MICROELECTRONIC ELEMENT WITH BOND ELEMENTS TO ENCAPSULATION SURFACE
A microelectronic structure includes a semiconductor having conductive elements at a first surface. Wire bonds have bases joined to the conductive elements and free ends remote from the bases, the free ends being remote from the substrate and the bases and including end surfaces. The wire bonds define edge surfaces between the bases and end surfaces thereof. A compliant material layer extends along the edge surfaces within first portions of the wire bonds at least adjacent the bases thereof and fills spaces between the first portions of the wire bonds such that the first portions of the wire bonds are separated from one another by the compliant material layer. Second portions of the wire bonds are defined by the end surfaces and portions of the edge surfaces adjacent the end surfaces that are extend from a third surface of the compliant later.
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The subject matter of the present application relates to a microelectronic element including a semiconductor chip with structures to achieve improved reliability when assembled with external microelectronic components, including compliant connection structures, and methods of fabricating the microelectronic element.
Semiconductor chips are flat bodies with contacts disposed on a front surface that are connected to internal electrical circuitry of the chip. The chips are typically packaged to form a microelectronic package having terminals that are electrically connected to the chip contacts. The terminals of the package may then be connected to an external microelectronic component, such as a circuit panel.
Microelectronic devices such as semiconductor chips typically require many input and output connections to other electronic components. The input and output contacts of a semiconductor chip or other comparable device are generally disposed in grid-like patterns that substantially cover a surface of the device (commonly referred to as an “area array”) or in elongated rows which may extend parallel to and adjacent each edge of the device's front surface, or in the center of the front surface. Typically, devices such as chips must be physically mounted on a substrate such as a printed circuit board, and the contacts of the device must be electrically connected to electrically conductive features of the circuit board.
Semiconductor chips are commonly provided in packages that facilitate handling of the chip during manufacture and during mounting of the chip on an external substrate such as a circuit board or other circuit panel. For example, many semiconductor chips are provided in packages suitable for surface mounting. Numerous packages of this general type have been proposed for various applications. Most commonly, such packages include a dielectric element, commonly referred to as a “chip carrier” with terminals formed as plated or etched metallic structures on the dielectric. These terminals typically are connected to the contacts of the chip itself by features such as thin traces extending along the chip carrier itself and by fine leads or wires extending between the contacts of the chip and the terminals or traces. In a surface mounting operation, the package is placed onto a circuit board so that each terminal on the package is aligned with a corresponding contact pad on the circuit board. Solder or other bonding material is provided between the terminals and the contact pads. The package can be permanently bonded in place by heating the assembly so as to melt or “reflow” the solder or otherwise activate the bonding material.
Many packages include solder masses in the form of solder balls, typically about 0.1 mm and about 0.8 mm (5 and mils) in diameter, attached to the terminals of the package. A package having an array of solder balls projecting from its bottom surface is commonly referred to as a ball grid array or “BGA” package. Other packages, referred to as land grid array or “LGA” packages are secured to the substrate by thin layers or lands formed from solder. Packages of this type can be quite compact. Certain packages, commonly referred to as “chip scale packages,” occupy an area of the circuit board equal to, or only slightly larger than, the area of the device incorporated in the package. This is advantageous in that it reduces the overall size of the assembly and permits the use of short interconnections between various devices on the substrate, which in turn limits signal propagation time between devices and thus facilitates operation of the assembly at high speeds.
Mismatches or differences between coefficients of thermal expansion (“CTE”) of the components in such a package can adversely impact their reliability and performance. In an example, a semiconductor chip may have a lower CTE than that of a substrate or printed circuit board to which it is mounted. As the chip undergoes heating and cooling due to the use cycle thereof, the components will expand and contract according to their differing CTEs. In this example, the substrate will expand more and at a greater rate than the semiconductor die. This can cause stress in the solder masses (or other structures) used to both mount and electrically connect the semiconductor die and the substrate. Such stress can cause the solder mass to disconnect from either or both of the semiconductor die or the substrate, thereby interrupting the signal transmission that it otherwise facilitates. Various structures have been used to compensate for such variations in CTE, yet many fail to offer a significant amount of compensation on a scale appropriate for the fine pitch arrays being increasingly utilized in microelectronic packages.
