Thermal resistance simulation of IC packages using a three-dimensional boundary element method : Toshiki Sotaet al. Proceedings of the 22nd Symposium on Reliability and Maintainability, Tokyo, Japan. Union of Japanese Scientists and Engineers, 5 (June 1992)

Abstract

Plastic-encapsulated microcircuits (PEMs) are proposed for use in military systems to reduce cost and eliminate long-lead items such as packages and lids. Encapsulant materials must be evaluated for compatibility with devices and fine-wire bonds, and electrical stability on deposited elements and integrated-circuit devices. Reliability evaluations in screen tests and various temperature/humidity/bias environments are also essential prior to use in advanced packaging.Encapsulant reliability evaluation requires a test vehicle (MCM-C and MCM-L) to identify these key performance characteristics to assure environmental and mechanical protection because no complete multichip test vehicle, however, is available for use. An encapsulant test vehicle in previous work was modified by substituting a Sandia ATC04 chip and a silver-comb-pattern array with varying feature sizes, using only a single nichrome-resistor network, and adding a deposited comb pattern. The unpassivated resistor and a silver-comb pattern offer both a go/no-go and quantitative test for screening encapsulants and the Sandia chip facilitates stress measurements on the die as well as thermal dissipation evaluation with resistance heaters on the chip.An industry-standard encapsulant, Hysol® FP 4450, was modified to improve thermal conductivity. Exact filler selection and loading were optimized, balancing dispensability, wear, and flow characteristics. Control materials (Hysol® FP 4450) and improved, thermally conductive versions were exposed to short-term screen tests, long-term humidity, and elevated temperature storage testing. Thermal conductivity of Hysol® FP 4450 was improved by approximately 200% and both materials were comparable in temperature/humidity/bias and highly accelerated stress testing as well as thermal cycling and elevated temperature storage.