基于电-热-机械应力多物理场的IGBT焊料层健康状态研究

Healthy Evaluation on IGBT Solder Based on Electro-Thermal-Mechanical Analysis

绝缘栅双极晶体管(IGBT)模块失效将导致功率变流器故障,而IGBT主要失效模式之一——焊料层疲劳则主要是由于温度分布不均匀和材料参数不匹配引起的热应力造成。因此研究IGBT模块温度-机械应力分布特性,对变流器安全评估尤其重要。基于所建立的IGBT功率模块电-热-机械应力多物理场模型,分析了IGBT模块稳态以及瞬态下的热-机械应力分布特性规律。基于论文提出的模型,针对IGBT焊料层疲劳失效,分析了焊料层空洞位置以及大小对功率模块热-机械应力的影响规律,结果表明焊料层热应力最大值出现在焊料层边角以及空洞边缘处,相同面积下拐角空洞更容易导致IGBT模块失效,而且芯片结温随着中心空洞半径增加而升高,当空洞率达到50%时,结温温升达到5.10℃,严重时将会导致模块失效。基于能量微分以及热应力理论,本文提出了基于温度梯度评估焊料层运行状况的方法,并从理论以及仿真模拟层面,验证了该方法的准确性,并分析了不同焊料层失效程度对温度梯度的影响规律,发现温度梯度变化规律与结温变化规律一致,且灵敏度高,具有可追踪故障点位置的优点。

The failure temperature, and the main of insulated gated bipolar transistor （IGBT） strongly depends on junction reason for solder delamination is the thermal stress caused by uneven temperature distribution and coefficients of thermal expansion （CTE） mismatch. Therefore, accurate electro-thermal-mechanical model is essential to maintain an efficient operation. This paper presents an electro-thermal- mechanical model and analyzes the characteristics of steady and transient states. Based on the presented model, the failure behavior of solder joint is discussed; the effects of voids on the thermal-mechanical characteristic are analyzed. Results indicate the max value of thermal stress locates on the edge of solder layer and the martin of void. In addition, corner void has great influence on chip temperature. That is, the junction temperature increases with the percentage of center void increases. The junction temperature is 5.10℃ when the percentage of void reaches 50%. Based on the theory of heat energy and thermal stress, a method based on temperature gradient is proposed for evaluating the operation status of solder layer. It is verified that this method is an efficient way to monitor the operation of status of IGBT module. Moreover, the variation of temperature gradient under different degrees of solder failure is analyzed, and the change laws are the same as those of junction temperature. Simulation results indicate this method has a high sensitivity and can track the failure position.