Electrolyte media for the deposition of tin alloys and methods for depositing tin alloys
View Patent ↗An electroplating bath medium for electroplating articles with a tin-cobalt, tin-nickel, or tin-cobalt-nickel alloy comprises: at least one tin salt; an alloying metal salt comprising a cobalt salt and/or a nickel salt; a complexant comprising a hydroxycarboxylic acid or alkali metal salt thereof such as a sodium or potassium gluconate or heptonate complexant; boric acid; and a bath soluble substituted phenolic compound. The current regime applied to the plating bath can include time intervals of direct current and of pulsed current in order to selectively control the deposition of tin by activation or diffusion control.
1. A process for electroplating a substrate with a tin alloy, which alloy comprises from about 2% by weight to about 15% by weight of alloying metal, said process comprising:
a) contacting the substrate with an electroplating bath comprising:
1. a soluble stannous tin salt;
2. a soluble salt of the alloying metal; and
3. a complexing agent;
b) applying a current regime in which a direct current having a substantially constant current density is applied for a first time interval and a pulsed current is applied for a second time interval, wherein said first time interval and said second time interval are consecutive,
wherein the pulsed current comprises a first pulse period at a first current density and a second pulse period in which the current density is substantially zero, wherein the first pulse period and the second pulse period are alternated, whereby a duty cycle of pulsed current is established; and
wherein during the first time interval the alloying metal is deposited along with the tin and during the second time interval substantially only tin is deposited.
2. A process as claimed in claim 1 wherein the alloying metal is selected from the group consisting of cobalt, nickel and combinations of the foregoing.
3. A process according to claim 1 wherein the electroplating bath further comprises boric acid.
4. A process according to claim 1 wherein the tin salt is selected from the group consisting of stannous sulphate, stannous chloride, stannous methanesulphonate, stannous fluoborate, stannous phenolsulphonate and stannous toluenesulphonate.
5. A process according to claim 1 wherein the alloying metal salt is selected from the group consisting of cobalt sulphate, nickel sulphate, cobalt chloride, nickel chloride, cobalt methanesulphonate, nickel methanesulphonate, cobalt fluoborate, nickel fluoborate, cobalt phenolsulphonate, nickel phenolsulphonate, cobalt toluenesulphonate and nickel toluenesulphonate.
6. A process according to claim 1 wherein the complexing agent is selected from the group consisting of mono-, di- or poly-hydroxy carboxylic acids or alkali metal salts thereof.
7. A process according to claim 1 wherein the electroplating bath further comprises a grain refining agent comprising a bath soluble substituted phenolic compound of the formula:
where n is an integer from 1 to 100, m is 2 or 3 and R1 is either a phenolic group of the formula:
where R2 is a (C1-C14) alkyl group or, an alpha or beta naphthalene group of the formula:
and,
R3 is H, CH 2 CH 2 OH, CH 2 CH 2 CH 2 OH, CH 2 CH(OH)CH 2 SO 3 H or CH 2 CH 2 CH 2 SO 3 H.
8. A process as claimed in claim 1 wherein the first time interval is from about 10 seconds to about 100 seconds and second time interval is from about 20 seconds to about 200 seconds.
9. A process as claimed in claim 1 wherein the pulsed current has a frequency of from about 10 Hz to about 500 Hz.
10. A process as claimed in claim 1 wherein said first current density is substantially the same as the current density in the first time interval.
11. A process as claimed in claim 10 wherein the duty cycle of the pulsed current is from about 20% to about 50%.
12. A process as claimed in claim 1 wherein the substrate is a bearing and the electroplated tin alloy coating constitutes a bearing overlay.
13. A process as claimed in claim 1 , wherein the electroplating bath comprises an anionic wetting agent.
14. A process as claimed in claim 1 , wherein the electroplating bath comprises a salt selected from the group consisting of sodium sulphate, ammonium chloride, and combinations of the foregoing.