Advanced Materials and Design for Electromagnetic Interference Shielding

Advanced Materials and Design for Electromagnetic Interference Shielding Xingcun Colin Tong f-ep) CRC Press VV^ J Taylor&. Francis Group Boca Raton London New York CRC Press is an imprint of the Taylor Sc Francis Group, an informa business

Preface Author xiii xv Chapter 1 Electromagnetic Interference Shielding Fundamentals and Design Guide 1 1.1 Concepts of Electromagnetic Interference and Electromagnetic Compatibility 1 1.1.1 EMI Problems and Common Concerns 2 1.1.2 EMI Emissions and Controlling Methods 3 1.1.2.1 Conducted EMI Emission 4 1.1.2.2 Radiated EMI Emission 5 1.1.3 EMC Regulations and Testing Standards 8 1.1.3.1 The International Standard 9 1.1.3.2 FCC Standard 9 1.1.3.3 European Standard 10 1.1.3.4 Military Standard 10 1.2 EMI Shielding Principles 11 1.2.1 Shielding Effects in the E-Field and H-Field 11 1.2.2 Shielding Effectiveness 13 1.2.2.1 Absorption Loss 14 1.2.2.2 Reflection Loss 15 1.2.2.3 Multiple Reflection Correction Factor 16 1.2.3 Shielding Modeling in Practice 18 1.2.3.1 Metallic Enclosure 18 1.2.3.2 EMI Gasket 19 1.2.3.3 Shield with Apertures 20 1.2.3.4 Cavity Resonance 23 1.3 EMC Design Guidelines and EMI Shielding Methodology 24 1.3.1 Design for EMC 24 1.3.2 Shielding Methods and Materials Selection 27 1.3.2.1 Shielding Housing and Enclosures 27 1.3.2.2 Gasketing 29 1.3.2.3 Integral Assembly 30 1.3.2.4 Corrosion and Material Galvanic Compatibility 31 1.3.3 Environmental Compliance 32 1.3.3.1 RoHS Directive 33 1.3.3.2 WEEE Directive 34 References 35 v

Chapter 2 Characterization Methodology of EMI Shielding Materials 37 2.1 Shielding Effectiveness Measurement 37 2.1.1 Testing Methods Based on MIL-STD-285 38 2.1.2 Modified Radiation Method for Shielding Effectiveness Testing Based on MIL-G-83528 39 2.1.3 Dual Mode Stirred Chamber 39 2.1.4 Transverse Electromagnetic (ТЕМ) Cell 40 2.1.5 Circular Coaxial Holder 42 2.1.6 Dual Chamber Test Fixture Based on ASTM ES7-83 42 2.1.7 Transfer Impedance Methods 42 2.1.7.1 Transfer Impedance of Coaxial Cables 43 2.1.7.2 Transfer Impedance Method for Shielding Effectiveness Measurement of Conductive Gaskets 43 2.2 Electrical and Thermal Conductivities 45 2.2.1 Electrical Conductivity and Contact Resistance 45 2.2.2 Thermal Conductivity 46 2.3 Permeability and Permittivity 47 2.3.1 Permeability 47 2.3.2 Permittivity 48 2.3.3 Characterization of Permeability and Permittivity 48 2.4 Mechanical Properties 49 2.4.1 Uniaxial Tensile Testing 49 2.4.2 Hardness 50 2.4.3 Poisson's Ratio 50 2.4.4 Stress Relaxation 50 2.4.5 Contact Force 51 2.4.6 Friction Force 52 2.4.7 Permanent Set 52 2.5 Surface Finish and Contact Interface Compatibility 52 2.5.1 Corrosion and Oxidation Protection 53 2.5.1.1 Noble Finish Selection 53 2.5.1.2 Nonnoble Finishes 54 2.5.2 Solderability of Surface Finishes 55 2.5.3 Effects of Mating Cycles and Operating Environments on Contact Finishes 57 2.5.4 Galvanic Corrosion and Contact Interface Compatibility 58 2.6 Formability and Manufacturability 58 2.6.1 Bending Formability 59 2.6.2 Effect of Strain Hardening on Formability 60 2.6.3 Anisotropy Coefficient 61 2.6.4 Springback during Metal Strip Forming 62 2.7 Environmental Performance Evaluation 62 2.7.1 Thermal Cycling 63 2.7.2 Thermal Aging 63 2.7.3 Gaseous Testing 63

