best practices factory

Pb-Free Workshop © Ronald C. Lasky, Timothy Jensen 2003

Implementing Pb-Free Assembly at Your Factory

Ronald C. Lasky, Ph.D., PESenior Technologist Indium Corp

Visiting Professor, DartmouthTimothy Jensen

Indium CorpFeb 2004

Slide #1 Pb-Free Workshop © Ronald C. Lasky, Timothy Jensen 2003

Agenda• Pb-Free World Status• Alloy Selection• Getting Your Facility Ready: Best Practices• PWB and Component Finishes• Solder Paste Pre-Screening• Overview of Motorola Implementation• Large Board and Wave Soldering Issues

All slides available at www.pb-free.com


Dr. Ron Lasky• Native of Binghamton• Graduate of BCC, Cornell,

BU, Cornell– PhD in materials science

• NYS Professional Engineer• More than 20 years in

electronic and optoelectronic packaging at IBM, Universal Instruments, Cookson(Alpha)

• Author of 5 books• Currently a Senior

Technologist for Indium and a Visiting Professor at Dartmouth College


Electronics: Still the Largest Industry

• Holding at $1 trillion– Bigger than automotive– But Food?

• $170/yr x 6 billion > $1 T

• Typical long term growth is 6-8% CAGR– Vs 2-4 % for economies in good times– Early 2000s down slightly


All assembled on 30-35K lines!

The Electronic Industry: $1.1T

Military, $89 Automotive, $52

Industrial and Medical, $113

Consumer, $123

Communications, $300

Computer, $429

Source: Prismark


Courtesy Prismark


System Cost: $1K PC

Connectors: 3%:

Housing and I/O: 16%

Discretes: 4%

ICs: 27%

Assembly & Test: 14%SGA & Profit: 16%Distribution: 14%R&D: 2%

Substrates: 4%

Solder: 0.05%!Source: Prismark


What is a Printed Circuit Board (PCB)?• Starts with a PWB• Solder Paste is printed• IC, passive, active

components are placed

• Reflow melts the solder• The finished PCB is

tested• Thru hole assembly may

also be performed

Source: The Internet


Cross Section of a PQFP Component

The silicon die is the heart of electronics, it produces all ofdigital and analog functions. The material and leads that enclose the die are called the package. The resulting device called a component, a component package or a semiconductorpackage.

Courtesy:Prismark

1.2 centsper lead

Silicon DieMolding CompoundNitto Denko

8 cents

Wire BondedTanaka

18 cents

LeadframeShinko

91 cents

Die Attach AdhesiveAblestik0.4 cents

1.2 centsper lead

Silicon DieMolding CompoundNitto Denko

8 cents

Wire BondedTanaka

18 cents

LeadframeShinko

91 cents

Die Attach AdhesiveAblestik0.4 cents


• The relentless size reduction of passives

• Assembling the 0201 is one of the current process challenges

• A trillion assembled each year

Source: The Internet


PWB Assembly

Pick and Place

Reflow OvenChip Shooter

Hand Mount and OptoWave or Selective

SolderInspection/Test

Stencil Printer

Sources: DEK, UIC, Electrovert


Pb-free Initiatives & Global Trends


Current Pb-free Legislation

• WEEE/ROHS directives

• Japanese Home Electronics Recycling Law

• USA? Some state activity, nothing federal– EPA: ‘Deal with Electronics or We Will’


Pb-free Legislation• EU Ratifies WEEE / ROHS directive

– Dec 2002 EU parliament passed legislation to ban use of:

• Pb, Hg, Cd, Cr VI, PBB, PBDE– Affects ALL products sold after July 2006.

• Exceptions– Telecom equipment until 2010– High lead solder applications (>85% lead alloy)

– Recycling program enforced June 2005.


Pb-free Legislation• Japanese Pb-free Activity

– No direct ban on using Pb– MITI proposed recycling legislation in May 1998.– Japan home electronics recycling law requires

OEMs to collect and recycle 4 major products since April 2001.

– These measures, as well as marketing advantage, are pushing major Japanese companies to be more environmentally conscience


Japanese Pb-free Products

• Matsushita / Panasonic announcement– By March 2003 – Over 70 million PCBs

(approximately 12,000 product models) will be built using a Pb-free solder.

• Products have been built in over 100 different factories


MJ70 Minidisc Player MJ30 Minidisc Player

Panasonic Pb-Free Examples


H845L Camcorder PC Audio Board, Flora 220CX

Hitachi Pb-Free Examples


Is Pb-Free a good thing?


True or False

• Electronics is a major contributor to environmental lead. ⇒FALSE

– Batteries: 4,000,000 tons– Bullets: 200,000 tons– Electronics: 18,500 tons < 0.5%– Not to mention tire balancing weights!

• About 100,000 tons/year


True or False

• The level of lead in the blood of US residents has increased since 1945 ⇒ FALSE

• Paint and gasoline reductions have had a stunningly positive effect.


Average US Lead Levels in Micrograms per Deciliter of Blood

0

5

10

15

20

25

30

1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995

Year

Pb( µ

g/dl

)


Pb does Leach• Pb Leach Testing

– Use water with a pH of 7-7.05– Pb will not leach very much at this pH

• In acid water, Pb does leach• After all, we banned Pb from

plumbing for good reason• However, no measurable results in a

“real life” experiment


Pb-Free Solder Alloys

• Present alloys chosen to replace Sn/Pb are Sn/Ag/Cu alloys

• Ag-containing Solders also Leach – EPA Groundwater Leaching Tests

• ALL Pb-free silver-containing solders fail– “Lead-free Solders: A Push in the Wrong Direction?”

Ed Smith, K-Tec Inc.– “Reliability & Leachate Testing of Pb-free Solder

Joints” – Thomas Woodrow, Boeing


Pb-Free Solder Alloys

• Silver containing replacements – Are we taking a wrong turn?

• Silver is toxic• Silver is a biocide• Silver is known to kill more than 650 different viral,

bacterial and fungal organisms• Also, Silver will kill most marine life


Pb-Free Initiative Summary

• Simply changing from SnPb to SnAgCu may not fix the problem

• Recycling must be the long term answer• Expect more legislation and higher landfill costs in

the years to come!

Despite the data, Pb-free solder in the Electronics Industry is going to happen…


Pb-Free Alloy Selection


Alloy Selection Overview

• Potential Alloy Overview• General Alloy Search• Sn/Ag/Cu in Depth


Alloy Decision Process• The melting point should be as close to

Sn/Pb eutectic as possible• The alloy must be eutectic or very close to

eutectic• It must contain no more than three

elements• Use of existing patents should be avoided

to ease implementation• Reliability should be equal or better than

Sn/Pb Edwin Bradley – NEMI chairperson, Motorola


Options

• Current Alloy List• Alloy properties• Pros & Cons of each


Options: Current Alloy List

– Sn/Ag– Sn/Cu– Sn/Ag/Cu– Sn/Ag/Cu/Sb

– Sn/Ag/Bi/X– Sn/Sb– Sn/Zn– Sn/Bi


Options: Current Alloy List

– Sn/Ag– Sn/Cu– Sn/Ag/Cu– Sn/Ag/Cu/Sb

– Sn/Ag/Bi/X– Sn/Sb– Sn/Zn– Sn/Bi


Scientific Realities: 91Sn/9Zn• Melting point = 199°C• Zinc reacts with both acids and bases• All flux/vehicles are mildly acidic at room

temperature• Which means shelf-life is in the order of

days, not months!• Also may need conformal coating once in

place - Zn oxidizes very readily


Scientific Realities: 96.5Sn/3.5Ag• Melting point = 221°C• Years of experience• Relatively poor wetting• Poor thermal cycling (-40/+125)

