Corrosion Resistant Barrier Formed by Vapor Phase Tin Reflow

Abstract

A copper substrate for use as a contact having tin plating, nickel plating and gold plating overlying the substrate. A combination of tin plating is applied over a copper substrate; nickel plating is applied over the tin plating; and gold plating is applied over the nickel plating to form a stack. The stack is then processed by a vapor phase tin reflow step that results in the formation of intermetallics and eliminates stannous oxide layers that may otherwise form on the tin layer. The intermetallic layers provide excellent corrosion resistance, and serve as diffusion barriers to prevent the further migration of either nickel atoms or copper atoms into the tin, and tin atoms outwardly into either the nickel or the copper. Regardless of the thickness, the interfaces are substantially free of oxides, in particular tin oxide, and not prone to delamination.

What is claimed is: 
     
         1 . A plated contact, comprising:
 a metallic substrate;   a tin plating over the metallic substrate;   nickel plating over the tin-plating;   gold plating over the nickel plating;   an intermetallic lamina of nickel-tin forming an interface with the tin layer and the nickel layer, the intermetallic lamina free of stannous oxide due to vapor phase reflow of tin; and   wherein the plated contact is characterized by resistance to delamination.   
     
     
         2 . The plated contact of  claim 1  further comprising a solid solution of nickel-gold between the nickel plating and the gold plating. 
     
     
         3 . The plated contact of  claim 1  wherein the metallic substrate comprises copper. 
     
     
         4 . The plated contact of  claim 1  wherein the nickel-tin intermetallic lamina comprises at least one intermetallic selected from the group consisting of Ni 3 Sn 4 , Ni 3 Sn and Ni 3 Sn 2 . 
     
     
         5 . The plated contact of  claim 4  wherein the nickel-tin intermetallic lamina has a thickness of about 1 micron.