Pb-Free Wave Soldering

Project

Denis Barbini, Vitronics Soltec,

ChairPaul Wang,

Microsoft, Co-Chair

APEX 2007

1

Phase I Project ParticipantsPhase I Project Participants

2

Denis BarbiniVitronics Soltec, Inc.Stratham, NH, USA

dbarbini@vsww.com

Paul WangMicrosoft, Inc.

Mountain View, CA, USApauwang@microsoft.com

Peter BioccaITW Kester, Inc.Allen, TX, USA

pbiocca@kester.com

Quyen ChuJabil, Inc.

San Jose, CA, USAquyen_chu@jabil.com

Tim DickCisco Systems, Inc.San Jose, CA, USAtidick@cisco.com

Denis JeanPlexus, Inc.

Neenah, WI, USAdenis.jean@plexus.com

Stuart LonggoodDelphi CorporationKokomo, IN, USA

stuart.e.longgood@delphi.com

Chrys SheaCookson Electronics, Inc.

Jersey City, NJ, USAcshea@cooksonelectronics.com

Keith SweatmanNihon Superior, Inc.

Nihon Superior Co., Ltd.Osaka, Japan

k.sweatman@nihonsuperior.co.jp

Mike YuenFoxconn, Inc.

Houston, TX, USAmike.yuen@foxconn.com

3

2007 iNEMI Wave Roadmap2007 iNEMI Wave Roadmap

Courtesy: iNEMI

4

Lead Free Wave Soldering Project GoalsLead Free Wave Soldering Project GoalsThis investigation looks to determine the impact of process parameters and materials on the wave

soldering process and solder joint formation.

This study aims to provide insight into the process issues that one will encounter so that arational implementation strategy for a robust lead free wave soldering process can be achieved.

The Phase I iNEMI Lead Free Wave Soldering Project focused on three critical areas: • Materials Selection

Fluxes, alloys, components, and board complexity.• Process Optimization

Defined “Window of Opportunity” based on flux amount, preheat temperature, contact time, soldertemperature, wave configuration, and atmosphere.

• Solder Joint Yield Defined failure levels and defect types using inspection criteria – IPC class 3 combined with best practices, yield determined by hole fill characterized by 5DX data analysis.

The result of Phase I is to lay the foundation for a broader effort to characterize thereliability of through-hole joints on a test vehicle specifically designed to test the norms andpractices used in tin lead wave soldering and develop new standards for lead free wavesoldering.

5

Getting StartedGetting Started““brainstormingbrainstorming””

Experimental design and execution

Equipment setup and data reporting

Materials

6

Design of Experiment for Phase IDesign of Experiment for Phase I• Taguchi Methodology Chosen

–Time and cost efficient for studying multiple variables.–DoE based on standard Taguchi L18 (21 x 37)orthogonal array.

• Variable Selection–Brainstorming to collect list of possible variables for wave solder process. This represented perspectives of many areas of assembly.–Review by team members to prioritize list.–Discussion and consensus vote to pick final selection.

Inner Array VariablesAtmosphere,

conveyor speed, preheat temperature,

flux quantity, flux type, chip wave,

solder temperature, board thickness

Outer Array Noise FactorsSAC 305, Sn100C, SACx, SnPb,

CuOSP finish,Pb-free HASL finish

7

Machine ConfigurationMachine ConfigurationDelta Wave Solder machineFluxer:Spray fluxer FC7 for Alcohol and OAFC16 for VOC free Pump supply system

Preheat configuration:Forced convectionForced convection Calrod Profiles Attributes

Flux amount and penetrationMass measurement and pH paperPreheating Temp:ECD Super Mole Contact Time:ECD Wave Rider

Solder pot configuration:Chip wave Main wave

Nitrogen:Inerting Blanket system betweenwaves: 30-50-80 l/min

8

Test Vehicle Test Vehicle ““SkateSkate””(Cookson Design)

No connection Shorter spokes on WW Longer spokes on WW Direct to ground plane(Cookson Design)

