Negative-tone Photodefinable Underfill Having High Resolution and Appropriate Thermal Fluidity

Abstract

Photodefinable wafer level underfill (PWLUF) has been evaluated for chip to substrate stacking. The good fluidity of PWLUF after patterning is required for chip and substrate stacking. PWLUF was designed using polyimide, acrylates, epoxides and some additives. It was difficult to improve the fluidity of patterned PWLUF keeping resolution by changing the composition ratio of acrylates and epoxides. On the other hand, PWLUF using the polyimide oligomer obtained by increasing end capping agent ratio improved the fluidity as well as the resolution. The chip to substrate stacks afford void-free bump soldering without underfill entrapment. We also successfully demonstrated the reflow soldering process using PWLUF.