vii 2.7.4 Pore Corrosion and Fretting Corrosion 63 2.7.5 Temperature and Humidity Testing 64 2.7.6 Dust Sensitivity Test 64 2.7.7 Vibration and Shock Test 65 References 65 Chapter 3 EMI Shielding Enclosure and Access 67 3.1 Enclosure Design and Materials Selection 67 3.2 Magnetic Field Shielding Enclosure 73 3.2.1 Basics of Magnetic Shielding 73 3.2.2 Magnetic Shielding Materials Selection 74 3.2.3 Magnetic Shielding Enclosure Design Consideration 76 3.3 Shielding Enclosure Integrity 78 3.4 Specialized Materials Used for Shielding Enclosure 82 3.4.1 EMI Gaskets 82 3.4.1.1 Metal Strip Gaskets 82 3.4.1.2 Knitted Metal Wire Gaskets 83 3.4.1.3 Metal-Plated Fabric-over-Foam (FOF) 84 3.4.1.4 Electrically Conductive Elastomer (ECE) Gaskets 84 3.4.2 Magnetic Screening Materials 84 3.4.3 Shielding Tapes 85 3.4.4 Thermoformable Alloys 85 3.4.5 Honeycomb Materials 85 3.4.6 Painted or Plated Plastic Enclosures 86 3.4.7 Conductive Composite Shielding Materials 86 3.5 Summary 86 References 87 Chapter 4 Metal-Formed EMI Gaskets and Connectors 89 4.1 Introduction 89 4.2 Metal Strip Selection and Performance Requirement 90 4.3 Copper Beryllium Alloys 91 4.3.1 Phase Constitution and Primary Processing of CuBe Strips 91 4.3.2 Performance and Availability of CuBe Alloys 95 4.3.2.1 High-Strength Alloys 95 4.3.2.2 High-Conductivity CuBe Alloys 97 4.3.2.3 Nickel Beryllium 97 4.4 Copper-Nickel-Tin Spinodal Alloys 97 4.4.1 Composition and Physical Properties 97 4.4.2 Strip Gauges and Temper Designations 99 4.4.3 Mechanical Properties and Bending Formability 100 4.4.4 Stress-Relaxation Resistance 101 4.4.5 Heat Treatment and Spinodal Decomposition 101 4.4.6 Surface Cleaning, Plating, and Soldering 103

viii Contents 4.4.7 Elastic Performance 103 4.4.8 Shielding Effectiveness 104 4.4.9 Fatigue Strength 104 4.4.10 Some Considerations to Improve Performance of CuNiSn Gasketing 105 4.5 Copper-Titanium Alloy 107 4.6 Stainless Steel 108 4.7 Other Materials Options 110 4.7.1 Phosphor Bronze 110 4.7.2 Brass Ill 4.7.3 Nickel Silver Ill 4.7.4 Other High Strength and High Conductive Copper Alloys 112 4.8 Design Guideline of Metal Gaskets and Connectors 113 4.8.1 Primary Approaches 114 4.8.2 Some Special Design Options 115 4.8.3 Gasketing Design Guideline 116 4.9 Fabrication Process and Types of Metal Gaskets and Connectors 118 4.9.1 Progressive Die Forming 118 4.9.2 Roll Forming 119 4.9.3 Multiple-Slide Stamping 120 4.9.4 Photoetching 120 4.9.5 Typical Part Profiles 120 4.10 Mounting Methods and Surface Mating Assurance 122 4.11 Summary 124 References : 124 Chapter 5 Conductive Elastomer and Flexible Graphite Gaskets 127 5.1 Introduction 127 5.2 Raw Material Selection and Conductive Elastomer Fabrication 128 5.2.1 Base Binder Materials 128 5.2.1.1 Silicone 128 5.2.1.2 Fluorosilicone 129 5.2.1.3 Ethylene Propylene Diene Monomer (EPDM) 129 5.2.1.4 Fluorocarbon 129 5.2.1.5 Natural Rubber and Butadiene-Acrylonitrile 129 5.2.2 Conductive Fillers 129 5.2.3 Fabrication of Conductive Elastomer Materials 130 5.3 Conduction Mechanism and Processing Optimization of Conductive Elastomer Materials 131 5.3.1 Conduction Mechanism and Process Parameters 131 5.3.2 Appearance Properties and Performance Evaluation 133 5.3.2.1 Physical and Mechanical Properties 133 5.3.2.2 Electrical Properties 135 5.3.2.3 Thermal Properties 137 5.4 Conductive Elastomer Gasket Design Guideline 137 5.4.1 Flange Joint Geometry and Unevenness 138

