November ❘ December 2004 IT Pro 431520-9202/04/$20.00 © 2004 IEEE Published by the IEEE Computer Society

Zinc Whiskers: Hidden Cause ofEquipment Failure

Jay Brusse and Michael Sampson

D uring a one-month period, a NASAdata center experienced at least 18 cat-astrophic power supply failures innewly installed mass memory storage

devices. The ensuing failure investigation deter-mined that the causes of failure were electricalshort circuits. But what had prompted suchrepeated short circuits in modern, typically reli-able systems? The investigation concluded thatfor many years small metallic filaments, practi-cally invisible to the unaided eye, had been grow-ing from the underside of the raised floor tiles andfloor support structures. Maintenance activity toinstall the new equipment dislodged many ofthese conductive filaments, which were then dis-tributed throughout the data center by the forced-air cooling systems. Many of these particles weredrawn into the equipment power supplies, wherethey bridged exposed conductors, causing elec-trical failures. Only then did the data center man-agers become acquainted with the phenomenonscientists call zinc whiskers.

If you manage a data center, especially one thatsits on a raised floor, zinc whiskers might eventu-

ally have an impact on youroperations.

WHAT ARE ZINCWHISKERS?

Zinc whiskers, as the nameimplies, are tiny hair-like fila-ments of zinc that actually

grow from certain zinc-coated metal surfaces.Figure 1 shows zinc whiskers, which are typicallyless than a few millimeters long and only a fewthousandths of a millimeter wide.Because of theirminiscule dimensions, zinc whiskers can beextremely difficult to see without magnificationand proper illumination.

The whisker formation process consists of anunpredictable incubation period—typically last-ing months or even years without any growth atall—followed by a period of growth at rates ashigh as 1 mm/year. Many zinc-coated surfacesmay never grow whiskers. Unfortunately, accel-erated techniques do not currently exist to pre-dict if, when, and to what extent a zinc-coatedsurface will produce zinc whiskers.

Despite the first identification of zinc whiskersin the 1940s, their precise growth mechanismremains unknown today. In the decades since,research aimed specifically at the zinc whiskerphenomenon has been limited. However, duringthis same time, researchers have written morethan 100 reports or studies about tin whisker for-mation, a process that many agree is closelyrelated to the zinc whisker phenomenon. Evenwith the large effort to study tin whiskers, identi-fication of their growth mechanism(s) has alsoremained elusive. The NASA Goddard TinWhisker (and Other Metal Whisker) Web site(http://nepp.nasa.gov/whisker) lists many of theavailable reference materials on the subject of tinand zinc whisker formation.

Are unexplained short circuitsplaguing electronic equipment? If it’s operating in a raised-floordata center, zinc whiskers growing from the floor tiles could be the cause.

Resources

Potential Health Hazards?

Inside

44 IT Pro November ❘ December 2004

hardware (such as nuts, bolts, washers, equip-ment racks, housings, and rails). Recently,however, the most frequently reported sourceappears to be the zinc-plated underside of theraised-access floor tiles and the support struc-tures (pedestals and stringers) commonlyused in computer data centers.Figure 2 showsa typical raised-access floor system.

Raised-floor tiles, pedestals, and stringersare often constructed from steel to provideadequate strength.A thin zinc coating—fromelectroplating or hot dip galvanization(HDG)—is commonly applied to protect thesteel from corrosion. This thin zinc film is atrisk for forming zinc whiskers over time.Figure 2b shows one type of access floor tileknown to form zinc whiskers. Figure 3 showsthe tile’s underside;a high-intensity light heldparallel to the surface reveals what appear tobe fuzzy dust-like formations. Closer exami-nation reveals that the dust-like appearanceis actually millions of zinc whiskers shownmagnified in Figure 1.

Investigators have reported many cases ofzinc whiskers growing on zinc-electroplated

structures, and some report that HDG coatings areimmune to the whisker phenomenon. However, we haverecently seen one report citing evidence of zinc whiskers(some as long as 0.3 mm after one year in service) growing

on floor tiles and support struc-tures that the manufactureradvertised as HDG. So we rec-ommend caution when usingany zinc coating in applicationswhere zinc whiskers could posea hazard.

