Effects of Humidity and Organic Coating on Surface Potential Propagation in Passivated Devices

Potential propagation over the surface of hermetically sealed or plastic coated semiconductor products may produce failure. A special test structure has been used to characterize the rate of propagation as a function of a number of parameters: humidity, temperature and selected organic coatings. A surface memory effect associated with exposures to humid ambients is discussed. This effect may explain in part the surprisingly wide range of surface instability observed in units hermetically sealed using state-of-the-art packaging techniques. Organic coatings, e.g. silicone varnish, reduce the influence of humidity at temperatures below 90°C. Arrhenius plots obtained in detailed studies at high temperatures allow estimation of stability performance in the 150°C to 200°C range as a function of material composition and curing time.