other contaminants from the surface, and/or it may involve roughening the seal-ring area by chemical etching, laser ablating, mechanical grinding or sandblasting this area. This roughening increases the surface area of the sheet seal-ring, thereby providing increased adhesion for the subsequently deposited metallization materials, if the sheet seal-ring is to be metallized prior to joining to the frame seal-ring area 310 or to other substrates or device package bases.
Referring now to
It will be appreciated that it may be necessary or desirable to protect the finished surfaces 314 and/or 316 in the window portion 312 of the sheet (e.g., the portions that will be optically active in the finished cover assembly) from damage during the roughening process. If so, the surfaces 314 and/or 316 may be covered with semiconductor-grade “tacky tape” or other known masking materials prior to roughening. The mask material must, of course, be removed in areas where the etching/grinding will take place. Sandblasting is probably the most economical method of selectively removing strips of tape or masking material in the regions that will be roughened. If sandblasting is used, it could simultaneously perform the tape removal operation and the roughening of the underlying sheet.
Referring now to
A fourth option for metallizing the sheet seal-ring area 318 of the sheet 304 is so-called cold-gas dynamic spray technology, also known as “cold-spray”. This technology involves the spraying of powdered metals, alloys, or mixtures of metal and alloys onto an article using a jet of high velocity gas to form continuous metallic coating at temperatures well below the fusing temperatures of the powdered material. Details of the cold-gas dynamic spray deposition technology are disclosed in U.S. Pat. No. 5,302,414 to Alkhimov et al. It has been determined that aluminum provides good results when applied to glass using the cold-gas dynamic spray deposition. The aluminum layer adheres extremely well to the glass and may create a chemical bond in the form of aluminum silicate. However, other materials may also be applied as a first layer using cold-spray, including tin, zinc, silver and gold. Since the cold-gas dynamic spray technology can be used at low temperatures (e.g., near room temperature), it is suitable for metallizing materials having a relatively low melting point, such as polycarbonates or other plastics, as well as for metallizing conventional materials such as glass, alumina, and ceramics.
For the initial metallic layer deposited on the sheet 304, it is believed that any of chromium, nickel, aluminum, tin, tin-bismuth alloy, gold, gold-tin alloy can be used, this list being given in what is believed to be the order of increasing adhesion to glass. Other materials might also be appropriate. Any of these materials can be applied to the sheet seal-ring area 318 using any of the CVD or PVD technologies (e.g., sputtering) previously described. After the initial layer 602 is deposited onto the sheet seal-ring area 318 of the nonmetallic sheet 304, additional metal layers, e.g., second layer 604, third layer 606 and fourth layer 608 (as applicable) can be added by any of the deposition methods previously described, including solution bath plating. It is believed that the application of the following rules will result in satisfactory thicknesses for the various metal layers. Rule No. 1: the minimum thickness, except for the aluminum or tin-based metals or alloys which will be bonded to the gold-plated Kovar alloy frame: 0.002 microns. Rule 2: the minimum thickness for aluminum or tin-based metals or alloys deposited onto the sheet or as the final layer, which will be bonded to the gold-plated Kovar alloy frame: 0.8 microns. Rule 3: the maximum thickness for aluminum ortin-based metals or alloys deposited onto the sheet or as the final layer, which will be bonded to the gold-plated Kovar alloy frame: 63.5 microns. Rule 4: the maximum thickness for metals, other than chromium, deposited onto the sheet as the first layer and which will have other metals or alloys deposited on top of them: 25 microns. Rule 5: the maximum thickness for metals, other than chromium, deposited onto other metals or alloys as intermediate layers: 6.35 microns. Rule 6: the minimum thickness for metals or alloys deposited onto the sheet or as the final layer, which will act as the solder for attachment to the gold-plated Kovar alloy frame: 7.62 microns. Rule 7: the maximum thickness for metals or alloys deposited onto the sheet or as the final layer, which will act as the solder for attachment to the gold-plated Kovar alloy frame: 101.6 microns. Rule 8: the maximum thickness for chromium: 0.25 microns. Rule 9: the minimum thickness for gold-tin solder, applied via inkjet or supplied as a solder preform: 6 microns. Rule 10: the maximum thickness for gold-tin solder, applied via inkjet or supplied as a solder preform: 101.6 microns. Rule 11: The minimum thickness for immersion zinc; 0.889 microns. Note that the above rules apply to metals deposited using all deposition methods other than cold-gas dynamic spray deposition.
For cold spray applications, the following rules apply: Rule 1: the minimum practical thickness for any metal layer: 2.54 microns. Rule 2: the maximum practical thickness for the first layer, and all additional layers, but not including the final Kovar alloy layer: 127 microns. Rule 3: the maximum practical thickness for the final Kovar alloy layer: 12,700 microns, i.e., 0.5 inches.
By way of example, not to be considered limiting, the following metal combinations are believed suitable for seal-ring area 318 when bonding the prepared sheet 304 to a Kovar alloy-nickel-gold frame 302 (i.e., Kovar alloy core plated first with nickel and then with gold) using thermal compression (TC) bonding, or sonic, ultrasonic or thermosonic bonding.
The assembly sequence can also be to first bond the frame/spacer and window sheet together to form a hermetically sealed window unit, and later, to bond this window unit to the substrate. A third assembly sequence can also be to first bond the frame/spacer and substrate together and later, to bond this substrate/frame/spacer unit to the window. In some instances, an intermediate material, also referred to as an interlayer material, maybe employed between the substrate and the frame/spacer and/or between the frame/spacer and the window sheet. It will be understood that, while the examples described herein are believed suitable for metallizing the seal-ring surface of a sheet or lens prior to bonding in applications where metallization is used, in some other embodiments employing diffusion bonding (i.e., thermal compression bonding), metallization of the seal-ring area on the sheet or lens may be omitted altogether when joining the sheet/lens to the frame or another substrate of the device package base.
EXAMPLE 1
By way of further example, not to be considered limiting, the following metal combinations and thicknesses are preferred for seal-ring area 318 when bonding the prepared sheet 304 to a Kovar alloy-nickel-gold frame 302 using thermal compression (TC) bonding, or sonic, ultrasonic or thermosonic bonding.
EXAMPLE 17
As indicated above, the previous examples are believed suitable for application of, among other processes, thermal compression bonding. TC bonding is a process of diffusion bonding in which two prepared surfaces are brought into intimate contact, and plastic deformation is induced by the combined effect of pressure and temperature, which in turn results in atom movement causing the development of a crystal lattice bridging the gap between facing surfaces and resulting in bonding. TC bonding can take place at significantly lower temperatures than many other forms of bonding such as braze soldering.
Referring now to
Referring still to
In this example, the base seal-ring area 320 is on the frame face opposite frame seal-ring area 310, and may utilize the same layers of nickel 704 overlaid by gold 706 to facilitate eventual welding to the package base 104. In some instances, the gold 706 will not be overlaid on the nickel 704.
In some embodiments, the frame 302 will serve as a “heat sink” and/or “heat spreader” when the cover assembly 300 is eventually welded to the package base 104. It is contemplated that conventional high temperature welding processes (e.g., manual or automatic electrical resistance seam welding or laser welding) may be used for this operation. If the metallized glass sheet 304 were welded directly to the package base 104 using these welding processes, the concentrated heat could cause thermal stresses likely to crack the glass sheet or distort its optical properties. However, when a metal frame is attached to the transparent sheet, it acts as both a heat sink, absorbing some of the heat of welding, and as a heat spreader, distributing the heat over a wider area such that the thermal stress on the transparent sheet 304 is reduced to minimize the likelihood of cracking or optical distortion. Kovar alloy is especially useful in this heat sink and heat spreading role as explained by Kovar alloy's thermal conductivity, 0.0395, which is approximately fourteen times higher than the thermal conductivity of Corning 7052 glass, 0.0028.
Another important aspect of the frame 302 is that it should be formed from a material having a CTE that is similar to the CTE of the transparent sheet 304 and the CTE of the package base 104. This matching of CTE between the frame 302, transparent sheet 304 and package base 104 is beneficial to minimize stresses between these components after they are joined to one another so as to ensure the long term reliability of the hermetic seal therebetween under conditions of thermal cycling and/or thermal shock environments.
