Since automotive electronic components are used under severe temperature conditions, the reliability of thermal fatigue resistance of solder joints is important. In this study, a series of experimental and analytical investigations were performed to develop a method of evaluating the thermal fatigue life of solder joints. First, tensile and creep tests were carried out on two kinds of commonly used solders, 63Sn-37Pb and 95Pb-5Sn, to determine their mechanical properties. Using the measured properties, constitutive equations for the solders based on elasticity and creep were formulated. Next, a nonlinear finite element analysis was performed on structures with Si chips and Cu plates joined together with solders under thermal cycling. The validity of the analysis was verified by an experiment using a diffused type strain gauge formed on a Si chip surface. Third, the fatigue test of bulk 63Sn-37Pb solder was carried out to obtain data for fatigue life prediction. It was found that the temperature, the frequency and the strain hold had little effect on the fatigue life of solder and that the fatigue life was controlled by inelastic strain range. Finally, the thermal strain at the solder joint of a chip resistor was analyzed and the thermal fatigue life was predicted from the calculated inelastic strain range and the fatigue data of solder. Good agreement was obtained between the prediction and the thermal cycling test results in respect of the location for crack initiation and the fatigue life at the bottom of the chip.
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