Overview

This study is motivated by the need to understand and predict the complex stress distributions, transfer mechanisms, warpage, and potential failures arising from the encapsulation of devices in plastic. Failures like delaminations, package cracking, and metal shift occur due to the build-up of residual stress and warpage in the packages because of the TCE mismatch between the package materials as the package cools from its moulding temperature to room temperature. The correct use of finite element tools for these problems is emphasised. Finite element techniques are used to predict the internal package stress distribution and help explain the stress transfer mechanism between the die, die paddle, and plastic after moulding. Out-of-plane shear stress components are shown to be responsible for experimentally observed metal shift patterns on the die surface. Delaminations dramatically alter the internal stress state within a package, increasing the tensile stress in the plastic and so the likelihood of plastic cracks, the stress on wire bonds, and the incidence of wire bond failure. The application of finite element techniques to predict the post-mould warpage of both thermally enhanced PQFPs and TQFPs is described. Simulations of a thermally enhanced PQFP warpage based on standard modelling assumptions alone fail to predict either its magnitude or its direction correctly. The modelling assumptions need to be modified to include the chemical shrinkage of the moulding compound to enable accurate predictions of package warpage to be made, particularly when the packages are asymmetric in structure. Microsystem packaging in both plastic and 3D package body styles is reviewed. Although microsystem packaging is derived from IC packaging, additional requirements for microsystems not common to IC packaging are highlighted. The assembly stresses on a novel microsystem, incorporating a micromachined silicon membrane pump integrated into a 3D plastic encapsulated vertical multichip module package (MCM-V), are analysed.

Full Product Details

Author:   Gerard Kelly
Publisher:   Springer
Imprint:   Springer
Edition:   1999 ed.
Dimensions:   Width: 17.00cm , Height: 1.10cm , Length: 24.40cm
Weight:   0.910kg
ISBN:  

9780792384854

ISBN 10:   0792384857
Pages:   134
Publication Date:   30 April 1999
Audience:   College/higher education ,  Professional and scholarly ,  Undergraduate ,  Postgraduate, Research & Scholarly
Format:   Hardback
Publisher's Status:   Active
Availability:   In Print  
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Table of Contents

1. An Introduction to Plastic Packaging.- 1.1 Manufacturing sequence for a PQFP.- 1.2 Properties of packaging materials.- 1.3 Stress induced failures of plastic packages.- References.- 2. A Review of Package Stress Modelling.- 2.1 Introduction.- 2.2 Analytical approaches to package modelling.- 2.3 Finite element methods.- References.- 3. Thermomechanical Stress in a PQFP.- 3.1 Introduction.- 3.2 Origin of thermomechanical stress in TCE mismatched materials.- 3.3 Finite element analysis of a PQFP.- 3.4 2D representation of a 3D structure.- 3.5 Interpretation of die encapsulation stress.- 3.6 Mechanism of stress transfer.- 3.7 Deformation of the package structure.- 3.8 Die surface compressive stress distribution.- 3.9 Material and geometric factors which influence encapsulation stress.- References.- 4. The Correlation of Modelling with Measurements and Failure Modes.- 4.1 Introduction.- 4.2 Measurement of die stress with stress sensors.- 4.3 Simulated die surface stress.- 4.4 Comparison between measured and modelled encapsulation stress.- 4.5 Analytical model.- 4.6 The correlation of simulations with failure modes.- 4.7 Influence of delamination on stress.- 4.8 Analysis of stress in a wire bond.- References.- 5. Accurate Prediction of PQFP Warpage.- 5.1 Introduction.- 5.2 Warpage of a 208 lead power PQFP package.- 5.3 Variation of power PQFP warpage with temperature.- 5.4 Significance of chemical shrinkage for asymmetric packages.- 5.5 Warpage of a small body size PQFP.- 5.6 Warpage of a large body size PQFP.- 5.7 Warpage sensitivity of both large and small body size PQFPs.- 5.8 Asymmetric structure of BGA packages.- References.- 6. Microsystem Packaging in Plastic and in 3D.- 6.1 Introduction.- 6.2 Microsystem packaging — Lessons from IC packaging.- 6.3 3D packagingmethodologies.- 6.4 3D microsystem packaging — a European example.- 7. Concluding Remarks.- 7.1 Problems remaining to be solved.- 7.2 A comment on the numerical tools.- 7.3 For the Future.- References.- References.- Appendices.- A- Analytical model of encapsulation stress.- A.1 Force equilibrium.- A.2 Strain compatibility.- B- Fundamentals of stress and strain.- B.1 Direct and shear stress conventions.- B.2 Longitudinal strain and Poisson’s ratio.- C- Axial stress and bending stress.

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