Epoxy-additive interaction studies of thermally reworkable underfills for flip-chip applications

Reworkable underfill encapsulant is the key to address the non-reworkability of the flip-chip-on-board packages. This paper presents work on epoxy-additive interaction studying to develop reworkable additive-modified underfills. Four additives that have the potential to provide epoxy reworkability are selected. Their interactions with epoxy composition before, during, and after epoxy curing are studied. The results show that all additives retain their thermal decomposition feature after they are incorporated into the epoxy formulation, and they do not adversely affect the epoxy properties. However, when the additive decomposition temperature is reached, the decomposition of the additive caused a big CTE jump in the epoxy matrix. Additionally, the adhesion of the epoxy matrix is greatly reduced. These two changes are considered important to provide reworkability to the epoxy. Based on the epoxy-additive interaction study, two additives are selected for developing reworkable additive-modified epoxy underfills.