Reliability Performance Study of Molding Compounds on High Voltage Molded Leaded Package

High voltage devices are gaining more attention and are widely used in many applications especially on automotive that requires higher reliability performance. The reliability performance of molding compounds for two types of products with different polarities from the same package are compared during HTRB testing at 150°C in this study. The device vehicles identified for this study are transistors from a typical high-power (350-500V) Cu-wire bonded plastic molded leaded package. During High Temperature Reverse Bias (HTRB) test, high electrical fields are applied on the device, this tends to drive the transport of ionic elements from the encapsulation materials such as molding compounds towards the die which may cause an accumulation of charges at the highly active areas like ball bond intermetallic compound (IMC), die top passivation and mold compound layer interface. This paper investigated the ion movement in molding compounds towards the ball bond IMC and die passivation depends on the applied bias direction of the two product types resulting to two different failure signatures observed. Furthermore, critical mold compound material properties and their role on the ball bond IMC degradation and device leakage current on die passivation and mold compound layer interface due to ionic movement during high voltage test conditions were discussed. A study trial was conducted to validate the performance of different molding compounds capable of delamination-free package after MSL1 on selected device vehicles for investigation and analysis. High voltage HTRB reliability test results showed that failure signature on devices where positive bias was applied resulted to IMC ball bond degradation while devices where negative bias was applied resulted to a leakage current failure. Higher leakage current failures were found to be driven by the increase in voltage applied while ball bond degradation was more driven with the increase in temperature and test duration. The failure mechanisms from the failed units were further studied and discussed in this paper. Decapsulation and SEM images were gathered to visually inspect the samples, EDX was then performed to identify presence of ionic accumulation on active areas, while ball bond inspection was conducted to compare the failure signature between the positive and negative biased high voltage devices. Overall results from this study provides a better understanding on the behavior of molding compounds and failure mechanisms related to molded leaded packages for high voltage applications.