Metal Whiskers: Failure Modes & Mitigation Strategies - NEPP - NASA

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Metal Whisker Melting Current -- Pt. 2 • Metal whiskers are also coated with electrically insulating films – Tin oxides, Zinc oxides, moisture films, et al • Direct MECHANICAL contact by the whisker to another conductor does NOT guarantee ELECTRICAL contact – For Electrical Contact, the potential difference must exceed “dielectric breakdown” of the insulating films – For tin and zinc whiskers, independent groups have confirmed the oxide film breakdown ranges from ~ 0.2V to ~ 45V Electrical Current Flow through this Tin Whisker did not occur until V applied ~ 3 V at which point the Whisker promptly melted December 5, 2007 Metal Whiskers: Failure Modes and Mitigation Strategies See Backup Slides for a Suggested Circuit for Measuring Metal Whisker Resistance 12
Sustained Metal Vapor Arcing • Gaps shorter than a few tens of microns can support a sustained arc at potential differences of 12 to 14 volts, and currents of 0.1 to 0.3 amperes. – See “Electrical Contacts” by Paul G. Slade, part three • However, as the arc gap increases, the EMF needed to sustain the arc increases, as does the current. – GSFC testing of FM08 style fuses with metal filaments ~5 mm long finds ~ 75 volts at more than 30 amperes is needed to generate a sustained arc across this arc gap when P ~1 torr December 5, 2007 Metal Whiskers: Failure Modes and Mitigation Strategies Tin Whiskers Growing on Armature Of Relay Produced Metal Vapor Arc G. Davy, "Relay Failure Caused by Tin Whiskers", Northrop Grumman, Technical Article, October 2002 http://nepp.nasa.gov/whisker/reference/tech_papers/davy2002-relay-failure-caused-by-tin-whiskers.pdf 13
Page 1 and 2: Metal Whiskers: Failure Modes and M
Page 3 and 4: What are Tin or Zinc or Cadmium Whi
Page 5 and 6: Whisker Resistant Metal Coatings
Page 7 and 8: 1960’s Vintage Transistor Guess W
Page 9 and 10: “There is a name for those who su
Page 11: Metal Whisker Melting Current -- Pt
Page 15 and 16: My Whisker “Stress Relaxation The
Page 17 and 18: Three Whisker Mitigation Strategies
Page 19 and 20: NASA Goddard Whisker Mitigation Stu
Page 21 and 22: Uralane 5750 - 2 Mils Thick 9-Years
Page 23 and 24: 2 Mils Uralane = Very Effective Whi
Page 25 and 26: Whiskers Lift and Peel Conformal Co
Page 27 and 28: Thank Goodness for Euler Buckling a
Page 29 and 30: Effects of Conformal Coating -- 2
Page 31 and 32: Contact Information Jay Brusse Pero
Page 33 and 34: Tin Whiskers Forming “Circus Tent
Page 35 and 36: A Few Recent Whisker Experiences
Page 37 and 38: • Basic Equipment: - Binocular Mi
Page 39 and 40: Field Technicians and Failure Analy
Page 41 and 42: "The Five Stages of Metal Whisker G
Page 43: An Example of “Melting” a Tin W

Metal Whiskers: Failure Modes & Mitigation Strategies - NEPP - NASA

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