| Research Abstract |
Sn-Pb alloys are used currently as a solder in electrical and electronic industries. In recent years, however, it has been claimed that there is a possibility of polluting the environment with toxic Pb contained in the solder. Much attention has been paid to the development of Pb-free solder alloys in various countries. In this study, it was aimed to develop some Pb-free solder alloys utilizing an interesting relation between the melting temperature and the alloy composition which was discovered by present investigator.
In the first year, 17-types Sn-based alloys containing Ag, Bi, Zn and In were designed as the first step candidate alloys. All of them were designed so as to have the same melting temperature as that of Sn-Pb solder, 456K. Measured melting temperatures of these alloys were within the range of 453-466K, and this results supported the usefulness of the melting temperature estimation method.
In the second year, some fundamental experiments were made in order to obtain inform
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ation which is necessary for the design of second step candidate alloys. The effect of alloying elements, Zn, Ag, Cd, In, Sb, Pb and Bi on the hardness, electrical resistivity, lattice constant and wettability of Sn based alloy was measured. It was shown that the addition of all alloying elements increased the hardness and resistivity of Sn alloys. Among these elements, Bi has the largest hardening effect due to the large distortion of Sn crystal lattice. The addition of Pb, Ag, Bi was found to improve the wettability of Sn alloys with copper plate. By using obtained semi-quantitative information, 6-types of Sn-Zn and Sn-Bi based alloys containing Ag and In were designed. It was found that Sn-Zn based sencond candidate alloys had similar mechanical properties to those of Sn-3.5Ag-0.7Bi, the most promising alloy as Pb-free solder for the next generation. Also, Sn-Bi based candidate alloys had equal wet-ability with Cu plate. Based on these experiments, it was demonstrated that Pb-free solder alloys could be developed efficiently by employing the present melting temperature estimation method. Less
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