A1 Sn 3.5Ag 12 12 1282 1987 8A11 Sn 4Ag 1Cu 14 14 2340 2552 3A14 Sn 4Ag 0.5Cu 14 14 2108 2579 5A21 Sn 2.5Ag 0.8Cu 0.5Sb 14 14 2378 2378 2A32 Sn 4.6Ag 1.6Cu 1Sb 1Bi 15 15 2161 2161 4A62 Sn 3.4Ag 1Cu 3.3Bi 14 14 1864 2527 6A66 Sn 3.5Ag 1.5In 14 14 2387 2577 1B63 Sn/Pb Control 13 13 1845 2607 7

Alloy Code Composition Rank# on

Test#

Failed

1st Failure (cycle)

Last Failure (cycle)

Source: NCMS


Scientific Realities: 58Sn/42Bi• Melting point = 138 °C• Years of experience• Poor shock resistance• 1% Ag addition strengthens this alloy• Low MP eliminates temperature issues

with components and board


Scientific Realities: Sn/Ag/Cu• Melting Point = 217°C• Cu improves wettability, creep, thermal

fatigue• High solderability & reliability


Scientific Realities: Sn/Ag/Cu/Sb• Melting point = 215 – 217°C• 0.5% Sb may strengthen alloy• May be considered for wave soldering by

effectively lowering Ag content• Patented composition may limit worldwide

availability• Four part alloy makes manufacturing

consistency less reliable.


Scientific Realities: Sn/Ag/Bi• Melting Point = 210 - 215 °C• Bi lowers melting point & improves

wettability of SnAg alloys• Avoid using in presence of Pb:

• a 96°C ternary alloy(Sn/Pb/Bi) may form


Pb-free Alloy Investigation

• Phase 1: DOE to analyze 10 probable alloy solutions using Sn/Pb as Benchmark

• Phase 2: Optimize flux chemistry


Alloy Performance Investigation

Alloy Solidus Liquidus

63Sn37Pb 182.1 183.096.5Sn3.5Ag 219.7 220.899.3Sn0.7Cu 225.7 227.0

95.5Sn3.8Ag0.7Cu 216.3 217.593.6Sn4.7Ag1.7Cu 215.9 217.1

96.2Sn2.5Ag0.8Cu0.5Sb 216.9 218.291.7Sn3.5Ag4.8Bi 202.1 215.190.5Sn7.5Bi2Ag 190.6 214.7

58Bi42Sn 136.3 138.595Sn5Sb 238.3 240.3

89Sn8Zn3Bi 190.6 195.4


Pb-free Alloy Investigation

• 5 Individual studies performed– Wetting– Shelf life– Tack time– Solder Ball– Visual reflow inspection

• Performance ranked 0-10 for each category


Print paste (offset)

Reflow

Cu pad

Solder bump

Unwetted Cu

70%

spread

R&D Test #1: Wetting


40%

4

50%

5

70%

7

Wetting Examples


R&D Test #2: Shelf Life

SLI Description0 Overall instability > 25%2 Overall instability = 20-25%4 Overall instability = 15-20%6 Overall instability = 10-15%8 Overall instability = 5-10%10 Overall instability = 0-5%

Shelf life was based on the percentage change in viscosity over time. The length of the test

was 30 days.


Time

Tack

00

0 2

86

4

10

R&D Test #3: Tack Stability


SBI Number of solder balls0 Did not reflow1 > 501, with some reflow2 401-5003 301-4004 201-3005 151-2006 101-1507 51-1008 21-509 11-2010 0-10

R&D Test #4: Solder Balling


Alloy Investigation- Results

1. Sn63/Pb372. Sn91.7/Bi4.8/Ag3.53. Sn90.5/Bi7.5/Ag24. Sn95.5/Ag3.8/Cu0.75. Sn42/Bi586. Sn93.6/Ag4.7/Cu1.7

7. Sn99.3/Cu0.78. Sn96.2/Ag2.5/Cu0.8/Sb0.59. Sn95/Sb510. Sn96.5/Ag3.511. Sn89/Zn8/Bi3


BAD

BEST

2

6

10

R&D Test #5: Visual


Winner- Sn/Ag/Bi ???

• Bi addition lowers melting point & improves wetting

• BUT……..Concerns with• Fillet Lift• Low temperature ternary alloy

formation with Pb contamination


50

75

100

125

150

175

200

225

250

Sn-3.8Ag-0.7Cu

Sn-2Ag-2Bi Sn-2Ag-4Bi Sn-2Ag-7.5Bi Sn-10.5Bi Sn-12Bi

0%Pb3% Pb6% Pb

Ons

et T

emp,

deg

. C

Sn-Bi-PbPeritectic Sn-Bi-Pb Eutectic

Sn-Pb-AgEutectic

Pb Contamination ConcernsWhy Bi alloys are not the short-term solution


Ref: Zequn Mei, Fay Hua, and Judy Glazer, “SN- BI- X SOLDERS”, SMTA International, San Jose, CA, Sept. 13- 17, 1999.

Sn/Ag/Bi on Sn/Pb Finish

Sn/Ag/Bi with Pb contamination after 1 reflow

Sn/Ag/Bi with Pb contamination after thermal cycling


Ref: “Lead-Free Solder Project Final Report”, NCMS Report 0401RE96 , August 1997.

Sn/Ag/Bi Fillet Lift


Bismuth Alloy Summary

• Sn-Ag-Bi alloys show formation of: – Eutectic 96C phase at Bi > 10.5%Bi– Peritectic 135C phase Bi > 4%Bi

In the presence of Pb.• Sn-Ag-Cu alloys show formation of:

– Eutectic 179C phase.• Wetting occurs at liquidus, so it is key melt

temp variable.• PCB finish can affect wetting temperature due

to base metal diffusion into solder.


ConclusionPb-free Paste - SnAgCu

• Challenges:– higher processing temperatures– wettability– must wet to a variety of metallizations


NEMI Alloy Summary• NEMI Chosen Alloy

– 95.5Sn/3.9Ag/0.6Cu– 217 C liquidus

• Pb-Free is now driven by both market factors and now legislation

• SnAgCu preferred short/medium term solution– NEMI, JEITA, IDEALS all agree on Sn/Ag/Cu

• When components become completely Pb-Free, SnAgBi may become preferred solution– Lower process temp– Excellent wettability


Eutectic of Sn-Ag-Cu soldersB. Boettinger, K. W. Moon of NIST performed studies to determine the true Sn-Ag-Cu eutectic.

Alloys in shaded area have freezing range <10°C.

0 0.5 1 1.5 2 2.5wt% Cu

0

1

2

3

4

5

6

7

8

wt%

Ag

250 C

230 C

270 C

220 C

230 C 270

C

290

C

250

C

230

C

310

C

Estimation of Ternary Liquidus Surface, 10/23/99 Based on Marquette saturation data, with NWU and NIST thermal analysis.

Ag3Sn

Cu6Sn5

SnNIST experimental work showed that the composition is approximately Sn3.5Ag 0.9Cu. (+/- 0.1%) (In agreement with Loomis and Fine)


Relative Material Costs

• Sn $5.06/kg• Zn $1.06/kg• Cu $1.94/kg• Bi $5.63/kg• In $250.00/kg• Ag $180.00/kg• Sb $1.75/kg• Pb <$1.00/kg


Pb-Free Cost

• All the lead-free alloys are more expensive than the lead-containing alloys– Raw material costs are higher– Currently there is no economy of scale– Minimal Production experience

compared to Sn/Pb powder production


Which SAC to Use?

