Lead-free solder with low copper dissolution

Abstract

Lead-free solder compositions suitable for joining electronic devices to printed wiring boards, which comprises by weight 0.2 to 0.9% copper, 0.006 to 0.07% nickel, 0.03 to 0.08% bismuth, less than 0.5% silver, less than 0.010% phosphorus, and a balance of tin and inevitable impurities. A solder composition embodying this invention finds particular application in automated wave-soldering machines where conventional lead-free solders dissolve excessive copper from printed wiring circuitry and component terminations.

1 . A lead-free solder composition containing consisting essentially of 0.2 to 0.9% by weight of copper, 0.006 to 0.07% by weight of nickel, 0.03 to 0.08% by weight of bismuth, less than 0.5% by weight of silver, less than 0.010% by weight of phosphorus, and the balance of tin.  
   
   
       2 . The lead-free solder composition according to  claim 1 , wherein the copper content falls within a range of between 0.5% by weight and 0.7% by weight.  
   
   
       3 . The lead-free solder composition according to  claim 1 , wherein the nickel content falls within a range of between 0.04% by weight and 0.06% by weight.  
   
   
       4 . The lead-free solder composition according to  claim 1 , wherein the bismuth content falls within a range of between 0.05% by weight and 0.07% by weight.  
   
   
       5 . A lead-free solder composition containing consisting essentially of 0.2 to 0.9% by weight of copper, 0.006 to 0.07% by weight of nickel, 0.03 to 0.08% by weight of bismuth, and the balance of tin.  
   
   
       6 . The lead-free solder composition according to  claim 5 , further containing silver in an amount not larger than 0.5% by weight.  
   
   
       7 . The lead-free solder composition according to  claim 5 , further containing phosphorus in an amount not larger than 0.010% by weight.  
   
   
       8 . The lead-free solder composition according to  claim 5 , wherein the copper content falls within a range of between 0.5% by weight and 0.7% by weight.  
   
   
       9 . The lead-free solder composition according to  claim 5 , wherein the nickel content falls within a range of between 0.04% by weight and 0.06% by weight.  
   
   
       10 . The lead-free solder composition according to  claim 5 , wherein the bismuth content falls within a range of between 0.05% by weight and 0.07% by weight.