BRIEF SUMMARY OF THE INVENTIONAn aspect of the present disclosure relates to a microelectronic structure including a first semiconductor die having first and second oppositely facing surfaces and a plurality of electrically conductive elements at the first surface. The structure also includes wire bonds having bases joined to respective ones of the conductive elements. The wire bonds further have free ends remote from the bases, the free ends being remote from the substrate and the bases and including end surfaces thereon. The wire bonds define edge surfaces extending between the bases and end surfaces thereof. A compliant material layer overlies and extends from the first surface of the semiconductor die outside of the bases of the wire bonds. The compliant material layer further extends along first portions of the edge surfaces of the wire bonds at least adjacent the bases thereof and fills spaces between the first portions of the wire bonds such that the first portions of the wire bonds are separated from one another by the compliant material layer. The compliant material layer further has a third surface facing away from the first surface of the semiconductor die. Second portions of the wire bonds are defined by the end surfaces and portions of the edge surfaces adjacent the end surfaces that are uncovered by the third surface and extend away therefrom.
The first portions of the wire bonds can be encapsulated entirely by the compliant material. Further, the second portions of the wire bonds can be moveable with respect to the bases thereof. In an example, the compliant material layer can have a Young's modulus of 2.5 GPa or less.
The second portions of the wire bonds can extend along axes of the wire bonds that are disposed at angles of at least 30 degrees with respect to the third surface. The end surfaces of the wire bonds can be positioned above the third surface by a distance of at least 50 microns. Further, the end surfaces of the wire bonds can be positioned above the third surface at a distance of less than 200 microns.
The semiconductor die can further define edge surfaces extending between the first and second surfaces, and the compliant material layer can further include edge surfaces extending from the third surface thereof to the first surface of the semiconductor die so as to be substantially coplanar with the edge surfaces of the semiconductor die. At least one of the wire bonds can have a shape such that the wire bond defines an axis between the free end and the base thereof and such that the wire bond defines a plane. In such an example a bent portion of the at least one wire bond can extending away from the axis within the plane. The shape of the at least one wire bond can be further such that a substantially straight portion of the wire bond extends between the free end and the bent portion along the axis.
The microelectronic structure can further include conductive metal masses joined with the second portions of the wire bonds and contacting the third surface of the compliant material layer. In such an example, at least one of the conductive metal masses encapsulates at least some of the second portion of a respective one of the wire bonds. The conductive metal masses can be configured to join the second portions of the wire bonds with external conductive features by reflow thereof.
In an example, the semiconductor die can be a first semiconductor die having a first region and a second region surrounding the first region. The electrically conductive elements of the first semiconductor die can be within the second region. The microelectronic structure in such an example, can further include a second semiconductor die mounted on the first semiconductor die within the first region. The second semiconductor die can be electrically connected with at least some of the conductive elements of the first semiconductor die. The compliant material layer can cover the second semiconductor die.
In another example, the semiconductor die can be a first semiconductor die having a first region and a second region surrounding the first region. The electrically conductive elements of the first semiconductor die can be within the second region. The microelectronic structure can further include a second semiconductor die mounted on the first semiconductor die within the first region. The second semiconductor die can have first and second oppositely facing surfaces and a plurality of electrically conductive elements at the first surface facing away from the first surface of the first semiconductor die. Additional wire bonds can have bases joined to respective ones of the conductive elements of the second semiconductor die. The additional wire bonds can further have free ends remote from the bases, and the free ends can be remote from the first surface of the second semiconductor die and the bases and including the end surfaces thereon. The wire bonds can define edge surfaces extending between the bases and end surfaces thereof. The compliant material layer can further overlie and extend from the first surface of the second semiconductor die outside of the bases of the additional wire bonds, and the compliant material layer can further extending along first portions of the edge surfaces of the additional wire bonds. Second portions of the additional wire bonds can be defined by the end surfaces and portions of the edge surfaces extending from the end surfaces that are uncovered by and extend away from the compliant material layer at the third surface.
Another aspect of the present disclosure can relate to a microelectronic package including a microelectronic element having a first semiconductor die with first and second oppositely facing surfaces and a plurality of electrically conductive elements at the first surface. The element can further have wire bonds with bases joined to respective ones of the conductive elements at the first surface and end surfaces, the end surfaces being remote from the substrate and the bases. Each of the wire bonds extends from the base to the end surface thereof. A compliant material layer overlies and extends from the first portion of the first surface of the substrate and fills spaces between first portions of the wire bonds such that the first portions of the wire bonds are separated from one another by the compliant material layer. The compliant material layer has a third surface facing away from the first surface of the substrate, and second portions of the wire bonds are defined by at least portions of the end surfaces of the wire bonds that are uncovered by the compliant material layer at the third surface. The package further includes a substrate having a fourth surface and a plurality of terminals exposed at the fourth surface. The microelectronic element is mounted on the substrate with the third surface facing the fourth surface and at least some of the wire bonds are joined, at the second portions thereof, to respective ones of the terminals.
