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 eBookISBN: 0-306-48153-7 Print ISBN: 1-4020-7233-3 ©2004 Kluwer Academic Publishers NewYork, Boston, Dordrecht, London, Moscow Print ©2003 Kluwer Academic Publishers Dordrecht All rights reserved No part of this eBook maybe reproducedor transmitted inanyform or byanymeans,electronic, mechanical, recording, or otherwise, without written consent from the Publisher Created in the United States of America Visit Kluwer Online at: http://kluweronline.com and Kluwer's eBookstoreat: http://ebooks.kluweronline.com DEDICATION TO JUDY TABLE OF CONTENTS Preface xiii Acknowledgements xv CHAPTER 1: Hybrids vs MMICs 1 CHAPTER 2: Basic Concepts 5 2.1 Introduction 5 2.2 Maxwell's Laws 5 2.3 Permittivity and Permeability 6 2.4 Free Space Wavelength 7 2.5 Propagation velocity 8 2.6 Decibel Scale (dB) 9 2.7 Q Measurements 9 2.8 Small Signal (S-Parameters) 10 CHAPTER3: Planar Waveguides 13 3.1 Impedance 13 3.2 Microstrip 15 3.2.1 Guide Wavelength 18 3.3 Coplanar 21 3.4 Stripline 24 CHAPTER4: Current Flow and Loss Considerations 29 4.1 Dielectric losses 29 4.1.1 Tan 29 4.1.2 Anisotropy 32 4.2 Conductor losses 35 4.2.1 Guide length losses 35 4.2.2 Attenuation 35 4.2.3 Return Loss 35 4.2.4 VSWR,VoltageStandingWaveRatio 37 4.2.5 SkinDepth 39 4.2.6 Adhesion layers 44 4.2.7 Surfaceroughness 49 CHAPTER5: Substrates 55 viii 5.1 Glass 55 5.2 Singlecrystals 57 5.3 Polycrystalline ceramics 57 5.3.1 Fabrication 57 5.3.1.1 Powder pressing 57 5.3.1.2 Tape casting 59 5.3.1.3 Rollcompaction 60 5.3.1.4 Lamination 61 5.3.1.5 Glazing 62 5.3.2 Substrate characteristics 63 5.4 Lowtemperature cofired (LTCC) 70 5.5 Clad Materials 73 5.5.1 Glass transitiontemperature 73 5.5.2 Material properties 73 5.5.3 Fabrication 81 5.5.4 Mechaical patterning 85 5.6 Cleaning 87 5.6.1 Wet processes 88 5.6.2 Dry processes 88 5.7 Safety 90 CHAPTER6: Thick Film 93 6.1 Screenprinting 93 6.2 Metal foil screens 98 6.3 Lithographically definedthickfilm 101 6.3.1 Photoengravable thick film 102 6.3.2 Photoimagablethickfilm 103 6.4 Additivetechniques 105 6.4.1 Metal-organics 105 6.4.2 Direct write 107 6.4.3 Direct bond 109 CHAPTER7: Thin Film 113 7.1 Physical vapor deposition 113 7.1.1 Evaporation 113 7.1.1.1 Filament 113 7.1.1.2 Electronbeam 114 7.1.2 Sputtering 115 7.1.2.1 DC 116 7.1.2.2 RF 117 ix 7.1.2.3 Magnetron 118 7.1.2.4 Reactive 119 CHAPTER8: Dielectric Deposition 123 8.1 PELPCVD 123 8.2 Anodization 124 CHAPTER9: Polymers 129 9.1 MaterialProperties 128 9.1.1 Moisture absorption 130 9.1.2 Mechanical properties 131 9.1.3 Glasstransitiontemperature 131 9.1.4 Planarization 131 9.2 Deposition 132 9.2.1 Spincoating 132 9.2.2 Spray coating 133 9.2.3 Screenprinting 134 9.2.4 Other deposition methods 134 9.3 Patterning 136 9.3.1 Wetetching 136 9.3.2 Dryetching 136 9.3 Photosensitive polymers 138 CHAPTER 10 Processing Strategies 141 CHAPTER 11: Photolithography 143 11.1 Photoresist 143 11.1.1 Spin-on 146 11.1.2 Spraying 148 11.1.3 Rollercoating 148 11.1.4 Meniscuscoating 149 11.1.5 Electrodeposited 150 11.1.6 DryFilm 151 11.1.7 Dip coating 153 11.2 Artwork and masks 156 11.3 Exposure 160 11.3.1 Non-colllimated 161 11.3.2 Largeflood 161 11.3.3 Short flood 161 11.3.4 Collimated 162 11.3.5 Laser exposure 163 x CHAPTER 12: Electroplating 169 12.1 General 169 12.2 Inorganic additives 171 12.3 Organic additives 172 12.4 Waveforms 174 12.4.1 Asymmetric dc 174 12.4.2 Pulse 175 12.5 Field density 180 12.6 Electroless 182 CHAPTER 13: Etching 185 13.1 Wetetching 185 13.2 Dry etching 186 13.2.1 Sputtering 186 13.2.2 Ionbeammilling 187 13.2.3 Reactive techniques 190 13.3 Etchingeffectsonimedance 191 CHAPTER14 Components 195 14.1 Passive components 195 14.1.1 Resistors 195 14.1.2 Attenuators 202 14.1.3 Capacitors 205 14.1.3.1 Parallel plate 211 14.1.3.2 Interdigitated 217 14.1.4 Inductors 218 14.2 Transmission line components 220 14.2.1 Reciprocal dividers/combiners 220 14.2.2 Filters 224 CHAPTER 15 Packaging 229 15.1 Level ofIntegration 230 15.2 Interconnects 231 15.2.1 Round wire 232 15.2.2 Strip ribbon 234 15.2.3 Modified TAB 237 15.2.4 Integrated wiring 239 15.2.5 Enclosures 239 xi 15.2.6 Thermal expansion 240 15.2.7 Substrate attachment 241 15.2.8 Grounding 243 15.2.9 Vias 243 15.2.10 Platability 249 15.2.11 Time domainreflectometry (TDR) 251 CHAPTER16: Superconductivity 257 16.1 Properties ofHigh-Tc materials 259 16.2 Materials considerations 261 16.3 Substrate materials 262 16.4 Expansion coefficient 263 16.5 Buffer (barrier) layers 263 16.6 Film formation 263 16.6.1 Off-axis sputtering 263 16.6.2 Pulsed laser deposition 264 16.6.3 Evaporation 265 16.6.4 Metalorganic 265 16.7 Patterning 266 16.7.1 Wetetching 266 16.7.2 Dry etching 267 CHAPTER 17: MEMS 269 APPENDIX A: Definition of symbols 271 APPENDIX B: Company directory 273 APPENDIX C: Conversion table 275 APPENDIXD: Graphicevaluationofw/hand formicrostrip 277 SUBJECT INDEX 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 ofhigh 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 expandingrequirements 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 ofnew materials and processes. Among these are new powder technologies for photo- engravable 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 ofadvancements 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 ofthe figures and tables originally published by other authors, I have reproduced their data "as is". As such, the conversion table, Appendix E, may be ofsomehelp.