Contamination and ESD Control in High-Technology Manufacturing

ROGER W. WELKER is founder and Principal Scientist at R. W. Welker Associates, an independent consulting firm specializing in complex contamination, electrostatic discharge, and quality control issues. His technical expertise is in manufacturing technology, cleanroom and ESD protected workplace management, cleaning process development, analysis, and statistics. R. NAGARAJAN, PhD, is Professor in the Department of Chemical Engineering at the Indian Institute of Technology, Madras. He has fifteen years' R&D experience in contamination control and chemical integration with IBM's Storage Systems Division inSan Jose, California.CARL E. NEWBERG is President and Director of Laboratory Operations for River's Edge Technical Service/MicroStat Laboratories.

• Preface xv1 Fundamentals of Contamination Control 11.1 Introduction 11.1.1 Contamination Sources 11.1.2 Contamination Adhesion Forces 31.1.3 Contamination Control Methods 91.2 Glossary of Contamination Control Terms 101.3 Specifying Contamination in Air and on Surfaces 131.4 Sources of Contamination 161.5 Contamination Control Requirements 181.5.1 Airborne Particle Requirements 181.5.2 Chemical Vapor Contamination Control Limits 331.5.3 Ionic Contamination Control Limits 351.5.4 Magnetic Contamination Control Limits 371.5.5 Surface Contamination Rates and Air Ionization 371.5.6 Contact Transfer and In Situ Contamination 381.5.7 Airflow Requirements 391.5.8 Pressure Requirements and Enclosure Exhausts 391.5.9 Maintenance Requirements 401.5.10 Other Requirements 431.5.11 Summary of Requirements 431.6 Pertinent Standards 43References and Notes 46Additional Reading 462 Fundamentals of ESD Control 482.1 Introduction and Historical Perspective 482.2 Glossary of Electrostatic Charge Control Terms 522.3 Sources of Electrostatic Charge 562.3.1 Static Electricity 572.3.2 Effects of Electrostatic Charge and Discharge 652.3.3 Failure Modes in High-Technology ESD-SensitivityDevices 672.4 Requirements of ESD Control 682.4.1 Determining ESD Damage Sensitivity 692.4.2 Electrically Explosive Device ESD Modeling 742.5 Building the ESD-Safe Workplace 752.5.1 Surface Resistivity of Materials 752.5.2 Grounding 772.5.3 Identification of and Access to an ESD-Safe Work Area 782.5.4 ESD-Protective Floor Coverings 782.5.5 Work Surfaces and Table Mats 812.5.6 Wrist Strap Ground Points 832.5.7 Air Ionization Systems 832.5.8 Relative Humidity 882.5.9 Chairs and Stools 902.5.10 Trash Cans 902.5.11 Cathode-Ray Tube Displays 912.5.12 Field Potential Limits 932.5.13 Tools and Fixtures 942.5.14 Conveyors 942.6 ESD Controls for People 952.6.1 Wrist Strap and Coiled Cord 952.6.2 Training and Certification Program 952.6.3 Cleanroom Gowns and ESD Lab Coats 972.6.4 Footwear 982.6.5 Gloves, Liners, and Finger Cots 1002.7 Consumables and Accessories 1002.7.1 Packaging 1002.7.2 Desiccants 1022.7.3 Tote Boxes, Bins, and Other Shipping Containers 1022.7.4 Notebooks and Sheet Protectors 1042.7.5 Swabs and Wipers 1042.7.6 Paper 1042.7.7 Tape 1042.8 Personnel Equipment and Procedures for Its Use 1052.8.1 Wrist Straps and Wrist Strap Monitors 1052.8.2 Sit–Stand Protocol 1062.9 Transportation of ESD-Sensitive Products 1062.10 Inspections and Record Keeping 1062.10.1 Daily Visual Inspection 1062.10.2 Periodic Instrumental Inspection 1072.10.3 Testing Protocols 1092.11 ESD Control Program 1122.12 ESD and Contamination Control 1152.13 Useful Reference Standards 116References and Notes 1173 Sampling and Analysis Methods 1193.1 Introduction 1193.2 Classification of Analysis Methods 1193.2.1 Functional