Mechanics of Microelectronics - Springer Link

Mechanics of Microelectronics

SOLID MECHANICS AND ITS APPLICATIONS Volume 141 Series Editor:

G.M.L. GLADWELL Department of Civil Engineering University of Waterloo Waterloo, Ontario, Canada N2L 3GI

Aims and Scope of the Series The fundamental questions arising in mechanics are: Why?, How?, and How much? The aim of this series is to provide lucid accounts written by authoritative researchers giving vision and insight in answering these questions on the subject of mechanics as it relates to solids. The scope of the series covers the entire spectrum of solid mechanics. Thus it includes the foundation of mechanics; variational formulations; computational mechanics; statics, kinematics and dynamics of rigid and elastic bodies: vibrations of solids and structures; dynamical systems and chaos; the theories of elasticity, plasticity and viscoelasticity; composite materials; rods, beams, shells and membranes; structural control and stability; soils, rocks and geomechanics; fracture; tribology; experimental mechanics; biomechanics and machine design. The median level of presentation is the first year graduate student. Some texts are monographs defining the current state of the field; others are accessible to final year undergraduates; but essentially the emphasis is on readability and clarity.

For a list of related mechanics titles, see final pages.

Mechanics of Microelectronics by

G.Q. ZHANG Philips Semiconductors and Delft University of Technology, The Netherlands

W.D. VAN DRIEL Philips Semiconductors and Delft University of Technology, The Netherlands and

X.J. FAN Intel Corporation, U.S.A.

A C.I.P. Catalogue record for this book is available from the Library of Congress.

ISBN-10 ISBN-13 ISBN-10 ISBN-13

1-4020-4934-X (HB) 978-1-4020-4934-7 (HB) 1-4020-4935-8 (e-book) 978-1-4020-4935-4 (e-book)

Published by Springer, P.O. Box 17, 3300 AA Dordrecht, The Netherlands. www.springer.com

Printed on acid-free paper

All Rights Reserved © 2006 Springer No part of this work may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission from the Publisher, with the exception of any material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. Printed in the Netherlands.

CONTENTS Preface …………………………………………………………………… 1. Microelectronics Technology ………………………………………… 1. Introduction ………………………………………………………. 1.1 A Heart of Silicon .………………………………………… 1.2 In a Little Black Box……………………………………… 2. Baseline CMOS …………………………………………….…….. 2.1 Diffusion …………………………………………………. 2.2 Patterning ………………………………………………… 2.3 Deposition …………………………………………….… … 2.4 Planarization ………………………………………….… … … 2.5 Integration …………………………………………….… 2.6 Interconnect …………………………………………….… 3. Non-CMOS Options ………………………………………….….. 3.1 Memory ………………………………………………… … 3.2 Analog/RF ………………………………………………... 3.3 Passive Integration ……………………………………..… 3.4 High-Voltage/Power …………………………………….... 3.5 Sensors and Actuators ……………………………………. 4. Packaging …………………………………………………….….. 5. Systems ……………………………………………………….….. 6. Conclusions ………………………………………………….…… 7. References …………………………………………………….…. 8. Nomenclature ………………………………………………….…

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2. Reliability Practice ………………………………………….………… 1. Introduction …………………………………………………….... 2. Reliability Assessment ……………………………………………. 2.1 Burn In ……………………………………….……………. 2.2 Biased Moisture Test …………………………………..… 2.3 Unbiased HAST and Steam Test ……………………….… 2.4 Bake and Extended High Temperature Storage Test …….. 2.5 Electromigration Testing on Devices and Packages …….…

35 35 37 38 38 39 39 40

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Contents 2.6 Moisture Sensitivity Test ………………………………… 2.7 Temperature Cycling and Temperature Shock Tests …….. 2.8 Power Cycle Testing ………………………………….… … 2.9 Mechanical Testing…………………………………….…. 2.10 Design for Manufacturability, Reliability, and Testability (Df MRT)………………………………… 3. Reliability Statistics……………………………………….….…. .. 3.1 Life Distributions ………………………………………..… 3.2 Confidence Level .…………………………………….….. 4. Acceleration Factor Models …………………………….………... 4.1 Arrhenius Relationship …………………………….……… 4.2 Peck’s Model ………………………………………..……. 4.3 Temperature-Voltage-Relative Humidity Model (Eyring model) …………………………………….….….. 4.4 Coffin-Manson Model ………………………………..…… 4.5 Norris-Landzberg Model …………………………….…… 5. Failure Mechanisms…………………………………….….…….. 5.1 General … ……………………………………….……….… 5.2 Examples of Failure Mechanisms …………………….… … 6. Conclusions ……………………………………….………….….. 7. References ……………………………………….……………..… 8. Exercises ……………………………………….…….………….. .

