Mixed alloy lead-free solder paste

Abstract

This invention is to a mixed alloy lead-free solder paste, a method of making the solder paste, and a method of using the solder paste. The solder paste comprises particles of a first alloy and a second alloy, mixed in a flux. The liquidus temperature of the first alloy and the liquidus temperature of the second alloy differ by not greater than about 15° C.

1 . A mixed alloy solder paste comprising: 
 particles of a first alloy having a liquidus temperature and a solidus temperature which differ by not greater than 20° C.;    particles of a second alloy having a liquidus temperature and a solidus temperature which differ by not greater than 20° C.; and    flux, wherein the particles of the first and second alloy are mixed with the flux and the liquidus temperature of the first alloy and the liquidus temperature of the second alloy differ by not greater than 15° C.    
   
   
       2 . The method of  claim 1 , wherein the particles of the first alloy have a liquidus temperature and a solidus temperature which differ by not greater than 15° C., and the particles of the second alloy have a liquidus temperature and a solidus temperature which differ by not greater than 15° C.  
   
   
       3 . The method of  claim 1 , wherein the particles of the first alloy have a liquidus temperature and a solidus temperature which differ by not greater than 10° C., and the particles of the second alloy have a liquidus temperature and a solidus temperature which differ by not greater than 10° C.  
   
   
       4 . The method of  claim 1 , wherein the liquidus temperature of the first alloy and the liquidus temperature of the second alloy differ by not greater than 10° C.  
   
   
       5 . The method of  claim 1 , wherein the liquidus temperature of the first alloy and the liquidus temperature of the second alloy differ by not greater than 5° C.  
   
   
       6 . The method of  claim 1 , wherein the first alloy comprises Sn, Ag and at least one additional metal.  
   
   
       7 . The method of  claim 6 , wherein the at least one additional metal is selected from the group consisting of Cu, Zn, Bi, Ni and In.  
   
   
       8 . The method of  claim 1 , wherein the second alloy comprises Sn and Ag.  
   
   
       9 . A mixed alloy lead-free solder paste comprising 
 particles of a first alloy of Sn—Ag—Cu;    particles of second alloy of Sn—Ag; and    flux, wherein the particles of the first and second alloy are mixed with the flux.    
   
   
       10 . The mixed alloy lead-free solder paste of  claim 9 , wherein the first alloy comprises from 2.3 wt. % to 4.3 wt. % Ag, and from 0.4 wt. % to 1.2 wt. % Cu, with the remainder being Sn.  
   
   
       11 . The mixed alloy lead-free solder paste of  claim 9 , wherein the first alloy comprises from 2.5 wt. % to 4.1 wt. % Ag, and from 0.5 wt. % to 1.0 wt. % Cu, with the remainder being Sn.  
   
   
       12 . The mixed alloy lead-free solder paste of  claim 9 , wherein the second alloy comprises from 2.0 wt. % to 5.0 wt. % Ag, with the remainder being Sn.  
   
   
       13 . The mixed alloy lead-free solder paste of  claim 9 , wherein the second alloy comprises from 2.3 to 4.2 wt. % Ag, with the remainder being Sn.  
   
   
       14 . A method of making solder paste, comprising: 
 providing particles of a first alloy having a liquidus temperature and a solidus temperature which differ by not greater than 20° C.;    providing particles of a second alloy having a liquidus temperature and a solidus temperature which differ by not greater than 20° C., wherein the liquidus temperature of the first alloy and the liquidus temperature of the second alloy differ by not greater than 15° C.; and    mixing the particles of the first and second alloy with a flux to form a solder paste.    
   
   
       15 . The method of  claim 14 , wherein the mix of particles in the solder paste is comprised of at least 50 wt. % of the first alloy and not greater than 50 wt. % of the second alloy.  
   
   
       16 . The method of  claim 14 , wherein the mix of particles in the solder paste is comprised of from 50 wt. % to 90 wt. % of the first alloy and from 10 wt. % to 50 wt. % of the second alloy.  
   
   
       17 . A method of soldering an electrical component to a substrate, comprising: 
 applying a mixed alloy lead-free solder paste to a substrate, the mixed alloy lead-free solder paste comprising particles of a first alloy of Sn—Ag—Cu; particles of second alloy of Sn—Ag; and flux, wherein the particles of the first and second alloy are mixed with the flux;    placing an electrical component on the mixed alloy lead-free solder paste;    heating the electrical component, substrate and solder paste to melt and flow the first alloy and second alloy; and    cooling the electrical component, substrate and melted first alloy and second alloy to affix the electrical component to the substrate.    
   
   
       18 . The method of  claim 17 , wherein the first alloy comprises from 2.3 wt. % to 4.3 wt. % Ag, and from 0.4 wt. % to 1.2 wt. % Cu, with the remainder being Sn.  
   
   
       19 . The method of  claim 17 , wherein the first alloy comprises from 2.5 wt. % to 4.1 wt. % Ag, and from 0.5 wt. % to 1.0 wt. % Cu, with the remainder being Sn.  
   
   
       20 . The method of  claim 17 , wherein the second alloy comprises from 2.0 wt. % to 5.0 wt. % Ag, with the remainder being Sn.  
   
   
       21 . The method of  claim 17 , wherein the second alloy comprises from 2.3 to 4.2 wt. % Ag, with the remainder being Sn.