This Photo Gallery contains examples of EEE Parts and related hardware that have grown metal whiskers.  This photo gallery is by no means a complete archive of the types of parts that have been known to whisker, but instead contains only those part types for which NASA GSFC has been able to obtain permission to share photographic evidence.   The growth of whiskers is NOT unique to a specific part type but rather is related to the materials and processes used to plate the components as well as the subsequent environment/handling conditions to which the parts are exposed.  As such, users are urged to exercise caution when selecting components that are plated with materials and processes that are prone to whisker formation.

Photo of the Month Archive

Capacitors

These commercial (size 0805) ceramic chip capacitors have pure tin plated terminations over a nickel barrier layer.  The user mounted them using conductive epoxy (i.e, not reflow soldered) and after thermal cycle testing discovered the tin whisker farm.  After thermal cycling max. whisker lengths of 100 microns were observed.  HOWEVER, after additional room ambient storage (6 - 8 months) the whiskers continued to grow with some in excess of 200 microns (max. length ~240 microns).  It has NOT been experimentally shown whether soldering these parts to the board would have eliminated the whisker concern through either reflow of the terminations or mixing of "most" of the termination surface with the mounting solder (typically tin/lead based).  See NASA GSFC Experiment #5 for more info.

Photos Courtesy of I. Hernefjord & NASA Goddard

Capacitor, Variable Air Spaced

In 1946 Howard Cobb of the Aircraft Radio Corporation (ARC) published an article "Cadmium Whiskers" that many consider to be the first public reference describing how metal whisker growth affected the proper functioning of electronic systems.  In his article he describes how cadmium whisker formation on the cadmium-coated plates of variable air-spaced capacitors were producing plate to plate short circuits in radio equipment used during World War II.  The news that cadmium coatings could produce damaging whiskers reached others such as Bell Laboratories (less than 20 miles from ARC) who switched from cadmium to tin and zinc coatings only later to discover that these metals also sometimes produce damaging metal whiskers.

The specimen shown below is a 1960s era variable air-spaced capacitor (similar to the one described by Cobb) that uses a tin-plated frame. The extensive tin whisker formation on this capacitor extend in excess of 8-millimeters in some cases. NASA Goddard greatly appreciates Frank Nikolajsen, a vintage radio collector in Denmark, for contacting us and then donating this treasure piece for analysis and historical preservation.

See a video of this air capacitor demonstrating their extreme lengths and flexibility in normal air flow

Images courtesy of NASA-GSFC

Circuit Breakers

Circuit Breaker Contacts

The images below depict tin whiskers growing on the "bright" tin-plated copper contacts inside of a circuit breaker. 

Read More About the Field Failures Experienced as a Result of the Tin Whiskers on These Circuit Breakers

Source:  Anonymous

Connectors

Wire Wrap Terminals

Tin-plated wire wrap terminals below grew a very high density (#/area) of tin whiskers having sufficient length to bridge adjacent terminals. 
Read more about this experience in the following GE Power Management Service Bulletin

Images courtesy of GE Industrial

ZIFF Socket 

ZIFF Socket below has tin whiskers growing from tin-plated surfaces immediately adjacent to areas where the pin presses against the contact.
Metal whisker growth has frequently been observed in applications where surfaces are subjected to externally applied pressure.
Source - anonymous (circa 2006)

Source: Anonymous

Connector, D-Sub, Tin-Plated Shell

Connector shells are often plated with tin, zinc or cadmium finishes for corrosion protection. 
The examples below show tin whiskers and zinc whiskers growing from D-subminiature connector shells including an example of a whisker bridging from the connector shell to a gold-plated connector pin

Images Courtesy of NASA-GSFC

Connector, D-Sub, Zinc-Plated Shell

Images Courtesy of NASA-GSFC

Connector, Circular, Cadmium-Plated Shell

The following circular connector shell is CADMIUM-plated.  Connectors like this were used as feed-thrus on a thermal vacuum test chamber.  The cadmium whisker formation on this shell resulted in shell to pin electrical short circuits that interrupted testing of space flight hardware.

Source: Anonymous

Connector, Universal Serial Bus (USB), Video Monitor

Universal Serial Bus (USB) connectors frequently have tin-plated surfaces.  The following photos show tin whiskers forming on USB connectors used on video monitor circuit card assemblies.

