RF/MICROWAVE HYBRIDS Basics, Materials and Processes
RF/MICROWAVE HYBRIDS Basics, Materials and Processes by Richard Brown Richard Brown Associates, Inc. Shelton, CT KLUWER ACADEMIC PUBLISHERS NEW YORK, BOSTON, DORDRECHT, LONDON, MOSCOW
ebook ISBN: 0-306-48153-7 Print ISBN: 1-4020-7233-3 2004 Kluwer Academic Publishers New York, Boston, Dordrecht, London, Moscow Print 2003 Kluwer Academic Publishers Dordrecht All rights reserved No part of this ebook may be reproduced or transmitted in any form or by any means, electronic, mechanical, recording, or otherwise, without written consent from the Publisher Created in the United States of America Visit Kluwer Online at: and Kluwer's ebookstore at: http://kluweronline.com http://ebooks.kluweronline.com
DEDICATION TO JUDY
TABLE OF CONTENTS Preface Acknowledgements xiii xv CHAPTER 1: Hybrids vs MMICs 1 CHAPTER 2: 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 Basic Concepts Introduction 5 Maxwell's Laws 5 Permittivity and Permeability 6 Free Space Wavelength 7 Propagation velocity 8 Decibel Scale (db) 9 Q Measurements 9 Small Signal (S-Parameters) 10 5 CHAPTER 3: Planar Waveguides 3.1 Impedance 3.2 Microstrip 3.2.1 Guide Wavelength 3.3 Coplanar 3.4 Stripline 13 13 15 18 21 24 CHAPTER 4: Current Flow and Loss Considerations 29 4.1 Dielectric losses 29 4.1.1 4.1.2 Tan Anisotropy 29 32 4.2 Conductor losses 35 4.2.1 4.2.2 Guide length losses Attenuation 35 35 4.2.3 Return Loss 35 4.2.4 4.2.5 VSWR, Voltage Standing Wave Ratio Skin Depth 37 39 4.2.6 Adhesion layers 44 4.2.7 Surface roughness 49 CHAPTER 5: Substrates 55
viii 5.1 5.2 5.3 5.4 5.5 Glass Single crystals Polycrystalline ceramics 5.3.1 Fabrication 5.3.1.1 5.3.1.2 5.3.1.3 5.3.1.4 5.3.1.5 Powder pressing Tape casting Roll compaction Lamination Glazing 5.3.2 Substrate characteristics Low temperature cofired (LTCC) Clad Materials 5.5.1 Glass transition temperature 5.5.2 Material properties 5.5.3 Fabrication 5.5.4 Mechaical patterning 5.6 Cleaning 5.6.1 5.6.2 5.7 Safety Wet processes Dry processes CHAPTER 6: Thick Film 6.1 6.2 6.3 Screen printing Metal foil screens Lithographically defined thick film 6.3.1 6.3.2 Photoengravable thick film Photoimagable thick film 6.4 Additive techniques 6.4.1 Metal-organics 6.4.2 Direct write 6.4.3 Direct bond CHAPTER 7: Thin Film 7.1 Physical vapor deposition 7.1.1 Evaporation 7.1.1.1 Filament 7.1.1.2 Electron beam 7.1.2 Sputtering 7.1.2.1 DC 7.1.2.2 RF 55 57 57 57 57 59 60 61 62 63 70 73 73 73 81 85 87 88 88 90 93 93 98 101 102 103 105 105 107 109 113 113 113 113 114 115 116 117
ix 7.1.2.3 7.1.2.4 Magnetron Reactive CHAPTER 8: Dielectric Deposition 8.1 PELPCVD 8.2 Anodization CHAPTER 9: Polymers 9.1 Material Properties 128 9.1.1 Moisture absorption 9.1.2 Mechanical properties 9.1.3 Glass transition temperature 9.1.4 Planarization 9.2 Deposition 9.2.1 9.2.2 9.2.3 9.2.4 Spin coating Spray coating Screen printing Other deposition methods 9.3 Patterning 9.3.1 9.3.2 Wet etching Dry etching 9.3 Photosensitive polymers 138 118 119 123 123 124 129 130 131 131 131 132 132 133 134 134 136 136 136 CHAPTER 10 Processing Strategies 141 CHAPTER 11: Photolithography 11.1 Photoresist 11.1.1 Spin-on 11.1.2 Spraying 11.1.3 Roller coating 11.1.4 Meniscus coating 11.1.5 Electrodeposited 11.1.6 Dry Film 11.1.7 Dip coating 11.2 11.3 Artwork and masks Exposure 11.3.1 Non-colllimated 11.3.2 Large flood 11.3.3 Short flood 11.3.4 Collimated 11.3.5 Laser exposure 143 143 146 148 148 149 150 151 153 156 160 161 161 161 162 163
x CHAPTER 12: 12.1 12.2 12.3 12.4 12.5 12.6 Electroplating General Inorganic additives Organic additives Waveforms 12.4.1 Asymmetric dc 12.4.2 Pulse Field density Electroless CHAPTER 13: Etching 13.1 Wet etching 13.2 Dry etching 13.2.1 Sputtering 13.2.2 Ion beam milling 13.2.3 Reactive techniques 13.3 Etching effects on imedance CHAPTER 14 Components 14.1 Passive components 14.1.1 Resistors 14.1.2 Attenuators 14.1.3 Capacitors 14.1.3.1 Parallel plate 14.1.3.2 Interdigitated 14.1.4 Inductors 14.2 Transmission line components 14.2.1 14.2.2 Reciprocal dividers/combiners Filters CHAPTER 15 Packaging 15.1 Level of Integration 15.2 Interconnects 15.2.1 Round wire 15.2.2 Strip ribbon 15.2.3 Modified TAB 15.2.4 Integrated wiring 15.2.5 Enclosures 169 169 171 172 174 174 175 180 182 185 185 186 186 187 190 191 195 195 195 202 205 211 217 218 220 220 224 229 230 231 232 234 237 239 239
xi CHAPTER 16: 16.1 16.2 16.3 16.4 16.5 16.6 15.2.6 15.2.7 15.2.8 15.2.9 15.2.10 15.2.11 Thermal expansion Substrate attachment Grounding Vias Platability Time domain reflectometry (TDR) Superconductivity Properties of High-Tc materials Materials considerations Substrate materials Expansion coefficient Buffer (barrier) layers Film formation 16.6.1 16.6.2 16.6.3 16.6.4 16.7 Patterning 16.7.1 16.7.2 Off-axis sputtering Pulsed laser deposition Evaporation Metalorganic Wet etching Dry etching 240 241 243 243 249 251 257 259 261 262 263 263 263 263 264 265 265 266 266 267 CHAPTER 17: MEMS 269 APPENDIX A: Definition of symbols APPENDIX B: Company directory APPENDIX C: Conversion table APPENDIX D: Graphic evaluation of w/h and SUBJECT INDEX 271 273 275 for microstrip 277 279
