Lead-free solder alloy

Abstract

A lead-free solder alloy suitable for use in flow soldering of electronic components to printed wiring boards comprises 0.1-3 wt % of Cu, 0.001-0.1 wt % of P, optionally 0.001-0.1 wt % of Ge, and a balance of Sn. The solder alloy may further contain at least one element of Ag and Sb in a total amount of at most 4 wt %, and/or at least one element of Ni, Co, Fe, Mn, Cr, and Mo in a total amount of at most 0.5 wt % in order to strengthen the alloy, and/or at least one element of Bi, In, and Zn in a total amount of at most 5 wt % in order to lower the melting point of the alloy.

What is claimed is:  
     
         1 . A lead-free solder alloy comprising 0.1-3 wt % of Cu, 0.001-0.1 wt % of P, 0-0.1 wt % of Ge, and a balance of Sn.  
     
     
         2 . A lead-free solder alloy as claimed in  claim 1  wherein the content of Ge is 0.001-0.1 wt %.  
     
     
         3 . A lead-free solder alloy as claimed in  claim 1  which further contains one or more strength-improving elements.  
     
     
         4 . A lead-free solder alloy as claimed in  claim 3  wherein the one or more strength-improving elements comprise at least one of Ag and Sb in a total amount of at most 4 wt %.  
     
     
         5 . A lead-free solder alloy as claimed in  claim 3  wherein the one or more strength-improving elements comprise at least one element selected from the group consisting of Ni, Co, Fe, Mn, Cr, and Mo in a total amount of at most 0.5 wt %.  
     
     
         6 . A lead-free solder alloy as claimed in  claim 1  which further contains one or more melting point-lowering elements.  
     
     
         7 . A lead-free solder alloy as claimed in  claim 7  wherein the one or more melting point-lowering elements comprise at least one of Bi, In, and Zn in a total amount of at most 5 wt %.  
     
     
         8 . A soldered joint formed from a lead-free solder alloy as claimed in  claim 1 .  
     
     
         9 . A soldered joint as claimed in  claim 8  wherein the soldered joint is formed by flow soldering.  
     
     
         10 . A method of performing flow soldering comprising using a lead-free solder alloy as claimed in  claim 1 .  
     
     
         11 . A method as claimed in  claim 10  wherein the flow soldering is wave soldering.