• Melting Point Comparison• Wetting Comparison• Long Term Cost Comparison


DSC of Actual Samples fromSolder Vendor A

216.67 °C216.54 °C216.65 °CAverage

216.75 °C216.35 °C216.71 °CSample 3

216.56 °C216.38 °C216. 49 °CSample 2

216.70 °C216.89 °C216.76 °CSample 1

95.5Sn/3.8Ag/0.7Cu

95.5Sn/4.0Ag/0.5Cu

96.5Sn/3.0Ag/0.5Cu


IPC DSC Comparing SAC305 Suppliers

216.0 °C217.25 °C223.45 °CAverage:

216.0 °C216.7 °C220.3 °CSample 2:

216.0 °C217.8 °C226.6 °CSample 1:

Supplier 3Supplier 2Supplier 1

Source: IPC-SPVC-WP-006


Comparing the Wetting Forces

Difference in wetting per J-STD test procedure not statistically significant between SAC alloys.

Source: IPC-SPVC-WP-006


SAC Actual Wetting

Source: CEMCEX2003 Seelig et al


Long Term Relative Costs

• Sn/Pb = 1x• SAC305 = 2.15x • 95.5Sn/3.8Ag/0.7Cu = 2.3x• SAC405 = 2.35x


Alloy Summary• Sn/Ag/Cu (SAC) is the best current option• Sn/Ag/Bi worth consideration is Pb

contamination is not an issue.• Sn/Bi doped with 1% Ag could be a viable

option for assemblies with tight temperature restrictions.

• SAC305 ranks slightly higher than other SAC alloys due to cost and performance.


Getting Your Facility Ready: Pb-Free Implementation

Best Practices


Pb-Free Best Practices• Assess Yourself

– Crucial with Pb-free• Throughput Maximization• CIP• Process Software to Help• Use the Right Tools

– Statistical Thinking– DOE– SPC


An SMT Process

ActivitiesPeople

Materials

Equipment

Procedures

ProductRequirements

A Product

MeetsRequirements

•On time•Under cost


Assessment Categories

• DFM, Process and Equipment• Materials Supply and Validation• DOE, SPC, CIP• Training and Failure Analysis• Developed from pooled information

from industry experts


DFM, Process and EquipmentRanking Key: 0 = strongly disagree or don't know , 3 = disagree, 5= neutral, 7 = agree, 10 = strongly agree

1 10

2 8

3 3

4 9

5 9

6 9

7 9

8 Our process engineers have a disciplined and proven strategy to improve quality: 9

9 3

10 9

Total Score out of 120 98

Ratings:World Class = > 95Above Average = 75 - 94Average = 55 - 74Below Average < 55

Your score places you as "World Class" in DFM, Process and Equipment for SMT assembly. Your clearly recognize the importance of these topics in your assembly processes. This score still offers some opprotunity for improvement. Look at your results on each question and develop an action plan for improvement if appropriate.

The engineer(s) responsible for component placement knows how to balance and optimize the placement equipment. He assures that this operation is performed on all jobs: The engineer in charge of the reflow process assures that the reflow profile matches the solder paste specification:Our process engineers have a disciplined and proven strategy to improve productivity:

Our process equipment is "qualified" with a test and evaluation procedure that is founded on DOE principles:

There is a process engineer or team of engineers responsible for implementing new processes and technology:

We have a documented and functioning DFM system that includes design ground rules (DGRs). Our entire organization is strongly committed to DFM. DFM is a way of life (this question counts 3 times): Our DGRs are established by using designed experiments and statistical process control:

The process engineers know how to run all of the equipment:

The engineer(s) responsible for stencil printing knows how to design a stencil


Materials Supply and ValidationRanking Key: 0 = strongly disagree or don't know , 3 = disagree, 5= neutral, 7 = agree, 10 = strongly agree

1 0

2 8

3 5

4 7

5 7

6 4

7 4

8 The type (i.e. 2, 3, 4, 5) of the solder paste we use matches the application requirement: 4

9 6

10 6



We evaluate our solder pastes and/or materials with a systematic evaluation procedure, such as "The 12 Board Paste Evaluator" (shown below) or DOE to assure its performance (this question counts 3 times): My engineers have read and understand the solder paste and materials specs and assure they match our use conditions:The response to pause of my solder paste is adequate for my applications:

The cost of my solder paste and/or materials is not the main criteria for its purchase:

Your score places you below average among users of SMT materials. This position offers overwhelming opportunities for improvement. Look at your results on each question and develop an action plan for improvement. Your organization has an urgent need to recognize that evaluating your solder pastes and materials is a most important activity.

The printed volume consistency of my solder paste is best of breed:

My materials supplier(s) understand(s) my process and business needs, we treat each other like partners:

Few, if any end of line defects can be traced to inadequacies of my solder paste and/or materials:

Our organization has a systematic method to assure that the materials/components for future jobs are being prepared while current jobs are being run:Our organization has a systematic method to assure that we have an uninterrupted supply of materials from our vendors:


DOE, SPC, CIPRanking Key: 0 = strongly disagree or don't know , 3 = disagree, 5= neutral, 7 = agree, 10 = strongly agree

1 3

2 8

3 2

4 2

5 5

6 9

7 9

8 9

9 8

10 8



We measure our unscheduled downtime:

We measure our line efficiency:

Your score places you as average in DOE, SPC and CIP for SMT assembly. This position offers significant opportunities for improvement. Look at your results on each question and develop an action plan for improvement. Having an effective CIP program is vital for success.

We measure our work in process time:

We know our process's Cp and Cpk:

We have a statistical process control program and use the resulting data effectively to monitor and improve our processes:

Quality is everyone's job:

Productivity is everyone's job:

Our process engineers use designed experiments to optimize our processes and evaluate equipment and materials:

We have a continuous improvement plan that is effective, uses metrics, and is recognized as valuable by the entire organization (this question counts 3 times):We measure our process uptime:


Training and Failure AnalysisRanking Key: 0 = strongly disagree or don't know , 3 = disagree, 5= neutral, 7 = agree, 10 = strongly agree

1 9

2 8

3 5

4 3

5 8

6 4

7 4

8 4

9 6

10 6



Your score places you as above average in Training and Failure Analysis for SMT assembly. This score still offers considerable opportunity for improvement. Look at your results on each question and develop an action plan for improvement, if appropriate.

Our operators cannot change the process equipment's operating parameters:

Our engineers know and use analytical problem solving and brainstorming techniques to perform failure analysis:

There is a process line escalation policy that is understand by all (e.g. if the line is down and remains down this information gets escalated in a documented fashion):

We can perform failure analysis or vend this task out:

Our staff has all ot the tools necessary to perform their jobs:

Our process engineer's yearly performance review is related to process improvement goals:

Our organization has a sophisticated training program for all levels of our staff (this question counts 3 times):

Our engineers understand the difference between common cause and special cause failures and use this knowledge in process troubleshooting:Our engineers use sophisticated modeling tools, like StencilCoach, Reflow Coach and LineBalancer to help them model processes and perform "what if" analysis:Management uses costing tools like ProfitPro to perform financial "what if" analysis, before making financial investments in equipment etc:


Line Level Metrics Line Efficiency (%) First Pass Yield (%)

20

4060

80100

GoalStart

96

9798

99

100

Goal

Start

9594

Line Uptime (%)

40 50 60 70 80 90 100

WIP (hrs)

7 6 5 4 3 2 1


But No Matter What You do, Have a CIP

• Assess yourself• Establish/Measure Metrics

– Paste Volume– Productivity Metrics– Pareto Defects

• Monitor Success/Develop Action Plan

• Fix the Problems


Software Tools to Help• In addition to AuditCoach™• Stencil Coach™

– Helps design stencils including PIP• WaveCoach™• LineSimulator™

– Simulates entire line, much easier than Arena®

• ReflowCoach™


Stencil Design: StencilCoach™

Calculations Recommendations: PW=1-3+ P/2

W = PW - 2 to 3

AR= W/t > 1.5

Pitch Pad Width PW Aperture W Stencil Aspect ARRectangular Aperatures (P - mils) (PW - mils) OK? (W -mils) OK? Thickness Ratio OK?

