Contamination and ESD Control in High Technology Manufacturing
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Preface xv
1 Fundamentals of Contamination Control 1
1.1 Introduction 1
1.1.1 Contamination Sources 1
1.1.2 Contamination Adhesion Forces 3
1.1.3 Contamination Control Methods 9
1.2 Glossary of Contamination Control Terms 10
1.3 Specifying Contamination in Air and on Surfaces 13
1.4 Sources of Contamination 16
1.5 Contamination Control Requirements 18
1.5.1 Airborne Particle Requirements 18
1.5.2 Chemical Vapor Contamination Control Limits 33
1.5.3 Ionic Contamination Control Limits 35
1.5.4 Magnetic Contamination Control Limits 37
1.5.5 Surface Contamination Rates and Air Ionization 37
1.5.6 Contact Transfer and In Situ Contamination 38
1.5.7 Airflow Requirements 39
1.5.8 Pressure Requirements and Enclosure Exhausts 39
1.5.9 Maintenance Requirements 40
1.5.10 Other Requirements 43
1.5.11 Summary of Requirements 43
1.6 Pertinent Standards 43
References and Notes 46
Additional Reading 46
2 Fundamentals of ESD Control 48
2.1 Introduction and Historical Perspective 48
2.2 Glossary of Electrostatic Charge Control Terms 52
2.3 Sources of Electrostatic Charge 56
2.3.1 Static Electricity 57
2.3.2 Effects of Electrostatic Charge and Discharge 65
2.3.3 Failure Modes in High-Technology ESD-SensitivityDevices 67
2.4 Requirements of ESD Control 68
2.4.1 Determining ESD Damage Sensitivity 69
2.4.2 Electrically Explosive Device ESD Modeling 74
2.5 Building the ESD-Safe Workplace 75
2.5.1 Surface Resistivity of Materials 75
2.5.2 Grounding 77
2.5.3 Identification of and Access to an ESD-Safe Work Area 78
2.5.4 ESD-Protective Floor Coverings 78
2.5.5 Work Surfaces and Table Mats 81
2.5.6 Wrist Strap Ground Points 83
2.5.7 Air Ionization Systems 83
2.5.8 Relative Humidity 88
2.5.9 Chairs and Stools 90
2.5.10 Trash Cans 90
2.5.11 Cathode-Ray Tube Displays 91
2.5.12 Field Potential Limits 93
2.5.13 Tools and Fixtures 94
2.5.14 Conveyors 94
2.6 ESD Controls for People 95
2.6.1 Wrist Strap and Coiled Cord 95
2.6.2 Training and Certification Program 95
2.6.3 Cleanroom Gowns and ESD Lab Coats 97
2.6.4 Footwear 98
2.6.5 Gloves, Liners, and Finger Cots 100
2.7 Consumables and Accessories 100
2.7.1 Packaging 100
2.7.2 Desiccants 102
2.7.3 Tote Boxes, Bins, and Other Shipping Containers 102
2.7.4 Notebooks and Sheet Protectors 104
2.7.5 Swabs and Wipers 104
2.7.6 Paper 104
2.7.7 Tape 104
2.8 Personnel Equipment and Procedures for Its Use 105
2.8.1 Wrist Straps and Wrist Strap Monitors 105
2.8.2 Sit-Stand Protocol 106
2.9 Transportation of ESD-Sensitive Products 106
2.10 Inspections and Record Keeping 106
2.10.1 Daily Visual Inspection 106
2.10.2 Periodic Instrumental Inspection 107
2.10.3 Testing Protocols 109
2.11 ESD Control Program 112
2.12 ESD and Contamination Control 115
2.13 Useful Reference Standards 116
References and Notes 117
3 Sampling and Analysis Methods 119
3.1 Introduction 119
3.2 Classification of Analysis Methods 119
3.2.1 Functional Laboratory Tests 121
3.2.2 Nonfunctional Tests: Objective Laboratory Tests 124
3.3 Sampling of Contaminants in Air, in Liquids, and on Surfaces 133
3.3.1 Contaminants in Air 133
3.3.2 Contaminants in Liquids 134
3.3.3 Surface-Borne Contaminants 135
3.4 Organic Contamination Analysis Methods 136
3.4.1 Water Break Test 136
3.4.2 Contact Angle Measurement 136
3.4.3 Optically Stimulated Electron Emission Technique 137
3.4.4 Nonvolatile Residue Test 137
3.4.5 Organic Sampling Techniques 137
3.4.6 Central Atmospheric Monitoring System 138