PREFACE xiii In 1991 this author published a monograph[l] based on his experience teaching microwave hybrid materials and processing technology at the annual ISHM (now the International Microelectronics and Packaging Society, IMAPS) symposia. Since that time, the course has been presented at that venue and on-site at a number of industrial and government organizations. The course has been continually revised to reflect the many evolutionary changes in materials and processes. Microwave technology has existed for almost 175 years. It was only after the invention of the klystron, just before World War II, that microwave design and manufacture moved from a few visionaries to the growth the industry sees today. Over the last decade alone there have been exploding applications for all types of high frequency electronics in the miltary, automotive, wireless, computer, telecommunications and medical industries. These have placed demands, unimaginable a decade ago, on designs, materials, processes and equipment to meet the ever expanding requirements for increasingly reliable, smaller, faster and lower cost circuits. Microwave electronics is realized by monolithic microwave integrated circuits (MMICs), or hybrid microwave integrated circuits (HMICs). Growth in the computer and wireless industries in particular, has spurred the volume manufacture of both products. Mass fabrication of 300mm silicon (Si) and gallium arsenide (GaAs) wafers is being introduced. Additionally, efforts are ongoing to perfect Si and GaAs, moving toward the creation of defect-free crystals, leading to new levels of performance. Hybrid technologists have responded as well to compliment the MMIC efforts. The past decade has witnessed innovative advances in many areas, leading to a variety of new materials and processes. Among these are new powder technologies for photoengravable and photo-definable thick film inks, allowing the use of thick films at frequencies once reserved for thin films. New generation liquid, dry and electrophoretic resists with improved application and sensitivity have appeared on the market. New organic-based substrate composites, organic encapsulants, via technology, planar and buried passives and technology (low temperature co-fired and multi-chip modules) for advanced packaging and interconnects are being exploited to take advantage of advancements in monolithic technology. This text is directed to acquaint technical managers, engineers and technicians, either with experience, or just enetering the field, with the capabilities and limitations of the materials and processes used for fabricating high frequency circuits. It is essentially introductory in nature. Where possible, equations have been kept simple and to a minimum. Unfortunately, there is little consistency with measurement units and notation. In many of the figures and tables originally published by other authors, I have reproduced their data "as is". As such, the conversion table, Appendix E, may be of some help.
xiv This text begins with an introduction to hybrid technology and basic high frequency principles. Following these, the major forms of transmission waveguide are discussed, and then current flow and loss considerations. Substrates, thick and thin film deposition, polymers, artwork, masks, photolithography, subtractive, additive and semi-additive methods, electro- and electroless plating and etching are covered. Passive and transmission line components are then treated within the confines of process requirements. With this background established, the text is directed toward the effects of processing and materials on passive and transmission line-based components. Packaging is discussed with emphasis on inductance considerations. Materials and processes for superconductive components are briefly highlighted. 1. R. Brown, Materials and Processes for Microwave Hybrids, International Microelectronics and Packaging Society, ISHM, Reston, VA., (1991)
ACKNOWLEDGEMENTS xv This book is really the product of contributions from many people. It is impossible to recognize the advice and suggestions of everyone. However, many colleagues from industry freely gave their time on a variety of topics. A special thank you is extended to the editorial staff at Kluwer for their Jobian patience. I also want to acknowledge the many vendors who sent catalogues and answered innumerable questions, and I want to express my appreciation to all those who gave me permission to use their material and graphics for this text. As such, certain commercial materials, equipment and processes are identified in the text for illustration. Their use neither implies endorsement nor recommendation by the author. Also no implication is implied or expressed that any of the said materials, equipment or processes are the best available or suitable for the purpose. If anyone has been omitted, it was inadvertent. The author assumes sole responsibility for all errors and omissions.