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BiographyDr. Qing Tan is a staff engineer for Motorola Inc. His areas of interest include: self-aligning soldering for opto-electronic packaging; thermosonic bonding for flip chip assembly; solder bumping, joining and reliability; and Finite Element modeling. AbstractA Zn layer is formed on the aluminum pad of an integrated circuit prior to the deposition of electroless Ni/P and immersion Au layers and the subsequent formation of a eutectic Pb-Sn solder bump from stencil-printed solder paste. Different zincation levels are observed from visual inspection of the bond pad. These zincation levels can be in evidence on the same wafer. As a result, it was necessary to determine the significance of the individual bond pad's coloratiodzincation level in order to guarantee the reliability of solder bumps. The integrity of the solder bumps was evaluated through contact resistance measurement, bump shear, and stud pull after thermal conditioning. The results show that, although the zincation level has measurable influence on the bump strength, both electrical and mechanical properties of the bumps are acceptable for all zincation levels.

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Reliability performance is still the major concern for flip chip interconnection. While solder fatigue is believed to be the contributing factor for packaging failure and is the most widely studied for flip chip soldering, experimental work in this study find out solder fatigue itself is seldom the driving force for early failure. With the introduction of underfill, failures solely due to solder fatigue usually have a cycling life that is much longer than the required failure cycle. It is the other failure modes that result in early failure. This paper analyzed the major failure sources for flip chip assembly using eutectic solder. These failure mechanisms could usually resulted in early failure for the assembly. Failure mechanisms presented in this study include: underfill void, underfill delamination, underfill cracking, die cracking (horizontal and vertical), substrate cracking, and passivation crack or delamination. Discussion will also be given on how to avoid these issues.