Pulse plating process for deposition of gold-tin alloy

Abstract

The invention relates to a solution for use in connection with the deposition of a gold-tin alloy on an electroplatable substrate. This solution generally includes water, stannous tin ions, a complexing agent to render the stannous tin ions soluble, and complexed gold ions. Optionally, a deposit conditioning agent can be added to the solution to assist in providing a uniform and bright deposit. The solution has a pH of between about 2 and about 10 and the deposit has a gold content of between about 65% to about 90% by weight and a tin content between about 10% and about 35% by weight. An advantageous way for providing a stable gold-tin deposit is by a pulse plating technique.

1 . A method for electroplating of a gold-tin alloy deposit on a substrate which comprises contacting the substrate with a solution comprising water, stannous tin ions, a complexing agent to render the stannous tin ions soluble, and complexed gold ions, with the solution having a pH of between about 2 and about 10, and applying a pulsed current though the solution to provide a gold-tin alloy electrodeposit upon the substrate, wherein the pulsed current comprises an uninterrupted, sequential, off-on, continuously repeating pulsing sequence upon a base current applied across plating cell electrodes that applies high and low current densities in the solution for predetermined millisecond time periods.  
     
     
         2 . The method of  claim 1 , wherein the complexed gold ions are present in the form of a solution soluble cyanide complex, and the stannous tin ions are present is in the form of a solution soluble organotin complex.  
     
     
         3 . The method of  claim 2 , wherein the gold complex is monovalent gold cyanide or trivalent gold cyanide, and the organotin complex is stannous citrate, stannous oxalate, or stannous iminodiacetate.  
     
     
         4 . The method of  claim 1 , wherein the deposit has a gold content of between about 65% and about 90 % by weight and a tin content of between about 10% and about 35% by weight.  
     
     
         5 . The method of  claim 1 , wherein the complexed gold ions are gold cyanide or gold sulfite complexes and are present in an amount of between about 2 g/l and about 20 g/l and the solution has a pH of about 8 or less.  
     
     
         6 . The method of  claim 1 , which further comprises a deposit conditioning agent in an amount sufficient to enhance the appearance or uniformity of the gold-tin deposit.  
     
     
         7 . The method of  claim 6  wherein the deposit conditioning agent is 2,2′-dipyridyl, an polyethylene imines, (others) and are present in an amount effective to enhance the smoothness or brightness of the gold-tin deposit.  
     
     
         8 . The method of claim I which further comprises an antioxidant in an amount sufficient to maintain the tin ions as stannous tin ions, wherein the antioxidant is catechol, hydroquinone, or phenolsulfonic acid and is present in the solution in an amount of between about 0.1 g/l and about 20 g/l.  
     
     
         9 . The method of  claim 1 , further comprising one or more of thallous, plumbous or arsenious ions in an amount effective to provide grain refinement to the deposit.  
     
     
         10 . The method of  claim 1 , wherein the pulsed current is off from about 1 to about 25 milliseconds and then is on for about 1 millisecond to about 25 milliseconds to provide the pulsed current.  
     
     
         11 . The method of  claim 1 , wherein the base current is between about 1 ASF and about 20 ASF and the pulsed current ranges from about 0.1 ASF to about 8 ASF.  
     
     
         12 . The method of  claim 1   1 , wherein the base current is between about 2 ASF and about 10 ASF and the pulsed current ranges from about 0.2 ASF to about 5 ASF.  
     
     
         13 . The method of  claim 11 , wherein the pulsed current is on for a shorter time than when it is off.  
     
     
         14 . The method of  claim 13 , wherein the additional current is off for between about 5 milliseconds and about 10 milliseconds followed by being on for about 1 millisecond to about 4 milliseconds.