The second portions of the wire bonds can be electrically and mechanically joined to the terminals by conductive metal masses. The microelectronic package can further include a molded dielectric layer formed over at least a portion of the fourth surface of the substrate and extending away therefrom so as to extend along at least a portion of the microelectronic element. The Young's modulus of the molded dielectric layer can be greater than the Young's Modulus of the compliant material layer. The compliant material layer can have a Young's modulus of less than 2.5 GPa.
The wire bonds can further define edge surfaces extending between the bases and end surfaces thereof, and the compliant material layer can extend along portions of the edge surfaces of the wire bonds at least adjacent the bases thereof and within the first portions of the wire bonds. Portions of the edge surfaces of the wire bonds that extend from the end surfaces thereof can be uncovered by the compliant material layer around entire circumferences thereof at the third surface thereof.
Another aspect of the present disclosure relates to a method for making a microelectronic structure. The method includes forming wire bonds on a semiconductor die, the semiconductor die having first and second oppositely facing surfaces and a plurality of electrically conductive elements at the first surface. The wire bonds are formed having bases joined to respective ones of the conductive elements and having end surfaces remote from the substrate and the bases. Edge surfaces of the wire bonds extend between the bases and the end surfaces. The method further includes forming a compliant material layer overlying and extending from the first surface of the semiconductor die outside of the bases of the wire bonds. The compliant material is further formed to extend along portions of the edge surfaces of first portions of the wire bonds to fill spaces between the first portions of the wire bonds and to separate the first portions of the wire bonds from one another. The compliant material layer is further formed to have a third surface facing away from the first surface of the substrate with second portions of the wire bonds being defined by at least the end surfaces and portions of the edge surfaces of the wire bonds that are uncovered by the conductive material layer at the third surface so as to extend away therefrom.
The method can further include the step of mounting the microelectronic package on a substrate with the third surface facing a surface of the substrate. The surface of the substrate can have terminals at the surface thereof, and the mounting can include joining at least some of the second portions of the wire bonds with the terminals. The second portions of the wire bonds can be joined with the terminals including reflowing of conductive metal masses joined with the second portions of the wire bonds. At least one of the conductive metal masses can encapsulate at least some of the second portion of a respective one of the wire bonds at least after the reflowing thereof. In an alternative example, the second portions of the wire bonds can be joined with the terminals including reflowing of conductive metal masses joined with the terminals.
The method can further include forming a molded dielectric over at least a portion of the surface of the substrate and extending away therefrom so as to extend along at least a portion of the compliant material layer and along at least a portion of the semiconductor die.
The compliant material layer can be deposited over the semiconductor die so as to cover the wire bonds, including the end surfaces thereof, and forming the compliant material layer can further include removing a portion thereof to form the third surface thereof and to uncover the second portions of the wire bonds. Alternatively, forming the compliant material layer can include molding the compliant material over the semiconductor die so as to form the third surface thereof such that the second portions of the wire bonds extend therefrom.
Forming the wire bond can include severing a wire segment joined with one of the conductive elements at least by pressing the wire segment into contact with a secondary surface using a capillary of a bonding tool so as to form the end surface of the wire bond remote from the base.
Turning now to the figures, where similar numeric references are used to indicate similar features, there is shown in
The microelectronic element 10 of
Conductive elements 28 are at the first surface 14 of semiconductor die 12. As used in the present description, when an electrically conductive element is described as being “at” the surface of another element having dielectric structure, it indicates that the electrically conductive structure is available for contact with a theoretical point moving in a direction perpendicular to the surface of the dielectric structure toward the surface of the dielectric structure from outside the dielectric structure. Thus, a terminal or other conductive structure that is at a surface of a dielectric structure may project from such surface; may be flush with such surface; or may be recessed relative to such surface and exposed through a hole or depression in the dielectric. Conductive elements 28 can be flat, thin elements of a solid metal material such as copper, gold, nickel, or other materials that are acceptable for such an application, including various alloys including one or more of copper, gold, nickel or combinations thereof. In one example, conductive elements 28 can be substantially circular.
