Solderability enhancement by silver immersion printed circuit board manufacture

Abstract

A process used during manufacture of printed circuit boards comprises protecting metal pads and/or through-holes to provide a tarnish-resistant and solderable coating. In the method, the pads and/or through-holes are bright-etched, metal plated, preferably by an immersion process, and treated with a tarnish inhibitor. The tarnish inhibitor may be incorporated into the immersion plating bath. The metal plating is usually with silver or bismuth and the pads and/or through-holes comprise copper.

1 . A process for improving the solderability of a metal surface, said process comprising treating the metal surface with an immersion silver plating solution, said solution comprising:
 a). a soluble source of silver ions;   b). an acid;   c). an additive selected from the group consisting of fatty amines, fatty amides, quaternary salts, and ethoxylated versions of any of the foregoing.   
     
     
         2 . A process according to  claim 1  wherein the silver plating solution also comprises material selected from the group consisting of imidazoles, benzimidazoles, imidazole derivatives and benzimidazole derivatives. 
     
     
         3 . A process according to  claim 1  wherein the metal surface comprises copper. 
     
     
         4 . A process according to  claim 3  wherein the silver plating solution also comprises a material selected from the group consisting of imidazoles, benzimidazoles, imidazole derivatives, and benzimidazole derivatives. 
     
     
         5 . An immersion silver plating solution comprising
 (i) a soluble source of silver ions,   (ii) an acid and   (iii) an additive selected from the group consisting of fatty amines, fatty amides, quaternary salts, and ethoxylated versions of any of the foregoing.   
     
     
         6 . An immersion plating solution according to  claim 5  also comprising a material selected from the group consisting of imidazoles, benzimidazoles, imidazole derivatives, and benzimidazole derivatives. 
     
     
         7 . A printed circuit board having metal pads, metal through holes or combination thereof, the metal pads, metal through-holes or combination thereof being formed of copper and comprising an immersion silver plate thereon, the silver plate having been formed by a process comprising treating the metal surface with an immersion silver plating solution comprising a soluble source of silver ions, and acid, and an additive selected from the group consisting of fatty amines, fatty amides, quaternary salts, and ethoxylated versions of any of the foregoing. 
     
     
         8 . The printed circuit board as set forth in  claim 7  comprising components attached to silver plated copper metal pads and/or through holes thereof. 
     
     
         9 . The printed circuit board as set forth in  claim 8 , said components having been attached subsequent to immersing said silver plated copper metal pads in said plating solution comprising said additive. 
     
     
         10 . The printed circuit board as set forth in  claim 8  wherein said component(s) are selected from the group consisting of resistors and transistors. 
     
     
         11 . The printed circuit board as set forth in  claim 9  wherein said component(s) are selected from the group consisting of resistors and transistors. 
     
     
         12 . The printed circuit board as set forth in  claim 7  comprising a bare board. 
     
     
         13 . The printed circuit board as set forth in  claim 7  wherein said silver plate has been deposited from a silver immersion plating solution comprising a material selected from the group consisting of imidazoles, benzimidazoles, imidazole derivatives, and benzimidazole derivatives. 
     
     
         14 . The printed circuit board as set forth in  claim 8  wherein said silver plate has been deposited from a silver immersion plating solution comprising a material selected from the group consisting of imidazoles, benzimidazoles, imidazole derivatives, and benzimidazole derivatives. 
     
     
         15 . The printed circuit board as set forth in  claim 9  wherein said silver plate has been deposited from a silver immersion plating solution comprising a material selected from the group consisting of imidazoles, benzimidazoles, imidazole derivatives, and benzimidazole derivatives. 
     
     
         16 . The printed circuit board as set forth in  claim 10  wherein said silver plate has been deposited from a silver immersion plating solution comprising a material selected from the group consisting of imidazoles, benzimidazoles, imidazole derivatives, and benzimidazole derivatives. 
     
     
         17 . The printed circuit board as set forth in  claim 11  wherein said silver plate has been deposited from a silver immersion plating solution comprising a material selected from the group consisting of imidazoles, benzimidazoles, imidazole derivatives, and benzimidazole derivatives. 
     
     
         18 . The printed circuit board as set forth in  claim 12  wherein said silver plate has been deposited from a silver immersion plating solution comprising a material selected from the group consisting of imidazoles, benzimidazoles, imidazole derivatives, and benzimidazole derivatives.