The latest underfill materials for flip-chip applications

Underfill materials faces two issues regarding reliability. One is the presence of voids affecting the reliability of the flip chip package. The narrow gaps of flip chip packages cause fluidity problems. The effects of filler size and filler content of the underfills were investigated. The second is the high temperature reflow compatibility. The underfill materials, when subjected to high temperature reflow, tend to cause delamination between the chip and the underfill. To solve this problem, increasing the adhesive property of the underfill material was attempted by investigating the glass transition temperature, elastic modulus, toughness using different resins and filler content. On the other hand, the moisture absorption ratio of the underfill material did not affect the resistance to soldering heat by much. Based on these findings, new underfill materials with high fluidity and high temperature reflow compatibility were developed. These new materials did not cause voids and did not have delamination even when treated by the LEVEL 3 JEDEC preconditioning test at 260 degree C reflow.