Member formed with coating film having tin as its main component, coating film forming method and soldering method

Abstract

A member having a coating film capable of suppressing whisker generation is provided. The coating film ( 3 ) including a plurality of crystalline grains ( 3 a ) made of tin or tin alloy is formed above the surface of the base member ( 1 ). An intermetallic compound ( 3 b ) of tin and the first metal is being formed along the crystalline grain boundaries of the coating film.

1 . A coating film forming method comprising steps of:
 forming over a base member an underlying layer containing a first metal capable of forming an intermetallic compound with tin;   forming a coating film on the underlying layer by plating tin or tin alloy; and   performing a heat treatment under a condition that the first metal in the underlying layer diffuses in crystalline grain boundaries of the coating film and intermetallic compound of tin and the first metal is formed along the crystalline gain boundaries of the coating film.   
     
     
         2 . The coating film forming method according to claim  6 , wherein the first metal is nickel. 
     
     
         3 . The coating film forming method according to claim  6 , wherein the heat treatment step performs the heat treatment at a temperature of 0.65 to 0.80 time a melting point in absolute temperature of the crystalline grains constituting the coating film. 
     
     
         4 . The coating film forming method according to claim  8 , wherein a heat treatment time of the heat treatment step is 3 to 30 minutes.