40 40 41 42 43 44 44 51 52 52 53 53 54 55 55 55 56 61 62 63

3. Thermal Management………………………………….……………… 65 1. Introduction ………………………………………….…………... 65 2. Heat Transfer Basics ………………………………….…….…… 68 2.1 Conduction ……………………………………….………. 68 2.2 Convection ……………………………….…….………… 72 2.3 Radiation………………………………….…….………… 76 2.4 Remarks on Thermal Resistance ……………….………… 80 2.5 Typical Thermal Properti es…………………….………… 81 3. Thermal Design of Assemblies ……………………….……….…. 82 4. Thermal Design for a SQFP ………………………….…………. . 87 5. Heatsink Design Choices …………………………….………….. 89 6. Conclusions/Final Remarks ………………………………….…... 91 7. References ……………………………………….…………….…. 92 8. Exercises ……………………………………….…….………….. . 93 4. Introduction to Advanced Mechanics … ……………………………… 95 1. Introduction ……………………………………….….………….. 95 2. Stress and Strain ………………………………………..………... 97 2.1 Analysis of Stress……………………………….………… 97 2.2 Analysis of Strain ………………………………………... 101 2.3 Thermal Strain and Thermal Stress ……………….……… 103

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2.4 Thermoelasticity …………………………………………. 104 2.5 Geometric Nonlinearity ………………………………….. 109 2.6 Material Nonlinearity ……………………………………. 110 2.7 Contact Nonlinearity ……………………………….…….. 120 3. Failure Criteria ……………………………….…………………. 122 3.1 Failure of Ductile Materials ……………………………… 122 3.2 Failure of Brittle Materials – Maximum Normal Stress Theory................................................................................. 124 3.3 Fatigue Failure …………………………………………… 124 4. Fracture Mechanics ……………………………………….……... 126 4.1 Linear Elastic Fracture Mechanics ………………………. 126 4.2 Elasto-Plastic Fracture Mechanics ………………….……. 132 4.3 Fatigue Crack Propagation ………………………………. 134 4.4 Mixed-Mode Fracture ……………………………….…… 135 4.5 Crack Closure ……………………………………………. 138 4.6 Singularity of Angular Corner of a Homogeneous Material............................................................................... 140 4.7 Interface Fracture Mechanics ………………………..…… 141 5. Finite Element Method ……………………………………….….. 147 5.1 Introduction …………………………………………….… 147 5.2 Treatment of Nonlinearity in Finite Element Analysis …... 148 5.3 Finite Element Implementation in Fracture Mechanics ….. 158 5.4 Advanced Techniques in Finite Element Analysis …….… 162 6. References ………………………………………………………... 165 7. Exercises ……………………………………………………….… 166 5. Thermo-Mechanics of Integrated Circuits and Packages ………… 169 1. Introduction ………………………………………………….…… 169 2. Manufacturing Processes and Testing Methods …………………. 171 2.1 IC Backend Processes ……………………………….…… 171 2.2 Packaging Processes ……………………………………... 174 2.3 Reliability Testing for IC Packages ……………………… 177 3. Thermo-Mechanics of IC Backend Processes …………………… 179 3.1 IC Material Characterization ………………………….….. 180 3.2 Wafer Warpage as a Function of Temperature ……….….. 183 3.3 Nano-Indentation ………………………………………… 185 3.4 IC Interface Toughness Characterization ………………... 188 3.5 Other IC Material Characterization Techniques …………. 190 3.6 Typical IC Material Properties …………………………... 191 3.7 Finite Element Modelling for Backend Processes .…….… 191 4. Thermo-Mechanics of Packaging Processes ………………….…. 206 4.1 Packaging Material Characterization ………………….…. 207 4.2 Silicon Anisotropy ……………………………………….. 208

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Contents 4.3 Characterization of Thermosetting Resins ………………. 210 4.4 Advanced Experimental Techniques for Packaging Stresses and Deformations ……………………………….. 214 4.5 Package Interface Toughness Characterization ………..… 216 4.6 Typical Packaging Material Properties …………………... 221 4.7 Finite Element Modelling for Packaging ………………… 222 5. Thermo-Mechanics of Coupled IC Backend and Packaging Processes......................................................................................... 245 5.1 Effect of IC Metal Design on Passivation Crack and Pattern Shift Occurrence .............................................. 246 5.2 Effect of Package Structure on IC-Compound Interfacial Delamination..................................................... 253 6. Case Studies ……………………………………………………… 259 6.1 Reliability Predictions of Thermo-Mechanical Integrity of the Damascene Process .................................................. 259 6.2 Simulation-based Material Selection for a TBGA Package.. 263 7. References ………………………………………………….…….. 271 8. Exercises ………………………………………………….……… 278

