by Jim Grady
In recent years zinc whisker induced electrical short circuits have been cited as the root cause of costly computer system failures world wide. So what are zinc whiskers and why are they and the problems they cause getting more attention now than ever before?
What IS a Zinc Whisker?
Zinc whiskers are tiny (as in microscopic) conductive filaments or crystals of zinc that are typically less than a few millimeters long and only a few thousandths of a millimeter in diameter. The hair-like crystals literally erupt from the surface of the metal surface adding material from the base pushing the whisker outward.
The incubation period for whiskers varies tremendously from a few months to, more typically, years and even decades. Once incubation has occurred growth rates can be as much as one millimeter per year.
Where do they COME from?
The two tiles are relatively easy to identify. Electro-plated tiles have wood or wood-composite cores with a flat sheet steel underside. The metal cladding has a uniform dull gray appearance although some may be slightly shiny due to the addition of brighteners. The undersides of HDG tiles are shiny with an irregular triangular pattern on the surface.
Raised floor tiles are used in computer rooms to create an easily accessed space under the floor for routing power and network cabling. Most importantly though is that the under-floor space is also used to circulate conditioned air to cool component filled cabinets and racks.
What PROBLEMS do they cause?
Zinc Whisker contamination is not always immediately diagnosed. In fact, whisker related failures are often mistakenly attributed to things like manufacturer defects and power surges.
Problems that may signal a zinc whisker problem are frequent power source failures (especially after floor tiles have been disturbed), equipment reports of faulty conditions, system resets and intermittent failures or abnormalities.
NOT a NEW problem
For the next fifty years interest in metal whiskers was limited to a select handful of industries most notably Telecommunications and Aerospace. However, the 21st century has experienced a renaissance in whisker research fueled by new regulations aimed at improving electroplated metals for increasingly sensitive and critical applications.
In the computer industry whisker issues have become more prominent as technology requires more circuitry in less space. Reduced geometrics (spacing between conductors) in modern electronics makes zinc whiskers a greater hazard than in older electronics where spacing was wider and the same whiskers were not able to bridge. Today's electronics also use lower circuit voltages that may be too low to melt whiskers creating permanent shorts.
Other reasons for increasing concern about zinc whisker problems have to do with the facilities in which the electronic components are housed. Computer facilities are aging to ten, twenty and thirty years which means that zinc whiskers have had sufficient time to incubate and grow to lengths where they have the potential to become a problem.
These same facilities are also experiencing more frequent maintenance and upgrading requiring that whisker prone structures be moved dislodging zinc whiskers and releasing them into the IT environment.
Determining if you HAVE them
If visual inspection reveals the presence of zinc whiskers, the next step is to do the requisite science. This is done by providing surface samples for testing in an environmental lab.
Samples can be obtained with wipes or tape lifts. The method will be stipulated by the lab you choose to do the sample assessment. Samples should be taken from a variety of locations throughout the room and great care must be exercised in handling tiles. If in doubt, ask your lab's personnel for their advice.
Once you HAVE them, can you GET RID of them?
The first thing to do is nothing. So long as you don't disturb the structures that are producing the whiskers, the likelihood of dislodging them is greatly reduced. This is only a short-term solution however because sooner or later you'll need to do something that will require you to move a tile.
One solution that has been tried without success is to paint the undersides of tiles suspected to have zinc whiskers. Researchers who have experimented with this technique have shown that the zinc whiskers will eventually grow through the layers of paint.
Some facility managers tip toe into the problem by replacing a few tiles that they think are the culprits. This approach is doomed since the assumption that there are only a few bad tiles is usually wrong and the problem worsens as tiles are mishandled releasing more of the whiskers.
The only "final solution" is to remove the contaminant producing materials altogether and properly clean the entire sub-floor plenum. Removing an old raised floor, replacing it with new understructure and tiles and thorough decontamination of the plenum is a job for professionals.
Jim Grady is an owner and serves as Chief Operations Officer of Environmental Protocol Corporation. EPC specializes in providing environmental solutions associated with building and maintaining Information and Communication Technology (ICT) facilities
Most people wouldn't recognize a zinc whisker if it came up and … but it may have nothing to do with most people and lots to do with zinc whiskers.
Potentially, any metal objects that have been electro-plated with Zinc can produce zinc whiskers but the most frequently reported source is certain types of raised floor tiles that have a zinc electro-plated coating. It should be noted that researchers are in general agreement that tiles manufactured using Hot Dipped Galvanization as the plating process do not grow whiskers.
Whiskers that remain attached to their host are not a problem. They become a contaminant only after they have broken off to circulate through the under floor air space and migrate into the electronics.
The people at Bell Laboratories initiated the first comprehensive studies of the zinc whisker phenomenon in 1951. Their interest in zinc whisker research stemmed from equipment failures experienced by Bell Telephone in 1948 which were eventually traced to shorts caused by whiskers originating from electro-plated components in their system.
The easiest way to determine if zinc whiskers are present in your computer room is to do a visual inspection of the "usual suspects." This can be done by tilting a suspect tile on its edge and viewing it against a dark background using a flashlight to highlight the shiny filaments.
The answer to that question is one of those "good news, bad news" answers. The good news is, YES, you can rid yourself of zinc whiskers. The bad news is it usually isn't an easy problem to solve.
First published in "the Operator", February 2006
