technical challenges of rohs compliance by leo lambert eptac corp, manchester, nh for for...

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.


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



Conductive anodic filament (CAF) failure is thegrowth or electromigration of copper in a PCB.


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 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

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


Sn/Ag/Cu Solder Joint FailureSn/Ag/Cu Solder Joint Failure


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


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.


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

technical challenges of rohs compliance by leo lambert eptac corp, manchester, nh for for...

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