In this study, the simultaneous role of thermal cycling and electric current on the microstructure and degradation behavior of solder joints was investigated. For this purpose, FEM simulations and experimental works were performed on IGBT modules with the diverse solder joint thicknesses of 50, 70 and 90 μm. The results showed that the thermal cycling effect is a dominant factor in degradation of solder joints in thin solder layer (50 μm) which is due to the intensified stress triaxiality and higher accumulated creep energy per volume of the solder layer. However, in thicker solder joints (90 μm), the joule heating effect of electric current comes into play and accompanies with the thermal cycling effect to degrade the solder joint. This event is due to the fact that the thicker layer has a higher resistance to the electric current and induces more accumulated energy. This phenomenon is inconsistent with the thermal cycling effect which has an inverse relation with the solder thickness. Finally, it was revealed that an optimum solder thickness (70 μm) includes the minimum accumulated energy from simultaneous effects of thermal cycling and joule heating.

在这项研究中，研究了热循环和电流对焊点的微观结构和降解行为的同时作用。为此，对具有50、70和90μm不同焊点厚度的IGBT模块进行了FEM仿真和实验工作。结果表明，热循环效应是薄焊料层（50μm）中焊点退化的主要因素，这是由于应力三轴性增强和每层焊料层的累积蠕变能量更高。然而，在较厚的焊点（90μm）中，电流的焦耳热效应开始发挥作用，并伴随着热循环效应而使焊点退化。该事件是由于以下事实：较厚的层对电流具有更高的电阻，并且会感应出更多的累积能量。这种现象与热循环效应不一致，热循环效应与焊料厚度成反比。最后，发现最佳的焊料厚度（70μm）包括来自热循环和焦耳加热的同时影响的最小累积能量。