technical challenges of rohs compliance by leo lambert eptac corp, manchester, nh for for...
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Technical Challenges of Technical Challenges of RoHS ComplianceRoHS Compliance
byby
Leo LambertLeo LambertEPTAC Corp, Manchester, NHEPTAC Corp, Manchester, NH
forfor
Implementing Lead-Free Electronics Implementing Lead-Free Electronics WorkshopWorkshop
February, 28, 2006February, 28, 2006
Design and Manufacturing Design and Manufacturing ImpactsImpacts
Component identificationComponent identification Component lead platingComponent lead plating Component selectionComponent selection Board designs from the perspective of Board designs from the perspective of
selecting solderable coatingsselecting solderable coatings Immersion silver or TinImmersion silver or TinGold ENIGGold ENIGOSPOSP
Manufacturing process changesManufacturing process changes
Design and Manufacturing Design and Manufacturing Impacts Impacts
Higher heat profilesHigher heat profiles LaminatesLaminates
Number of thermal cyclesNumber of thermal cycles Components and compatibility of those Components and compatibility of those
components to the new thermal profilescomponents to the new thermal profilesBake cycles and double sided mounting on Bake cycles and double sided mounting on
assembliesassemblies Reflow processesReflow processes
Higher temperatures and longer dwell timesHigher temperatures and longer dwell times
LaminatesLaminates
Must have lead free solderable Must have lead free solderable coatingscoatings
Must comply with list of identified Must comply with list of identified RoHS materialsRoHS materials
Must be able to meet new thermal Must be able to meet new thermal excursion temperatures.excursion temperatures.
Users must understand Tg and Td Users must understand Tg and Td Review CAF (Conductive Anodic Review CAF (Conductive Anodic
Filament) resistanceFilament) resistance
Laminate Requirements for Lead Laminate Requirements for Lead Free ProcessesFree Processes
Recommend Temperature of Decomposition (ASTM Recommend Temperature of Decomposition (ASTM D-3850 test method) testing using the 2 percent D-3850 test method) testing using the 2 percent weight loss for reporting the performance weight loss for reporting the performance characteristics of more thermally robust laminate characteristics of more thermally robust laminate materials.materials.
Recommend all laminate material data sheets report Recommend all laminate material data sheets report T288°C (Time to delamination at 288°C) as well as T288°C (Time to delamination at 288°C) as well as T260°CT260°C
Time to Delamination test results better indicate Time to Delamination test results better indicate performance in higher temperature lead free performance in higher temperature lead free assemblyassembly
Laminate Requirements for Lead Laminate Requirements for Lead Free ProcessesFree Processes
Recommend CAF (Cathodic Anodic Filament) testing per IPC Recommend CAF (Cathodic Anodic Filament) testing per IPC TM-650 Section 2.6.25.TM-650 Section 2.6.25.
Recommend reporting 5X Thermal Shock at 260°C results Recommend reporting 5X Thermal Shock at 260°C results as a key indicator of material performance in higher as a key indicator of material performance in higher temperature lead free assembly applications.temperature lead free assembly applications.
Most non-dicy cured FR-4 laminate materials made using Most non-dicy cured FR-4 laminate materials made using Novolac-type catalyst are more thermally robust and should Novolac-type catalyst are more thermally robust and should be part of this testing.be part of this testing. Several non-dicy FR-4 laminate materials using Novolac-type Several non-dicy FR-4 laminate materials using Novolac-type
catalyst have now been developed (with T288°C Time to catalyst have now been developed (with T288°C Time to Delamination data)Delamination data)
Adapted from Lead-free Reflow Oven and Rework Machine Status by Jaspir Bath, Solectron, 2004
CAFCAFConductive Anodic Conductive Anodic
FilamentFilamentGrowthGrowth
CAF CAF
First identified by Bell Labs in 1976First identified by Bell Labs in 1976Conductive, subsurface filament Conductive, subsurface filament
growth from the anode in high growth from the anode in high voltage (400V) boards, exposed to voltage (400V) boards, exposed to high humidity, i.e. greater than 80% high humidity, i.e. greater than 80% Rh.Rh.
