Structure-Properties of Acrylic Rubber/Epoxy Adhesive by Reaction-Induced Phase Decomposition

The advancement in the miniaturization of electric devices requires high performance diebond adhesive films for semiconductor packages. The diebond film should have high thermal-stress resistance and good retention of adhesive properties. To achieve such performance and reliability, we choose a rubber-rich epoxy adhesive. In the present work, we investigated the influence of reactive site of acrylic rubber (ACM), cure agent and curing condition on the performance of diebond film. In the early stage of curing, ACM/epoxy/curing agent (e.g., DDM: diaminodiphenylmethane) system was a single-phase mixture. As the cure reaction proceeded, phase separation took place via the spinodal decomposition, induced by the increase in the molecular weight of epoxy. The reaction-induced spinodal decomposition was confirmed by the characteristic change in light scattering profile with curing time. Phase contrast microscopy and atomic force microscopy also revealed the formation of regularly phase-separated structure characteristic to the spinodal decomposition. The periodic distance of the structure varied in a wide range, from a few μm to ten nm. The higher amount of reactive site (glycidylmethacrylate) in ACM and the lower cure temperature rendered the shorter periodic distance. The shorter periodic distance yielded the higher adhesive strength. However, much shorter distance of 10 nm resulted in poor adhesive strength. The sub-μm structure seems to lead to optimum strength. The 10 nm structure material showed low thermal expansion and nice transparency.