基于结构函数的功率VDMOS器件热特性分析

Analysis of Thermal Characteristics of Power VDMOS Based on Structural Functions

基于结构函数理论,运用改进电学测试法,对同一器件管壳与基板间的不同界面进行研究,发现其积分结构函数曲线发生了分离;通过该分离点确定器件稳态结壳热阻值,获得了器件内部各结构层的热阻分布。比较测试结果与理论值,两者基本一致。该测试方法简单、方便,比传统热阻测试法准确且重复性好。对比了采用不同封装工艺的器件的微分结构函数,观察发现,其峰值位置发生了偏移;进一步的超声波扫描证实了偏移的原因是存在焊料层空洞,提出了相应的改善措施。研究表明,利用结构函数理论分析功率VDMOS器件热特性是一种准确而可靠的方法。

An improved electrical test method based on structural function theory was employed to analyze power VDMOS devices with different interface contacts between case and plate. Steady-state thermal resistance between chip and case was measured by separated integral structure function curves, and thermal resistances of all layers of the device were obtained with structural function. The measured and calculated values of various materials were essentially conformable. The proposed test method was simple and convenient, and it had better accuracy and repeatability, compared with conventional test methods. Shift was observed on the peak of differential structural function by comparing devices with different packaging technologies. Scanning acoustic microscopy （SAM） indicated that the shift was caused by solder void. And method for improvement was put forward. It has been demonstrated that structural functions are reliable and powerful tools for analyzing thermal characteristics of power VDMOS.