The Effect of Toughening of No-Flow Underfill on Fillet Cracking of Flip-Chip Device

摘要

The effect of toughening agents and modification of epoxy on fillet cracking was investigated Nylon, polycarbonate (PC) and polysiloxanes with amine and epoxy functional group were employed as the toughening agents. Nylon and PC were miscible and reacted with epoxy resin, and the homogeneous phase was found. However Nylon and PC were no effective to enhance the anti-fillet cracking of the no-flow underfill. In case where the epoxy was modified with polysiloxanes, the 2nd phase with fine particle size was formed and the size of the panicle depended on the toughening agent. The morphology was observed by scanning electron microscopy (SEM) and confirmed by dynamic mechanical measurement (DMA) measurement. The physical properties such as the fracture toughness, flexual modulus, coefficient of thermal expansion (CTE), and adhesion were measured and the liquid-liquid thermal shock (LLTS) test under―5～125℃ were performed with different formulations. One of the formulations, toughened by amine/epoxy terminated polysiloxane, which has higher die shear strength, lower modulus, and higher toughness, passed 1000 cycles of the LLTS test. As such, in order to obtain high reliable no-flow underfill, the physical properties of the no-flow underfill should be well controlled and balanced. Finally correlation between physical properties of no-flow underfill and anti-fillet cracking capability for those approaches was discussed.