Vitronics Present

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 SOTs

Through Hole Inspection Criteria

ThroughHole

Penetration

Through Hole PenetrationSAC Alloy: Defect at top quartile

(

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


Conveyor speed Solder temp

Thru Hole Filling @ 48 Pins Connector

Flux amount: HighPreheat: medium 120CConveyor speed: medium 130 cm/minSolder temp.: 265 C

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 CDrag speed: medium 5 mm/sSolder temp.: 290 C

The

Larg

erth

eBe

tter

5.72.00.7

200

175

150

125

10015011580

10.05.00.5

200

175

150

125

100320290260


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


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


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


Dip time Solder temp

Multi Wave - Bridging

Flux amount: HighPreheat: low 80 CDip time: 3 sSolder temp.: 320C

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 C 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

]

320C290C260C

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


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


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 C

Wave soldering - 265 C - 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


Select Wave soldering - 290 C - 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


Mutli Wave soldering - 320 C - 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


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.



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


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/cm2Preheat temperature = 120 CConveyor speed = 130 cm/minSolder temperature = 265 C

SelectWaveFlux amount = 5.7 mg/cm2Preheat temperature = 80 CDrag speed = 5 mm/secSolder temperature = 290 C

MultiWaveFlux amount = 14.0 mg/cm2Preheat temperature = 80 CDip time = 3 secSolder temperature = 320 C

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

Documents

Vitronics Present