The Simulation of Thermomechanically Induced Stress in Plastic Encapsulated IC Packages / Edition 1

by Gerard Kelly

Overview

One of the greatest challenges facing package manufacturers is to develop reliable fine pitch thin packages with high leadcounts, capable of dissipating heat, and deliver them in volume to the market in a very short space of time. How can this be done? Firstly, package structures, materials, and manufacturing processes must be optimised. Secondly, it is necessary to predict the likely failures and behaviour of parts before manufacture, whilst minimising the amount of time and money invested in undertaking costly experimental trials. In a high volume production environment, any design improvement that increases yield and reliability can be of immense benefit to the manufacturer. Components and systems need to be packaged to protect the IC from its environment. Encapsulating devices in plastic is very cheap and has the advantage of allowing them to be produced in high volume on an assembly line. Currently 95% of all ICs are encapsulated in plastic. Plastic packages are robust, light weight, and suitable for automated assembly onto printed circuit boards. They have developed from low pincount (14-28 pins) dual-in-line (DIP) packages in the 1970s, to fine pitch PQFPs (plastic quad flat pack) and TQFPs (thin quad flat pack) in the 1980s-1990s, with leadcounts as high as 256. The demand for PQFPs in 1997 was estimated to be 15 billion and this figure is expected to grow to 20 billion by the year 2000.

Product Details

ISBN-13:	9780792384854
Publisher:	Springer US
Publication date:	04/30/1999
Edition description:	1999
Pages:	134
Product dimensions:	6.69(w) x 9.61(h) x 0.24(d)

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.