Abstract
In electronic wire weld between the Al tub and CP wire plated pure Sn, single-crystal Sn whiskers easily form and can cause problems such as short circuits. We found that the growth of Sn whiskers in the weld zone of Al electrolytic condenser leads was suppressed by controlling the cooling rates of the weld. We observed that the whisker formed only when Al and Sn are mixed. Following the examination of the effect of the microstructure in order to understand the whisker formation mechanism and how to prevent whisker growth we concluded that the microstructure is strongly affected by the cooling time Tc from 933K (Al melting point) to 503K (Sn melting point) of the weld. The whisker did not form in weld when the cooling time Tc is 230s, for example, air cooling by using the simulated Al-Sn alloy. The Sn phase grain was large, i.e. more than several hundred μm. On the other hand, the large number of Sn whisker were observed in the case of Tc=20s. The size of Sn phase is about 5μm. Finally, there was no whisker when the cooling time Tc was 7s, e.g. by the cupper chill plate. The Sn phase grain size is smaller than 1μm that is comparable to the minimum diameter of a whisker. . Considering the microstructure of weld, the whisker growth can be prevented with respect to the size of the Sn phase, i.e. larger than several hundred micron or smaller than one micron.
