In situ Plating And Soldering Of Materials Covered With A Surface Film
The disclosed subject matter provides systems and methods for etching and/or metal plating of substrate materials. An exemplary method in accordance with the disclosed subject matter for metal-plating or etching a substrate includes submerging portions of the substrate in a first bath of chemical solution, performing in-situ laser ablation of the substrate to achieve an immersion plated pattern with a first cation, plating-up the immersion plated pattern with the first cation in the first bath, and plating-up the immersion plated pattern with a second cation in a second bath. The same or another exemplary method can utilize a reel-to-reel system. The plating-up can begin after patterning by immersion plating is complete. Further, a single plating pattern can be used to define a pattern and the same bath can be used to plate the immersion pattern, thereby achieving a uniform thickness of the pattern.
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This application claims the benefit of U.S. Provisional Application No. 61/041,630, filed Apr. 2, 2008, U.S. Provisional Application No. 61/078,596, filed Jul. 7, 2008, U.S. Provisional Application No. 61/117,499, filed Nov. 24, 2008 and U.S. Application No. 61/119,535, filed Dec. 3, 2008, each of which is incorporated by reference in their entirety herein, and from which priority is claimed.
FIELDThe present application relates to systems and methods for metal plating and etching of substrates. More particularly, the application relates to metal plating, soldering and etching of readily oxidizable substrates or other substrates with thin layers that inhibit metal plating.
BACKGROUNDMetal plating of articles or base substrates is a common industrial practice. A metal layer can be coated or plated on the surface of an article, for example, for decoration, reflection of light, protection against corrosion, or increased wearing quality. Articles or base substrates, which are made of metal or non-metallic material, can be plated with suitable coating metals using techniques such as electroplating, electroless plating, metal spraying, hot dip galvanizing, vacuum metallization or other available processes.
Plating by electrolysis, or electroplating, is a commonly used technique for metal plating because it permits the control of the thickness of the plating. Cadmium, zinc, silver, gold, tin, copper, nickel, and chromium are commonly used plating/coating metals. In immersion or electroless plating, some metals are directly precipitated, without electricity, from chemical solutions onto the surface of the substrates. The silvering of mirrors is a type of plating in which silver is precipitated chemically on glass. Any of the common metals and some nonmetals, e.g., plastics, with suitably prepared (e.g., etched) surfaces can be used as the article or base substrate material.
However, some metals (e.g., aluminum and refractory metals like tungsten, tantalum and molybdenum), which have desirable physical or structural properties for use as base substrate material, are extremely difficult to plate by simple immersion plating or electroplating techniques. The difficulty in plating these metals can, for example, be related to the propensity of these metals to oxidize in air, as a result of which an interfering metal-oxide or insulating layer forms on any exposed or etched surface of these metals. The interfering metal-oxide or insulating layer hinders reduction of metal ions, which is required for metal plating. Therefore, techniques for metal plating readily-oxidizable materials (such as tungsten, tantalum and aluminum) commonly involve a number of expensive and tedious substrate preparation steps, which are designed to avoid or inhibit the formation of surface layers which can interfere with the plating processes. For example, a common technique for metal plating onto an aluminum substrate involves first zincating and then gold plating the aluminum substrate prior to plating the aluminum substrate with a metal of choice. For substrates or articles made from refractory metals such as tantalum and tungsten, the substrate preparation steps prior to metal plating often involve cumbersome high temperature processing steps.
The interfering surface oxide layers formed on these readily-oxidizable metals also hinders etching of the surface of these metals, which can be necessary prior to any substrate preparation steps themselves. The surface oxide layer coating inhibits the dissolution of the metal under conventional etching conditions. Again, a number of fairly harsh steps are required to prepare the substrate surfaces for etching. See e.g., Modern Electroplating (3rd edition), F. Lowenheim, Ed. John Wiley & Sons Inc. (1974), pp. 591-625, which is hereby incorporated by reference in its entirety. Further discussion of electroless plating of common materials that require multistep processing to achieve metal plating due to presence of interfering surface films can, for example, be found, in Electroless Plating: Fundamentals and Applications, Glenn O. Mallory and Juan B. Hajdu, Eds. American Electroplaters and Surface Finishers Society (1990), pp. 193-204, also incorporated by reference herein.
There remains a need to improve metal plating, soldering and etching of substrates, including simplifying techniques for metal plating of substrates having awkward surface geometries (e.g., cylindrical, non-planar or enclosed surfaces) which are prone to having interfering surface films form, for example, during conventional metal plating, soldering and etching processes or steps. Further, there remains a need to improve substrate preparation techniques (e.g., removal of native or preformed surface oxide layers) prior to plating or etching action.
SUMMARYThe disclosed subject matter provides systems and methods for etching and/or metal plating of substrate materials, including but not limited to, use of light sources (e.g. laser beams) for in situ surface conditioning of hard to plate substrates (e.g. aluminum, which is hard to plate due to readily forming inhibiting surface layers (e.g., a natural surface oxide)).
In one exemplary embodiment, a surface (e.g. an aluminum surface) is plated by directing focused light (e.g. a laser) onto the surface through a plating electrolyte (e.g., a copper sulfate solution) while at the same time applying a fixed negative voltage to the surface with respect to a counter electrode. In one embodiment, the electrolyte is relatively transmissive to the light source (e.g. laser light).
Another exemplary method in accordance with the disclosed subject matter for metal-plating or etching a substrate includes submerging portions of the substrate in a first bath of chemical solution, laser ablating the substrate (e.g. laser ablating a thin layer of the surface of the substrate) to achieve an immersion plated pattern with a first cation, plating-up the immersion plated pattern with the first cation in the first or second bath, and plating-up the immersion plated pattern with a second cation in a second bath. The same, or other exemplary methods can utilize a reel-to-reel system. The plating-up can begin after patterning is complete. Further, a single plating pattern can be used to define a pattern and the same bath can be used to plate the immersion pattern, thereby achieving a uniform thickness of the pattern.
An exemplary method utilizing a reel-to-reel system can further include using a scanning mirror in combination with the movement of the substrate located on one of two or more reels. Further the scanning mirror can be controlled by a processing unit programmed to have a prescribed pattern that results in distributing a beam spatially, while still contacting the substrate passing though a chemical solution.
An exemplary system in accordance with the disclosed subject matter for metal-plating or etching a substrate that includes a laser, a first bath including a first chemical solution and a first counter electrode and coupled to a first power supply utilizing a switch for producing mechanical motion of the substrate, and a second bath including a second chemical solution and the first counter electrode and coupled to a second power supply.
Another exemplary system in accordance with the disclosed subject matter provides a system for metal-plating or etching a substrate that includes a bath, and a scanning mirror coupled to a lens and a laser for ablating the substrate (e.g. ablating a thin layer of the surface of the substrate) in the bath to achieve the plating or etching. A reel-to-reel system can be utilized to control the movement of the substrate.
Another exemplary method in accordance with the disclosed subject matter includes depositing a chemical solution layer on a surface of the substrate, and laser ablating the substrate through the chemical solution layer to achieve the plating or etching. The same or another exemplary method can irradiate the substrate, for example, by passing a laser beam emitted from the laser through a lens. The lens can be, for example, a lens with a focal length greater than about 30 centimeters. The same or another embodiment can utilize a reel-to-reel system. In certain embodiments, the depositing of the chemical solution layer on a surface of the substrate can include depositing the chemical solution layer on two surfaces of the substrate. In the same or another embodiment, the laser ablating of the substrate can be performed utilizing a plurality of mirrors to laser ablate the substrate from more than one angle simultaneously.
An exemplary system for metal-plating or etching a substrate includes a first bath, a supply tank for depositing a layer of chemical solution onto a surface of the substrate, and a laser optically coupled to a lens for ablating the surface of the substrate in the first bath to achieve plating or etching. The same or another exemplary system can use a reel-to-reel system to control the movement of the substrate. The same or another embodiment, the system can further include a second bath separated from the first bath by a first partition, the second bath containing an electrode for electroplating the substrate. In one embodiment, the supply tank can be the first bath. In the same or another embodiment, the system can further include a second partition, positioned adjacent to a wall of the first bath such that a channel is formed in which the layer of chemical solution is deposited onto two surfaces of the substrate. The system can further include a plurality of mirrors for directing a laser beam produced by the laser to irradiate the substrate surface from more than one angle.
