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Zinc "whiskers"



A discussion started in 1995 & continuing through 2010 -- add your Q to bring it back to the Hot Topics page.

(1995)

Have you ever heard of zinc whiskers? I haven't.

A colleague is claiming that the SCRATCHED zinc plated low carbon steel enclosure of an AC power supply is causing zinc whiskers to be found within the product that the AC power supply is located in.

The exterior surface of the power supply is slightly scratched, but there is one rather large scratch, 1/8" x 1/2", present. This scratch has caused bare metal to be exposed with no signs of corrosion present. All other scratches do not cause bare metal to be exposed.

Any information is appreciated.

Thanks.

Peter S [last name deleted for privacy by Editor]
- Tucson, Arizona


Yes!

Zinc Whiskers are unfortunately real, and have been involved in a product liability case where a patient on an apnea monitor died. See 'The Phenomenon of Zinc Whisker Growth and the Rotary Switch' by J.R.Downs and R.M.Francis in the Aug. '94 issue of Metal Finishing magazine.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(1995)

We've also found this to be true with Cadmium plated parts. Required conditions included that the base metal (steel) was not stress relieved and that the atmosphere in the system was relatively high in RH (moisture content). On samples we worked with several years ago, whiskers to 1/4 inch length could be caused to grow under these circumstances within days. Stress-relieving the base metal solved the problem.

Wolf Penzel



(1995)

There was a question earlier about zinc whiskers. I was wondering if anyone has heard of whiskers appearing with tin-zinc plating?

Thanks

Mike Ulinski



(1996)

Hello,

We are a sizable Electronics company, using a lot of Zinc plated chassis for our Internet routers. We have been plagued by Zinc Whiskers lately, and we would like to learn more about them. Where would we find books, publications, information about them. Where do we start ?

Thank you.

Noel V [last name deleted for privacy by Editor]
Internet Routers


(1996)

Tin whiskers have been a well documented phenomenon for decades, but I hadn't heard of zinc whiskers until the above-referenced law case written up in the Aug. '94 issue of Metal Finishing magazine.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(1998)

I'm a hardware engineer for a large computer company and we too have been plagued with this problem. I found microscopic zinc whiskers coming from the sheet metal frame that holds our electronic backpanels in place.

The whiskers would cause (in some instances 500 to 2500 ohm shorts to ground ) raising havoc with our electronics. We are currently going back to our sheetmetal supplier to try and find any reason for this. At this point it appears to be only on some of the sheetmetal parts. I have found quite a bit of info on-line by searching for tin plating. I still can't believe that this was found back in the 1940's by Bell Labs and we are still seeing this today!

Willis D [last name deleted for privacy by Editor]


(1998)

All the discussion above is so interesting! I am surprised that such a major phenomenon is coming into light just recently, especially in the electronics industry where it could cause disasters.

Has anyone done any study as to why this happens? Do whiskers grow even if the surface is chromated or painted? I recall one experience 15 years ago where I had faced a similar problem on 5 micron wide Al interconnects on ICs. Everything was fine until we deposited PVD SiO2 to seal Al lines, and we found chunks of metal disappearing, and never found where it went. We used to call them mouse-bites. My study indicated that it was stress induced mass transfer. After modifying the process to minimize stress, the bites disappeared.

Mandar Sunthankar
- Fort Collins, Colorado


(1998)

Indeed, tin whiskers have been recognized for decades and well understood for many years. Stress reduction and/or a small percentage of lead (or possibly bismuth) can stop them. Whiskers of zinc and cadmium may be more recent discoveries, although their cause is apparently the same, as is their cure. I have it on pretty good authority from a manufacturer of zinc alloy plating processes that the new alloy plates are less susceptible to whiskers than plain zinc, for the same reason than tin-lead is less susceptible than pure tin, but I don't know of anything being published in that direction yet.

Only recently did I find out that cadmium cannot be used in deep space applications because of a sublimation mass transfer phenomenon, Mandar. Can you enlighten us on that one?

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(1998)

Ted, the explanation for cadmium sublimation in space is relatively simple compared to the zinc-whisker phenomenon. Cadmium vaporizes (sublimes) easily on earth at elevated temperatures from its solid state, without melting. Also, it sublimes at lower and lower temperatures as the surrounding pressure decreases. If its vapor pressure is higher than the surrounding pressure, it will sublime. In space, the air pressure decreases to 10E-8 Torr and below as the distance from earth is increased beyond about 20 miles. At these air pressures, cadmium will just disappear at room temperature (25 C). The other phenomenon in space is collision with oxygen atoms in thin air when the spacecraft is moving at high speed. This erodes and pits softer metals quickly.

Just to add to my note above about cadmium sublimation in space: there are several dozen elements and compounds or alloys that exhibit the same property as cadmium in space, and consequently are useless in many space applications. These include cadmium compounds and alloys, Zinc and zinc alloys, Magnesium, Selenium, tellurium and alloys, even pure silver and its compounds, just to name a few.

Mandar Sunthankar
- Fort Collins, Colorado


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