In the case of the NASA datacenter, investigators observedwhisker densities on the order ofmillions per single floor tile(each with an area of 4 squarefeet). At the time of the equip-ment failures, these zinc-electro-plated floor tiles were approxi-mately 10 years old.

Zinc whiskers on the under-side of raised-floor structuresmight seem to be a long dis-tance from electronic systemsthat operate above the floor.However, the NASA reviewdetermined that routine main-tenance activities in the datacenter—including the lifting,sliding,and reinstalling of access

D A T A C E N T E R S

WHERE DO ZINC WHISKERS GROW?Zinc whisker growth has been documented on a wide

range of zinc-coated materials including electrical com-ponents (such as electromagnetic relays) and mechanical

Figure 1. Zinc whiskers (here, magnified100×) growing on the underside of a

raised-access floor tile.

Figure 2. Typical raised-access floor system.

A data center floor system with one tile up, permitting a view of the support-ing pedestals and stringers; such a raised-floor arrangement facilitates under-floor cable routing. The subfloor space also serves as an air plenum (a). In thistop and side view of one type of floor tile (b), cutting a tile reveals a vinyl topsurface attached to a 1 inch thick wood fiber core. The core has a thin sheet ofzinc-electroplated steel attached to its bottom and sides.

Many of these whiskers are 1 mm or more in length.

(a) (b)

November ❘ December 2004 IT Pro 45

floor tiles and the pulling of electrical cablein the subfloor space—could dislodgewhiskers. Because of a whisker’s small sizeand weight, the subfloor, forced-air coolingsystem can easily redistribute whiskersthroughout the facility.

For efficient cooling, the forced-air systemtypically pressurizes the subfloor space withchilled air. Perforated floor tiles and air ventsprovide channels through which the cool air—and along with it, zinc whiskers—can pass intothe above-floor space. Ultimately, manywhiskers can pass into the electronic hardwarethrough vents and fans on the equipment.Once inside the equipment, zinc whiskers cancause various electrical failures, ranging fromintermittent to permanent short circuits.

Whisker debris can also become a physicalimpediment to moving parts or obscure opti-cal surfaces and sensors within some equip-ment (such as disk or tape drives). Figure 4shows a graphical representation of this zincwhisker failure mechanism.

WHEN TO SUSPECT A ZINC WHISKER ATTACKA review of the published literature and discussions with

several other affected organizations have revealed the fol-lowing common attributes of most zinc-whisker-causedfailures in data centers:

• Inexplicable system failuresbegan concurrent with (orwithin weeks of) mainte-nance activities requiringthe handling of or impactsto floor tiles. Power supplyfailures are the most obvi-ous because of the impactthey have on system opera-tion. However, failures ofother electronic systems(logic cards, motherboards,memory devices, and so on)can also occur with lessobvious but potentially seri-ous effects.

• Newer equipment seems tobe more susceptible to fail-ure than older equipment.

• Equipment located adja-cent to floor vents seemsmore susceptible to failure.

• Users might not thoroughlyinvestigate periodic or inter-mittent system failures un-

less permanent hardware failures begin to occur or sub-stantial system downtime occurs. Invoking service con-tracts and warranties sometimes means that probleminvestigation stops as soon as the vendor supplies replace-ment equipment.

Figure 3. Underside of the zinc-electroplated-steel floor tile in Figure 2b.

Dimensions arenot to scale

Air flo

w

Whisker debris drawninto equipment

causes short circuits

5

Forced-air systemrecirculates

whisker debris

3

Whiskers growbeneath floor from

zinc-plated structures(tiles, pedestals, and

stringers)

1

Bumping or sliding floor structures can dislodge whiskers

2Whisker debris distributed throughoutdata center (through

perforated tiles or vents)

4

Figure 4. Zinc whisker failure mechanism in a raised floor setting.

The sparkling dust-like surface is actually millions of zinc whiskersshown magnified in Figure 1.

46 IT Pro November ❘ December 2004

Other concerns, such as those we discuss in the“Potential Health Hazards?” sidebar could alsobecome a problem.

