Selection of Optimum Cu Content in Cu Bearing Tin-Lead Solder(Materials, Metallurgy & Weldability)

概要

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Dissolution rate of copper in a molten 60Sn-40Pb solder was theoretically studied. The rate constant was calculated using the experimental data and physical constants. The temperature dependence of the rate constant, namely, the apparent activation energy of dissolution was 0.17eV/atom. The rate constant in a molten 60Sn-40Pb solder containing previously added copper was also calculated through the same process, and the relation between these two rate constants with and without copper addition was made clear. According to the comparison of calculated values with measured ones, it was proved that the dissolution of a fine copper wire can be well approximated by the semi-experimental equation when the volume of the molten solder was large enough compared with that of the fine copper wire. Besides, 60Sn-40Pb/Cu quasibinary eutectic solder (0.23wt% Cu) was proposed as the means to minimize the erosion of fine copper wires in the molten solder. It was proposed that the initial dissolution rate of a fine copper wire was given as the mathematical product of the rate constant of dissolution and the equilibrium solubility of copper in a molten solder. The apparent activation energy was determined to be 0.48eV/atom.
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