Development of CAE System for Fatigue Strength Design of Solder Joints in Surface Mount Devices

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In order to study the get a cyclic stress-strain hysteresis in microelectronic solder joints during a temperature cyclic test, a TSOP,a BGA and a LCCC were modeled for FEA,and a stress-strain evaluating system for solder joints has been developed. The analytic results show that for a temperature cyclic test, long high-temperature and low-temperature dwell times do not contribute to the cyclic strain range in solder joint so much. Based upon the results of the strain analyzes, some efficient testing processes of temperature cycling and mechanical fatigue experiments for the microelectronics solder joint were proposed, and the cycling tests were carried out. The experimental results show a good agreement with the analytic results. The proposed thermal cyclic accelerated test method can save over 50% testing time than an usual methods, and the experimental results showed that the proposed mechanical fatigue test method can be used as a good accelerated test method for the thermal fatigue strength of solder joints. It was shown that the fatigue life of TSOP and BGA solder joints could be estimated by Manson-Coffin's low as N_f=A DELTAepsilon_<in>^n. Further more a CAE system for fatigue strength estimation of solder joints has been developed based upon the statistical optimization method (SOM) and experimental results. It was shown that SOM could be used as a very practical tool to conduct fatigue design of solder joints. The fatigue life of BGA solder joints subjected to operating conditions was estimated, and the results showed that the fatigue life is greatly affected by not only the temperature changing range but also by the mean temperature. In the CAE system, a mathematical programming (successive quadratic programing) was employed to solve the optimization problem of the weight of solder joints.