US20140326605A1

US20140326605A1 - Electroplating contacts with silver-alloys in a basic bath

Info

Publication number: US20140326605A1
Application number: US13/886,337
Authority: US
Inventors: Min Zheng; Jerzy Gazda
Original assignee: Tyco Electronics Corp
Current assignee: TE Connectivity Corp
Priority date: 2013-05-03
Filing date: 2013-05-03
Publication date: 2014-11-06
Also published as: WO2014179506A1

Abstract

A method for silver-alloy plating an electrical contact and a silver-alloy plated electrical contact are provided. The method includes cleaning the electrical contact by removing contaminates and exposing the electrical contact to at least one of an acid or base. The method includes preparing a sliver-alloy plating bath including water, a silver complex, and a metal complex, the metal complex being at least one of nickel or cobalt. The method includes silver-alloy plating the electrical contact in the silver-alloy plating bath, wherein the plating bath has a pH of greater than 7. The metal complex forms about 0.3% to about 50% by weight of a content of a silver-alloy plated deposit.

Description

FIELD OF THE INVENTION

The subject matter described herein generally relates to silver plated electrical contacts and more specifically silver-alloy plated electrical contacts in a basic electroplating bath.

BACKGROUND OF THE INVENTION

Electrical connectors include electrical contacts that are frequently plated with a metal compound to improve various properties of the electrical contact. For example, plating the contact may improve a coefficient of friction of the contact. As such, less force is required to insert the contact into a corresponding contact. Accordingly, damage to the electrical contact may be avoided. Additionally, plating the electrical contact may improve a durability of the contact thereby reducing wear on the electrical contact and enabling the electrical contact to be used in harsh environments. Moreover, plating the contact may reduce electromigration and tarnishing of the electrical contact.
Typically, electrical contacts are plated with gold. Gold is generally durable and provides a low coefficient of friction, and a low level contact resistance. However gold increases the costs associated with plating the electrical contact. As an alternative to gold, electrical contacts may be plated with silver, which is generally cheaper than gold. However, silver is much softer than gold and provides less durability than gold. Additionally, silver has a high coefficient of friction and is subject to electromigration and tarnishing.
Silver-alloy plated contacts that do not suffer from one or more of the above drawbacks would be desirable in the art.

BRIEF DESCRIPTION OF THE INVENTION

In an exemplary embodiment, a method for silver-alloy plating an electrical contact is provided. The method includes cleaning the electrical contact by removing contaminates and exposing the electrical contact to at least one of an acid or base. The method includes preparing a sliver-alloy plating bath including water, a silver complex, and a metal complex, the metal complex being at least one of nickel or cobalt. The method includes silver-alloy plating the electrical contact in the silver-alloy plating bath, wherein the plating bath has a pH of greater than 7.
In another exemplary embodiment, a silver-alloy plated electrical contact is provided. The silver-alloy plated electrical contact is formed in a silver-alloy plating bath having a silver complex, a metal complex including at least one of nickel or cobalt. The metal complex forms about 0.3-50% by weight of a content of a silver-alloy plated deposit.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is perspective view of a connector formed in accordance with an exemplary embodiment.

FIG. 2 is flowchart of a method for silver-alloy plating an electrical contact in accordance with an embodiment.

FIG. 3 is a flowchart of a method for silver-alloy plating an electrical contact in accordance with another embodiment.

FIG. 4 is a microscopic photograph of a silver-alloy plating on an electrical contact in accordance with an embodiment of the present disclosure using silver thiosulfate.

FIG. 5 is a microscopic photograph of a silver-alloy plating on an electrical contact in accordance with an embodiment of the present disclosure using silver succinimide.

Wherever possible, the same reference numbers will be used throughout the drawings to represent the same parts.

