Nanostructured Palladium-Based Alloys and Related Methods

Abstract

This document describes an article including multiple layers of electrical contact portions and a method for applying the contact portions to a substrate. The article may include a substrate on which multiple layers of electrical contact portions are formed. In some embodiments, the electrical contact portions include multiple metal layers.

Description

Technical Field

[0001] Generally described are articles and methods for providing palladium-based alloys for electrical contacts. Background Art

[0002] Metal alloys have many uses in the design and manufacture of articles. Such articles can be used in a variety of applications, including for electronic spaces such as electrical connectors. Different applications can have different performance / property requirements. For example, for certain electrical connector applications, properties such as hardness, ductility, resistivity, and corrosion resistance may be important. To provide certain property enhancements, the composition and structure of the alloy can be designed. Summary of the Invention

[0003] The articles and methods described herein can use nickel-tungsten alloys and palladium-based alloys to form electrical contacts between materials.

[0004] In one aspect, an article for providing an electrical contact is described, the article comprising: a substrate; a first layer over the substrate; and a second layer over the substrate, wherein the first layer comprises a nanocrystalline nickel-tungsten alloy, and wherein the second layer comprises a nanocrystalline palladium-based alloy containing a second metal.

[0005] In another aspect, an article for providing an electrical contact is described, the article comprising a substrate, a first layer over the substrate, and a second layer over the substrate, wherein the first layer comprises a nanocrystalline nickel-tungsten alloy, wherein the second layer comprises a nanocrystalline palladium-based alloy containing a second metal, and wherein the low-level contact resistance of the article is not greater than 10 mOhm.

[0006] In various aspects, a method of manufacturing an electrical contact, the method comprising: providing a substrate; electrodepositing a nanocrystalline nickel-tungsten over the substrate; electrodepositing a metal layer over the substrate; and electrodepositing a nanocrystalline palladium-based alloy containing a second metal over the substrate.

[0007] When considered in conjunction with the accompanying drawings, other advantages and novel features of the present invention will become apparent from the following detailed description of various non-limiting embodiments of the present invention. In the event of conflicts and / or inconsistent disclosures in this specification and the documents incorporated by reference, this specification shall prevail. Brief Description of the Drawings

[0008] Non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, which are schematic and not intended to be drawn to scale. In the figures, each identical or nearly identical component shown is generally represented by a single reference numeral. For clarity, not every component is labeled in every figure, nor is every component of every embodiment of the present invention shown, where illustration is not necessary to enable one of ordinary skill in the art to understand the present invention. In the figures:

[0009] Figures 1A to 1C A stack configuration of three electrical contacts including nickel-tungsten (XT) and a palladium-based alloy is schematically depicted according to a set of embodiments;

[0010] Figure 2 is a graph of the initial low-level contact resistance (LLCR) of a palladium-antimony alloy / palladium-antimony alloy covered electrical contact compared to a palladium-antimony / gold covered electrical contact according to a set of embodiments; and

[0011] Figure 3 shows a description of a dynamic immersion corrosion test according to some embodiments. Detailed Description

[0012] Describes articles (e.g., electrical contacts, coatings) including a palladium-based alloy on a substrate and methods for applying a palladium-based alloy coating for an electrical contact. The article can include a substrate on which a palladium-based alloy is formed. The palladium-based alloy can be a nanocrystalline palladium-based alloy. In some embodiments, the article includes multiple layers (e.g., a palladium-based alloy layer, a first layer, a second layer, a metal layer). For example, an electrical contact can include at least two layers each having a different composition. One layer (e.g., the first layer) can include a nickel-tungsten alloy, and another layer (e.g., the second layer) can include a palladium-based alloy. In some embodiments, the article includes at least four layers (e.g., a palladium-based alloy layer, a nickel-tungsten layer, a metal layer). Generally, the metal layer includes one (e.g., only one) or more metals. In some cases, at least some (e.g., all) of the layers of the article can be applied using an electrodeposition process. As further described below, articles including a multi-layer electrical contact can exhibit desirable properties and characteristics, including, for example, excellent immersion corrosion properties and a low-level contact resistance (LLCR) below a specific threshold. The article can be used in various applications, including for electrical applications and / or electronic applications such as electrical connectors.

[0013] The articles described above and elsewhere in this document can improve the finished connector coating and reduce or eliminate the use of other metals (e.g., rhodium). Palladium-based alloys can improve the performance of electrical contacts with respect to key performance metrics such as wear durability, powered immersion corrosion performance, salt spray endurance, heat age tolerance, and industrial mixed flowing gas corrosion resistance. The nanostructured palladium-based alloys described herein have improved hardness and strength over pure palladium. Unique features of the disclosed alloy systems are improved hardness, reduced microcrystalline size, and more favorable performance in corrosion tests, namely salt spray (ASTM B117) and powered immersion corrosion.

