Development and Evaluation of Photodefinable Wafer Level Underfill

Abstract

Photodefinable wafer level underfill has been developed and its design concept has been verified, that is, the removal of underfill on the top of bumps enables the excellent quality of bump connection without underfill entrapment. The photodefinable composition using carboxylic type polyimide shows poor resolution, whereas the phenol type polyimide based Photo WLUF, CD3000B, has good patterning properties. CD3000B could form underfill patterns having 15 μm diameter holes on 25 μm Cu bumps through conventional photolithography processes. The bonded samples showed the seamless bump junction and passed moisture sensitivity level 2 and thermal cycling reliability test.