DETAILED DESCRIPTION OF THE INVENTION

Provided is an exemplary silver-alloy plated contact and a process of manufacturing a silver-alloy plated contact. Embodiments of the present disclosure, for example, in comparison to plated contacts and processes of manufacturing plated contacts that do not include one or more of the features disclosed herein, reduce or eliminate corrosion, reduce or eliminate delamination, provides harder silver deposits, reduce coefficient of friction, and improve wear durability.
FIG. 1 is a perspective view of a connector 50 formed in accordance with an embodiment. The connector 50 includes a body 52 having a plurality of cavities 54. Electrical contacts 56 are inserted into the cavities 54. The contacts 56 are high-reliability contacts that have been stamped and formed. The contacts 56 are formed for use in applications that require contact durability, for example, military, aircraft, satellite, missile applications, automotive, communications or the like. The contacts 56 are configured to withstand high temperatures, high amounts of shock and vibration, and the like. The contacts 56 are formed from a conductive material, for example, copper. After forming the contacts 56, at least a portion of each contact 56 is covered with a hard silver-alloy plating layer to inhibit corrosion, reduce coefficient of friction, reduce contact resistance, and increase durability.
In an exemplary embodiment, the silver plated electrical contact 56 is formed in a silver-alloy plating bath having a molar concentration of a silver complex of about 0.01M to about 0.5M and a molar concentration of a metal complex of about 0.01M to about 0.5M. The silver complex may be at least one of silver thiosulfate or silver succinimide and may form about 55 percent to about 99.7 percent by weight, or alternatively about 90 percent to about 99.7 percent by weight, or alternatively about 95 percent to about 99.7 percent by weight of a content in a resulting silver-alloy deposit on a contact. The metal complex may be at least one of nickel or cobalt and may form about 0.3 percent to about 50 percent by weight, or alternatively about 0.3 percent to about 10 percent by weight, or alternatively about 0.3 percent to about 5 percent by weight of a content in a resulting silver-alloy deposit on contact 56. In one embodiment, the silver-alloy plated electrical contact 56 has a grain size of silver that is sub-micron, as shown in FIGS. 4 and 5. The contact 56 may include nickel plating that is plated on the contact 56 before the contact 56 is formed in the silver-alloy plating bath. Moreover, the contact 56 may include a silver, gold or palladium strike plating that is formed on the contact 56 after the contact 56 is nickel plated and before the contact 56 is silver-alloy plated. In one embodiment, the silver-alloy plating bath also includes at least one brightener of an amine group additive or polyethyleneimine (PEI). Other suitable examples of brighteners include, but are not limited to, thiourea, polyethylene glycol, sodium saccharin, and 2-Butyne-1,4-diol. For example, the silver plating bath may have a concentration of PEI of approximately 2000 parts per million or less. In another embodiment, silver plating bath may have a concentration of sodium saccharin of 1 g/L or less or alternatively a concentration of 2-Butyne-1,4-diol of 1 g/L or less.
It should be noted that the connector 50 and the electrical contacts 56 shown in FIG. 1 are exemplary only. The various embodiments and processes described herein may be utilized with any suitable connector and/or electrical contact.
FIG. 2 is a flowchart of a method 100 for silver plating an electrical contact in accordance with an embodiment. At 102, an electrical contact is formed. The electrical contact may be any suitable contact for transmitting electrical signals. The electrical contact may be made from any suitable conductive material, for example, copper or a copper alloy. The electrical contact may be a stamped and formed contact. Alternatively, the electrical contact may be formed using an appropriate die. The electrical contact is configured to have at least a portion thereof silver-alloy plated. For example, a mating end of the electrical contact may be configured for silver-alloy plating. Optionally, the entire electrical contact may be configured for silver-alloy plating.
At 104, the electrical contact is degreased. During degreasing, a chemical may be used to remove oils, such as machining fluids, or other contaminants from the electrical contact. For example, the electrical contact may be degreased using petroleum, chlorine, or alcohol based solvents to dissolve the machining fluids and other contaminants. At 106, the electrical contact is rinsed to remove any degreasing chemicals therefrom. For example, the electrical contact may be rinsed with water.
At 108, the electrical contact undergoes acid activation. The acid activation may be performed with a series of at least one of acids or bases to remove unwanted contaminants from a surface of the electrical contact to reduce poor plating. Additionally, the acid activation may be performed with a weak acid etch or with a proprietary solution. At 110, the electrical contact is rinsed again.