[0014] The palladium-based alloys as described herein can include a second metal. The second metal included in the palladium-based alloy can include Sb, Re, Co, Ir, Os, Pt, Rh, Ru, W, and / or Sn. In some embodiments, the palladium-based alloy is a palladium-antimony alloy (Pd-Sb) and can exhibit some of the unique features described above. However, in other embodiments, other palladium-based alloys can be prepared and can also be nanostructured. Antimony at variable alloy concentrations from 3 atomic % to 33 atomic % is added to a palladium substrate. The resulting alloys are supersaturated solid solutions with a palladium crystal structure. These alloys can be nanocrystalline. In some embodiments, the palladium-based alloy containing antimony as the second metal can exhibit a hardness greater than 600 HV. Reciprocating wear durability testing of Pd-Sb (cap on flat geometry) in combination with Pd-Sb resulted in more than 10,000 wear durability cycles (50 fG, 0.25 Hz in the case of a 3 mm oscillating wiper), where the Pd-Sb layer remained intact.

[0015] As described above, palladium-based alloys containing antimony as a second metal can contain high antimony contents (25 wt% to 35 wt%). Addition of antimony to palladium-based alloys can reduce the microcrystalline size, thus greatly improving the hardness and wear resistance of the alloys. Lower antimony concentrations (up to 10 wt%) in palladium-based alloys also improve hardness, however electroplated coatings are generally highly stressed, thus requiring some additional measures to improve wear performance. High antimony palladium-based alloys can have much lower stress during plating, can be deposited quite rapidly and can form thick films without cracking (e.g., films up to at least 30 μm thick do not crack). Low stress Pd-Sb alloys perform well in wear tests. Unexpectedly, high antimony palladium-based alloys can also exhibit very good corrosion resistance, as demonstrated by dynamic immersion corrosion tests.

[0016] Palladium-based alloys containing Re (e.g., Pd-Re) are also described. The Re content of the alloys can be relatively low, up to 3 atomic %. Higher concentrations of rhenium are possible using tools known to those skilled in the art. In some embodiments, the Pd-Re alloys are nanocrystalline and the resulting alloys are supersaturated solid solutions having a palladium crystal structure.

[0017] The palladium-based alloys described herein (e.g., Pd-Sb, Pd-Re) can be nanocrystalline. As used herein, a "nanocrystalline" structure refers to a structure in which the number average size of the grains (e.g., microcrystals) is less than one micrometer. The number average size of the grains gives equal statistical weight to each grain and is calculated as the sum of the diameters of all spherical equivalent grains divided by the total number of grains in a representative volume of the bulk. In some embodiments, the number average size of the grains can be less than 200 nm, less than 100 nm, less than 50 nm, less than 25 nm, and / or less than 10 nm. In some embodiments, the number average size of the grains can be greater than 1 nm, greater than 5 nm, greater than 10 nm and / or greater than 25 nm. It is understood that all suitable combinations of the above ranges are possible (e.g., 5 nm to 100 nm, 10 nm to 50 nm, 15 nm to 35 nm, etc.).

[0018] Palladium-based alloys (e.g., Pb-Sb) can be used alone as a coating or as part of a stack of multiple plating layers. In some embodiments, the palladium-based alloys can be used as an electrical contact or as part of an electrical contact. For example, now referring to Figure 1A, the electrical contact portion includes a palladium-based alloy as a "Pd alloy" layer having a thickness of 120 μm to 160 μm. In some embodiments, the palladium-based alloy can be directly plated onto nickel or a nickel alloy. By using the palladium-based alloy as described herein, an alternating stack of plating layers is advantageous, particularly from the perspective of reducing the overall use of rhodium alloys as used in certain existing systems and reducing the total cost. For example, compared to Figure 1A compared to Figure 1B schematically shows only one rhodium alloy layer. Additionally, when compared to Figure 1A and Figure 1B compared to Figure 1C schematically shows the absence of a rhodium alloy. However, other stack configurations are possible, and those skilled in the art can configure the stack orientation for a particular use.

[0019] As described above, the palladium-based alloy can be used as a stack in a multi-layer stack. Now referring to Figure 1A , a substrate (e.g., a Cu substrate) can have a palladium-based alloy above the substrate as a first layer (e.g., 120 μin to 180 μin Pd alloy). The substrate can also have a nickel-based alloy above the substrate (e.g., 40 μin to 80 μin XT layer). In some embodiments, an optional metal layer can also be above the substrate. For example, in Figure 1A the substrate has an optional copper metal layer (e.g., 40 μin to 120 μin Cu) directly adjacent to the substrate. As shown in the figure, in addition to additional metal layers such as a RhRu layer, a strike layer or flash layer such as an Au flash layer can also be located between the palladium-based alloy layers. In some embodiments, using the palladium-based alloy can avoid using certain metal layers. For example, in Figure 1B only one RhRu metal layer appears, while the substrate, the palladium-based alloy, and the nickel-based alloy are still present in the stack. In some embodiments, the stack includes a substrate, an optional metal layer adjacent to the substrate, and a nickel-based alloy and a palladium-based alloy above the substrate, as schematically shown in Figure 1C . An optional strike layer or flash layer (e.g., an Au or Pd strike layer) can be between the palladium-based alloy layer and the nickel-based alloy layer because such a layer can promote adhesion between the two layers, as shown in Figure 1C . The above-described stack can be used as an electrical contact portion; however, other arrangements are possible, as described below and elsewhere herein.

