Lead Free Wave and Selective Soldering...
Transcript of Lead Free Wave and Selective Soldering...
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Ursula Marquez de Tino
April 2007
Lead Free Wave and SelectiveSoldering Technologies
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Vitronics Soltec
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Vitronics Soltec
• Surface Mount Technology Lab – UIC– Binghamton, NY
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Agenda
• Process Optimization for Wave Soldering –INEMI Project
• Process Optimization for Selective Soldering –Elcoteq Project
• Major Concerns with Liquid SolderingTechniques– Solder contamination– Cu dissolution
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Process OptimizationWave Soldering
INEMI Project
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Acknowledge
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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
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Taguchi Experiment
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Machine Configuration
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Test Vehicle
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4 Days of Soldering
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Analysis of Bridging SAC 305
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Occurrence of Bridging onQFP
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Bridging Through Hole Components
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Interactions of ProcessParameters on Bridging
To avoid bridging
Select proper flux amount
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Optimal Settings
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Open Joints on SOT’s
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Through Hole Inspection Criteria
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ThroughHole
Penetration
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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.
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Optimized Process
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Confirmation Run
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Influence of Copper Tie - In
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Evaluation of Optimized Liquid SolderingTechniques: Wave vs Selective
Test s objective:Compare Wave soldering,
Multiwave Soldering, andSelectWave Soldering.
SelectWave and Multiwave areSelective Soldering Techniques
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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
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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.
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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
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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.
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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.
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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.
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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.
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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
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Tensile Strength Analysis
Instron:Max. load = 5 kNSpeed = 0.5 mm/min (slow to make
to have the crack in the solder)
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Failure Mechanisms
• Barrel failure• Partial solder and barrel failure• Solder failure• Component failure
Component lead
Solder
Copper barrel Topside fillet
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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.
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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.
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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.
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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
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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)
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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
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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
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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
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Soldering TechnologyAffects Process and Yield
MultiWave Soldering – Faster yet flexible but, processis determined by most challenging board element.
Wave SelectWave MultiWave
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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
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Major Concerns in LiquidSoldering
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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
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Alloy Analysis
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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
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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
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Thanks