Tin-Based Plating Film and Method for Forming the Same

Abstract

The present invention provides a tin-based two-layered plating film exhibiting suppressed whisker growth comprising a lower layer of a tin plating film or tin alloy plating film comprising 5% by weight or less of at least one metal selected from the group consisting of cobalt, copper, bismuth, silver, and indium, and 95% by weight or more of tin, and an upper layer of a tin plating film or tin alloy plating film comprising 5% by weight or less of at least one metal selected from the group consisting of cobalt, copper, bismuth, silver and indium, and 95% by weight or more of tin. The tin-based plating film of the present invention is a lead-free tin plating film or tin alloy plating film, exhibits suppressed whisker growth over an extended period, and can further be formed relatively easily without complicated steps.

1 . A tin-based two-layered plating film exhibiting suppressed whisker growth comprising, 
 a lower layer of a tin plating film or tin alloy plating film comprising 5% by weight or less of at least one metal selected from the group consisting of cobalt, copper, bismuth, silver, and indium, and 95% by weight or more of tin, and    an upper layer of a tin plating film or tin alloy plating film comprising 5% by weight or less of at least one metal selected from the group consisting of cobalt, copper, bismuth, silver and indium, and 95% by weight or more of tin.    
   
   
       2 . A tin-based plating film of  claim 1 , wherein the lower layer has a film thickness of 0.1 to 20 μm, and the upper layer has a film thickness of 0.025 to 5 μm.  
   
   
       3 . A tin-based plating film of  claim 1 , wherein the lower layer is a matt or semi-bright tin plating film or tin alloy plating film, and the upper layer is a bright or semi-bright tin plating film or tin alloy plating film.  
   
   
       4 . A tin-based plating film of  claim 1 , wherein the lower layer is a matt tin plating film, and the upper layer is a bright tin alloy plating film.  
   
   
       5 . A tin-based plating film of  claim 1  further comprising an undercoat plating layer under the lower layer of the tin-based two-layered plating film, the undercoat plating layer being: 
 (1) a plating film of Ni or Cu,    (2) a plating film of Sn, Sn—Co alloy, Sn—Cu alloy, Sn—Bi alloy, Sn—Ag alloy, or Sn—In alloy, or    (3) a two-layered plating film consisting of the first layer of Ni or Cu, and the second layer of Sn, Sn—Co alloy, Sn—Cu alloy, Sn—Bi alloy, Sn—Ag alloy or Sn—In alloy for is ormed on the first layer.    
   
   
       6 . A product comprising the tin-based plating film of  claim 1  formed on a substrate.  
   
   
       7 . A method for forming a tin-based plating film exhibiting suppressed whisker growth, the method comprising the steps of forming on a substrate by electro- or electroless plating a lower layer of a tin plating film or a tin alloy plating film comprising 5% by weight or less of at least one metal selected from the group consisting of cobalt, copper, bismuth, silver, and indium, and 95% by weight or more of tin, and subsequently forming by electro- or electroless plating an upper layer of a tin plating film or tin alloy plating film comprising 5% by weight or less of at least one metal selected from the group consisting of cobalt, copper, bismuth, silver, and indium, and 95% by weight or more of tin.  
   
   
       8 . A method for forming a tin-based plating film exhibiting suppressed whisker growth, the method comprising the steps of forming on a substrate by electro- or electroless plating a undercoat plating layer as a barrier layer, the undercoat plating layer being: 
 (1) a plating film of Ni or Cu,    (2) a plating film of Sn, Sn—Co alloy, Sn—Cu alloy, Sn—Bi alloy, Sn—Ag alloy, or Sn—In alloy, or    (3) a two-layered plating film consisting of the first layer of Ni or Cu, and the second layer of Sn, Sn—Co alloy, Sn—Cu alloy, Sn—Bi alloy, Sn—Ag alloy or Sn—In alloy formed on the first layer,    subsequently forming by the method of  claim 7  a tin plating film or tin alloy plating film as a lower layer, and forming a tin plating film or tin alloy plating film as an upper layer.    
   
   
       9 . A product comprising the tin-based plating film of  claim 2  formed on a substrate.  
   
   
       10 . A product comprising the tin-based plating film of  claim 3  formed on a substrate.  
   
   
       11 . A product comprising the tin-based plating film of  claim 4  formed on a substrate.  
   
   
       12 . A product comprising the tin-based plating film of  claim 5  formed on a substrate.