[0020] As described above, the article described herein may include a substrate. A variety of different substrates may be suitable. In some cases, the substrate may comprise a conductive material such as a metal, metal alloy, intermetallic material, etc. Suitable base materials include steel, stainless steel, copper and copper alloys (such as brass or bronze materials), aluminum and aluminum alloys, nickel and nickel alloys, polymers having a conductive surface and / or surface treatment, and transparent conductive oxides, etc. In some embodiments, a copper base material is preferred. In some embodiments, the substrate may be formed essentially of one material (e.g., a single material layer or a bulk material). In other embodiments, the substrate is formed of more than one layer of different materials.

[0021] The substrate may be in the form of various shapes and sizes. For example, the substrate may be a strip. In some cases, the substrate may be perforated. In some cases, the substrate may be a discrete component.

[0022] A multilayer coating may be formed on the substrate. In some cases, the coating (e.g., a layer, a metal layer, a nanocrystalline nickel-tungsten layer, a nanocrystalline palladium-based alloy layer) substantially covers the entire outer surface area of the substrate. In some cases, the coating only covers a part of the outer surface area of the substrate. For example, the coating may only cover one outer surface of the substrate. In some cases, some parts of the substrate may be masked when forming the coating so that the coating is selectively formed on certain parts of the substrate while leaving other parts of the substrate uncoated. In some embodiments, one or more layers in the coating may be selectively deposited (e.g., using a mask) during formation. That is, one or more layers (e.g., a metal layer such as Au or Rh) may only cover a part of the underlying layer or the outer surface area of the substrate.

[0023] The first layer may be an optional metal layer such as a copper layer above the substrate. For example, as Figure 1B shown, an optional metal layer (e.g., 40uin to 120uin Cu) may be directly on the Cu substrate base. In some embodiments, an additional optional metal layer such as a nickel-based layer (e.g., Figure 1B the XT layer schematically depicted) may be directly coated on the optional metal layer. Next, an optional flash layer or strike layer may be directly adjacent to the nickel-based layer, followed by a palladium-based alloy layer, as in Figure 1B shown. An additional layer (e.g., the RhRu alloy layer as Figure 1B shown) may be adjacent to the palladium-based alloy layer.

[0024] In some cases, the first metal layer comprises nickel. The nickel can be in the form of nickel metal (e.g., substantially pure metal). In some cases, the first metal layer comprises a nickel-based alloy. In some cases, the nickel alloy further comprises tungsten and / or molybdenum (e.g., nickel-tungsten alloy, nickel-molybdenum alloy, nickel-tungsten-molybdenum alloy). The nickel alloy can be in the form of a solid solution. Other nickel alloys can also be used. For example, the nickel alloy can further comprise cobalt, phosphorus, and / or palladium. In some cases, the weight percentage of nickel in the alloy can be from 25 weight percent to 85 weight percent; and in some cases, from 50 weight percent to 80 weight percent. In these cases, the remainder of the alloy can be tungsten and / or molybdenum. Other weight percentages outside of this range can also be used. For example, in some embodiments and for certain applications, the weight percentage of tungsten in the alloy can be greater than or equal to 10 weight percent; in some cases, greater than or equal to 14 weight percent; in some cases, greater than or equal to 15 weight percent; and in some cases, greater than or equal to 20 weight percent. In some cases, the total weight percentage of tungsten in the alloy is less than or equal to 50 weight percent; in some cases, the total weight percentage of tungsten in the alloy is less than or equal to 45 weight percent; in some cases, the total weight percentage of tungsten in the alloy is less than or equal to 40 weight percent; in some cases, the total weight percentage of tungsten in the alloy is less than or equal to 35 weight percent; in some cases, the total weight percentage of tungsten in the alloy is less than or equal to 30 weight percent; and in some cases, the total weight percentage of tungsten in the alloy is less than or equal to 20 weight percent.

[0025] In some cases, the first metal layer can have a specific microstructure. For example, the first metal layer can have a nanocrystalline microstructure. As used herein, a "nanocrystalline" structure refers to a structure in which the number average size of the grains is less than one micrometer. The number average size of the grains provides the same statistical weight to each grain and is calculated as the sum of the diameters of all spherical equivalent grains divided by the total number of grains in a representative volume of the body. In some embodiments, the number average size of the grains can be less than 200 nm, less than 100 nm, less than 50 nm, less than 25 nm, and / or less than 10 nm. In some embodiments, the number average size of the grains can be greater than 1 nm, greater than 5 nm, greater than 10 nm, and / or greater than 25 nm. It should be understood that all suitable combinations of the above ranges are possible (e.g., 5 nm to 100 nm, 10 nm to 50 nm, 15 nm to 35 nm, etc.). In some embodiments, the first metal layer can have an amorphous structure. As is known in the art, an amorphous structure is a non-crystalline structure characterized by the absence of long-range symmetry in the atomic positions. Examples of amorphous structures include glass or glass-like structures.

[0026] In some embodiments, the thickness of the first metal layer can be greater than 0.1 micron, greater than 0.25 micron, greater than 0.5 micron, greater than 1.0 micron, and / or greater than 2.0 microns. In some embodiments, the thickness is less than 20.0 microns, less than 10.0 microns, less than 5.0 microns, less than 3.0 microns, less than 2.0 microns, less than 1.0 micron, and / or less than 0.5 micron. It should be understood that all suitable combinations of the above ranges are possible (e.g., 0.1 micron to 5.0 microns, 0.25 micron to 3.0 microns, 0.5 micron to 2.0 microns, etc.).