Laboratory Tests 1213.2.2 Nonfunctional Tests: Objective Laboratory Tests 1243.3 Sampling of Contaminants in Air, in Liquids, and on Surfaces 1333.3.1 Contaminants in Air 1333.3.2 Contaminants in Liquids 1343.3.3 Surface-Borne Contaminants 1353.4 Organic Contamination Analysis Methods 1363.4.1 Water Break Test 1363.4.2 Contact Angle Measurement 1363.4.3 Optically Stimulated Electron Emission Technique 1373.4.4 Nonvolatile Residue Test 1373.4.5 Organic Sampling Techniques 1373.4.6 Central Atmospheric Monitoring System 1383.4.7 Electron Spectroscopy for Chemical Analysis 1393.4.8 Gas Chromatography/Mass Spectroscopy 1393.4.9 Secondary Ion Mass Spectroscopy 1393.5 Ionic and Inorganic Contamination Analysis Methods 1393.6 Electrostatic Discharge Methods 1413.6.1 Tribocharge Testing 1413.6.2 Bulk and Surface Resistance Measurements 1423.6.3 Air Ionizer Testing 1443.6.4 Typical ESD Field Instruments 1453.7 Numerical Simulation 1463.8 Algebraic Predictive Modeling 1473.9 Statistical Analysis Methods 1503.9.1 Basic Statistical Analysis Tools 1503.9.2 Gage Capability Analysis of Cleanliness Measurement Methods 151Additional Reading 156References and Notes 1564 Facilities Design: Contamination- and ESD-safe Work Areas 1584.1 Introduction 1584.2 Basics of Cleanroom Design 1594.2.1 What Can Be Called a Cleanroom 1594.2.2 What It Takes to Make a Cleanroom Work 1614.2.3 How Filters Work 1624.3 Cleanrooms 1654.3.1 Non-Unidirectional-Flow (Conventional or Mixed-Flow) Cleanrooms 1664.3.2 Air Ionization for Non-Unidirectional-Flow Cleanrooms 1684.3.3 Unidirectional Flow: 100% Filter Coverage 1694.3.4 Air Ionization in Unidirectional-Flow Cleanrooms 1744.3.5 Adding a Perforated Raised Floor 1744.3.6 Balancing a Room Using a Perforated Raised Floor 1754.3.7 Airflow Balancing After Tool Installation 1764.3.8 Solid vs. Perforated Work Surfaces 1814.3.9 Parts Storage Locations 1814.3.10 Horizontal Unidirectional-Airflow Cleanrooms 1824.4 Cleanroom Construction and Operating Costs 1834.5 Modern Energy-Saving Approaches 1844.5.1 Unidirectional-Flow Clean Benches 1844.5.2 Isolators and Minienvironments 1864.5.3 Point-of-Use Clean Air Cleanrooms 1874.5.4 Tunnelizing an Existing Ballroom Cleanroom 1884.5.5 Minienvironments 1904.6 Other Design Considerations 1914.6.1 Doors and Air Showers 1914.6.2 Pass-Throughs 1924.6.3 Equipment Pass-Throughs 1934.6.4 Service Areas 193References and Notes 1935 Getting Clean Parts and Getting Parts Clean 1955.1 Introduction 1955.2 Historical Perspective 1965.3 Gross and Precision Cleanliness Protocols 1975.3.1 Approaches to Specifying Cleanliness Levels 1995.4 Design for Manufacturability and Cleanability 2025.4.1 Design-for-Manufacturability Guidelines 2025.4.2 Design-for-Cleanability Guidelines 2035.4.3 Cleanability Indexes for Indirect Cleanliness Measurements 2035.4.4 Design-for-Cleanability Planning Considerations 2065.4.5 Design-for-Cleanability Management Considerations 2165.5 Process Design Guidelines 2165.5.1 Use of Water-Soluble Cutting Fluids 2175.5.2 Minimizing Work in Progress by Implementing Continuous-Flow Manufacturing 2185.5.3 Rinsing After Machining 2185.5.4 Parts Handling After Final Cleaning 2185.5.5 Soldering and Flux Removal 2195.5.6 Clean–Then Assemble vs. Assemble–Then Clean 2195.6 Cleaning Processes 2205.6.1 Particles in Liquid Baths 2215.6.2 Boundary Layers 2215.6.3 Ultrasonic Cleaning 2215.6.4 Spray Cleaning 2255.6.5 Spin-Rinse Dryer Cleaning 2285.6.6 Vapor Degreasing 2305.6.7 Chemical Cleaning 2305.6.8 Solvent Cleaning 2305.6.9 Mechanical Agitation Cleaning 2315.6.10 Manual Cleaning 2315.6.11 Specialty Cleaning 