For window assemblies that will be attached to package bases formed of ceramic, alumina or Kovar alloy, Kovar alloy is preferred for use as the material for the frame 304. Although Kovar alloy will be used for the frames in many of the embodiments discussed in detail herein, it will be understood that Kovar alloy is not necessarily suitable for use with all transparent sheet materials. Additionally, other frame materials besides Kovar alloy may be suitable for use with glass. Suitability is determined by the desire that the material of the transparent sheet 304, the material of the frame 302 and the material of the package base 104 all have closely matching CTEs to insure maximum long-term reliability of the hermetic seals.
Referring now to
The next step of the manufacturing process is to heat the junction region 804 until a joint is formed between the frame 302 and the sheet 304 all along the junction region, whereby a hermetic seal circumscribing the window portion 312 is formed. It is necessary that during the step of heating the junction region 804, the temperature of the window portion 312 of the sheet 304 remain below its glass transition temperature, TG as well as below the softening temperature of the sheet 304, to prevent damage to the finished surfaces 314 and 316. The softening point for glass is defined as the temperature at which the glass has a viscosity of 107.6 dPa s or 107.6 poise (method of measurement: ISO 7884-3). The current invention contemplates several options for accomplishing this heating. A first option is to utilize thermal compression (TC) bonding, also known as diffusion bonding, including conventional hot press bonding as well as Hot Isostatic Press or Hot Isostatic Processing (HIP) diffusion bonding. As previously described, TC bonding, also known as diffusion bonding involves the application of high pressures to the materials being joined such that a reduced temperature is required to produce the necessary diffusion bond. Rules for determining the thickness and composition of the metallic layers 610 on the sheet 304 were previously provided, for TC bonding to, e.g., a Kovar alloy, nickel or gold frame such as illustrated in
Alternatively, employing resistance welding at the junction area 804 to add additional heat in addition to the TC bonding could allow preheating the window assemblies to less than 380° C. and possibly reduce the overall bonding process time. In another method, the TC bonding could be accomplished by fixturing the cover assembly components 302 and 304 using heated tooling that would heat the junction area 304 by conduction. In yet another alternative method, electrical resistance welding can be used to supply 100% of the heat required to achieve the necessary TC bonding temperature, thereby eliminating the need for furnaces, ovens, etc. or specialized thermally conductive tooling.
After completion of TC bonding or other welding processes, the window assembly 300 is ready for final processing, for example, chamfering the edges of the cover assembly to smooth them and prevent chipping, scratching, marking, etc., during post-assembly, cleaning, marking or other operations. In some instances, the final processing may include the application of a variety coatings to the window and/or to the frame.
Referring now to
Block 904 represents the step of applying surface treatments to the sheet, e.g., scratch-resistant or anti-reflective coatings, as previously described. In addition to these permanent surface treatments, block 904 also represents the sub-steps of applying tape or other temporary masks to the surfaces of the sheet to protect them during the subsequent steps of the process. It will be appreciated that the steps represented by block 904 are optional and that one or more of these steps may not be present in every embodiment of the invention. The process then proceeds to block 906 as indicated by the arrow.
Block 906 represents the step of preparing the seal-ring area on the sheet to provide better adhesion for the metallic layers, if such metallic layers are used. This step usually involves roughening the seal-ring area using chemical etching, mechanical grinding, laser ablating or sandblasting as previously described. To the extent necessary, block 906 also represents the sub-steps of removing any masking material from the seal-ring area. Block 906 further represents the optional steps of cleaning the sheet (or at least the seal-ring area of the sheet) to remove any greases, oils or other contaminants from the surface of the sheet. As previously discussed, such cleaning steps may be performed regardless of whether the seal-ring area is to be metallized (i.e., to promote better adhesion of the metallic layers) or is to be left unmetallized (i.e., to promote better diffusion bonding of the unmetallized sheet). It will be appreciated that the steps represented by block 906 are optional and that some or all of these steps may not be present in every embodiment of the invention. The process then proceeds to block 908 as indicated by the arrow.
Block 908 represents the step of metallizing the seal-ring areas of the sheet. The step represented by block 908 is mandatory only when the desired bond of sheet 304 to frame 302 is a metal-to-metal bond since at least one metallic layer must be applied to the seal-ring area of the sheet. It is possible, for instance by use of diffusion bonding processes, to bond the sheet 304 to frame 302 without first metallizing sheet 304. In most embodiments, block 908 will represent numerous sub-steps for applying successive metallic layers to the sheet, where the layers of each sub-step may be applied by processes including CVD, PVD, cold-spray or solution bath plating as previously described. Following the steps represented by block 908, the sheet is ready for joining to the frame. However, before the process can proceed to this joining step (i.e., block 916), a suitable frame must first be prepared.
Block 910 represents the step of obtaining a pre-fabricated frame, preferably having a CTE that closely matches the CTE of the transparent sheet from block 902 and the CTE of the package base. In most cases where the base is alumina or Kovar alloy, a frame formed of Kovar alloy will be suitable. As previously described, the frame may be formed using, e.g., stamping, die-casting or other known metal-forming processes. The process then proceeds to block 912 as indicated by the arrow.
Block 912 represents the step of grinding, polishing and/or otherwise flattening the seal-ring areas of the frame as necessary to increase its flatness so that it will fit closely against the seal-ring areas of the transparent sheet. It will be appreciated that the steps represented by block 912 are optional and may not be necessary or present in every embodiment of the invention. The process then proceeds to block 914 as indicated by the arrow.
Block 914 represents the step of applying additional metallic layers to the seal-ring areas of the frame. These metallic layers are sometimes necessary to achieve compatible chemistry for bonding with the metallized seal-ring areas of the transparent sheet. In most embodiments, block 914 will represent numerous sub-steps for applying successive metallic layers to the frame. Block 914 further represents the optional steps of cleaning the frame (or at least the seal-ring area of the frame) to remove any greases, oils or other contaminants from the surface of the frame. As previously discussed, such cleaning steps may be performed regardless of whether the seal-ring area of the frame is to be metallized with additional metal layers or is to be used without additional metallization. Once the steps represented by block 914 are completed, the frame is ready for joining to the transparent sheet. Thus, the results of process block 908 and block 914 both proceed to block 916 as indicated by the arrows.
Block 916 represents the step of clamping the prepared frame together with the prepared transparent sheet so that their respective metallized seal-ring areas are in contact with one another under conditions producing a predetermined contact pressure at the junction region circumscribing the window portion. This predetermined contact pressure between the seal-ring surfaces allows thermal compression (TC) bonding of the metallized surfaces to occur at a lower temperature than would be required for conventional welding (including most soldering and brazing processes). The process then proceeds to block 918 as indicated by the arrow.
Block 918 represents the step of applying heat to the junction between the frame and the transparent sheet while maintaining the predetermined contact pressure until the temperature is sufficient to cause thermal compression bonding to occur. In some embodiments, block 918 will represent a single heating step, e.g., heating the fixtured assembly in a furnace. In other embodiments, block 918 will represent several sub-steps for applying heat to the junction area, for example, first preheating the fixtured assembly (e.g., in a furnace) to an intermediate temperature, and then using resistance welding techniques along the junction to raise the temperature of the localized area of the metallic layers the rest of the way to the temperature where thermal compression bonding will occur. The thermal compression bonding creates a hermetic seal between the transparent sheet material and the frame. The process then proceeds to block 920 as indicated by the arrow.
In the illustrated example, metallized seal-ring areas arejoined using diffusion bonding/thermal compression bonding in which the predetermined pressure is applied first (block 916) and the heat is applied second (block 918). It will be appreciated, however, that the use of diffusion bonding is not limited to these specific conditions. In some other embodiments, the sheet and/or frame may not be metallized prior to bonding. In still other embodiments, the heat may be applied first until the desired bonding temperature is reached, and the predetermined pressure may be applied thereafter until the diffusion bond is formed. In yet additional embodiments, the heat and pressure may be applied simultaneously until the diffusion bond is formed.
