Near neutral pH tin electroplating solution

Abstract

The present invention relates to a solution for use in connection with the deposition of tin or tin alloys on platable portions of substrates. This solution comprises water; tin ions in an amount sufficient to provide a tin deposit on platable portions of substrates; a complexing agent of an acid or salt thereof that is stable at a pH of above 5.5 and below 10 present in an amount sufficient to render the metal ion soluble in the solution; and a surfactant of an alkoxylated polyalcohol present in an amount sufficient to complex the metal and render it soluble in the solution to facilitate deposition of tin upon the platable portions of the substrates.

1 . A solution for use in connection with the deposition of tin or tin alloys on platable portions of substrates, which comprises: 
 water;    tin ions in an amount sufficient to provide a tin deposit on platable portions of substrates;    a complexing agent of an acid or salt thereof that is stable at a pH of above 5.5 and below 10 present in an amount sufficient to render the metal ion soluble in the solution; and    a surfactant of an alkoxylated polyalcohol present in an amount sufficient to facilitate deposition of tin upon the platable portions of the substrates;    wherein the solution has a pH in the range of above 5.5 to below 10, adjusted, if necessary, by the addition of a suitable pH adjusting agent.    
   
   
       2 . The solution of  claim 1  wherein the tin ions are present as a solution soluble salt selected from the group consisting of tin alkane sulfonates, tin sulfates, or tin chlorides.  
   
   
       3 . The solution of  claim 1  wherein the complexing agent is selected from the group consisting of gluconic acid, an alkali or alkaline earth metal gluconate, heptagluconic acid, an alkali or alkaline earth metal heptagluconate, pyrophosphoric acid or an alkali or alkaline earth metal pyrophosphate.  
   
   
       4 . The solution of  claim 1  wherein the surfactant is a liquid alkoxylated polyol based on a pentaerythritol, trimethylolpropane, neopentyl glycol or a mixture thereof reacted with ethylene oxide, propylene oxide or mixtures thereof.  
   
   
       5 . The solution of  claim 1  wherein the surfactant is present in an amount of between about 0.01 and about 20 g/l.  
   
   
       6 . The solution of  claim 1  having a pH of between 6 and 8.  
   
   
       7 . The solution of  claim 1  wherein the complexing agent and metal ion are present in a concentration ratio of between about 2:1 and 9:1 to reduce or minimize agglomeration of the substrates during plating.  
   
   
       8 . The solution of  claim 1  wherein the complexing agent is present in an amount of between 25 and 200 g/l and the tin ions are present in an amount of between 5 and 100 g/l.  
   
   
       9 . The solution of  claim 1  further comprising a divalent lead salt in an amount sufficient to deposit a tin-lead alloy from the solution.  
   
   
       10 . The solution of  claim 1  which further comprises an antioxidation agent in an amount sufficient to inhibit oxidation of the tin ions in the solution.  
   
   
       11 . The solution of  claim 1  which further comprises a conductivity salt in an amount sufficient to increase the conductivity of the solution.  
   
   
       12 . The solution of  claim 11 , wherein the conductivity salt is an alkali or alkaline metal sulfate, sulfonate, or acetate compound.  
   
   
       13 . The solution of  claim 1 , further comprising an agent to promote anode dissolution.  
   
   
       14 . The solution of  claim 13 , wherein the anode dissolution agent is potassium methane sulfonate, ammonium chloride or a metal sulfide salt.  
   
   
       15 . A method for electroplating a tin deposit on platable portions of substrates which comprises contacting such substrates with the solution of  claim 1  and passing a current though the solution to provide tin deposits on the platable portions of the substrates without causing significant agglomeration of such substrates during electroplating.  
   
   
       16 . The method of  claim 15  wherein the substrates include electroplatable and non-electroplatable portions and which further comprises passing current though the solution to provide tin deposits on the electroplatable portions of the substrates without deleteriously affecting the non-electroplatable portions of the substrates.