Another exemplary method for metal-plating or etching a substrate from more than one angle simultaneously includes submerging portions of the substrate in a first bath of chemical solution, and laser ablating the surface of the substrate using a plurality of mirrors to irradiate the substrate from two or more angles to achieve the plating or etching. This method can further include plating-up the substrate with a cation in the first bath. In the same or another embodiment, this method can further include transferring the substrate to a second bath, and plating-up the substrate with a cation in the second bath. In one embodiment, a single laser is used to perform said in-situ laser immersion plating. In an alternative embodiment, two lasers are used to perform said in-situ laser immersion plating.
An exemplary system for metal-plating or etching a substrate (e.g. an awkward, non-planar (i.e., curved or cylindrical), or enclosed plating surface) from more than one angle simultaneously includes a bath containing a chemical solution, at least one lens, and at least one light source (e.g. laser) coupled to a plurality of mirrors for irradiating the substrate from more than one angle simultaneously with laser beams passed through the lens or lenses. For example, one or more (e.g. a set of) optical elements is used to direct laser light onto substrates having awkward non-planar (i.e., curved or cylindrical), or enclosed plating surfaces.
For example, in one embodiment one or more optical elements (e.g. semitransparent and totally reflecting mirrors) is used to irradiate all 360 degrees of an aluminum wire substrate circumference as the wire is drawn from one reel to a second windup reel through the electrolyte. Other optical elements (e.g., spherical bi-convex, planar convex, or cylindrical lenses) can be used to focus the light on the substrate. Alternatively, the laser light can be directed onto the wire substrate by way of an optical fiber (light pipe). The tip of the fiber can extend into the electrolyte or be otherwise externally positioned to direct the light into the electrolyte. A focusing lens can be positioned at the tip of the fiber as needed to focus the light on the substrate. In one embodiment, semistransparent mirrors refer to mirrors that transmits between 25-50% of incoming light.
An optical fiber (light pipe) can also be used for in situ plating of the inside of a tube-shaped substrate (e.g., aluminum tubing), which is immersed in the electrolyte. The optical fiber (light pipe) extends into the tubing and directs laser light onto plating surfaces on the inside wall of the tubing. The optical fiber and/or the tubing substrate also can be attached to a mechanical rotational and translational mechanism. The light pipe and the tubing can be moved laterally while rotating so that the entire inside of the tubing surface is irradiated. A lens can be positioned at the end of the optical fiber to focus the light onto the inside of the tubing wall.
The aforementioned plating methods allow aluminum to be soldered after plating a small amount of copper. Without the copper plating, aluminum generally cannot be soldered. However, other metals such as nickel, chrome, silver and the like can also be plated in situ on the aluminum by means of the laser in order to allow soldering of the aluminum.
Further, the aforementioned plating methods can allow substrates (e.g., aluminum) to be soldered by direct plating of a soldering material onto the substrate without any intermediate layer (e.g., copper).
In another embodiment, aluminum wires can be plated with a copper overlayer. Such Al—Cu composite wires can be advantageously used for high frequency transmission lines. At sufficiently high frequencies, the skin depth effect will cause the high frequency current to be carried by the copper overlayer. Thus, the aluminum, which is much less expensive than copper, can be used as the central core of the wire, while a relatively thin layer of copper plated onto the aluminum, with higher electrical conductivity, carries the current. This particular embodiment achieves reduction in cost, as compared to a pure copper wire.
Other embodiments of the present application provide methods and systems for in situ oxide removal from the surface of metals to be plated (or removal of other inhibiting films from the metals) by means of a UV or femtosecond set of laser pulses. In certain embodiments, the metal is either immersed in the solution in which plating or etching is to occur, or the oxide is covered with a film of solution (e.g on the order of 0.1 to 1 mm) through which the laser can readily penetrate to remove the oxide. After the oxide ablation, the sample is removed to the solution (preferably rapidly removed) in which plating (or etching) is to occur. In either case, the substrate to be plated or etched is in solution during ablation. In an alternate embodiment, the substrate from which the oxide is to be removed is immersed in an inert gas during the laser ablation processing by the femtosecond or UV laser, after which it is quickly transferred and immersed into an etching or plating solution for etching or plating respectively. In yet another embodiment, the laser processing can take place in a first electrolyte, then transferred to a second electrolyte for plating or etching.
Other embodiments of the present application provide methods and systems to prevent unwanted depositions in areas not subjected to the laser energy by introducing a source of steam in the reel to reel plating system to cause oxidation. For example, certain embodiments employ steam, incident on the surface of the Al or other oxide coated metal to be plated, to increase the thickness of the natural oxide coating. The laser fluence for removing the oxide is then adjusted to enable removal of the thicker oxide in designated areas on the metal to be plated/etched while at the same time preventing unwanted depositions in areas not subjected to the laser oxide removal source (e.g. a laser).
Further features of the disclosed subject matter, its nature, and various advantages will be more apparent from the following detailed description of the preferred embodiments and the accompanying drawings, wherein like reference characters represent like elements throughout, and in which:
The disclosed subject matter provides systems and methods for metal plating, soldering and etching of substrate materials which have awkward geometries (e.g., cylindrical outer surfaces, inside tube surfaces).
International Published Patent Application No. WO 2006/086407, which is hereby incorporated by reference, discloses systems and methods for plating and/or etching of hard-to-plate metals (e.g., aluminum and refractory metals like tungsten, tantalum and molybdenum) which have desirable physical or structural properties for use as base substrate material, but are extremely difficult to plate by simple immersion plating or electroplating techniques. The difficulty in plating these metals can, for example, be related to their propensity to oxidize in air, as a result of which an interfering metal-oxide or insulating layer forms on any exposed or etched surface of these metals. The interfering metal-oxide or insulating layer hinders reduction of metal ions, which is required to cause metal plating. The systems and methods described in the aforementioned patent application are designed to overcome the deleterious effect of superficial coating or oxide layers that interfere with the plating or etching of certain metal substrates. The systems and methods involve in situ removal of coating materials from the surfaces of the metal substrates while the substrates are either submerged in plating or etching solutions, or are positioned in a proximate enclosure just prior to submersion in the plating or etching solutions. This in situ removal of coating layers can be achieved by pulse heating or photoablation of the substrate and the inhibiting coating layers. Electrical energy or laser light energy can be used for this purpose.
Like the systems and methods described in International Patent Application No. PCT/US06/04329 for plating substrates that are usually coated with interfering thin surface films, the systems and methods described herein employ in situ techniques to remove or inhibit the interfering thin surface film on the substrate surfaces, even if the latter have awkward geometries.
The in situ removal techniques can exploit optical energy absorption to remove or inhibit the interfering thin surface films on substrate work surfaces before metal plating, etching or solder deposition. An energy beam, which is generated by a suitable optical source (e.g., a laser), is directed onto the surface of a substrate. Optical absorption of the directed energy beam can lead to localized heating and/or photodecomposition (also known as ablative photodecomposition) of the interfering thin surface films.
The systems and methods of the disclosed subject matter are described herein with reference to aluminum (e.g., Al wire) as an exemplary hard-to-plate substrate material. Aluminum is of widespread industrial interest because of its high electrical conductivity and its comparatively low cost vis-à-vis copper for similar applications (e.g., for electricity transmission). However, aluminum is difficult to plate or solder using conventional electroplating/soldering methods. The systems and methods described herein enable plating, soldering and/or etching of aluminum and other hard-to-plate metals without requiring the conventional multiple surface pre-conditioning steps that include the use of very harsh chemicals (e.g., HF). Aluminum can be plated simply by directing focused light onto the substrate surfaces disposed in an electroplating cell. The light is focused onto the substrate surface through the electroplating solution (e.g., copper sulfate).
Laser beam 120, which can be generated by a CW or pulsed laser 130, is directed to be incident on the circumference of wire 110 from multiple directions (e.g., all directions, 360 degrees) by a suitable optical arrangement 140. As shown in
It will be understood that vertically oscillating semi-transparent mirror 140A produces only a vertical displacement of laser beam 120, since any parallel faced transparent plate causes light to exit in the same direction at the same angle with respect to the normal to the mirror surface at which it enters the transparent plate. However, the varying vertical displacement due to the mirror's oscillation will cause a shift in the beam that allows it to impinge on different parts of the target (wire 110) in plating solution (not shown).
Laser beam 120 (generated by a CW or pulsed laser 130) is directed to be incident on a spot 360 on the inner surface of tube 110 by an exemplary optical arrangement, which includes an optical fiber 320 and other optical elements (e.g., lens 340) disposed within the interior of tube 310. Suitable mechanical supports (e.g., optical fiber supports 330) are placed at or near the end of optical fiber 320 within tube 310. Tube 310 is mechanically translated and rotated so that spot 360 can be moved (relatively) across all the portions of the inner surface of tube 310 designated for plating.