3.4.7 Electron Spectroscopy for Chemical Analysis 139
3.4.8 Gas Chromatography/Mass Spectroscopy 139
3.4.9 Secondary Ion Mass Spectroscopy 139
3.5 Ionic and Inorganic Contamination Analysis Methods 139
3.6 Electrostatic Discharge Methods 141
3.6.1 Tribocharge Testing 141
3.6.2 Bulk and Surface Resistance Measurements 142
3.6.3 Air Ionizer Testing 144
3.6.4 Typical ESD Field Instruments 145
3.7 Numerical Simulation 146
3.8 Algebraic Predictive Modeling 147
3.9 Statistical Analysis Methods 150
3.9.1 Basic Statistical Analysis Tools 150
3.9.2 Gage Capability Analysis of Cleanliness Measurement Methods 151
Additional Reading 156
References and Notes 156
4 Facilities Design: Contamination- and ESD-safe Work Areas 158
4.1 Introduction 158
4.2 Basics of Cleanroom Design 159
4.2.1 What Can Be Called a Cleanroom 159
4.2.2 What It Takes to Make a Cleanroom Work 161
4.2.3 How Filters Work 162
4.3 Cleanrooms 165
4.3.1 Non-Unidirectional-Flow (Conventional or Mixed-Flow) Cleanrooms 166
4.3.2 Air Ionization for Non-Unidirectional-Flow Cleanrooms 168
4.3.3 Unidirectional Flow: 100% Filter Coverage 169
4.3.4 Air Ionization in Unidirectional-Flow Cleanrooms 174
4.3.5 Adding a Perforated Raised Floor 174
4.3.6 Balancing a Room Using a Perforated Raised Floor 175
4.3.7 Airflow Balancing After Tool Installation 176
4.3.8 Solid vs. Perforated Work Surfaces 181
4.3.9 Parts Storage Locations 181
4.3.10 Horizontal Unidirectional-Airflow Cleanrooms 182
4.4 Cleanroom Construction and Operating Costs 183
4.5 Modern Energy-Saving Approaches 184
4.5.1 Unidirectional-Flow Clean Benches 184
4.5.2 Isolators and Minienvironments 186
4.5.3 Point-of-Use Clean Air Cleanrooms 187
4.5.4 Tunnelizing an Existing Ballroom Cleanroom 188
4.5.5 Minienvironments 190
4.6 Other Design Considerations 191
4.6.1 Doors and Air Showers 191
4.6.2 Pass-Throughs 192
4.6.3 Equipment Pass-Throughs 193
4.6.4 Service Areas 193
References and Notes 193
5 Getting Clean Parts and Getting Parts Clean 195
5.1 Introduction 195
5.2 Historical Perspective 196
5.3 Gross and Precision Cleanliness Protocols 197
5.3.1 Approaches to Specifying Cleanliness Levels 199
5.4 Design for Manufacturability and Cleanability 202
5.4.1 Design-for-Manufacturability Guidelines 202
5.4.2 Design-for-Cleanability Guidelines 203
5.4.3 Cleanability Indexes for Indirect Cleanliness Measurements 203
5.4.4 Design-for-Cleanability Planning Considerations 206
5.4.5 Design-for-Cleanability Management Considerations 216
5.5 Process Design Guidelines 216
5.5.1 Use of Water-Soluble Cutting Fluids 217
5.5.2 Minimizing Work in Progress by Implementing Continuous-Flow Manufacturing 218
5.5.3 Rinsing After Machining 218
5.5.4 Parts Handling After Final Cleaning 218
5.5.5 Soldering and Flux Removal 219
5.5.6 Clean-Then Assemble vs. Assemble-Then Clean 219
5.6 Cleaning Processes 220
5.6.1 Particles in Liquid Baths 221
5.6.2 Boundary Layers 221
5.6.3 Ultrasonic Cleaning 221
5.6.4 Spray Cleaning 225
5.6.5 Spin-Rinse Dryer Cleaning 228
5.6.6 Vapor Degreasing 230
5.6.7 Chemical Cleaning 230
5.6.8 Solvent Cleaning 230
5.6.9 Mechanical Agitation Cleaning 231
5.6.10 Manual Cleaning 231
5.6.11 Specialty Cleaning 232
5.7 Drying Processes 234
5.7.1 Spin-Rinse Drying 234
5.7.2 Forced-Air Drying 234
5.7.3 Vacuum Drying 235
5.7.4 Adsorption Drying 235
5.7.5 Chemical Drying 235
5.8 Cost of Cleaning 236
5.9 Vendor Process Contamination Checklist 236
5.10 Case Studies: Cleaning Equipment and Cleaning Process Design 246
5.11 Details on the Clean-Then Assemble and Assemble-Then Clean Procedures 252
