Abstract

After wafer-die sawing process, sometimes silicon (Si) dust on microchip Al bondpads is difficult to be cleaned away by DI water, especially at pinhole/corrosive areas caused by galvanic corrosion, thus resulting in non-stick on pads (NSOP) problem in assembly process. To eliminate NSOP problem due to Si dust contamination, in this paper, we will study the mechanism of Si dust contamination and propose a concept of Si dust corrosion. A theoretical model will be introduced so as to explain Si dust contamination and corrosion problem during wafer die sawing process. Based on the mechanism proposed, Si dust contamination and corrosion is related to galvanic corrosion as OH- ions generated from galvanic corrosion will not only react with Al to cause Al corrosion, but also react with Si dust to cause Si dust corrosion. During Si dust corrosion, poly-H2SiO3 and Si-Al-O complex compounds will be formed on Al bondpads, especially at the pinholes/corrosive areas. Poly-H2SiO3 and Si-Al-O complex compounds are “gel-like” material and stick onto the surface of bondpads. It is insoluble in water and difficult to be cleaned away by DI water during or after wafer die sawing process and will cause bondpad discoloration or/and NSOP problem. Some eliminating methods of Si dust contamination and corrosion on Al bondpads during wafer die sawing process are also discussed.

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