Failure analysis on the sealing glass insulator of semiconductor device with low resistance abnormity

A semiconductor device adopts glass insulators to realize the sealing insulation between metal leads and case. Abnormal low resistance phenomenon between the metal lead and shell take places in several devices after working under normal pressure, temperature and humidity for a certain period. The normal resistance is usually at the level of Megohm, while the abnormal resistance is instable and from one hundred ohm to several Kilohm only. Fluorescent dye method can demonstrates the micro cracks on the glass insulator surface which cannot be observed by optical microscope or scanning electron microscope. According to the results of series of tests, micro cracks may absorb the moisture in the environment by capillary action, leading the sodium and potassium ion in glass getting free. Such free ions are ranged in order when applying the electric field, which consequently forms different and unstable low resistance paths leading to the failure.