Read More About these USB connectors from CALCE's www site here:

Images Courtesy of CALCE-University of Maryland

Connector, Universal Serial Bus (USB), Mother Board

Universal Serial Bus (USB) connectors frequently have tin-plated surfaces.  The following photos show tin whiskers forming on two different types of  USB connectors used on PC motherboard circuit card assemblies.

Read More About these USB connectors from CALCE's www site here:

Images Courtesy of CALCE-University of Maryland

Connector, Octal Type

The connector below is an octal type connector with circular cross-section pins on the plug-in side (left side of first image below) and rectangular cross-section pins on the right angle mount solderable contacts (right side of first image).  The pins are pure tin-plated.  Tin whiskers were found on the rectangular cross section pins while performing an inspection of a module reported to have failed in a commercial electric power utility application due to tin whisker shorts originating from a microcircuit also used in this assembly.

Images Courtesy of NASA-GSFC

Crystal

Crystal, Tin-Plated Case

The leads on this crystal are made of Kovar (Fe-Ni-Co alloy) with a Nickel barrier layer having a final pure tin finish.  Prior to installation the user dipped the leads into tin-lead solder to improve solderability.  However, a small portion of the leads (close to the package) remained pure tin finish.  This pure tin region produced tin whiskers that shorted the lead to case causing field failures

Read More about this Crystal and the Benefits & Limitations of Hot Solder Dip to Mitigate Tin Whisker Growth

Source: Anonymous

Discrete Semiconductors

Diodes, Axial Lead, Tin-Plated

Axial-leaded diodes having tin-plated terminals have exhibited tin whisker formation.  
In 2005 the Dominion Millstone Nuclear Power Station experienced a reactor shutdown that was traced to an inadvertent alarm signal produced by a tin whisker short circuit from diodes like these.
Read the article here:

Image Courtesy of Dominion-Millstone Power Station

Images Courtesy of T. Riccio/STPNOC

Transistor, Metal Case, Tin-Plated

The package of these transistors used extensively in vintage radios is tin-plated. Tin whiskers growing on the internal surfaces of the package have produced short circuit failures of these transistors.

Read More about these Transistors and how a community of vintage radio collectors have combated the mysterious source of electrical short circuit failures.

Images Courtesy of NASA-GSFC and Paul Stenning

Relay, Electromagnetic, Tin-Plated Steel Armature

The hermetic relay shown below (age ~14 years) has an iron armature that has been plated with PURE TIN.  The armature is INTERNAL to the packaged relay  and cannot be seen by the user unless the device is destructively opened for analysis.  As noted by the images, numerous tin whiskers are clearly visible  (even via naked eye inspection) growing from the armature.  Some whiskers are approaching 3 mm in length which is more than sufficient length to create a  short internal to this device.
Read More About the Failures Attributed to Metal Vapor Arcing initiated by tin whiskers inside this relay.

See a Video of Whiskers Inside this Relay Demonstrating Extreme Flexibility When Subjected to Air Currents

Relay, Electromagnetic, Tin-Plated Case, Terminals & Header

The Relays shown below are plated with pure tin.  This plating exists over the entire case, header and the hook terminals that will normally have stranded wire soldered to the end of the hooks.  Whisker shorts can occur due to whiskers growing from either the case, header or the terminals.  Even when terminals have wire soldered to the hooks, whiskers have been observed growing from the base of the terminals near the glass to metal seals.

Images Courtesy of NASA-GSFC

Images Courtesy of Space Systems Loral

Hybrids and Microcircuits

Hybrid Microcircuit

The photo below is of the package lid of a hybrid microcircuit.  The lid was plated with pure tin. This whisker was found growing on the on the surface of the lid that was facing INSIDE the of the device.  Other whiskers were also found on the lids with some as long as 2 mm.  
In previous (unrelated) reports, whiskers similar to the one shown below on hybrid package lids have been reported to cause field failures in Phoenix Missiles¹ and F-15 radar systems² 
1) L. Corbid, "Constraints on the Use of Tin Plate in Miniature Electronic Circuits", Proceedings 3^rd International SAMPE Electronics Conference, pp. 773-779, June 20-22, 1989.
2) B. Nordwall, "Air Force Links Radar Problems to Growth of Tin Whiskers", Aviation Week and Space Technology, June, 20, 1986, pp. 65-70

Images Courtesy of NASA-GSFC

Photos Courtesy of Peter Bush (State University New York at Buffalo)

Resistors

Potentiometers

In 2005 Westinghouse Nuclear published a service bulletin describing how metal whisker formation on certain potentiometer cans could produce power supply interruptions.