In the context of plating aluminum (and other hard-to-plate materials),
Two-dimensional plating can also be achieved in machine 400 by controlling the speed of the stock to give y-direction plating with x-direction plating provided by only one scanning mirror 440A.
The arrangement of mirrors 440A for scanning the laser beam in two-directions can also be used for plating a stationary piece of thick stock 560 submerged in the electrolyte. However, scanning mirrors 440A typically can be able to scan only relatively small areas without the beam spot turning elliptical because of a severe slant angle at large scanning distances. The elliptical distortion of the beam spot decreases the incident power/area. Therefore, for plating large areas of stock 560, some motion of the stock itself can be required (
The systems and methods can be advantageously used to deposit/plate solder materials onto otherwise hard-to-solder materials (e.g., Al). The solder materials (including, for example, lead-free solders) can be deposited directly on the substrate (e.g., aluminum) without the use of intermediate plating materials (e.g., copper).
The disclosed subject matter also provides systems and methods for metal plating and etching of substrates that are covered by interfering surface films. The plating and etching methods involve in situ removal of the interfering surface films or surface preparation in such a way that plating/etching becomes possible. The in situ removal of the interfering surface films can be obtained by in situ application of heat, laser light, or mechanical abrasion, or by similar ex situ methods including, for example, placing the substrate in a reducing gas atmosphere. Accordingly, various plating/etching cell arrangements are provided for in situ application of resistive heating, laser light, mechanical abrasion, or reducing gas to the subject substrate just prior to or even as the subject substrate is undergoing etching or plating processes.
The disclosed subject matter provides convenient manufacture of metal-plated articles that are made from structurally desirable substrate materials, which are readily oxidizable (e.g., aluminum, and refractory metals). For these metal-plated articles, the metal plating is deposited on or bonded directly to the underlying substrate material obviating the need for intermediate substrate modification or seed layers. The disclosed subject matter, for example, enables manufacture of metal-plated aluminum articles in which the metal coating (e.g., nickel) is deposited directly on the aluminum substrate without any intervening zinc or gold seed layers.
Many materials, particularly metals, develop an oxide coating or can have some other form of a thin surface layer, which can act as a protective coating. For those cases, it is necessary to remove the oxide or coating in some manner prior to subjecting the material to plating or etching. The removal of such surface layers is necessary for electroplating, electroless plating, immersion plating, electro etching and chemical etching of the material. The various plating/etching systems or arrangements described herein are designed to remove the protective coatings either while or just before the materials are submerged in the electrolyte, which is used for carrying out the desired plating/etching processes. These plating/etching systems or arrangements allow removal of interfering coatings or surface films on a substrate (e.g., where the coating or surface film is a naturally grown oxide) without requiring any subsequent exposure, or at least any significant subsequent exposure, of the substrate to air prior to placing it in a plating/etching cell. Some of the plating/etching systems are designed so that suitable preprocessing or coating removal procedures are carried out in close proximity to the plating/etching bath, either in air or in a controlled atmosphere enclosure. Further, the plating/cell systems are designed to reduce and simplify the number of processing steps common in conventional metal plating/etching processes that are performed in separate baths, tanks or ovens, and in particular to avoid the cumbersome high temperature processing steps.
Metallization/etching processing can take place in situ or immediately after oxide removal so that there is no significant exposure of the substrate to air between the oxide removal and the plating/etching processing. The disclosed processes avoids conventional expensive and somewhat cumbersome coating removal procedures such as are presently required in plating onto, for example, an aluminum substrate.
Conventional procedures for metal plating aluminum substrates involve a number of procedures to overcome the deleterious effects of aluminum oxide coatings that form on exposed aluminum surfaces. These procedures can include zincating followed by gold plating before the metal of choice can be plated onto the aluminum substrate. By application of the disclosed subject matter, interfering aluminum oxide materials can be readily removed in situ by any of the several techniques described herein, which avoid exposing the substrate material to air (or oxygen) or limit such exposure to less than a few seconds. Short exposures to air of about 1 to 10 seconds have been shown to be benign with respect to plating and etching quality. Thus, plating and etching can be initiated immediately or within 1-10 seconds after the interfering coating materials on the aluminum substrate are removed. This in situ processing also can be similarly advantageous for metal plating or etching of refractory metal substrates such as tungsten, tantalum, titanium, molybdenum and rhenium.
An exemplary plating/cell arrangement or system, which is designed for in situ processing of difficult substrates (i.e., substrates whose outer surfaces are coated by an interfering film that makes direct plating or etching difficult or impossible), can include a fluid-holding tank which can hold a fluid electrolyte (e.g., copper sulfate, nickel sulfate or other chemical solutions), an electroless plating solution (e.g., electroless gold) or a chemical etchant (e.g., hydrogen fluoride, sodium hydroxide or the like). The tank can be suitably sized so that the subject substrate (which is preferably electrically conductive) can be fully submerged or partially submerged in the fluid. This exemplary plating/cell arrangement or system can be modified to include an enclosure in close proximity or attached to the fluid-holding tank. This enclosure can be used for substrate preprocessing including coating removal prior to submerging the substrate in the fluid tank.
In one embodiment of a plating/etching cell arrangement, heat is applied to the substrate while submerged in the plating/etching solution to remove the offending film or coating from the surfaces of the substrate. The heat can be applied as resistive heat, which is locally generated by passing a high current through the substrate. The high current flow can be intermittent. A first voltage/current source, whose leads are connected to opposite ends of the substrate, is provided for this purpose. The voltage/current source can be any suitable pulser or pulsed voltage source that can produce a high current. Suitable pulsers produce pulses that are that are greater than approximately 100 ps wide. The resistive or Joule heating due to the passage of current within the substrate serve to heat the substrate, whereby this heat can lead to dissolution or disintegration of the offending coating. The offending coating can be removed, for example, by ablation, melting, or cracking due to differential thermal expansion. Once the coating has been removed and the pulser is no longer operating, the substrate can remain free of coating in the plating or etching fluid for at least about 0.1 second, but often for a much longer time on the order of minutes.
In a variation of the disclosed processes, coating removal procedures, which can be similar to the heating procedures, mechanical or other coating removal procedures described above, can be performed before submerging the substrate in the fluid tank. For such processes, the plating/etching cell system or arrangement can be provided with a separate enclosure in close proximity or attached to the fluid tank. The separate enclosure can have a controlled atmosphere, which can be beneficial to the coating removal process. For example, a reducing gas (e.g., HF gas) atmosphere can be used to remove an offending substrate coating (e.g., an oxide coating) by chemical reduction of the coating. Further, for example, an inert gas atmosphere can be used to hinder oxide regrowth during heat or mechanical coating removal procedures. In some instances when mechanical removal of the coating can be successfully achieved in an air ambient, the provision of a separate coating removal enclosure in the plating/etching cell arrangement can be unnecessary.
In any of the plating/etching cell systems or arrangements including arrangements in which resistive Joule heating is utilized for removing a coating while the substrate is submerged in the fluid tank, a coating-free substrate can act as a working electrode while submerged in the fluid. A suitably positioned counter electrode can be submerged in the tank fluid for conducting electrolytic metal plating or etching. A second voltage/current source can be connected between the counter electrode and the substrate to provide current for electrolytic action. In the case where the fluid is an electrolyte, the second voltage/current source can be activated at suitable times to cause electrolytic plating or etching of the substrate when the substrate surface is free of the offending coating. Thus steady (continuous wave) or pulse plating and etching can be accomplished.
In a typical electroplating/electroetching process using the disclosed subject matter in which both the coating removal process and the plating/etching process occur within the plating bath, the second source of voltage can be applied immediately after the current pulse applied by the first voltage source (used for resistive Joule heating) is terminated. Alternatively, the second voltage/current source can be activated even before or during the application of the current pulse to remove the substrate coating. In instances where the fluid in the tank is an electrolyte, it also can be possible to obtain exchange plating (e.g., immersion plating) without the use of the second voltage source for certain electrolyte and substrate combinations. If the electrolyte fluid contains a more noble metal than the substrate material then, once the offending coating is removed from the substrate surface, the more noble metal atom will plate or deposit on the surface by replacing an exposed substrate surface atom.
