Clad solder thermal interface material

Abstract

A clad solder thermal interface material is described. In one example the material has a first layer of solder, a second layer of solder clad to the first layer of solder, the second layer having a melting temperature lower than the melting temperature of the first layer, and a third layer of solder clad to the first layer of solder opposite the second layer, the third layer having a melting temperature lower than the melting temperature of the first layer.

1 . A method comprising:
 providing a first strip of solder having a melting temperature lower than a solder reflow furnace temperature and less than about 200° C.;   providing a second strip of solder having a melting temperature higher than the first strip of solder higher than the solder reflow furnace temperature and higher than about 235° C.;   providing a third strip of solder having a melting temperature lower than the second strip of solder lower than the solder reflow furnace temperature and less than about 200° C.;   rolling the first, second, and third strips of solder to clad the second strip with the first and third strips.   
     
     
         2 . The method of  claim 1 , wherein rolling comprises rolling to establish a metallurgical bond between the second strip and the first and third strips. 
     
     
         3 . The method of  claim 1 , wherein the metallurgical bond is established by forcing the strips into contact without exposure to the ambient. 
     
     
         4 . The method of  claim 1 , wherein the melting temperatures of the first and third strips are the same. 
     
     
         5 . (canceled) 
     
     
         6 . (canceled) 
     
     
         7 . The method of  claim 1 , wherein the melting temperature of the second strip is above about 260° C. 
     
     
         8 . The method of  claim 1 , wherein the second strip comprises at least one of AuSn and SnSb. 
     
     
         9 . The method of  claim 1 , wherein the first and third strips comprise at least one of SnBi, SnIn and SnGa. 
     
     
         10 . The method of  claim 1 , wherein the rolling is sufficient to cause a massive reduction in the cross-sectional area of the strips. 
     
     
         11 - 20 . (canceled) 
     
     
         21 . The method of  claim 1 , further comprising applying the rolled strips to a semiconductor die as a solder thermal interface material. 
     
     
         22 . The method of  claim 1 , further comprising melting the rolled strips to form a joint between a die and a die cover of a semiconductor package. 
     
     
         23 . The method of  claim 22 , wherein the die cover comprises an integrated heat spreader and wherein the rolled strips are melted at the melting temperature of the first layer and of the second layer. 
     
     
         24 . The method of  claim 1 , further comprising:
 attaching a package cover to a die using the rolled strips, the package cover and the die forming at least a portion of a package;   bonding the package cover to the die by melting the strips at a first temperature;   attaching the package to a substrate after bonding the package cover by heating solder between the package and the substrate to a second temperature higher than the first temperature, wherein the second temperature does not melt the rolled strips.   
     
     
         25 . The method of  claim 24 , wherein bonding the package cover comprises producing a homogenous material from the rolled strips with a higher melting temperature than the first temperature. 
     
     
         26 . The method of  claim 25 , wherein the higher melting temperature is higher than the second temperature. 
     
     
         27 . The method of  claim 24 , wherein bonding the package cover comprises bonding a first layer of cladding of the rolled strips to the package cover and bonding a second layer of cladding of the rolled strips to the die.