Cure shrinkage analysis of epoxy molding compound

Abstract EGA (ball grid array), one of the structures Used for semiconductor packages, involves a laminated structure. BGA inevitably involves significant warpage, owing to differences in shrinkage among constituent materials. The extent of warpage is governed by total shrinkage (= cure shrinkage + thermal shrinkage) of the epoxy molding compound that encapsulates the IC chip. In particular, the cure shrinkage exerts great influence on warpage. Cure shrinkage has been understood as the decrease in free volume at the time of curing. However, the cure shrinkage rate cannot be sufficiently explained by the free volume of the cured epoxy resin. We have developed an evaluation method 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.