Solder joint structure, soldering method, and electronic-component manufacturing apparatus using the same structure and the method

Abstract

A structure of solder joint structure formed of zinc-based lead-free solder having excellent characteristics is disclosed. Between a first lead-free solder layer and a soldering pad, the following layers are formed: a tin-copper alloy layer formed on the pad; a first alloy layer formed of second lead-free layer of which main ingredients are tin and silver; and a second alloy layer formed between the first alloy layer and the first lead-free solder. This structure allows forming the solder joint structure formed of zinc-based lead-free solder having high joint strength.

1 . A solder joint structure for soldering a lead of an electronic component to a soldering pad formed of copper foil at a predetermined place on an insulated substrate with lead-free solder, the solder joint structure comprising:
 a first alloy layer including a second lead-free solder layer connected to a tin-copper alloy layer formed on the pad; and   a second alloy layer formed between the first alloy layer and a first lead-free solder layer.   
   
   
       2 . The solder joint structure of  claim 1 , wherein the first lead-free solder has a substantially identical melting point to that of the second lead-free solder. 
   
   
       3 . The solder joint structure of  claim 1 , wherein the first lead-free solder comprises tin and zinc. 
   
   
       4 . The solder joint structure of  claim 1 , wherein the second lead-free solder comprises tin and indium. 
   
   
       5 . The solder joint structure of  claim 1 , wherein the tin-copper alloy layer is formed by melting the second lead-free solder layer formed in advance on the pad. 
   
   
       6 . The solder joint structure of  claim 1 , wherein the second alloy layer is formed by melting the first alloy layer and the first lead-free solder layer together. 
   
   
       7 . The solder joint structure of  claim 1 , wherein the second alloy layer comprises copper and zinc. 
   
   
       8 . The solder joint structure of  claim 1 , wherein the second alloy layer is formed by consuming copper molecules existing around a boundary between the second alloy layer and the first alloy layer into which the copper molecules diffuse from the tin-copper alloy layer. 
   
   
       9 . The solder joint structure of  claim 1 , wherein the first alloy layer has a thickness greater than a diffusing distance of zinc molecules existing in the first lead-free solder layer, the zinc molecules diffusing when the first lead-free solder is melted.