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EP06 view

A SCIENTIFIC GUIDE TO SURFACE MOUNT TECHNOLOGY

by C. LEA

Pages--569+xvi; Tables--48; Figures--392; Size--23 x 15 cm.
ISBN 0 901150 22 3

Code: EP05

Contents of this page:

Description
Some Worldwide Reviews
About the author
Table of Contents

Description

The advantages of surface mounting electronic components, rather than insertion mounting leaded components, are a reduced board size and weight, an increased performance and reliability and a fully automated, rationalised production.

The purpose of this book is to give the reader a better scientific understanding of the physical mechanisms involved in the implementation of this novel technology. The aim is that, through a scientific perception, both the manufacturing efficiency and the product reliability will benefit from the revolutionary step of surface mounting, in offering the electronic assembly industry solutions to the new problems that are firmly based, technically and scientifically.

This book presents a full and rationalised coverage of all the major aspects of surface mounting technology, giving the underlying principles involved which in turn offer guidelines for design, assembly, inspection and test. The scientific underpinning of SMT is illustrated using existing components, substrates and soldering techniques, but in a format such that the guidelines can be readily extended for continued use as the technology inevitably progresses.

Some Worldwide Reviews

"This is the most difficult book I have ever had in my hands to review. Why? A reviewer has for task to try and point out as impartially as possible the strong and weak points of the work in question. In this case, critical as I am known to be, the strong points are easy to find, but I have had really to work to find any weak ones! Of course, this does not necessarily mean that I agree with every word in it, there is still room for opinions to be expressed. In short, if this book does not become the ‘standard’ reference work on the subject for the next few years, I’ll eat my hat (if I had one!).

Finally, a few words of a general nature. At first, I was daunted by the fact that the references were in a block at the end of the book, rather than at the end of each chapter. After reading a few chapters, I had become used to the idea. By the end of the book, I found it was indeed preferable. This reference list is very complete and shows that Dr Lea has not only done his homework, but, as he admits in the preface, he has drawn heavily on the publications of third parties, naming a few of them. The reference list is also completed by a list of the authors of the references in alphabetical order. As in all the Electrochemical Publications books, there is an excellent index. Also as in all of them, the quality of printing, paper, typesetting, layout and binding is irreproachable. In short, this book is a must for all those who wish to know more about any aspect of SMT and is an excellent example of how to write and present an ‘applied science’ treatise. Thoroughly recommended!"

Hybrid Circuits (UK)

 

"The author is to be congratulated on his masterly, scientific approach in assisting to resolve the many problems in surface mount and general soldering which until very recently would have been regarded as a black art.

Dr Lea’s grasp of the subject in the context of his physico-mathematical understanding of the processes involved in soldering is expressed with exceptional lucidity. The style of presentation is particularly appealing to the reviewer who was able to relax in reading long sections of the book at a time."

Circuit World (UK)

About the author

After gaining a first class Honours BSc degree in physics and a PhD in surface physics, both from the University of Southampton, Colin Lea spent two years on the faculty of the University of Chicago before joining the National Physical Laboratory in 1971. Within the Surfaces and Interfaces Group, Dr Lea heads the research in the science of metal wetting. In 1980 he set up the NPL Soldering Science and Technology Club which now comprises well over 100 companies associated with all aspects of the electronic assembly industry. The success of this Club has led to the inauguration of the Surface Mount Club at NPL. Dr Lea is a Fellow of the Institute of Physics and a Member of the Institute of Metals.

Table of Contents

PREFACE

 

CHAPTER ONE

Overview

1.1 A new technology

1.1.1 Types of surface mounting components

1.1.2 New substrate materials

1.1.3 The assembly process

1.2 Advantages of surface mounting

1.3 Critical issues in SMT

1.4 The future of SMT

 

