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Published: 1979

Total Pages: 51

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Glass-to-metal seals on electronic component packages make it possible to obtain electrical feed-thru while maintaining hermeticity throughout severe environmental exposure. As a result of this study, it was determined that sealed sub-assemblies will generally pass the least severe thermal shock requirement of MIL-STD-883, but that the same (previously accepted) lots will exhibit a 6%, or higher, failure rate as a result of manufacturing stresses imposed by cover welding, delidding, and thermal bakes or soaks. During this study, the use of tighter controls on the more critical glass sealing processes was shown to reduce the reject rate to less than 1%. Success in matched glass- seal making depends on the use of three thermal treatments for Kovar: de- carburizing, pre-oxidation and sealing. This report deals specifically with pre- oxidation and sealing. An oxide film on Kovar, prior to sealing, promotes glass wetting and provides for the development of a chemical-mechanical bond at the glass-metal interface. A determination for residual intergranular oxide is useful for judging the quality of a matched glass-to-metal seal where pre- oxidation is a requisite for sealing. Residual oxides can be detected by metallographic techniques, and the range of 2.0 - 6.5 micrometers is appropriate for high quality glass seals. Other effects are also detectable by the evaluation of metallographic cross-sections of sealed packages. These include volume fraction of bubble formation, bubble size, bubble distribution, glas- metal separation and other interface criteria.