[0027] The second layer of the coating can be a metal layer. In some embodiments, the second layer is formed over the substrate. In some embodiments, the second layer is formed directly on the first layer. In other embodiments, an intermediate layer is formed between the first layer and the metal layer. For example, an intermediate strike layer (e.g., comprising Pd and / or Au) can be formed between the first layer and the second layer for various purposes such as enhancing adhesion.

[0028] The second layer comprises a palladium-based alloy. The palladium-based alloy can comprise a second metal (i.e., a metal different from palladium). In some embodiments, the palladium-based alloy includes palladium-antimony. In some embodiments, the palladium-based alloy includes palladium-rhenium. The palladium-based alloy can be in the form of palladium metal (e.g., substantially pure metal). The palladium-based alloy can be in the form of a solid solution. In some embodiments, it is preferred that the second layer comprises a palladium-antimony alloy. Other palladium alloys can also be used. In some embodiments, the weight percentage of palladium and / or rhenium in the palladium-based alloy (e.g., the remainder being substantially palladium) can be at least 25 weight percent, at least 30 weight percent, or at least 35 weight percent. In some embodiments, the weight percentage of antimony and / or rhenium in the palladium-based alloy (e.g., the remainder being substantially palladium) can be less than 35 weight percent, less than 30 weight percent, or less than 25 weight percent. It should be understood that all suitable combinations of the above ranges are possible (e.g., 25 weight percent to 30 weight percent, 25 weight percent to 35 weight percent, 30 to 35, etc.). Other weight percentages outside of this range can also be used.

[0029] The concentration of the second metal (e.g., antimony and / or rhenium) can also be described in atomic percentage (i.e., atomic %). In some embodiments, the concentration of the second metal in the palladium alloy (e.g., the remainder is substantially palladium) is at least 3 atomic %, at least 5 atomic %, at least 10 atomic %, at least 15 atomic %, at least 20 atomic %, at least 25 atomic %, at least 30 atomic %, or at least 33 atomic %. In some embodiments, the concentration of the second metal in the palladium alloy is not greater than 33 atomic %, not greater than 30 atomic %, not greater than 25 atomic %, not greater than 20 atomic %, not greater than 15 atomic %, not greater than 10 atomic %, not greater than 5 atomic %, or not greater than 3 atomic %. Combinations of the above ranges are possible (e.g., at least 3 atomic % and not greater than 33 atomic %). Other ranges are also possible.

[0030] In some cases, the second layer can have a specific microstructure. For example, the second metal layer can have a nanocrystalline microstructure. In some embodiments, the number-average size of the grains (e.g., microcrystals) can be less than 200 nm, less than 100 nm, less than 50 nm, less than 25 nm, less than 10 nm, and / or less than 5 nm. In some embodiments, the number-average size of the grains can be greater than 1 nm, greater than 5 nm, greater than 10 nm, and / or greater than 25 nm. It should be understood that all suitable combinations of the above ranges are possible (e.g., 5 nm to 100 nm, 10 nm to 50 nm, 15 nm to 35 nm, etc.). In some embodiments, the second layer can have an amorphous structure.

[0031] In some embodiments, the thickness of the second layer can be greater than 0.01 microns, greater than 0.1 microns, greater than 0.25 microns, greater than 0.5 microns, and / or greater than 1.0 microns. In some embodiments, the thickness is less than 25.0 microns, less than 10.0 microns, less than 5.0 microns, less than 2.5 microns, less than 1.0 microns, and / or less than 0.5 microns. It should be understood that all suitable combinations of the above ranges are possible (e.g., 0.1 microns to 10.0 microns, 0.25 microns to 5.0 microns, 0.5 microns to 3.0 microns, etc.). The third layer of the electrical contact portion can be a metal layer. In some embodiments, the third metal layer is formed directly on the second layer. In other embodiments, an intermediate layer is formed between the second layer and the third layer.

[0032] In some embodiments, there is a third layer. The third layer can be a metal layer. In some embodiments, the third layer comprises one or more noble metals. Examples of suitable noble metals include Ru, Rh, Os, Ir, Pd, Pt, Ag, and / or Au. In some embodiments, the noble metal is selected from Ru, Os, Ir, Pd, Pt, Ag, and Au, or a combination thereof. In some embodiments, gold can be preferred. In some embodiments, palladium can be preferred. In some embodiments, Au can be preferred. In some embodiments, the metal layer consists essentially of one noble metal. In some cases, the noble metal is not rhodium and / or not ruthenium. In other cases, the metal layer can comprise an alloy containing at least one noble metal and at least one other metal. The other metals can be selected from Ni, W, Fe, B, S, Co, Mo, Cu, Cr, Zn, and Sn, etc.

[0033] In some cases, the third layer can have a specific microstructure. For example, the third layer can have a nanocrystalline microstructure. In some embodiments, the number-average size of the grains can be less than 200 nm, less than 100 nm, less than 50 nm, less than 25 nm, and / or less than 10 nm. In some embodiments, the number-average size of the grains can be greater than 1 nm, greater than 5 nm, greater than 10 nm, and / or greater than 25 nm. It should be understood that all suitable combinations of the above ranges are possible (e.g., 5 nm to 100 nm, 10 nm to 50 nm, 15 nm to 35 nm, etc.). In some embodiments, the third layer can have an amorphous structure.