Microelectronic element 10 further includes a plurality of wire bonds 32 joined to at least some of the conductive elements 28. Wire bonds 32 are joined at a base 34 thereof to the conductive elements 28 and extend to a corresponding free end 36 remote from the base 34 and from the first surface 14 of semiconductor die 12, the free ends 36 being within the extending portions 40 of the wire bonds 32. The ends 36 of wire bonds 32 are characterized as being free in that they are not connected or otherwise joined to semiconductor die 12 or any other conductive features within microelectronic element 10 that are, in turn, connected to semiconductor die 12. In other words, free ends 36 are available for electronic connection, either directly or indirectly as through a solder ball or other features discussed herein, to a conductive feature of a component external to microelectronic element 10, such as, for example, a printed circuit board (“PCB”) or another substrate with conductive contacts or terminals thereat. The fact that ends 36 held in a predetermined neutral position by, for example, compliant material layer 42 (as described further below) or otherwise joined or electrically connected to another external component does not mean that they are not “free”. Conversely, base 34 is not free as it is either directly or indirectly electrically connected to semiconductor die 12, as described herein. As shown in
The particular size and shape of base 34 can vary according to the type of material used to form wire bond 32, the desired strength of the connection between wire bond 32 and conductive element 28, or the particular process used to form wire bond 32. Example methods for making wire bonds 32 are and are described in U.S. Pat. No. 7,391,121 to Otremba and in U.S. Pat. App. Pub. Nos. 2012/0280386 (“the '386 Publication”) and 2005/0095835 (“the '835 Publication,” which describes a wedge-bonding procedure that can be considered a form of wire bonding) the disclosures of which are incorporated herein by reference in their entireties.
Wire bonds 32 can be made from a conductive material such as copper, gold, nickel, solder, aluminum or the like. Additionally, wire bonds 32 can be made from combinations of materials, such as from a core of a conductive material, such as copper or aluminum, for example, with a coating applied over the core. The coating can be of a second conductive material, such as aluminum, nickel or the like. Alternatively, the coating can be of an insulating material, such as an insulating jacket. In an example, the wire used to form wire bonds 32 can have a thickness, i.e., in a dimension transverse to the wire's length, of between about 15 μm and 150 μm. In other examples, including those in which wedge bonding is used, wire bonds 32 can have a thickness of up to about 500 μm. In general, a wire bond is formed on a conductive element, such as conductive element 28 within contact portion 30 using specialized equipment.
As described further below, during formation of a wire bond of the type shown and described herein, a leading end of a wire segment is heated and pressed against the receiving surface to which the wire segment bonds, typically forming a ball or ball-like base 34 joined to the surface of the conductive element 28. The desired length of the wire segment to form the wire bond is drawn out of the bonding tool, which can then cut the wire bond at the desired length. Wedge bonding, which can be used to form wire bonds of aluminum, for example, is a process in which the heated portion of the wire is dragged across the receiving surface to form a wedge that lies generally parallel to the surface. The wedge-bonded wire bond can then be bent upward, if necessary, and extended to the desired length or position before cutting. In a particular embodiment, the wire used to form a wire bond can be cylindrical in cross-section. Otherwise, the wire fed from the tool to form a wire bond or wedge-bonded wire bond may have a polygonal cross-section such as rectangular or trapezoidal, for example.
The extending portions 40 of the wire bonds 32 can form at least a part of a connection feature in an array formed by respective extending portions 40 of a plurality of wire bonds 32. Such an array can be formed in an area array configuration, variations of which could be implemented using the structures described herein. Such an array can be used to electrically and mechanically connect the microelectronic element 10 to another microelectronic structure, such as to a printed circuit board (“PCB”), a substrate (in a packaged configuration for microelectronic element 10, an example of which is shown in
Microelectronic element 10 further includes a compliant material layer 42 formed from a dielectric material having a Young's modulus of less than about 2.5 GPa. As shown in
The example of wire bonds 32 shown in
Wire bond 32 can be configured such that a first portion 52 thereof, on which the end surface 38 is defined, extends generally along a portion of the axis 50. The first portion 52 can have a length that is between about 10% and 50% of the total length of wire bond 32 (as defined by the length of axis 50, for example). A second portion 54 of the wire bond 32 can be curved, or bent, so as to extend away from the axis from a location adjacent the first portion 52 to an apex 56 that is spaced apart from the axis 50. The second portion 54 is further curved so as to be positioned along axis 50 at a location at or near base end 35 and to also extend away from the axis 50 to apex 56 from the side of base end 35. It is noted that first portion 52 need not be straight or follow axis 50 exactly and that there may be some degree of curvature or variation therein. It is also noted that there may be abrupt or smooth transitions between first portion 52 and second portion 54 that may themselves be curved. It is noted, however, that the wire bonds 32 depicted in
Further, both first 52 and second 54 portions of the wire bond 32 can be configured such that any portions thereof that do not intersect axis 50 are all on the same, single side of axis 50. That is, some of first and second portions 52 and 54 may be, for example, on a side of axis 50 opposite the apex 56 of the curved shape defined by second portion 54; however, any such portions would be in areas of the wire bond 32 that axis 50 intersects at least partially. In other words, first and second portions 52 and 54 of wire bond 32 can be configured to not fully cross axis 50 such that the edge surface 37 within those portions is only spaced apart from axis 50 on a single side of axis 50. In the example of
Wire bond 32 can be such that the apex 56 defined within second portion 54 of wire bond can be either exterior to the angle 58, as shown in
In an example, various ones of wire bonds 32 can be displaced in different directions and by different amounts throughout microelectronic element 10. Such an arrangement allows for microelectronic element 10 to have an array of extending portions 40 that is configured differently on the level of surface 44 compared to on the level of first surface 14 of semiconductor die 12. For example, an array can cover a smaller overall area or have a smaller pitch on surface 44 than at the first surface 14 of semiconductor die 12. In a variation of the microelectronic element 10 of
As shown in
As discussed above, wire bonds 32 can be used to connect microelectronic element 10 with an external component.