Images Courtesy of T. Riccio/STPNOC

Potentiometer, Internal Structures

The following potentiometers were used as calibration pots in oscilloscopes from the 1970s.  Mis-operation of the oscilloscope were diagnosed to be the result of the metal whiskers growing from the internal components of the potentiometer shorting its case to the wiper..

Images courtesy of Alan Douglas/UK Vintage Radio Forum

Transformers

Transformer Cans

The supplier of these transformer cans originally supplied them with tin-lead (Sn-Pb) finishes.  In response to international legislation (e.g., RoHS) they switched to pure tin coatings without changing part numbers nor issuing a product change notice to their customers.  Fortunately, for the user who provided NASA Goddard with these samples, the external appearance of the cans was different enough to encourage him to provide them to us for a closer look. Thanks to Steve Battel for sharing these samples with us.

See a Video of these transformer cans

Images Courtesy of NASA-GSFC

After receiving these pictures of concern the supplier responded:

"We appreciate your loyalty for so many years and your email concerning the whisker growth. The push to be RoHS compliance has caused us to switch our plating process and introduce new materials that are environmental friendly but they in turn created other problems. I sent your concerns to our product manager and I hope we can do something about it."

Wave Guides

Wave Guide, Tin-Plated Flange (Documented in 2004)

The images below depict tin whiskers found growing from the tin-plated flange of a Ka band waveguide.  The high density of whiskers, some approaching 5-mm long, were found within several weeks of receipt of product by the waveguide user. In the end application whiskers of this size and density produced signal reflections and losses that affected the electrical performance of the waveguide.

Read More about the Tin Whiskers Found on this Wave Guide

Images Courtesy of Ingemar Hernefjord

Mechanical Hardware and Structures

Bus Rails and Bus Bars

Bus Rail, Zinc-Plated Steel (Documented in 2001)

The images below depict ZINC whiskers found growing on a zinc electroplated steel bus rail.  This rail also has a yellow chromate finish which obviously did not inhibit whisker formation.  Whiskers up to several millimeters long were observed.  The user of this bus rail determined the zinc whiskers were the root cause of catastrophic electrical shorting failure during a thermal vacuum test.

ADDITIONAL GALLERY of Zinc Whisker Photos on this Bus Rail

Source: Anonymous

Bus Bar, Tin-Plated Copper

The following bus bar is made of copper that has been tin-coated.  It was installed in manufacturing equipment used by a large paper mill in Sweden.  It is suspected that tin whisker growth from bus bars like this one may have initiated Metal Vapor Arcs on at least three separate occasions resulting in significant damage and equipment down-time.

Read more about the tin whiskers on this bus bar

Sample provided by Anders Johansson
Optical Photos courtesy of NASA-GSFC
SEM photos courtesy of Lyudmyla Panashchenko

Cable Trays

The following images document the growth of zinc whiskers from zinc-coated steel wire cable trays made by two different manufacturers.  Each cable tray is reportedly made from "pre-galvanized" steel where pre-galvanizing indicates that the steel wire was hot dip galvanized (i.e., zinc coated by immersion into molten zinc) and then the cable trays were made by welding together the already zinc-coated steel wire into the final cable tray structure. 

A summary report documenting the zinc whisker growths on each cable tray can be found here:

Zinc Whiskers on "Cable Tray #1" 

Zinc Whiskers on "Cable Tray #2"

Samples provided by Greg Camburn
Analyses by NASA - GSFC

Card Guides

Card Guides, Tin-Plated Beryllium Copper

In March 2006 the Space Shuttle Program discovered a massive tin whisker infestation on the printed circuit board "card guides" (aka card rails, card retainers) used to guide and hold the printed circuit boards inside of numerous avionics boxes.  The card guides were made of beryllium-copper then plated with pure tin coating. Tin whiskers up to 24-millimeters long were observed although most whiskers were on the order of several millimeters in length.