CHAPTER TWO

Components

2.1 Introduction

2.2 Towards miniaturisation

2.2.1 Use of board area

2.2.2 Move away from DIL packages

2.3 Surface mounting semiconductor packages

2.3.1 SOIC packages

2.3.2 SOT packages

2.3.3 Cylindrical diode packages

2.3.4 Leadless ceramic chip carriers

2.3.5 Plastic leaded chip carriers

2.3.6 Flatpacks and quad packs

2.3.7 Land grid arrays

2.3.8 Modified through-hole components

2.3.9 Sockets

2.4 Bare chips

2.4.1 Wire bonding

2.4.2 Tape automated bonding

2.4.3 Flip-chip

2.5 Comparison of IC packaging options

2.5.1 Board area requirement

2.5.2 Conductor lengths

2.6 IC package construction and materials

2.6.1 Plastic packages

2.6.2 Ceramic packages

2.6.3 Leadframes

2.7 Passive components

2.7.1 Capacitors

2.7.1.1 Ceramic chip capacitors

2.7.1.2 Cylindrical ceramic capacitors

2.7.1.3 Plastic capacitors

2.7.1.4 Tantalum chip capacitors

2.7.1.5 Aluminium electrolytic capacitors

2.7.2 Resistors

2.7.3 Other passive components

2.8 Thermal characteristics of SMCs

2.8.1 Temperature-dependent effects

2.8.2 Thermal parameters

2.8.3 Temperature coefficient of expansion

2.9 Component packing

2.9.1 Bulk

2.9.2 Tape

2.9.3 Magazine

 

CHAPTER THREE

Substrates

3.1 Introduction

3.2 Compatibility of thermal expansion

3.2.1 Matched TCE

3.2.2 Compliant joint

3.2.3 Compliant substrate

3.3 Thermal management

3.3.1 Heat dissipation by conduction

3.3.2 Heat dissipation by convection

3.3.3 Heat dissipation by radiation

3.3.4 Relative rôles of heat transfer mechanisms

3.4 Interconnection density

3.4.1 Interconnection requirements

3.4.2 Blind, buried and thermal vias

3.5 Types of substrate and interconnection

3.5.1 Organic substrates

3.5.1.1 Phenolic laminates

3.5.1.2 Epoxy laminates

3.5.1.3 Polyimide laminates

3.5.1.4 Other organic laminates

3.5.1.5 The copper foil

3.5.1.6 The glass cloth

3.5.1.7 Comparative properties of organic laminates

3.5.1.8 PCB fabrication with organic laminates

3.5.2 Matched TCE substrates: ceramics

3.5.2.1 Thin film circuitry

3.5.2.2 Thick film circuitry

3.5.3 Matched TCE substrates: laminates

3.5.4 Metal core substrates

3.5.4.1 Porcelain enamelled steel

3.5.4.2 Organic metal-core substrates

3.5.4.3 Multiwire

3.5.5 Compliant substrates

3.5.6 Polymer thick film circuits

3.5.7 Comparison of substrate-interconnection systems

 

CHAPTER FOUR

Design and Assembly

4.1 Assembly variations

4.1.1 SMCs single-sided

4.1.2 SMCs double-sided

4.1.3 Mixed assembly, SMCs single-sided

4.1.4 Mixed assembly, SMCs double-sided

4.2 PCB layout

4.2.1 Factors affecting PCB layout

4.2.2 Design constraints from the placement

operation

4.2.3 Design constraints from the soldering

operation

4.2.4 Design constraints from the testing operation

4.2.5 Preferred component layouts

4.2.6 Conductor routing

4.3 Component footprints

4.3.1 Placement accuracy

4.3.2 Typical footprints

4.3.3 Solder masks

4.3.4 Conductor fan-outs

4.3.5 Thermal mounting

4.4 Computer-aided design

4.5 Component placement

4.5.1 Hand assembly

4.5.2 Sequential and simultaneous placement

4.5.3 Selection criteria for placement machines

4.5.4 Placement machine functions

4.6 Chip-on-board assembly

4.6.1 Die bonding

4.6.2 Wire bonding

4.6.3 Tape-automated bonding

4.6.4 Flip-chips

4.6.5 Beam leads

4.6.6 Encapsulation

 

CHAPTER FIVE

Wave Soldering

5.1 Introduction

5.2 Temporary adhesive bonding

5.2.1 Application of adhesive

5.2.2 Curing the adhesive

5.3 Fluxing the board

5.3.1 Application of the flux

5.3.1.1 Foam fluxing

5.3.1.2 Wave fluxing

5.3.1.3 Spray fluxing

5.3.2 Monitoring flux density

5.4 Preheating the board

5.5 The solder wave

5.5.1 Wave generation

5.5.2 The soldering process

5.5.3 Wave shape

5.5.4 Shadowing

5.5.5 Jet wave

5.5.6 Dual wave

5.6 The solder alloy

5.6.1 The choice of alloy

5.6.2 Impurities in the solder

5.6.3 Oxidation of the solder

5.7 Oil in the solder wave

5.7.1 Reduction of solder bridges

5.7.2 Types of oil

5.7.3 Application of the oil

5.7.4 Colophony addition

5.8 Air knife

5.9 Circuit board finish

5.10 Wave soldering defects

5.10.1 Inserted components

5.10.2 Surface mounted components

5.10.2.1 Avoidance of bridges by pattern design

 

