Patent Application
20230279575
The present invention relates to a method for forming nanolaminate structures, and more particularly, to plating a substrate with nanolayers of a first metal and a second metal which are either deposited as a pure metal or an alloy of metals, using an electrolytic plating process.
In many fields today, devices are being created from very small components required to withstand extreme conditions of stress, corrosion or temperature. To support and interconnect these and other components, as well as to provide small-scale structural components, there is growing need for structural components with desired mechanical characteristics, such as modulus of elasticity, elongation, and/or yield strength, with the required mechanical characteristic dependent on the particular application.
For example, given the relatively small size of many of today's electronic components, maintaining reliable electrical contact between components, such as between an Integrated circuit and a printed circuit board, has become very difficult. A component providing such connection must be a conductive material, as well as provide a minimum force to maintain the electrical contact. One solution for providing reliable electrical contact between one component and another component is to use an interposer device comprising a plurality of very small metal springs to maintain mechanical contact. However, the mechanical properties of Individual metals may be inadequate to properly torm such springs. For example, copper may prove too soft, while nickel may prove too brittle. It has been found that by fabricating such springs from a combination of metals, rather than from a single metal, some of the spring properties of the resulting composition are improved. Such an interposer device comprising micro-springs formed from multiple layers of metals is disclosed in U.S. Pat. No. 6,442,039.
Small mechanical features are typically plated or sputtered so as to form components. Generally, nanolaminates are formed via sputtering. However, as those skilled in the art will appreciate, sputtering is an expensive process and currently is only capable of creating nanolaminate structures of a limited size.
Electrolytic plating techniques for forming very thin layers of metals upon a substrate are well known. Such contemporary electrolytic plating techniques are commonly utilized for applying very thin layers of highly conductive materials such as gold, silver and platinum upon less conductive materials such as copper, for example, coating electrical contacts in a connector.
It Is known to use electrolytic plating processes to form multilayer nanolaminate materials shown by U.S. Pat. No. 6,547,944 B2, but only by using multiple metal ions in a single bath and varying the plating current density in a manner so as to plate a layer of one metal ion (the more noble metal) and then changing the plating current density to plate an alloy of the two metals. The alloy can be made to be substantially one of the plated metals (the less noble metal) and a small amount of the other (more noble) metal by controlling the ratio of the concentration of the two metal ions so that the more noble metal ion concentration is very small.
For the method disclosed in U.S. Pat. No. 6,547,944 B2 the low concentration of the more noble metal slows the process down significantly. In addition, the number of metals and their order in the layer stack that can be plated is limited by the ability to control the plating current density precisely. The critical current density for each metal depends on the separation between the metals on the galvanic scale and most metal pairs will overlap in the critical plating density so many of the layers will consist of alloys of the metals in the solution without significant control.
In view of the foregoing, it is desirable to provide a method for forming multiple layer nanolaminate structures utilizing a simple and comparatively inexpensive plating process, wherein structures having comparatively large surface areas and many layers can be plated in a reliable and economically feasible manner and the metal (or alloy) deposited for each layer is independently controlled.
The present invention is directed to a method for forming nanolaminate structures. The method comprises plating a cathode with at least one layer of a first metal, and at least one layer of a second metal, using an electrolytic plating process utilizing one or more plating cells with different plating solutions for the metals forming the layers.
The features, aspects, and advantages of the present invention will be more fully understood when considered with respect to the following detailed description, appended claims and accompanying drawings, wherein:
The detailed description set forth below in connection with the appended drawings is intended as a description of the presently preferred embodiments of the invention; and is not intended to represent the only form in which the present invention may be constructed or utilized. The description sets forth the construction and functions of the invention, as well as the sequence of steps for operating the invention in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention.
The present invention comprises a method for forming nanolaminate structures. The method comprises plating a cathode with a plurality of alternating nanolayers of a first metal and a second metal. The cathode is plated using an electrolytic plating process, wherein the plate current, and thereby the current density of the electrolytic process, is controlled such that the current density at the electrolytic cell cathode is maintained within a predefined range.