[0034] In some embodiments, the thickness of the third layer can be greater than 0.01 microns, greater than 0.05 microns, greater than 0.1 microns, greater than 0.25 microns, greater than 0.5 microns, greater than 1.0 microns, and / or greater than 5.0 microns. In some embodiments, the thickness is less than 10.0 microns, less than 5.0 microns, less than 2.0 microns, less than 1.0 microns, less than 0.5 microns, less than 0.25 microns, and / or less than 0.1 microns. It should be understood that all suitable combinations of the above ranges are possible (e.g., 0.05 microns to 5.0 microns, 0.1 microns to 3.0 microns, 0.1 microns to 2.0 microns, 0.25 microns to 0.75 microns, etc.).

[0035] In some embodiments, an article (e.g., an electrical contact, a coating) can include a fourth layer. However, it should be understood that in other embodiments, there can be no fourth layer. The fourth layer of the article can be a metal layer. In some embodiments, the fourth metal layer is formed directly on the third metal layer. In other embodiments, an intermediate layer is formed between the third metal layer and the fourth metal layer.

[0036] In some embodiments, the fourth layer comprises a platinum group metal (e.g., Group 10, ruthenium, rhodium, palladium, osmium, iridium, and / or platinum). In some cases, the platinum group metal may preferably be rhodium. It has been observed that particularly attractive properties (e.g., immersion corrosion) can be achieved when the fourth metal layer comprises rhodium. Rhodium may be in the form of rhodium metal (e.g., substantially pure). In some cases, rhodium may be in the form of an alloy with one or more other metals (e.g., noble metals). Other compositions may also be suitable for the fourth metal layer.

[0037] In some cases, the fourth layer (e.g., the fourth metal layer) may have a specific microstructure. For example, the fourth metal layer may have a nanocrystalline microstructure. In some embodiments, the number-average size of the grains may be less than 200 nm, less than 100 nm, less than 50 nm, less than 25 nm, and / or less than 10 nm. In some embodiments, the number-average size of the grains may be greater than 1 nm, greater than 5 nm, greater than 10 nm, and / or greater than 25 nm. It should be understood that all suitable combinations of the above ranges are possible (e.g., 5 nm to 100 nm, 10 nm to 50 nm, 15 nm to 35 nm, etc.). In some embodiments, the fourth metal layer may have an amorphous structure.

[0038] In some embodiments, the thickness of the fourth layer may be greater than 0.01 microns, greater than 0.05 microns, greater than 0.1 microns, greater than 0.25 microns, greater than 0.5 microns, greater than 1.0 microns, and / or greater than 2.5 microns. In some embodiments, the thickness is less than 10.0 microns, less than 5.0 microns, less than 2.0 microns, less than 1.0 microns, less than 0.5 microns, less than 0.25 microns, and / or less than 0.1 microns. It should be understood that all suitable combinations of the above ranges are possible (e.g., 0.01 microns to 10.0 microns, 0.05 microns to 5.0 microns, 0.05 microns to 2.0 microns, or 0.1 microns to 0.5 microns, etc.).

[0039] In some embodiments, the electrical contact includes a first layer comprising nickel (e.g., nickel-tungsten alloy), and a second layer comprising palladium (e.g., palladium-antimony alloy). In some embodiments, the electrical contact further includes a third layer (e.g., strike layer, flash layer) and a fourth layer (e.g., fourth layer comprising rhodium and / or ruthenium) comprising gold and / or palladium. This arrangement of layers unexpectedly exhibits particularly excellent properties, including excellent immersion corrosion properties (e.g., with or without an applied bias). Some other particularly excellent properties can include desired coloring (e.g., desired chroma / hue, color stability over time, etc.), excellent wear resistance, and stable surface conductivity (e.g., as measured by the EIA 364 test protocol, the contact resistance varies by less than 1 ohm, less than 100 m-ohm, less than 50 m-ohm, less than 25 m-ohm, and / or less than 10 m-ohm with testing).

[0040] It should be understood that the article (e.g., the electrical contact) can include any combination of the above layers. For example, the article can include a palladium-based alloy (e.g., nanocrystalline palladium-based alloy), followed by a nickel-based alloy (e.g., nanocrystalline nickel-tungsten alloy), or can include a nickel-based alloy, a strike layer (e.g., Au), followed by a palladium-based alloy layer. Additionally, it should be understood that the electrical contact can include more than four layers (e.g., a fifth layer, a sixth layer, a seventh layer, etc.) and more than four metal layers. However, in some embodiments, the electrical contact can include only four layers. In some embodiments, the electrical contact can include fewer than four layers (e.g., one or both of the first, second, and third metal layers described above may not be present). In some embodiments, the electrical contact can include only two layers, such as a palladium-based alloy layer and a nickel-based alloy layer. For example, the coating can include the fourth layer described above and one (or more) other layers (e.g., the first layer, the second layer, and / or the third layer).