2325.7 Drying Processes 2345.7.1 Spin-Rinse Drying 2345.7.2 Forced-Air Drying 2345.7.3 Vacuum Drying 2355.7.4 Adsorption Drying 2355.7.5 Chemical Drying 2355.8 Cost of Cleaning 2365.9 Vendor Process Contamination Checklist 2365.10 Case Studies: Cleaning Equipment and Cleaning Process Design 2465.11 Details on the Clean–Then Assemble and Assemble–Then Clean Procedures 2525.11.1 Cleaning Strategies 2535.11.2 Case Studies: CTA and ATC 2555.11.3 Case Study Results and Discussion 2625.12 Particle Size Distributions 2645.12.1 MIL-STD- 1246 2645.12.2 Analytical Methods 2655.12.3 Extraction Methods Tested 2665.12.4 Results 2665.13 Tool Part Cleanliness 272References and Notes 2736 Tooling Design and Certification 2766.1 Introduction 2766.1.1 Tooling Design Process 2776.1.2 Applications and Limitations of Tooling Design 2786.2 Contamination and ESD Control Requirements 2796.3 Maintenance Requirements 2806.3.1 (Basics of a) Wipe-Down Procedure 2806.3.2 Maintenance Wipe-Down 2816.3.3 Engineering Changes 2826.3.4 Summary of Requirements 2826.4 General Design Alternatives 2836.4.1 Eliminating Contamination Generators 2836.4.2 Relocating Contamination Generators 2846.4.3 Enclosing and Evacuating Contamination Generators 2856.5 Materials 2936.5.1 Guidelines for Materials 2936.5.2 Guidelines for Wear 2976.5.3 Guidelines for Plastics 3016.6 Surface Treatments 3086.6.1 Paints 3096.6.2 Anodizing and Related Treatments 3106.6.3 Electroplating, Electropolishing, and Other Treatments 3116.6.4 Cautions About Coatings 3116.6.5 Synergistic Coatings 3116.6.6 Relative Wear Properties of Coatings 3126.6.7 Surface Texture and Porosity 3126.7 Selection and Evaluation of Components 3136.7.1 Pneumatic Devices 3146.7.2 Linear Motion Guides 3146.7.3 Electric Motors 3146.7.4 Process Piping and Point-of-Use Filtration 3156.7.5 In Situ Monitoring Equipment 3166.7.6 Hand Tools 3176.8 Tool and Workstation Layout 3186.8.1 Flow Control Enclosures, Minienvironments, and the Standard Machine Interface 3186.8.2 Putting the Cleanroom Tool Together 3226.9 Cleanroom Certification of Automated Tooling 3256.9.1 Statistical Requirements for Sampling 3276.9.2 Analytical Equipment and Methods 331References and Notes 334Additional Reading 3347 Continuous Monitoring 3367.1 Introduction 3367.1.1 Approaches to Monitoring 3377.1.2 Traditional Airborne Particle Measurements 3387.1.3 Critical and Busy Sampling 3397.1.4 Modified Data Collection Protocol 3397.1.5 Ongoing Use of Critical and Busy Sampling 3407.1.6 Case Studies: Traditional vs. Critical and Busy Sampling 3417.1.7 Trend, Cyclic, and Burst Patterns of Particle Generation 3467.1.8 Case Studies: Other Applications of Continuous Monitoring 3487.1.9 Summary and Conclusions 3507.2 Continuous Contamination Monitoring 3507.2.1 Electronically Multiplexed Monitoring 3507.2.2 Pneumatically Multiplexed Particle Monitoring 3517.3 Continuous Monitoring of Manufacturing 3527.3.1 Air Quality 3527.3.2 Process Fluid Purity 3557.3.3 The Value of 100% Sampling 3567.3.4 Cleanliness of Surfaces and Electrostatic Charge 3587.4 Evaluation of In Situ Monitoring in an Aqueous Cleaning Application 3597.4.1 Description of Experiment 3607.4.2 Experimental Results 3627.4.3 Management Using ISPM 3707.4.4 Conclusions 3717.5 Antennas for Electrostatic Charge Monitoring 372References and Notes 3728 Consumable Supplies and Packaging Materials 3748.1 Introduction 3748.2 Cleanroom and ESD Gloves 3758.3 Functional vs. Nonfunctional Testing 3768.3.1 Functional Materials Qualification Tests 3768.3.2 Nonfunctional Testing: Objective Laboratory Measurements 3778.3.3 ESD Considerations in Glove