Hermetic-equivalent packaging of data accumulator MCM-L modules for general aviation avionics applications

This paper presents the results of comparative testing of standard encapsulants versus inorganic hermetic-equivalent protective coatings in a full factorial study that also compares wire-bond assembly versus flip-chip assembly and supplemental encapsulant/underfill die protections versus no encapsulant/underfill protection. The demonstration multichip modules (MCMs) included two design versions, flip-chip and wire-bond, of a general aviation data accumulator MCM. Full wafer probe testing was performed both before and after the supplemental ChipSeal^TM processing and flip-chip wafer bump processing steps. ChipSeal^TM and flip-chip wafer processing steps were shown to cause no yield degradation of the the two different wafer types used in the MCMs. Known good die (KGD) screening of all ICs in the modules was used to keep infant mortality failures out of the reliability test results. Preliminary substrate reliability investigations determined that BT and polyimide laminate materials are suitable for robust MCM-L applications. Reliability testing includes vibration in step-stress exposures from 2 to 44 g(RMS), thermal cycling for 2000 cycles from -55 to +125°C, 85°C/85% RH high humidity testing accelerated by pre-conditioning and power cycling, and 130°C bias highly accelerated stress testing (HAST). Comparative reliability results are presented for identical circuit designs in flip-chip versus wire-bonded assemblies, with and without the protective inorganic coatings, and with and without organic encapsulant/underfill protection