Cure shrinkage analysis of epoxy molding compound

BGA (ball grid array), one of the structures used for semiconductor package s, involves a laminated structure. BGA inevitably involves significant warp age, owing to differences in shrinkage among constituent materials. The ext ent of warpage is governed by total shrinkage (= cure shrinkage + thermal s hrinkage) of the epoxy molding compound that encapsulates the IC chip. In p articular, the cure shrinkage exerts great influence on warpage. Cure shrin kage has been understood as the decrease in free volume at the time of curi ng. However, the cure shrinkage rate cannot be sufficiently explained by th e free volume of the cured epoxy resin. We have developed an evaluation met hod based on the epoxy group reaction ratio, and have eventually confirmed that cure shrinkage depends on the reaction ratio of the epoxy group after curing, and on epoxy group density.