Reliability Issues and Mitigation Strategies for RoHS Compliant Assemblies Dan Amiralian

RoHS -Potential Reliability Issues RoHS – The EU Mandate to eliminate lead and enhance the recycling of electronics has generated seemingly equal amounts of concern and confusion. This presentation is intended to be a BRIEF overview of major reliability concerns and real-world mitigation strategies.

Don’t Let This Happen to YOU Knowledge Overcomes Fear

Widespread Technical Concerns Component Plating Tin Whiskers Creeping Corrosion Connector Plating Fretting Corrosion Stress Relaxation Board Plating Long-Term StorageChampagne Voiding Black Pad Solder WettingTin Pesting Kirkendall Voiding Electromigration Solder Contamination Board FlexingMechanical Shock Insufficient Hole Fill Fillet CrackingPad Liftoff Popcorning (MSD) Ceramic CapacitorsPCB MaterialConductive Anodic Filaments

What do the experts say? "There are three kinds of lies: lies, damn lies, and statistics." – Mark Twain

Range of Opinion Lead-free (SAC) is better than lead SAC is no different than lead SAC has issues, but they can be overcome SAC has issues that present real-world problems that require mitigation We need to go back to lead

Which Watch Swiss Swatch Switch Is applying for exemption to go back to SN63/37 due to reliability issues 30% Failure Rate Crystals Shorting Sub 32mil (.8mm) parts shorting 5% field failure rate to date This is not a unique experience

Keep it Simple – Two Major Concerns Process Alloy used to solder Process Parameters Specific Concerns SMT BGA PTH Components Potential Contamination Inability to withstand process Finishes Unacceptable number of variables

A Reasoned Approach RoHS isn’t going away There IS a reason High-Reliability electronics are exempt There ARE ways to mitigate reliability issues

Focusing on the Real World Not enough attention paid to COMPONENT issues Most mitigation plans do not fit the real world Too much academic information and propaganda – not enough “in the trenches” information.

Component Issues The Most Common failures are with the MOST COMMON Components Highest Incidence of Failures: Capacitors, PEMs and PCBs Inventory Control issues can lead to Pb contamination BGAs Package Sizes and Finishes are a concern

Chip Capacitors Major Concern UMD study of field failures from 70 companies revealed 30% of ALL failures were Capacitors – mainly MLCCs

Multi-Layer Chip Capacitor Failure Characteristics Faults not recognized by normal screening techniques Most likely in high capacitance devices of low voltage rating Not visible on the outside of the device Capacitance does not change but the leakage current may change dramatically

Why Do MLCC Fail at a Greater Rate with Pb Free Alloys? Pb-Free alloys require higher temperature and longer dwell times Cooling rate needs to be tightly controlled Pb-Free alloys are stiffer More stress on component MLCCs may have inherent problems On cutting edge of material use

How Do I Mitigate MLCC Cracking in the Real World? Existing Designs: Review Design and Access Potential Limit Requirement for Reworking MLCCs Develop Reserve New Designs: Place on top side only – be mindful of stress Select more Robust Components Limit Requirement for Reworking MLCCs Develop Reserve

# 2 PEMs Plastic Encapsulated Microelectronics Tin Whiskers (Matte Finish) Popcorning Wire Bonds Flux Process Compatibility Wetting (Ag Pd) Process Cycles Processes and Practices Previously Permissible with SN63 need to be revisited

Mitigating PEM Failures Review Allowed Processes Wavesolder Heat Cycles Review Component Specifications MSD Peak Temperature and Dwell Lead Frame Scoring vis-à-vis Wavesolder Develop Valid Failure Reporting and Reserve

RoHS Printed Circuit Board (WEEE Compliant) A variety of RoHS Compatible Finishes OSPENIGSilverTinSAC HASL Material RoHS FR4ISOLAPolyclad Special Issues Shelf LifeEnvironmentAppearance

Printed Circuit Board Finish Survey – EU 31% ENIG 30% Don't Know 12% Pure Sn 9% Silver 9% Other 6% Sn Ag Cu 3% Pd/Au Traditional FR4 after RoHS Processing Pad Finish, Tg, Td and Z-Axis Expansion are Important Factors

PCB Recommendations ENIG Long History Best Overall Performance ISOLA 410 / 620 or Equivalent Designed for RoHS Best overall characteristics

Through Hole Considerations RoHS Alloys do not act like SN63 MUCH longer wetting time Higher Temperature – STIFFER Material Poor up-flow, Cracking and Pad Lift are real concerns

Mitigation of PTH Concerns PROCESS MUST BE MORE FINELY DESIGNED AND CONTROLLED Trade-Offs need to be accessed Aspect Ratio to Specification Performance has to be reconciled Board FLEX / SHOCK

Ball Grid Array Concerns

RoHS Concerns -Ball Grid Array Voiding Solder Fragility Thermal Issues Mechanical Shock Issues Plastic Devices High Pin Count Devices Process Cycles

Mitigation of BGA Concerns PROCESS VALIDATION LIMIT VARIABLES Understand Risk Over Time it will become obvious that High Pin Count BGAs and Multi- Cycled BGAs processed RoHS WILL fail much more often, especially under certain conditions

The BEST Mitigation Strategy for RoHS Compliant Assemblies is Choosing the RIGHT PARTNER Dan Amiralian