Adhesion Study on Underfill Encapsulant Affected by Flip Chip Assembly Variables

摘要

The underfill material is a polymeric adhesive which is being used in the flip-chip device. It encapsulates the solder joints by filling the gap between silicon die and organic substrate. Within a typical flip chip assembly, there are interfaces between the various components, namely, substrate, solder mask, flux residual, underfill encapsulant and die passivation layer, etc. Maintaining the good adhesion condition, both as-made and after aging, for these interfaces is vital for the expected performance of the flip chip device assembly, where underfill material is employed to enhance the reliability of the flip-chip device dramatically as compared to the non-underfilled one. A large portion of the previous adhesion study was focused on the underfill material itself, however, this paper will look into the effects of the different assembly factors, such as solder mask, flux residual, underfill and IC chip passivation, etc., upon the adhesion strength between these interfaces. The influence of some accelerated aging tests on the adhesion durability will also be investigated. This could provide device/board level insights into the interfacial adhesion of the flip chip assembly.