Tin whisker-free printed circuit board

This invention relates to a process for depositing a first coating of substantially pure tin and a second or subsequent cap layer of one or more alloys of at least two immersion platable metals selected from tin, silver, bismuth, copper, nickel, lead, zinc, indium, palladium, platinum, gold, cadmium, ruthenium and cobalt onto a metal surface such as copper or copper alloys used, e.g., for electrodes or various electronic circuit elements. More particularly, this invention relates to immersion plating of a first coating of substantially pure tin and at least one cap layer of an alloy comprising at least two of the above immersion platable metals on copper, copper alloys, and other metals on printed circuit boards by chemical displacement using an electroless immersion, spray, flood or cascade plating application process. Still more particularly, this invention relates to the use of such plating solutions in the manufacture of printed circuit boards. A printed circuit board including electrical circuitry formed on an outer surface of the printed circuit board, the circuitry comprising copper or a copper alloy; a final finish on the circuitry, the final finish including a coating of tin on the copper or copper alloy circuitry; and an alloy cap layer on the tin coating, the alloy cap layer comprising at least two immersion-platable metals. The immersion platable metals in the alloy cap layer may be at least two metals selected from tin, silver, bismuth, copper, nickel, lead, zinc, indium, palladium, platinum, gold, cadmium, ruthenium and cobalt. The circuitry remains whisker free and solderable.