Thermosetting flux and solder paste

Abstract

The invention aims to provide a thermosetting flux suitable for solder bonding of a semiconductor element and an electronic part and making solder bonding with a high bonding strength and a high heat resistant strength at a high temperature possible and a paste containing the flux and a non-lead type solder paste and with respect to the thermosetting flux, an epoxy resin, a hardening agent, and at least one of rosin derivatives having functional groups reactive on the epoxy resin and selected from maleic acid-modified rosin, a fumaric acid-modified rosin, and acrylic acid-modified rosin are used. The flux can be used in form of a solder paste while being mixed and kneaded with the non-lead type solder alloy powder.

1 . A thermosetting flux comprising 
 an epoxy resin,    a hardening agent, and    at least one of rosin derivatives having functional groups reactive on the epoxy resin, selected from maleic acid-modified rosin, a fumaric acid-modified rosin, and acrylic acid-modified rosin.    
   
   
       2 . The flux according to the  claim 1 , wherein the ratio of the rosin derivative is 5 to 50% by weight in the thermosetting flux.  
   
   
       3 . The flux according to the  claim 1 , wherein the equivalent ratio of the epoxy group of the epoxy resin and the reactive group of the hardening agent is 0.5 to 1.5.  
   
   
       4 . The thermosetting flux according to the  claim 3 , wherein the equivalent ratio of the epoxy groups of the epoxy resin and the reactive groups of the hardening agent 0.8 to 1.2.  
   
   
       5 . The thermosetting flux according to the  claim 1 , wherein the rosin derivative is maleic acid-modified rosin.  
   
   
       6 . The thermosetting flux according to the  claim 1 , wherein the hardening time of the epoxy resin is within 30 minutes at the soldering temperature.  
   
   
       7 . A solder paste comprising a thermosetting flux containing an epoxy resin, a hardening agent, and at least one rosin derivative having a functional group reactive on the epoxy resin and selected from a maleic acid-modified rosin, a fumaric acid-modified rosin, and acrylic acid-modified rosin and a non-lead type solder alloy powder as well.  
   
   
       8 . The solder paste according to the  claim 7 , wherein the addition amount of the thermosetting flux to the solder paste is not more than 5 parts by weight and not less than 15 parts by weight to 100 parts by weight of the solder paste.  
   
   
       9 . The solder paste according to the  claim 7 , wherein melting points of the epoxy resin and the hardening agent are the melting point of the non-lead type solder alloy or lower.  
   
   
       10 . The solder paste according to the  claim 7 , wherein the hardening temperature of the epoxy resin in the solder paste is the melting point of the non-lead type solder alloy or higher.  
   
   
       11 . The solder paste according to the  claim 7 , wherein hardening time of the epoxy resin is within 30 minutes at the soldering temperature.  
   
   
       12 . The solder paste according to the  claim 7 , wherein the non-lead type solder alloy has a melting point in a range of 150 to 300° C.  
   
   
       13 . The solder paste according to the  claim 12 , wherein the non-lead type solder alloy has a melting point in a range of 180 to 280° C.  
   
   
       14 . The solder paste according to the  claim 7 , wherein solder paste contains at least one of an antioxidant and an anti-corrosion agent.  
   
   
       15 . A soldering method comprising at least steps of applying a solder paste comprising a thermosetting flux containing an epoxy resin, a hardening agent, and at least one rosin derivative having a functional group reactive on the epoxy resin and selected from a maleic acid-modified rosin, a fumaric acid-modified rosin, and acrylic acid-modified rosin and a non-lead type solder alloy powder to an object part of a substrate having an electrode to be bonded and then mounting an object part to be bonded on the substrate; pre-heating the substrate and the mounted part at 150 to 180° C. for 0.1 to 10 minutes; and heating the resulting substrate and the mounted part at 200 to 300° C. for 0.1 to 30 minutes.  
   
   
       16 . The soldering method according to the  claim 15 , wherein the object part to be bonded is a power semiconductor element.