The assembly 24 can further include a molded dielectric layer 68 that can, for example, be molded over the surface of the substrate 46 facing microelectronic element 10. The molded dielectric layer 68 be an encapsulant, for example, and can fill spaces between the solder masses 66 and can contact the substrate 46 and the third surface 44 of the compliant material layer 42 in the area therebetween. Molded dielectric 68 can further extend outwardly along substrate 46 and upwardly along the edge surfaces 45 and 23 of the compliant material layer 42 and of semiconductor die 12, respectively, and can optionally cover microelectronic element 10 by extending over second surface 16 of semiconductor die 12. Substrate 46 can include package terminals opposite contact pads 48 or other structures to facilitate connection of the package assembly 24 with an external component.
In another example, a microelectronic element can similarly be joined directly with a printed circuit board (“PCB”) in place of substrate 46. Such a PCB can be assembled within an electronic device such that connection of microelectronic element 10 with the PCB can be done in assembling microelectronic element 10 with such a device. Further, such assembling can be carried out without the incorporation of a molded dielectric.
In either such assembly or application of a microelectronic element 10 as described herein, the structure of the wire bonds 32, along with the incorporation of compliant material layer 42 according to the principles described herein, can help improve the reliability of the attachment of microelectronic element 10 with a substrate in a package assembly or with a PCB (or other component). In particular, the reliability of the connections therebetween, which in the case of microelectronic element 10, is made between the extending portions 40 of wire bonds 32 and corresponding conductive features of the connected component (e.g. contact pads 48) can be improved relative to, for example, a direct connection between contacts of a semiconductor die and terminals of a substrate. This improvement can be accomplished by the ability of wire bonds 32 to flex or bend to accommodate relative movement between the conductive elements 28 of semiconductor die 12 and the contact pads 48 of substrate 46 (or PCB or other similar structure). Such movement can be caused by handling of the components, movement of the device, e.g., in which microelectronic element 10 or an assembly thereof is used, or testing of the microelectronic element 10 or assembly 24. Further, such relative movement can be caused by expansion and corresponding contraction of the components during the use cycle thereof caused by heat generated by the components and/or surrounding structures. Such thermal expansion is related to the coefficient of thermal expansion (“CTE”) of the components, and the relative movement between components in different structures can be caused by a difference, or mismatch, in the CTEs of the various structures or the materials thereof. For example, a semiconductor die can have a CTE of between about 2 and 5 parts per million per degree, Celsius (ppm/° C.). In the same assembly, a PCB or substrate can have a CTE of 15 ppm/° C. or greater.
The CTE of either component can be a “composite” CTE, which refers to a the CTE of the finished structure, which can approximate, but may not exactly match, the CTE of the primary material from which such a structure is constructed and can depend on the construction of the structure and the presence of other materials with different CTEs. In an example, the CTE of the semiconductor die can be on the order of Silicon or another semiconductor material, from which the die is primarily constructed. In another example, substrate 46 can have a CTE on the order of PTFE or another dielectric material, from which substrate 46 can be constructed.