Nanolaminates may comprise up to 1000, 5000 or even 10,000 or more metallic nanolayers, with each layer being less than approximately 1000 nanometers, i.e., 1 micron, in thickness. By controlling the thickness of the layers between approximately 0.5 and 1000 nanometers, preferably between 0.8 and 100 nanometers, a dramatic improvement in the mechanical properties of the nanolaminate, as compared to the mechanical properties of either of the individual constituent metals, is achieved. Such nanolayers are preferably formed by plating metals onto a substrate, in accordance with practice of the present invention.
The yield strength, hardness, modulus of elasticity, elongation and other properties of the resulting nanolaminate structure may all be controlled by controlling the thickness of the metal layers. Thus, nanolaminate structures are extremely well suited to such microscopic applications as forming conductive spring structures, for example, in a connector. By using nanolaminates, and controlling the thickness of the metal layers, microscopic structures are created having desired mechanical properties, such as springs having desired size, force and elasticity characteristics. Depending on the application, particular electrical, thermal or magnetic characteristics may also be desired, which may also be produced by controlling the layer thickness within the nanolaminate.
By controlling individual layer thickness in a nanolaminate, the mechanical properties of the laminate may be improved over the same mechanical properties of the individual metals or alloys comprising the layers of the nanolaminate. For example, while the yield strength of copper is approximately 6,000 psi, and the yield strength of nickel is approximately 30,000 psi, the yield strength of a nanolaminate formed of nanolayers of copper and nickel-copper alloy may be improved by greater than a factor of 10, with the yield strength of the nanolaminate approaching 400,000 psi.
It will be appreciated by those skilled in the art that the ions in the solutions may be provided by salts of the metals, such as copper sulfate. It will be further appreciated that there are several approaches to controlling the proper ion concentration in the solutions as it is used. In the preferred embodiment, an inert anode is utilized, and as ions are plated onto the cathode, i.e., the substrate, they are depleted from the solution. It has been found for example, for copper plating solution that a change in the ion concentration of approximately+−0.5% has little or no effect on the plating. Thus, plating may continue until such ions are depleted from the bath to change the concentration by +−0.5%, at which time the ions in the bath must be replenished. It will be appreciated by those skilled in the art that the concentrations of the respective ions in the bath may be properly maintained by “on the fly” addition of solution to the bath so that the plating process will not be interrupted.
It will be further appreciated by those skilled in the art that other methods of maintaining proper ion concentration may be used, such as; for example, replacing the inert anode with a metal or alloy anode that corresponds to the respective ion concentration(s) in the solutions.
In one exemplary embodiment, the substrate onto which the metallic nanolayers are plated comprises a cylindrical mandrel. It will be appreciated by those skilled in the art that this substrate can include any conductive surface, such as metals, films, metallized plastics or any other conductive surface known in the art. It will be further appreciated that “mandrel” is used in the broadest sense of the word, as known to those skilled in the art, to include such other conductive surfaces. By using a mandrel, and plating the layers of metal(s) onto the mandrel, a variety of shapes of nanolaminates may be formed. By forming indentations or protrusions on the mandrel, corresponding structures are formed on the nanolaminate. By use of etching or other conventional techniques, portions of the layer may be removed, so that the resulting nanolaminate structure may be in a variety of forms, such as a spring.
In the preferred embodiment, the mandrel is a stainless steel cylinder or sheet. The thickness of the mandrel may vary, depending on the application. In one embodiment, the mandrel is a 1/8 inch thick by 4.5 inch OD tube.
The substrate, i.e., mandrel, is plated according to a predefined pattern. The pattern may be defined by providing a mask for the mandrel, such that the mandrel is only plated in desired areas, i.e., according to the predefined pattern. It will be appreciated by those skilled in the art that the pattern to be plated may also be defined by using photoresist and developing the same to create a pattern for plating, or any other technique known in the art for creating electrically conductive patterns or shapes. Alternatively, the border of the plating cell can be modified to form the final shape of the structure.