[0041] As described above, the layers of the electrical contact can be formed using an electrodeposition process. Electrodeposition generally involves depositing a material (e.g., an electroplating) on a substrate by contacting the substrate with an electrodeposition bath and passing an electric current through the electrodeposition bath between two electrodes, i.e., due to the potential difference between the two electrodes. For example, the methods described herein can involve providing an anode, a cathode, an electrodeposition bath (also referred to as an electrodeposition fluid) associated with (e.g., in contact with) the anode and the cathode, and a power source connected to the anode and the cathode. In some cases, the power source can be driven to generate a waveform for producing the coating, as described more fully below.

[0042] Typically, different layers (e.g., metal layers) can be applied using separate electroplating baths. In some cases, individual articles (e.g., substrates, electrical contacts) can be connected such that they can be sequentially exposed to separate electroplating baths, e.g., in a reel-to-reel process. For example, the articles can be connected to a common conductive substrate (e.g., a strip). In some embodiments, each electroplating bath can be associated with a separate anode, and the interconnected individual articles can generally be connected to a cathode.

[0043] The electroplating process can be adjusted by changing the potential applied between the electrodes (e.g., potential control or voltage control) or by changing the current or current density allowed to flow (e.g., current control or current density control). In some embodiments, direct current (DC) electroplating, pulsed current electroplating, reverse pulsed current electroplating, or a combination thereof can be used to form (e.g., electroplate) a coating. In some embodiments, reverse pulsed electroplating can be preferred to form, for example, a barrier layer (e.g., a nickel-tungsten alloy). Pulses, oscillations, and / or other variations in voltage, potential, current, and / or current density can also be incorporated during the electroplating process, as described more fully below. For example, pulses of controlled voltage can be alternated with pulses of controlled current or current density. Typically, during the electroplating process, a potential can exist on the substrate to be coated (e.g., the base material), and changes in the applied voltage, current, or current density can cause changes in the potential on the substrate. In some cases, the electroplating process can include using a waveform that includes one or more segments, where each segment involves a specific set of electroplating conditions (e.g., current density, current duration, electroplating bath temperature, etc.), as described more fully below.

[0044] Some embodiments of the present invention relate to electroplating methods in which the grain size of the electroplated material (e.g., metal, alloy, etc.) can be controlled. In some embodiments, selecting a specific coating (e.g., electroplating) composition, such as the composition of an alloy deposit, can provide a coating with a desired grain size. In some embodiments, the electroplating methods (e.g., electroplating conditions) described herein can be selected to produce a specific composition, thereby controlling the grain size of the deposited material.

[0045] In some embodiments, a coating, an electrical contact, or a portion thereof can be electrodeposited using direct current (DC) electroplating. For example, a substrate (e.g., an electrode) can be positioned in contact with (e.g., immersed in) an electroplating bath containing one or more substances to be deposited on the substrate. A constant steady-state current can be passed through the electroplating bath to produce a coating or a portion thereof on the substrate. In some embodiments, the potential applied between the electrodes (e.g., potential control or voltage control) and / or the current or current density allowed to flow (e.g., current control or current density control) can be varied. For example, pulses, oscillations, and / or other variations in voltage, potential, current, and / or current density can be incorporated during the electroplating process. In some embodiments, pulses of controlled voltage can be alternated with pulses of controlled current or current density. In some embodiments, pulse current electroplating, reverse pulse current electroplating, or a combination thereof can be used to form (e.g., electrodeposit) a coating.

[0046] In some cases, a bipolar waveform can be used that includes at least one forward pulse and at least one reverse pulse (i.e., a "reverse pulse sequence"). In some embodiments, at least one reverse pulse immediately follows at least one forward pulse. In some embodiments, at least one forward pulse immediately follows at least one reverse pulse. In some cases, the bipolar waveform includes multiple forward and reverse pulses. Some embodiments can include a bipolar waveform that includes multiple forward and reverse pulses, each pulse having a specific current density and duration. In some cases, using a reverse pulse sequence can allow adjustment of the composition and / or grain size of the resulting coating.

[0047] It should be understood that other techniques can be used to produce an article (e.g., an electrical contact) as described herein, including but not limited to electroless plating processes, vapor processes (e.g., physical vapor deposition, chemical vapor deposition, ion vapor deposition, etc.), sputtering, spraying, powder-based processes, slurry-based processes, and the like.

[0048] As described above, an article including a multi-layer coating can exhibit desirable properties and characteristics, including, for example, excellent immersion corrosion properties. The immersion corrosion properties described herein can be measured at 22 °C in a three-electrode temperature-controlled jacketed cell. The cell includes a platinum wire as a counter electrode and an Ag / AgCl reference electrode in a saturated KCl solution. A sample (e.g., a coated article) is immersed in a test solution such as artificial sweat (e.g., artificial sweat manufactured according to ISO 3160), and a positive bias voltage (e.g., 5 volts) is applied to the sample. The time to failure (e.g., in minutes) is measured.

[0049] There are several types of failures that can be characterized in different ways. As used herein, the time to reach "initial visible failure" is defined as the test time until the earliest visible corrosion indication of the sample to the naked eye.