Block 920 represents the step of completing the window assembly. Block 920 may represent merely cooling the window assembly after thermal compression bonding, or it may represent additional finishing processes including chamfering the edges of the assembly to prevent chipping, cracking, etc., marking the assembly, coating the window and/or the frame with one or more materials, or other post-assembly procedures. The process of this embodiment has thus been described.
It will be appreciated that in alternative embodiments of the invention, conventional welding techniques (including soldering and/or brazing) may be used instead of thermal compression bonding to join the frame to the transparent sheet. In such alternative embodiments, the steps represented by blocks 916 and 918 of
In an alternative embodiment, braze-soldering is used to join the frame 302 to the metallized sheet 304. In this embodiment, a solder metal or solder alloy may be utilized as the final layer of the metallic layers 610 on the metallized sheet 304, and clamping the sheet 304 to the frame 302 at a high predetermined contact pressure is not required. A solder metal or solder alloy preform may be utilized as a separate, intermediate item between the frame 302 and the sheet 304 instead of having a solder metal or solder alloy as the final layer of the metallic layers 610 on the metallized sheet 304. Light to moderate clamping pressure can be used: 1) to insure alignment during the solder's molten phase; and 2) to promote even distribution of the molten solder all along the junction region between the respective seal-ring areas; thereby helping to insure a hermetic seal, however, this clamping pressure does not contribute to the bonding process itself as in TC bonding. In most other respects, however, this embodiment is substantially similar to that previously described.
The following examples, not to be considered limiting, are provided to illustrate the details of the metallic layers 610 in the sheet seal-ring area 318 that are suitable for braze-soldering to a Kovar alloy/nickel/gold frame 302 such as that illustrated in
While numerous examples herein show the use of eutectic Au—Sn, other applications may utilize non-eutectic Au—Sn, or other eutectic or non-eutectic solders for attaching the window. This allows subsequent use of a higher melting temperature solder to attach the unit to a higher level assembly without melting the window bond.
By way of further examples, not to be considered limiting, the following combinations are preferred for the metallic layers 610 in the sheet seal-ring area 318 for braze-soldering to a Kovar alloy/nickel/gold frame 302 such as that illustrated in
Referring now to
In this embodiment, when the preform solder 1000 is used for braze-soldering to hermetically join the transparent sheet 304 to the frame 302, instead of positioning the frame and the sheet directly against one another, the frame 302 and the sheet 304 are instead positioned against opposite sides of the solder preform 1000 such that the solder preform is interposed between the frame seal-ring area 310 and the sheet seal-ring are 318 along a continuous junction region that circumscribes the window portion 312. After the frame 302 and sheet 304 are positioned against the solder preform 1000, the junction region is heated until the solder preform fuses forming a solder joint between the frame and sheet all along the junction region. The heating of the junction region may be performed by any of the procedures previously described, including heating or preheating in a furnace, oven, etc., either alone or in combination with other heating methods including resistance welding. It is required that during the step of heating the junction region, the temperature of the window portion 312 of the sheet 304 remain below the glass transition temperature TG and the softening temperature such that the finished surfaces 314 and 316 on the sheet are not adversely affected.
The current embodiment using a solder preform 1000 can be used for joining a metallized sheet 304 to a Kovar alloy/nickel/gold frame such as that illustrated in
The following examples, not to be considered limiting, are provided to illustrate the details of the metallic layers 610 and the sheet seal-ring area 318 that are suitable for braze-soldering to a Kovar alloy/nickel/gold frame in combination with a gold-tin solder preform or other suitable solder alloy preforms, including, but not limited to tin-copper-silver alloys.
EXAMPLE 61
By way of further examples, not to be considered limiting, the following combinations are preferred for the metallic layers 610 and the sheet seal-ring area 318 for braze-soldering to a Kovar alloy/nickel/gold frame in combination with a gold-tin soldered preform. In addition to having a frame of Kovar alloy/nickel/gold, materials other than kovar may be employed as the frame's base material and the overlying layer or layers may be nickel without the gold, or combinations of two or more metals including, but not limited to nickel and gold.
EXAMPLE 76
Referring now to
embodiments, the inkjet deposited material, which may or may not be solder, may be used to create an innerlayer or interlay preform that would be employed for use in TC bonding or HIP diffusion bonding as described in previous examples herein. Details of the metallic layers 610 in the sheet seal-ring area 318 that are suitable for a soldering to a Kovar alloy/nickel/gold frame 302 such as that illustrated in
Referring now to
Referring specifically to
It will be appreciated that, unless specifically noted otherwise, the initial steps of obtaining a transparent sheet having a window portion with finished top and bottom surfaces, preparing the seal-ring area of the sheet and metallizing the seal-ring area of the sheet are substantially identical to those described for the previous embodiments and will not be described in detail again.
Referring now also to
Referring now also to
Referring now to
The following examples, not to be considered limiting, are provided to illustrate the details of the metallic layers, denoted collectively by reference numeral 1207 for forming a frame/heat spreader compatible with hard glass transparent sheets and Kovar alloy or ceramic package bases. The deposition of materials other than Kovar alloy may be used as the final layer whenever Kovar Alloy is indicated as the final layer, depending upon the characteristics of the transparent sheet 304 and of the package base 104, especially their respective CTEs.
EXAMPLE 91
By way of further examples, not to be considered limiting, the following combinations are preferred for the metallic layers 1207 for forming a frame/heat spreader compatible with hard glass transparent sheets and Kovar or other alloys or ceramic package bases. The deposition of materials other than Kovar alloy may be used as the final layer whenever Kovar Alloy is indicated as the final layer, depending upon the characteristics of the transparent sheet 304 and of the package base 104, especially their respective CTEs.
EXAMPLE 103
After the deposition of the metal layers using the cold gas dynamic spray deposition, it may be necessary to grind or shape the top surface of the built-up frame 1212 to a predetermined flatness before performing additional steps to ensure that a good contact will be made in later bonding. Another process which may be used, either alone or in combination with shaping the top surface of the built-up frame, is the depositing of additional metal layers onto the built-up frame/heat spreader 1212 using solution bath plating. The most common reason for such plated layers is to promote a good bonding when the frame/heat spreader is adjoined to the package base 104. In a preferred embodiment, the additional metallic layers applied to the built-up frame 1212 include a layer of nickel directly over the cold gas dynamic spray deposited metal having a thickness within the range of about 0.002 microns to about 25 microns and, in some instances, then solution bath plating a layer of gold over the nickel layer until the gold layer has a thickness within the range from about 0.0508 microns to about 0.508 microns.
Referring now to
The next step of the process is to use cold gas dynamic spray deposition to deposit frame/heat spreader metal onto any previously deposited metal layers in the frame attachment area 1200. This step is represented by block 1410. As previously described in connection with
The cold spraying of the powdered heat spreader material is continued until the new layer 1206 reaches the thickness required to serve as a heat spreader/integral frame. This would represent the end of the process represented by block 1410. For some applications, the built-up heat spreader/frame 1212 is now complete and ready for use. For other applications, however, performing further finishing operations on the heat spreader/frame 1212 may be desirable.
For example, it is known that significant residual stresses maybe encountered in metal structures deposited using cold-gas dynamic spray technology as a result of the mechanics of the spray process. These stresses may make the resulting structure prone to dimensional changes, cracking or other stress-related problems during later use. Annealing by controlled heating and cooling is known to reduce or eliminate residual stresses. Thus, in some applications, the integral heat spreader/frame 1212 is annealed following its deposition on the sheet 304. This optional step is represented by block 1411 in
It will be appreciated that there are flatness requirements for the sealing surface at the “top” of the heat spreader (which is actually projecting from the bottom surface 316 of the sheet). If these flatness requirements are not met via the application of the heat spreader material by the cold spray process, it will be necessary to flatten the sealing surface at the next step of the process. This step is represented by block 1412 in
Finally, as previously described, in some embodiments additional metal layers are plated onto the integral frame/heat spreader 1212. These optional plating operations, such as solution bath plating layers of nickel and gold onto a Kovar alloy frame, are represented by block 1414 in
Referring now to
Further regarding the multi-aperture frames illustrated in
Except for the details just described, the multiple-aperture frame 1502 of this embodiment shares material, fabrication and design details with the single aperture frame 302 previously described. In this regard, a preferred embodiment of the frame 1502 is primarily formed of Kovar alloy or similar materials and more preferably, will have a Kovar alloy core with a surface layer of gold overlaying an intermediate layer of nickel as previously described.