6. Characterization and Modelling of Moisture Behaviour…………… 281 1. Introduction ……………………………………………………… 282 2. Moisture Diffusion Modelling ……………………………..…..…. 285 2.1 Diffusion in Multi-Material System ……………….…….. 285 2.2 Application to PBGA Package …………………….…….. 289 2.3 Moisture Desorption ……………………………….…….. 291 3. Characterization of Moisture Diffusivity and Saturation Concentration…………………………………………….………. 292 3.1 Diffusivity Measurement ………………………………… 292 3.2 Saturated Moisture Concentration ……………………….. 296 4. Vapour Pressure Modelling ……………………………….….…. 298 4.1 Micromechanics-based Vapour Pressure Model …….…... 298 4.2 Vapour Pressure as External Loading in Delaminated Areas………………………………………………..……. 305 4.3 Vapour Pressure-Induced Expansion ……………….……. 307 4.4 Whole-Field Vapour Pressure Modelling …….….….…… 308 4.5 Failure Mechanism………………………………….……. 309 4.6 Underfill Selection for Flip Chip BGA Package for Moisture Performance ………………………………... 309 5. Hygroscopic Swelling Characterization & Modelling ……….….. 311 5.1 Hygroscopic Swelling Characterization ……………….… 311 5.2 Hygroscopic Swelling Modelling for FCBGA Package … 327

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6. Single Void Instability Behaviour Subjected to Vapour Pressure and Thermal Stress ……………………………………………… 330 6.1 Void Behaviour at Bulk ………………………………….. 331 6.2 Void Behaviour at Interface ……………………………... 336 7. Interface Strength Characterization and Modelling ……………... 338 7.1 Mechanics of Interfacial Delamination ………………….. 338 7.2 Interfacial Fracture Toughness …………………….…….. 341 7.3 Interface Modelling using Cell Element …………….…… 342 8. Case Studies ……………………………………………….…….. 345 8.1 Integrated Stress Study for QFN Package …………….…. 345 8.2 BGA Moulding Compound Selection with Optimal Resistance to Moisture Induced Failures ………………… 361 9. References …………………………………………………….…. 370 10. Exercises …………………………………………………….….. 374 7. Characterization and Modelling of Solder Joint Reliability………. 377 1. Introduction ……………………………………………………… 377 1.1 Low Cycle Fatigue Loading .…………………………….. 379 1.2 Thermally Induced Solder Joint Reliability ……………… 381 2. Analytical-Empirical Prognosis of the Reliability ………………. 385 3. Thermo-Mechanical Characteristics of Soft Solders ……………. 389 3.1 Eutectic Sn-Pb-(Ag) Solder ……………………………… 396 3.2 Tin-Based Lead Free Solders ……………………………. 399 3.3 Discussion on the Solder Creep Characteristics ……….… 405 3.4 Primary Creep ……………………………………………. 408 4. Data Evaluation and Life-time Estimation ………………….…… 410 5. Case Studies ……………………………………………………… 418 5.1 Comparing Different Creep Laws for a Ceramic Capacitor and a PBGA on FR-4 Boards ……………………………. 418 5.2 Comparison of Predicted and Test Results for Surface Mount Quartz Components ................................................ 428 5.3 Parametric Study on Chip Size Packages ………………… 438 5.4 Flip Chip on Board Assemblies ………………………….. 449 6. References ………………………………………………….…….. 462 … 466 7. Exercises ………………………………………………………… 8. Virtual Thermo-Mechanical Prototyping …………………….…… 469 1. Introduction ………………………………………………….…… 469 2. Strategy, Methodology and Procedures of Virtual Prototyping …. 473 2.1 Strategy and Methodology ………………………….……. 473 2.2 Procedures ……………………………………………….. 477

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Contents 3. Fundaments of Simulation-based Optimisation …………….…… 480 3.1 Design of Experiments (DOE) ……………………….….. 480 3.2 Response Surface Models (RSM) ………………….….…. 482 3.3 Design Optimisation ……………………………………... 489 3.4 Reliability and Robustness Analysis ………….…………. 507 4. Case Studies ……………………………………………….…….. 512 4.1 Analytical Examples ………………….…………….……. 512 4.2 Industrial Application Cases …………….………….……. 517 5. Conclusions ………………………………………………….…… 531 6. References …………………………………………………….…. 532 7. Exercises ……………………………………………………….… 534

