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Short answer
A tin whisker is a thin, electrically conductive, crystalline filament of tin that can grow out of a tin-plated surface, especially electroplated tin. Whiskers are typically a few microns across and usually several millimetres long, long enough to bridge conductors and cause short circuits. It is an electronics reliability issue, not a laboratory technique.
Definition and scope
NASA Goddard’s Electronic Parts and Packaging (NEPP) program describes whiskers as electrically conductive, crystalline structures of tin that sometimes grow from surfaces where tin is used as a final finish, especially electroplated tin. A whisker is a single hair-like filament growing outward from the surface; this distinguishes it from a dendrite, which grows along a surface.
Size and growth
According to NASA NEPP, whiskers are usually several millimetres long and rarely exceed 10 mm. Typical diameters are a few microns; some exceed 10 µm and few are under 100 nm. Reported growth rates range from 0.03 to 9 mm per year, and the incubation period before growth can run from days to years.
Types or related concepts
NASA NEPP separates tin whiskers from several things that can look similar or cause similar faults.
- Whiskers vs dendrites. A whisker is a single filament growing outward from the surface; a dendrite grows along a surface.
- Whiskers vs debris. NASA lists debris as its own failure mode: broken-off whiskers can bridge conductors or contaminate optical surfaces. The whisker is the source, the loose fragment is the hazard.
- Whiskers vs metal vapor arc. A metal vapor arc is not a kind of whisker but a consequence: a solid whisker is vaporised into a plasma of highly conductive metal ions that can carry hundreds of amperes, most likely at reduced pressure.
Why tin whiskers grow
NASA NEPP states that there is no single accepted growth mechanism. The factors it lists as proposed drivers are:
- residual stress in the plating;
- intermetallic formation;
- externally applied compressive stress;
- bending or stretching after plating;
- scratches;
- a mismatch in the coefficient of thermal expansion between plating and substrate.
Because the cause is not settled, NASA frames mitigation as risk reduction rather than a guarantee that growth cannot occur.
How tin whiskers cause failures
The table below restates the failure modes NASA NEPP documents on its Tin Whisker Homepage.
| Failure mode | What NASA NEPP describes |
|---|---|
| Stable short circuit | A whisker bridges conductors and the short persists; most likely in low-voltage, high-impedance circuits. |
| Transient short circuit | A whisker shorts conductors, then fuses open, so the fault can appear and disappear. |
| Metal vapor arc | A solid whisker is vaporised into a plasma of highly conductive metal ions that can carry hundreds of amperes; most likely at reduced pressure. |
| Debris | Broken-off whiskers can bridge conductors or contaminate optical surfaces. |
NASA also maintains a documented history of whisker-related failures in electrical systems (Leidecker and Brusse, 2006), listed on the same site.
How whiskers are controlled in practice
The NASA NEPP guidance on mitigation, as published on its Tin Whisker Homepage, runs as follows:
- Avoid pure tin plated components where possible.
- Tin-lead plating is acceptable when the alloy contains a minimum of 3% lead by weight.
- Verify the plating composition after procurement: NASA notes some products sold as “No Pure Tin” were later found to be pure tin.
- Where pure tin cannot be avoided, options include solder dip, replating, and conformal coating or foam encapsulation. NASA reports a coating of Arathane 5750 about 2 to 3 mils thick helped contain growth. NASA also hosts a paper on the limitations of hot solder dip for whisker mitigation.
- Evaluate the application-specific risk, including geometry, how critical the mission is and its duration.
Standards that address tin whiskers
IEC 62483:2013 (Edition 1.0, published 2013-09-25) is titled “Environmental acceptance requirements for tin whisker susceptibility of tin and tin alloy surface finishes on semiconductor devices.” The IEC states that it describes the methodology for environmental acceptance testing of tin-based surface finishes and mitigation practices for tin whiskers on semiconductor devices. The IEC also states that the methodology may not be sufficient for applications with special requirements, such as military and aerospace.
IEC 62483 is based on JEDEC documents: JESD201A (environmental acceptance requirements for tin whisker susceptibility) and JESD22-A121 (measuring whisker growth). A JEDEC/IPC joint guideline, JP002, addresses whisker theory and mitigation. Consult the documents themselves for test conditions; this page does not reproduce them.
Why lead-free rules raised the profile
NASA NEPP notes that the EU RoHS and WEEE directives set a June 2006 deadline to eliminate most uses of lead. That drove interest in pure tin finishes, and lead alloyed with tin is believed to inhibit whisker growth. NASA states that pure tin lacks a proven test method and is risky for high-reliability systems.
Where it matters for labs and instrument fleets
Laboratories rely on circuit boards inside analysers, controllers and power supplies, and whiskers are a possible cause of unexplained intermittent faults because transient shorts can fuse open. The checklist below is derived only from the NASA guidance above and is a prompt for questions to put to an equipment manufacturer, not a test procedure.
- Ask what finish is used on component leads and connectors, and whether the manufacturer has verified composition rather than relying on a “no pure tin” label.
- Where tin-lead is claimed, ask whether the alloy meets the 3% minimum lead by weight that NASA cites.
- If pure tin is present, ask what mitigation applies (conformal coating, replating, solder dip) and whether it suits the geometry and service life.
- Weigh the consequence of failure: NASA ties acceptable risk to mission criticality and duration, and the IEC says its methodology may not suffice for special-requirement applications.
For related reference, see the CASRAI guides on IEC 60617 electrical schematic symbols, hygrometer calibration and the ellipsometer for examples of instrument measurement pages.
Common misunderstandings
- “Whiskers are dendrites.” NASA distinguishes them: a whisker grows outward as a single filament, while a dendrite grows along a surface.
- “They appear quickly or not at all.” NASA reports incubation from days to years and no single accepted mechanism, so absence of whiskers early is not proof of absence later.
- “Lead-free means whisker-free.” NASA states the reverse risk: eliminating lead drove pure tin use, and pure tin lacks a proven test method.
- “A standard test certifies safety for every use.” The IEC states that IEC 62483 may not be sufficient for military, aerospace or similar special requirements.
Frequently asked questions
What is a tin whisker?
A conductive, crystalline filament of tin that grows outward from a tin-finished surface, typically a few microns wide and up to several millimetres long (NASA NEPP).
How fast do tin whiskers grow?
Reported rates range from 0.03 to 9 mm per year, after an incubation period that can last from days to years (NASA NEPP).
Can a tin whisker cause an intermittent fault?
NASA describes transient shorts, where a whisker shorts conductors and then fuses open, as one documented failure mode.
Does lead prevent tin whiskers?
NASA states that lead alloyed with tin is believed to inhibit whiskers and accepts tin-lead plating containing at least 3% lead by weight.
Which standard covers tin whisker testing?
IEC 62483:2013 covers environmental acceptance testing of tin-based finishes on semiconductor devices and is based on JEDEC JESD201A and JESD22-A121.
Sources
- NASA Goddard NEPP, Tin Whisker Homepage and Basic Information: nepp.nasa.gov/whisker (read 2026-11-08).
- IEC, IEC 62483:2013 publication record: webstore.iec.ch/publication/7089 (read 2026-11-08).
- JEDEC JESD201A, JESD22-A121 and JEDEC/IPC JP002, cited by name as related documents.
