Evaluation of quasi-hermetic packaging solutions for active microwave devices and space applications

A methodology is proposed to estimate the actual influence of important factors during steady-state Temperature Humidity Bias (THB) aging tests on SiN-passivated MMICs: temperature-humidity effects, bias conditions and protection by silica-filled epoxy resins dispensed by a dam-and-fill process. In this work, accelerated aging tests on microwave devices used for space applications were carried out, with or without bias. After 3000 hours of storage at 85°C/85%RH, there was no catastrophic failure. Only devices with PHEMT showed electrical degradations of some DC electrical parameters after 1000 hours of test. In another 1600 hours series of tests, bias parameter was added. Devices with PHEMT exhibited electrical breakdowns, especially under reverse biasing of the gate-source junction and before the required 1000 hours of test. The failed parts were localized by surface observation using optical and scanning electron microscopy. The failure electrical signatures were correlated by electrical simulations. In order to prepare future investigation on encapsulated devices, it was determined moisture diffusivity and content at saturation of commercial dam and fill resins. The actual protection time and the effects of bias conditions of encapsulated MMICs during THB tests were specified. These parameters can be taken into account for further analysis of the reliability of encapsulated active microwave devices for space applications.