Printed Circuit Boards

Printed Circuit Boards

Authors: R. Khandpur

Published: August 2005

eISBN: 9780071589253 0071589252 | ISBN: 9780071464208

Contents

Preface

1. Basics of Printed Circuit Boards

1.1 Connectivity in Electronic Equipment

1.1.1 Advantages of Printed Circuit Boards

1.2 Evolution of Printed Circuit Boards

1.3 Components of a Printed Circuit Board

1.4 Classification of Printed Circuit Boards

1.4.1 Single-sided Printed Circuit Boards

1.4.2 Double-sided Printed Circuit Boards

1.4.3 Multi-layer Boards

1.4.4 Rigid and Flexible Printed Circuit Boards

1.5 Manufacturing of Basic Printed Circuit Boards

1.5.1 Single-sided Boards

1.5.2 Double-sided Plated Through-holes

1.5.3 Multi-layer Boards

1.5.4 Flexible Boards

1.6 Challenges in Modern PCB Design and Manufacture

1.7 Major Market Drivers for the PCB Industry

1.8 PCBs with Embedded Components

1.9 Standards on Printed Circuit Boards

1.10 Useful Standards

2. Electronic Components

2.1 Basics of Electronic Components

2.1.1 Active vs Passive Components

2.1.2 Discrete vs Integrated Circuits

2.1.3 Component Leads

2.1.4 Polarity in Components

2.1.5 Component Symbols

2.2 Resistors

2.2.1 Types of Resistors

2.2.2 Packages

2.2.3 Characteristics

2.3 Variable Resistors or Potentiometers

2.4 Light-dependent Resistors (LDRs)

2.5 Thermistors

2.6 Capacitors

2.6.1 Types of Capacitors

2.6.2 Packages

2.6.3 Performance of Capacitors

2.7 Variable Capacitors

2.8 Inductors

2.9 Diodes

2.10 Special Types of Diodes

2.10.1 Zener Diode

2.10.2 Varactor Diode

2.10.3 Varistor

2.10.4 Light Emitting Diodes (LED)

2.10.5 Photodiode

2.10.6 Tunnel Diode (TD)

2.11 Transistors

2.11.1 Bipolar Transistors

2.11.2 Power Transistors

2.11.3 Darlington Transistors

2.11.4 Field-effect Transistors

2.11.5 Insulated Gate Bipolar Transistor (IGBT)

2.11.6 Transistor Type Numbers

2.12 Thyristors

2.13 Integrated Circuits (ICs)

2.14 Linear Integrated Circuits

2.14.1 Operational Amplifiers (OP-AMP)

2.14.2 Three-terminal Voltage Regulator

2.15 Digital Integrated Circuits

2.15.1 Logic Circuits

2.16 Microprocessors

2.17 Semiconductor Memories

2.17.1 Random Access Memory

2.17.2 Read Only Memory

2.18 Microcontrollers

2.19 Surface Mount Devices

2.19.1 Surface Mount Devices

2.19.2 Surface Mounting Semiconductor Packages

2.19.3 Packaging of Passive Components as SMDs

2.20 Heat Sinks

2.21 Transformer

2.22 Relays

2.23 Connectors

2.24 Useful Standards

3. Layout Planning and Design

3.1 Reading Drawings and Diagrams

3.1.1 Block Diagram

3.1.2 Schematic Diagram

3.2 General PCB Design Considerations

3.2.1 Important Design Elements

3.2.2 Important Performance Parameters

3.3 Mechanical Design Considerations

3.3.1 Types of Boards

3.3.2 Board Mounting Techniques

3.3.3 Board Guiding and Retaining

3.3.4 Input/Output Terminations

3.3.5 Board Extraction

3.3.6 Testing and Servicing

3.3.7 Mechanical Stress

3.3.8 Board Thickness

3.3.9 Important Specifications and Standards

3.4 Electrical Design Considerations

3.4.1 Conductor Dimensions

3.4.2 Resistance

3.4.3 Capacitance Considerations

3.4.4 Inductance of PCB Conductors

3.4.5 High Electrical Stresses

3.5 Conductor Patterns

3.6 Component Placement Rules

3.6.1 Conductor Width and Thickness

3.6.2 Conductor Spacing

3.6.3 Conductor Shapes

3.6.4 Conductor Routing and Locations

3.6.5 Supply and Ground Conductors

3.7 Fabrication and Assembly Considerations

3.8 Environmental Factors

3.8.1 Thermal Considerations

3.8.2 Contamination

