Flux and solder paste

Abstract

A soldering flux of the present invention contains, as a base resin, an acrylic resin (A) having an acid value of 0 to 70, and an acrylic resin (B) having an acid value of 30 to 230. The acrylic resin (A) is obtained by polymerization of a monomer mixture containing alkyl (meth)acrylate having an alkyl group having carbon atoms of 12 to 23. The acrylic resin (B) is obtained by polymerization of a monomer mixture containing alkyl (meth)acrylate having an alkyl group having carbon atoms of 6 to 10. The acid value of the acrylic resin (B) is higher than the acid value of the acrylic resin (A), and a difference between these two resins is 15 or more.

1 . A soldering flux comprising:
 an acrylic resin (A) as a base resin which has an acid value of 0 to 70 and is obtained by polymerization of a monomer mixture containing alkyl (meth)acrylate having an alkyl group having carbon atoms of 12 to 23; and   an acrylic resin (B) as a base resin which has an acid value of 30 to 230 and is obtained by polymerization of a monomer mixture containing alkyl (meth)acrylate having an alkyl group having carbon atoms of 6 to 10,   wherein the acid value of the acrylic resin (B) is higher than the acid value of the acrylic resin (A), and a difference between the acid values of these two resins is 15 or more.   
     
     
         2 . The soldering flux according to  claim 1 , wherein a content of the acrylic resin (A) is 10 to 30% by mass in a total amount of flux, and a content of the acrylic resin (B) is 10 to 30% by mass in the total amount of flux. 
     
     
         3 . The soldering flux according to  claim 1 , wherein the acrylic resin (A) is an acrylic resin obtained by polymerization of a monomer mixture containing at least 50% by mass of alkyl (meth)acrylate having an alkyl group having carbon atoms of 12 to 23. 
     
     
         4 . The soldering flux according to  claim 1 , wherein the acrylic resin (B) is an acrylic resin obtained by polymerization of a monomer mixture containing at least 50% by mass of alkyl (meth)acrylate having an alkyl group having carbon atoms of 6 to 10. 
     
     
         5 . The soldering flux according to  claim 1 , wherein the acrylic resin (A) has a weight average molecular weight of 30000 or less. 
     
     
         6 . The soldering flux according to  claim 1 ,
 wherein the acrylic resin (B) has a weight average molecular weight of 30000 or less.   
     
     
         7 . A solder paste composition comprising the soldering flux according to  claim 1 , and solder alloy powder.