Solder-glass attachment in Cerdip/Cerquad packages: thermally induced stresses and mechanical reliability

The authors discuss the major requirements for the mechanical properties of solder glasses and ceramics in cerquad flat packages (CQFP) and develop a simple and easy-to-use stress-evaluation model aimed at assessing thermal stresses in the glass seals of ceramic packages. The authors also demonstrate how a probabilistic approach can be applied to ensure low and compressive stresses in the glass seals, and describe the results of qualification tests for the CQFP packages. For a reliable solder glass seal in a hermetic ceramic package, it is recommended that the same material be used for all the ceramic components and that the coefficient of thermal expansion of this material be close and somewhat larger than the coefficient of thermal expansion of the solder glass, especially at low temperatures, when the expected thermally induced stresses are the greatest. It is also important that the sealing be performed at the lowest possible temperature and that the solder glass material possess high fracture toughness, high strain-to-failure, good shock resistance, low Young's modulus, and good adhesion with ceramics.<
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