The plating/etching cell arrangement also can be used for an electroless plating (using a fluid which is an electroless plating solution). In such application, a catalyst in the electroless solution leads to plating without any applied voltage to the substrate electrode. Accordingly, it is not necessary to use the counter electrode and second voltage source to produce plating. Similarly, when a chemical etchant is used as the tank fluid, etching of the substrate can readily occur without the use of the counter electrode or second voltage source once the surface coating is removed by heat or mechanical treatment.
In yet another version of the in situ plating/etching cell arrangement, the first voltage/current source, which is used to heat the substrate for in situ removal of the offending coating layers, can be replaced as a heat energy source by any suitable energy beam that can penetrate the fluid or the gas in the enclosure of the alternate embodiment to reach the substrate surface. The energy beam (e.g., a light beam) can be generated by a laser. The laser beam can be directed onto the substrate surface through an optical fiber or an optical wave-guide (e.g., a light pipe). Alternatively, the laser beam can, in certain instances, be directed onto the substrate through the electrolyte without the use of a light pipe or optical fiber.
Similar localized surface heating can occur with the use of either the voltage source or the laser beam as the heat or photoablative energy source for removing the substrate coating while the substrate is submerged or is in the preprocessing enclosure. The plating/etching cell arrangement can be configured with a suitable fluid stirring mechanism to mitigate any local boiling of the fluid or bubble formation in contact with the substrate. For example, a circulating flow system using pump can be used as a fluid stirring mechanism. The circulating flow system can be pressurized by way of the pump and use gravity flow to form a complete closed system for agitating the fluid. Alternatively or additionally, a mechanical magnetic stirrer can be placed within the fluid containing tank to maintain fluid agitation as is well known to those skilled in the art.
In an alternate version of the plating/etching cell arrangement, a movable scraping or abrasion tool is provided to remove the offending coating by applying mechanical force to the substrate. The scraping or abrasion tool can be scanned across the substrate to remove the substrate's coating. Mechanical removal of the offending coating can be in addition or as an alternate to, other removal techniques described herein, such as heat-based removal (i.e., using the first voltage source or the energy source to remove the coating of the substrate in situ).
An exemplary scraping or abrasion tool can be a mechanical scribe with a sharpened end, which is placed in intimate contact with the substrate surface. In operation, the scribe mechanically penetrates the coating. The mechanical scribe can be driven by a motorized moveable arm, which is preferably digital data processing device controlled. As the scribe traverses the areal dimensions of the substrate, the coating is removed from the substrate surface. Removal of the coating allows plating and etching of the substrate surface to occur immediately thereafter, while the scribe and the substrate are submerged in the plating/etching solution or, alternatively, while the scribe and substrate are positioned in the preprocessing enclosure.
In some versions of the plating/etching cell arrangement in which the offending coating is removed within the plating/etching bath, the mechanical scribe can be used in conjunction with the first voltage source to remove a coating by application of both resistive (Joule) heating and mechanical force to the substrate surface. In such versions, the mechanical scribe can be made from conducting material, which allows localized current to flow from the scribe to the substrate. In a preferred embodiment of such a version of the plating/etching cell arrangement, the mechanical scribe is disposed to make contact with the back of the substrate (which can be sheet or flat stock). In this configuration, current that is supplied from the first voltage source flows through the substrate and heats the front of the substrate to remove the coating on the front surface of the substrate to be plated or etched (i.e. the surface facing the counter electrode).
The in situ plating/etching cell arrangements can be configured to operate with reel-to-reel material handling systems that are commonly used in industrial processing of long lengths of wire or sheet flat stock. In these reel-to reel material handling systems, the unprocessed substrates (i.e., long length of wire or sheet flat stock) are wound on a donor reel and fed into the processing fluid (tank fluid) by a series of support wheels. Processed substrates are similarly picked up by a series of wheels and wound on a mechanically driven take-up reel. The disclosed in situ plating/etching cell arrangements can be provided with suitable scrapers for mechanically removing the offending coating on the substrate surface in situ in the processing fluid or in a small preprocessing enclosure in close proximity to the fluid. For example, the substrates can be driven or pulled through a die that removes the coating by way of a sharpened inner peripheral die surface (i.e. a knife edge). The substrate feed rate can be adjusted by suitably setting the speed of the reels. The substrate feed rate for the plating/etching processes can be selected so that the wire or flat stock substrates remain submerged in the plating/etching tank fluid for at least 0.1 s, as the substrates are pulled through the die using the mechanically driven take-up reel. The shape of the die (e.g., circular or rectangular) can be designed in consideration of the shape of the substrate material (e.g., wire or flat stock).
In some versions of the plating/etching cell arrangements, the die structures can be used in conjunction with the first source of voltage to apply heat to wire or flat stock substrates as they pass through the die. For example, opposite ends of a die can be used to pass current and to cause heating as the wire or flat stock passes through the die. This heating mechanism can be used as an alternate or an additional mechanism for removal of surface coatings. In another embodiment, heat can be generated directly in the wire or flat stock by contacting a voltage source by means of sliding contacts to the wire/flat stock directly, thereby using the resistance of the wire/flat stock in conjunction with current flow to generate the necessary heat to remove the coating.
After removal of surface coatings using the die, a second voltage can be applied to the wire or flat stock substrate across from a counter electrode to cause electroplating or electroetching.
Examples of plating/etching processes and cell arrangements are further described herein with reference to
In general, a plating bath can be an electroless, electroplating or immersion plating or other chemical solution. For etching, the bath can be a chemical etchant such as sodium hydroxide or any other etchant known to those skilled in the art. For electroetching, the etchant can, for example, be a copper sulfate solution. Plating/etching cell arrangement 100 can be provided with an optional counter electrode 104, which is used only for those applications that utilize either electroplating or electroetching. For immersion plating and electroless plating as well as for chemical etching, use of this electrode is unnecessary. A galvanostat 105 can provide the required electrolytic current for electroplating and electroetching. A simple voltage/current supply can also be used in its place. It will be understood that for electroless and immersion plating as well as for chemical etching, galvanostat 105 and counter electrode 104 need not be used.
Initially in the plating/etching process, a high current pulse is passed through substrate 103 using a first source of current/voltage (i.e. pulse generator 109). Pulse generator 109, which can be connected across opposite ends of substrate 103 by wires 110 and 111, supplies current pulses through substrate 103. Pulse generator 109 can be any suitable current source capable of generating current pulses, which, for example, have spans ranging from tens of pico seconds to continuous wave (CW). The current pulses can be designed to heat substrate 103 or its surfaces while it is immersed in 102. Substrates 103 or its surfaces can be heated sufficiently by the current pulses so that the interfering surface coating is removed. For electroplating and electroetching, a second source of voltage/current is provided by source 113. Source 113 can be utilized prior to the heating current pulse applied by pulse generator 109, concurrently, or at any time thereafter.
A fluid circulation system can be set up to agitate the fluid contained in tank 101 to avoid or inhibit boiling or bubbling in the fluid at the surfaces of substrate 103, which can be induced by localized heating caused by passage of the current pulse. The circulation system can include a pump 106 with an input 107 to tank 101, and a drain 108.
Laser 207, which is disposed external to tank 201, can be configured so that its output light is directed into a light pipe or light fiber 206 extending into tank 201. Light fiber 206 can be suitably oriented so that the laser light output is incident on substrate 203. Laser 207 can be suitably pulsed to generate light pulses with pulse widths (e.g., ranging from a few femtoseconds, or ps, to hundreds of microseconds). For some applications longer pulses extending to cw operation can be used. A laser voltage control unit 208 can be used to set the pulse width and pulse intensity of laser 207. Laser 207 can have a laser wavelength in the range of about 0.1-10 micrometers. Laser 207 can, for example, be a near infrared or infrared laser emitting radiation at wavelengths that are suitable for absorption in and heating of the substrates. The intensity and duration of the laser light incident on substrate 203 can be theoretically or empirically designed to remove coatings from the surface of substrate 203 by heating. The coatings/substrate can be sufficiently heated to bring about coating removal by ablation, differential expansion of the coating and the substrate leading to cracking of the coating, melting or any by other mechanism. Alternatively, laser 207 can be an ultraviolet laser emitting radiation at wavelengths that are suitable for photoablative decomposition and removal of the inhibiting layer without substantial heating of the substrates.
