Hermetic-equivalent packaging of GPS MCM-L modules for highreliability avionics applications

Results are presented of comparative reliability testing of multichip modules (MCM's) fabricated with laminate substrates, and protected with various bare-die coatings. The demonstration MCM's included two design versions (flip-chip and wire-bond) of the digital portion of global positioning system (GPS) receiver multichip modules. This paper summarizes the results for the wire-bonded constructions. Standard encapsulants and new inorganic coatings (Dow Coming's ChipSeal(R) hermetic coating materials') were evaluated in environmental stress exposures corresponding to high reliability avionics applications. Full wafer probe testing was performed both before and after the supplemental ChipSeal processing and dip-chip wafer bump processing steps. ChipSeal and flip-chip wafer processing steps were shown to cause no yield degradation on wafer lots of five different IC types used in the overall program. The environmental test results demonstrate that MCM-L units with bare die packaging can be designed for very robust reliability applications such as military and other high reliability avionics