Accordingly, a CTE mismatch between materials can cause relative movement between the conductive elements 28 of semiconductor die 12 and the contact pads 48 of substrate 46 (or another structure, such as a PCB or the like) as the semiconductor die 12 and the substrate 46 expand and contract during thermal cycling of the assembly 24 thereof because the semiconductor die 12 and substrate 46 expand at different rates and by different amounts in response to the same temperature change. This can cause displacement of the contact pads 48 with respect to the conductive elements 28, particularly in the peripheral areas of the substrate 46 or the semiconductor die 12 (i.e. toward edge surfaces 23 thereof) or in other areas depending on the particular configurations of the components and/or conductive elements 28 and contact pads 46.
The flexibility of wire bonds 32 along the respective lengths thereof can allow the end surfaces 38 thereof to displace with respect to the bases 34 in a resilient manner. Such flexibility can be used to compensate for relative movement of the associated conductive elements 28 and contact pads 46 between which the wire bonds 32 are connected. Because wire bonds 32 are flexible, however, they may not themselves be able to reliably support semiconductor die 12 relative to substrate 46 or other structure. For example, the flexing of unsupported wire bonds 32 could lead to adjacent wire bonds 32 coming into contact with one another, which could cause shorting or otherwise damage wire bonds 32 or the associated components. Accordingly, compliant material layer 42 is configured to separate wire bonds 32 from each other and to adding to the structural rigidity along the height thereof, while permitting desired flexing of wire bonds 32 to compensate for displacement of contact pads 46 relative to conductive elements 28. Accordingly, compliant material layer 42 can be made of a resiliently deformable (i.e. compliant) composition such as a material with a Young's modulus of less than 2.5 GPa. Further, compliant material layer 42, as mentioned above, can be dielectric so as to electrically insulate the wire bonds 32 from one another without requiring additional coatings or the like. Suitable materials for compliant material layer include silicone, benzocyclobutene (“BCB”), epoxy, or the like.
In such a structure, it may be beneficial to configure microelectronic element 10 to be able to make a connection with substrate 12 with the connection being robust enough to cause and flexing of wire bonds 32 within compliant layer 42 (which requires deformation of compliant layer 42). The extending portions 40 of wire bonds 132 can be configured to achieve such a connection. For example, by being uncovered by compliant material layer 42 so as to be physically separated therefrom, extending portions 40 allow conductive metal masses 66 to completely surround at least some of the edge surfaces 37 of wire bonds 32 within extending portions 40, which can provide a more robust connection than one achieved by a mass 66 that simply extends along a side thereof, for example. To allow adequate access for a conductive metal mass 66 to surround a extending portion 40, the extending portions 40 can be oriented relative compliant material layer 42 such that the axes 50 of wire bonds 32 within extending portions 40 are at an angle of between about 30° and 90° with respect to surface 44. Further, the strength of the bond can be increased by structuring wire bonds 32 and compliant material layer 42 such that extending portions have a height above surface 44 of 200 μm or less. In an example, extending portions 40 can have heights of between 50 and 200 μm.
In some examples where a molded dielectric 68 is also included in an assembly 24 with microelectronic element 10, the molded dielectric can itself be compliant, with a Young's modulus that, in an example, can be greater than that of compliant material layer 42 and, in a further example, less than that of either semiconductor die 12 or substrate 46.
A second semiconductor die 122 is mounted on semiconductor die 112 within first region 118. In the example shown in
In the example of
In such a structure, it may be desired to configure wire bonds 232a and 232b with heights sufficient to compensate for a CTE mismatch among components, as described above. In this structure, wire bonds 232a and 232b can be configured with a height sufficient to provide a desired height for extending portions 240 and sufficient compensation for displacement of features with which they are connected due to CTE mismatch. Displacement of contact pads on a substrate, for example, relative to the conductive elements 228a may be greater than with respect to conductive elements 228b because displacement is greater towards the peripheries of such structures. Accordingly, wire bonds 232b may have heights that are less than would be necessary within a similarly-sized microelectronic element including only one semiconductor die.
