WAVE SOLDERING

REFLOW SOLDERING SELECTIVE SOLDERING

China - Korea - Singapore- Malaysia - USA - Netherlands - Germany

Lead Free Wave Soldering

Ursula MarquezOctober 18, 2003

Wave Soldering RoadmapParameter Metric 2003 2005 2007 2009 2015 Comments

Wave Solder Flux VOC free/Halogen Free (%/%) 18/90 23/92 27/95 30/95 90/95

Wave Lead-Free Alloy

Utilization % (other/SAC) SnPb 50/50 30/70 10/90 10/90 Low Tm alloy will exist for low end product

Minimum feasible pitch in PTH layout mil 75 60 40 20 16

Selective soldering alternative will provide the alternative

technical need

Conversion Costs - Model Changeover

Time*

Hours in Wave Dynamic profiling 4 2 1 0.5 0.5 Drastic reduction once profile

library is established

Conventional/Selective Wave Soldering

utilization % (conventional/selective) 90/10 75/25 60/40 60/40 60/40

SMT paste in hole/Wave Soldering

Utilization % 10/90 30/70 30/70 50/50 50/50

Potential conversion is needed to achieve hole fill for thinner PCB. Reflow connector need

higher T capability, LCP.

Pre-heat Process Temperature

0C 90~110 140~160 140~160 140~160 140~160

Wave pot Temperature

0C 250-260 260~270 260~270 260~270 260~270

Enviroment process N2/Air 50/50 80/20 80/20 80/20 90/10

2007 Elimination of alcohol base fluxes - EU

Facts on Lead Free Wave Soldering

• Damage of components and boards tighter process window.

• High rate of reaction with other metals solderpot materials and board finishes.

• Enhanced process tuning and repeatability.

• Throughput reduction board complexity.

• Energy consumption flux type.

• Solder shrinkage and joint surface appearance.

Lead Free Wave Soldering Profile

• Preheat Temperature 120C• Peak Temperature 260C• Topside Temperature < reflow temperature

Wave Soldering Alloy Choice - Europe vs China

• Unlike reflow soldering SnAgCu dominates as the lead free alternative, lead free wave soldering has several practical lead free alternatives.

Europe

China

New Hampshire Facility

Sn3.9Ag0.6Cu (NEMI composition)

• SnCuNi (Nihon Superior patented alloy)

• SnPb• Sn0.3Ag0.6Cu

(Alpha Alloy)

Denis Barbini, Advanced Technologies Manager

(603)772-7778

Ursula Marquez, Process and Research Engineer

(607)779-5016

Single sided boards

• Typical solder temperature 255 - 260 ºC.• Conveyor speed high

(approx. 150 cm/min).• Wire support• Alloy most of times SnCu, SnCuNi or

SnAgCu.

• Low cost board materials likeCEM or FR2.

Double sided boards

Board materials such as FR4 or othermaterials with high Tg value are appropriate.

• Typical solder temperature 260-265 ºC.• Longer contact time for good wetting

(SnPb + 0-5 seconds).• Typical Alloys: SnAgCu or SnCuNi.• Risk: Danger for re-melting components.

Process Optimization for SnAg Wave Soldering• Comparison of process as a function of flux.

SnAgFlux A

THPenetration

Bridging SolderBalling

Solder Excess Oxides RESULT

Pot Temperature Low 0 0 0 0 255°CAtmosphere N2 0 0 0 0 AirContact Time 0 0 0 Short 0 2.3 secSmart Wave On 0 0 On 0 OnPreheat Temperature High 0 0 High 0 HighFlux Amount High 0 0 0 0 LowBoard Finish 0 0 0 NiAu 0 0

SnAgFlux B

THPenetration

Bridging SolderBalling

Solder Excess Oxides RESULT

Pot Temperature 0 High Low High 0 270°CAtmosphere N2 N2 0 0 N2 N2Contact Time Long Short 0 Short Short 2.3 secSmart Wave On On 0 0 On OnPreheat Temperature High 0 0 High 0 HighFlux Amount High High Low 0 High HighBoard Finish 0 0 NiAu NiAu NiAu NiAu

Preheating Compatibility

• A forced convection preheater is recommended for VOC free water based fluxes.

• Depending on Board technology and complexity, 3 types of preheat technology can be employed.

• The energy required to evaporate a water based flux is significantly higher.