3.8.3 Shock and Vibration

3.9 Cooling Requirements and Packaging Density

3.9.1 Heat Sinks

3.9.2 Packaging Density

3.9.3 Package Style and Physical Attributes

3.10 Layout Design

3.10.1 Grid Systems

3.10.2 Layout Scale

3.10.3 Layout Sketch/Design

3.10.4 Layout Considerations

3.10.5 Materials and Aids

3.10.6 Land Requirements

3.10.7 Manual Layout Procedure

3.10.8 Layout Methodology

3.11 Layout Design Checklist

3.11.1 General Considerations

3.11.2 Electrical Considerations

3.11.3 Mechanical Considerations

3.12 Documentation

3.12.1 Documentation File

3.13 Useful Standards

4. Design Considerations for Special Circuits

4.1 Design Rules for Analog Circuits

4.1.1 Component Placement

4.1.2 Signal Conductors

4.1.3 Supply and Ground Conductors

4.1.4 General Rules for Design of Analog PCBs

4.2 Design Rules for Digital Circuits

4.2.1 Transmission Lines

4.2.2 Problems in Design of PCBs for Digital Circuits

4.3 Design Rules for High Frequency Circuits

4.4 Design Rules for Fast Pulse Circuits

4.4.1 Controlled Impedance Considerations

4.5 Design Rules for PCBs for Microwave Circuits

4.5.1 Basic Definitions

4.5.2 Strip Line and Microstrip Line

4.5.3 Transmission Lines as Passive Components

4.5.4 General Design Considerations for Microwave Circuits

4.6 Design Rules for Power Electronic Circuits

4.6.1 Separating Power Circuits in High and Low Power Parts

4.6.2 Base Material Thickness

4.6.3 Copper Foil Thickness

4.6.4 Conductor Width

4.6.5 Resistive Drop of Voltage

4.6.6 Thermal Considerations

4.7 High-density Interconnection Structures

4.7.1 Drivers for HDI

4.7.2 Advantages of HDI

4.7.3 Designing for HDI

4.8 Electromagnetic Interference/Compatibility (EMI/EMC)

4.9 Useful Standards

5. Artwork Generation

5.1 What is Artwork?

5.2 Basic Approach to Manual Artwork

5.2.1 Ink Drawing on White Card Board Sheets

5.2.2 Black Taping on Transparent Base Foil

5.2.3 Red and Blue Tape on Transparent Polyester Base Foil

5.3 General Design Guidelines for Artwork Preparation

5.3.1 Conductor Orientation

5.3.2 Conductor Routing

5.3.3 Conductor Spacing

5.3.4 Hole Diameter and Solder Pad Diameter

5.3.5 The Square Land/Pad

5.4 Artwork Generation Guidelines

5.4.1 No Conductor Zone

5.4.2 Pad Centre Holes

5.4.3 Conductor and Solder Pad Joints

5.5 Film Master Preparation

5.5.1 Photographic Film

5.5.2 Exposure through Camera

5.5.3 Dark Room

5.5.4 Film Development

5.6 Automated Artwork Generation

5.7 Computer- Aided Design (CAD)

5.7.1 System Requirements

5.8 Basic CAD Operation

5.8.1 Layout Procedure

5.8.2 Library Manager

5.8.3 Component Placement

5.8.4 Conductor Routing

5.8.5 Checking

5.9 Design Automation

5.9.1 How to Judge CAD Systems?

5.10 Manual Versus Automation in PCB Design

5.11 Photoplotter

5.11.1 Vector Photoplotter

5.11.2 Raster (Laser) Plotters

5.11.3 Talking to Photoplotters

5.12 Computer-Aided Manufacturing (CAM)

5.13 Data Transfer Mechanisms

5.14 PCB Design Checklist

5.15 Useful Relevant Standards

6. Copper Clad Laminates

6.1 Anatomy of Laminates

6.1.1 Fillers (Reinforcements)

6.1.2 Resins

6.1.3 Copper Foil

6.2 Manufacture of Laminates

6.2.1 Materials

6.2.2 Process

6.3 Properties of Laminates

6.3.1 Electrical Properties

6.3.2 Dielectric Strength

6.3.3 Dielectric Constant

6.3.4 Dissipation Factor

6.3.5 Insulation Resistance

6.3.6 Surface Resistivity

6.3.7 Volume Resistivity

6.3.8 Dielectric Breakdown

6.4 Types of Laminates

6.4.1 Phenolic Laminates

6.4.2 Epoxy Laminates