After a desired length of the wire has been drawn out of the capillary so as to extend above first surface 14 of semiconductor die 12 at an appropriate distance for the height of the wire bond to be formed (which can also include positioning of the wire to achieve a desired location for the free end 36 thereof and/or shaping of the wire bond 32 itself), the wire is severed to detach the wire bond 32 at the end surface 38 from a portion of the wire that remains in the capillary and is used in the formation of a successive wire bond. This process is repeated until the desired number of wire bonds is formed. Various steps and structures can be used to sever the wire bonds 32, including electronic flame-off (“EFO”), various forms of cutting or the like, examples of which are provided in U.S. patent application Ser. Nos. 13/462,158 and 13/404,408, and in U.S. Pat. No. 8,372,741. A further example of wire bond severing is discussed below with respect to
After formation of the desired number of wire bonds 32, compliant material layer 42 can be formed by depositing the desired material in a flowable state over in-process unit 10″, as shown in
As discussed above, the microelectronic element 10 resulting from the above steps, or variations thereof, can be packaged on a substrate or mounted on a PCB. Either of these subsequent steps can be carried out in a similar manner. In an example shown in
In a variation of the mounting steps of
Either of the above-discussed steps (from
Variations of the above-described method steps can also be used to form and package or mount the multi-die arrangements shown in
In this particular set of method steps, after a desired length of the wire 74 has been drawn out of capillary 70 for the desired height of the wire bond to be formed, the wire 77 is severed and appropriately positioned using a face 76 of the capillary 70 and a secondary surface 80. As shown in
In another example, the element can be fixed relative to the bonding tool in the area of the semiconductor die 12.
In the example shown in
After deformation of area 78 of wire 74, the capillary 70 is then moved back toward a final desired position for the free end 36 of the wire bond 32 to-be formed. This position can be directly above base 43 or can be laterally displaced therefrom, as discussed above with respect to the examples of
Capillary 70 can then be moved away from surface 14 to apply tension to the segment of wire 74 (which can be clamped or otherwise secured within capillary 70) between capillary 70 and base 34. This tension causes wire 74 to break within area 78, as shown in
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.
Claims
1. A microelectronic structure, comprising:
- a semiconductor die having first and second oppositely facing surfaces and a plurality of electrically conductive elements at the first surface;
- wire bonds having bases joined to respective ones of the conductive elements, the wire bonds further having free ends remote from the bases, the free ends being remote from the substrate and the bases and including end surfaces thereon, the wire bonds defining edge surfaces extending between the bases and end surfaces thereof; and
- a compliant material layer overlying and extending from the first surface of the semiconductor die outside of the bases of the wire bonds, the compliant material layer further extending along first portions of the edge surfaces of the wire bonds at least adjacent the bases thereof and filling spaces between the first portions of the wire bonds such that the first portions of the wire bonds are separated from one another by the compliant material layer, the compliant material layer further having a third surface facing away from the first surface of the semiconductor die, wherein second portions of the wire bonds extend away from the third surface, the second portions including the free ends of the wire bonds.
2. The microelectronic structure of claim 1, wherein the first portions of the wire bonds are encapsulated entirely by the compliant material, and wherein the second portions of the wire bonds are moveable with respect to the bases thereof.
3. The microelectronic structure of claim 1, wherein the compliant material layer has a Young's modulus of 2.5 GPa or less.
4. The microelectronic structure of claim 1, wherein the second portions of the wire bonds extend along axes of the wire bonds that are disposed at angles of at least 30 degrees with respect to the third surface.
5. The microelectronic structure of claim 1, wherein the end surfaces of the wire bonds are positioned above the third surface by a distance of at least 50 microns.
6. The microelectronic structure of claim 1, wherein the semiconductor die further defines edge surfaces extending between the first and second surfaces, and wherein the compliant material layer further includes edge surfaces extending from the third surface thereof to the first surface of the semiconductor die so as to be substantially coplanar with the edge surfaces of the semiconductor die.
7. The microelectronic structure of claim 1, wherein at least one of the wire bonds has a shape such that the wire bond defines an axis between the free end and the base thereof and such that the wire bond defines a plane, a bent portion of the at least one wire bond extending away from the axis within the plane.
8. The microelectronic structure of claim 7, wherein the shape of the at least one wire bond is further such that a substantially straight portion of the wire bond extends between the free end and the bent portion along the axis.
9. The microelectronic structure of claim 1, further including conductive metal masses joined with the second portions of the wire bonds and contacting the third surface of the compliant material layer.
10. The microelectronic structure of claim 9, wherein at least one of the conductive metal masses encapsulates at least some of the second portion of a respective one of the wire bonds.
11. The microelectronic structure of claim 9, wherein the conductive metal masses are configured to join the second portions of the wire bonds with external conductive features by reflow thereof.
12. The microelectronic structure of claim 1, wherein:
- the semiconductor die is a first semiconductor die having a first region and a second region surrounding the first region;
- the electrically conductive elements of the first semiconductor die are within the second region;
- the microelectronic structure further includes a second semiconductor die mounted on the first semiconductor die within the first region, the second semiconductor die being electrically connected with at least some of the conductive elements of the first semiconductor die; and
- the compliant material layer covers the second semiconductor die.
