Development of Shortening Process Time in SBB

ABSTRACT A fast curing process in SBB (Stud Bump Bonding) technology has been developed. SBB technology is one of the flip chip packaging technologies. There are several features in SBB technology. First of all, it is friendly to the earth environment because of lead free technology. Secondly, it has excellent contact reliability through flexible bonding obtained by using conductive adhesive. However it takes a long time (more than six hours) to cure the conventional underfill resin in conventional SBB process. The curing time of new underfill resin could be shortened to 5 minutes by newly developed SBB process. As a result, high productivity in SBB technology can be achieved. Generally, when the fast curing type of underfill resin is cured, a large thermal expansion stress of the underfill resin occurs in vertical direction and this stress pushes up the LSI chip. Such phenomena causes damage in SBB bonding portion and the bonding resistance becomes unstable. In order to solve the above problem, we have developed new process, which the underfill resin was pressed from the back of the LSI chip with a light load while the underfill resin was cured. As a result, in spite of curing the underfill resin in a short time, a low and stable bonding resistance was obtained. The bonding resistance was kept stable in several reliability tests such as heat shock test and moisture storage test. An original air-pressure curing machine has been developed by which many CSPs after underfilled can be pressure-cured easily in batch processing. Therefore the tact time of curing for each CSP can be shortened and high productivity can be realized.