6.4.3 Glass Cloth Laminates

6.4.4 Prepreg Material [B-Stage]

6.4.5 PTFE (Polytetrafluoroethylene) Laminates

6.4.6 Polyester Laminates (Mylar Lamination)

6.4.7 Silicone Laminates

6.4.8 Melamine Laminates

6.4.9 Polyamide Laminates

6.4.10 Teflon Laminates

6.4.11 Mixed Dielectric Laminates

6.5 Evaluation of Laminates

6.5.1 Laminate Testing

6.5.2 Surface and Appearance

6.5.3 Water Absorption

6.5.4 Punchability and Machinability

6.5.5 Peel Strength

6.5.6 Bond Strength

6.5.7 Solder Resistance

6.5.8 Warp and Twist

6.5.9 Flexural Strength

6.5.10 Flammability

6.5.11 Glass Transition Temperature

6.5.12 Dimensional Stability

6.5.13 Copper Adhesion

6.6 Useful Standards

7. Image Transfer Techniques

7.1 What is Image Transfer?

7.2 Laminate Surface Preparation

7.2.1 Manual Cleaning Process

7.2.2 Mechanical Cleaning

7.2.3 Test for Cleanliness

7.3 Screen Printing

7.3.1 Screen Frame

7.3.2 Screen Cloth

7.3.3 Screen Preparation

7.3.4 Squeegees

7.4 Pattern Transferring Techniques

7.4.1 Screen Stencil Method

7.4.2 Indirect Method [Transfer Type Screen Method]

7.4.3 Knife-cut or Hand-cut Film Process

7.4.4 Photographic Techniques

7.5 Printing Inks

7.5.1 Ultraviolet Curing Inks

7.6 Printing Process

7.6.1 Manual Screen Printing Process

7.6.2 Automatic or Semi-automatic Screen Printing Process

7.7 Photo Printing

7.7.1 Liquid Photo-resist (Wet Film Resist)

7.7.2 Dry Film Photo-resists

7.8 Laser Direct Imaging (LDI)

7.8.1 Benefits of LDI

7.9 Legend Printing

7.10 Useful Standards

8. Plating Processes

8.1 Need for Plating

8.2 Electroplating

8.2.1 The Basic Electroplating Process

8.2.2 Faraday's Laws of Electrolysis

8.2.3 Water Quality

8.2.4 pH of a Solution

8.2.5 Buffer

8.2.6 Anodes

8.2.7 Anode Bags

8.2.8 Pre-treatment for Electroplating

8.3 Plating Techniques

8.3.1 Immersion Plating

8.3.2 Electroless Plating

8.3.3 Electroplating

8.4 General Problems in Plating

8.5 General Plating Defects

8.5.1 Voids

8.5.2 Blow Holes

8.5.3 Outgassing

8.6 Special Plating Techniques

8.6.1 Through-hole Plating

8.6.2 Reel-to-Reel Selective Plating

8.6.3 Brush Plating

8.6.4 Finger Plating

8.6.5 Conductor Metal Paste Coating

8.6.6 Reduction Silver Spraying

8.7 Metal Distribution and Plating Thickness

8.7.1 Analysis of Solution (Wet Chemical Analysis)

8.7.2 Physical Tests for Solutions

8.7.3 Testing of Electrodeposits

8.8 Considerations for Shop Floor

8.8.1 Plating Shop Layout

8.8.2 Equipment

8.9 Additive Processing

8.9.1 Fully Additive Process

8.9.2 Semi Additive Process

8.9.3 Partially Additive Process

8.10 Solder Mask

8.10.1 Solder Resist Classification

8.10.2 Liquid Film Solder Mask

8.10.3 Dry Film Solder Masking

8.10.4 Resolution

8.10.5 Encapsulation

8.10.6 Surface Topography Resist Thickness

8.10.7 Placement Assistance

8.10.8 Reliability of Solder Mask

8.10.9 Soldering and Cleaning

8.10.10 Tenting of Vias

8.10.11 Solder Mask over Bare Copper [SMOBC]

8.11 Conformal Coatings

8.11.1 Materials for Conformal Coatings

8.11.2 Methods of Applying Conformal Coatings

8.11.3 Standards for Coatings

8.12 Useful Standards

9. Etching Techniques

9.1 Etching Solutions and Chemistry

9.1.1 Ferric Chloride

9.1.2 Hydrogen Peroxide — Sulphuric Acid

9.1.3 Chromic-Sulphuric Acid

9.1.4 Cupric Chloride

9.1.5 Ammonium Persulphate

9.1.6 Alkaline Ammoniacal/Ammonium Chloride

9.2 Etching Arrangements

9.2.1 Simple Batch Production Etching

9.2.2 Continuous Feed Etching

9.2.3 Open Loop Regeneration

