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12 SMT Magazine • December 2017 Part 2 of the series outlines the Bi effects on 63Sn37Pb solder material, which have been sub- stantiated by years of field performance prior to lead-free implementation. This should serve as the sound baseline for further discussion on the subject. The incorporation of Bi in Sn-containing sol- ders is expected to affect both physical proper- ties and mechanical properties of the resulting solder materials. This includes melting tempera- ture, wetting ability, strength, plastic strain and fatigue behavior . The direct addition of a suffi- cient amount of Bi to a eutectic alloy (e.g., 63Sn- 37Pb) also alters its eutectic behavior or deviates from eutecticity. The DSC thermogram below of 63Sn37Pb plus 1 wt.% Bi indicates that 63Sn37Pb essentially maintains its eutectic property. How - ever, at 2 wt.% Bi, the range of melting starts to appear, departing from the eutectic point. An extensive study was carried out on the effects of a minor addition of Bi to SnPb eu- tectic solder. The following table summariz- es the effects of addition of Bi to 63Sn37Pb up to 5 wt.% on the basic mechanical properties and the melting temperature. The dosages of 2 wt.% and 5 wt.% Bi were added to 63Sn37Pb, respectively, by separately replacing Sn or Pb. In by Dr. Jennie S. Hwang CEO, H-TECHNOLOGIES GROUP SMT PROSPECTS & PERSPECTIVES Figure 1: DSC Thermogram of 63Sn37Pb added with 1 wt.% Bi.

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