关键词: 热敏电阻, 共晶焊, 应力, 有限元分析法

Abstract: Inorder to study and solve the problem that the resistance values of thermistors increase after eutectic soldering, the failed thermistors are observed by scanning electron microscope (SEM) and cracks are found in them. The stresses generated by the thermistors after eutectic soldering are analysed by the finite element analysis method. The results show that the locationsof the maximum principal stressesarebasicallyconsistent with the locations of cracks, and the directions of the maximum principal stressesare orthogonal to the directions of the cracks, which indicate that the cracks are caused by stresses. The relationship between the maximum principal stresses on the thermistors and the solder thicknesses is analyzed.The analysis results show that the thicker the solder thicknessesare, the smaller the stresses generated by the thermistors during eutectic soldering. Through the verification test, it can be seen that using appropriately thickened solder for eutectic soldering of thermistors, the appearances of thermistors after eutectic soldering are good, there are no cracks, and the resistance values don’t increase.Therefore, the thermistor cracking can be prevented by increasing the solder thickness.

Key words: thermistor, eutectic soldering, stress, finite element analysis method