9.2.4 Closed Loop Regeneration

9.3 Etching Parameters

9.4 Equipment and Techniques

9.4.1 Immersion Etching

9.4.2 Bubble Etching

9.4.3 Splash Etching

9.4.4 Spray Etching

9.5 Etching Equipment Selection

9.6 Optimizing Etchant Economy

9.7 Problems in Etching

9.7.1 Under-etching or Under-cut

9.7.2 Overhang

9.8 Facilities for Etching Area

9.9 Electrochemical Etching

9.10 Mechanical Etching

10. Mechanical Operations

10.1 Need for Mechanical Operations

10.2 Cutting Methods

10.2.1 Shearing

10.2.2 Sawing

10.2.3 Blanking of PCBs

10.2.4 Milling

10.2.5 Routing of PCBs

10.3 Hole Punching

10.4 Drilling

10.4.1 Drill Bit Geometry and its Importance

10.4.2 Types of Drill Bits

10.4.3 Drill Bit Inspection

10.4.4 Drill Bit Sizes

10.4.5 Tool Life and Re-grinding (Re-pointing)

10.4.6 Requirements in Drilling

10.4.7 Drill Speed, Feed and Withdrawal Rates

10.4.8 Function of Clean Holes

10.4.9 Drill Entry and Exit (Back-up) Materials

10.4.10 Use of Drill Bush/Collar

10.4.11 Drilling and Types of Laminates

10.4.12 Drilling Problems

10.4.13 Drilling Machines

10.5 Microvias

10.5.1 Photo-formed Vias

10.5.2 Plasma Etching

10.5.3 Laser-formed Vias

10.6 Use of UV Laser for Drilling PCB

10.7 Hybrid Laser Drilling Process

10.8 Useful Standards

11. Multi-layer Boards

11.1 What are Multi-layers?

11.2 Interconnection Techniques

11.2.1 Conventional Plated Through-hole

11.2.2 Buried Via

11.2.3 Blind Vias

11.3 Materials for Multi-layer Boards

11.3.1 Resin System

11.3.2 Reinforcement Materials

11.3.3 Prepreg

11.3.4 Copper Foil

11.4 Design Features of Multi-layer Boards

11.4.1 Mechanical Design Considerations

11.4.2 Electrical Design Considerations

11.5 Fabrication Process for Multi-layer Boards

11.5.1 General Process

11.5.2 Lamination

11.5.3 Post-lamination Process

11.5.4 Multi-layer Drilling

11.5.5 Schematic Key for Multi-layer Built-ups

11.6 Useful Standards

12. Flexible Printed Circuit Boards

12.1 What are Flexible Printed Circuit Boards?

12.2 Construction of Flexible Printed Circuit Boards

12.2.1 Films — Types and Their Characteristics

12.2.2 Foils

12.2.3 Adhesives

12.3 Design Considerations in Flexible Circuits

12.3.1 Difference in Design Considerations of Rigid and Flexible Circuits

12.3.2 Step-by-step Approach to Designing of a Flex Circuit

12.3.3 Designing for Flexibility and Reliability

12.4 Manufacture of Flexible Circuits

12.5 Rigid Flex Printed Circuit Boards

12.6 Terminations

12.7 Advantages of Flexible Circuits

12.8 Special Applications of Flexible Circuits

12.9 Useful Standards

13. Soldering, Assembly and Re-working Techniques

13.1 What is Soldering?

13.2 Theory of Soldering

13.2.1 The Wetting Action

13.2.2 Surface Tension

13.2.3 Creation of an Inter-metallic Compound

13.2.4 The Wetting Angle

13.3 Soldering Variables

13.3.1 Temperature and Time Taken for Soldering

13.3.2 Tarnish-free Surface

13.3.3 Application of Right Flux and Proper Solder

13.4 Soldering Material

13.4.1 Solder

13.4.2 Flux

13.5 Soldering and Brazing

13.5.1 Solders for Hard Soldering/Brazing

13.6 Soldering Tools

13.6.1 Soldering Iron

13.7 Other Hand Soldering Tools

13.7.1 Cutters

13.7.2 Pliers

13.7.3 Strippers

13.7.4 Bending Tools

13.7.5 Heat Sinks

13.7.6 General Cleaning Tools

13.8 Hand Soldering

13.8.1 Hand Soldering Requirements

13.8.2 Steps in Hand Soldering

13.8.3 Soldering Leadless Capacitors

13.9 PCB Assembly Process

13.9.1 Leaded Through-hole Assembly

13.9.2 Surface Mount Assembly