Will cause failures if shorting Will cause failures if shorting between anode and cathode.between anode and cathode.Adapted from “Conductive Anodic Filament (CAF) Formation
by Laura Turbini, W. Jud Ready and Brian A. Smith of Georgia Institute of Technology
Conductive Anodic Filament Conductive Anodic Filament CAFCAF
Found most likely to occur at following Found most likely to occur at following locations:locations:
PTH to PTHPTH to PTHLine to LineLine to LinePTH to LinePTH to LineLayer to LayerLayer to Layer
Standardizing a Test Method for Conductive Anodic Filament Growth Failure By Clarissa Navarro, Isola Laminate Systems.
Conductive Anodic Filament Conductive Anodic Filament CAFCAF
Factors driving concerns:Factors driving concerns: Increased operating temperaturesIncreased operating temperatures
Under the hood applications.Under the hood applications. High density of holesHigh density of holes High Humidity (80%Rh)High Humidity (80%Rh) High voltage (~3 – 8 V/mil)High voltage (~3 – 8 V/mil) Multiple thermal cyclesMultiple thermal cycles Soldering FluxSoldering Flux
Standardizing a Test Method for Conductive Anodic Filament Growth Failure By Clarissa Navarro, Isola Laminate Systems.
Conductive Anodic Filament Conductive Anodic Filament CAFCAF
Conductive anodic filament (CAF) failure is thegrowth or electromigration of copper in a PCB.
Standardizing a Test Method for Conductive Anodic Filament Growth Failure By Clarissa Navarro, Isola Laminate Systems.
Electrochemical Migration in the Electrochemical Migration in the Age of Pb-FreeAge of Pb-Free
What does Pb-Free mean to What does Pb-Free mean to electrochemical migration (ECM)?electrochemical migration (ECM)? New plating materialsNew plating materials New interconnect materialsNew interconnect materials New flux chemistriesNew flux chemistries
ECM and alternative platingsECM and alternative platings ENIG and ImSn dependent upon ENIG and ImSn dependent upon
plating qualityplating quality ImAg dependent upon electric fieldImAg dependent upon electric field
Sn-Based AlloysSn-Based Alloys Use environment likely to be acidic Use environment likely to be acidic
with the presence of oxygen and with the presence of oxygen and halideshalides
Potential for order of magnitude Potential for order of magnitude increase in corrosion rateincrease in corrosion rate
ComponentsComponents
Lead free components will require:Lead free components will require: An awareness of moisture sensitivity An awareness of moisture sensitivity Meeting new temperature excursion Meeting new temperature excursion
profilesprofiles Identification of parts relative to solderable Identification of parts relative to solderable
coatingcoating Providing proper storage containers and Providing proper storage containers and
environmentsenvironments Training of material handling personnelTraining of material handling personnel
Marking CategoriesMarking CategoriesPb-free category :Pb-free category : Identifies the general family of Identifies the general family of
materials used for the 2nd level materials used for the 2nd level interconnect including solder paste, interconnect including solder paste, lead/terminal finish, and terminal lead/terminal finish, and terminal material/alloy solder ballsmaterial/alloy solder balls e1: SnAgCue1: SnAgCu e2: Other Sn alloys – no Bi or Zn e2: Other Sn alloys – no Bi or Zn
(SnCu, SnAg, SnAgCu…)(SnCu, SnAg, SnAgCu…) e3: Sne3: Sn e4: Pre-plated (Ag, Au, NiPd, e4: Pre-plated (Ag, Au, NiPd,
NiPdAu, (no Sn)NiPdAu, (no Sn) e5: SnZn, SnZnX (no Bi)e5: SnZn, SnZnX (no Bi) e6: Contains Bie6: Contains Bi e7: Low Temperature solder e7: Low Temperature solder
(<150(<150ooC) containing indium but C) containing indium but no bismuthno bismuth
e8, e9 unassigned categoriese8, e9 unassigned categories
Adapted from Courtesy IPC-1066
Component MarkingsComponent Markings
e1 = SnAgCu (i.e. e1 = SnAgCu (i.e. solder balls) solder balls)
e2 = Other Sn e2 = Other Sn alloys (i.e. SnCu, alloys (i.e. SnCu, SnAg) SnAg)
e3 = Sn (i.e. matte e3 = Sn (i.e. matte Sn) Sn)
e4 = pre-plated e4 = pre-plated (i.e. NiPdAu, NiPd)(i.e. NiPdAu, NiPd)
Marking SymbolsMarking Symbols
Pb-free SymbolPb-free Symbol Can be used as an option Can be used as an option
to replace the phrase to replace the phrase “lead-free” on labels or “lead-free” on labels or wherever practical on wherever practical on components/devices, components/devices, boards, assemblies, etc. boards, assemblies, etc. Pb-free Category SymbolPb-free Category Symbol
Marking HierarchyMarking Hierarchy If two or more solder alloys If two or more solder alloys
are used, the reflow are used, the reflow category will be shown category will be shown first, then the wave solder first, then the wave solder category alloy will follow.category alloy will follow.