Power Consumption

• Comparison of power consumption for:– tin lead process

• VOC free flux• Alcohol flux

– SnAgCu process • VOC free flux• Alcohol flux

• In this study, the basis of comparison is the processing of 1 kg of solder.

• Product was a 9.6”x9.6” motherboard.

Power Consumption

• SnPb Alcohol 15.6 kWh per 143 boards• SnPb VOC free 16.9 kWh per 143 boards• SnAgCu Alcohol 18.2 kWh per 162 boards• SnAgCu VOC free 19.5 kWh per 162 boards

• Increase of 3% from tin lead to SnAgCu due to board count. 15% increase based on time usage.

• Increase of 8% from Alcohol to VOC free.

Wave Optimization

Impact of Temperature on Soldering and Joint Quality

250°C

260°C 270°C

265°C

Time - Temperature Relationship For Double Sided Boards w/ Plated Through Holes

Parameters Values

Soldering Temp 2500C, 2600C, 2650C

Soldering Time 4 sec, 3.5 sec, 3 sec

Preheat Temp 1200C

Monitoring the Alloy Composition

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 affect process and joint quality

• Cu6Sn5 formation • Transition from eutectic to pasty range

Alloy Analysis

Contamination Lead Free Alloys Solder 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

Dross and Lead FreeControlling Cost and Process

• Dross formation of SnPb = Lead Free• Use of Nitrogen reduces dross formation• Cost analysis nitrogen vs amount of dross

No increase of the dross formation is recognized:

Solderpot Compatibility with Lead Free Alloys

Delta Solderpot

The Problem: FeSn2 Crystals

How & Why FeSn2 Forms, and How to Deal with It! • Sn will react with the Fe in pot materials

forming FeSn2.

• Pot materials are vulnerable where solder flow is at its highest. Also a function of temperature.

• Different alloys have different reactivities with Iron bearing materials.– Sn/Ag/Cu, Sn/Cu/Ni, Sn/Pb

• How to deal with this:– material selection!– identification of critical parts!

Solder Pot Internal MaterialsCompatibility study

Contamination and dissolution of iron can be minimized with the use of a correct coating:

Increase iron content in lead-free solder indicates the presence of Fe2Sn crystals.

Stainless 304 Stainless 316 Melonite QPQ V-S coating

High Temperature Diffusion Controlled Coating

• Light Blue Fe• Red Coating• Green Sn

Upgrading, Cleaning, New Solderpot

• All Delta’s built 2001 to Present are Lead Free Compatible

• Cleaning is not Recommended Due To:– Long time - up to a week– Hard labor, hazardous materials– Contamination issues

• Multiple examples of end users wasting 10K due to careless behavior.

Case Study

A Lead Free Application with Surface Mount and Wave Technologies

The Problem• Poor pull Strength of a Tin Lead Finish QFP

with Sn/Ag/Cu Solder Joint• After Reflow Process, Pull Force =12 N• After Wave Process, Pull Force = 5-7 N

QFP Analysis• QFP Lead has a Sn/Pb finish on an Iron Ni

Base• QFP is Undergoing a Secondary and

Unintended Reflow Process

Intermetallic as an Indicator of Good Soldering

• Joint to Pad interface has a good intermetallic.

• However, no intermetallic on joint to lead.

Component Lead

Intermetallic?

Contamination?

Cu Pad

Intermetallic

Closer Look at the Joint

• Yellow is Fe; Pink is Sn; Blue is Cu; Light Blue is lead

Conclusions and Recommendations

• Poor Pull Strength is the Result of Lead Contamination and Diffusion of Finish into the Joint Leaving the Exposed Lead Material.

• Possible other Causes are Board Warpage, Component Warpage.

• Avoid Unintended Double Reflow!– Customer fabricated specific QFP heat

sinks to resolve double reflow• Do NOT Mix Tin Lead and Lead Free.

What is Lead Free?

• JEITA limits lead content to 0.1%• RoHS / WEEE directive limits lead content to

0.1%

Sn/Bi with 0.5% Pb

Sn/Bi with 30% Pb

Conclusions

• Metallurgical considerations should be taken into account when mixing various metals from the different sources.

• Contamination changes the original alloy by:

– lowers melting point of original alloy.

– extends melting range.

– results in the formation of different alloys.

