lead free wave and selective soldering...

Ursula Marquez de Tino

April 2007

Lead Free Wave and SelectiveSoldering Technologies

Vitronics Soltec

Vitronics Soltec

• Surface Mount Technology Lab – UIC– Binghamton, NY

Agenda

• Process Optimization for Wave Soldering –INEMI Project

• Process Optimization for Selective Soldering –Elcoteq Project

• Major Concerns with Liquid SolderingTechniques– Solder contamination– Cu dissolution

Process OptimizationWave Soldering

INEMI Project

Acknowledge

Objective

• Impact of process parameters andmaterials on solder joint formation– Define process window based on flux

amount, preheat temperatures, contacttime, solder temperature, waveconfiguration, and atmosphere

– Materials selection: fluxes, alloys,components and board complexity

– Solder Joint Yield: characterize by hole fillusing 5 DX

Taguchi Experiment

Machine Configuration

Test Vehicle

4 Days of Soldering

Analysis of Bridging SAC 305

Occurrence of Bridging onQFP

Bridging Through Hole Components

Interactions of ProcessParameters on Bridging

To avoid bridging

Select proper flux amount

Optimal Settings

Open Joints on SOT’s

Through Hole Inspection Criteria

ThroughHole

Penetration

Through Hole PenetrationSAC Alloy:• Defect at top quartile

(<75% total hole fill) waspredominate defect.

• Most pins had only onedefect.

• That defect wasinsufficient solder at Slice3 (top quartile).

• There was no majordifference betweenobserved defects withdifferent surface finishes.

• DPMO for SAC on HALbetween 50 and 300.

Optimized Process

Confirmation Run

Influence of Copper Tie - In

Evaluation of Optimized Liquid SolderingTechniques: Wave vs Selective

Test s objective:Compare Wave soldering,

Multiwave Soldering, andSelectWave Soldering.

SelectWave and Multiwave areSelective Soldering Techniques

Selected Materials

Materials for this experimentwere defined by customer:

• Alloy - SAC305• Flux – Interflux 2005 C• Board finish – OSP• Board: double sided,SMT/Through Hole components

Phase I: Wave Soldering

Machine Configuration forDelta:

• Nozzle spray fluxer – FC7(alcohol base flux)

• Preheat configuration:Calrod-Forced convection-IRlamps

• Combi wave former:Chip + smart wave

• Nitrogen on wave(20-40-60 liter/min) Taguchi: 9 runs with

5 repetitions.

The

Smal

ler

the

Bett

er

6.33.21.6

40

30

20

15012090

18013080

40

30

20

265260255

Flux amount Preheat temp

Conveyor speed Solder temp

Wave Soldering - Bridging SOT

The

Larg

erth

eBe

tter

6.33.21.6

250

200

150

100

15012090

18013080

250

200

150

100

265260255

Flux amount Preheat temp

Conveyor speed Solder temp

Thru Hole Filling @ 48 Pins Connector

Flux amount: HighPreheat: medium 120ºCConveyor speed: medium 130 cm/minSolder temp.: 265 ºC

Determination of OptimizedParameter Settings for Wave Soldering

Phase I: SelectWave Soldering

Machine configuration formySelective 6748:

• Dropjet fluxer: 130 microns(alcohol flux)

• Preheat configuration:IR lamps (2 stations)

• Select nozzle: 12 mm• Nitrogen: 50 l/min• Solder drainage

conditioner on

Taguchi: 9 runs with5 repetitions.

Determination of OptimizedParameter Settings for SelectWave Soldering

Flux amount: HighPreheat: low 80 ºCDrag speed: medium 5 mm/sSolder temp.: 290 ºC

The

Larg

erth

eBe

tter

5.72.00.7

200

175

150

125

10015011580

10.05.00.5

200

175

150

125

100320290260

Flux amount Preheat temp

Drag speed Solder temp

Select Wave - Thru Hole Penetration

The

Smal

ler

the

Bett

er

5.72.00.7

2.0

1.5

1.0

0.5

0.0

15011580

10.05.00.5

2.0

1.5

1.0

0.5

0.0

320290260

Flux amount Preheat temp

Drag speed Solder temp

Select Wave - Bridging

Low drag speed and high temperatures result in pad lifting.

Phase I: MultiWave soldering

Machine Configuration formySelective 6748:

(preheat conditions similar toSelectWave)

• Dropjet fluxer: 130 microns• IR lamps (2 stations)• Multi plate with 2 nozzles• Nitrogen: 200 l/min

Taguchi: 9 runs with5 repetitions.

Determination of OptimizedParameter Settings for MultiWave Soldering

The

Larg

erth

eBe

tter

14.09.73.7

240

225

210

195

180

15011580

531

240

225

210

195

180

320290260

Flux amount Preheat temp

Dip time Solder temp

Multi Wave - Through hole penetration

The

Smal

ler

the

Bett

er14.09.73.7

25

20

15

10

515011580

531

25

20

15

10

5320290260

Flux amount Preheat temp

Dip time Solder temp

Multi Wave - Bridging

Flux amount: HighPreheat: low 80 ºCDip time: 3 sSolder temp.: 320ºC

Small flux amount results in webbing, flags, bridging.

Confirming the Optimized Process

All confirmation run boards arenow in thermal cycling chambers.

