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Your Transition to Lead Free

Book Description
Our industry is making one of its most challenging and evolutionary steps in going from SnPb to Pb free products. The issues are many and they must be well understood to avoid costly mistakes or misspoken statements. In this course you will learn the most critical pieces about the transition to Pb free. It is the most extensive and broadest coverage of this topic available anywhere.

The transition to Pb free first starts with understanding the directives and global trends. Then learn about the possible alloy replacements, their pros and cons along with the environmental considerations and reliability; each backed up with testing and data. The PWB finishes are dealt with in detail covering a wide range of optional finishes. That is followed by what the effects are of intermixing different board finishes, PWB plating types and solder alloys: addressing both forward and backward compatibility. Next, another important topic, tin whiskers are explained in a detail not seen anywhere else. Now you are only half way through!

The next section gets into failure modes such as CAF, causes and solving tombstoning and voids, Pb free printing issues, Pb free reflow profiles (old compared to new recommendations) and how they relate to a variety of defects during reflow that can be solved by making slight changes. Learn what Motorola gained from extensive testing such as drop tests. Finally one more very important topic is covered, wave soldering. It covers topics such as tin pest, tin corrosion, fluxing, setup and the optional pin in paste process.

Table of Contents

Chapter 1	9
Pb-free Initiatives and Global Trends
1.1 What is the Industry Size?	10
1.2 What is the Industry Breadth?	10
1.3 What you do is important	10
1.4 Where is the Market?	11
1.5 How about Electronics and the Environment?	11
1.6 A Major Change?	11
1.7 What is the WEEE Directive?	12
1.8 List the Categories of Electronics Included	12
1.9 What is the RoHS Directive?	13
1.10 List the Categories of Electronics Included	13
1.11 What are the RoHS Exemptions?	14
1.12 So what does this mean?	14
1.13 What are some of the Logistical Concerns?	14
1.14 What are the steps you can take?	15
1.15 What about China RoHS?	15
1.16 What about USA RoHS?	15
1.17 What are Japanese “Green” Products?	16
1.18 Why is Pb-free is only a piece of RoHS Compliance	16
Chapter 2	17
Pb-free Alloy Selection
2.1 Solder as it is Today	18
2.2 List the Desirable Pb-free Characteristics	18
2.3 List the Pb-free Paste Options	18
2.4 What is the impact on Paste Costs?	19
2.5 What are Drop-in Solutions?	19
2.6 List some of the Pb-free Paste Options	20
2.7 What is the problem with 91Sn9Zn?	20
2.8 What is the problem with 96.5Sn3.5Ag?	21
2.9 How about SAC Alloys?	21
2.10 How about SnAgCuSb?	22
2.11 How about 58Sn42Bi?	22
2.12 How about SnAgBi?	22
2.13 What are the SnAgBi Concerns?	22
2.14 What looks like the Industry Choice?	24
2.15 What are the SAC Concerns?	25
2.16 What are the Things to Remember?	26
Chapter 3	27
Is Pb-free a Good Thing?
3.1 What are the Environmental Implications?	28
3.2 List the Sources of Environmental Lead	28
3.3 Why Target Pb in WEEE?	28
3.4 What about Pb-Free Solder Alloys?	29
3.5 What is The Decision?	29
3.6 Is Pb-Free a good thing?	30
Chapter 4	31
Pb-free Alloy Reliability
4.1 Why worry about reliability?	32
4.2 What about Thermal Cycling Performance?	32
4.3 What about Thermal Fatigue for BGAs?	33
4.4 What about creep?	34
4.5 What does Isothermal Mechanical Cycling include?	35
4.6 When is Out of Plane Bending a problem?	36
4.7 Describe Mechanical Shock?	37
4.8 Summarization of the technical considerations	38
Chapter 5	39
Pb-free Components
5.1 What do you need to know about Pb-free Components?	40
5.2 What are the Component Finish Options?	40
5.3 What about Sn Whiskers: Growth? 41
5.4 What about Sn Whiskers: Intermetallic Formation?	41
5.5 What is Copper Diffusion: Increasing Whisker Growth?	44
5.6 What is the Whisker Index?	44
5.7 Explain about Sn Whiskers: CTE Mismatch	45
5.8 What about Sn Whiskers: Other Causes?	46
5.9 What about Sn Whiskers: Mitigation?	46
5.10 What about Reliability of Various Component Finishes?	46
5.11 How to make the switch	47
5.12 How about Forward/Backward Compatibility?	47
5.13 What about Component Suppliers?	48
5.14 What are the Labeling Issues?	48
5.15 What are Other Component Concerns?	49
5.16 List Other Component Concerns	50
5.17 What is the Cost Impact?	51
Chapter 6	53
Pb-free Surface Finish
6.1 Why the Surface Finish Requirements?	54
6.2 What is the Industry Choice for Surface Finish?	54
6.3 What about Pb-free HASL? (Hot Air Solder Level)	55
6.4 What about ENIG? (Electroless Nickel Immersion Gold)	55
6.5 What about using OSP? (Organic Solder Preservatives)	56
6.6 What about using IAg? (Immersion Silver)	56
6.7 What about using ISn? (Immersion Tin)	57
6.8 Surface Finish Comparison	58