REMEDIATIONThe affected NASA data center implemented some

short-term corrective actions while evaluating long-termsolutions to its zinc whisker problem.The short-term cor-rective actions included replacing the affected power sup-plies; the new power supplies came with a protectiveinsulating compound that coats most of the exposed elec-tronic circuitry. This coating will minimize (not necessar-

D A T A C E N T E R S

CAUSES FOR RENEWED INTERESTDuring the course of this problem investiga-

tion, engineers supporting NASA GoddardSpace Flight Center learned that numerousorganizations (financial, engineering, educa-tional, governmental, and so on) have experi-enced problems with zinc whiskers, as the“Resources” sidebar indicates. Several factorsappear to contribute to the apparent increasein reported failures:

• Continuous miniaturization of electronic com-ponents. Technological advances have led tomore densely packed circuitry and tighterspacing between conductors. As a result,smaller conductive particles can now causeshort circuits.

• Reduction in circuit voltages and currents.Many newer electronic systems operate atlower voltages and currents. Energy availablefrom these components might not be suffi-cient to melt a zinc whisker, resulting inincreased risk for permanent shorts.

• Age of existing floor structures.Many facilitieshave zinc-electroplated floor structures thatare 10,20,or 30 years old or more.Thus,wherezinc-electroplated floor structures are in use,whiskers have had time to grow to lengthscapable of bridging exposed conductor spac-ings in most modern electronic systems.

• Increased maintenance and upgrade activityin raised-floor facilities. Any activity in theraised-floor facility that involves handling ormoving floor structures can potentially dis-lodge zinc whiskers, if the structures arealready infested with these growths. In today’shigh-technology environment, it is more com-monplace for computing facilities to undergoregular maintenance activity to perform taskssuch as adding or removing hardware; repo-sitioning or reconfiguring the equipment; orgeneral troubleshooting.

• Failure investigations (and corrective action) frequentlyconsider electrical power spikes or inadequate coolingas the problem sources before identifying zinc whiskersas a suspect. Techniques for investigating these othercauses might involve significant handling of floor tilesand can actually generate additional whisker-inducedproblems.

• Most data center managers have never heard of zincwhiskers until the problem affects their systems.

➤ “Are Zinc Whiskers Growing in Your Computer Room?”R. Hill, Data Clean Corp.; http://www.dataclean.com/pdf/zincwhiskers3.pdf.

➤ “Testing Your Mettle: Zinc Whiskers in the Data Center,”B. Brown, Network World, Nov. 2004, http://www.nwfusion.com/news/2004/110104widernetwhiskers.html

• “Pesky ‘Whiskers’ Zap PCs in Secretary of State’s Office,”Aldo Svaldi, The Denver Post, 1 July 2004, pp. C-01.

• “Precautions Against Zinc Whiskers,” Compaq Corp., PowerRequirements for Non-Stop Himalaya Servers—429905-001, http://h71033.www7.hp.com/TechPubs/PDF/Power_Requirements/TPSEC05.pdf.

• “What Nasty Little Things Are Lurking Inside Your DataCenter?” S. Tucker, Unisys World Monthly, Nov. 2002;http://www.unisysworld.com/monthly/2002/11/whiskers.shtml.

• “Zinc Whisker Abatement,” Worldwide Environmental Ser-vices; http://www.wes.net/field_engineering_services-zinc_whisker_detail.htm.

• “Zinc Whiskers: Could Zinc Whiskers Be Impacting YourElectronics?” J. Brusse, Apr. 2003; http:// nepp.nasa.gov/whisker/reference/tech_papers/Brusse2003-Zinc-Whisker-Awareness.pdf.

• “Zinc Whisker Contamination: A Paper on the Effect andAbatement of Zinc Whiskers in Data Processing Centers,”D. Loman, HP Services; http://www.dataclean.com/pdf/ZincWhiskerWhitePaper.pdf.

• “Zinc Whiskers Growing on Raised Floor Tiles are CausingConductive Contamination Failures and EquipmentShutdowns,” The Uptime Institute; http://www.upsite.com/TUIpages/tuiflashzinc.html.

