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