Mechanism of underfill voids formation in flip chip packaging

Voids in flip chip packaging of organic land grid array (OLGA) caused by the inclusion of air, other gases and moisture were studied and experiments were designed to understand the cause of void formation. Reactions among the solder mask, flux residue, underfill and solder bump were investigated to understand the mechanism of voids formation during the assembly of the underfill flip chip packages. The results showed that the position and shape of the voids could provide the evidence of root cause. The paper also discusses procedures to eliminate the said voids