Mechanical Stress Reliability Factors for Packaging GaAs MMIC and LSIC Components

Microwave monolithic integrated circuits (GaAs-MMIC's) and large-scale integrated circuits (GaAs-LSIC's) are being used in advance ground, airborne, or space-based Systems having severe environmental and dynamic loads. GaAs-MMIC and GaAs-LSIC chips are fragile because they are thin and large and also because GaAs is an inherently Weak material. Data are provided for the fracture stress (
\sigma
f
) of GaAs monolithic circuits based upon starting GaAs materials, wafer-thinning procedures, chip-dicing methods, and chip size. Using strength data obtained for 1) four-point compressive loading and 2) biaxial compressive loading, Weibull plots of fracture data are obtained which have been related to materials, processes, and size. For a brittle material such as GaAs the flaw size and population resulting from processing perturbs the strength of the material. The effects of surface flaws (scratches) have been determined by obtaining data for mechanically lapped versus chemically thinned chips. Edge flaw effects (cracks) have been investigated from strength data for mechanically sawed versus chemically diced chips. The effects of bulk imperfections, such as dislocations, have been investigated by obtaining data for liquid encapsulated Czochralski (LEC) versus horizontal Bridgman (HB) GaAs chips, it is Shown that large and thin GaAs monolithic circuits can he processed with high fracture strength and that fracture strength characterization allows for the prediction of safe stress limits.