Effects of coefficient of thermal expansion mismatch on solder attached GaAs MMICs

The reliability effects of a GaAs solder attachment to a variety of different materials with a diverse range of coefficients of thermal expansion (CTE) are examined. Failure mechanisms included fractures or cracks through the devices, as well as cracking of the corners. GaAs devices are placed under tensile stress with materials such as Kovar experienced severe cracking and corner fracture through long-term reliability screening. Devices placed under compressive stress, on the other hand, did not degrade through life testing unless the CTE mismatch was greater than or equal to 16.5 ppm/ degrees C. From this evaluation, the CTE range at which GaAs can be reliably attached and expected to operate without failures through 1000 cycles of MIL-STD thermal cycling was defined.<>