The transparent sheet 1504 for the multi-unit assembly can be formed from any type of transparent material as previously discussed for sheet 304. In this embodiment, however, the sheet 1504 has a plurality of window portions 1512 defined thereupon, with each window portion having finished top and bottom surface 1514 and 1516, respectively. A plurality of sheet seal-ring areas 1518 are denoted by cross-hatching surrounding each window portion in
The next step of the process of manufacturing the multi-unit assembly 1500 is to prepare the sheet seal-ring areas 1518 for metallization. As noted earlier, each sheet seal-ring area 1518 circumscribes a window portion of the sheet 1504. The sheet seal-ring areas 1518 typically have a configuration which closely matches the configuration of the frame seal-ring areas 1510 to which they will eventually be joined. It will be appreciated, however, that in some cases other considerations will affect the configuration of the frame grid, e.g., when electrical resistance heating is used to produce bonding, then the seal-ring areas 1518 must be connected to form the appropriate circuits. The steps of preparing the sheet seal-ring areas 1518 for metallization is substantially identical to the steps and options presented during discussion of preparing the frame seal-ring area 310 on the single aperture frame 302. Thus, at a minimum, preparing the sheet seal-ring area 1518 typically involves a thorough (e.g., plasma, solvent or detergent) cleaning to remove any contaminants from the surfaces and typically also involves roughening the seal-ring area by chemical etching, laser ablating, mechanical grinding or sandblasting this area.
The step of metallizing the prepared sheet seal-ring areas 1510 of the sheet 1502 are substantially identical to the steps described for metallizing the frame seal-ring area 310 on the single aperture frame 302. For example, the metal layers shown in Examples 1 through 120 can be used in connection with thermal compression bonding, for soldering where the solder material is plated onto the sheet as a final metallic layer, and can be used in connection with soldering in combination with a separate gold-tin of solder preform and also for soldering in connection with solders deposited or formed using inkjet technology.
The next step of the process is to position the frame 1502 against the sheet 1504 (it being understood that solder preforms or solder layers would be interposed between the frame and the sheet if braze soldering is used to join the frame 1502 to the sheet 1504) such that each of the window portions 1512 overlays one of the frame apertures 1508, and that for each such window portion/frame aperture combination, at least a portion of the associated frame seal-ring area 1510 and at least a portion of the associated sheet seal-ring area 1518 contact one another along a continuous junction region that circumscribes the associated window portion. This operation is generally analogous to the steps of positioning the frame against the sheet in the single aperture embodiment previously described. If diffusion bonding is used to join the frame 1502 to the sheet 1504, an interlayer or innerlayer between the frame 1502 to the sheet 1504 may or may not be employed.
Referring now to
The next step of the process is heating all of the junction regions until a metal-to-metal joint is formed between the frame 1502 and the sheet 1504 all along each junction region, thus creating the multi-unit assembly 1500 having a hermetic frame/sheet seal circumscribing each window portion 1512. If diffusion bonding is used to join the frame 1502 and the sheet 1504, the bond could be between the outermost metal layer of the frame and the non-metallized sheet 1504. It will be appreciated that any of the heating technologies previously described for joining the single aperture frame 302 to the single sheet 304 are applicable to joining the multi-aperture frame 1502 to the corresponding multi-window sheet 1504.
Referring now to
Referring now to
The next step in this process is metallizing the prepared frame attachment areas on the sheet, i.e., this metallization may be performed using a cold gas dynamic spray technology or where the layers are relatively thin, using a CVD, physical vapor deposition or other conventional metal deposition techniques. It will be appreciated that the primary purpose of this step is to apply metal layers necessary to obtain good adhesion to the transparent sheet 1704 and/or to meet the metallurgical requirements for corrosion prevention, etc.
Referring now to
The next step of the process which, while not required is strongly preferred, is to flatten, if necessary, the seal-ring area 1726 of the sprayed-on frame 1722 to meet the flatness requirements for joining it to the package base 104. This flattening can be accomplished by mechanical means, e.g., grinding, lapping, polishing, etc., or by other techniques such as laser ablation.
The next step of the process, which, while not required, is strongly preferred, is to add additional metallic layers, e.g., a nickel layer and preferably also a gold layer, to the seal-ring area 1726 of the sprayed-on frame 1722 to facilitate welding the cover assembly to the package base 104. These metallic layers are preferably added using a solution bath plating process, e.g., solution bath plating, although other techniques may be used.
The next step of the process is dividing the multi-unit assembly 1700 along each frame wall section common between two window portions 1712 while, at the same time, preserving and maintaining the hermetic seal circumscribing each window portion. After dividing the multi-unit 1700, a plurality of single aperture cover assemblies 1728 (shown in broken line) will be produced, each one being substantially identical to the single aperture cover assemblies produced using the method described in
As previously described, heating the junction region between the metallized seal-ring area of the transparent sheet and the seal-ring area of the frame is required for forming the hermetic seal therebetween. Also as previously described, this heating may be accomplished using a furnace, oven, or various electrical heating techniques, including electrical resistance heating (ERH). Referring now to
Referring first to
Referring now to
Referring now to
After bonding the sheet 1804 to the frame 1802 to form the multi-unit assembly, the sheet electrode portion 1830 and the frame electrode portion 1834 can be cut away and discarded, having served their function of providing electrical access for external electrodes (or other electrical supply members) to the metallized seal-ring areas of the sheet and frame, respectively. The removal of these “sacrificial” electrode portions 1830 and 1834 may occur before or during the “dicing” process step, i.e., the separating of the multi-unit assembly into individual cover assemblies. It will be appreciated that any of the technologies previously described herein for separating a multi-unit assembly into individual cover assemblies can be used for the dicing step of separating a multi-unit assembly fabricated using ERH heating.
Where ERH is to be used for manufacturing multiple cover assemblies simultaneously, the configuration of the sheet-window/frame-grid array and/or the placement of the electrodes portions within the sheet-window/frame-grid array may be selected to modify the flow of current through the junction region during heating. The primary type of modification is to even the flow of current through the various portions of the sheet-window/frame-grid during heating to produce more even temperatures, i.e., to avoid “hot spots” or “cold spots.”
Referring now to
Referring to
It will be understood that a metal frame such as 1802 or 1902, which may contain one or more added layers on its exterior, including but not limited to metal or metal alloy layers, may be diffusion bonded to a non-metallized sheet using ERH techniques to apply heat to the frame. The amount of temperature rise throughout the thickness of the non-metallized sheet will depend on the intensity and duration of the application of the electrical power (voltage and amperage) to the frame, as well as other factors. An innerlayer or interlayer material may be employed between the frame and the sheet during the diffusion bonding process, as discussed previously.
It will further be appreciated that the terms “thermal compression bonding” (and its abbreviation “TC bonding”) and “diffusion bonding” are used interchangeably throughout this application. The term “diffusion bonding” is preferred by metallurgists while the term “thermal compression bonding” is preferred in many industries (e.g., semiconductor manufacturing) to avoid possible confusion with other types of “diffusion” processes used for creating semiconductor devices. Regardless of which term is used, as previously discussed, diffusion bonding refers to the family of bonding methods using heat, pressure, specific positive or negative pressure atmospheres and time alone to create a bond between mating surfaces at a temperature below the normal fusing temperature of either mating surface. In other words, neither mating surface is intentionally melted, and no melted filler material is added, nor any chemical adhesives used.