At 112, a sliver-alloy plating process is performed. The silver-alloy plating process includes preparing a silver-alloy plating bath. In an exemplary embodiment, an aqueous silver-alloy plating bath is formed having deionized water, a silver complex, and a metal complex. For example, the silver for the silver complex may be provided as silver nitrate. In one embodiment, the silver-alloy plating bath includes about 1.7 gram/Liter (g/L) to about 17 g/L of silver as silver nitrate and about 6 g/L to about 63 g/L of sodium thiosulfate to form the silver complex as a silver thiosulfate. In one embodiment, a sodium metabisulfite is added as a supporting electrolyte to the silver complex at a concentration of about 1.9 g/L to about 19 g/L. In another embodiment, the silver-alloy plating bath includes about 1 g/L to about 5 g/L of silver as silver nitrate and about 10 g/L to about 20 g/L of succinimide to form the silver complex as silver succinimide. The silver complex is at a molar concentration of about 0.01M to about 0.5M or alternatively about 0.01M to about 0.1M in the silver-alloy plating bath.
The metal complex may be provided as a nickel compound or cobalt compound, such as nickel sulfate or nickel sulfamate or cobalt sulfate or cobalt sulfamate. In one embodiment, the silver-alloy plating bath includes about 15.7 g/L to about 77 g/L of nickel as nickel sulfate or nickel sulfamate and about 25.8 g/L to about 130 g/L sodium citrate and about 5 g/L to about 35 g/L of ammonia hydroxide to form the metal complex as nickel citrate-ammonia. In one embodiment, the metal complex may be a cobalt compound, such as cobalt sulfate or cobalt sulfamate. For example, the silver-alloy plating bath may include about 15.7 g/L to about 77 g/L of cobalt as cobalt sulfate and about 25.8 g/L to about 130 g/L sodium citrate and about 5 g/L to about 35 g/L of ammonia hydroxide to form the metal complex as cobalt citrate-ammonia. The metal complex is at a molar concentration of about 0.01M to about 0.5M or alternatively about 0.01M to about 0.1M in the silver-alloy plating bath. The molar ratio of metal complex to silver complex is from about 20:1 to about 1:1 or alternatively about 10:1 to about 5:1. The metal complex forms about 0.3% to about 50% by weight of a content of a silver-alloy plated deposit
The pH of the silver-alloy plating is preferably greater than 7. The pH of the silver-alloy plating bath may be adjusted to about 7 to about 11, or alternatively about 8 to about 10, or alternatively about 8 to about 9, using ammonia hydroxide. The silver-alloy plating process also includes silver-alloy plating the electrical contact in the silver-alloy plating bath. The silver-alloy plating process can be performed in a conventional high-speed, spot, or jet plating process. The silver-alloy plating process may be performed at room temperature or in the temperature range of about 20° C. to about 50° C. The silver-alloy plating process may be performed at a cathode current density of about 5 ampere:/square foot (A/ft²or ASF) to about 40 A/ft².
In one embodiment, polyethyleneimine (PEI), with a molecular weight of approximately 500-2000 grams per mole, may be added to the silver-alloy plating bath at concentration of 1000 parts per million. The addition of PEI may result in a silver-alloy plating deposit having crystalline structure at a sub-micron size range and a lower coefficient of friction. Alternatively, brighteners such as thiourea, polyethylene glycol, sodium saccharin, and 2-Butyne-1,4-diol may be added. The brighteners may be added to the silver-alloy plating bath at a targeted concentration of approximately 1 g/L or less.
After the silver plating process, the electrical contact is rinsed, at 114. At 116, the electrical contact is dried. Optionally, the electrical contact may be baked. In one embodiment, the electrical contact may be annealed. For example, the electrical contact may be annealed at 125° C. for 100 hours.
FIG. 3 is a flowchart of a method 200 for silver plating an electrical contact in accordance with another embodiment. At 202 an electrical contact is formed. The electrical contact may be formed as set forth in the method 100 shown in FIG. 2. At 204, the electrical contact is degreased and, at 206, the electrical contact is rinsed to remove any degreasing chemicals therefrom. The electrical contact may be degreased and rinsed as set forth in the method 100 shown in FIG. 2. At 208, the electrical contact undergoes acid activation and, at 210, the electrical contact is rinsed again. The electrical contact may undergo acid activation and be rinsed as set forth in the method 100 shown in FIG. 2.
At 212, the electrical contact undergoes nickel plating. In one embodiment, the electrical contact may be nickel plated using electroplating. Alternatively, the electrical contact may be nickel plated using electroless nickel plating. The nickel plating layers provide additional strength and durability to the electrical contact. The nickel plating process may be performed with nickel and/or nickel alloys. The nickel plating process may also improve a corrosion resistance of the electrical contact. After nickel plating, the electrical contact is rinsed, at 214, as described in method 100 shown in FIG. 2.
At 216, the electrical contact undergoes silver strike plating. Strike plating forms a thin layer of silver plating on the electrical contact. For example, the strike plating layer may be less than approximately 0.1 micrometer thick. The strike plating layer may provide additional adherence to the electrical contact. Accordingly, the strike plating layer may serve as a foundation for subsequent plating processes. In an exemplary embodiment, the strike plating layer forms a foundation for a silver plating layer. After the silver strike plating process, the electrical contact is rinsed, at 218.
