China - Korea - Singapore- Malaysia - USA - Netherlands - Germany WAVE SELECTIVE REFLOW SOLDERING SOLDERING SOLDERING Lead Free Wave Soldering Ursula Marquez October 18, 23
Wave Soldering Roadmap Parameter Metric 23 25 27 29 215 VOC free/halogen Free (%/%) 18/9 23/92 27/95 3/95 9/95 Utilization % (other/sac) SnPb 5/5 3/7 1/9 1/9 Minimum feasible pitch in PTH layout mil 75 6 4 2 16 Selective soldering alternative will provide the alternative technical need Conversion Costs Model Changeover Time* Hours in Wave Dynamic profiling 4 2 1.5.5 Drastic reduction once profile library is established Conventional/Select ive Wave Soldering utilization % (conventional/selective) 9/1 75/25 6/4 6/4 6/4 Wave Solder Flux Wave Lead-Free Alloy SMT paste in hole/wave Soldering Utilization % 1/9 3/7 3/7 5/5 5/5 Pre-heat Process Temperature 9~11 14~16 14~16 14~16 14~16 Wave pot Temperature C 25-26 26~27 26~27 26~27 26~27 N2/Air 5/5 8/2 8/2 8/2 9/1 Enviroment process C Comments 27 Elimination of alcohol base fluxes - EU Low Tm alloy will exist for low end product Potential conversion is needed to achieve hole fill for thinner PCB. Reflow connector need higher T capability, LCP.
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 Energy consumption board complexity. flux type. Solder shrinkage and joint surface appearance.
Lead Free Wave Soldering Profile Preheat Temperature 12C Peak Temperature 26C 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 Sn3.9Ag.6Cu (NEMI composition) SnCuNi (Nihon Superior patented alloy) SnPb Sn.3Ag.6Cu (Alpha Alloy) Denis Barbini, Advanced Technologies Manager (63)772-7778 Ursula Marquez, Process and Research Engineer (67)779-516
Single sided boards Low cost board materials like CEM or FR2. Typical solder temperature 255-26 ºC. Conveyor speed high (approx. 15 cm/min). Wire support Alloy most of times SnCu, SnCuNi or SnAgCu.
Double sided boards Board materials such as FR4 or other materials with high Tg value are appropriate. Typical solder temperature 26-265 ºC. Longer contact time for good wetting (SnPb + -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. SnAg Flux A Pot Temperature Atmosphere Contact Time Smart Wave Preheat Temperature Flux Amount Board Finish TH Penetration Low N2 On High High Bridging SnAg Flux B Pot Temperature Atmosphere Contact Time Smart Wave Preheat Temperature Flux Amount Board Finish TH Penetration N2 Long On High High Bridging High N2 Short On High Solder Balling Solder Excess Oxides RESULT Short On High NiAu 255 C Air 2.3 sec On High Low Solder Balling Low Low NiAu Solder Excess Oxides RESULT High Short High NiAu N2 Short On High NiAu 27 C N2 2.3 sec On High High 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 25 C 265 C 26 C 27 C
Time - Temperature Relationship For Double Sided Boards w/ Plated Through Holes Parameters Values Soldering Temp 25C, 26C, 265C Soldering Time 4 sec, 3.5 sec, 3 sec Preheat Temp 12C
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.2%. Can make joint formation brittle. Driving cause: Fe % increases as pot materials dissolve. Pb contamination: maximum amount.1%. Formation of low melting segments, cracking and other defects Driving cause: Mix alloys, solderpot contamination
Dross and Lead Free Controlling 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 Materials Compatibility study Contamination and dissolution of iron can be minimized with the use of a correct coating: Stainless 34 Stainless 316 Melonite QPQ V-S coating Increase iron content in lead-free solder indicates the presence of Fe2Sn crystals.