9. Challenges and Future Perspectives ………………………………. 537 1. Introduction ……………………………………………………… 537 2. Mechanical Related Characteristics of Microelectronics ……….. 538 3. Reliable Inputs ……………………………………..…….….…… 542 3.1 Design Inputs …………………………………….………. 542 3.2 Failure Inputs …………………………………….………. 543 4. Tests and Experiments …………………………………………… 545 5. Material and Interface Behaviour ……………………………….. 546 5.1 Material Behaviour ………………………………………. 546 5.2 Interface Strengths ……………………………………….. 547 6. Multi-scale Mechanics …………………………………….……... 549 6.1 Introduction ……………………………………….……… 549 6.2 Hierarchy of Methods for Mechanical Modelling ……..… 551 6.3 Handshaking between Approaches ……………….……… 556 6.4 Summary and Outlook ………………….…………….…. 558 7. Multi-Physics Modelling ……………………….………….…….. 560 8. Advanced Simulation Tools ……………………………….……... 561 9. Conclusions ……………………………………………….……… 561 10. References ……………………………………………….……… 562

PREFACE

Microelectronics has pervaded our lives for the past fifty years, with massive penetration into health, mobility, security, communications, education, entertainment, and virtually every aspect of human lives. In the past decades, as the main stream, these progresses are powered by Moore’s law, focusing on IC miniaturization down to nano dimensions and siliconon-chip (SoC) based system integration. While microelectronics community continues to invent new solutions around the world to keep Moore’s law alive, there are ever-increasing awareness, R&D effort, and business drivers to push the development and application of “More than Moore” (MtM) that are based upon or derived from silicon technologies but do not simply scale with Moore’s law (with typical examples as RF, HV and power, sensors and actuators, MEMS/NEMS, system-in-package (SiP), heterogeneous integration, etc.). This emerging trend is partially triggered by the increasing social needs for high level microelectronic systems including non-digital functionalities, the necessity to speed up the innovative product creation and to broaden the product portfolio of existing wafer fabs, and the limiting cost and time factors of advanced SoC development. Along with the major technology development trends characterized by Moore’s law and “More than Moore”, the business trends are mainly characterized by cost reduction, shorter-time-to-market and outsourcing. The combination of these technology and business trends leads to increased design complexity, decreased design margins, increased chances and consequences of failures, decreased product development and qualification times, increased gap between technology advance and development of fundamental knowledge, and increased difficulties to meet quality, robustness and reliability requirements. Based on the root cause analyses from observed failures of microelectronics during different life cycles, it is found that, among others, thermo-mechanical (thermal, mechanical and thermo-mechanical) related failures account for about 65% of total failures in microelectronics, and they originate mostly from the product/process design phase. Thermo-mechanical xi

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reliability is becoming one of the major bottlenecks for both current and future microelectronics technologies. Due to the lack of available mechanics knowledge on one hand, and nonsufficient attention and R&D effort from both the academia and industry on the other hand, unfortunately, thermo-mechanical design and qualification of microelectronics are still largely depending on one’s experience, supported by some qualitative numerical simulations. As a result, many design cycles are needed: from material development/pre-selection to concept design, to building and testing multiple physical prototypes. It is hard to achieve competitive designs with shorter-time-to-market, optimized performance, low costs, and guaranteed quality, robustness and reliability. Therefore, there is an urgent need to exploit and develop advanced knowledge of mechanics for microelectronics to enable the development of innovative thermomechanical design methods and tools. Driven by our strong motivation and experience of leading and participating in many relevant research, development, and graduate education activities, ranging from microelectronics technologies to fundaments of mechanics, we present this book, as our obligation, to graduate students in universities, researchers, engineers and managers in industries. Our aims are to provide industry and academia with the cutting edge methods and solutions for various thermo-mechanical related problems of microelectronics in a systematic way, and also the development roadmap of mechanics for microelectronics. The book chapters are written by the worldwide leading experts with both profound theoretical achievement and rich industrial experience, containing essential and detailed information about the state-ofthe-art theories, methodologies, way of working and real industrial case studies.

Acknowledgements We would like to thank for their contributions to the book, A.J. van Roosmalen, J. Zhou, R. Dudek, E. Eggink, J.H.J. Janssen, F. G. Kuper, and N. Tzannetakis. We also would like to make acknowledgment to many of our colleagues who have contributed to this book in one way or another, among them, D. van Campen and M. Geers from Technical University of Eindhoven; L.J. Ernst, F. van Keulen, L.G. Wang, C. Yuan from Delft University of Technology; R. van Silfhout, M. van Gils, D.G. Yang, J. Beijer, O. van der Sluis, J. Bisschop, Y. Li, and many others from Philips. G.Q. Zhang is particularly grateful to his wife Suping, his son Luke and his daughter Romy for their motivating, understanding and supporting. W.D. van Driel is grateful to his partner Ciel for her support and understanding on the many evenings at home he has spent on writing and

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editing this book. X.J. Fan is grateful to have the opportunity working together with his wife, Jenny, and the support from their son Bill.

G.Q. Zhang W.D. van Driel X.J. Fan May of 2006