Endurance of thermoset resins for flip chip encapsulation

The adhesion or endurance between underfills and die, as well as between underfills and printed circuit board (PCB) is examined. Two types of thermosetting plastic underfills, one commercial product called J and another called IME are investigated. The formulations of both underfills are protected by a nondisclosure agreement. Further, the effects of flux coating on active surface and humidity conditioning on the adhesion are also investigated. The results show that the IME underfill is stronger than J underfill, and the failure mode for IME underfill always occurs at solder resist /board.