ix 5.4.2 Applied Clamping/Compressive Force and Deformation Range 139 5.4.3 Gasket Profile and Materials Selection 141 5.4.4 Flange Materials and Joint Surface Treatment 145 5.5 Conductive Elastomer Gasket Fabrication 146 5.5.1 Extrusion 146 5.5.2 Molding 147 5.5.3 Form-in-Place and Screen Printing 148 5.5.4 Reinforced Shielding Gaskets with Oriented Wires and Metal Meshes 149 5.6 Conductive Elastomer Gasket Installation and Application 149 5.7 Comparable Flexible Graphite Gaskets 152 5.7.1 Flexible Graphite and Its Properties 153 5.7.2 Fabrication and Application of Flexible Graphite Gaskets 155 5.8 Summary 157 References 157 Chapter 6 Conductive Foam and Ventilation Structure 159 6.1 Introduction 159 6.2 Waveguide Aperture and Ventilation Panel 159 6.2.1 Waveguide Aperture and Its Design 160 6.2.2 Materials Selection and Fabrication Options 163 6.3 Conductive Foam and Integral Window Structure 165 6.3.1 Conductive Plastic Foam and Vent Panels 165 6.3.2 Integral EMI Window Structure 168 6.4 Metallized Fabrics and Fabric-over-Foam 169 6.4.1 Metallized Fabrics 170 6.4.2 Fabric-over-Foam 171 6.5 Summary 175 References 175 Chapter 7 Board-Level Shielding Materials and Components 177 7.1 Introduction 177 7.2 Board-Level Shielding Design and Materials Selection 178 7.2.1 Basic Principles of Board Circuit EMC Design 178 7.2.1.1 PCB Layout 178 7.2.1.2 Power Decoupling 179 7.2.1.3 Trace Separation 179 7.2.1.4 Grounding Techniques 180 7.2.1.5 Chassis Construction and Cabling 180 7.2.2 Board-Level Shielding Design with Proper Materials Selection 181 7.3 Board-Level Shielding Components and Their Manufacturing Technology 185

7.3.1 Metal Cans 186 7.3.1.1 Single-Piece Shielding Cans 186 7.3.1.2 Two-Piece Cans 189 7.3.1.3 Multilevel Shielding and Multicompartment Cans 190 7.3.2 Metal-Coated Thermoform Shields 190 7.3.2.1 snapshot Shield 191 7.3.2.2 Form/Met Shield 192 7.3.2.3 Formable Shielding Film 196 7.4 Conductive Coating Methods Used for EMI Shielding Components 196 7.4.1 Electroplating 197 7.4.1.1 Electroless Plating 197 7.4.1.2 Electrolytic Plating 198 7.4.1.3 Tin Plating and Tin Whisker Growth in EMI Shielding Systems 199 7.4.1.4 Immersion Surface Finishes 202 7.4.2 Conductive Paints 204 7.4.3 Vapor Deposition 205 7.4.4 Conductive Coating Application and Design Consideration for EMI Shielding 206 7.5 Board-Level Shielding with Enhanced Heat Dissipating 207 7.5.1 Minimizing EMI from Heat Sinks 207 7.5.2 Combination of Board-Level Shielding and Heat Dissipation 207 7.5.3 Thermal Interface Materials (TIMs) for Thermal-Enhanced Board-Level Shielding 208 7.6 Summary 211 References 212 Chapter 8 Composite Materials and Hybrid Structures for EMI Shielding 215 8.1 Introduction 215 8.2 Knitted Wire/Elastomer Gaskets 215 8.2.1 Fabrication Process and Materials Selection 216 8.2.2 Knitted Wire Gasket Performance 218 8.2.3 Typical Gasket Types and Mounting Methods 219 8.3 EMI Shielding Tapes 221 8.4 Conductive Fiber/Whisker Reinforced Composites 224 8.4.1 Materials Selection and Process of Conductive Composites 225 8.4.2 Carbon Fiber/Whisker Reinforced Materials 226 8.4.3 Metal Fiber/Whisker Reinforced Composites 227 8.4.4 Nanofiber Reinforced Polymer Composites 229 8.5 Hybrid Flexible Structures for EMI Shielding 230 8.6 Electroless Metal Deposition for Reinforcements of Composite Shielding Materials 231

