A Metallographic Test for Glass-To-Metal Seal Quality

Glass-to-metal seals on IC lead frames, transistor headers and other electronic component packages make it possible to obtain electrical feed-thru while maintaining hermeticity throughout severe environmental exposure such as that required by MIL-STD-883. In the more exacting applications, the hermeticity requirement is most consistently met by the use of the so-called matched seal. Many of these seals use ASTM Alloy F15 (Kovar) and a glass with matching coefficient of expansion. In practice, industry specialists do the glass-seal work and the component fabricator uses the purchased part to complete a hermetic assembly. Despite the widespread, and long-standing development of glass-seal technology, the industry seems plagued with component failure due to loss of hermeticity. This study describes the use of metallographic techniques for seal quality determination.