According to the present invention, the thickness of the nanolaminate structure, preferably the thickness of each nanolayer of the nanolaminate structure, is controlled so as to provide a nanolaminate structure having a modulus of elasticity or other mechanical property with approximately a desired value. As those skilled in the art will appreciate, the thickness of the layers is controlled by a combination of factors, including time in the bath, temperature, ion concentration, and current. Thus, according to the present invention, mechanical properties of the nanolaminate structure may be controlled by controlling the thickness of the layers which define the nanolaminate structure.
Referring now to
In the preferred embodiment, during operation the anode assembly containing a solution of one metal ions is held in place on the rotating mandrel until a layer of the desired thickness is deposited. The anode assembly is then removed from the mandrel and replaced by another anode assembly containing a solution of different metal ions and held in place on the rotating mandrel until a second layer of the second metal of desired thickness is deposited onto the first layer. The process, first one anode assembly then the second anode assembly is repeated until the desired number of layers have been deposited.
It is clear to those skilled in the art that this process is not limited to just two anodes and two metals, but any number of anode assemblies and metals may be used to deposit a nanolayer deposit consisting of any number of layers of metals or alloys deposited in any order desired.
Depending on the purity of each deposit desired, the remnant solution left behind after depositing a layer may be removed by rinsing with solvent before depositing the next layer. Also, it is not necessary that the plating solutions/ions be chemically compatible with one another. For example, plating solutions consisting of metal ions dissolved in an organic solvent may be used in the appropriate anode assembly and additional layers using aqueous plating solutions and be used for other metal layers.
Since each layer is being deposited out of its own solution in its own anode assembly, the characteristics of each layer (pure metal or alloy composition) is controlled independently from any of the other layers being deposited.
Referring now to
The Rectifier (9) and/or Controller (10) supply current and voltage to the Anodes (12,16) and Cathode (11). The Cathode (11) rotates on the shaft so new Nano-layers can be applied during each rotation. Plating Solutions (20,21) carry the metal ions to the inert barriers on the Anodes (12,16) where the ions are deposited on the cathode. The pumps (26) move the solutions (20,121) around the apparatus. The Anodes are very close to the Cathode (11) and can be compressed onto the Cathode (11), separated only by the inert barrier materials. The Squeegees (13,15,17,19) clean excess fluids from the Cathode (11). The Rinse Water Spray (14,18) wash residual solutions (20,21) from the Cathode(11). The Catchments (23,24) and Reservoirs (25) catch fluids used in the process for reuse.
The Rectifier (9) and/or Controller (10) supplies current and voltage to the Anodes (12,16) and Cathode (11). The Cathode (11) rotates on the shaft so the surface of the Cathode (11) passes by the Anodes (12,16). Plating Solutions (20,21) are pumped to the inert barrier materials in the space between the Anodes (12,16) and the spinning Cathode (11) where the current flowing from the Rectifier (9) or Controller (10) pulls metal ions from the Solutions (20,21) and deposits the ions on the Cathode (11). The excess solution drains from the Anodes (12,16) into the respective Catchments (23,24). Additional Solution (20,21) is removed from the Cathodes (11) by the Solution Squeegees (13,17) and drains to the Catchments (23,24). As the Cathode rotates, residual Solution (20,21) is cleaned from the Cathode by the Rinse Water Spray (14,18), and the water drains to the Water Reservoir (25) naturally or is actively removed by the Rinse Water Squeegees (15,19). At this time the cathode has rotated nearly 180° and is prepared for plating the next Nano-laminate layer with the opposite brush/solution.
See illustrations and photos. Analogous devices can be found for all mechanical and electrical components of the system in existing industrial installations for tank plating, brush plating, and rotating machinery.
The embodiment that is described here generally is a tubular cathode that rotates under one or more brush plating anodes. Other mechanical configurations are possible. In this configuration, where the anode is separated from the cathode by a non-conductive porous wrapping, what is important is that the cathode and anode move relative to each other. This can be accomplished by holding the cathode still and moving the anode system across the cathode. Or the anode system can be held still and the cathode is moved laterally past the anode system. Alternatively, the cathode could be a disk that rotates under the anode system. Clearly, alternative anode/cathode configurations are possible and practical that would allow nano-laminate layers to be built up on a cathode and which is the best to use depends on the specific application.
