TW System Failures

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TW System Failures
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TW System Failures
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TW System Failures
http//www.calce.umd.edu/lead-free/tin-whiskers/
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TW Component Failures
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TW Component Failure
http//nepp.nasa.gov/whisker/index.html
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The Tin Whiskers Team

• A special interest professional group
• Initiated by U of MD Reliability Engineering
• Computer Aided Life Cycle Engineering (CALCE))
• Supported by DoD Reliability Component Engrs.
• STANDARD Missile 3 (SM-3), and
• Plastic Encapsulated Microcircuits (PEMs)
• Charter Dissemination, Characterization,
  Mitigation.
• G53 RMA Section Involvement
• Weekly tele-cons since May 2002
• Marking and Packaging Requirements Research

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The Tin Whiskers Team

• ARMY, Redstone
• BMPCOE
• Boeing, Anaheim
• Boeing, Canoga Park
• Boeing, El Segundo
• Boeing, Seattle
• CALCE _at_ Univ. of MD
• Corfin Industries
• Honeywell, Clearwater
• Honeywell, Tucson
• NASA, Goddard
• NASA, JPL
• NAVY, China Lake

• NAVY, Corona
• NAVY, Dahlgren
• NEMI
• Northrop Grumman
• Raytheon, El Segundo, Goleta, Lexington,
  McKinney, Plano, Portsmouth, St. Pete, Sudbury
• Raytheon, Tucson
• Sandia National Lab
• USAF, Eglin
• USAF, Wright Patterson

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Tin Whisker Team Current Work

• Disseminate information on the whisker risks,
• Developing a risk evaluation guide,
• Provided a supplier warning letter,
• Conducting experiments to determine key factors
  affecting whisker growth,
• Propose industry wide marking requirements,
• Defining experiments and seeking support to
  optimize re-dip, re-flow processes
• Proposing experiments to optimize conformal
  coating mitigation strategies.

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TW Interim Preventative Mitigation

• By Specification
• No Pure Tin Allowed! (some full Mil not safe)
• If Tin is Permitted, special processes must be in
  place
• Matte finish, re-flow, solder dip and
• Hard Conformal Coat.
• Component and Container Labeling Requirements
• Supplier Database, Supplier Letters
• Incoming Inspection Tests
• X-Ray Fluorescence (XRF)
• Developed as a tool to evaluate plating thickness
• Optimized for low-cost / high-volume work
• Full system costs around 30k

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TW Interim Preventative Mitigation (2)

• Incoming Inspection Tests (cont)
• Energy Dispersive Spectroscopy of X-Rays (EDS)
• Attached to a SEM
• Good for detailed analysis and probing of spatial
  variations in composition
• Full system costs around 200k
• Inductively Coupled Plasma (ICP)
• Very accurate (when calibrated to sample)
• Works best on bulk material rather than plating

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Trends Seen by the Tin Whisker Team

• Can be avoided for now, but the problem will
  increase
• More and more pure Sn will be used (supply 2),
• Labeling inconsistency, lack of standardization
• Tin may replace solder finish without
  documentation or part number change (in some
  cases).
• Eventually most electronics Pb-free,
• specially processing will be needed
• Confusion missing a DoD or Navy wide Strategic
  Plan
• This Just Out Reducing the Risk of Tin
  Whisker-Induced Failures in Electronic Equipment
• EIA Engineering Bulletin GEBx 20-Apr-03 Draft.

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Zinc (Zn) Whiskers

• Brusse2003-Zinc Whisker Awareness.pdf

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Conclusions

• The Metal Whisker Problem Presents a Real Hazard
  to Electronic System Reliability
• The Risk Will Increase Until a Comprehensive
  Strategic Plan is Developed to Deal With
• Tin Finishes on components and parts in
  Long-life, Maintenance-limited Systems and
• Zinc Finishes in COTS Enclosures, Computer Rooms,
  and Electronic Labs.

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Metal Whisker Hazard Summary

• The Metal Whisker Problem
• We are forced to cope with pure metallic (Sn
  Zn) finishes that have a propensity for growing
  whiskers.
• The Impact of Metal Whiskers
• Short circuits, some inserting undetectable
  errors, some causing catastrophic failures, all
  lowering reliability.
• Managing the Problem
• The Tin Whiskers Team is working to disseminate
  and mitigate the risk as much as is possible,
  without a central authority.
• Trends Expectations
• The use of pure Tin finishes will increase. The
  risk can be managed if given the appropriate
  attention.

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Extra Metal Whiskers

• Extra Metal Whisker Slides

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Metal Whisker Micrographs
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Not the Only Pb-free Problem

• While pure Tin is the predominate lead finish, it
  is not the only one
• No agreement on a standard solder
• Flow temperatures mostly higher
• Adhesion issues
• Appearance issues (some resemble eutectic
  cold-solder joint)
• Manufacturing issues
• Thermal cycle reliability issues.