As previously described, diffusion bonding utilizes a combination of elevated heat and pressure to hermetically bond two surfaces together without first causing one or both of the adjoining surfaces to melt (as is the case with conventional soldering, brazing and welding processes). When making optical cover assemblies, wafer level assemblies or other temperature-sensitive articles, it is almost always required that the bonding temperatures remain below some upper limit. For example, in optical cover assemblies, the bonding temperature should be below the TG and the softening temperature, TS, of the sheet material so as not to affect the pre-existing optical characteristics of the sheet. As another example, in wafer level assemblies, the bonding temperature should be below the upper temperature limit for the embedded micro device and/or its operating atmosphere (i.e., the gas environment inside the sealed package). However, the specific temperature and pressure parameters required to produce a hermetic diffusion bond can vary widely depending upon the nature and composition of the two mating surfaces being joined. Therefore, it is possible that some combinations of transparent sheet material (e.g., glass) and frame material (e.g., metals or metallized non-metals), or some combinations of frame materials and substrate materials (e.g., silicon, alumina or metals), will have a diffusion bonding temperature that exceeds the TG and/or the TS of the sheet material, or that exceeds some other temperature limit. In such cases, it might appear that diffusion bonding is unsuitable for use in hermetically joining the components together if the temperature limits are to be followed. In fact, however, it has been discovered that the use of “interlayers,” i.e., intermediate layers of specially selected material, placed between the sheet material and the frame, or between the frame material and the substrate material, can cause hermetic diffusion bonding to take place at a substantially lower temperature than if the same sheet material was bonded directly to the same frame material, or if the same frame material was bonded directly to the same substrate material. Note that the terms “interlayers” and “innerlayers” are used interchangably throughout this application, as both terms may be encountered in the art for the same thing.
A properly matched interlayer improves the strength and hermeticity (i.e., gas tightness or vacuum tightness) of a diffusion bond. Further, it may promote the formation of compatible joints, produce a monolithic bond at lower bonding temperatures, reduce internal stresses within the bond zone, and prevent the formation of extremely stable oxides which interfere with diffusion, especially on the surface of Al, Ti and precipitation-hardened alloys. The interlayer is believed to diffuse into the parent material, thereby raising the melting point of the joint as a whole. Depending upon the materials to be joined by diffusion bonding, the interlayer material could be composed of a metal, a metal alloy, a glass material, a solder glass material including solder glass in tape or sheet form, or other materials. In the diffusion bonding of BT5-1 Ti alloy to Armco iron, an interlayer of molybdenum foil 0.3 mm thick has been used. Reliable glass-to-glass and glass-to-metal bonds are achieved with metal interlayers such as Al, Cu, Kovar, Niobium and Ti in the form of foil, usually not over 0.2 mm thick. The interlayers are typically formed into thin preforms shaped like the seal ring area of the mating surfaces to be joined.
It is important to distinguish the use of diffusion bonding interlayers from the use of conventional solder preforms and other processes previously disclosed. For purposes of this application, an interlayer is a material used between sealing surfaces to promote the diffusion bonding of the surfaces by allowing the respective mating surfaces to diffusion bond to the interlayer rather than directly to one another. For example, with the proper interlayer material, the diffusion bonding temperature for the joint between the sheet material and interlayer material, and for the joint between the interlayer material and the frame material, may be substantially below the diffusion bonding temperature of a joint formed directly between the sheet material and the frame material. Thus, use of the interlayer allows diffusion bonding of the sheet to the frame at a temperature which is substantially below the diffusion bonding temperature that would be necessary for bonding that sheet material and that frame material directly. The hermetic joint is still formed by the diffusion bonding process, i.e., none of the materials involved (the sheet material, the interlayer material nor the frame material) melts during the bonding process. This distinguishes diffusion bonding using interlayers from other processes such as the use of solder preforms in which the solder material actually melts to form the bond between the materials being joined. It is possible to use materials conventionally used for solders, for example, Au—Sn solder preforms, as interlayers for diffusion bonding. However, when used as interlayers they are used for their diffusion bonding properties and not as conventional solders (in which they melt).
The use of interlayers in the production of window assemblies or other packaging may provide additional advantages over and above their use as promoting diffusion bonding. These advantages include interlayers which serve as activators for the mating surfaces. Sometimes the interlayer materials will have a higher ductility in comparison to the base materials. The interlayers may also compensate for stresses which arise when the seal involves materials having different coefficients of thermal expansion or other thermal expansion properties. The interlayers may also accelerate the mass transfer or chemical reaction between the layers. Finally, the interlayers may serve as buffers to prevent the formation of undesirable chemical or metallic phases in the joint between components.
Referring now to
Referring now to
Referring now to
Referring again to
In further embodiments of the current invention, it has been discovered that clean, i.e., unmetallized, glass windows may be directly bonded to frames of Kovar or other metallic materials using diffusion bonding. This is in addition to the diffusion bonding of metallized glass windows to Kovar frames as previously described. Optionally, the direct diffusion bonding of unmetallized glass windows to metallic frames may be enhanced through the use of certain compounds, e.g., molybdenum-manganese, on the frames. Whether the glass is metallized or unmetallized, the diffusion bonding is most commonly performed in a vacuum, however, it may be performed in various other atmospheres. The use of oxidizing atmospheres is typically not required, however, as any resulting oxides tend to be dispersed by pressures encountered in the bonding operation. In still other embodiments, of the invention, diffusion bonding can be used for joining frames made of Kovar and other metallic materials directly to sheets or wafers of semiconductor materials including silicon and gallium arsenide (GaAs).
Since successful diffusion bonding requires the mating surfaces being bonded to be brought into intimate contact with one another, the surface finish characteristics of the mating surfaces may be important parameters of the invention. It is believed that the following mating surface parameters will allow successful diffusion bonding between the mating surfaces of Kovar frames and thin sheet materials including, but not limited to, Kovar to metallized glass, Kovar to clean (i.e., unmetallized) glass, Kovar to metallized silicon, Kovar to clean (i.e., unmetallized) silicon, Kovar to metallized gallium arsenide (GaAs) and Kovar to clean (i.e., unmetallized) GaAs: Parallelism of sheet material (i.e., uniformity of thickness) within the range of±about 12.7 microns; Surface flatness (i.e., deviation in height per unit length when placed on ideal flat surface) within range from 5 mils/inch to about 10 mils/inch; Surface roughness not more than about 16 micro-inches (0.4064 microns). These surface parameters can also be used for diffusion bonding of Kovar directly to Kovar, e.g., to manufacture built-up metallic frames.
The temperature parameters for diffusion bonding between the mating surfaces of Kovar frames and the thin sheet materials described above are believed to be within the range from about 40% to about 70% of the absolute melting temperature, in degrees Kelvin, of the parent material having the lower melting temperature. When diffusion bonding is used for bonding optically finished glass or other transparent materials, the bonding temperature may be selected to be below the TG and/or the softening temperature of the for the glass other transparent materials, thereby avoiding damage to the optical finish. Depending upon the bonding temperature selected, in some embodiments the application of optical and/or protective coatings to the transparent sheets (i.e., that become the windows) may be performed after the bonding of the sheets to the frames, rather than before bonding. In other embodiments, some of the optical and/or protective coatings may be applied to the glass sheets prior to bonding, while other coatings may be applied subsequent to bonding. With regard to pressure parameters, a pressure of 105.5 kg/cm2 (500 psi) is believed suitable for diffusion bonding Kovar frames and the thin sheet materials previously described.
It will be noted that since the diffusion bonding occurs at high temperature, the CTE of the glass sheet should be matched to the CTE of the metallic frame. To the extent that the CTEs cannot be completely matched (e.g., due to non-linearities in the CTEs over the range of expected temperatures), then it is preferred that the CTE of the glass sheet be lower than the CTE of the metallic frame. This will result in the metallic frame shrinking more than the glass sheet as the combined window/frame assembly cools from its elevated bonding temperature (or from an elevated operational temperature) back to room temperature. The glass will therefore be subjected primarily to compression stress rather than tension, which reduces the tendency for cracking.
Referring now to
Typically, the same bonding technique will be used for bonding both the internal and external frames to the window, however, this is not required. Similarly, the internal and external bonds will typically be formed at the same time, however, this in not required. The internal frame 2072 must, however, be hermetically bonded to the window 2080 to produce a hermetic window assembly. A hermetic bond is not typically required for bonding the external frame 2074 to the window 2080, however, it may be preferred for a number of reasons.
