Solder Preforms and Solder Alloy Assembly Methods

Abstract

A method of assembling components, such as electronic components, onto a substrate, such as an electronic substrate, includes applying solder paste to an electronic substrate to form a solder paste deposit, placing a low temperature preform in the solder paste deposit, processing the electronic substrate at a reflow temperature of the solder paste to create a low temperature solder joint, and processing the low temperature solder joint at a reflow temperature that is lower than the reflow temperature of the solder paste. Other methods of assembling components and solder joint compositions are further disclosed.

What is claimed is: 
     
         1 - 9 . (canceled) 
     
     
         10 . A method of assembly, comprising:
 applying low temperature solder paste to an electronic substrate to form a solder paste deposit;   placing a high temperature preform in the solder paste deposit; and   processing the electronic substrate at a reflow temperature that is appropriate for the low temperature solder paste to create a low temperature solder joint resulting from a dissolution of the high temperature solder preform into the low temperature solder paste deposit.   
     
     
         11 . The method of  claim 10 , wherein the low temperature solder paste is a composition consisting of tin and bismuth. 
     
     
         12 . The method of  claim 11 , wherein the composition consists of 42% by weight tin and 58% by weight bismuth. 
     
     
         13 . The method of  claim 11 , wherein the composition further consists of silver. 
     
     
         14 . The method of  claim 10 , wherein the reflow temperature of the solder joint is between 190-200° C. 
     
     
         15 . A solder joint comprising:
 49-53% by weight tin;   0-1.0% by weight silver;   0-0.1% by weight copper; and   balance bismuth.   
     
     
         16 . The solder joint of  claim 15 , wherein the reflow temperature of the solder joint is between 190-200° C.