[0050] As used herein, the time to reach "functional failure" is the test time until the connector formed by the sample no longer functions, as defined by the low level contact resistance (LLCR) measured according to EIA - 364 - 23B on its mating surface being greater than 50 mOhm. In some embodiments, the functional failure can be the test time until the LLCR measured according to EIA - 364 - 23B on the mating surface is greater than 100 mOhm; in some embodiments, greater than 250 mOhm; in some embodiments, greater than 1 Ohm; and in some embodiments, greater than 10 Ohm. In some embodiments, the time to reach functional failure is the test time until the connector formed by the sample no longer functions, as defined by the change in LLCR measured according to EIA - 364 - 23B on its mating surface being greater than or equal to 10 mOhm; in some embodiments, greater than 15 mOhm; in some embodiments, greater than 20 mOhm; in some embodiments, greater than 50 mOhm; in some embodiments, greater than 100 mOhm; in some embodiments, greater than 250 mOhm; and in some embodiments, greater than 1 Ohm.

[0051] As used herein, the time to reach "apparent corrosion" failure can be defined as the test time until the earliest corrosion products of the size and location described in EIA - 364 - 53B, "Nitric Acid Vapor Test, Gold Finish Test Procedure for Electrical Connectors and Sockets", have a frequency greater than 2%; in some embodiments, greater than 10%; and in some embodiments, greater than 15%.

[0052] One of ordinary skill in the art will recognize that visible corrosion along the edges of a multi - layer coating is typically caused by "edge effects" and is generally not counted as a failure indication during a given test. One of ordinary skill in the art will also recognize that local processing defects, incorrect cleaning or activation of the sample prior to layer synthesis, or mechanical or chemical damage exposure of the multi - layer coating prior to testing can render a given test invalid, regardless of the type of failure being evaluated.

[0053] The excellent immersion corrosion characteristics of an article including multiple layers of electrical contact portions can be characterized by the time to failure in an immersion corrosion test. For example, in some embodiments, the time for a multi-coated article to reach failure (e.g., initial visible failure, functional failure, and / or apparent corrosion failure) is at least 5 minutes at 5 volts in artificial sweat; in some embodiments, at least 10 minutes at 5 volts in artificial sweat; in some embodiments, at least 20 minutes at 5 volts in artificial sweat; in some embodiments, at least 40 minutes at 5 volts in artificial sweat; in some embodiments, at least 80 minutes at 5 volts in artificial sweat; and in some embodiments, at least 100 minutes at 5 volts in artificial sweat. In some embodiments, the time to reach initial visible failure is less than 360 minutes at 5 volts in artificial sweat, less than 240 minutes at 5 volts in artificial sweat, or less than 120 minutes at 5 volts in artificial sweat.

[0054] The article can be used in various applications, including electrical applications such as electrical connectors (e.g., plug-in). Non-limiting examples of electrical connectors include infrared connectors, data and / or power connectors (e.g., USB connectors), video connectors (e.g., HDMI connectors), audio connectors (e.g., 3.5 mm audio plugs), battery chargers, battery contacts, automotive electrical connectors, etc.

[0055] The following examples are intended to illustrate certain embodiments of the present invention and not to exemplify the full scope of the present invention.

[0056] Example 1

[0057] The following example describes the preparation and characterization of a palladium-based alloy Pd-Sb using antimony as the second metal.

[0058] The Pd-Sb alloy was electroplated onto a Pd strike layer over 2 μm of nickel-tungsten over a copper alloy C7025 base metal. The plating was deposited on flat specimens as well as on "caps" that were 1 mm hemispherical domes. The low-level contact resistance of the resulting samples was evaluated. Without any wipes at the contact interface, the mating force was monotonically increased from 25 gF to 1000 gF using a plunger-type contact probe. Two configurations were tested: 1) mating a PdSb alloy cap with a similarly plated PdSb alloy flat specimen; and 2) mating a cap plated with 0.75 μm of hard Au over 2 μm of nickel-tungsten with a flat specimen plated with PdSb. Figure 2 The results showed low and stable contact resistance for these new coatings.

[0059] A variety of Pd-Sb alloys are fabricated by electroplating onto a copper substrate. The crystallite size is determined by X-ray diffraction. The samples are sectioned and the hardness is measured by Vickers hardness testing. The antimony content is measured by XRF and reported in Table 1 as weight percentage.

[0060] Table 1.

[0061]

[0062] Example 2

[0063] The preparation of a palladium-based alloy Pd-Re with rhenium as the second metal is described below.

[0064] The Pd-Re alloy is electroplated onto a copper substrate. The Re content can be varied by changing the plating conditions or the Re content in the bath. The samples are sectioned and the hardness is measured by Vickers hardness testing. The rhenium content is measured by SEM / EDS and reported in Table 2 as atomic percentage.

[0065] Table 2.

[0066]

[0067] Compared with other Pd alloys such as Pd-Ni and Pd-Co, this Pd alloy exhibits improved resistance to dynamic immersion corrosion. The test method for dynamic immersion corrosion is shown in Figure 3 and components coated with Pd-Sb are tested using this configuration.

[0068] Example 3

[0069] The Pd-Sb alloys prepared as described herein are compared with certain existing Pd-Ni alloys below.