(t - mils) (AR)50 26 TRUE 23 TRUE 6 3.833 TRUE 325 15 TRUE 12 TRUE 6 2.000 TRUE 320 12 TRUE 10 TRUE 5 2.000 TRUE 316 10 TRUE 8 TRUE 5 1.600 TRUE 412 8 TRUE 6 TRUE 4 1.500 TRUE 435 19 TRUE 17 TRUE 6 2.833 TRUE 3

Recommendations: PW=0-2+ P/2

D = PW - 2 to 3

ArR=D/4t >0.66

Pitch Pad Dia Pad Dia Aperture D Stencil Area ArRCircular Aperatures (P - mils) (PD - mils) OK? Diameter OK? Thickness Ratio OK?

(D-mils) (t-mils) (ArR)40 21 TRUE 19 TRUE 5 0.95 TRUE 3

Solder Paste Type

Solder Paste Type

Aperture Width > 4-5 particle diameters

Aspect Ratio = W/t > 1.5

Aspect Ratio

t

W

Area Ratio

D

t

Aopening= πD2/4Awall=πDt =>ArR=D/4t

Circular Aperture Diameter > 8 particle diameters

ArR = D/4t > 0.66


Pin-in-Paste

Inputs OutputsSolder Pad Diameter (mils) 76 V = 2Vf +Vh-Vp Cubic Mils

Pin diameter mils 18 Vf 17585.147PTH diameter mils 30 Vh 40997.784PWB Barrel Length mils 58 Vp 14759.202Paste Reduction Factor 0.52 V 61408.876

Solder Paste Volume Needed 118093.992

If Pin is Square…... Stencil MetricsLength - mils 18 Stencil Thickness - mils 7Width - mils 22 Side: If Square Aperture - mils 129.887Equivalent Pin Dia mils 22.454 Radius: If Round Aperture - mils 73.281

Rectangular? If First Side is (mils): 80Second Side should be (mils: 210.882

Instructions: Tstencil metricscomponent inCells D32-33 aor stencil ape

Vf

Vp

Vh

Vsolder= 2Vf + Vh - Vp

Vf= Fillet Volume (Pappus-Gu

Vh= PWB Hole Volume

Vp= Pin Volume


Time 265Temp 240

Time-s 0 90 140 190 230 250 295 325Temp-C 30 100 150 209 217 230 217 120

Thruput CalculatorTunnel Length cm 249 Thruput Bds/min 2.84 Obeys Lee Dwell Criteria? YesBelt Speed cm/min 71 Profile Time (min) 3.51Product Length cm 20Product Spacing cm 5

Time

Tem

pera

ture

217

C

ReflowCoachTM


Ramp Up to 217 C

0

50

100

150

200

250

0 50 100 150 200 250 300 350 400

Time (seconds)

Tem

pera

ture

(C)

Lower LimitUpper LimitUser Profile


Time Above Liquidus

215

220

225

230

235

240

245

250

255

260

0 20 40 60 80 100

Time (seconds)

Tem

pera

ture

(C)

User ProfileHi RampLow RampTemp MaxTemp MinTime MinTime Max


Ramp Down

120

130

140

150

160

170

180

190

200

210

220

290 295 300 305 310 315 320 325 330

Time (Seconds)

Tem

pera

ture

(C)

Low RampHi RampUser Profile


The Tools to Do the Job Right

• Statistical Thinking• DOE• SPC


ParetosHistograms

CommonCauses

SpecialCauses

ProcessVariation

ControlCharts

Statistical Thinking

Ref: Sheri Flori


Statistical Thinking…The Case of the Squirrel

• The greatest birder in MA was being harassed by squirrels

• It was a crisis• Even squirrel proof

feeders designed by NASA wouldn’t work

• We needed to apply BMT!


So I Got Serious

A Crossman BB/Pellet Gun


X

X

The first shot with BBs.What should I do?


X

X

The second shot.

X


X

X

The third shot andfourth.

X

X

X

What is it telling me?


X

X

I try pellets.

XX

X

What is this telling me?


Accuracy and Precision• Accuracy: How close

to the measured.• Precision: How

repeatable• Examples of:

– Poor accuracy and precision (BB’s)

– Good precision, poor accuracy (pellets w/ bad sighting)

TargetValue

MeasuredValue

Accuracy

Repeatability(Precision)


USLLSL

USLLSL

LSL USLProcess Variation = Lost $

Ref: Sheri Flori


Common Cause• Natural, expected variation• Controllable• What are examples of CC

in calibrating the pellet gun

Special Cause• Unnatural, not expected• Possible examples in pellet gun calibration

Types of Variation

Knob twiddling can correct neither!


An SMT Electronic Assembly DOE Example


Score

Random Variation =Variance: Sr

2

Average = 82N

umbe

r of R

ound

s

Random Variation:Dr. Ron Golf Scores


Tiger’s Scores Dr. Ron

∆= Differencein averages

Implies that there is a greater difference between Tiger and Dr. Ron, than among them ∆2 >> Sr

2

Num

ber o

f Rou

nds

STiger

Variation from Factors: Tiger vs Dr. Ron

SDr. Ron

8268


For example: Phil Mickelson and David Toms. Then, ∆2 << Sr

2

∆

Num

ber o

f Rou

nds

Score

Sr

When Variation from Factor Change is Small…….


DOE Uses ANOVA• ANOVA (Analysis of Variance)

– Compares S2 to ∆• The F Statistic:

• Large F => factors have a significant effect on result

• “Large” varies with sample size, typically > 4 for 95% confidence

2

2

rSF ∆

∝


A Good Stencil Print

*Illustrations courtesy of MPM Corporation


High Speed UFP Printing

• The objective is to perform High Speed Ultra-Fine Pitch Stencil Printing.

• Print speed, separation speed and wipe frequency need to be minimized to reach this goal.

• Target is 8 second cycle time with current cycle time >20 seconds


1010

00

55

LOADLOAD SEPARATESEPARATEPRINTPRINTVISIONVISION UNLOADUNLOAD

21.8 sec.

WipeWipe

Cycle Time Breakdown

• 10 inch wide board printed at 1 inch• 2 s Load + 2 s Vision + 10 s Print + 5 s Separate + 1.8 s Unload + 1 s Wipe = 21.8 sec


1010

00

55

LOAD SEP.PRINTVISION UNLOAD Wipe

Cycle Time Breakdown

Objective:1.8 s Load + 1.8 s Vision + Print + Separate + 1.5 s Unload + Wipe < 8sec


Factors• A: Print Speed: 1=4, 2=6, 3=8 inch/sec• B: Separation Speed: 1 = 1, 2 = 1.5 sec• C: Wipe Freq: 1= 1/8, 2= 1/12

– 1/8 adds 0.875 sec, 1/12 adds 0.6 secs

• D: Stencil Type: 1= Efab, 2 = Laser• E: Paste: Vendor A =1, Vendor B =2• Full Factorial• Assume no interactions• Aperture: W= 8, t= 5, L= 64 mils=>2560 mils3

• Desire paste volume to be +/- 10% of aperture volume

• Response: Solder Paste Volume

Number of Runs:3x2x2x2x2=48Not that many!


Source DF Seq SS Adj SS Adj MS F P

Print Sp 2 175117 175117 87558 2.48 0.096

Separati 1 104533 104533 104533 2.97 0.093

Paste Ty 1 559008 559008 559008 15.86 0.000

Stencil 1 274519 274519 274519 7.79 0.008

Wipe Fre 1 902008 902008 902008 25.60 0.000

Error 41 1444731 1444731 35237

Total 47 3459917

For stencil and paste, we can reject H0 with confidence. Hence, we can select

the better choice for each of these factors and re-experiment to optimize total speed.

MiniTab Results

Minitab is available Free for 30 days atMinitab.com!


