Soldering flux and method for bonding semiconductor element

Abstract

The method for bonding a semiconductor element comprises the step of applying to solder bumps 10 of a semiconductor chip 12 a soldering flux 16 which contains a thermosetting resin, a polyhydric alcohol and an organic acid and in which the thermosetting resin remains uncured after reflow-bonding, the step of reflow-bonding the solder bumps 10 to the electrodes 18 of the circuit board 20 with the soldering flux 16 while melting the solder bumps 10, and the step of filling an underfill material 22 between the semiconductor chip 12 and the circuit board 20 with the soldering flux 16 being left, the underfill material 22 containing a thermosetting resin of the same group as the thermosetting resin contained in the soldering flux 16 and at least one of a curing agent and a cure catalyst for curing the thermosetting resins.

1 . A soldering flux to be used in reflow-bonding a solder bump formed on a first substrate to an electrode formed on a second substrate, comprising:
 a first thermosetting resin, a polyhydric alcohol and an organic acid,   the first thermosetting resin remaining uncured after the reflow-bonding.   
   
   
       2 . A soldering flux according to  claim 1 , wherein
 the first thermosetting resin is bisphenol F cyanate ester, bisphenol A cyanate ester, or phenol novolak resin cyanate ester.   
   
   
       3 . A soldering flux according to  claim 1 , wherein
 the polyhydric acid is dihydric alcohol of a 100-250 molecular weight and/or trihydric alcohol of a 100-150 molecular weight.   
   
   
       4 . A soldering flux according to  claim 1 , in which
 a content ratio of the first thermosetting resin is 30-70 wt %, a content ratio of the polyhydric alcohol is 20-60 wt %, and a content ratio of the organic acid is 2-20 wt %, and which further includes:   a viscosity modifier by a 1-10 wt % content ratio.