One benefit of window assemblies having the so-called “sandwiched” frame configuration is to equalize the stresses on the internal and external surfaces, 2076 and 2078, respectively, of the transparent sheet 2080 that are caused by differential thermal expansion characteristics of the frames 2072 and 2074 and sheet (due to unequal CTE), e.g., during cooling after bonding, or during thermal cycling. Put another way, when a window assembly has a frame bonded to only one surface, uneven expansion and contraction between the frame and sheet may produce significant shear stresses within the sheet. These shear stresses may be strong enough to cause shear failure (e.g., cracking or flaking) within the transparent sheet even though the window-to-frame bond itself remains intact. When a frame is bonded to both the internal and external surfaces of the window, however, the shear stresses within the glass (or other transparent material) may be significantly reduced. This is particularly true if the same material or material having similar CTEs are used for both the internal and external frames. This stress-equalization through the thickness of the window increases the reliability and durability of the assembled window during subsequent thermal cycling and/or physical shock.
Sandwiched construction may be used in window assemblies or in WLP assemblies. Sandwiched construction with internal and external frames is especially advantageous where the sheet and frame materials have significantly different CTEs. In addition to the stress balancing features of sandwiched construction, use of an external frame on the sheet may have additional benefits, including: enhancing thermal spreading across the window; enhancing heat dissipation from the assembly; serving as an optical aperture; facilitating the aligning/fixturing or clamping of the device during bonding or assembly to higher level assemblies; and to display working symbolization.
Referring now to
Referring now specifically to
Referring now specifically to
Referring now to
Briefly, the steps for forming the package 2100 are as follows: A first frame-attachment area 2104 is prepared on the surface of the wafer substrate 2006 of the subject micro-device. This first frame-attachment area 2104 has a plan (i.e., configuration when viewed from above) that circumscribes the micro-device or micro-devices 2004 on the substrate 2006. A second frame-attachment area 2106 is prepared on the surface of the window 2016. The second frame-attachment area 2106 typically has a plan substantially corresponding to the plan of the first frame-attachment area 2104. The execution order the previous two steps is immaterial. Next, the frame/spacer 2014 is positioned between the substrate 2006 and the window 2016. The frame/spacer 2014 has a plan substantially corresponding to, and in register with, the plans of the first and second frame-attachment areas 2104 and 2106, respectively. If applicable, the solder preforms 2102 and 2103 or diffusion bonding interlayers 2102 and 2103 are interposed at this time between the frame/spacer 2014 and the frame-attachment areas 2104 and/or 2106. Finally, the substrate 2006, frame/spacer 2014 and window 2016 are bonded together (facilitated by solder or glass preforms 2102 and 2103 or diffusion bonding interlayers 2102 and 2103, if applicable) to form a hermetically sealed package encapsulating micro-device 2004 within, but allowing light to travel to and/or from the micro-device through the transparent aperture area 2108 of the window.
It will be understood that diffusion bonding of the package 2100 can be performed in a single (combined) step or in a number of sub-steps. For example, all five components (sheet 2016, first interlayer 2102, frame 2014, second interlayer 2103 and substrate 2006) could be stacked in a single fixture and simultaneously heated and pressed together to cause diffusion bonds to form at each of the sealing surfaces. Alternatively, the window sheet 2016 maybe first diffusion bonded to the frame 2014 using first interlayer 2102 (making a first subassembly), and then this first subassembly may be subsequently diffusion bonded to the substrate 2006 using second interlayer 2103. In another alternative, the frame 2014 could be diffusion bonded to the substrate 2006 using second interlayer 2103, and then the transparent sheet 2016 may subsequently be bonded to the sub-assembly using first interlayer 2102. The choice of which bonding sequence to be used would, of course, depend upon the exact materials to be used, the heat sensitivity of the transparent material in the sheet 2016, the heat sensitivity of the micro device 2004 and, perhaps, other parameters such as the expansion characteristics of the frame 2014 and interlayer materials.
It will further be appreciated that the current invention is similar in several respects to the manufacturing of the “stand-alone” hermetic window assemblies previously described. The preparing of the frame-attachment areas 2106 of the window 2016 may be performed using the same techniques previously described for use in preparing the sheet seal-ring area 318, including cleaning, roughening, and/or metallizing with one or more metallic layers as set forth in the earlier Examples 1-96.
While the transparent windowpane 2016 may be roughened (e.g., in preparing the frame-attachment area 2106) to promote adhesion of the first metallic layer being deposited onto it (e.g., by CVD or PVD), the wafer substrate 2006 will not typically be roughened in the same manner. Instead, the initial metallic layer on the wafer substrate 2006 will typically be deposited using conventional wafer fabrication techniques. Where conventional methods of wafer fabrication include the requirement or option of etching a silicon or GaAs wafer to promote adhesion of a metal's deposition, then the same practice maybe followed in preparing the frame attachment area 2104 on the wafer substrate 2006 when building WLP devices.
Other wafer or substrate materials include, but are not limited to, glass, diamond and ceramic materials. Some ceramic wafers are known as alumina wafers. These alumina wafers or substrates may be multi-layer substrates, and maybe manufactured using Low-Temperature Co-Fired (LTCC) or High-Temperature Co-Fired (HTCC)materials and processes. LTCC and HTCC substrates often have internal and external electrical circuitry or interconnections. This circuitry is typically screen printed onto the ceramic or alumina material layer(s) prior to co-firing the layers together.
Also, any of the bonding techniques and parameters previously described for use on window assemblies may be used to hermetically bond the WLP components to one another, including diffusion bonding/TC bonding with or without the use of interlayers, soldering using a solder preform and soldering using inkjet-dispensed solders. The primary difference is that when making “stand-alone” window assemblies, only two primary components (namely, the transparent sheet/window 304 and frame 302) are bonded together, while when making WLPs, three primary components (namely, the window 2016, frame 2014 and substrate 2006) are bonded together (sometimes simultaneously). Of course, when producing WLPs using soldering techniques, additional components may be required, for example one or more solder preforms 2102 or a quantity of inkjet-dispensed solder. The solder preforms, diffused, may be attached to the top and/or bottom of the frame 2014 as one step in the manufacture of that item. This will simplify the alignment of the three major components of the WLP assembly. It will, of course, be appreciated that this pre-attachment of the solder preforms to the frame is also applicable to the “stand-alone” window assemblies previously described. One of the methods for attaching solder preforms to the window 2016, frame 2014 and/or substrate 2006 is to tack the preform in place using a localized heat source.
Prior to soldering components together, cleaning the surfaces of the solder preforms and/or the metallized surfaces of the window 2016, frame 2014 and/or substrate 2006 maybe necessary to remove surface oxides. It is desirable to avoid using fluxes during the soldering process to eliminate the need for post-soldering or defluxing. Several surface preparation technologies are available to prepare the metal and solder surfaces for fluxless soldering.
Several other processes may be used for preparing the surfaces of window assemblies or WLP components for soldering to avoid the need to remove fluxes after soldering. A first option is to use what is known in the trade as a no-clean flux. This type of flux is intended to be left in place after soldering. A second option is the use of gas plasma treatments for improving solderablity without flux. For example, a non-toxic fluorine-containing gas may be introduced that reacts at the surface of the solder. This reaction forms a crust on the solder and dissolves upon remelt. The welds and joints formed are equal to or better than those formed when using flux. Such plasmas offer benefits including the removal by reduction of oxides and glass to promote improvements in solderability and wire bondability. Such treatments have been indicated on thick film copper, gold and palladium. Additional candidate gases for leaving a clean oxide-free surface include hydrogen and carbon monoxide plasma. Still further candidate gases include hydrogen, argon and freon gas combinations. One version of plasma treatment is known as Plasma-Assisted Dry Soldering (PADS). The PADS process coverts tin oxide (present in fluxless solders when unstable reduced tin oxide reoxidizes upon exposure to air) to oxyfluorides that promote wetting. The conversion film breaks up when the solder melts and allows reflow. The film is understood to be stable for more than a week in air and for more than two weeks when the parts are stored in nitrogen.
