Development of test vehicles for evaluating plastic-encapsulant reliability and improving thermal conductivity of encapsulant materials

Plastic-encapsulated microcircuits (PEMs) are proposed for use in military systems to reduce cost and eliminate long-lead items such as packages and l ids. Encapsulant materials must be evaluated for compatibility with devices and fins-wire bonds, and electrical stability on deposited elements and in tegrated-circuit devices. Reliability evaluations in screen tests and vario us temperature;humidity,bias environments are also essential prior to use i n 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, howe ver, is available for use. An encapsulant test vehicle in previous work was modified by substituting a Sandia ATC04 chip and a silver-comb-pattern arr ay with varying feature sizes, using only a single nichrome-resistor networ k, and adding a deposited comb pattern. The unpassivated resistor and a sil ver-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 c hip. An industry-standard encapsulant. Hysol " FP 4450, was modified to improve thermal conductivity. Exact filer selection and loading were optimized, bal ancing dispensability, wear, and flow characteristics. Control materials (H ysol " FP 1450) and improved, thermally conductive versions were exposed to short-term screen tests, long-term humidity, and elevated temperature stor age testing. Thermal conductivity of Hysol " FP 4450 was improved by approx imately 200% and both materials were comparable in temperature/humidity/bia s and highly accelerated stress testing as well as thermal cycling and elev ated temperature storage. (C) 1997 by IMAPS. Published by Elsevier Science Ltd. All rights reserved.