Development of high reliability underfill material

As an encapsulant for flip chip packages, underfill materials play an important role for the purpose of protection from thermal stress and environmental stress. We have developed an excellent reliability underfill material based on the following concepts: (1) cured underfill material coefficient of thermal expansion (CTE) which is close to that of the solder ball; (2) excellent adhesion to plastic circuit board; (3) little change in material properties after moisture uptake. The material can be cured for 60 min, has JEDEC level 3 reliability and passes 1000 cycle temperature cycling tests. In order to shorten the cure schedule of this material, we have studied the following: (a) an additive agent with hydrophobic structure; (b) a catalyst. Based on these studies, we have developed a shorter cure (30 min.) type underfill.