CHAPTER SIX

Solder Pastes

6.1 Introduction

6.2 The solder powder

6.2.1 Solder particle shape

6.2.2 Solder particle size

6.2.3 Oxide content

6.2.4 Solids content

6.3. The flux in the paste

6.3.1 Fluxes soluble in organic liquids

6.3.2 Water soluble fluxes

6.4 The solder alloy

6.4.1 Reflow temperature

6.4.2 Physical properties

6.4.3 Metallurgical systems

6.4.3.1 Tin-lead systems

6.4.3.2 Tin-lead-silver systems

6.4.3.3 Tin-silver systems

6.4.3.4 Tin-antimony and tin-lead-antimony systems

6.4.3.5 Lead-indium and tin-indium systems

6.4.3.6 Tin-bismuth and tin-lead-bismuth system

6.4.4 Metal purity

6.5 Application of the paste

6.5.1 Screen printing

6.5.2 Stencil application

6.5.3 Syringe dispensing

6.5.4 Pin transfer

6.6 Paste rheology

6.6.1 Viscosity

6.6.2 Measurement of paste viscosity

6.6.3 Screenability

6.6.4 Slump

6.6.5 Tackiness

6.7 Drying the solder paste

6.7.1 Storage after drying

6.8 Handling and storage of solder pastes

6.9 Voids in the solder fillets

6.9.1 Flux activation

6.9.2 Solvent

6.9.3 Pre-heating

6.10 Solder balls

6.10.1 Solder balling test

6.11 Solder paste design appraisal

 

CHAPTER SEVEN

Reflow Soldering Using Radiant Heating

7.1 Introduction

7.2 Radiation heat transfer

7.2.1 The electromagnetic spectrum

7.2.2 Basic definitions

7.2.3 Planck’s law

7.2.4 Wien’s law

7.2.5 Stefan-Boltzmann law

7.2.6 Kirchoff’s law

7.2.7 Lambert’s law—diffuse emission

7.2.8 Heat transfer by diffuse radiation

7.2.9 Heat transfer coefficient

7.2.10 Penetration of radiation

7.3 Infra-red energy sources

7.3.1 Tungsten filament sources

7.3.2 Nichrome filament sources

7.3.3 Area emission sources

7.4 Workpiece characteristics

7.4.1 Absorptivity of materials

7.4.2 Surface roughness and directional emissivity

7.4.3 Thermal degradation

7.4.4 Geometrical effects

7.5 The gaseous environment

7.5.1 Air

7.5.2 Nitrogen

7.5.3 Hydrogen-nitrogen

7.6 Infra-red processing

7.6.1 Infra-red character

7.6.2 Furnace design

7.6.3 Estimate of heating requirements

7.6.4 Heating cycles

7.6.5 Instrumentation and control

 

CHAPTER EIGHT

Solder Reflow by Fluid Heat Transfer

8.1 Introduction

8.2 Heat transfer from a fluid

8.2.1 Heat transfer coefficient

8.2.2 Heat flow in the workpiece

8.2.3 Evaluation of heat transfer

8.2.4 Condensation heat transfer

8.2.4.1 Vertical and inclined surfaces

8.2.4.2 Horizontal surfaces

8.2.4.3 Cooling tubes

8.2.4.4 Workpiece surface condition

8.3 Properties of the heat transfer fluid

8.4 Vapour phase soldering

8.4.1 The soldering system

8.4.2 The primary fluid

8.4.2.1 Fluid chemistry

8.4.2.2 Heat transfer properties

8.4.2.3 Solder reflow properties

8.4.2.4 Operating power requirements

8.4.2.5 Resin flux solubility

8.4.2.6 Thermal degradation—toxicity

8.4.2.7 Thermal degradation—corrosivity

8.4.2.8 Consumption of fluid

8.4.3 The secondary fluid

8.4.4 Production vapour phase systems

8.4.4.1 Heating

8.4.4.2 Condensing

8.4.4.3 Secondary injection

8.4.4.4 Fluid filtration

8.4.4.5 Cycling process control

8.5 Liquid phase soldering

8.5.1 Comparison of heat transfer in liquid and

vapour

8.5.2 Practical tests of liquid phase soldering

 