6.9 Summary of different finishes	59
Chapter 7	61
Failure Modes
7.1 What is Conductive Anode Filament Growth (CAF)?	62
7.2 What causes Tombstoning?	63
7.3 What are the Tombstoning Rates?	64
7.4 What can be done to Minimize Tombstoning?	66
7.5 What about Mixed Alloys?	67
7.6 What is Voiding?	69
7.7 How do the Alloys Compare for Voiding?	70
7.8 How can you prevent Voiding in Reflow?	71
7.9 What causes Voids in Vias?	72
7.10 What are the Inspection Issues?	74
Chapter 8	77
Implementation
8.1 What is the European Lead Free survey?	78
8.2 What about the ELFNET Survey?	78
8.3 What is the Current status of EU Pb-Free?	80
8.4 Where is a Pb-Free Readiness Assessment Tool?	81
8.5 What is the Pb-free RAT?	81
8.6 WEEE/RoHS Experts are valuable	84
8.7 What to Think about for your BOM?	84
8.8 How do you Work with your suppliers?	85
8.9 How to go about Choosing a new Paste?	85
8.10 What percent are RoHS compliant suppliers?	87
8.11 What are Homogenous Materials?	89
8.12 How do you do Planning for Review?	90
Chapter 9	93
Pb-Free Printing and Placement
9.1 What is the Approximate Distribution of Process Related Defects?	94
9.2 How Many Factors Affect your Print Quality?	94
9.3 What is Motorola’s Process Criteria?	94
9.4 How do you do a Paste Evaluation and Selection Strategy?	95
9.5 What items are Related to your Paste Selection?	96
9.6 What are Paste Responses?	96
9.7 What is the Paste Evaluation?	96
9.8 What’s the 12 Board Paste Evaluator?	97
9.9 What are the Effects of Viscosity?	97
9.10 What are the effects of Viscosity and Temperature?	98
9.11 What is the Motorola Flux Tackiness Measurement?	99
9.12 What is the effect on Solder Paste Stencil Life?	99
9.13 What are the Effects of Short Stencil Life?	99
9.14 What was the objective of the Motorola Stencil Printing Evaluation?	100
9.15 What was the results of Response to Pause Test?	100
9.16 What are the Effects of Poor Response to Pause?	101
9.17 How do you go about Measuring Shear Thinning Effect?	101
9.18 What is the Solder Paste resistance to Shear Thinning?	102
9.19 Why worry about Solder Balls in Passive Assembly?	102
9.20 What are Poor Gasketing results?	103
9.21 Why the Importance of Wall/Pad Ratio?	103
9.22 What changes for Stencil Design?	103
Chapter 10	105
Pb-Free Reflow
10.1 What is the Approximate Distribution of Process Related Defects?	106
10.2 What is crucial for Pb-free Reflow?	106
10.3 What are the (Old) RDRP Profiles?	107
10.4 What changes for the (New) Convection Ovens?	108
10.5 What is unique about the (Old) IR Oven Profile Design?	108
10.6 What is different about the (New) Convection Oven Profile Design?	109
10.7 What are the unique Profiles and Defect Mechanisms?	109
10.8 Explain Defect Mechanism Analysis 1	109
10.9 Explain Defect Mechanism Analysis 2	110
10.10 Explain Defect Mechanism Analysis 3	110
10.11 Explaining Defect Mechanism Analysis 4	111
10.12 Explaining Defect Mechanism Analysis 5	111
10.13 Explaining Defect Mechanism Analysis 6	111
10.14 Explaining Defect Mechanism Analysis 7	112
10.15 Explaining Defect Mechanism Analysis 8	112
10.16 Reflow Profile Summary	113
10.17 Recap of the Motorola Reflow Profile Evaluation	113
10.18 What was the Coalescence?	114
10.19 Compare Reflow Profile and Coalescence	115
10.20 How about the Wetting?	115
10.21 State Motorola’s Conclusion	116
Chapter 11	117
Pb-Free Reliability Issues
11.1 Understand the Reliability of Pb-free	118
11.2 What was the Motorola Reliability Evaluation?	118
11.3 What was the Motorola Test Vehicle?	118
11.4 What was the Motorola Drop Evaluation?	119
11.5 What was the Motorola Thermal Shock Evaluation?	119
Chapter 12	121
Pb-Free Wave Soldering & Alternative Soldering Methods
12.1 Which components get Wave Soldering?	122
12.2 List some Pb-free Wave Challenges	123
12.3 What is Tin Pest?	123
12.4 When does Tin Corrosion occur?	124
12.5 What are the industry Pb-free Wave Recommendations?	124
12.6 What is crucial about Fluxing?	125
12.7 List the Pb-free Wave Setup Rules of Thumb	125
12.8 How do you Calculate Dwell Time?	126
12.9 What is the Pin-in-Paste (PIP) Process?	126
12.10 What are the PIP Concerns?	126
12.11 How do you do the PIP Stencil Design?	127
12.12 What are PIP Stencil Design Steps 1 & 2?	127
12.13 What is PIP Stencil Design Step 3?	128
12.14 What is PIP Stencil Design Step 4?	128
12.15 Show some Common PIP Stencil Designs	129
12.16 Show a Poor PIP Stencil Design	129
12.17 What are Solder Preforms?	129
12.18 What are some PIP Considerations?	130
12.19 What to consider in PIP Solder Paste Selection?	130
12.20 What is an option for PIP Stencil Printing?	131
12.21 What about PIP Component Selection?	131
12.22 State the Pb-free Wave & Alternative Soldering Methods Summary	132

Authors:
Dr. Ronald C. Lasky, PhD, PE
Indium Corporation, Dartmouth College
Katherine Hickey, MEM, EIT
Neovention, Dartmouth College
Amish Peevasharn MS, EIT
Neovention, Dartmouth College
Pages: 235

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