Selection 3798.4 Glove Use Strategies 3818.5 Initial Qualification vs. the Need for Ongoing Lot Certification 3818.6 Glove Washing 3838.6.1 Early Observations with Natural Rubber Latex Gloves 3838.6.2 Gloves Washability 3848.6.3 Nitrile Glove Performance 3878.6.4 Glove Washing Conclusions 3888.7 ESD Performance of Gloves 3888.7.1 Materials Selection for ESD Properties 3898.7.2 Specifying the ESD Performance of Cleanroom Gloves and Glove Liners 3898.7.3 Testing Considerations 3918.7.4 Factors That Affect the ESD Performance of Gloves 3928.8 Glove Laundering 3968.8.1 Cost–Benefit Problem 3978.8.2 Polyurethane Glove Laboratory Properties 3978.8.3 ESD Performance 3988.8.4 Chemical Contamination 3998.8.5 Wear Characteristics 3998.8.6 Laundering Tests 4018.8.7 Impact of Laundering and Reuse on Glove Cost 4018.8.8 Conclusions 4028.9 Wipers and Swabs 4028.9.1 Selecting the Correct Wiper or Swab 4038.10 Reusable and Disposable Packaging Materials 4058.10.1 ESD Consideration in Packaging 4058.10.2 Carbon-Filled Polymers 4058.10.3 Metal Loading 4068.10.4 Topical and Incorporated Organic Agents 4068.10.5 Copolymer Blends 4078.11 Facial Coverings 407References and Notes 4089 Controlling Contamination and ESD From People 4109.1 Introduction 4109.2 People as a Source of Contamination 4109.2.1 Skin and Hair 4119.2.2 Fingerprints 4139.2.3 Bacteria and Fungi 4149.2.4 Spittle Droplets 4149.2.5 Street Clothing 4159.2.6 Other Forms of Contamination 4169.3 Typical Gowning Protocols 4179.3.1 Inner Suit 4189.3.2 Hair Cover (Bouffant) 4199.3.3 Woven Gloves 4199.3.4 Barrier Gloves 4209.3.5 Facial Cover 4209.3.6 Hood and Powered Headgear 4219.3.7 Frock, Coverall, and Two-Piece Suit 4229.3.8 Shoe Covers, Booties, and Special Shoes 4249.3.9 Suggested Frequency of Change 4269.4 Procedures for Entering a Cleanroom 4269.4.1 Pre-Change Room Procedure 4279.4.2 Wipe-Down 4279.4.3 Hairnet and Face Mask 4289.4.4 Shoe Cleaners 4299.4.5 Handwashing 4309.4.6 Changing into Cleanroom Garments 4319.4.7 Powered Headgear 4339.4.8 Footwear 4339.4.9 Shoe Cleaners and Tacky Mats 4369.5 Behavior in a Cleanroom 4379.5.1 Working in a Cleanroom 4389.5.2 HEPA Filters 4399.5.3 Raised Floors 4399.5.4 Glove Awareness 4399.6 Procedures for Exiting a Cleanroom 4399.6.1 Knee-High Booties 4409.6.2 Frock or Jumpsuit 4409.6.3 Head Covering 4409.6.4 Hairnets, Gloves, and Disposable Shoe Covers 4419.7 Relationship between Attire and Class Achieved 4419.8 Procedures for Entering an ESD-Safe Work Area 4439.8.1 Behavior in an ESD-Safe Work Area 4449.8.2 ESD-Safe Work Area in a Cleanroom 4459.9 Garments and Laundry Services 4469.9.1 Garment Options 4469.9.2 Measurements of Garment Cleanliness 4469.9.3 Selection of Fabrics 4489.9.4 Design and Construction of Garments 4489.9.5 Selection of a Cleanroom Laundry Service 449References and Notes 44910 Layout of Change Rooms 45110.1 Principles of Efficient Change Room Design 45110.2 Case Studies: Change Rooms 45410.3 Entering the Cleanroom 46710.3.1 Planning a Trip into the Cleanroom 46810.3.2 Pregowning Actions 46910.3.3 Dressing in Cleanroom Garments 46910.3.4 Finishing Dressing 46910.4 Exiting the Cleanroom 47010.5 Other Considerations 472References and Notes 47411 Procedures and Documentation 47511.1 Hierarchy of Documents and Audits 47511.2 Operator Self-Check 47611.3 Noninstrument Audits 47811.4 Instrument Audits 47911.5 Independent Audits 48011.6 Managing Use of the Audit Scorecard 48111.7 Typical Survey 48311.8 Case Study: Broken Magnet Procedure 48811.8.1 Definition of a Broken Magnet 48911.8.2 Recommendations for the Broken Magnet Procedure 489Reference 491Index 493