CHAPTER NINE

Other Attachment Methods

9.1 Introduction

9.2 Hot-plate solder reflow

9.2.1 Heat conduction through the workpiece

9.3 Local conductive heating

9.3.1 Single-lead soldering

9.3.2 Multiple-lead soldering

9.3.3 Collet soldering

9.3.4 Resistance soldering

9.3.5 Local heat conduction in a workpiece

9.4 Local hot gas soldering

9.5 Laser soldering

9.5.1 The laser

9.5.1.1 The physical mechanism

9.5.1.2 The Nd:YAG laser

9.5.1.3 The carbon dioxide gas laser

9.5.2 Selecting the laser for SMT

9.5.2.1 Efficiency of heating

9.5.2.2 Power levels and pulse duration

9.5.2.3 Damage to the board

9.5.2.4 Fluxless soldering

9.5.2.5 Multiple beam laser soldering

9.5.3 The laser-soldering system

9.5.4 Practical soldering with a laser

9.5.4.1 Application of solder

9.5.4.2 Laser beam angle

9.5.5 Joint metallurgy

9.5.6 Intelligent laser soldering

9.5.7 Desoldering and repair by laser

9.5.8 Summary of advantages of laser soldering

9.5.9 Laser safety

9.6 Assembly with adhesives

9.6.1 Conductive adhesives

9.6.2 Application of the adhesive

9.6.3 Adhesive curing

9.6.4 Strength of conductive adhesive joints

 

CHAPTER TEN

Solderability

10.1 Introduction

10.2 Wettability

10.2.1 Speed and degree of wetting

10.2.2 Surface tension

10.2.3 Thermodynamics of wetting

10.2.4 Liquid meniscus shapes

10.3 Wetting by solder

10.3.1 Effect of solder alloy

10.3.2 The rôle of surface composition

10.3.3 Effect of surface roughness

10.3.4 Hysteresis of wetting

10.3.5 Degrees of wetting

10.3.6 The phenomenon of de-wetting

10.3.7 The need for a flux

10.4 Time-variant changes in wettability

10.4.1 The rôle of solderable coatings

10.4.2 The ageing process

10.4.3 Intermetallic compound growth

10.4.3.1 Cooling and solidification

10.4.3.2 Intermetallic phases

10.4.4 Growth of intermetallic phases in contact with solid Sn or Sn-Pb

10.4.4.1 Copper substrate

10.4.4.2 Other substrates

10.4.5 Growth of intermetallic phases in contact with liquid Sn or Sn-Pb

10.4.6 Effect of the intermetallic layer on solderability

10.4.7 Dissolution of terminations in molten solder

10.4.8 The oxidation and corrosion of solderable surfaces

10.4.9 Accelerated ageing treatments

10.4.9.1 Relative humidity

10.4.9.2 The relevance of accelerated ageing tests

10.5 The assessment of solderability

10.5.1 Solder dip method

10.5.2 Area-of-spread test

10.5.3 Meniscus shape method

10.5.4 The wetting balance

10.5.4.1 Theoretical wetting force

10.5.4.2 Interpretation of wetting balance curves

10.5.4.3 Wetting balance for surface mounting components

10.5.4.4 Scanning mode wetting balance

10.5.5 The globule balance

10.5.5.1 Globule size

10.5.5.2 Specimen-solder contact

10.5.5.3 Restriction of solder rise

10.5.5.4 Thermal response of globule block

10.5.5.5 Comparison between globule balance and wetting

balance

10.5.6 Rotary dip method

10.6 Surface of standard solderability

10.7 Movement of components during soldering

10.7.1 Floating and swimming of components

10.7.2 Tombstoning of components

 

CHAPTER ELEVEN

The Solder Fillet

11.1 Introduction

11.2 Metallurgy of the solder

11.2.1 Tin

11.2.2 Tin-lead alloys

11.2.3 Strength properties of solder

11.2.4 The phase diagram

11.2.5 Diffusion reactions

11.2.6 Cooling curves

11.2.7 Alloying and impurity elements

11.3 Fatigue in solder joints

11.3.1 Prediction of fatigue life

11.3.2 Origin of fatigue in solder joints

11.3.3 Fatigue mechanisms of solder

11.3.4 Fatigue life of leadless ceramic chip carriers

11.3.5 Effect of frequency and hold time

11.3.6 High frequency fatigue

11.3.7 Effect of solder fillet geometry

11.3.8 Effect of substrate material

11.3.9 Effect of solder alloy

11.3.10 Effect of joint microstructures

11.3.11 Effect of temperature

11.3.12 Effect of test conditions

11.3.13 Choice of failure criterion

11.3.14 Validity of fatigue-life predictions

11.3.15 Fatigue conditions of solder joints in service

 

