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, complexed gold ions, and an alloy stabilization agent that includes an imine functional group. The alloy stabilization agent is present in an amount sufficient to stabilize the composition of the gold-tin deposit over a usable current density range. The solution has a pH of between about 2 and about 10 and the deposit having a gold content less than about 90% by weight and a tin content greater than about 10% by weight. An advantageous way for providing the desired deposit is by a pulse plating technique.

1 . A solution for use in connection with the deposition of a gold-tin alloy on an electroplatable substrate, which comprises water, stannous tin ions, a complexing agent to render the stannous tin ions soluble, complexed gold ions, and an alloy stabilization agent that includes an imine functional group and is present in an amount sufficient to stabilize the alloy composition and enable a gold-tin deposit to be provided, with the solution having a pH of between about 2 and about 10 and the deposit having a gold content less than about 90% by weight and a tin content greater than about 10% by weight.  
   
   
       2 . The solution of  claim 1  wherein the alloy stabilization agent is a polyalkylene imine having a molecular weight of between about 600 and about 2000 and is present in an amount of between about 0.1 ml/l to about 10 ml/l.  
   
   
       3 . The solution of  claim 2  wherein the alloy stabilization agent is a polyethylene imine and 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.  
   
   
       4 . The solution of  claim 1  wherein the complexing agent for the stannous tin ions is an organic acid or a salt thereof.  
   
   
       5 . The solution of  claim 4  wherein the stannous ions are present in an amount of between about 1 g/l and about 20 g/l and the organic acid is present in an amount of between about 10 g/l and about 300 g/l.  
   
   
       6 . The solution of  claim 4  wherein the complexing agent for the stannous tin ions is oxalic acid, citric acid, gluconic acid, ascorbic acid, malonic acid, iminodiacetic acid or a solution soluble salt thereof, and the solution has a pH of about 8 or less.  
   
   
       7 . The solution of  claim 1  wherein the complexed gold ions are gold cyanide or gold sulfite complexes.  
   
   
       8 . The solution of  claim 7  wherein the complexed gold ions are present in an amount of between about 2 g/l and about 20 g/l.  
   
   
       9 . The solution of  claim 1  further comprising an antioxidant in an amount sufficient to maintain the tin ions as stannous tin ions.  
   
   
       10 . The solution of  claim 9  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.  
   
   
       11 . The solution of  claim 1 , having a pH of about 8 or less.  
   
   
       12 . The solution of  claim 1 , having a pH of between about 3 and about 5.5.  
   
   
       13 . A method for electroplating of a gold-tin alloy deposit on a substrate which comprises contacting the substrate with the solution of  claim 1  and passing a current though the solution to provide a gold-tin alloy electrodeposit thereon.  
   
   
       14 . A method for electroplating a gold-tin alloy deposit on composite articles that include electroplatable and non-electroplatable portions which comprises contacting such articles with the solution of  claim 1  and passing a current though the solution to provide a gold-tin alloy metal electrodeposit on the electroplatable portions of the articles without deleteriously affecting the non-electroplatable portions of the articles.  
   
   
       15 . 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, complexed gold ions, and an alloy stabilization agent, with the solution having a pH of between about 2 and about 10 and the deposit having a gold content less than about 90% by weight and a tin content greater than about 10% by weight, and applying a pulsed current though the solution to provide a gold-tin alloy electrodeposit upon the substrate.  
   
   
       16 . The method of  claim 15 , wherein the pulsed current comprises an uninterrupted, sequential, off-on, continuously repeating pulsing sequence across plating cell electrodes that applies high and low current densities in the solution for predetermined millisecond time periods.  
   
   
       17 . The method of  claim 16 , 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.  
   
   
       18 . The method of  claim 16 , which further comprises providing a base current upon which the pulsed current is applied.  
   
   
       19 . The method of  claim 18 , 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.  
   
   
       20 . The method of  claim 18 , 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.  
   
   
       21 . The method of  claim 18 , wherein the pulsed current is on for a shorter time than when it is off.  
   
   
       22 . The method of  claim 21 , 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.  
   
   
       23 . The method of  claim 15  wherein the alloy stabilization agent includes an imine functional group and is present in an amount sufficient to stabilize the alloy composition and enable a gold-tin deposit to be provided, 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.  
   
   
       24 . A method for electroplating a gold-tin alloy deposit on composite articles that include electroplatable and non-electroplatable portions which comprises contacting such articles with a solution comprising water, stannous tin ions, a complexing agent to render the stannous tin ions soluble, complexed gold ions, and an alloy stabilization agent, with the solution having a pH of between about 2 and about 10 and the deposit having a gold content less than about 90% by weight and a tin content greater than about 10% by weight, and pulsing a current though the solution to provide a gold-tin alloy metal electrodeposit on the electroplatable portions of the articles without deleteriously affecting the non-electroplatable portions of the articles.  
   
   
       25 . The method of  claim 24 , wherein the pulsed current comprises an uninterrupted, sequential, off-on, continuously repeating pulsing sequence across plating cell electrodes that applies high and low current densities in the solution for predetermined millisecond time periods.  
   
   
       26 . The method of  claim 25 , wherein the pulsed current is off from about 1 millisecond to about 25 milliseconds and then is on for about 1 millisecond to about 25 milliseconds to provide the pulsed current.  
   
   
       27 . The method of  claim 25 , which further comprises providing a base current upon which the pulsed current is applied.  
   
   
       28 . The method of  claim 27 , 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.  
   
   
       29 . The method of  claim 27 , 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.  
   
   
       30 . The method of  claim 27 , wherein the pulsed current is on for a shorter time than when it is off.  
   
   
       31 . The method of  claim 30 , 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.  
   
   
       32 . The method of  claim 24  wherein the alloy stabilization agent includes an imine functional group and is present in an amount sufficient to stabilize the alloy composition and enable a gold-tin deposit to be provided, 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.