• “Zinc Whiskers on Floor Tiles,” Infinite Access Floors;http://www.accessfloors.com.au/zincwhiskers.htm.

• “Zinc Whisker Induced Failures in Electronic Systems,”ERA Technology, Winter 2003, http://www.era.co.uk/news/rfa_feature_06.asp.

• “Whisker Alert,” Japan Electronics & Information Tech-nology Industries Association (JEITA), Jan. 2002; http://it.jeita.or.jp/infosys/info/whisker/ (in Japanese).

Resources

November ❘ December 2005 IT Pro 47

ily prevent) the risk of future power supply short circuitsfrom zinc whisker debris.

The affected data center also reduced activities thatrequire the significant handling of floor tiles.

For long-term solutions, NASA is evaluating proposalsfrom industry professionals that include, but are not lim-ited to

• the carefully planned and controlled removalof all affected or suspicious tiles and supportstructures, while protecting equipment andpersonnel;

• thorough cleaning of the data center envi-ronment, using vacuums with HEPA (high-efficiency particulate air) filters to remove asmuch whisker debris as possible; and

• the installation of replacement floor struc-tures that are not prone to zinc whisker for-mation, including all-aluminum or steel structures withconductive epoxy powder coatings or paints instead ofzinc for corrosion protection.

Simply washing whisker-infested materials is not aneffective long-term remedy.Whiskers can grow back.Andthough cleaning and then coating whisker-prone surfacesmight work, whiskers could possibly grow through someconformal coatings, depending on their properties andthicknesses. Long term testing is certainly needed to vali-date such remediation approaches.

D ata center managers should take zinc whisker identi-fication,detection,and mitigation seriously.Improperprocedures could produce additional hazards and fail-

ures. Rather than attempt to conduct these activities alone,organizations at risk for zinc-whisker-related problemsshould seek expert advice. Possible information sourcesinclude the suppliers of electronic hardware; the originalsupplier of the floor structures; professional data centercleaning or disaster recovery companies; and professionalsin medicine, or occupational health and safety.

We encourage data center managers to review equip-ment maintenance records as well as the equipment self-diagnostic fault logs for abnormally high failure rates.Suchtrends, especially if concurrent with floor-handling activi-ties, could indicate an active zinc whisker problem.

Unfortunately, this zinc whisker failure mechanismappears to be quite widespread, while awareness by facil-ity or data center management personnel appears to berather limited.We hope this report will help other organ-izations to identify a potentially serious hazard before theyexperience problems. ■

Jay Brusse is a senior components engineer at QSS GroupInc. in Greenbelt, Maryland. Contact him at jay.a.brusse.1@gsfc.nasa.gov.

Our investigation of the NASA data center raisedconcerns about potential health hazards from zincwhisker exposure. NASA is still reviewing this issue,but our initial research did not identify any specific

studies or published guidance.Several sources discuss the toxicity of zinc

in other forms, particularly zinc oxide in theform of granules, powder, fumes, and dust.In these forms, zinc seems generally benignwhen inhaled or swallowed, except in veryhigh concentrations. Inhalation of zincfumes can have more serious effects.Variousinformal reports on zinc whiskers suggest nohealth implications from exposure; however,these reports lack cited references from

medical or occupational-health professionals.Other research suggests that the shape of airborne

fibers can be an important factor regarding the poten-tial pathologic effects on the lung, specifically alength-to-width ratio of 100 to 1 or greater. Zincwhiskers commonly exceed this ratio.

Potential Health Hazards?

Michael Sampson is the manager of the NASA ElectronicParts and Packaging Program. Contact him at michael.j.sampson@nasa.gov.

For further information on this or any other computingtopic, visit our Digital Library at http://www.computer.org/publications/dlib.

We acknowledge the NASA EEE Parts Assurance Group(NEPAG) for its support in investigating tin and zinc metalwhisker formations. We also thank Henning Leidecker (NASAGoddard) and Jong Kadesch (Orbital Sciences Corp.) for theirinvaluable participation on our metal whisker investigationteam at the NASA Goddard Space Flight Center.