As in the previously described methods for manufacture of individual and multiple window assemblies for hermetically packaging discrete micro-devices, the selection of compatible materials for the various components for the manufacture of WLPs is another aspect of the invention. For example, each of the primary components (e.g., window, frame/spacer and wafer substrate) of the WLP will preferably have closely matched CTEs to insure maximum long-term reliability of the hermetic seal. The frame/spacer 2014 may be formed of either a metallic material or of a non-metallic material. The best CTE match will be achieved by forming the frame/spacer 2014 from the same material as either the wafer substrate 2006 or the window 2016. However, gallium arsenide (GaAs) and silicon (Si) (i.e., the materials typically used for the wafer substrate) and most glasses (i.e., the material that is typically used for the window) are relatively brittle, at least in comparison to most metals and metal alloys. These non-metallic materials are therefore typically not as preferred for forming the frame/spacer 2014 as are metals or metal alloys, because the metals and metal alloys typically exhibit better resistance to cracking. In fact, the use of a metal or metal alloy for the frame/spacer 2014 is believed to provide additional resistance to accidental cracking or breaking of the wafer substrate 2006, window 2016 and complete WLP 2002 after bonding. When a metallic frame/spacer 2014 is employed, it will preferably be plated with either gold alone, or with nickel and then gold, sometimes to facilitate diffusion bonding or soldering, but more often, to provide a surface on the frame/spacer that provides various kinds of protection between the frame/spacer and the atmosphere inside the package. If, however, a non-metallic frame/spacer 2014 is employed, then it might be metallized to facilitate diffusion bonding or soldering. The metal layers used on the frame/spacer 2014 may be the same as those used on the windowpane 304 for the manufacture of window assemblies, e.g., the final layer might be one of chromium, nickel, tin, tin-bismuth and gold.
In selecting compatible materials for the components of WLPs, it is recognized that silicon (Si) has a CTE ranging from about 2.6 PPM/° K at 293° K to about 4.1 PPM/° K at 1400° K. If it is assumed that the operating temperatures for micro-devices such as MEMS and MOEMS will be within the range from about −55° C. to about +125° C., and that the expected diffusion bonding or soldering temperatures will be within the range from about +250° C. to about +500° C., it may be interpolated that silicon wafers of the type used for WLP substrates will have a CTE within the range from about 2.3 PPM/° K to about 2.7 PPM/° K. One metallic material believed suitable for use in frame/spacers 2014 that will be bonded to silicon (Si) substrates is the alloy known as “Low Expansion 39 Alloy,” developed by Carpenter Specialty Alloys. Low Expansion 39 Alloy is understood to have a composition (weight percent; nominal analysis) as follows: about 0.05% C, about 0.40% Mn, about 0.25% Si, about 39.0% Ni, and the balance Fe. Low Expansion 39 Alloy has a CTE that is understood to range from about 2.3 PPM/° K over the interval of 25° C. to 93° C., to about 2.7 PPM/° K at 149° C., to about 3.2 PPM/° K at 260° C., and to about 5.8 PPM/° K at 371° C.
Similarly, it is recognized that gallium arsenide (GaAs) of the type used for WLP wafer substrates has a nominal CTE of about 5.8 PPM/° K. Based on material suppliers' data, Kovar alloy is understood to have a CTE ranging from about 5.86 PPM/° K at 20° C. to about 5.12 PPM/° K at 250° C. Thus, Kovar alloy appears to be a good choice for frame/spacers 2014 that will be bonded to GaAs substrates. Another material believed suitable for frame/spacers 2014 that will be bonded to GaAs substrates is the alloy known as Silvar™, developed by Texas Instruments Inc.'s Metallurgical Materials Division, of Attleboro, Mass. It is understood that Silvar™ is a derivative of Kovar with CTE characteristics closely matched to GaAs devices.
With regard to the window/lens for WLPs, it is believed that all of the glasses previously described for use in the manufacture of individual and multiple window assemblies having Kovar frames, e.g., Corning 7052, 7050, 7055, 7056, 7058 and 7062, Kimble (Owens Corning) EN-1, Kimble K650 and K704, Abrisa soda-lime glass, Schott 8245 and Ohara Corporation S-LAM60, will be suitable for the window/lens 2016 of WLPs having a GaAs substrate 2006. Pyrex glasses and similar formulations are believed suitable for the window/lens 2016 of WLPs having silicon substrates 2006. The properties of Pyrex, per the Corning website, are: softening point of about 821° C., annealing point of about 560° C., strain point of about 510° C., working point of about 1252° C., expansion (0-300° C.) of about 32.5×10−7/° C., density of about 2.23 g/cm3, Knoop hardness of about 418 and refractive index (at 589.3 nm) of about 1.474.
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In some embodiments, the inner surface of the window sheet 2600 may be scribed, e.g., with a diamond stylus, through each portion of the frame-attachment area 2602 to facilitate breaking apart of the MS-WLP assembly during singulation. The scribing of the window sheet 2600 would obviously be performed prior to bonding or joining it to the frame/spacer 2402. Where the frame/spacer 2402 includes grooved members such as those illustrated in
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After bonding, the MS-WLP assembly 2700 is cut apart, or singulated, to form a plurality of hermetically sealed packages containing one or more micro-devices each. There are several options carrying out the singulation procedure. However, since the window sheet 2600, frame 2402 and wafer substrate 2202 are bonded together, simply scribing and breaking the window sheet (as was done for the multiple stand-alone window assemblies) is not practical. Instead, at least the window sheet 2600 or the wafer substrate 2202 must be cut. The remaining portion may then either be cut, or scribed and broken. It is believed that the best result will be obtained by cutting the wafer substrate 2202 using a wafer-dicing saw, and then either scribing-and-breaking the window sheet 2600, or cutting the window sheet using a similar dicing saw.
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When electrical-resistance heating (“ERH”) is used to facilitate diffusion bonding or soldering of the components of a MS-WLP assembly, the electrical current is typically applied so that it flows through both the window/frame junction and the frame/substrate junction simultaneously. To facilitate this ERH heating, the configuration of the MS-WLP assembly may be modified to provide “sacrificial” metallized areas (i.e., areas that will be discarded later) on the window sheet and wafer substrate for placement of ERH electrodes. Preferably, the electrode placement areas on the substrate and window will be accessible from directions substantially perpendicular to the wafer.
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During bonding of WLP assemblies, there are two bonds that should typically occur simultaneously: the junction between the frame/spacer and the window sheet and the junction between the frame/spacer and the wafer substrate. As was described previously, however, the window may first be bonded only to the frame, and later, using ERH, the window/frame assembly can be attached to the substrate of the device. As was previously described in the process for the manufacturing of stand-alone window assemblies, the configuration of the metal frame and placement of ERH electrodes may be critical for even heating using ERH heating techniques. Similarly, for MS-WLP devices, the metallization patterns and ERH electrode placement locations on the wafer substrate and the window sheet may be important to achieving even heating. Therefore, the size/shape of the frame including possibly excess or sacrificial features, and the metallization patterns on both the window sheet and the wafer substrate should be concurrently designed, modeled (e.g., using software simulation) and prototyped to ensure even heating of the bonded surfaces/features.
It will be appreciated that the previous embodiment describes a method for manufacturing MS-WLP assemblies which is suited for micro-devices having opposite-side electrical connection pads. Referring now to
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As in previous embodiments, the inner surface of the window sheet 3700 maybe scribed, e.g., with a laser or diamond stylus, through each portion of the frame-attachment area 3702 to facilitate breaking apart of the MS-WLP assembly during singulation. Where the frame/spacer 3602 includes grooved members such as those illustrated in
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Of course, if the assembly 3800 is to be bonded using solder technology, then solder preforms (not shown) having a plan substantially corresponding with the frame-attachment areas are also positioned between the frame/spacer 3602 and the frame-attachment areas of the window sheet 3700 and substrate 3402 prior to bonding. Any of the previously described bonding technologies may be used to effectuate the bond between the components. If the assembly 3800 is to be bonded using diffusion bonding technology, then when using interlayer preforms (not shown), these preforms will have a plan substantially corresponding with the frame-attachment areas and are also positioned between the frame/spacer, 3602 and the frame-attachment areas of the window sheet 3700 and/or between the frame/spacer 3602 and substrate 3402 prior to bonding. The MS-WLP assembly 3800 will look essentially the same before bonding and after bonding (except for incorporation into the bond area of any solder preforms or interlayers for diffusion bonding).