[0070] The Pd-Sb alloy is coated onto copper alloy substrate connector pins to different thicknesses and with an Sb content of 30 atomic %. The pins are exposed to different voltages and durations to measure the performance response compared to existing commercial alloys as shown in Table 3 below.

[0071] Table 3.

[0072]

[0073] Although several embodiments of the present invention have been described and illustrated herein, those of ordinary skill in the art will readily envision various other means and / or structures for performing the functions and / or obtaining the results and / or one or more of the advantages described herein, and each of such variations and / or modifications is considered to be within the scope of the present invention. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary, and the actual parameters, dimensions, materials, and / or configurations will depend upon the specific one or more applications in which the teachings of the present invention are used. Those skilled in the art will recognize or be able to ascertain using no more than routine experimentation many equivalents to the specific embodiments of the invention described herein. Accordingly, it is to be understood that the foregoing embodiments are presented by way of example only, and that within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described and claimed. The present invention pertains to each and every individual feature, system, article, material, and / or method described herein. In addition, any combination of two or more such features, systems, articles, materials, and / or methods, if such features, systems, articles, materials, and / or methods are not mutually inconsistent, is included within the scope of the present invention.

[0074] Unless the context clearly dictates otherwise, a noun in the singular form and without an article in the specification and claims herein shall be understood to mean "at least one."

[0075] As used herein in the specification and claims, the phrase "and / or" shall be understood to mean "one or both" of the elements so conjoined, i.e., in some instances the elements coexist and in other instances the elements exist separately. Unless the context clearly dictates otherwise, there may optionally be other elements in addition to those expressly identified by the "and / or" conjunction, whether related or unrelated to those expressly identified. Thus, as a non-limiting example, when used in conjunction with open-ended language such as "comprising," reference to "A and / or B" in one embodiment may refer to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); and so forth.

[0076] As used herein in the specification and in the claims, "or" shall be understood to have the same meaning as "and / or" as defined above. For example, when separating items in a list, "or" or "and / or" shall be understood to be inclusive, i.e., including at least one of the elements or list of elements, but also including more than one of them, and optionally including additional unrecited items. Only terms specifically stating the contrary, such as "only one" or "exactly one", or when used in the claims "consisting of...", will refer to including exactly one element of a list of elements or list of elements. Generally, when preceded by exclusive terms (such as "either", "one of", "only one of" or "exactly one of"), the term "or" as used herein shall be understood to denote only exclusive alternatives (i.e., "one / kind or the other / kind, but not both"). When used in the claims, "consisting essentially of..." will have its ordinary meaning as used in the field of patent law.

[0077] As used herein in the specification and in the claims, when referring to a list of one or more elements, the phrase "at least one" shall be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements, and not excluding any combination of elements in the list of elements. This definition also allows that there may optionally be elements other than those specifically recited in the list of elements referred to in the phrase "at least one", whether related or unrelated to those specifically recited. Thus, as a non-limiting example, "at least one of A and B" (or equivalently, "at least one of A or B", or equivalently, "at least one of A and / or B") in one embodiment may refer to at least one A, optionally including more than one A, without B (and optionally including elements other than B); in another embodiment, it may refer to at least one B, optionally including more than one B, without A (and optionally including elements other than A); in yet another embodiment, it may refer to at least one A, optionally including more than one A, and at least one B, optionally including more than one B (and optionally including other elements); and so on.

[0078] Some embodiments may be embodied as methods, in which multiple embodiments have been described. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed that perform the acts in a different order than shown, which may include different (e.g., more or fewer) acts than those described, and / or may involve performing some acts simultaneously, even if those acts are shown as sequential in the embodiments specifically described above.

[0079] The use of ordinal terms such as "first", "second", "third", etc. in a claim to modify the claim element itself does not mean any precedence, order, or sequence of one claim element with respect to another claim element or the chronological order of acts of a method of performing, but is used merely as a label to distinguish one claim element having a certain name from another element having the same name (but using an ordinal term) to distinguish claim elements.

[0080] In the claims as well as in the specification above, all transitional phrases such as "comprising", "including", "carrying", "having", "containing", "involving", "holding", etc. shall be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases "consisting of" and "consisting essentially of" shall be closed or semi-closed transitional phrases, respectively, as set forth in section 2111 of the Patent Examination Procedure Manual of the United States Patent and Trademark Office.

Claims

1. An article, comprising: a substrate; and a layer over the substrate; wherein the layer comprises a nanocrystalline palladium-antimony alloy having an antimony concentration of 25 wt% to 35 wt% of the alloy.

2. The article according to claim 1, comprising a second layer.

3. The article according to claim 2, wherein, the second layer comprises Au and / or Pd.

4. The article according to claim 1 or 2, comprising a third layer.

5. The article according to claim 4, wherein, the third layer comprises rhodium metal.

6. The article according to claim 1 or 2, wherein the substrate comprises copper.

7. The article according to claim 1 or 2, wherein the nanocrystalline palladium-antimony alloy has a hardness of at least 600 HV.

8. The article according to claim 1 or 2, wherein the nanocrystalline palladium-antimony alloy has a crystallite size of no greater than 12 nm.

9. The article according to claim 1 or 2, wherein the nanocrystalline palladium-antimony alloy has a crystallite size of at least 5 nm.

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