Fine pitch low-cost bumping for flip chip technology

In this paper, a low-cost and fine pitch bumping process by electroless Ni-Au bumping for the UBM (under bump metallurgy) and stencil printing for the solder bump is studied. The solder bumps are made of eutectic SnPb. The pitches of the solder bumps range from 300 /spl mu/m to 200 /spl mu/m for various stencil openings from 210 /spl mu/m to 125 /spl mu/m. The regular bump height is 90 /spl mu/m for the 200 /spl mu/m pitch. The pad opening size is also controlled as a variable. The kinetics of zincating on an Si-Cu surface and on an Al surface are compared. It is found that zincating replacement on the Al-Si-Cu surface is much more rapid than on the Al surface and the dissolution rate of Al-Si-Cu is also faster than that of Al. Finally, the quality of the low-cost solder bumping process is evaluated by shear tests and reliability tests.