After bonding, the window sheet 3700 of the assembly 3800 may be viewed as including primary strip portions 3802, which overlie the plurality of encapsulated micro-devices 3300, secondary strip portions 3804, which are interposed between the primary strips and overlie rows of non-encapsulated contact pads 3403, and end strip portions 3806, which are disposed at each end of the window sheet and also overlie rows of non-encapsulated contact pads 3403. During singulation of the assembly 3800, the secondary and end strip portions 3804 and 3806, respectively, of the window sheet are cut away and discarded, these parts being essentially “sacrificial.” Further during singulation, the substrate 3402 is divided along cut lines (denoted by arrows 3808) between the columns of micro-devices 3300 and contact pads 3403 to form multi-unit strips. The separating of the window sheet may be performed using saws, lasers or other conventional means, while the dividing of the substrate may be performed using saws, lasers, or by snapping along a score line.
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During the singulation of multi-unit strips 3900, at least the window sheet 3700 or the wafer substrate portion 3902 must be cut. The remaining portion may then either be cut, or scribed and broken. It is believed that the best result will be obtained by cutting the wafer substrate portion 3902 using a wafer-dicing saw, and then either scribing-and-breaking the window sheet 3700, or cutting the window sheet using a similar dicing saw.
While the invention has been shown or described in a variety of its forms, it should be apparent to those skilled in the art that it is not limited to these embodiments, but is susceptible to various changes without departing from the scope of the invention.
Claims
1. A hermetically sealed micro-device package encapsulating a micro-device and including a transparent window allowing light to pass into and out of a cavity containing the micro device, comprising:
- a semiconductor substrate having a micro-device operably disposed thereupon, the substrate having a first frame-attachment area formed thereupon having a plan that circumscribes the micro-device;
- a sheet of transparent material having a window aperture portion defined thereupon, the sheet having a second frame-attachment area formed thereupon having a plan that circumscribes the window aperture portion; and
- a frame/spacer positioned between, and hermetically bonded to, the semiconductor substrate and the transparent sheet, the frame including a continuous sidewall having a plan on one side substantially corresponding to, and substantially in register with, the plan of tie fit frame-attachment area, having a plan on the opposite side substantially corresponding to, and substantially in register with, the plan of the second frame-attachment area, and having a height that exceeds the height of the micro-device.
2. A package in accordance with claim 1, wherein the semiconductor substrate is substantially formed of silicon (Si).
3. A package in accordance with claim 1, wherein the semiconductor substrate is substantially formed of gallium arsenide (GaAs).
4. A package in accordance with claim 1, wherein the frame is formed of a material having a CTE substantially matched to the CTE of the transparent sheet and to the CTE of the semiconductor substrate.
5. A package in accordance with claim 1, wherein at least one of the hermetic bond between the frame and the semiconductor substrate and the hermetic bond between the frame and the transparent sheet is formed by diffusion bonding.
6. A package in accordance with claim 5, wherein both the hermetic bond between the frame and the semiconductor substrate and the hermetic bond between the frame and the transparent sheet are formed by diffusion bonding.
7. A package in accordance with claim 6, wherein the hermetic diffusion bond between the frame and the semiconductor substrate and the hermetic diffusion bond between the frame and the transparent sheet are formed in accordance with the following steps:
- pressing the substrate and the sheet against the frame with sufficient force to produce a first predetermined contact pressure along a first junction region between the frame and the first frame-attachment area of the substrate and a second predetermined contact pressure along a second junction region between the frame and the second frame-attachment area of the sheet;
- heating the first junction region to produce a first predetermined temperature along the first junction region;
- heating the second junction region to produce a second predetermined temperature along the second junction region;
- maintaining the first predetermined contact pressure and the first predetermined temperature until a diffusion bond is formed between the frame and the substrate all along the first junction region; and
- maintaining the second predetermined contact pressure and the second predetermined temperature until a diffusion bond is formed between the frame and sheet all along the second junction region.
8. A package in accordance with claim 5, wherein during bonding of the frame to the semiconductor substrate and during bonding of the frame to the transparent sheet, the temperature of the window aperture portion of the sheet remains below the glass transition temperature (TG) of the transparent material.
9. A multi-package assembly including a plurality of hermetically sealed cavities hermetically separated from one another by frame sidewalls, each of the cavities containing a micro-device positioned below a transparent window aperture allowing light to pass into and out of the cavity, the assembly comprising:
- a unitary semiconductor substrate having a plurality of micro-devices operably disposed thereupon, the substrate having a first frame-attachment area formed thereupon having a plan that circumscribes each of the micro-devices;
- a unitary sheet of transparent material, the sheet having a second frame-attachment area from thereupon having a plan that circumscribes a plurality of transparent window aperture positions of the sheet;
- a frame including a plurality of sidewalls, the sidewalls collectively having a plan on one side of the frame that substantially corresponds to, and is substantially in register with, the plan of the first frame-attachment area, having a plan on the opposite side of the frame that substantially corresponds to, and is substantially in register with, the plan of the second frame-attachment area, and having a height that exceeds the height of the micro-devices as disposed on the substrate;
- wherein the semiconductor substrate, frame and transparent sheet are hermetically bonded together along the first and second frame attachment areas to form a plurality of hermetically sealed cavities separated from one another by the frame sidewalls, each of the cavities containing a micro-device positioned below one of the window aperture portions of the sheet.
10. A multi-package assembly in accordance with claim 9, wherein the semiconductor substrate is substantially formed of silicon (Si).
11. A multi-package assembly in accordance with claim 9, wherein the semiconductor substrate is substantially formed of gallium arsenide (GaAs).
12. A multi-package assembly in accordance with claim 9, wherein at least one of the hermetic bond between the frame and the semiconductor substrate and the hermetic bond between the frame and the transparent sheet is formed by diffusion bonding.
13. A multi-package assembly in accordance with claim 12, wherein both the hermetic bond between the frame and the semiconductor substrate and the hermetic bond between the frame and the transparent sheet are formed by diffusion bonding.
14. A multi-package assembly in accordance with claim 13, wherein the hermetic diffusion bond between the frame and the semiconductor substrate and the hermetic diffusion bond between the frame and the transparent sheet frame formed in accordance with the following steps:.
- pressing the substrate and the sheet against the frame with sufficient force to produce a first predetermined contact pressure along a first junction region between the frame and the first frame-attachment area of the substrate and a second predetermined contact pressure along a second junction region between the frame and the second frame-attachment area of the sheet;
- heating the first junction region to produce a first predetermined temperature along the first junction region;
- heating the second junction region to produce a second predetermined temperature along the second junction region;
- maintaining the first predetermined contact pressure and the first predetermined temperature until a diffusion bond is formed between the frame and the substrate all along the first junction region; and
- maintaining the second predetermined contact pressure and the second predetermined temperature until a diffusion bond is formed between the frame and sheet all along the second junction region.
15. A multi-package assembly in accordance with claim 9, wherein cutting through selected sidewalls will divide the assembly into discrete sub-assemblies, each of the discrete sub-assemblies including at least one hermetically sealed package containing a micro-device positioned below a transparent window aperture.
16. A multi-package assembly in accordance with claim 15, wherein at least some of the sidewalls of the frame are grooved to a reduced thickness at locations between adjacent cavities, thereby facilitating subsequent cutting through of the grooved sidewalls to divide the assembly.
17. A hermetically sealed micro-device package encapsulating a micro-device and including a transparent window allowing light to pass into and out of a cavity containing the micro-device, the package being formed by dividing a multi-package assembly in accordance with claim 9 into smaller sub-assemblies.
Type: Application
Filed: May 27, 2005
Publication Date: Dec 15, 2005
Inventor: David Stark (Evergreen, CO)
Application Number: 11/140,593