The moving Cathode could be replaced with moving Anodes, but there must be movement between those devices. The squeegees and rinsing can be replaced with any suitable method of cleaning the cathode between the application of layers. A singe Anode could be used with a solution having 2 or more metal ions using ion concentration in the solution and voltage current control to preferentially plate an alloy—commercial solutions are available mixed so as to allow an alloy to be plated (for instance tin-lead alloy for solder). A single metal can be plated to create Nano-layers of a single material in order to control grain structure (epitaxial) or other crystal growth/configuration. Referring to some illustrations, the reservoirs or catchments can be combined with the container that holds the solution. (This is shown in some illustrations.) Some of the pumps may be replaced with gravity feeds. Additional “stages” can be added around the perimeter to plate 3 or 4 or more metals. Once the process variables are understood, the anode, first wiper, rinse, second wiper and potentially drying functions can be combined into a single unified Nano-plating “head” to simplify installation and promote consistency.
The anode brushes can be shaped in a way that varies the plating rate along the brush. The large brushes can be divided into several smaller sections with the electrical power to each section controlled independently to plate faster or slower as the cathode moves relative to the anode. This allows patterns to be plated within the layers.
A strip of conductive material can be wound helically around the cathode drum as seen in
Thus, either substantially pure metal or an alloy of metals may be plated at any desired layer. For example, it is described in accordance with the present invention to alternately plate layers of substantially pure metal (for example, copper and nickel layers) so as to form a plurality of alternating layers thereof or to plate layers of a controlled alloy deposition. For example, there are commercially available plating solutions for plating an alloy of nickel and cobalt. Using this method alternating layers of copper and a nickel-cobalt alloy may be plated at any layer thickness for each layer and as many layers as desired.
In the preferred embodiment the solution flows from the (29) input end of the cavity to the (30) output end. The anode is held against the upper surface of the cavity by a (31) stainless steel screw that extends to the outside through a seal and provides a contact for bringing plating current to the anode.
This embodiment needs a good seal around the cavity to maintain a continuous path from the anode to the mandrel through the solution making it more difficult to establish sealed movement between the anode and mandrel. Movement is not necessary, rather the solution is changed for each layer during plating.
Unlike the other embodiments (
Alternatively, the cavity of the embodiment shown in
Referring now to
The nanolaminate structure 33 is formed upon the mandrel 32 utilizing an electrolytic plating process, as described in detail below.
Referring now to
As those skilled in the art will appreciate, such a nanolaminate structure may be utilized to form various different desired structural and/or electrical components. According to the present invention, mechanical properties of the nanolaminate structure 33 are controlled, so as to facilitate the fabrication of a nanolaminate structure having such desired properties. For example, the modulus of elasticity may be controlled by varying the thickness of the layers which comprise the nanolaminate layers 34, 35 and 36, which comprise the nanolaminate structure 33. In one embodiment, the nanolaminate structure comprises alternating layers of 1) a more noble metal, such as copper, and 2) a less noble metal, such as nickel. The thickness of each of the individual layers determines the value of the desired mechanical property. While the illustrated nanolaminate structure is shown having only three layers for simplicity, it should be understood that nanolaminate structures having 100, 500, or more (as many as desired), each layer having the thickness that is desired for that individual layer, can be provided in accordance with practice of the present invention.
Referring now to
As shown in block 52, an electrolytic plating cell assembly is formed such that the mandrel 10 defines one electrode thereof. More than one plating cell may be used to plate alternating layers by moving the plating cell (anode assembly) alternatively over the mandrel or moving the mandrel under the plating cells sequentially. Alternatively, a single plating cell may be used and the solution changed sequentially.
As shown in block 53, the plating current of the cell is controlled in a manner which results in a layer comprising of the desired metal or alloy.