SPC and Variables Data

• Data relating to a specific process step

• Quantitative• Can be used to monitor and improve

process performance• Example: Solder Paste Volume• Variables data are crucial for an

effective SPC Plan


Process Data: Attribute Data• Data that relates to the

performance of the product

• Examples:– Shorts– Opens– Missing Component

• Important, but cannot be measured to improve process performance

• Any plan should strive to relate attribute data to variables data and develop a CIP around this relationship

0

50

100

150

200

250

300

350

Shorts Opens MissingCompnent

Solder Balls

Pareto Attribute Data


Variables Data Example

Solder Paste Volume Solder Paste Volume

Shor

ts

Ope

ns

Lower Spec LimitUpper Spec Limit

= Average


Variables Data: Solder Paste Volume

LSL USL

Solder Paste Volume

Proc

ess

Occ

urre

nces

LCL UCL


Control Chart for SPC

Sigma 3

Sigma 2

Sigma 1

Sigma 1

Sigma 2

Sigma 3

UCL

LCL

Centerline

USL

LSL


Solder Paste ASolder Paste B


2001000

1900

1800

1700

1600

Xbar and R Chart

Subgr

Mea

n5

1

5

Mean=1750

UCL=1898

LCL=1602

600

400

200

0

Ran

ge

22

R=255.9

UCL=541.0

LCL=0

200190180

Last 25 Subgroups1950

1800

1650

1500

Subgroup Number

Valu

es

21001400

Capability PlotProcess Tolerance

III

III

IISpecifications

Within

Overall

200017501500

Normal Prob Plot

220017001200

Capability Histogram

WithinStDev:Cp:Cpk:

1101.061.06

OverallStDev:Pp:Ppk:

111.6341.051.05

Process Capability Sixpack for Print VolumePaste B


2001000

2050

1800

1550

1300

Xbar and R Chart

Subgr

Mea

n

1

1

111

66111

66151111

51

6

11156

11155

1

521

22

1

2222

1

2212

1

2

8

5 6115111

2

15111656

1

15

1

6

1

2

1

1211

11

11

8

165

611

622

1

61

6611

62

11

6

1

6512

1

5

155

1111

5116222

1

2

112

Mean=1750

UCL=1898

LCL=1602

1500

1000

500

0

Ran

ge 1

1

1

111111222

1

1

2

1

211

1

11111

12

1

1

1111

11

2

1

1

21111

2

1

2

1

1211

2

112222111

11111

2

111111

2

111

1

112

1111

21122

122

1111

2

1

11

222

1

22122

1

1

11

111

21

1

112

1

2

1122

1211

2

1

2

11

22222

111

12

1

2

1

21211

11

22

1

2

1

22111

2

1

22

111

212

1

2

11

222112

1

2112

R=255.9

UCL=541.0

LCL=0

200190180

Last 25 Subgroups2500

2000

1500

1000

Subgroup Number

Valu

es

21001400

Capability PlotProcess Tolerance

III

III

IISpecifications

Within

Overall

26001600600

Normal Prob Plot

25001500500

Capability Histogram

WithinStDev:Cp:Cpk:

1101.061.06

OverallStDev:Pp:Ppk:

273.1520.430.43

Process Capability Sixpack for Print VolumePaste A


Best Practices Summary

• Assess Yourself• Use Metrics• Develop and Implement Action Plan• Monitor Success• Continuously Improve


Pb-Free Board/Component Finishes

Board Finishes– Immersion Ag– OSP– Electroless Ni/Immersion

Au– Immersion Sn

Component Finishes– Sn/Pb– 100% Sn– Pd/Ag– Ni/Pd– Ni/Sn– Ni/Au– Ni/Pd/AU

Pb Contamination and ability to withstand the higher reflow temperatures are the main concerns.


Component Finishes: Pure Sn

• Easiest and most obvious choice• Sn Whiskers still a major concern• So TI recommends Ni/Pd/Au


Structure of PbStructure of Pb--Free Free PreplatedPreplated FinishesFinishes

PALLADIUM: MINIMUM OF 3u”

NICKEL: 40 - 60 u”

Pd / Ni STRIKE: < 5 u”

Ni STRIKE: < 5 u”

COPPER BASE METAL COPPER BASE METAL

NICKEL: 20 - 80 u”

PALLADIUM: 0.2-6.0 u”

GOLD: 30-150 ANGSTROMSNiPd finish: Past

• NiPdAu structure shown has been in use since early 1990s.

• Enhanced wetting performance with NiPdAu finish seen in solderability tests.

• See TI Application Note SZZA026 for complete evaluation of NiPdAu finish.

NiPdAu finish: Present

Courtesy: James Huckabee, TI


NiPdAuNiPdAu (SOP) Board Mount: Visual Appearance(SOP) Board Mount: Visual Appearance

Visual Appearance Results: All solder joints exhibited a heel fillet height at least one times the lead thickness and evidence of wetting to the sides of the leads. This performance would be considered acceptable for all 3 classes of products identified in IPC-A-610C (general electronic products, dedicated service electronic products, and high performance electronic products.

Typical wetting NiPdAu finished SOP components with SnPbAg solder, NiAuPWB finish.

Typical wetting NiPdAu finished SOP components with SnAgCu solder, NiAuPWB finish.

Courtesy: James Huckabee, TI


PWB Surface Finish Summary

Hazard to Manufacture

Availability

Cost (To HASL)

Wire Bonding

Contact Connections

Fine pitch quality

Thickness (microinches)

LowHighLowModerateHigh

LimitedVery LimitedHighModerateHigh

1X1X0.3X2X1X

LimitedNot Recommended

Not RecommendedLimitedNot

Recommended

GoodGoodNot RecommendedGoodFair

ExcellentExcellentExcellentExcellentPoor

3 - 1240 – 608 - 20Au: 3 - 8

Ni 50 - 150100 – 1000

ImAgImSnOSPENIGHASL


2006 Finish Estimations

Projections courtesy of Enthone, Cookson ElectronicsAdditional slides available at www.pb-free.com


Immersion Ag

• Low Cost• Planar Surface• Compatible with touchpads /

solderless connections (if thicker Ag is used)

• 2 – 10 microinches typical thickness

Additional slides available at www.pb-free.com


ImAg Issue #1: Tarnish

• Just like Ag silverware, this finish will yellow over time– Will occur during assembly– Often, purely cosmetic

• Solderless connections appear very tolerant of tarnish

• Thicker Ag less prone to tarnishAdditional slides available at www.pb-free.com


ImAg Issue #2: Migration

• The presence of moisture and current can cause the migration of Ag ions

• Migrate from cathode to anode forming dendrites that reduce resistance…may eventually form a short



ImAg Issue #2: Migration

*graph from www.alphametals.com

NO SIGN OF DENDRITIC GROWTH


ImAg Issue #3: Premature Intermetallic Failure



ImAg Issue #3: Premature Intermetallic Failure

• Thick Ag finishes tarnish less and are more compatible with solderlessconnections, but…– Thick Ag means more organic co-deposit– Organic co-deposit must be forced out of

molten solder– Non-expulsion of organics can result in

microvoids along board/solder intermetallicAdditional slides available at www.pb-free.com


Pb-Free Solder Paste Evaluation: Pre-Screening

Since there are 10-20 solder paste suppliers, it is essential to narrow down the Pb-free candidates prior to actual physical

evaluation


Lot-to-Lot Viscosity Stability


Typical Pb Contamination

Pb Content Must be less than 0.05%


Pb-Free Reliability

• Surface Insulation Resistance– Test procedure in J-STD-004– 7-day test to determine if flux residue with

affect electrical reliability• Electromigration

– Test procedure in Telcordia GR-78– 21-day test for electrochemical migration


Pb-Free Supplier Support

• Assess your company needs against supplier capabilities.– Are they available globally?– Are they available locally?– Can they accommodate changing

requirements?


