Joining a chip to a substrate with solder alloys having different reflow temperatures

Abstract

A method including forming a first solder bump on a chip, the first solder bump made of a first alloy, and forming a second solder bump on a chip, the second solder bump made of a second alloy, where the first alloy has a different alloy concentration and is different from the second alloy.

What is claimed is: 
     
         1 . A method comprising:
 forming a first solder bump on a chip, the first solder bump made of a first alloy; and   forming a second solder bump on a chip, the second solder bump made of a second alloy,   wherein the first alloy has a different alloy concentration and is different from the second alloy.   
     
     
         2 . The method of  claim 1 , wherein the first and second alloys comprise at least one common element. 
     
     
         3 . The method of  claim 1 , wherein the first solder bump will be used to subsequently form a solder first connection for high current density power transfer, and wherein the second solder bump will be used to subsequently form a second solder connection for low current density signal transfer. 
     
     
         4 . The method of  claim 1 , wherein the first and second alloys comprise copper, silver, tin, or some combination thereof. 
     
     
         5 . The method of  claim 1 , wherein the first and second alloys are lead-free. 
     
     
         6 . The method of  claim 1 , wherein the first and second alloys comprises silver, the first alloy having a different silver concentration than the second alloy. 
     
     
         7 . The method of  claim 1 , wherein the first and second alloys comprise silver, and the first solder alloy having a higher silver content than the second solder alloy. 
     
     
         8 . The method of  claim 1 , wherein the first and second alloys both comprise a first element and a second element, the first element having a higher concentration than the second element, and the first solder alloy having a higher concentration of the first element than the second solder alloy. 
     
     
         9 . A structure comprising:
 a first solder connection between a substrate and a chip, the first solder connection made of a first alloy;   a second solder connection between the substrate and the chip, the second solder connection made of a second alloy,   wherein the first alloy has a different alloy concentration than the second alloy.   
     
     
         10 . The structure of  claim 9 , wherein the first solder connection is intended for high current density, and the second solder connection is intended for low current density. 
     
     
         11 . The structure of  claim 9 , wherein the first alloy has better electromigration resistance than the second alloy. 
     
     
         12 . The structure of  claim 9 , wherein the first alloy forms a stiffer solder connection than the second alloy.