Method of preparing printed circuit boards with terminal tabs

Abstract

A method for rapidly stripping solder or tin from a substrate, such as copper, without adversely affecting the substrate in the preparation of circuit boards having terminal tabs. The composition comprises hydrofluoric acid or salts thereof, ammonia and an oxygen source such as hydrogen peroxide. The use of a soluble metal complexer peroxide stabilizer enables use of larger percentages of fluoride and peroxide to materially increase the life and capacity of the product. The composition is especially useful in a process of rapidly stripping solder from copper terminal tabs of a printed circuit board, following which the exposed copper tab is plated with a more noble metal.

I claim: 
     
       1. The method of rapidly stripping a layer of metal selected from the group consisting of lead-tin solder and tin from a layer of copper on a fiberglass circuit board without adversely affecting the copper and fiberglass, said process comprising the steps of exposing the solder to a composition comprising the ammonium bifluoride in the range of 10% to 25% by weight, hydrogen peroxide in the range of 1% to 5% by weight, and water in the range of 89% to 70% by weight for a time sufficient to remove the solder, and rinsing the said composition from the copper after the solder has been effectively stripped and before the copper and plastic have been adversely affected. 
     
     
       2. The method of claim 1 wherein the solder has a composition of 60 parts tin and 40 parts lead. 
     
     
       3. The method of claim 1 wherein the layer of copper includes terminal tab portions adapted for connection to an ancillary circuit. 
     
     
       4. The method of rapidly stripping a layer of metal selected from the group consisting of lead-tin solder and tin from a layer of copper on a plastic resin circuit board without adversely affecting the copper and board, said process comprising the steps of exposing the solder to a composition comprising ammonium bifluoride in the range of 5% to 50% by weight, hydrogen peroxide in the range of 1% to 35% by weight, a soluble metal complexer inhibitor of 0.1% to 10% by weight, and the balance of water for a time sufficient to remove the solder, and rinsing the said composition from the copper after the solder has been effectively stripped and before the copper and board have been adversely affected. 
     
     
       5. The method of claim 4 wherein the layer of copper includes terminal tab portions adapted for connection to an ancillary circuit. 
     
     
       6. The method of claim 4 wherein said metal complexer inhibitor comprises triisopropanolamine of 0.1% to 5.0% by weight and 0.1% to 5% by weight of a 75% acid equivalent phosphate complex. 
     
     
       7. The method of rapidly stripping a layer of metal selected from the group consisting of lead-tin solder and tin from a layer of copper on a plastic resin circuit board without adversely affecting the copper and board, said process comprising the steps of: exposing the solder to a composition comprising ammonium bifluoride in the range of 5% to 50% by weight, hydrogen peroxide in the range of 1% to 35% by weight and the balance of water for a time sufficient to remove the solder, and rinsing the said composition from the copper after the solder has been effectively stripped and before the copper and board have been adversely affected.