CHAPTER TWELVE

Post-assembly Operations

12.1 Cleaning

12.1.1 To clean or not to clean?

12.1.2 Effects of contamination

12.1.2.1 Corrosion

12.1.2.2 Leakage currents

12.1.2.3 Coating de-bonding

12.1.2.4 White residues

12.1.2.5 Insulating contact surfaces

12.1.3 Solubility

12.1.3.1 Dissolution

12.1.3.2 Solubilisation

12.1.3.3 Flux solubility

12.1.3.4 Metal abietates

12.1.3.5 Solubility parameter theory

12.1.3.6 Solvent temperature

12.1.3.7 Surface wetting by solvents

12.1.3.8 Capillary penetration

12.1.3.9 Shear stress cleaning

12.1.4 Cleaning with organic solvents

12.1.4.1 Azeotropic systems

12.1.4.2 Chlorinated solvents

1 2.1.4.3 Fluorinated solvents

12.1.5 Aqueous cleaning

12.1.5.1 Water-soluble flux removal

12.1.5.2 Aqueous removal of rosin flux

12.1.6 Cleaning techniques

12.1.6.1 Liquid solvent cleaning

12.1.6.2 Vapour solvent cleaning

12.1.6.3 Spray solvent cleaning

12.1.6.4 Ultrasonic agitation

12.1.6.5 Water cleaning

12.1.7 Cleaning considerations specific to surface mounted

assemblies

12.1.8 Measurement of cleanliness

12.1.8.1 Techniques for contamination assessment

12.1.8.2 Levels of ionic contaminants

12.1.8.3 Levels of non-ionic contaminants

12.1.8.4 Insulation resistance tests

12.1.8.5 Permissible ionic contamination

12.2 Inspection of soldering quality

12.2.1 Visual inspection

12.2.1.1 Classification of defects

12.2.1.2 Chip component solder fillets

12.2.1.3 Leaded component solder fillets

12.2.1.4 Leadless chip carrier solder fillets

12.2.2 X-ray inspection of solder joints

12.2.3 Laser inspection of solder joints

12.2.4 Scanning acoustic microscopy

12.2.5 Evaluation of solder joint inspection

12.3 Post-assembly testing

12.3.1 A testing strategy

12.3.2 Test efficiency

12.3.3 In-circuit testing

12.4 Rework and repair

12.4.1 Reworking solder fillets

12.4.2 Replacing components

12.4.2.1 Heated collet

12.4.2.2 Hot gas

12.5 Protective coatings

12.5.1 Protective concepts

12.5.1.1 Conformal coatings

12.5.1.2 Non-conformal coatings

12.5.1.3 Potted coating

12.5.2 Methods of application

12.5.3 Types of coatings

 

CHAPTER THIRTEEN

Quality and Reliability

13.1 Introduction

13.2 Reliability behaviour

13.3 Reliability functions

13.3.1 Random failures

13.3.2 Wear-out failures

13.4 Accelerated assessment of reliability

13.4.1 Ageing mechanisms

13.4.2 Thermal acceleration

13.4.3 Temperature-sensitive parameters

13.4.4 Electrical acceleration

13.4.5 Damp heat acceleration

13.5 Practical reliability

13.5.1 Component reliability

13.5.2 Assembly reliability

13.5.3 Zero-hour quality

 

CHAPTER FOURTEEN

Economics and Trends

14.1 SMT growth

14.1.1 Growth of infrastructure

14.1.2 Growth of technology

14.2 Economics of SMT

14.2.1 Manufacturing costs

14.2.2 Assembled system costs

14.2.3 Increased sales potential

14.2.4 The economic decision

14.2.5 Introducing SMT

14.3 Trends

14.3.1 Surface mounting components

14.3.2 Surface mounting technology in Europe

14.3.3 Surface mounting technology in Japan

14.3.4 Surface mounting technology in USA

14.4 The challenge of surface mounting technology

 

 

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 Page last revised 11.02.05

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