Board Specification–64 mil–93 mil–135 mil–CuOSP–HASL

Alloys–SAC 305–SACX–Sn100C–SnPb

Components–QFP’s, SOT, Passives–PCI, Berg Stick

9

Experimental ExecutionExperimental Execution

SpeedFt/min

(cm/min)1 5 N2 4.5 (138) med med OA on 255 0.0622 1 N2 3 (92) low low Water on 255 0.0623 16 Air 6 (183) low high Alcohol on 255 0.0944 12 Air 2 (61) high med Alcohol on 255 0.1355 14 Air 3.5 (107) med high Water off 255 0.1356 9 N2 6 (183) high low OA off 255 0.0947 10 Air 3 (92) low high OA off 265 0.0628 2 N2 3 (92) med med Alcohol off 265 0.0949 15 Air 4.5 (138) high low Alcohol on 265 0.062

10 7 N2 5 (152) low med Water on 265 0.13511 6 N2 4.5 (138) high high Water on 265 0.09412 17 Air 5 (152) med low OA on 265 0.13513 13 Air 4.5 (138) low med OA on 275 0.09414 4 N2 3.5 (107) low low Alcohol off 275 0.13515 8 N2 6 (183) med high Alcohol on 275 0.06216 11 Air 3 (92) med low Water on 275 0.09417 3 N2 2 (61) high high OA on 275 0.13518 18 Air 6 (183) high med Water off 275 0.062

Board Thickness

Flux Quantity

Flux Type

Chip Wave Solder Temp (°C)

Actual Run Order

DOE Standard

OrderAtmospher

e

Preheat Temp

Required for logistics reason

10

Data CollectionData Collection““working hardworking hard””

Bridging

Through Hole Penetration

11

Analysis: Bridging with SAC 305Analysis: Bridging with SAC 305

SAC 305 on SAC 305 HASL

Total shorts on HASL: 299

SAC 305 on OSP

Total shorts on OSP: 451

12

5DX Measurement Calculation5DX Measurement Calculation

Confirmed by select cross sectioning and typical X-Ray techniques

13

Through Hole Inspection CriteriaThrough Hole Inspection Criteria

No defect DefectS3-25%

DefectS3-25%S1-50%

DefectS3-25%S1-50%S4-75%

DefectAll Slices

DefectS2-0%

DefectS3-25%S1-50%S4-75%

DefectS4-75%

Void

14

AnalysisAnalysis““interestinginteresting””

Influence of process parameters and materials

Optimized Process

Confirmation

15

Occurrence of Bridging on QFPOccurrence of Bridging on QFP

16

Determination of Optimized Parameters for Minimal BridgingDetermination of Optimized Parameters for Minimal BridgingSm

alle

r the

Bet

ter AirN it rogen

30

20

10

H ighMediumLow H otW armC ool

H ighMediumLow

30

20

10

33551880330 Of fOn

275265255

30

20

10

0.1350.0940.062

A tm osphere B elt speed P rheat tem p

F lux am ount F lux ty pe C hipw av e

S older tem p B oard thckn

Bridging SAC305 - HAL boards

Smal

ler t

he B

ette

r A i rNi tro g e n

4 0

3 0

2 0

Hig hM e d iu mL o w Ho tWa rmCo o l

Hig hM e d iu mL o w

4 0

3 0

2 0

3 3 5 51 8 8 03 3 0 O ffO n

2 7 52 6 52 5 5

4 0

3 0

2 0

0 .1 3 50 .0 9 40 .0 6 2

A tm o sp h e re B e l t sp e e d P rh e a t te m p

Flu x a m o u n t Flu x typ e Ch ip wa ve

S o l d e r te m p B o a rd th ckn

B ridging SAC305 - O SP boards

General RemarkFor the PCI connector, as the board thickness increased, the lead protrusion decreased.For the Berg Stick connector, the lead protrusion was kept constant over the three board thicknesses by mechanical means.

Bridging was found to be correlated to lead protrusion.