Pb-Free Solder Paste Evaluation: Printing through Reflow


Solder Paste Screen Printer64%

Incoming Components6%

Reflow15%

Component Placement15%

Approximate Distribution of Process Related Defects


Evaluating the Pb-Free Print Process: Four Main Paste Variables

• Viscosity Relative to Production Temperature

• Stencil Life• Response to Pause• Resistance to Excessive Shear

Thinning


Effects of ViscosityToo High

• Poor rolling• Blade Hang-up• Aperture clogging• Insufficients

Too Low

• Excessive deposit• Solder balling• Solder beading• Slumping• Bridging


Viscosity Vs. Temperature


Inspired by: MPM

Solder Paste Stencil LifeTack Life

-6

-5

-4

-3

-2

-1

0

1

2

3

4

0 5 10 15 20 25 30

Time (hrs)

Del

ta T

ack

Forc

e (g

ram

s/m

m2)

Brand XGood Paste


Effects of Short Stencil Life

• Variability in solder paste deposits• Loss of “up time”• Wasted paste, wasted money


Inspired by: MPM

Solder Paste Response to Pause

Response to Pause

0

5

10

15

20

25

30

35

40

45

50

0 2 4 6 8 10 12 14 16 18

Print Number

Volu

me

of P

rint (

cubi

c m

ils)

Brand XGood Paste

One Hour Pause


Effects of Poor Response to Pause

• Loss of up time• Paste deposition variability• Higher cost of “time for assists”


The Twelve Board Paste Evaluator

1. Start with enough paste for 12 prints2. Print 4 boards (no kneading)

3. Pause one hour, no kneading, print 4 more boards, repeat tests in 2

4. Pause one hour, no kneading, print 4 more boards, repeat tests in 2

Two hour sit, place,measure tack

Six hour sit, place,measure tack

1 Board, 1 hr sitthen reflow

1 Board, 3 hr sitthen reflow Repeat

Metrics to Measure:• Print Volume • Print Definition• Volume and Definition after Idle• Release from Aperture• Squeegee Hang up• Tack• Solder Joint QualityFor Final Candidates•Coalescence•Reflow Window•J Standards

The above is good, but should also test for shear thinning!


Solder Paste Resistance To Shear Thinning

0

10

20

30

40

50

0 60 120 180 240

Time (minutes)

Tack

(gra

ms)

Acceptable

Unacceptable


Effects of Excessive Shear Thinning

• Excessive deposit volume• Slumping• Bridging• Balling/Beading


Measuring Shear Thinning Effect• Often overlooked in solder paste evaluations.• Discovered once a solder paste is implemented into

production (too late).• Requires many print strokes, thus many boards to

discover.• One suggested technique:• 1. Place fresh paste onto stencil (Repeat for all pastes being evaluated)• 2. Set printer to run 30 knead strokes, wipe the underside of the stencil.• 3. Print one board• 4. Set printer to run 50 knead strokes, wipe the underside of the stencil. • 5. Print one board• 6. Set printer to run 100 knead strokes, wipe the underside of the stencil.• 7. Print one board• 8. Measure response variables on each printed board


Placement Capabilities: The Solder Paste Tack

• Should not be much different than standard Sn/Pb solder pastes

• Suggested evaluation technique:1. Using fresh paste, print three boards2. After 8 hours, place components onto one board3. After 24 hours, place components onto the second board4. After 48 hours, place components onto the third board5. Compare the results and determine which solder paste

lost more components, during the placement process, at each time interval


Evaluating Pb-Free Reflow• Most analyzed aspect of transition to pb-

free.• Primary Pb-free reflow response variables:

– Wetting– Appearance– Voiding– Solder Balling– Tombstoning

• Critical Evaluation Criteria:– Time above liquidus (TAL)– Peak temperature– Soak time


Pb-Free Profile VariablesReflow Profile for Indalloy #241

95.5Sn/3.8Ag/0.7Cu

0

50

100

150

200

250

300

0 1 2 3 4 5

Time (Min)

Tem

pera

ture

(C)

MP = ~217 C

Reflow Profile for Indalloy #24195.5Sn/3.8Ag/0.7Cu

0

50

100

150

200

250

300

0 1 2 3 4 5

Time (Min)

Tem

pera

ture

(C)

MP = ~217 C

Soak Zone TAL

PEAK


Reflow DOE

250 °C240 °C230 °CPeak Temp.

80 Sec.60 Sec.40 Sec.TAL

3 minutes2 minutes1 minuteSoak Time

HighMiddleLow

Are 27 profiles realistic with multiple solder pastes?


Categorizing the Response Variables

• Potential defects need to be ranked according to each individual process.– Which is more critical to the process?

• Probe testability• Residue color and quantity• Etc.

– Which is more detrimental to the product?• Voiding• Tombstoning• Bridging• Etc.


Analyzing the Overall Results

• 60 – 70% of all defects are attributed to the stencil printing process.– Should be considered the most important

for overall process consideration• Reflow is a new crucial variable for

Pb-Free– Not necessarily an issue for paste– Critical for components and boards


Paste Evaluation Summary• Pb-free transition requires a knowledge of

statistics and DOE to have a successful implementation.

• Pre-screening of solder pastes necessary to make evaluation practical in size.

• Printing and reflow require careful analysis to adequately distinguish between solder pastes.


Motorola Pb-Free CellphoneAssembly

Courtesy: Vahid Goudarzi, Motorola


Motorola’s Process Criteria• Paste must have good response to pause,

tack, slump and other printing metrics• The process/paste must show good

coalescence and solder joint quality in a broad reflow process window

• The reliability of the finished product must be as good or better than the standard Pbsolder

• The process must be simple and robust so that it can be transferred to other locations world wide


Paste Evaluation/Manufacturing Process Development

• Screen Printing Evaluation • Reflow Profile Development • Tackiness Measurement• Surface Insulation Resistance

(SIR) Evaluation


Lead-free solder paste suppliers & materials

A3B3

A1B1C1

A2B2C2

Phase # 1 Phase # 2 Phase # 3ABC

Paste Suppliers

Flux Vehicles

Paste evaluation & selection strategy:Work with 8 preferred paste suppliers to develop a lead-free solder paste that meets Motorola’s manufacturing quality & product reliability requirements

These studies were completed using Sn/Ag/Cu, Entek finish boards, & air atmosphere

Pb-free Solder Paste Evaluation

The Finalists:


Optimum Print Speed, Squeegee Pressure, & Snap Off was set per paste supplier recommendation and validated

Stencil Printing Evaluation• Objective: To ensure Pb-free paste

performs consistently as a function of time

• Variables:– Abandon time @ t=0, t=1, & t=4 hours– Solder paste (A1, B1, C1, A2, B2, C2, A3, B3)

• Output:– Volume measurement using laser system– Visually inspect for smearing and selected

apertures for clogs.


Selected Inspection SitesBased on gage R&R results

RSC

CSR

ABCDEF

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 171 819 2 02122 23 24

1 2 3 4 5 6 7 8 9 10 1112 13 14 15 16 171 81 9 20 21 22 23 24

OSP Finish Test Vehicle for Paste Evaluation


Pb-free Solder pastes performed well @ abandon time = 0h

Solder Paste Volumetric Measurement or 12 mils SMD pads @ t=0 h

200

300

400

Paste C1 Paste B3 Control All PairsTukey- Kramer

0.05

Vol

ume

Paste C2 Paste A1Paste B1


Paste C2 failed @ abandon time=1h

100

200

300

400

Paste B1Paste B3 Control All PairsTukey-Kramer

0.05

Vol

ume

Paste C1 Paste C2 Paste A1

Solder Paste Volumetric Measurement for 12 mils SMD pads @ t=1 h


Reflow Profile Development

• Objective: To determine reflow process window & identify a Pb- free paste which requires MINIMUM peak temp.

