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Reliability Issues and Mitigation Strategies Reliability Issues and Mitigation Strategies for RoHS Compliant Assembliesfor 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 FearKnowledge Overcomes Fear
Widespread Technical Concerns
Component Plating Tin Whiskers Creeping Corrosion
Connector Plating Fretting Corrosion Stress Relaxation
Board Plating Long-Term Storage Champagne Voiding
Black Pad Solder Wetting Tin Pesting
Kirkendall Voiding Electromigration Solder Contamination
Board Flexing Mechanical Shock Insufficient Hole Fill
Fillet Cracking Pad Liftoff Popcorning (MSD)
Ceramic Capacitors PCB Material Conductive 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 CapacitorFailure 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 FinishesOSP ENIG Silver Tin SAC HASL
MaterialRoHS FR4 ISOLA Polyclad
Special IssuesShelf Life Environment Appearance
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 The BEST Mitigation Strategy for RoHS Compliant Assemblies is Choosing the Compliant Assemblies is Choosing the
RIGHT PARTNERRIGHT PARTNER
Dan Amiralian