Adapted from Courtesy of Cogiscan
Moisture Sensitivity Moisture Sensitivity LevelsLevels
Impact of Lead FreeImpact of Lead Free on MSD on MSD
Level 1Level 1 UnlimitedUnlimited <30<30°C/85% °C/85% RHRH
Level 2Level 2 1 year1 year <30<30°C/60% °C/60% RHRH
Level Level 2a2a
4 weeks4 weeks <30<30°C/60% °C/60% RHRH
Level 3Level 3 168 hours168 hours <30<30°C/60% °C/60% RHRH
Level 4Level 4 72 hours72 hours <30<30°C/60% °C/60% RHRH
Level 5Level 5 48 hours48 hours <30<30°C/60% °C/60% RHRH
Level Level 5a5a
24 hours24 hours <30<30°C/60% °C/60% RHRH
Level 6Level 6 Time on Time on Label (TOL)Label (TOL)
<30<30°C/60% °C/60% RHRH
Ref : Pb-free IC Component Issues and IPC/JEDEC Specification Update, Rick Shook, Agere Systems
Adapted from Courtesy of Cogiscan
Impact of Lead FreeImpact of Lead Free on MSD on MSD
ReliabilityReliability
What do we know?What do we know?
Many Lead-Free studies were conductedMany Lead-Free studies were conducted
Typical Findings:Typical Findings:High quantities of failure were found to High quantities of failure were found to
be cracking of ceramic chip capacitors be cracking of ceramic chip capacitors when flexing the circuit board. when flexing the circuit board.
Pb-Free solder resulted in solder joints Pb-Free solder resulted in solder joints that were more rigid than those of that were more rigid than those of Sn/Pb.Sn/Pb.
Types of Capacitor FailuresTypes of Capacitor Failures11
Placement Cracks5%
Flex Cracks25%
Unknown13%
Thermal Shock Cracks
23%
Manufacturing Defects
34%
SnAgCu Flex Crack ExamplesSnAgCu Flex Crack Examples11
SnAgCu Flex Crack ExamplesSnAgCu Flex Crack Examples11
AcknowledgementsAcknowledgements
The previous slides were adapted from the following papers.The previous slides were adapted from the following papers.
1.1. Robustness of Surface Mount Ceramic Capacitors Assembled Robustness of Surface Mount Ceramic Capacitors Assembled with Pb-Free Solder, with Pb-Free Solder, by Nathan Blatau, Patrick Gormally, Vin by Nathan Blatau, Patrick Gormally, Vin Iannaccone, Laurence Harvilchuck and C. HillmanIannaccone, Laurence Harvilchuck and C. Hillman
2.2. Robustness of Surface Mount Aluminum Electrolytic Capacitors Robustness of Surface Mount Aluminum Electrolytic Capacitors When Subjected to Lead Free Reflow, When Subjected to Lead Free Reflow, by C. Wiest, N. Blatau, J. by C. Wiest, N. Blatau, J. Wright, R. Schatz, and C. HillmanWright, R. Schatz, and C. Hillman
Where Does It Happen?Where Does It Happen?
Flexing (Mechanical Stress) occurs in Flexing (Mechanical Stress) occurs in following areas:following areas:ManufacturingManufacturing
Soldering HandlingSoldering HandlingBoard separationBoard separationConnector installationConnector installationMechanical standoff installationMechanical standoff installationIn-circuit testingIn-circuit testingCustomer usageCustomer usage
Flex Cracking ExamplesFlex Cracking Examples
Adapted from “AVX MLCC Flexiterm Guarding Against Capacitor Crack Failures” byMark Stewart, Technical Information
Solder Joint CrackingSolder Joint Cracking
Tin/Lead Solder Joint FailureTin/Lead Solder Joint Failure
Adapted from: “A Comparison of the Isothermal Fatigue Behavior of Sn-AG-Cu to Sn-Pb Solder” By Nathan Blattau and Craig Hillman, DfRSolutions
Crack starts at the toe of the solder joint and propagates to the component.