With reference to
In plating/etching cell arrangement 300, an optional counter electrode 304 is attached to a galvanostat or voltage/current supply 305. For electroplating or electroetching of substrate 303, a voltage can be applied between counter electrode 304 and substrate 303 before, during, or after moving scribe 306 along the surface of the substrate 303. It will be understood that for electroless, immersion plating and chemical etching processes, galvanostat 305 and counter electrode 304 are not needed or activated.
In plating/etching cell arrangement 400, pointed scribe 410 is spring loaded and can rest on either the front or back surface of substrate 403. In the example shown, pointed scribe 410 rests on the back surface of substrate 403. Further, pointed scribe 410 can be mounted on moveable arm 406 so that it can be moved along the surface of substrate 403 in a controlled manner (using, for example, a controller and digital data processing device (not shown)). An optional insulation material 407 can cover portions of moveable arm 406 to isolate those portions electrically or chemically. As arm 406 together with spring loaded scribe 410 is moved along the back of substrate 403, a pulser 405 can deliver a pulse of current or a cw current (depending on the settings of pulser 405) through scribe 410. For this purpose, current pulser 405 can be connected to pointed scribe 410 and to substrate 403, by connecting wires 411 and 412, respectively. The current transmission through the point of contact of scribe 410 on the back of substrate 403 results in localized heating to remove localized regions of coating on both the front and back surface of 403.
Counter electrode 404, which faces the front surface of substrate 403, can be operated in conjunction with galvanostat or voltage source 408 at any time during the coating removal process to cause plating or etching of front surface regions of substrate 403. These front surface regions correspond to regions of the back of substrate 403 where scribe 410 has delivered current. In certain embodiments, the counter electrode can also be placed behind electrode 410 if the sample is thick and only the back surface is desired to be plated or etched. It will be understood that for electroless, immersion plating and chemical etching, galvanostat 408 and counter electrode 404 are not needed or activated.
The plating/etching cell arrangements can be adapted for use with known industrial material handling systems (e.g., reel-to-reel systems for wire and flat stock substrates).
An exemplary design of die 606 is shown in the inset in
In certain embodiments, die 503 and die 608 in plating/etching cell arrangements 500 (
It will be understood that metal plated layer 720 can be formed by exchange plating from the chemical solution, which can take place after in-situ removal of inhibiting or interfering surface coatings by application of heat pulses or abrading action (
With reference to
Mechanical abrasion die 804 also can serve as an electrical contact to wire or flat stock 806. A voltage source or potentiostat 807 connected to abrasion die 804 can be used to apply an electrical voltage to wire or flat stock 806 across from counter electrode 808 to obtain electroplating or etching action as coating-free wire or flat stock 806 passes through electrolyte 8001. Processed wire or flat stock 806 is drawn out of electrolyte 8001 and wound on pick-up reel 809.
In another embodiment of plating/etching cell arrangement 800, removal of unwanted surface coatings can be accomplished by chemical action. In such an embodiment, enclosure 803 can be configured to hold a reducing gas atmosphere (e.g., hydrogen) to treat the surfaces of passing wire or flat stock 806 to remove unwanted coatings.
It will be understood that in
Conversely, for certain applications in which air exposure times are not a significant issue (e.g., the plating or etching of cleaned aluminum), enclosure 803 can be completely dispensed with.
In preparation for plating or etching in tank 901, substrate 906 is first suspended in enclosure 901. A reducing gas (e.g., hydrogen) can be passed over substrate 906 through ports 903 and 912 to chemically reduce and remove unwanted surface coatings. After removal of the unwanted surface coatings, substrate 906 can be lowered through sliding door 905 into electrolyte 902 for plating or etching action on cleaned substrate surfaces. The intimate proximity of enclosure 904 and electrolyte 902 inhibits re-oxidation of substrate 906 between the coating removal and initiation of plating or etching action. For plating or etching action by electrolyte 902, a potential difference can be established between substrate 906 and a counter electrode 911 by connecting electrode 911 to the opposite polarity terminal of supply 910.
The disclosed subject matter also provides additional techniques and arrangements for in situ removal of inhibiting or interfering surface films to prepare substrates for plating and/or etching. These additional techniques include induction heating, microwave heating and mechanical stamping processes. The additional techniques can be individually used to prepare substrates for plating and/or etching. Alternatively, the techniques can be used in any suitable combination (e.g., abrading and stamping, stamping and microwave heating, etc.) to prepare substrates for plating and/or etching as known to a person of ordinary skill in the art.
Induction heating is a known method for providing fast, consistent heat to a metallic object. Induction heating is used in many manufacturing applications, including, for example, bonding, annealing, metal working and the like. In common induction heating arrangements, an ac coil (i.e., induction coil) is placed in close proximity to a work piece or substrate. The ac coil radiates a time-varying electromagnetic field, which induces eddy currents in a surface layer (“skin depth”) of the metal or metallic work piece/substrate. These eddy currents dissipate energy in the skin depth causing the temperature of the work piece/substrate to rise. The thickness of the “skin depth” of the metal or metallic work piece/substrate depends on the frequency of the ac current driving the induction coil and on the intrinsic electric conductivity of the metal or metallic work piece/substrate. The overall work piece/substrate heating is also a function of the thermal conductivity, geometry and the immediate environment of the work piece/substrate.
In the disclosed subject matter related to metal plating and etching, substrates are subjected to induction heating to remove inhibiting surface films or regrowth. The substrates can be inductively heated when they are either (1) submerged in a plating/etching solution bath or (2) contained within an inert atmosphere in a preparation chamber in close proximity to the plating/etching bath.
The substrates can be inductively heated using either continuous wave (cw) or pulse heating in the inert atmosphere to remove inhibiting oxide or other films. The frequency of the radiated electromagnetic field produced by the induction coil at least in part determines the depth of heating of the substrate. The higher the frequency of the radiated electromagnetic field the greater is the localized surface-like nature of the heating of the substrate, due to the well known electromagnetic skin depth effects. In most instances, there is no need to heat the bulk of the substrate for simply removing the inhibiting surface films. For localized surface heating, which is most effective for removal of inhibiting surface films, it can be desirable to use induction frequencies greater than 60 kHz. A practical frequency regime is at least 100 kHz or greater. Subjecting the substrate to GHz microwave radiation, which is typically generated by a magnetron, can be especially effective in removing the inhibiting film by localizing the heating to a thin surface region. A magnetron-microwave system for removing inhibiting films is also shown in
Induction heating or microwave irradiation heating for removing surface inhibiting films can be most effective in a preparation chamber separate from the plating/etching bath in order to inhibit heating of plating/etching solution itself.
In some instances, induction heating also can be exploited to heat substrates that are submerged in a plating/etching solution. Such induction heating is likely to also heat the plating/etching solution. Circulation and/or cooling of the plating/etching solution can overcome any undesirable or excessive heating of the plating/etching solution caused by induction heating.
As an alternative or in addition to the induction heating and/or magnetron heating techniques already described, ion beam heating can be used to prepare substrates for plating. The ion beam heating technique can be particularly suited for preparing “trenched” substrate topography for plating/etching.
Another mechanical surface film removal technique can be utilized to remove inhibiting coatings, for example, from substrates that are shaped by stamping processes. In such processes and with reference to
According to the disclosed subject matter, a substrate stamping operation is conducted in conjunction with and in close proximity to the metal/plating operations. The stamping operation is conducted just prior to moving the resultant shaped substrate into a plating or etching bath. The shaped substrates, free of inhibiting coatings after stamping, are moved rapidly to the plating bath in a short time interval to inhibit any significant re-oxidation.
The stamping operation can be carried out in air, vacuum, or an inert gas. With suitable selection of the stamping process parameters and conditions, the stamping operation makes it possible to plate onto the re-shaped metal substrates that normally cannot be plated or are difficult to plate due to inhibiting films. New types of substrate materials can be used to substitute or replace current substrate materials for industrial applications. For example, presently copper or copper alloys are used in the connector industry for making connectors. Conventional connectors are made by stamping copper substrates or sheets and then plating them (e.g., with gold). With the disclosed subject matter, it will be possible to use aluminum or titanium metal for connectors with plating occurring after stamping. The combination of stamping operations with metal/plating operations according to the disclosed subject matter is particularly suited for use by the connector industry in which stamping operations are usually undertaken prior to plating.
Alternatively or additionally, the inhibiting layer residing on material 6002 can be removed by means of laser heating or photoablation.
