The Accelerated Testing of Plastic Encapsulated Semiconductor Components

Elevated temperature and elevated humidity have been studied as stress factors for predicting the reliability of plastic encapsulated bipolar semiconductor components. The test transistors used in the study were encapsulated in a variety of epoxy resins and a silicone resin the purity of which were characterised by a determination of the conductivity of an aqueous extract of the resin. Both stress conditions induce failures modes due to gain degradation, leakage growth and increase in saturation voltages and, under humidity stress, the degree of degradation could be related to the resin purity. It is concluded that elevated temperature is not useful for predicting the reliability of epoxy encapsulated components but is useful for silicone encapsulated components operating above about 100°C. Humidity stress testing is shown to be valid and relevant for both epoxy and silicone encapsulated components operating below 100°C because of the water that will be present in the encapsulants in normal environmental conditions. It is proposed that the humidity stress factor for life predictive purposes is (RH)2 because this is directly related to the water content of the encapsulating resin and can be used as the basis of a physical model that explains the experimental observations in terms of the ionic impurity content of the resin.