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

为了研究微电子焊点在温度循环试验过程中的循环应力-应变迟滞现象，对TSOP、BGA和LCCC进行了有限元建模，建立了焊点应力-应变评估系统。分析结果表明，在温度循环试验中，较长的高温和低温停留时间对焊点循环应变范围的影响不大。在应变分析结果的基础上，提出了微电子焊点温度循环试验和机械疲劳试验的有效方法，并进行了循环试验。实验结果与分析结果吻合较好。实验结果表明，所提出的热循环加速试验方法比常规方法可节省50%以上的试验时间，可作为焊点热疲劳强度的一种较好的加速试验方法。结果表明，TSOP和BGA焊点的疲劳寿命可以用Manson-Coffin低值N_f=A DELTAepsilon_<in bb_0 ^n来估计。在此基础上，基于统计优化方法（SOM）和试验结果，开发了焊点疲劳强度CAE估计系统。结果表明，SOM是一种非常实用的焊点疲劳设计工具。对不同工作条件下BGA焊点的疲劳寿命进行了估算，结果表明，温度变化范围和平均温度对BGA焊点的疲劳寿命影响较大。在CAE系统中，采用数学规划（逐次二次规划）求解焊点重量的优化问题。

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.