Grain coarsening may be an area of high stress.
Sn/Ag/Cu Solder Joint FailureSn/Ag/Cu Solder Joint Failure
In this figure the In this figure the crack starts in the crack starts in the fillet and goes fillet and goes toward the toward the component.component.
The crack start The crack start further up the fillet further up the fillet then it does with then it does with Sn/Pb solder.Sn/Pb solder.
Next slide provides Next slide provides another exampleanother example
Adapted from: “A Comparison of the Isothermal Fatigue Behavior of Sn-AG-Cu to Sn-Pb Solder” By Nathan Blattau and Craig Hillman, DfRSolutions
Sn/Ag/Cu Solder Joint FailureSn/Ag/Cu Solder Joint Failure
Adapted from: “A Comparison of the Isothermal Fatigue Behavior of Sn-AG-Cu to Sn-Pb Solder” By Nathan Blattau and Craig Hillman, DfRSolutions
Lead ContaminationLead Contamination
Lead as an impurity Lead as an impurity goes to the last area goes to the last area of the joint to cool.of the joint to cool.
This forms a pocket This forms a pocket and disturbs the grain and disturbs the grain structure.structure.
The resultant lead rich The resultant lead rich areas have a lower areas have a lower melting temperature melting temperature and could cause and could cause dewetting during dewetting during solderingsolderingAdapted from “A Study of Lead-Contamination In Lead-free Electronics Assembly And Its Impact on Reliability”
by Karl Seeling and David Suraski, AIM, Inc.
BGAsBGAs
Typical Over Molded PBGA Typical Over Molded PBGA
Adapted from: PBGA Package Warpage and Impact on Traditional MSL Classification for Pb-Free Assembly By B.T. Vaccaro, R.L. Shook, E. Thomas, J.J. Gilbert, C. Horvath, A. Dairo and G.J. Libricz
BGA Concerns Due Higher BGA Concerns Due Higher Process Temperatures Process Temperatures
Typical Typical warpage due warpage due to increases in to increases in temperaturetemperature
Adapted from: PBGA Package Warpage and Impact on Traditional MSL Classification for Pb-Free Assembly By B.T. Vaccaro, R.L. Shook, E. Thomas, J.J. Gilbert, C. Horvath, A. Dairo and G.J. Libricz
BGA Concerns Due Higher BGA Concerns Due Higher Process TemperaturesProcess Temperatures
As can be seen as the As can be seen as the temperature increases temperature increases the shape of the the shape of the package changes package changes which can cause which can cause excess forces on the excess forces on the molten solder creating molten solder creating shorts.shorts.
Adapted from: PBGA Package Warpage and Impact on Traditional MSL Classification for Pb-Free Assembly By B.T. Vaccaro, R.L. Shook, E. Thomas, J.J. Gilbert, C. Horvath, A. Dairo and G.J. Libricz
Shrink Hole VoidsShrink Hole Voids
What are they and how do What are they and how do they happen?they happen?
Solidification process of SAC Solidification process of SAC alloys causes shrink holesalloys causes shrink holes
Slow cooling causes Slow cooling causes excessive shrinkage of the excessive shrinkage of the final eutectic solder phase final eutectic solder phase just before solidificationjust before solidification
It does not seem to impact It does not seem to impact reliabilityreliability
It is not a crack and does It is not a crack and does not continue to grow under not continue to grow under thermal or mechanical thermal or mechanical stressesstresses
Forward Process/Component Forward Process/Component CompatibilityCompatibility
Forward Compatibility: Forward Compatibility: Using Sn/Pb components in Pb-free processUsing Sn/Pb components in Pb-free process
Reported of an increase in voiding in PBGA Reported of an increase in voiding in PBGA solder ball joint due to flux trapping.solder ball joint due to flux trapping.
Also reported is resulting lead contamination Also reported is resulting lead contamination that may affect the solder joint structure and that may affect the solder joint structure and decrease its reliability.decrease its reliability.
Many component vendors including Intel do Many component vendors including Intel do not recommend using their components in not recommend using their components in forward or backward compatible assemblies.forward or backward compatible assemblies.
