Causes of corrosion of metallic parts of power semiconductor devices with protective coatings of KLT-30

When power semiconductor devices are sealed in air, the most active corrosive components are O/sub 2/, H/sub 2/O, and under certain conditions (deviations from the optimal conditions of hardening of the protective composition, low humidity, contaminated catalyst) HCl and CH/sub 3/COOH. Atmospheric oxygen causes formation of H/sub 2/O even when thoroughly dried air is used, as the result of thermooxidative degradation of the protective coating. The substances liberated: water, hexamethyltricyclosiloxane, oxygen-containing hydrocarbons (primarily HCOOH, CH/sub 3/COOH), and the products of heterolytic cleavage of cyclic dimethylsiloxanes by water tend to intensify corrosion of metallic parts of the devices. Corrosion is prevented completely if the devices are sealed in an inert-gas atmosphere after preliminary heating (150-180/sup 0/).