• Variables:– Peak temperature– Time above liquidus– Solder Paste (A1, B1, C1, A2, B2, C2, A3, B3)

• Output:– Coalescent performance– Solder joint quality


Pb-free 2X3 Full Factorial Reflow DOE• Minimize peak temp. to reduce thermal stress on Components• Interaction between peak temp. & time above liquidus

60Sec. 70Sec. 80Sec.

229C

237C

245C

Time Above Liquidus

Peak Tem

perature

Peak temp

Time above liquidus

Ramp rate

Lead-free reflow profile

P1

P2

P3

P7P4

P5

P6

P8

P9

Selected paste MUST perform equally well @ P1 through P9 in air atmosphere

Reflow Profile Matrix


Inspection criterion:Coalescent performance @ P1,P2, P3, P4, P5, P6, P7, P8 &P9

Poor Coalescent Good CoalescentPoor coalescent is attributed to powder oxidation during reflow

process in air atmosphere

Reflow Profile Development Cont.


Poor Solder Joint

Insufficient toe fillet

Good Solder Joint

Inspection criterion:Wetting performance @ P1,P2, P3, P4, P5, P6, P7, P8 &P9

Insufficient toe fillet results in field reliability issues

Reflow Profile Development Cont.


Flux Tackiness Measurement• Objective: To ensure flux provides sufficient

tackiness to hold components in place during manufacturing processes

• Variables:– Paste life @ t=0;t=1h t=2h; t=4h; t=8h – Pb-free solder pastes

• Output:– IPC-TM- 650 Test Procedure: Measure the force

required to Separate a 5mm diameter probe from paste– Shake Test -Automated vision inspection after

placement


IPC650 Tack Test - Tack test evaluation result

Tack Test

0

0.5

1

1.5

2

2.5

0 1 2 4 8

Time (Hrs)

Tack

(g/m

m2) Indium 51A

Indium 92JIndium 232-99-2Indium SMQ 230

Tack Test

0

0.5

1

1.5

2

2.5

0 1 2 4 8Time (Hrs)

Tack

(g/m

m2)

Control #1Control #2B1B3

Flux Tackiness Measurement Cont.


1) Populated PCBs after 0, 4, and 8 hours

2) Image components to determine X, Y, and Theta offsets.

3) Place PCBs on XY table of Chip Shooter & shake PCBs for 120 Sec.

4) Image components to determine X, Y, and Theta offsets

5) Determine delta for before & after shake process

0-1

23

0

-3

12

1

1

-1

21

0

10

-1

1

-4 -2 0 2 4 6

caps

switch

tantalum

caps

3.2x1.6

resistor

X-Offset Y-Offset Theta

Component placement offset after 120 second of shaking by chip shooter

Flux Tackiness Measurement Cont. To ensure flux provides sufficient tackiness to hold components in place during assembly process


Surface Insulation Resistance

Supplier B Surface Insulation Resistance Test

24 72 120 168 216 264 312 360 408 456Hours

Ohm

s Channel 1

Channel 11

Channel 21

Channel 153

Channel 163107

109

Motorola SIR Test Boards = B25 Test Board + Solder mask

SIR requirements is minimum of 10 8 Ohms


Printing PasteVisual Inspection

Volumetric data

ReflowP1,P5,P9

P1,P2,P3,P4,P5,P6,P7,P8,&P9

TackinessInstron IPC650

Shake Test

QualitySolder Joint

ALT

SIRJ-STD B25

Motorola

NT

NT

NT NT

NT NTNTNT

NTNT

NTNT

NTNTNT

NT NTNT

NTNT

NTNT

NT NT

Passed Failed NT Not tested

NTNT

NTNT

NTNT

NT

NT

Paste B3 met all requirements

Paste Final Evaluation ResultsPaste

A1PasteC1

Phase 1Paste

A2PasteC2

Phase 2PasteB3

PasteA3

Phase 3Paste

B1Paste

B2


Solder Coalescent Comparison @ P1, P5, & P9

B3

@

P1

B3

@

P1

B3

@

P5

B3

@

P5

B3

@

P9

B3

@

P1

B3

@

P1

B3

@

P1

B3

@

P1

B3@P1

B3

@

P5

B3@P9P9

B3@

P5

Good Coalescent

Supplier B paste

A1@P 1

A1@P5

A1

P9@

Poor Coalescent

Supplier A Paste

Paste A1 does not fully coalesce and result in grainy joint due to powder oxidation in air atmosphere

Paste Final Evaluation Results Cont.


No significant difference in solder joint fillet @ P1, P5, & P9 usingB3 solder paste

Lead-free @ P1(229;60)

Lead-free@ P9(245;80) Leaded @ 210 C

Lead-free @ P5(237;70)

Paste Final Evaluation Results Cont. Solder Joint Evaluation @ P1, P5, & P9


B3@P1

B3@P5

B3@P9

Sn/Pb

Solder Joint Evaluation @ P1, P5, & P9

No significant difference in solder joint fillet @ P1, P5, & P9 usingB3 solder paste

Paste A1

Insufficient toe fillet

Paste Final Evaluation Results Cont.


Intermetallic formationPaste Final Evaluation Results Cont.

P1 P5

P9

0.0023 mm 0.0025 mm

0.0025 mm


Recommened 235C profile

0

50

100

150

200

250

300

0 1 2 3 4 5 6 7 8

Time/min

Tem

p/C

Ramp 0.7 deg/sec

Peak 235CTime above 217C: 70s

Peak Temp. = 235 C +/- 5C; Time Above Liquidus = 70Sec +/ 10Sec

Recommended Profile for B3


Product Level & Solder Joint Reliability Evaluation

• Drop Test

• Shear Test

• Liquid-to-Liquid Thermal Shock

• ALT for different Products

Reliability Evaluation

Pb free solder joints MUST perform equal or better than leaded solder joints


1) Dropping products from 5 feet 2) Vert. & horiz.vibration for 2 hrs3) Thermal shock for 48 hrs4) Repeated step 1 thru. 3 X times 5) Measure % joint cracks on shields

Drop Test

Shield solder joint cracking is significantly reduced using B3

Pb-free radios

Shie

ld 1

Shie

ld 2

Shie

ld 3

Shie

ld 4

Shie

ld 5

Shie

ld 6

Shie

ld 7

0

5

10

15

20

25

% of crack

05

10152025

Shie

ld 1

Shie

ld e

2Sh

ield

3Sh

ield

4Sh

ield

5Sh

ield

6Sh

ield

7

Leaded radios

% of crack

Drop test vehicle

Shields

Reliability Evaluation Cont.


0.5mm CSP CSP

SOIC

0.5mm Conn.

BGA

0.5mm QFP

0.75mm CSP

0.8mm CSP

20X40 Cap.

DIME

0.5 mm CSP

• 6X6 mm Package size • 0.5 mm pitch partial array • 0.3 mm solder balls size

Solder Joint Reliability Evaluation Test Vehicle



•0

•1

•2

•3

•4

•5

•6

•7

•8

•9

•10

•Ceramic•Inductors

•Tantalum

•Capacitors

•Small

•Capacitors

•Ferrite Bead •Mid-size

•capacitors

•She

ar a

t fai

lure

(kg)

•[afte

r the

rmal

sho

ck]

•SnPb

•SnAgCu

Shear Test

No significant difference in shear force after LLTS.



