The Metal Whisker Hazard to Military

1
The Metal Whisker Hazardto Military COTS
Electronics

• A TECHNICAL BRIEF
• By
• Steve Cmiel
• [phone], CmielSJ_at_nswc.navy.mil
• WEAPONS SYSTEMS DEPARTMENT (G)
• Applied Systems Engineering Division (G50)
• Quality Engineering Branch (G53)
• Reliability, Maintainability Availability
  Section

2
Metal Whiskers Agenda

• The Metal Whisker Problem
• Overview, Definition, History, Current Status.
• The Impact of Metal Whiskers
• Detailed Description, Characteristics, and
  Failures.
• Managing the Problem
• The Team, Work Efforts, Mitigation Ideas.
• Trends Expectations
• Conclusions, Summary.

3
Hazard Overview

• Relevance applicable to systems with any ONE of
  the following characteristics
• Systems with high reliability requirements,
• Long term life or storage,
• Limited preventive maintenance, or
• Computer Rooms Electronics Laboratories with
  raised decks.
• Severity Shorted Circuits!
• Stable short circuits in low voltage, high
  impedance circuits (zeros-out logical bits)
• Transient short circuits (it can take more than
  50 milliamps (mA) to fuse or burn-open a metal
  whisker)
• Plasma arcing in vacuum - highly destructive
  phenomenon, vaporized metal may initiate a
  plasma arc that can conduct over 200 amps!
• Debris/Contamination - whiskers break loose and
  bridge isolated conductors or interfere with
  optical surfaces.

4
What Are Metal Whiskers?

• Single metallic crystals that grow from pure
  metal finishes
• Typically a few millimeters long with lengths of
  up to 10 mm observed, and having
• Typical diameters of a few microns or
  micro-meters (µm) with some as large as 10 µm
  reported.

5
Tin Whiskers
6
Tin Whiskers
7
Tin Whiskers
8
A Brief History of Metal Whiskers

• The phenomena was first observed in the 1940s,
• Confirmed as a electrical/electronic assembly
  failure mode by the mid 1950s,
• Virtually eliminated by military standards and
  specifications requiring lead in the 1960s,
• Researched in the 1970s and 1980s, and
• Returned with vengeance (attributed as the root
  cause of recent failures) in the early 2000s.

9
Why Has the TW Problem Returned?

• Getting the Lead Out (the Green menace)
• US banned lead from gasoline, paint, and
  plumbing
• Japan 2001, Electronics Recycle Law requires
  manufacturers to recover harmful materials
• EU abolition of lead, other metals, from
  electronics by 2006
• Pb-free (Lead-free) Electronics
• A landfill contribution of 36 for Electronics
  includes CRTs, cables (compare to 48 for storage
  batteries)
• Circuit Card Assemblies (CCAs) lt5
• Electronic solder 0.5 (by wt.) of total industry
  usage of lead
• No (Serious) Scientific Evidence
• But most readily leachable with current tests
• Standard Components do now, or will, use Pure Tin!

10
Component Vendors Going Pb-free

• Linkto suppliers.xls

11
Tin Whiskers Shape
12
Tin Whisker Cut
13
Summary of TW Characteristics

• Most Grow from Pure Surface Finishes
• Mechanically stressed, bright electroplate shows
  most growth
• Millimeter (mm) lengths, µm diameters
• Good conductivity
• Sn, Zn, Cd
• Could exhibit strange properties?

Physl. Rev. B 67 100,000 ballistic
magneto-resistance in stable Ni nano-contacts at
room temperature
14
Tin Whisker Pictures

• Grown on test coupon by Raytheon FAL, McKinney TX

15
Tin Whisker Pictures
16
Tin Whisker Pictures