• Thermo cycling 0 to 100 ºC• Pull test pin connector (after thermo

cycling)• Cross sections inter metallic's – SEM

For: Wave – Select Wave – Multi Wavesoldering

Tensile Strength Analysis

Instron:Max. load = 5 kNSpeed = 0.5 mm/min (slow to make

to have the crack in the solder)

Failure Mechanisms

• Barrel failure• Partial solder and barrel failure• Solder failure• Component failure

Component lead

Solder

Copper barrel Topside fillet

Tens

ileS

treng

th[N

]

320ºC290ºC260ºC

230

220

210

200

190

180

170

Tensile StrengthLead-free solder joint SAC305

SelectWave soldering

SelectWave Soldering

The board material is a regular FR4 material with a low Tg valuenot suitable for lead-free and selective soldering with high temperatures.

Pad lifting and material separation.

Wave SolderingTe

nsile

Stre

ngth

[N]

V=180cm/minV=130cm/minV=80cm/min

300

250

200

150

100

50

Tensile StrengthLead-free solder joint SAC305

Wave soldering

Poor hole filling (at high belt speed) result in lower tensile strength.

MultiWave SolderingTe

nsile

Stre

ngth

[N]

3sec@320C3sec@260C1sec@260C

250

225

200

175

150

Tensile StrengthLead-free solder joint SAC305

MultiWave soldering

Pad lifting is observed when dipped for 3 secondswith a high solder temperature.

Pull Testing - WaveTe

nsile

Stre

ngth

[N]

3000_cycles2000_cycles1000_cycles500_cycles0

250

225

200

175

150

125

Gerjan Diepstraten

Tensile strength after thermal cyclingThermal cycles 0 - 100 ºC

Wave soldering - 265 ºC - 3.7 seconds

Cu barrel weaken as TC increases

Pull Testing - SelectWaveTe

nsile

Stre

ngth

[N]

3000_cycles2000_cycles1000_cycles500_cycles0_cycles

250

225

200

175

150

125

Gerjan Diepstraten

Tensile strength after thermal cyclingThermal cycles 0 - 100 ºC

Select Wave soldering - 290 ºC - 2.5 seconds

90% mixed and solder failure up to 3000 AATC (90%barrel failures)

Pull Testing - MultiwaveTe

nsile

stre

ngth

[N]

3000_cycles2000_cycles1000_cycles500_cycles0_cycles

400

350

300

250

200

150

100

Gerjan Diepstraten

Tensile strength after thermal cyclingThermal cycles 0 - 100 ºC

Mutli Wave soldering - 320 ºC - 3 seconds

90% mixed and solder failure modes as TC increases. Largedeviation at 2000/3000 TC, different failure modes

Soldering TechnologyAffects Process and Yield

Wave Soldering – Fast and efficient but, process isdetermined by most challenging requirementresulting in exposing all components, flux, board toexcessive conditions. Allows for through holesoldering and SMD mass soldering.

Wave SelectWave MultiWave

Soldering TechnologyAffects Process and Yield

SelectWave Soldering – Flexible and exact but, process can beextended depending on number of joints to be processed.Defects are minimized to low numbers due to control oversoldering angle, flexible contact time per component, and fluxamount. Optimized through hole penetration and bridgeelimination is observed. Boards and components are onlyexposed to minimum requirements.

Wave SelectWave MultiWave

Soldering TechnologyAffects Process and Yield

MultiWave Soldering – Faster yet flexible but, processis determined by most challenging board element.

Wave SelectWave MultiWave

Optimized Soldering Process

• Each soldering process wasoptimized based on characterizingindividual parameter influence ondefect formation.

• This allowed for end user totroubleshoot the defect andimplement a robust solderingprocess for a given solderingtechnique

• High solder temperatures mayimpact board lifetime and result inpad lifting.

• Lower solder temperatures giveequal or even higher tensile strengthif topside solder fillet is achieved.

• Copper leaching depends on contacttime and solder temperature. Moredata will be collected.

WaveFlux amount = 6.3 mg/cm2

Preheat temperature = 120 ºCConveyor speed = 130 cm/minSolder temperature = 265 ºC

SelectWaveFlux amount = 5.7 mg/cm2

Preheat temperature = 80 ºCDrag speed = 5 mm/secSolder temperature = 290 ºC

MultiWaveFlux amount = 14.0 mg/cm2

Preheat temperature = 80 ºCDip time = 3 secSolder temperature = 320 ºC

Major Concerns in LiquidSoldering

Cu Content in Lead-free Alloys• The dissolution rate of Cu depends on:

• Solder temperature.• Copper content in the lead-free alloy

• Contamination above 1% has a potential to affectprocess and joint quality

• Cu6Sn5 formation• Transition from eutectic to pasty range

Alloy Analysis

Contamination Lead Free AlloysSolder Analysis

• Cu contamination: usually tolerable up to 1%.Driving cause:Dissolution of Cu from board material.

• Fe contamination: maximum amount 0.02%.Can make joint formation brittle.Driving cause:Fe % increases as pot materials dissolve.

Pb contamination: maximum amount 0.1%.Formation of low melting segments, crackingand other defectsDriving cause:Mix alloys, solderpot contamination

Copper Dissolution

1

23

Copper etched to highlight.Measure copper layer atthree different spots for10 samples.

Copper dissolution:Wave: -24% CuSelect Wave: -8% CuMulti Wave: -35% Cu

Thanks