At 220, a sliver-alloy plating process is performed. The silver-alloy plating process includes preparing a silver-alloy plating bath. In an exemplary embodiment, an aqueous silver-alloy plating bath is formed having deionized water, a silver complex, and a metal complex. For example, the silver for the silver complex may be provided as silver nitrate. In one embodiment, the silver-alloy plating bath includes about 1.7 gram/Liter (g/L) to about 17 g/L of silver as silver nitrate and about 6 g/L to about 63 g/L of sodium thiosulfate to form the silver complex as a silver thiosulfate. In one embodiment, a sodium metabisulfite is added as a supporting electrolyte to the silver complex at a concentration of about 1.9 g/L to about 19 g/L. In another embodiment, the silver-alloy plating bath includes about 1 g/L to about 5 g/L of silver as silver nitrate and about 10 g/L to about 20 g/L of succinimide to form the silver complex as silver succinimide. The silver complex is at a molar concentration of about 0.01M to about 0.5M or alternatively about 0.01M to about 0.1M in the silver-alloy plating bath.
The metal complex may be provided as a nickel compound or cobalt compound, such as nickel sulfate or nickel sulfamate or cobalt sulfate or cobalt sulfamate. In one embodiment, the silver-alloy plating bath includes about 15.7 g/L to about 77 g/L of nickel as nickel sulfate or nickel sulfamate and about 25.8 g/L to about 130 g/L sodium citrate and about 5 g/L to about 35 g/L of ammonia hydroxide to form the metal complex as nickel citrate-ammonia. In one embodiment, the silver-alloy plating bath may include about 15.7 g/L to about 77 g/L of cobalt as cobalt sulfate or cobalt sulfamate and about 25.8 g/L to about 130 g/L sodium citrate and about 5 g/L to about 35 g/L of ammonia hydroxide to form the metal complex as cobalt citrate-ammonia. The metal complex is at a molar concentration of about 0.01M to about 0.5M or alternatively about 0.01M to about 0.1M in the silver-alloy plating bath. The molar ratio of metal complex to silver complex is from about 20:1 to about 1:1, or alternatively about 10:1 to about 1:1, or alternatively about 10:1 to about 5:1. The metal complex forms about 0.3% to about 50% by weight of a content of a silver-alloy plated deposit for a silver-alloy plated electrical contact.
The pH of the silver-alloy plating is preferably greater than 7. The pH of the silver-alloy plating bath may be adjusted to about 7 to about 11, or alternatively about 8 to about 10, or alternatively about 8 to about 9, using ammonia hydroxide. The silver-alloy plating process also includes silver-alloy plating the electrical contact in the silver-alloy plating bath. The silver-alloy plating process can be performed in a conventional high-speed, spot, or jet plating process. The silver-alloy plating process may be performed at room temperature or in the temperature range of about 20° C. to about 50° C. The silver-alloy plating process may be performed at a cathode current density of about 5 ampere/square foot (A/ft²or ASF) to about 40 A/ft².
In one embodiment, polyethyleneimine (PEI), with a molecular weight of approximately 500-2000 grams per mole, may be added to the silver-alloy plating bath at concentration of 1000 parts per million. The addition of PEI may result in a silver-alloy plating deposit having crystalline structure at a sub-micron size range and a lower coefficient of friction. Alternatively, brighteners such as thiourea, polyethylene glycol, sodium saccharin, and 2-butyne-1,4-diol may be added. The brighteners may be added to the silver-alloy plating bath at a targeted concentration of approximately 1 g/L or less.
After the silver plating process, the electrical contact is rinsed, at 222. At 224, the electrical contact is dried. Optionally, the electrical contact may be baked. In one embodiment, the electrical contact may be annealed. For example, the electrical contact may be annealed at 125° C. for 100 hours.
FIG. 4 is a microscopic picture of the surface of a silver-alloy plated contact according to an embodiment of this disclosure. The silver complex used was silver thiosulfate and the metal complex used was nickel citrate-ammonia. The larger grains, labeled 400, are silver-nickel alloy and the smaller grains, labeled 402, are silver-nickel alloy. Using the procedure in the present disclosure allows for control of the nickel content in the deposit. The silver- nickel alloy grains 400 and 402 indicate that a higher hardness and great wear performance will be obtained from the coating.
FIG. 5 is a microscopic picture of the surface of a silver-alloy plated contact according to an embodiment of this disclosure. The silver complex used was silver succinimide and the metal complex used was nickel citrate-ammonia. The larger grains, labeled 500, are silver-nickel alloy and the smaller grains, labeled 502, are silver-nickel alloy. Using the procedure in the present disclosure allows for control of the nickel content in the deposit. The silver- nickel alloy grains 500 and 502 indicate that a higher hardness and great wear performance will be obtained from the coating.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

