This paper addresses the use of finite element (FE) techniques to predict residual warpage in plastic quad flat packs (PQFP's) after encapsulation. Experimental measurements of package warpage are used to validate FE models of the packages. Failure to incorporate mold compound chemical shrinkage into the FE analysis leads to erroneous predictions of package warpage. The warpage sensitivity of different packages to changes in downset is presented. The validated FE package models predict stress levels in packages which are 70% greater than those with temperature coefficient of expansion (TCE) shrinkage alone and questions the accuracy of previous simulations which do not include molding compound chemical shrinkage. j I:

This paper addresses the use of finite element techniques to predict warpage in plastic encapsulated IC's. A basic modeling assumption adopted in such analyses is that after ejection from the mold, warpage occurs due to the contraction of the molding compound as the package cools to room temperature. It is shown that this basic starting assumption can lead to incorrect, predictions of the package warpage. Measurements of the warpage of a plastic power package with temperature indicate that the package is significantly deformed at the molding temperature. This is attributed to chemical shrinkage of the molding comDound. A new F.E. model of package warpage after encapsulation is proposed which considers both the TCE shrinkage and chemical shrinkage of the molding compound. This leads to accurate predictions of warpage, particularly where heat spreaders make the package asymmetric. Measurements of a 208 lead power PQFP are used to verify this improved model. 0569-5503/94/0000-0102 $13.00 "1 994 IEEE

The performance and reliability of a low-cost threedimensional plastic moulded vertical multi-chip module concept is presented. Performance was evaluated using custom designed chips incorporating thermal, thermomechanical, electrical and reliability test structures. Results of performance are presented and are shown to correlate well with thermal, thermomechanical and electrical simulations. The thermal and thermomechanical performances are sufficient to allow use of the MCM-V technique in a wide range of applications without the need for special cooling techniques.Reliability testing to space level standards was carried out on 53 technology demonstrator modules incorporating the test chips and a high level of reliability has been demonstrated. I INTRODUCTIONMultichip modules (MCMs) are a significant advance in the field of packaging and interconnection due to the ability of MCMs to significantly increase electronic system performance and to reduce system size. However, two-dimensional MCMs, whether MCM-L, -C or -D all inevitably show a more or less linear increase in substrate area and overall system volume, and silicon-to-footprint area remains a constant or decreases, with increasing chip count. This can be overcome by the use of three-dimensional or vertical MCMs (MCMVs) in which silicon-to-footprint ratio actually increases with chip count and a number of novel techniques have been proposed and demonstrated in recent years [1-81. However, the majority of reported MCM-Vs proposed can only be manufactured using complex and expensive process sequences involving rerouting of IC metallisation, vacuum metallisation and photolithography, constricted IC interconnection techniques and generally expensive materials and fabrication processes. However, an MCM-V technique was proposed by Val [9] which could potentially allow a low-cost plastic-moulded MCM-V to bc manufactured using commonly available microelectronics packaging techniques with inherently low materials and fabrication costs. However, thermal, thermomechanical and electrical perfoimance and reliability remained to be demonstrated. In 1992, the authors commenced a collaborative project to demonstrate that high performance and reliability could be obtained for thls MCM-V technique. This paper presents the final results from that collaborative project, which finished successfully in July 1994 and which involved co-operation between Thomson CSF (project managers), Alcatel Espace, Implex, University of Sheffield and NMRC Ireland.To evaluate the performance and reliability of the MCM-V technique, the partners used custom designed test chips which were integrated in three different types of "technology demonstrators" to evaluate thermal, thermomechanical and electrical performance and long term reliability. The performance of the technology demonstrators was predicted by simulations and the simulations were correlated with the measured performance results. This has allowed the required thermal, thermomechanical and electrical design methodologies to be put in plac...

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