High Temperature Diffusion Controlled Coating Light Blue Fe Red Coating Green Sn
Upgrading, Cleaning, New Solderpot All Delta s built 21 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 1K 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 Component Lead Intermetallic? Contamination? Intermetallic Cu Pad Joint to Pad interface has a good intermetallic. However, no intermetallic on joint to lead.
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.1% RoHS / WEEE directive limits lead content to.1%
Sn/Bi with.5% Pb
Sn/Bi with 3% 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 >.5% SnCuNi
Impact of Pb Contamination >.5% Pb Phases
A Case Study of Process Development, Inspection, and Joint Performance
Assembly Process Top Side Reflow Process Bottom Side Wave Process
Initial Inspection - Defects Insufficient Solder Pin Hole/Solder Ball List of Defects Bridging* Sinking Skips* Solder Balling Pin Hole Solder Excess Knock Out* Wrong Polarity* Misregistration* Damage Component* * rework
Initial Inspection - Sinking Capacitors and Resistors Via in Pad 35 Opportunities/Board Total 336 Opportunities 2.5% of the resistors and capacitors located on via in pad showed this defect Sunk Hole Sunk Surface Sinking Defect at Time Zero 25% Sunk Surface Sunk Hole 75% 835 Defects
Cross Section Through Hole P5- Ni/Au Sn/Ag/Cu, Alcohol Sn/Cu/Ni, Alcohol Sn/Ag/Cu, VOC Free Sn/Cu/Ni, VOC Free
Cross Section - Cu OSP - P5 Sn/Ag/Cu, Alcohol Sn/Cu/Ni, Alcohol Sn/Ag/Cu, VOC Free Sn/Cu/Ni, VOC Free
Shrink Holes - Time Zero Sn/Cu/Ni, Ni/Au Sn/Ag/Cu, Cu OSP 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 Integrity Sn/Ag/Cu on ImmAg Cross Section 126 T 126 Chip Cap No crack growth observed in Cross Sections P2 Through Hole Crack initiation observed @ 5 cycles 126 T3 126 T5 P2 T5
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 Alloy PCB Finish ImmAg ImmSn Sn/Ag/Cu OSP Ni/Au ImmAg ImmSn Sn/Ni/Cu OSP Ni/Au SnPb HASL Flux System Device # 1 2 3 Alcohol 36F DNF 5 4 VOC Free NR 31B 1 DNF DNF Alcohol 36F DNF 4 DNF VOC Free NR 31B DNF 5 DNF Alcohol 36F DNF 3 2 VOC Free NR 31B DNF 5 DNF Alcohol 36F 4 4 5 VOC Free NR 31B 4 DNF 5 Alcohol 36F DNF DNF 5 VOC Free NR 31B 5 5 5 Alcohol 36F 5 5 DNF VOC Free NR 31B DNF 4 DNF Alcohol 36F 4 5 5 VOC Free NR 31B 2 4 DNF Alcohol 36F 4 2 DNF VOC Free NR 31B 4 4 3 Alcohol 36F 4 3 DNF Cycle with Detected Failure 3 Devices per Combination DNF = Did Not Fail
Examples of Lead Free Applications and Strategies Used for Wave Equipment Setup
Sn.5Cu.1Ni Melting Point 227 ºC Observations: Shiny solder joints. Wetting was improved by increasing the contact time and the solder temperature. Double sided board: Solder temperature 265 ºC and 3 seconds contact time (12 cm/min).
Sn.5Cu.1Ni melting 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.
Sn3.8Ag.7Cu Melting point 217 ºC Lead-free process: Water-based VOC free flux Conveyor 11 cm/min Machine: Delta Wave Preheater: Topside board: 129 ºC Calrod 395 ºC Forced convection 19 ºC IR Lamps 35%
Sn3.8Ag.7Cu Melting point 217 ºC Solder temperature: 26 C. Contact time:.5 + 2.5 seconds Chip wave: 28 rpm Main wave: 27 rpm
Conclusions Electronic industry is picking up lead-free wave soldering since beginning of 24. 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 24 CD-ROM is available.