As shown in block 54 either a second cell is emplaced over the previously deposited layer or a second solution replaces the first plating solution in the plating cell, and the plating current of the cell is controlled in a manner which results in a second layer comprising of the desired metal or alloy.
In either instance, the process shown in blocks 53 and 54 are repeated until the desired number of such layers is formed upon the mandrel. As was set forth above, the cycle time (or mandrel/anode relative speed and anode size), ion concentration, and current density are set to obtain the desired layer thickness.
For example, in one particular embodiment of the present invention, a cell utilizing a nickel solution with a concentration of nickel ions of 78 gm/L from nickel sulfate and a second cell utilizing a copper solution with a copper solution of 57 gm/L from copper sulfate were used with a rotating stainless-steel cathode with an outside diameter of 115 mm. For both cells, the plated width under the anode was masked to be 12.5 mm and the length of the anode was 25 mm. The mandrel was rotated at a rate of 60 RPM. Each cell was sequentially held on the mandrel for one revolution 500 times for a total plating thickness of 25 microns and plating time of 1.5 hour.
After the desired number of layers have been formed upon the mandrel, a backing substrate for the nanolaminate structure may optionally be formed upon the nanolaminate structure, preferably while the nanolaminate structure is still attached to the mandrel.
As shown in
Those skilled in the art will appreciate that the method for forming a nanolaminate structure of the present invention may be utilized along with various other technologies, so as to define the desired structure. For example, laser etching, ion milling, as well as various photolithographic techniques may be utilized so as to further define the desired features of the nanolaminate structure of the present invention.
It will be further appreciated that the steps of the method may be practiced in various orders. For example, a backing substrate, such as a flexible polymer, may be formed to the nanolaminate either before or after the nanolaminate is removed from the mandrel. In addition, masking and etching steps may be performed before or after a backing substrate is formed to the nanolaminate, and before or after the nanolaminate is removed from the mandrel.
The above descriptions of exemplary embodiments of methods for forming nanolaminate structures are illustrative of the present invention. Because of variations which will be apparent to those skilled in the art, however, the present invention is not intended to be limited to the particular embodiments described above. The scope of the invention is defined in the following claims.
Nano-Laminate coatings can improve electrical contacts. Electrical contacts should be made from highly conductive materials that also corrosion resistant, high strength, high modulus of elasticity, low contact resistance, high durability and wear resistance, and is non-toxic. Beryllium copper alloys are preferred for challenging applications because they have excellent mechanical properties and good conductivity. The “good” conductivity is still is less than many other copper alloys,
And it is expensive, not highly corrosion resistant, is typically plated with nickel and gold or palladium to improve its contact and wear resistance, and the beryllium is toxic. Yet it is among the “best” materials for challenging electrical contact products. Instead, we can take advantage of the forced small grain and grain boundary effects of the Nano-laminates to improve strength, elasticity, wear resistance, corrosion resistance, and include suitable contact interface materials, with less toxicity. A nanolaminate made from Copper, Nickel and Palladium will have these characteristics, and if plated on a highly conductive copper or copper-alloy core, we can get all the properties we want in one material made with a practical high-speed process.
The helical strip plating process with the shafts spaced such that 10 plating stages are positioned along each flat run of the belt with the strip wound around the shaft 25 times will achieve (10+10)*25=500 layers. These can be applied to each side to deposit a total of 1000 layers. The attached documents describe the plating parameters that, in this configuration using a 36″ wide belt with ˜6′ shaft-to-shaft separation, working on a 1.5″ wide strip helically wound around the belt, can electro-plate 0.001″ (25.4 uM) thick Nano-laminate coatings composed of 500 alternating layers on each side of strip with an output rate of nearly 100 ft/min.
Also, it can create: The large class of products made by stamping metal sheets or foils is likely to see benefits from this technology. Any product that has a thin coating either electro-deposited or coated by other means is similarly likely to see opportunities for improvement with this process. The contact or terminal making process as described above is one example.
The disclosures of U.S. Provisional Application No. 63/157,469, filed Mar. 5, 2021 are incorporated by reference herein in their entirety