Backward Process/Component Backward Process/Component CompatibilityCompatibility
Backward compatibility:Backward compatibility:Using Pb free components in Sn/Pb Using Pb free components in Sn/Pb
processprocessLead free BGAs are not recommended for Lead free BGAs are not recommended for
Sn/Pb assembly using temperature below Sn/Pb assembly using temperature below 220220ooC (428C (428ooF) because solder joints are F) because solder joints are poorly formed if the balls do not melt.poorly formed if the balls do not melt.May impact 2May impact 2ndnd level Interconnect reliability level Interconnect reliability
may be affectedmay be affectedIncrease tin whisker growthIncrease tin whisker growth
BGA Solder JointsBGA Solder Joints
Grain structure of alloy in BGA solder joint
Adapted from photos from Bob Willis
Tin/ Silver /Copper, Sn/ Ag / Tin/ Silver /Copper, Sn/ Ag / CuCu
Reflow Temperature 219 -217
Tin WhiskersTin Whiskers
Adapted from a publication of the National Electronics Manufacturing Center of Excellence
Columns
Striations
Rings
Adapted from iNEMI Tin Whisker Test Project, September 25, 2003
Tin WhiskersTin Whiskers
Tin Whiskers Growing on the Portion of a Bright" Tin-Plated Lead of a Crystal Oscillator (see inset above)that was NOT Immersed in Sn/Pb Solder during Hot Solder Dip Preparation Prior to Mounting
NEMI Experimental Tests for Tin NEMI Experimental Tests for Tin Whisker GrowthWhisker Growth
Tests:Tests: -55°C (+0, -10) / 85°C (+10, -0) air-air -55°C (+0, -10) / 85°C (+10, -0) air-air
temperature cycle (20minutes/cycle) up to temperature cycle (20minutes/cycle) up to 3000 cycles (500 cycles check points)3000 cycles (500 cycles check points)
60°C, 90±5%RH temperature / humidity 60°C, 90±5%RH temperature / humidity storage 9000 hrs (~1 year) with 1000 hr storage 9000 hrs (~1 year) with 1000 hr check pointscheck points
Ambient storage (~23°C, ~60%RH) up to Ambient storage (~23°C, ~60%RH) up to 18000 hours (~2 years) with 1000 hr 18000 hours (~2 years) with 1000 hr check pointscheck points
Copper DissolutionCopper Dissolution
Example microsection produced as part of the evaluation showing copper erosion on thecopper track. (IDEALS Lead Free Project)
Adapted from Lead-free Wave Soldering Process IssuesBy Bob Willis
Lead Free Solder Joints Lead Free Solder Joints
Good solder jointGood solder joint Fillet lifting on top Fillet lifting on top side of jointside of joint
Adapted from Lead-free Wave Soldering Process IssuesBy Bob Willis
PTH Solder JointPTH Solder Joint
Solder Lifting Off Pad.Solder Joint Cracking in Fillet
Corroded Solder Iron TipsCorroded Solder Iron Tips
Problem
1. Lead free solder alloys cause corrosion and abrasion at the stainless-steel based solder pot, pumps and solder channels
fragmentation at the solder shafts
Supplied by SEHO USA
Step 1: Solder Pot - De-Step 1: Solder Pot - De-AlloyingAlloying
Protection of the contact zones
To avoid problems caused by de-alloying of Fe, the replacement machine parts must be special coated which protects the parts against the aggressive solder alloy.
uncoated pump wheel after 6 month of use with Pb-free
solder alloy
composit-coatedpump wheels
Supplied by SEHO USA
Step 1: Solder Pot - De-Step 1: Solder Pot - De-AlloyingAlloying
Process ControlsProcess Controls
Monitor Monitor Solder paste quality and solderabilitySolder paste quality and solderabilityMaterial compatibility and solderabilityMaterial compatibility and solderabilityEquipment conveyor speedEquipment conveyor speedPreheat temperature profilesPreheat temperature profilesWave solder temperature profileWave solder temperature profileReflow oven profileReflow oven profileCleanliness monitoringCleanliness monitoringDocumentation presentationDocumentation presentation
In In SummarySummary
The program is a transition to lead-The program is a transition to lead-freefree
It is a major change in the industryIt is a major change in the industrySeveral supply chain and logistics Several supply chain and logistics
issues have been identifiedissues have been identifiedManaging the transition will test the Managing the transition will test the
capabilities of many existing capabilities of many existing procedures and systemsprocedures and systems
What is Needed to Make It What is Needed to Make It Work!Work!
Work as a TEAMWork as a TEAM