The acid or base used in tank 6005 is preferably the same acid or base used in plating bath 6011, which is contained in the second tank 6014. The acid or base used in tank 6005 is free of plating metal ions. Cross-contamination or compositional change of plating bath 6011 in second tank 6014 can result if fluids from the first bath adhere to material 6002 upon exiting tank 6005 and are transferred to tank 6014. To avoid such compositional change, material 6002 exiting tank 6005 can be wiped clean using, for example, wiper blades 6013. Wiped liquids can be collected in and drained from drag-out container 6008. Alternate methods of cleaning or drying (e.g. radiation from a heating lamp, a nitrogen gas blower and the like) can also be employed for the same purpose.
Plating of material 6002 takes place in plating bath 6011 in the second tank 6014, either galvanostatically or potentiostatically, using galvanostat/potentiostat (or voltage source) 6010. Material 6002 to be plated can be biased negatively relative to voltage source 6010 using grounded contact 6009. A counter electrode/contact 6012 can be biased positively directly from voltage source 6010. Both contacts 6009 and 6012 have ends positioned in second tank 6014 containing plating bath 6011 in order to contact material 6002. Pulse plating, which is well known to those skilled in the art, also can be used. After exiting second tank 6014, a third tank (not shown) can be used to rinse the plated material before it is re-wound on take-up reel 6003.
It is noted that
Additional examples of cell arrangements and plating/etching processes for substrates having inhibiting surface films are described herein with reference to
The high voltage and low voltage pulses are applied between substrate/working electrode 1803 and counter electrode 1804. (See
With reference to
In operation, voltage source 1908 generates high voltage pulses 2001 and low voltage pulses 2002 for reel-to-reel plating of substrate 1903. (See
Cell arrangement 2200 further includes provisions for modifying the free-standing jet plating or etching processes with an electromagnetic energy beam (e.g., an intense laser beam) directed collinearly along jet stream 2208. For this purpose, cell arrangement 2200 includes a pulsed laser 2210 which generates a laser beam 2202. Pulsed laser 2210 is aligned so that laser beam 2202 passes through window 2203 into pressure cell 2204 and then through electrode 2205 along nozzle 2207. On exiting pressure cell 2204, laser beam 2202 is guided by jet stream 2208 which acts as a wave guide or light pipe causing laser beam pulse 2202 and jet stream 2208 to travel collinearly. This wave guide or light pipe arrangement permits laser beam pulse 2202 and jet stream 2208 to be incident collinearly on surface portions of substrate 2209 presented for processing. Modification of electroplating and etching processes with an intense laser beam have been described, for example, in U.S. Pat. No. 4,497,692.
In cell arrangement 2200, a pulsed laser 2201 produces a set of one or more pulses 2202 of laser light for a total time on the order of 1 ps to 10 ms. The set of pulses 2202 is preferably triggered immediately after a new portion of the surfaces of substrate 2209 is presented to jet stream 2208 for processing by movement of robotic arm 2210. The pulsing of laser 2201 can be coordinated with the movement of robotic arm 2210 by digital data processing device 2215 which is interfaced with the robotic arm control system 2211.
In operation, laser pulses 2202 incident on substrate 2209 can be configured to have a power density on the order of 105 to 1010 W/cm2 in order to remove the inhibiting films from the surfaces of substrate 2209. Each laser pulse 2202 can have a pulse width or duration on the order of about 10 ps to 10 ms, and have a fluence of 1-5,000 mJ/pulse. These parameters can be selected on consideration of the cross sectional area of jet stream 2208 as well as the thermal properties of sample 2209 and the coatings thereon.
While laser 2202 is operated in a pulsed mode, jet stream 2208 can be operated in a continuous mode (cw) to activate the desired plating (or etching) processes on the surface of sample 2209. The desired plating or etching can occur after the inhibiting surface films have been removed by application of the high intensity laser pulses 2202. Robotic arm 2210 can move substrate 2209 so that any surface portion of 2209 can be plated (or etched) as determined by digital data processing device 2215, which synchronously controls robotic control system 2211 and the pulsing of laser 2201. In some embodiments, laser 2202 can be programmed so that after emitting a high intensity pulse 2202 that removes the inhibiting surface films, the laser emission drops to a much lower power level to induce laser-enhanced jet plating or etching as is well known in the literature.
In operation, different surface portions of substrate 2209 are moved under electrolyte volume 2303 by movement of robotic arm 2210 under the control of digital data processing device 2215. Like in the operation of cell arrangement 2200, pulsed laser 2201 generates a high intensity laser pulse (or a series of pulses) to remove inhibiting surface films from substrate 2209. The high intensity laser pulse, which can have a duration of a few picoseconds to milliseconds, is directed inside the volume of curtain 2301 on to substrate 2209 to remove inhibiting surface films from surface portions of substrate 2209 under electrolyte volume 2330. As described with reference to
The movement of substrate 2209 caused by robotic arm 2210 results in curtain 2301 being slid along the surface of substrate 2209. Curtain 2301 can have small holes to allow electrolyte 2213 to recirculate through volume 2303. Alternatively, an auxiliary pump (not shown) can be used to maintain a desired level of electrolyte 2213 inside volume 2303 that is defined by conically shaped flexible curtain 2301.
The foregoing merely illustrates the principles of the disclosed subject matter. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will be appreciated that those skilled in the art will be able to devise numerous modifications which, although not explicitly described herein, embody the principles of the disclosed subject matter and are thus within its spirit and scope. For example, it will be readily understood by those skilled in the art that the removal/plating processes, which utilize two tanks with their respective baths, can also be used for individual pieces of material without the use of the reel-to-reel material handling system described with reference to
Further, for example, the native oxide or inherent inhibiting layer on the substrate surface can be used as the equivalent of a contact mask in combination with the laser. The laser removes the portion of the oxide or inhibiting layer permitting plating or etching to occur in just those regions where the laser has removed the inhibiting layer. The plating or etching as well as the removal of the inhibiting layer or oxide can all occur in situ, i.e. within the plating or etching bath. The laser removes the oxide and thereby provides a maskless pattern on the substrate surface in preparation for plating by way of exchange (also known as immersion) plating. Here the laser pulse opens up the oxide while the sample is in the electrolyte. Once the oxide has been removed locally, exchange plating can occur, leaving a very thin layer of the metal in the electrolyte as a deposit on the substrate. During this portion of the operation, there is no potential applied and the exchange or immersion plating leaves a uniformly thin film on each of the areas opened up (oxide removed) by the laser. After that, electroplating or electroless plating can be made to occur on all the thin layers of near equal thickness resulting from the laser pulse and the immersion so that the entire pattern has a resulting uniform thickness. Similarly, the oxide surface layer can be removed by application of high voltage discharge pulse. Again, immersion plating can be allowed to take place followed by standard electroplating to increase the thickness of the immersion layer. Thereafter, a voltage can be applied to provide additional plating in the openings caused by voltage pulse that was used to build up the immersion plated layer.
The plate-up of the exchange plated layer can take place in the same bath in which oxide removal occurred or in a second bath. The second voltage used for plating/etching, which can be continuous or in the form of repetitive pulse, can have an amplitude on the order of about +/−1-3 V. For galvanostatic plating/etching, the second voltage pulse amplitude can be considerably higher depending, for example, on sample size.
In laboratory demonstrations, electroplated patterns of copper on stainless steel 316 substrate have been obtained by first pattern masking the substrate, then applying a voltage pulse to remove surface oxides in the mask openings followed by plating.
In an exemplary embodiment illustrated in
As another example, it can be desired to plate nickel onto aluminum, then plated up by tin. In that case, the laser can be applied to the oxide coated aluminum in nickel bath, the portions of the oxide removed from the sample then electroplated-up by nickel followed by electroplating (or electroless plating) in a tin bath. This technique can be used with a reel-to-reel system since it allows patterning to occur which will have equal thicknesses when the immersion plating is performed before any electroplating occurs since the immersion plating is self limiting and normally stops after a deposit ˜20-50 nm thickness. The plate-up can begin after the patterning by immersion plating is complete so that the entire electroplated pattern will have uniform thickness.
The above technique (after laser ablation) can be used for a single or multiple plating pattern (when immersion plating occurs first) to define the pattern. Then, after the immersion plating has taken place, the same bath can be used to electroplate the immersion pattern resulting in uniform thickness of the entire pattern.
Another method for a reel-to-reel plating system, as shown in
It therefore is a part of the disclosed subject matter to include, in certain embodiments, a scanning mirror pattern that results in distributing the beam spatially while still contacting the moving substrate as it passes through the electrolyte. In an exemplary embodiment, the total area covered by the scanning beam can be as small as 2×2 cm.