17

Interactions of Process Parameters on BridgingInteractions of Process Parameters on Bridging

To avoid bridgingSelect a proper flux, amount, and inert soldering environment

18

How to Minimize Bridging Based on Process and MaterialsHow to Minimize Bridging Based on Process and Materials

Recommended SettingsAtmosphere: NitrogenBelt speed: Med/HighPreheat temp: CoolFlux amount: High

Chip wave: OffSolder temperature: 265ºC

19

Open Joints/Skip on SOTOpen Joints/Skip on SOT’’ss

•The orientation of the SOT is a critical design factor. (1.5x more defects)

•Chip wave operation results in improved soldering results.(Double wave former prevents shadow effects)

20

Hole Fill Defect AnalysisHole Fill Defect Analysis

SAC 305

SpeedFt/min

(cm/min)HASL OSP

1 5 N2 4.5 (138) med med OA on 255 0.062 0.0 0.02 1 N2 3 (92) low low Water on 255 0.062 2.0 2.73 16 Air 6 (183) low high Alcohol on 255 0.094 41.0 44.04 12 Air 2 (61) high med Alcohol on 255 0.135 32.7 200.05 14 Air 3.5 (107) med high Water off 255 0.135 399.0 394.36 9 N2 6 (183) high low OA off 255 0.094 48.0 44.37 10 Air 3 (92) low high OA off 265 0.062 0.0 0.08 2 N2 3 (92) med med Alcohol off 265 0.094 3.0 0.09 15 Air 4.5 (138) high low Alcohol on 265 0.062 0.0 0.0

10 7 N2 5 (152) low med Water on 265 0.135 358.3 350.311 6 N2 4.5 (138) high high Water on 265 0.094 0.3 0.312 17 Air 5 (152) med low OA on 265 0.135 56.3 47.313 13 Air 4.5 (138) low med OA on 275 0.094 6.0 25.014 4 N2 3.5 (107) low low Alcohol off 275 0.135 56.7 80.315 8 N2 6 (183) med high Alcohol on 275 0.062 2.3 3.016 11 Air 3 (92) med low Water on 275 0.094 1.7 37.017 3 N2 2 (61) high high OA on 275 0.135 58.7 55.018 18 Air 6 (183) high med Water off 275 0.062 1.0 1.0

Board Thickness

SAC 305Flux Quantity

Flux Type

Chip Wave Solder Temp (°C)

Actual Run Order

DOE Standard

OrderAtmospher

e

Preheat Temp

21

Response: Mean CountAverage Number of Holes per Board w/<75% Fill

SAC305

020406080

100120140160180200

N2

Air

Slow Med

Fast

Coo

lW

arm

Hot

Flux

Flux

Med

Flux

Wat

erA

lcoh

ol OA

Chi

p O

nC

hip

Off

255

265

275

0.06

20.

094

0.13

5

305OSP

Impact of Process Impact of Process Parameters on Hole Parameters on Hole

FillFill

SAC 305SAC 305

Response: Mean CountAverage Number of Holes per Board w/<75% Fill

SAC305

020406080

100120140160180200

N2

Air

Slow Med

Fast

Coo

lW

arm

Hot

Flux

Flux

Med

Flux 33

018

6833

55

Chi

p O

nC

hip

Off

255

265

275

0.06

20.

094

0.13

5

305HASL

22

Confirmed Optimized ProcessConfirmed Optimized Process

Alloy Atmosphere Speed Preheat Temperature

Flux Amount Flux Type Solder

TemperatureBoard

Thickness

(ft/min) (°C) (°C) (mil)SAC 305 N2 3 130 Med Alcohol 265 62, 93, 135

SACx N2 3 110 Med Alcohol 265 62, 93, 135SN100C N2 3 110 Med Alcohol 265 62, 93, 135

• Process was confirmed by soldering at the defined process settings and materials.

23

Confirmation ResultsConfirmation Results

• Process confirmation was not positive for the 135 mil board indicating the influence of board complexity and lead protrusion.

No connection Shorter spokes Longer spokes Direct to G.P.

Board Thickness SAC305 SACx Sn100C

62 mil 0 0 093 mil 0 0 0

135 mil 2 7 3

24

TrendsTrends““learning as we golearning as we go””

Points of Interest

25

Influence of Copper TieInfluence of Copper Tie--InIn

Short spoke; no tie-in; long spoke; direct tie-in

Root Cause Analysis• An un-optimized process will

produce such results.• Board complexity – thickness

and layers – will significantly influence the process’ window of opportunity.

