Abstract
Electronic equipments and devices are being exposed to much more severe temperature environments than before. In the case of an equipment used in space, it is necessary to predict the thermal cycling life of solder joints under a low temperature environment below -100°C. Moreover, in the life assessment of solder joints, it is necessary to consider not only the simple shearing load condition but also the tension-compression and mixed mode load conditions in many cases.An attempt was made to investigate the influence of low temperature and load conditions on the low cycle fatigue properties of a solder material by carring out the tension-compression and torsional fatigue tests on the specimens of 36Pb62Sn2Ag solder at room temperature (20°C), -100°C and -140°C.The results obtained are as follows.(1) Although the ductility of 36Pb62Sn2Ag decreased at low temperatures (-100, -140°C) considerably in comparison with that at room temperature, no noticeable decrease in low cycle fatigue life was observed.(2) At low temperatures, the universal slope method and the Langer's method can be used effectively to predict the low cycle fatigue life. At room temperature, however, the test data indicate shorter life than the predicted value, and so the method suitable for predicting the high temperature low cycle fatigue life should be used.(3) All the tension-compression and torsional fatigue data at low and room temperatures can be unified approximately by using the equivalent strain of Mises' type. It is possible, therefore, to evaluate the low cycle fatigue life under a mixed mode load condition by use of the equivalent strain of Mises' type.
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