In an embodiment shown in
In an embodiment shown in
As shown in
Unless specified otherwise, the aforementioned methods and systems that employ light sources (e.g. lasers) to remove naturally formed metal oxides for in situ plating or etching can function based on thermal or non-thermal means. Generally, thermal mechanisms are often considered the main mechanism for metal oxide removal, and the embodiments described above have focused on thermal means.
In certain embodiments, however, laser radiation that utilizes photons result in the in situ non-thermal or near non-thermal (e.g. around 193 nm, or lower) removal of the oxide is employed in conjunction with any one of the methods and systems described in this application.
Advantages of non-thermal or near non-thermal oxide removal include 1) minimal deformation of the oxide coated substrate to be plated by limiting the accompanying shock wave due to otherwise thermal heating and 2) the oxide can be removed with a minimal removal of substrate material. Generally, the energy/area or fluence to remove an oxide is considerably less than that required to remove the metal itself.
Since the oxide removal utilizes systems of ablation that eliminate or greatly reduce thermalization or heating, melting can be minimized. Thus, the substrate can maintain its smooth surface contour, important in many plating applications.
In one embodiment, the amount of substrate material removal resulting from ablation can be far less than 1 micron in material depth. For example, A. V., Rode et al, Applied Surface Science 254, 3137 (2008), which is hereby incorporated by reference, describes the removal of 14 nm/pulse of copper under certain focusing conditions using femtosecond laser pulses, one of the mechanisms proposed herein. While not being bound by any particular theory, it is believed that in both UV laser ablation and femtosceond laser ablation, there is little thermalization between the excited electrons and the much heavier protons of the absorbing layer so that the electrons assume an antibonding state. As a result the atom in of the thin film ablates, vaporizes or disintegrates due to instability in a non-thermal manner.
A similar process is described by Haight et al in J. Vac. Sci. Technology B17, 3137 (1999), hereby incorporated by reference, in which femtosecond laser pulses are used to ablate a very thin film or layer of misplaced chromium metal on a glass mask. The non-thermal ablating process, using a femtosecond laser, restores the mask to its desired pattern without any damage to the underlying glass. If the glass were to be damaged by the metal removal, the mask would become worthless.
Two laser processes are described herein that can achieve non-thermal or near non-thermal oxide removal: 1) photo ablation using UV laser pulse or pulses and 2) femtosecond laser pulses. The first process, photo ablation with UV, uses a wavelength that causes an electron to be raised to an ionization level causing the atom or molecule to disintegrate. This ‘photoablation’ mechanism has been described in detail in numerous papers. See, e.g., A. V. Kabashin and M. Meunier, Femtosecond laser ablation in aqueous solutions: a novel method to synthesize non-toxic metal colloids with controllable size, Journal of Physics:Conference Series 59, 354 (2007); B. Wolff-Rottke, J. Ihlemann, H. Schmidt, and A. Scholl, ‘Influence of the laser-spot diameter on photo-ablation rates’, Appl. Physics A60, 13-17 (1995); J. Ihlemann, ‘Patterning of oxide thin films by UV-laser ablation,’ Journal of Optoelectronics and Advanced Materials 7, 1191 (2005); J. Ihlemann, A Scholl. H. Schmidt, B. Wolff-Rottke, ‘Nanosecond and femtosecond excimer-laser ablation of oxide ceramics’ Appl. Phys. A60, 411 (1995); and J. Ihlemann, K. Rubahn, Excimer laser micromaching: fabrication and applications of dieletric masks, Applied Surface Science 154-155, 587 (2000), each of which is hereby incorporated by reference in their entirety.
Depending on the uv wavelength, i.e. whether, for example, deep UV or deep near UV, i.e. 193 nm (excitation of gaseous ArF) to 306 nm (excitation of XeCl gas) respectively, the ablating mechanism can be, respectively, electronic and partly thermal or purely electronic. Fluences for this type of ablation are generally in the range 1-10 J/sq-cm, readily available from commercial lasers.
The second method is the use of very short pulses, typically in the femtosecond range, or alternatively in the picosecond range. Here the phonon-phonon and phonon-electron mean free paths, or more precisely the times for collisions to cause thermalization are considerably longer than the pulse duration so that the thermal diffusion cannot be used to explain either the material removal or the depth of thermal diffusion. Generally, such ablation is described in terms of multiphoton absorption which is closely related to the use of deep UV pulses. The multiphoton absorption causes sufficient excitation of the absorbing electron to lead to disintegration of the material.
In certain embodiments, uv pulses or the femtosecond pulses can also be utilized for in situ oxide removal in solution where the solution can be absorbing or where the laser can adversely affect the stability of the solution. In such embodiments, interactions between the solution and laser can be overcome for both UV and femtosecond ablation by using a minimum depth of solution over the material. This can be provided, for example, by continuous spraying of the solution on the material with the oxide layer to be removed or by having a thin layer of solution flowing over the substrate to be plated in the region where the laser is incident.
In one embodiment, excimer lasers are directed into various liquids, such as electrolytes, to achieve ablation of the oxide surface layers. Their use should be analogous to the use of pulsed visible lasers. However the use of femtosecond lasers in that mode could, in certain circumstances, not be ideal as there can be strong interaction between the femtosecond light and liquids. However, it is disclosed as an exemplary embodiment where the ablation takes place in an inert gas after which the substrate is then rapidly transferred into the electrolyte for plating. This embodiment is particularly suited for the use of fs lasers for oxide removal followed by plating/etching (see
Generally, it is preferable that one know the transmission spectrum of all the intended electrolytes, including sulfuric acid which can be used for the initial ablation, followed by rapid transfer to the desired plating solution. For example, the transmission of technic silver, gold and tin are about 100% transmitting from deep uv (about 200 nm to about 1 micron). Deterioration of tin solution has been observed with the use of ns laser pulses to remove the oxide from Al. Since the solution is essentially transparent over the wavelength range 200 to 900 nm, it is likely that the deterioration is due to the heating at the solution/substrate interface. It is therefore likely that the use of either uv (photoablation) or femtosecond pulses to remove the oxide will not result in this degradation.
There are a number of excimer lasers that have strong output in the ultraviolet, from about 157 to 351 nm. There also cw UV lasers and pulsed solid state lasers but the UV from those is generally considerably smaller in intensity and smaller in fluence that that obtainable from excimer lasers. There also exist a large number femtosecond lasers with very high intensity and therefore large fluences. For example one mJ at 50 fs translates to a power of 2×1010 W, which when focused to 1 sq mm generates a fluence 2×1012 W/cm2. All of these lasers can be used for the removal of oxides in situ without causing substantial heating.
For example, to remove aluminum oxide requires, in certain embodiments, on the order of ˜1 J/cm2 which is readily obtained with a 193 ArF laser where the unfocused output pulse is on order of 100 mJ with a repetition rte of 50 Hz (Coherent Complex Pro series). Similarly, the commercially available Coherent KrF Complex Pro series has an output of 150 mj/pulse, at 50 pps. For both of these lasers, oxide layers can be removed at high speeds. With the KrF laser focused to 0.2 square centimeters, it is then possible, with a single pulse, to remove 0.75 sq-cm of oxide in situ, with little substrate heating or ˜35 sq cm/s.
To remove an oxide from a metal in situ for subsequent plating or etching, the lasers for oxide removal can be scanned over the material using methods known by those of ordinary skill in the art. For example, in a reel to reel system, the motion of the substrate between the reels results in at least partial scanning without further accessories. Other methods utilize scanning mirrors or rotating mirrors to direct the laser to desired parts of the substrate.
Shown in
In order for the laser in situ processing to be effective, it is necessary to have the sample reside in an electrolyte that is reasonably transparent (e.g. 240 nm pulses in a nickel Watts bath) to the laser to be used for oxide removal. For purposes of illustration, curves taken with a spectrophotometer using a 1 cm cuvette are shown for a standard copper sulfate electrolyte and a nickel sulfate solution (Watts bath), in
It can be seen from the curves of
From these curves, it is clear that UV lasers in the range ˜250 nm would be suitable for in situ oxide removal in a Watts solution where, for example a KrF excimer laser at 248 nm would have a suitable wavelength, since it is substantially transparent at this wavelength as seen in
In one particular embodiment, which can be used in conjunction with any of the above described methods and systems, a process is provided to prevent unwanted depositions, if any, in areas not subjected to the laser energy. This has been discussed in Ref: T. Kikuchi, S. Z. Chu, S. Jonishi, M. Sakairi, and H. Takahashi, Electrochim. Acta, 47, 225 (2001), which is hereby incorporated by reference in its entirety. These authors used an additional oxidation step to increase the thickness of the natural oxide in order to reduce/eliminate unwanted plating.