5.11.1 Cleaning Strategies 253
5.11.2 Case Studies: CTA and ATC 255
5.11.3 Case Study Results and Discussion 262
5.12 Particle Size Distributions 264
5.12.1 MIL-STD- 1246 264
5.12.2 Analytical Methods 265
5.12.3 Extraction Methods Tested 266
5.12.4 Results 266
5.13 Tool Part Cleanliness 272
References and Notes 273
6 Tooling Design and Certification 276
6.1 Introduction 276
6.1.1 Tooling Design Process 277
6.1.2 Applications and Limitations of Tooling Design 278
6.2 Contamination and ESD Control Requirements 279
6.3 Maintenance Requirements 280
6.3.1 (Basics of a) Wipe-Down Procedure 280
6.3.2 Maintenance Wipe-Down 281
6.3.3 Engineering Changes 282
6.3.4 Summary of Requirements 282
6.4 General Design Alternatives 283
6.4.1 Eliminating Contamination Generators 283
6.4.2 Relocating Contamination Generators 284
6.4.3 Enclosing and Evacuating Contamination Generators 285
6.5 Materials 293
6.5.1 Guidelines for Materials 293
6.5.2 Guidelines for Wear 297
6.5.3 Guidelines for Plastics 301
6.6 Surface Treatments 308
6.6.1 Paints 309
6.6.2 Anodizing and Related Treatments 310
6.6.3 Electroplating, Electropolishing, and Other Treatments 311
6.6.4 Cautions About Coatings 311
6.6.5 Synergistic Coatings 311
6.6.6 Relative Wear Properties of Coatings 312
6.6.7 Surface Texture and Porosity 312
6.7 Selection and Evaluation of Components 313
6.7.1 Pneumatic Devices 314
6.7.2 Linear Motion Guides 314
6.7.3 Electric Motors 314
6.7.4 Process Piping and Point-of-Use Filtration 315
6.7.5 In Situ Monitoring Equipment 316
6.7.6 Hand Tools 317
6.8 Tool and Workstation Layout 318
6.8.1 Flow Control Enclosures, Minienvironments, and the Standard Machine Interface 318
6.8.2 Putting the Cleanroom Tool Together 322
6.9 Cleanroom Certification of Automated Tooling 325
6.9.1 Statistical Requirements for Sampling 327
6.9.2 Analytical Equipment and Methods 331
References and Notes 334
Additional Reading 334
7 Continuous Monitoring 336
7.1 Introduction 336
7.1.1 Approaches to Monitoring 337
7.1.2 Traditional Airborne Particle Measurements 338
7.1.3 Critical and Busy Sampling 339
7.1.4 Modified Data Collection Protocol 339
7.1.5 Ongoing Use of Critical and Busy Sampling 340
7.1.6 Case Studies: Traditional vs. Critical and Busy Sampling 341
7.1.7 Trend, Cyclic, and Burst Patterns of Particle Generation 346
7.1.8 Case Studies: Other Applications of Continuous Monitoring 348
7.1.9 Summary and Conclusions 350
7.2 Continuous Contamination Monitoring 350
7.2.1 Electronically Multiplexed Monitoring 350
7.2.2 Pneumatically Multiplexed Particle Monitoring 351
7.3 Continuous Monitoring of Manufacturing 352
7.3.1 Air Quality 352
7.3.2 Process Fluid Purity 355
7.3.3 The Value of 100% Sampling 356
7.3.4 Cleanliness of Surfaces and Electrostatic Charge 358
7.4 Evaluation of In Situ Monitoring in an Aqueous Cleaning Application 359
7.4.1 Description of Experiment 360
7.4.2 Experimental Results 362
7.4.3 Management Using ISPM 370
7.4.4 Conclusions 371
7.5 Antennas for Electrostatic Charge Monitoring 372
References and Notes 372
8 Consumable Supplies and Packaging Materials 374
8.1 Introduction 374
8.2 Cleanroom and ESD Gloves 375
8.3 Functional vs. Nonfunctional Testing 376
8.3.1 Functional Materials Qualification Tests 376
8.3.2 Nonfunctional Testing: Objective Laboratory Measurements 377
8.3.3 ESD Considerations in Glove Selection 379
8.4 Glove Use Strategies 381
8.5 Initial Qualification vs. the Need for Ongoing Lot Certification 381
8.6 Glove Washing 383
8.6.1 Early Observations with Natural Rubber Latex Gloves 383