26

Influence ofInfluence ofLead ProtrusionLead Protrusion

Hole fill and Bridging are directly affected and trends were quantified

27

ConclusionsConclusionsThis investigation determined the impact of process parameters and materials on the

wave soldering process and solder joint formation.

This study provided insight into the process issues that one will encounter during so that a

rational implementation strategy for a robust lead free wave soldering process can be achieved.

Phase I of this project provided information of each of the critical areas that was the focus.

Materials SelectionThe interaction of the various materials on the formation of defects was quantified.

Process OptimizationDetermined and tested the optimized process based on materials and parameter control.

Solder Joint Yield Defined failure levels and defect types using inspection criteria – IPC class 3 combined with best practices, yield determined by hole fill characterized by 5DX data analysis.

The result of Phase I was to lay the foundation for a broader effort to characterize thereliability of through-hole joints on a test vehicle specifically designed to test the

norms and practices used in tin lead wave soldering and develop new standards for lead free wavesoldering.

28

Phase IIPhase II““the end goalthe end goal””

Unique Board Design

Fixed Process

Lead Free Solder Joint Performance

29

GTLO Test VehicleGTLO Test Vehicle

30

T e s t C o n d i t i o n A l l o y T h i c k n e s s S u r f a c e F i n i s h

O S PN i A u

I m m A gH A S LO S PN i A u

I m m A gH A S LO S PN i A u

I m m A gH A S LO S PN i A u

I m m A gH A S LO S PN i A uO S PN i A uO S PN i A uO S PN i A uO S PN i A u

I m m A gH A S LO S PN i A u

I m m A gO S PN i A u

I m m A gH A S LO S PN i A u

I m m A gO S PN i A uO S PN i A uO S PN i A uO S PN i A uO S PN i A uO S PN i A uO S PN i A uO S PN i A uO S PN i A uO S PN i A uO S PN i A uO S PN i A uO S PN i A uO S PN i A uO S PN i A uO S PN i A uO S PN i A uO S P

0 . 0 9 3

0 . 0 9 3

S n C u N i0 . 0 6 2

0 . 0 9 3S A C x

0 . 0 6 2

0 . 0 9 3

S n P b

0 . 0 6 2

S A C

0 . 0 6 2

S A C

0 . 0 6 2

S n C u N i0 . 0 6 2

I n i t i a l A n a l y s i s ( X - s e c t i o n , X - r a y , P u l l ,

S h e a r , e t c … )

0 . 0 9 3S A C x

0 . 0 6 2

0 . 0 9 3

0 . 0 9 3

0 . 0 9 3

A T C - 4 0 t o 1 2 5 C

S n P b

0 . 0 6 2

0 . 0 9 3

0 . 0 9 3A T C 0 t o 1 0 0 C

S n P b0 . 0 6 2

S A C0 . 0 6 2

0 . 0 9 3

0 . 0 9 3D r o p

S n P b0 . 0 6 2

S A C0 . 0 6 2

0 . 0 9 3

0 . 0 9 3

V i b r a t i o n

S n P b0 . 0 6 2

S A C0 . 0 6 2

S n C u N i0 . 0 6 2

0 0 9 3

ScopeScope

Interest Test Alloy Thickness Surface FinishCore - Baseline - - - -Temp Age -40 to 125C SAC 0.093 OSPSelective Solder -40 to 125C SAC 0.093 OSPother -40 to 125C SAC 0.093 OSP

• 600 boards• 300,000 components• 3 alloys, 4 finishes, 1

flux, 2 thicknesses

31

AcknowledgementsAcknowledgements

• The authors and project members would like to gratefully thank the following people for support during the execution of Phase I and its analysis: John Norton, Norm Faucher, Gerjan Diepstraten, and Bruce Quigley for build support, Ursula Marquez de Tino for the many cross sections, Sam Greenfield for performing all of the 5DX analysis.

• The authors would also like to thank the management of each participating company for their support in this endeavor. Without their continued support, this project would not have achieved its Phase I goals.

Lead-Free Rework

Optimization Project

Project Chair: Jasbir Bath Solectron Corporation

Project Co-Chair: Craig Hamilton, Celestica

IPC APEX 2007February 20 , 2007