In certain embodiments of the present application, however, the presently disclosed subject matter proposes a different solution to prevent unwanted depositions in areas not subjected to the laser energy problem by introducing a source of steam in the reel to reel plating system. It is known that steam causes oxidation of aluminum and other metals (see for example U.S. Pat. No. 5,496,417. Certain embodiments employ steam, incident on the surface of the Al or other oxide coated metal to be plated, to increase the thickness of the natural oxide coating. The laser fluence for removing the oxide is then adjusted to enable removal of the thicker oxide in designated areas on the metal to be plated/etched. Due to the enhanced thickness, random plating can become much less likely if it occurs at all. The use of steam is cheaper and much more rapid as a means of enhancing oxidation, hence increasing oxide thickness, than the use of electrochemical anodizing as proposed in the above cited reference by Kikuchi et al.
The steam can be introduced in the early stages of a reel to reel plating system (e.g. prior to the point in which the substrate encounters the laser source and/or prior to the material entering the electrolyte source).
It will be understood that the foregoing is only illustrative of the principles of the disclosed subject matter, and that various modifications can be made by those skilled in the art without departing from the scope and spirit of the principles. Moreover, features of embodiments described herein can be combined and/or rearranged to create new embodiments.
Claims
1. A system for metal-plating and/or etching on a curved surface of a substrate by action of a chemical solution in a tank containing the chemical solution, the substrate covered by an interfering surface coating, the system comprising:
- a substrate-holding fixture disposed relative to the tank so that at least a portion of the curved surface of the substrate is submerged in the contained chemical solution;
- a light beam source adapted to emit a light beam, and
- one or more optical elements that optically couple the light beam source to the substrate-holding fixture, the one or more optical elements configured to direct the light beam in situ on the submerged portion of the curved surface of the substrate from multiple directions to remove the interfering surface coating thereon and to expose the submerged portion of the curved surface to the action of the chemical solution, thereby permitting metal-plating and/or etching directly on the curved surface of the substrate without interference by the surface coating.
2. The system of claim 1, wherein the light beam is a pulsed laser.
3. The system of claim 1, wherein the pulsed laser is selected from the group consisting of a UV laser and a femtosecond laser.
4. The system of claim 2, wherein the one or more optical elements comprises an oscillating optical element that reflects or refracts the light beam so that the light beam is incident upon the entire circumferential length of the curved surface of the substrate.
5. The system of claim 1, wherein the one or more optical elements comprises an optical fiber carrying the light beam.
6. The system of claim 1, wherein the curved surface is an interior surface of the substrate, and wherein the system further comprises a mechanism to rotate and translate the substrate relative to the light beam so that the light beam irradiation traverses the entire circumferential length of the curved surface of the substrate.
7. The system of claim 6, wherein the mechanism to rotate and translate the substrate relative to the light beam comprises a mechanism to rotate and translate the substrate relative to the tank containing the chemical solution.
8. A system for metal-plating and etching a two-dimensional surface of a substrate by action of a chemical solution in a tank containing the chemical solution, the substrate covered by an interfering surface coating, the system comprising:
- a substrate-holding fixture disposed relative to the tank so that at least a portion of the two-dimensional surface of the substrate is submerged in the contained chemical solution;
- a light beam source adapted to emit a light beam, and
- one or more optical elements that optically couple the light beam source to the substrate-holding fixture, the one or more optical elements configured to direct the light beam in situ on the submerged portion of the two-dimensional surface of
- the substrate to remove the interfering surface coating thereon and to expose the submerged portion of the two-dimensional surface to the action of the chemical solution, thereby permitting metal-plating and/or etching directly on the substrate without interference by the surface coating.
9. The system of claim 8, wherein the a one or more optical elements is configured to direct the light beam along at least a length of the two-dimensional surface.
10. The system of claim 8, further comprising a substrate translation mechanism which moves the substrate along at least a length of its two-dimensional surface under light beam irradiation.
11-29. (canceled)
30. A system for metal-plating or etching a substrate comprising:
- a laser;
- a first bath including a first chemical solution and a first counter electrode, and coupled to a first power supply utilizing a switch for producing mechanical motion of said substrate; and
- a second bath including a second chemical solution and said first counter electrode and coupled to a second power supply.
31. A system for metal-plating or etching a substrate comprising:
- a bath; and
- a scanning mirror coupled to a lens and a laser for ablating said substrate in said bath to achieve said plating or etching.
32. A system of claim 31, further comprising a reel-to-reel system to control the movement of said substrate.
33-38. (canceled)
39. A system for metal-plating or etching a substrate comprising:
- a first bath;
- a supply tank for depositing a layer of chemical solution onto at least one surface of said substrate; and
- at least one laser optically coupled to at least one lens for ablating said substrate in said first bath to achieve plating or etching.
40. The system of claim 39, further comprising a reel-to-reel system to control the movement of said substrate.
41. The system of claim 39, wherein said at least one lens is at least one lens with a focal length greater than 30 cm.
42. The system of claim 39, further comprising a second bath separated from said first bath by a first partition, said second bath containing an electrode for electroplating said substrate.
43. The system of claim 39, wherein said supply tank is said first bath.
44. The system of claim 39, further comprising a second partition, positioned adjacent to a wall of said first bath such that a channel is formed in which said layer of chemical solution is deposited onto at least two surfaces of said substrate.
45. The system of claim 39, further comprising of a plurality of mirrors for directing at least one laser beam produced by said at least one laser to irradiate said substrate from more than one angle.
46-50. (canceled)
51. A system for metal-plating or etching a substrate from more than one angle simultaneously comprising:
- a bath containing a chemical solution;
- one or more lenses;
- one or more lasers coupled to a plurality of mirrors for irradiating said substrate at least partially immersed in said chemical solution in said bath from more than one angle simultaneously with laser beams passed through said one or more lenses.
52. A system for the in situ removal of an inhibiting film on a metal substrate comprising;
- a substrate with an inhibiting film at least partially submerged in an electrolyte;
- a laser radiation source directed toward the substrate, the laser radiation selected from the group consisting of a UV laser and a femtosecond laser.
53. The system of claim 52 wherein said UV radiation is in the wavelength range 157-356 nm.
54. The system of claim 52 where said femtosecond laser pulses are in the wavelength range of from about 700 nm to about 1000 nm.
55. The system as in claim 52 with a counter electrode submerged in said electrolyte; a power supply connected to said substrate and counter electrode to commence with one of a group consisting of electroplating and electroecthing after removal of said oxide film by said laser irradiation.
56. The system of claim 52 wherein said substrate is removed from said electrolyte for one of plating and etching at a later time in any one of several suitable electrolytes.
57-58. (canceled)
59. A system for metal-plating and/or etching on a curved surface of a substrate by action of a chemical solution in a tank containing the chemical solution, the substrate covered by an interfering surface coating, the system comprising:
- a light beam source adapted to emit a light beam,
- a substrate;
- one or more optical elements that optically couple the light beam source to at least a portion of the substrate, the one or more optical elements configured to direct the light beam on the curved surface of the substrate from multiple directions to remove the interfering surface coating thereon; and
- a substrate-holding fixture disposed relative to the tank so that at least a portion of the curved surface of the substrate is submerged in the contained chemical solution;
- wherein the tank is located in proximity to the substrate coupled to the light beam source so as to permit metal-plating and/or etching directly on the curved surface of the substrate prior to reformation of the interfering surface coating.
60. The system of claim 59, wherein the light beam is a pulsed laser.
61. The system of claim 60, wherein the pulsed laser is selected from the group consisting of a UV laser and a femtosecond laser.
62. The system of claim 59, wherein the substrate-holding fixture comprises a reel to reel system.
63. The system of claim 62, wherein the reel to reel system comprises a steam source located so as to allow the steam to contact the substrate prior to being optically coupled to the light source.
Type: Application
Filed: Oct 4, 2010
Publication Date: Feb 24, 2011
Applicant: The Trustees Of Columbia University In The City Of New York (New York, NY)
Inventors: Robert J. Von Gutfeld (New York, NY), Alan C. West (Tenafly, NJ)
Application Number: 12/897,379
International Classification: C25D 17/00 (20060101); C25D 5/00 (20060101); C25F 7/00 (20060101);