What is claimed is:

1. A method for silver-alloy plating an electrical contact comprising:

cleaning the electrical contact by removing contaminates and exposing the electrical contact to at least one of an acid or base;

preparing a sliver-alloy plating bath including water, a silver complex, and a metal complex, the metal complex being at least one of nickel or cobalt; and

silver-alloy plating the electrical contact in the silver-alloy plating bath, wherein the plating bath has a pH of greater than 7.

2. The method of claim 1, wherein the pH of the plating bath is about 7 to about 11.

3. The method of claim 1, wherein the metal complex is nickel citrate-ammonia.

4. The method of claim 1, wherein the metal complex is cobalt citrate-ammonia.

5. The method of claim 1, wherein the silver complex is silver thiosulfate.

6. The method of claim 1, wherein the silver complex is silver succinimide.

7. The method of claim 1, wherein the silver complex is at a molar concentration of about 0.01M to about 0.5M.

8. The method of claim 7, wherein the silver complex is at a molar concentration of about 0.01M to about 0.1M.

9. The method of claim 1, wherein the metal complex is at a molar concentration of about 0.1M to about 0.5M.

10. The method of claim 1, wherein the molar ratio of metal complex to silver complex is from about 10:1 to about 1:1.

11. The method of claim 4, wherein a silver deposit on the electrical contact is about 55% to about 99% weight percent and a nickel deposit is the balance.

12. The method of claim 5, wherein a silver deposit on the electrical contact is about 90% to about 99% weight percent and a nickel deposit is the balance.

13. The method of claim 1, wherein the silver-alloy plating bath further includes brighteners.

14. A silver-alloy plated electrical contact formed in a silver-alloy plating bath having a silver complex, a metal complex including at least one of nickel or cobalt, wherein the metal complex forms about 0.3% to about 50% by weight of a content of a silver-alloy plated deposit.

15. The silver-alloy plated electrical contact of claim 14, wherein the metal complex forms about 0.3% to about 10% percent by weight of the content of the silver-alloy plated deposit.

16. The silver-alloy plated electrical contact of claim 14, wherein the metal complex is nickel citrate-ammonia or cobalt citrate-ammonia.

17. The silver-alloy plated electrical contact of claim 14, wherein the silver complex is silver thiosulfate.

18. The silver-alloy plated electrical contact of claim 14, wherein the silver complex is silver succinimide.

19. The silver-alloy plated electrical contact of claim 14, wherein the silver-alloy plating bath has a pH of greater than 7.