The dynamic strain generated under a Au plated microbump during ultrasonic flip-chip bonding has been measured using a Si thin-film strain gauge array to investigate its bonding behavior. The gauges were designed to be sensitive to the strain in both the horizontal and vertical directions. Measured results reveal that plated microbump bonds with a small deformation of the bump surface produced by friction. A comparative study between large bumps and microbumps was also carried out. The bonding behavior of plated microbumps has been found to be the same as that of the plated large bumps while it is different from that of ball bumps. In the case of the ball bumps, the flat contact region between the bumps and bonding pad at the initial stage of bonding is small because the bump surface is spherical. Hence, the expansion of this contact region (large deformation) is necessary for bonding of the bumps. On the other hand, in the case of the plated microbumps, the flat contact region between the bumps and bonding pad is large even at the initial stage of bonding. Hence, bonding is performed with a small deformation of the bump surface produced by friction. The difference in bonding behavior due to the bump shape can clearly explain why plated microbump bonds when a smaller pressure was applied during ultrasonic application than the pressure required for bonding of the ball bumps.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)