13.9.3 Combinations of Mixed Technologies

13.10 Solder Pastes for SMDS

13.10.1 Requirements of Solder Pastes

13.10.2 Composition of Solder Pastes

13.10.3 Solder Paste Application

13.10.4 Handling of Solder Paste

13.10.5 Stencil Printing of Solder Paste

13.10.6 Screen Printing of Solder Paste

13.10.7 Pre-forms of Solder

13.10.8 No-clean Solder Paste

13.11 Adhesive for Mixed Technology Assembly

13.11.1 Requirements of Adhesive

13.11.2 Application of Adhesive

13.12 Mass Soldering

13.12.1 Dip Soldering

13.12.2 Drag Soldering

13.12.3 Wave Soldering

13.12.4 Reflow Soldering

13.12.5 Vapour Phase System

13.13 Post-soldering Cleaning

13.13.1 Types of Contamination

13.13.2 Solvents and Cleaning Methods

13.14 Quality Control of Solder Joints

13.14.1 Good Quality Solder Joints

13.14.2 Common Soldering Faults

13.14.3 Solder Joint Defects and their Common Causes

13.15 Health and Safety Aspects

13.16 Electrostatic Discharge Control

13.16.1 Fundamentals of ESD

13.16.2 Electrostatic Voltages Generated by Various Operations

13.16.3 Sensitivity of Various Components to ESD Voltages

13.16.4 Electrostatic Protection

13.16.5 Anti-static Workstation

13.16.6 A Proper Assembly Environment

13.16.7 Component Handling

13.16.8 Special Considerations for Handling MOS Devices

13.16.9 Education/Certificate for ESD Control

13.17 Re-work and Repair of Printed Circuit Boards

13.17.1 Approaching Components for Tests

13.17.2 De-soldering Techniques

13.17.3 Replacement of Components

13.18 Repairing Surface Mounted PCBs

13.18.1 Cut all Leads

13.18.2 Heating Methods

13.18.3 Removal and Replacement of Surface Mount Devices

13.18.4 Re-work Stations

13.19 Useful Standards

14. Quality, Reliability and Acceptability Aspects

14.1 What is Quality Assurance?

14.1.1 Classification of Defects

14.1.2 Defectives

14.1.3 Acceptability Quality Level (AQL)

14.1.4 Quality Control Programme

14.1.5 Statistical Process Control and Sampling Plan

14.2 Testing for Quality Control

14.2.1 Characteristics for Testing for Quality Assurance

14.2.2 Designing a QA Programme

14.2.3 Incoming QA

14.2.4 Traceability

14.3 Quality Control Methods

14.3.1 Micro-sectioning

14.4 Testing of Printed Circuit Boards

14.4.1 Automatic Board Testing

14.4.2 Bare Board Testing (BBT)

14.4.3 Testing of Assembled Boards

14.5 Reliability Testing

14.5.1 Reliability of Printed Circuit Boards

14.6 Acceptability of PCBs

14.6.1 Acceptance Criteria

14.6.2 Inspection of Assembled PCBs

14.6.3 Inspection Techniques

14.6.4 Acceptability Criteria

14.7 Useful Standards

15. Environmental Concerns in PCB Industry

15.1 Pollution Control in PCB Industry

15.2 Polluting Agents

15.3 Recycling of Water

15.4 Recovery Techniques

15.4.1 Filtration

15.4.2 Water Use Reduction Technique

15.4.3 Ion Exchange System

15.4.4 Reverse Osmosis

15.4.5 Evaporative Recovery

15.4.6 Precipitation of Heavy Metals

15.4.7 Electrolytic Recovery

15.5 Air Pollution

15.5.1 Dust

15.5.2 Fumes

15.5.3 Clean Environment in Assembly Rooms

15.6 Recycling of Printed Circuit Boards

15.6.1 Present Approach to PCB Scrap Disposal

15.6.2 Characteristics of PCB Scrap

15.6.3 Dis-assembly of Equipment

15.6.4 Technologies of Recycling of PCBs

15.7 Environmental Standards

15.8 Safety Precautions for the Personnel

15.9 Toxic Chemicals in PCB Fabrication

15.10 Lead-free Soldering

15.10.1 Substitutes for Tin/Lead Solders

15.11 Useful Standards

Glossary

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References

Index