Variables:- Solder Paste (Paste B3 & Pb Paste)- Component Type ( 0402, 0603, 0805, BGAs, CSPs, VCO,

Transformer)

Output:- Electrical test at every 75 cycles for 450 cycles- Red dye analysis at 150, 300, and 450 cycles

Liquid-to-Liquid thermal shock evaluation (-55 °C to +125 °C)



Failed Joint

Passed Joint

Failed Joint

Red dye evaluation result

No significant difference in cracked area in leaded and Pb-free joints

Cra

ck a

rea,

%

-25

0

25

50

75

100

125

Pb-free Sn-Pb

Solder

All PairsTukey-Kramer 0.05

Joint crack data for different components

Liquid-to-Liquid thermal shock results after 450 cycles



Products Built with Pb-free Paste

* i1000 iDEN

* Concorde iDEN

* i1000 Charger

* i700 iDEN

* i85 iDEN

Products built with Pb-free solder paste and passed ALT


Manufacturing Issues• Tombstone Failures

• Air Voids on CSPs

• Logistics: Have a Plan to Avoid mixing SnPb and Pb-free Assembly


20X40 Tombstone FailuresLead-free Solder paste is more prone to tombstone failures due to higher coalescent force.

T1 T2T3 T3T4

T5

Before Reflow After Reflow

T1 & T2 : Tack ForceT3 : WeightT4 : Surface Tension (outside)T5 : Surface Tension (underneath)

T4 is significantly higher using lead-free solder paste

Manufacturing Issues Cont.


Blind Via

Tombstone failures are attributed to lead-free solder paste & blind vias

20X40 Tombstone Failures

Pads without blind vias did NOT show tombstone failures



20X40 Pad Design for Conventional PCB

Stencil design to minimize tombstone failures on pads with blind vias

.047"

.015" .018"

C .022"

.007"

.008"

.011"

0402 Stencil Aperture Openings

A*.041"

Evaluated Circle, ½ Circle, Rectangular (vertical & horizontal),Oblong, square stencil, etc.



Tombstone / floating Failures

Paste volume was reduced to eliminate tombstone failures on large discrete inductors



• 6X6 mm Package size • 0.5 mm pitch partial array • 0.3 mm solder balls size

Voids

DIME

0.5 mm CSP

Air voids on CSPsManufacturing Issues Cont.


Voids Mechanism in CSPs1) Solder bump oxidation 2) Flux out gassing



Air voids on CSPsBGA/CSPs are more prone to voids mainly due to leaded bumps on package & increased oxidation of powder due to higher reflow temp.

Variables:- Ramp Rate- Solder Paste

Outputs:- Number of voids- Void size

Paste B3

Solder Pastes

Ram

p Rate (D

eg./Sec.)

0.5

0.8

1.5

Paste #15 Paste #16

CSPs CSPs CSPs

CSPs CSPs CSPs

CSPs CSPs CSPs



Void Quantity VS. Ramp Rate

• Quantity of voids are not significantly affected by ramp rate• B3 shows significant reduction in void size as ramp rate increases

Air Voids in CSPs joints

5

10

15

20

25

0.5 Deg/sec 0.8 Deg/sec 1.5 Deg/sec

_ID_

All PairsTukey-Kramer

0.05

10

15

20

25

30

0.5 Deg/Sec 0.8 Deg/Sec 1.5 Deg/Sec

Ramp Rate

All PairsTukey-Kramer 0.05

Average V

oid Size (% of joint)


Void Size VS. Ramp Rate


Coalescent Performance Comparison

Pb-free Paste has a significantly higher Coalescent force

Pb-free Joint&Component Appearance4) Joint & Component Appearance

Pb Before Reflow

Pb Paste Before Reflow

Pb paste printed onto Cu coupon

Pb free Paste Before Reflow

Pb free paste printed onto Cu coupon

Pb Paste After Reflow

Pb paste fused onto Cu coupon Pb free paste fused onto Cu coupon

Pb free Paste After Reflow


PasteB3 Control(Pb)

Solder Joint Comparison


Shield Discoloration

Leaded reflow profile Lead-free reflow profile

SnO & SnO2 is formed after lead-free reflow process.

Oxidation does not affect electrical performance

Pb-free Joint &Component Appearance Cont.


Solder Paste Selection - Evaluated 19 different Pb-free solder pastes and selected B3 based on manufacturing and product level reliability requirements.

Manufacturing processes - Reflow profile, screen printing operation, tackiness evaluation, etc. completed

Reliability Evaluation - Pb-free solder joint reliability evaluation has shown equal or better performance compared to current materials

Components - 100% of the components Pb-free qualified

Electrical & Mechanical - 100% completed with NO issues

Quality - No manufacturing/product quality issues; DPHU goal were met

Motorola Pb-Free Implementation Summary


Motorola Pb-Free Summary

•Production since 09/04/01

•Many site implementation

•More than 1M cell phones have been shipped to the field

• No field reliability issues have been encountered


Wave Soldering and Large Board Issues


Lead-free Complex Board• Functional units were assembled using current materials,

equipment set and a no clean Pb-free solder paste

Pb-free thermal profile• linear heating ramp – 0.9 °C/s• average peak temperature - 247

°C• dwell time – 75s above 217 °C• Courtesy: Eddie Hernandez, HP

mid-range server board • materials

– surface finish: Ni/Au– board resin: hi Tg FR-4 resin– current component

technologies


Large Board Summary• Higher delta T on board => higher

peak T = 245oC– Reflow profiling and control much more

important• DOE needed for Process

Optimization• NiAu and OSP were successful• Similar manufacturing issues to

Motorola


Wave Soldering

• Must use SAC, not SnCu– SnCu does not process well and can cause

Tin Pest• Process Control is crucial


Transformation of Beta-Tin into Alpha-Tin in Sn-0.5Cu at T <10oC

Ref: Y. Karlya, C. Gagg, and W.J. Plumbridge, “Tin pest in lead free solders”, Soldering and Surface Mount Technology, 13/1 [2000] 39-40


Wave Soldering Overview

Fluxer

Preheating (IR) Preheating (IR) Exhaust

Laminar WaveChip Wave

Conveyor

Air KnifePreheating (CVX) Preheating (CVX)

CoolingFan

Inspired by Steve Breed, Speedline


The Process• Angle of Conveyor:

Typically fixed at 6o

• Conveyor Speed: – Thermal Mass Dependent – 150 cm/min typical

• Flux: According to Specs!• Preheat parameters:

– Too hot =>drives off flux– Too cool => no activation– Temp Rqmts depends on flux

type

• Wave Form– Don’t use chip wave if you

don’t have chips!

• Depth of Immersion: 50%• Solder Purity: Monitor

Monthly• Solder Temperature:

260oC


Adequate Fluxing is Crucial• Follow the flux and

sprayer specifications to assure coverage with in spec

• Measure coverage with a fluxometer

http://www.ecd.com/emfg/instruments/fluxometer/index.asp


Time

Tem

pera

ture

183

C

Board Bottom

Board Top

WaveEntrance of Wave:>100oC Alcohol Flux>120oC Water Flux

“KIC”: PWB Temp Profile

∆T<140oC

Ramp Rate: 2-4oC/s


WaveCoach™ can Help

Time (sec) 0 90 150 170 200 Conveyour Speed (m/min)Temp Top -C 30 70 90 Length of Waves (cm)Temp Bottom 120 235 160

Time in Wave (s) 3.86 PWB Bottom ∆T 115.00 Cool Down Rate (C/s) 2.50 PWB Bottom T at Wave 120.00 PWB Top T at WaveWithin Spec? FALSE FALSE TRUE TRUE

Results

Time

Tem

pera

ture

183

C

Board Bottom

Board Top


The Contour Wave FormPWB pulls solder over exit

Courtesy: Electrovert


Calculating:The Dwell Time

• Dwell time (DT) related to conveyor speed (CS) and “length” of wave (LW).– DT = LW/CS

• LW = 3 “, CS= 5’/min– What is DT?

• Use LevCheck™– Glass with grid


Optimizing the Process1. Setup the Fluxer2. Establish pre-heat

profile3. Set the contour

wave to just pull solder over the exit wing• Only use chip wave

if you have chips

4. Set depth of immersion at 50%

5. Monitor solder purity monthly• Alpha “Pot Rite”

program6. Set Solder

Temperature7. Set Dwell Time


Thanks for Coming!

Documents

best practices factory