Impact of Pb Contamination > 0.5%

SnCuNi

Impact of Pb Contamination > 0.5%

Pb Phases

A Case Study of Process Development, Inspection, and

Joint Performance

Assembly Process

Top SideReflow Process

Bottom SideWave Process

Initial Inspection - Defects

Insufficient Solder Pin Hole/Solder Ball

• Knock Out*• Wrong Polarity*• Misregistration*• Damage Component*

* rework

• Bridging*• Sinking• Skips*• Solder Balling• Pin Hole• Solder Excess

List of Defects

Capacitors and ResistorsVia in Pad

350 Opportunities/Board

Total 33600 Opportunities

2.5% of the resistors and capacitors located on via in pad showed this defect

Initial Inspection - Sinking

Sunk Hole Sunk Surface

Sinking Defect at Time Zero

25%

75%

Sunk SurfaceSunk Hole

835 Defects

Cross Section Through HoleP5- Ni/Au

Sn/Ag/Cu, Alcohol Sn/Ag/Cu, VOC Free

Sn/Cu/Ni, Alcohol Sn/Cu/Ni, VOC Free

Sn/Ag/Cu, Alcohol Sn/Ag/Cu, VOC Free

Sn/Cu/Ni, Alcohol Sn/Cu/Ni, VOC Free

Cross Section - Cu OSP - P5

Shrink Holes - Time Zero

Sn/Ag/Cu, Cu OSPSn/Cu/Ni, Ni/Au

Sn/Ag/Cu and Sn/Cu/Ni show:• Non-smooth surface due to

solidification behavior• Different in every joint

Sn/Ag/Cu, Ni/Au

Solder Joint IntegritySn/Ag/Cu on ImmAg

1206 T0

1206 T3000

1206 T5000

• Cross Section– 1206 Chip Cap

• No crack growth observed in Cross Sections

– P2 Through Hole• Crack initiation observed @ 5000

cycles

P2 T5000

Reliability Testing…Preliminary Results

• Product Level Reliability Results– Failure locations have yet to be identified– May or may not be wave soldered devices– Similar reliability for SnCuNi and SAC

1 2 3Alcohol 360F DNF 5000 4000

VOC Free NR 310B 1000 DNF DNFAlcohol 360F DNF 4000 DNF

VOC Free NR 310B DNF 5000 DNFAlcohol 360F DNF 3000 2000

VOC Free NR 310B DNF 5000 DNFAlcohol 360F 4000 4000 5000

VOC Free NR 310B 4000 DNF 5000Alcohol 360F DNF DNF 5000

VOC Free NR 310B 5000 5000 5000Alcohol 360F 5000 5000 DNF

VOC Free NR 310B DNF 4000 DNFAlcohol 360F 4000 5000 5000

VOC Free NR 310B 2000 4000 DNFAlcohol 360F 4000 2000 DNF

VOC Free NR 310B 4000 4000 3000SnPb HASL Alcohol 360F 4000 3000 DNF

Sn/Ni/Cu

ImmAg

ImmSn

OSP

Ni/Au

Device #

Sn/Ag/Cu

ImmAg

ImmSn

OSP

Ni/Au

Flux SystemPCB FinishAlloyCycle with Detected Failure3 Devices per CombinationDNF = Did Not Fail

Examples of Lead Free Applications

and Strategies Used for

Wave Equipment Setup

Sn0.5Cu0.1NiMelting Point 227 ºC

Observations:• Shiny solder joints.• Wetting was improved by increasing the contact time and thesolder temperature.

Double sided board:Solder temperature 265 ºC and 3 secondscontact time (120 cm/min).

Sn0.5Cu0.1Nimelting point 227 ºC

• An increase in solder balls is due to the higher solder temperature.

• Nitrogen may increase the solder balling.• Select Another solder resist.General remarks:• Solder appearance makes this alloy favourable.• Many applications in Japan.

Sn3.8Ag0.7CuMelting point 217 ºC

Preheater:Calrod 395 ºCForced convection 190 ºCIR Lamps 35%

Lead-free process:Water-based VOC free fluxConveyor 110 cm/minMachine: Delta Wave

Topside board: 129 ºC

Sn3.8Ag0.7CuMelting point 217 ºC

Solder temperature: 260 °C.Contact time: 0.5 + 2.5 secondsChip wave: 280 rpmMain wave: 270 rpm

Conclusions

• Electronic industry is picking up lead-free wave soldering since beginning of 2004.

• Companies started to invest in equipment and

experiments.

• If you don’t start now, you might be too late.

• Vitronics Soltec can help you with experiments

and the technology group.

• The new “5 Steps to Lead-free Soldering“

edition 2004 CD-ROM is available.