The new underfill materials with high adhesion strength for flip-chip applications

Epoxy acid anhydride materials are normally used as flow-type underfill materials. However, the underfill materials of this type, when humidified, tend to cause delamination at the interface with chips in solder reflow. To solve this problem, increasing the adhesive property of underfill material was attempted by investigating the relationship of adhesion strength with the glass transition temperature, high-temperature elastic modulus, and coefficient of moisture absorption for different resin compositions and different filler contents. As a result, the adhesion strength is higher and soldering heat resistance was found to be improved with higher glass transition temperature compositions. On the other hand, the adhesion strength was not affected by changes in the filler content. Based on these findings, an underfill material with high adhesion strength was developed. This new material did not cause delamination, even when treated by the level 2 JEDEC preconditioning test.