13. The microelectronic structure of claim 1, wherein:
- the semiconductor die is a first semiconductor die having a first region and a second region surrounding the first region;
- the electrically conductive elements of the first semiconductor die are within the second region;
- the microelectronic structure further includes a second semiconductor die mounted on the first semiconductor die within the first region, the second semiconductor die having first and second oppositely facing surfaces and a plurality of electrically conductive elements at the first surface facing away from the first surface of the first semiconductor die, and wherein additional wire bonds have bases joined to respective ones of the conductive elements of the second semiconductor die, the additional wire bonds further having free ends remote from the bases, the free ends being remote from the first surface of the second semiconductor die and the bases and including the end surfaces thereon, the wire bonds defining edge surfaces extending between the bases and end surfaces thereof; and
- the compliant material layer further overlies and extends from the first surface of the second semiconductor die outside of the bases of the additional wire bonds, the compliant material layer further extending along first portions of the edge surfaces of the additional wire bonds, wherein second portions of the additional wire bonds are defined by the end surfaces and portions of the edge surfaces extending from the end surfaces that are uncovered by and extend away from the compliant material layer at the third surface.
14. A microelectronic package, comprising:
- a microelectronic element, including a first semiconductor die having first and second oppositely facing surfaces and a plurality of electrically conductive elements at the first surface; wire bonds having bases joined to respective ones of the conductive elements at the first surface and end surfaces, the end surfaces being remote from the substrate and the bases, each of the wire bonds extending from the base to the end surface thereof; and a compliant material layer overlying and extending from the first portion of the first surface of the substrate and filling spaces between first portions of the wire bonds such that the first portions of the wire bonds are separated from one another by the compliant material layer, the compliant material layer having a third surface facing away from the first surface of the substrate, wherein second portions of the wire bonds extend away from the third surface, the second portions including the free ends of the wire bonds; and
- a substrate having a fourth surface and a plurality of terminals exposed at the fourth surface;
- wherein the microelectronic element is mounted on the substrate with the third surface facing the fourth surface and at least some of the wire bonds are joined, at the second portions thereof, to respective ones of the terminals.
15. The microelectronic package of claim 14, wherein the second portions of the wire bonds are electrically and mechanically joined to the terminals by conductive metal masses.
16. The microelectronic package of claim 14, further including a molded dielectric layer formed over at least a portion of the fourth surface of the substrate and extending away therefrom so as to extend along at least a portion of the microelectronic element.
17. The microelectronic package of claim 16, wherein the Young's modulus of the molded dielectric layer is greater than the Young's Modulus of the compliant material layer.
18. The microelectronic package of claim 14, wherein the compliant material layer has a Young's modulus of less than 2.5 GPa.
19. The microelectronic package of claim 14, wherein the wire bonds further define edge surfaces extending between the bases and end surfaces thereof, and wherein the compliant material layer extends along portions of the edge surfaces of the wire bonds at least adjacent the bases thereof and within the first portions of the wire bonds.
20. The microelectronic package of claim 19, wherein portions of the edge surfaces of the wire bonds that extend from the end surfaces thereof are uncovered by the compliant material layer around entire circumferences thereof at the third surface thereof.
21. A method for making a microelectronic structure, comprising:
- forming wire bonds on a semiconductor die, the semiconductor die having first and second oppositely facing surfaces and a plurality of electrically conductive elements at the first surface, the wire bonds being formed having bases joined to respective ones of the conductive elements and having end surfaces remote from the substrate and the bases, edge surfaces of the wire bonds extending between the bases and the end surfaces; and
- forming a compliant material layer overlying and extending from the first surface of the semiconductor die outside of the bases of the wire bonds, the compliant material further being formed to extend along portions of the edge surfaces of first portions of the wire bonds to fill spaces between the first portions of the wire bonds and to separate the first portions of the wire bonds from one another, wherein the compliant material layer is further formed to have a third surface facing away from the first surface of the substrate with second portions of the wire bonds extending away from the third surface, the second portions including the free ends of the wire bonds.
Type: Application
Filed: Sep 16, 2013
Publication Date: Mar 19, 2015
Applicant: INVENSAS CORPORATION (San Jose, CA)
Inventors: Belgacem Haba (Saratoga, CA), Richard Dewitt Crisp (Hornitos, CA), Wael Zohni (San Jose, CA)
Application Number: 14/027,571
International Classification: H01L 23/49 (20060101); H01L 21/48 (20060101);