Pan Pacific Symposium Conference Proceedings


RELIEVING Sn WHISKER GROWTH DRIVEN BY OXIDATION ON Cu LEADFRAME BY ANNEALING AND REFLOWING TREATMENTS

Authors: C. C. Wei, et al.
Date Published: 1/24/2008   Conference: Pan Pacific Symposium


Abstract: Currently, in the electronic packaging industries, Pb-free solders are replacing eutectic tin-lead. Most of components suppliers are looking forward the pure tin plated or tin-alloys electroplating as an alternative for the tin-lead plating. Thus, whisker growth a serious reliability issue for Sn finishes.

In this study, we discussed the annealing and reflowing process how to mitigate the growth of whiskers. The mechanism of whisker growth under the temperature/humidity storage test was investigated. It is found that corrosion was the driving force for the whisker growth. Thermal treatment was employed to mitigated the whisker growth, including annealing at 220 degrees C and reflowing at 268 degrees C. It is found that both heat treatments can reduce the whisker growth significantly. It is speculated that the heat treatment can relieve the residual stress in the leads, and make the microstructure change in the tin layer. Thus slow down the corrosion rate. In addition, reflowing treatment can change the columnar grain structure to equi-axed grain structure in some regions of the Sn film, resulting in a lower grain boundary rate for Sn self-diffusion. Therefore, the reflowed had the lowest growth rate of Sn whiskers.

Key words: tin whiskers, corrosion, relieving process



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