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Tin whiskers in computer flooring

2000

We have a situation where an existing computer site (around 10 years old) is being de-commissioned and it is desired to re-use the raised floor in a smaller site. The question has been raised as to what can be done about any potential zinc whisker issue.

No evidence exists of a zinc whisker problem with this floor and there seems to be no history of power supply problems or unexplained shutdowns.

Can anyone help me with the following questions:

Is there a simple way to determine if whiskers exist on the floor support structure or tiles ?

Is there a cleaning method which would remove any whiskers ?

Is there any solution other than replacing the floor ?

Would using a sealant, paint or cold zinc coating or possibly an acid etch clean reduce or possibly remove the problem assuming it exists ?

Your help would be appreciated.

Charles Hill
consulting - Canberra, Australia

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2005

Used computer room floor tiles can be a concern for conductive contamination. If the tiles are zinc plated, don't use them in your computer room. If you know they are zinc plated, throw them out regardless of whether you've had equipment failures or not. It is good to check the support structure in the same manner as you would check the tiles. I've seen zinc plating with "Peach fuzz" filaments or "zinc whiskers" on the tops of the pedestals and on the stringers as well as on the floor tiles.

If you are not sure and want to determine if the tiles are zinc plated, look at the type of construction. Is it a wood core or concrete core wrapped in sheet metal? If not it is probably OK, but if it is, look to see if the sheet metal is zinc plated or if it is hot dipped galvanized. You can tell the difference by looking for "Spangles" which would be present on galvanizing, but not on plating.

Galvanizing is the coating that looks like a metal garbage can. Zinc plating would have a smooth uniform look and may be either shiny or dull gray. The dull gray plating seems to have the most problems with Zinc Whiskers, but either way, I would discard the tiles if they are zinc plated.

Zinc whiskers are about a tenth the diameter of a human hair and are invisible under ordinary light. To see them, you must view them under a highly reflected light.

If you have already determined that the tiles are zinc plated don't use them, but if you want to do a little more checking on their condition, take look at the tiles in an area with subdued overhead lighting, or where you can turn the lights off. Shine a bright light (an LED flashlight works well) across the surface at a 90 degree angle, and look for "Peach fuzz" sized filaments or "whiskers". Dust will be randomly stuck to the tile, but the zinc whiskers will be rather uniform and may seem to "twinkle" in the bright light. Try this with several tiles from different areas of the room. Tiles that have not been disturbed are best because the zinc whiskers will have been scrapped off if the tile has been moved around.

Of course microscopic analysis or lab tests will confirm the presence of zinc whiskers, but I don't think you want that expense if you are reusing old floor tiles.

Leonard Lukomski
- Warren, Michigan

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2005

Charles, I just reread your note and see that I didn't answer all your questions.... Don't bother to clean the floor if it has zinc whiskers. Sealant or paints don't work either. Once the zinc whiskers have grown on the floor tiles they will grow back at a faster rate if removed. Because of their small size and the way they are formed, they will grow through paint or sealant. The only cure is to replace the zinc plated components of the raised floor, the tiles or the support structure.
I've seen floor panels that were five years old and just beginning to show signs of zinc whiskers. They were professionally cleaned and sealed. Less than one year later they looked as contaminated as they did before the process was done.
Zinc whiskers are only millimeters long and can short out the dense circuitry of today's computer equipment. The floor is not that valuable and isn't worth the effort.

Leonard Lukomski [returning]
- Warren, Michigan

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March 22, 2009

This is an update to provide some much sought after information and references, because Zinc Whiskers are an ongoing concern for data centers, computer rooms, medical facilities, and all forms of technology equipment.

NASA or NEPP, NASA Electronic Parts and Packaging Program Photos of computer room floor tiles and support structures are shown from the perspective of a general observation with the unaided eye, then under intensified illumination, then slight magnification, and finally SEM, Scanning Electron Microscope photos.
nepp.nasa.gov/whisker/photos/floor_tile/index.html

An often cited report from NASA engineering is "Zinc Whiskers, Could Zinc Whiskers be Impacting Your Electronics? Raise Your Awareness", by Jay Brusse, QSS Group, at NASA Goddard Space Flight Center, April 2, 2003. nepp.nasa.gov/whisker/reference/tech_papers/Brusse2003-Zinc-Whisker-Awareness.pdf

Additional information about Zinc Whiskers with photos is posted at the Metal Finishing web site, proving that HDG, Hot Dipped Galvanizing DOES produce zinc whiskers.
www.metalfinishing.com/editors_choice/articles/051108_Lahtinen.htm .

It has previously been assumed that HDG, Hot Dipped Galvanizing does not produce zinc whiskers. This report provides evidence to the contrary. Certain impurities in the HDG process contribute to the growth of Whiskers. This report also focuses on the floor support structure, the pedestals and stringers. "Two specimens were investigated. Figure 1 shows a hot-dip galvanized support structure. Extensive whisker growth is seen on the surface." Zinc Whiskers have even been observed on galvanized hardware such as nuts and bolts from the hardware store or lumber store when found in bins on the bottom shelf where the stock has not been disturbed.

NEPP, NASA Electronic Parts and Packaging Program has a great wealth of information about conductive contamination including Tin Whiskers, Zinc Whiskers found in computer rooms, and nine other metals and alloys that are a concern for the growth of conductive, metallic whiskers.
nepp.nasa.gov/whisker/other_whisker/#zinc

Tin Whiskers are found to cause concern in a variety of electronic equipment from space technology to medical devices and equipment. The NASA Whisker homepage has excellent information and many links.
nepp.nasa.gov/whisker/index.html

Leonard Lukomski [returning]
- Warren, Michigan