It is strongly believed that the application of conformal coating on the printed circuit boards helped to protect the circuitry from extensive electrical short circuit problems during the >15 years of field operations they endured.  However, it is believed that one failure during system level testing on the ground can be attributed to a tin whisker that detached from a card guide and managed to bridge a pair of conductors where the conformal coating was absent.

See a Video Describing the Effort to Remove, Replace and Retest the Space Shuttle hardware impacted by these whiskers.

See a Shorter Video of Tin Whiskers on Card Guides in Space Shuttle hardware  

Images Courtesy of the NASA Shuttle Logistics Depot (NSLD)

Floor Tiles (Raised) & Floor Support Structures

Floor Tiles and Support Structures, Zinc-Coated Steel

The whiskers below are ZINC WHISKERS.  They were found growing on the zinc-coated steel underside of raised floor tiles.  In these examples the floor tiles were part of a computer room in which zinc whisker debris was shed from the floor tiles especially during maintenance activities within the data center .  The conductive whisker debris was distributed around the room via the air cooling system.  Ultimately, some whisker debris was drawn inside of the electronic systems (e.g., servers, routers, disk arrays) operating in the data center resulting in catastrophic and/or intermittent short circuit failures.
See the presentation:  "Zinc Whisker Awareness:  Could Zinc Whiskers Be Impacting Your Electronics?" for More about Zinc Whiskers

ADDITIONAL GALLERY of Zinc Whisker Photos on Raised Floor Structures

Images Courtesy of NASA-GSFC

Hardware

Lock Washer

The following lock washer is tin-plated.  
Finding tin whiskers on this washer requires patience and familiarity with proper techniques to illuminate and inspect for metal whiskers.

See Video of this Lock Washer demonstrating how difficult it can be to inspect for tin whiskers using optical methods

Images Courtesy of NASA-GSFC

Pipe/Conduit

Steel Pipe, Zinc-Coated by Process of Hot Dip Galvanized (HDG)

This steel pipe was zinc-coated using a "hot dip galvanization" (HDG) process (i.e., immersed into molten zinc). Despite frequent claims to the contrary, HDG coatings are NOT immune to the formation of zinc whiskers as this specimen clearly shows.  The pipe had been kept in a warehouse storage for ~15 years prior to discovery of the whiskers.  Whiskers in excess of 10 millimeters have formed on this specimen.

Additional Photos and Measurements of this Zinc Whisker Infested Pipe (Courtesy of Lyudmyla Panashchenko)

Video of This Pipe Demonstrating How Whiskers Flex in the Presence of Electric Fields

Pipe sample donated to NASA Goddard by Reima Lahtinen
Optical photos courtesy of NASA-GSFC
SEM photos courtesy of Lyudmyla Panashchenko

Terminal Lugs

Terminal Lugs, Ring Type, Tin-Plated

The terminal rings shown below are plated with pure tin.  These terminal rings are commonly used in "crimp" type applications where a stranded wire is inserted into the barrel and crimped in place.  The ring terminal portion is most often mounted using a nut and bolt to adhere the ring to a conductive surface such as a chassis. Other terminal types shown include fast-on (spade) terminals.

These photos are of "unused/loose piece" terminal rings taken straight from the manufacturer's shipping containers.  In many cases the whiskers are found "inside" the crimp barrel of these parts which is protected from abrasion that can dislodge whiskers from the exposed surfaces.

See a Video of Tin Whiskers found Inside the Crimp Barrel of One of the Terminal Lugs shown below 

Images Courtesy of NASA-GSFC

Terminal Lugs, Spade Type, Tin-Plated

Images Courtesy of NASA-GSFC

Terminal Lugs, Tin-Plated, Manufacturer "A"

Images Courtesy of NASA-GSFC

Terminal Lug, Tin-Plated, Manufacturer "B"

Images Courtesy of NASA-GSFC

Test Points

Test Points, Tin-Plated

The test points shown here are "bright" tin-plated phosphor bronze loops.  They are commonly installed on PC Boards as access points for attaching test leads/probes to monitor signals and voltages during board level testing.

DISCLAIMER:
This website provides information about tin whiskers and related research. The independent research performed during the past 50+ years is so vast that it is impractical to cover all aspects of tin whiskers in this one resource. Therefore, the absence of information in this website about a particular aspect of tin whiskers should NOT be construed as evidence of absence.

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