xi 8.7 Summary 234 References 234 Chapter 9 Absorber Materials 237 9.1 Introduction. 237 9.2 Microwave Absorber Materials : 238 9.2.1 Resonant Absorbers 240 9.2.1.1 Dallenbach Tuned Layer Absorbers 240 9.2.1.2 Salisbury Screens 241 9.2.1.3 Jaumann Layers 242 9.2.2 Graded Dielectric Absorbers: Impedance Matching 242 9.2.2.1 Pyramidal Absorbers 242 9.2.2.2 Tapered Loading Absorbers 243 9.2.2.3 Matching Layer Absorbers 244 9.2.3 Cavity Damping Absorbers 244 9.3 Anechoic Chambers 245 9.3.1 Antennas 245 9.3.2 Absorber Materials Used in Anechoic Chambers 246 9.4 Dielectric Materials for Absorber Applications 246 9.5 Electromagnetic Wave Absorbers 249 9.6 Absorbing Materials Selection and Absorber Applications 251 9.6.1 Absorbing Materials and Absorber Types 251 9.6.2 Applications 252 9.6.2.1 Military 252 9.6.2.2 Commercial 253 9.7 Summary 253 References 254 Chapter 10 Grounding and Cable-Level Shielding Materials 257 10.1 Introduction 257 10.2 Cable Assembly and Its EMI Shielding Design 257 10.3 Cable-Level Shielding Materials 261 10.3.1 Metallic Shielding 261 10.3.2 Conductive Heat-Shrinkable Shielding 263 10.3.3 Ferrite Shielding Materials 264 10.4 Bonding and Grounding 267 10.4.1 Bonding 268 10.4.2 Grounding 269 10.4.2.1 Shields Grounded at One Point 270 10.4.2.2 Multigrounded Shields 271 10.4.2.3 Hybrid Grounding 271 10.5 Summary 271 References 272

xii Contents Chapter 11 Special Shielding Materials in Aerospace and Nuclear Industries 275 11.1 Introduction 275 11.2 Lightweight Shielding Materials for Aerospace Applications 275 11.2.1 Lightweight Radiation Shielding Material 276 11.2.2 Fiber Reinforced Composite Materials 277 11.2.3 Nanomaterials 279 11.2.4 Foam Structures 280 11.3 Radiation Shielding for Space Power Systems 281 11.3.1 Neutron Shielding Design and Materials Selection 282 11.3.2 Shielding Materials for Earth Neighborhood Infrastructure 282 11.3.3 Active Electromagnetic Shielding for Space Radiation 283 11.3.4 Optimization of Space Radiation Shielding 285 11.4 Nuclear Shielding Materials 286 11.5 Summary 289 References 291 Chapter 12 Perspectives and Future Trends 293 12.1 Introduction 293 12.2 Early Design-in for EMC and Optimal Design of EMI Shielding 293 12.3 Advanced Materials Selection for EMI Shielding 297 12.3.1 Materials Selection for EMI Shielding Enclosure/Cover/ Barrier 298 12.3.2 EMI Gasketing Material Selection 299 12.3.3 Other Shielding Materials Selection 301 12.4 Future Trends and Applications 302 12.4.1 EMI Shielding Design Techniques 302 12.4.2 Integrated Circuit-Level Shielding 303 12.4.3 Printed Circuit Board (PCB)-Level Shielding 305 12.4.3.1 Lightweight Shields for PCB-Level Shielding 305 12.4.3.2 Mold-in-Place Combination Gaskets for Multicompartment Shields 306 12.4.3.3 Rotary Form-in-Place Gaskets 307 12.4.4 EMI Shielding Modules or Enclosures 308 12.4.4.1 Conductive Foam with Z-Axis Conductivity 308 12.4.4.2 Dent-Resistant Vent Panels 309 12.4.4.3 Nanocomposite Shielding Materials 309 12.4.4.4 Ultrasoft Sculpted Fabric-over-Foam 310 12.4.5 Interconnecting Level Shielding 310 12.4.6 EMI Control or Immunity by Software 311 12.5 Summary 311 References - 312 Index 315