8.6.2 Gloves Washability 384
8.6.3 Nitrile Glove Performance 387
8.6.4 Glove Washing Conclusions 388
8.7 ESD Performance of Gloves 388
8.7.1 Materials Selection for ESD Properties 389
8.7.2 Specifying the ESD Performance of Cleanroom Gloves and Glove Liners 389
8.7.3 Testing Considerations 391
8.7.4 Factors That Affect the ESD Performance of Gloves 392
8.8 Glove Laundering 396
8.8.1 Cost-Benefit Problem 397
8.8.2 Polyurethane Glove Laboratory Properties 397
8.8.3 ESD Performance 398
8.8.4 Chemical Contamination 399
8.8.5 Wear Characteristics 399
8.8.6 Laundering Tests 401
8.8.7 Impact of Laundering and Reuse on Glove Cost 401
8.8.8 Conclusions 402
8.9 Wipers and Swabs 402
8.9.1 Selecting the Correct Wiper or Swab 403
8.10 Reusable and Disposable Packaging Materials 405
8.10.1 ESD Consideration in Packaging 405
8.10.2 Carbon-Filled Polymers 405
8.10.3 Metal Loading 406
8.10.4 Topical and Incorporated Organic Agents 406
8.10.5 Copolymer Blends 407
8.11 Facial Coverings 407
References and Notes 408
9 Controlling Contamination and ESD From People 410
9.1 Introduction 410
9.2 People as a Source of Contamination 410
9.2.1 Skin and Hair 411
9.2.2 Fingerprints 413
9.2.3 Bacteria and Fungi 414
9.2.4 Spittle Droplets 414
9.2.5 Street Clothing 415
9.2.6 Other Forms of Contamination 416
9.3 Typical Gowning Protocols 417
9.3.1 Inner Suit 418
9.3.2 Hair Cover (Bouffant) 419
9.3.3 Woven Gloves 419
9.3.4 Barrier Gloves 420
9.3.5 Facial Cover 420
9.3.6 Hood and Powered Headgear 421
9.3.7 Frock, Coverall, and Two-Piece Suit 422
9.3.8 Shoe Covers, Booties, and Special Shoes 424
9.3.9 Suggested Frequency of Change 426
9.4 Procedures for Entering a Cleanroom 426
9.4.1 Pre-Change Room Procedure 427
9.4.2 Wipe-Down 427
9.4.3 Hairnet and Face Mask 428
9.4.4 Shoe Cleaners 429
9.4.5 Handwashing 430
9.4.6 Changing into Cleanroom Garments 431
9.4.7 Powered Headgear 433
9.4.8 Footwear 433
9.4.9 Shoe Cleaners and Tacky Mats 436
9.5 Behavior in a Cleanroom 437
9.5.1 Working in a Cleanroom 438
9.5.2 HEPA Filters 439
9.5.3 Raised Floors 439
9.5.4 Glove Awareness 439
9.6 Procedures for Exiting a Cleanroom 439
9.6.1 Knee-High Booties 440
9.6.2 Frock or Jumpsuit 440
9.6.3 Head Covering 440
9.6.4 Hairnets, Gloves, and Disposable Shoe Covers 441
9.7 Relationship between Attire and Class Achieved 441
9.8 Procedures for Entering an ESD-Safe Work Area 443
9.8.1 Behavior in an ESD-Safe Work Area 444
9.8.2 ESD-Safe Work Area in a Cleanroom 445
9.9 Garments and Laundry Services 446
9.9.1 Garment Options 446
9.9.2 Measurements of Garment Cleanliness 446
9.9.3 Selection of Fabrics 448
9.9.4 Design and Construction of Garments 448
9.9.5 Selection of a Cleanroom Laundry Service 449
References and Notes 449
10 Layout of Change Rooms 451
10.1 Principles of Efficient Change Room Design 451
10.2 Case Studies: Change Rooms 454
10.3 Entering the Cleanroom 467
10.3.1 Planning a Trip into the Cleanroom 468
10.3.2 Pregowning Actions 469
10.3.3 Dressing in Cleanroom Garments 469
10.3.4 Finishing Dressing 469
10.4 Exiting the Cleanroom 470
10.5 Other Considerations 472
References and Notes 474
11 Procedures and Documentation 475
11.1 Hierarchy of Documents and Audits 475
11.2 Operator Self-Check 476
11.3 Noninstrument Audits 478
11.4 Instrument Audits 479
11.5 Independent Audits 480
11.6 Managing Use of the Audit Scorecard 481
11.7 Typical Survey 483
11.8 Case Study: Broken Magnet Procedure 488
11.8.1 Definition of a Broken Magnet 489
11.8.2 Recommendations for the Broken Magnet Procedure 489
Reference 491
Index 493
