[an error occurred while processing this directive]

Are Your Whiskers Going To Crash Your Computer?

By Rich Hill


If you think zinc whiskers are what happens when the tin man forgets to shave - guess again. Zinc whiskers are real and they could be growing right inside your computer room! Read on to learn what zinc whiskers are, where they come from, and what you can do about them.

WHAT ARE ZINC WHISKERS?
Zinc whiskers are a phenomenon that can occur on some wood-core computer room flooring panels. The whiskers grow on the underside (plenum side) of the floor panels. The whiskers are typically 2 microns in diameter and over time, (many years) the whiskers can grow to be several millimeters in length. While the whiskers are attached to the floor panel, they are basically benign. When the whiskers break free however, they become airborne and can circulate freely throughout the facility and get blown into your equipment.

WHAT HAPPENS?
You should remember that zinc is a metal and a conductor of electricity. If a whisker comes to rest on an exposed circuit card inside your equipment, it could cause a short; most likely an intermittent short. And as you know, an intermittent problem is the most difficult to detect and fix. While several victims of zinc whiskers have experienced complete failures, you may only suspect you have zinc whiskers when your equipment posts fault conditions or other abnormalities. You may also experience problems with your tapes and drives. Many victims of zinc whisker problems seem to experience an increase in problems when they migrate to new systems.

Zinc Whiskers are so small that the normal dust filters used on computer equipment are ineffective. If you want to stop zinc whiskers from entering your equipment you need HEPA filtration.

If you haven't heard about zinc whiskers before, you may be skeptical - It's easy to ignore a condition that is under the floor and barely visible at that. But the science behind zinc whiskers isn't a great mystery, nor is it really new. (Bell Labs reported on metal whiskering in the telecommunications industry back in the 1940s. Telecom companies are still dealing with whiskering from various metal sources today.) Ferrous metals such as steel are normally plated to prevent surface corrosion. Zinc is a very common plating material since it is fairly corrosion resistant, produces a good aesthetic appearance, and is reasonably inexpensive.

A normal bi-product of the plating process is high molecular level stresses in the plated metal. The crystalline structure within the metal will attempt to relieve the internal stress by enlarging the structure through the growth of crystals. The growth path is outward and the material is literally pushed out of the surface of the metal. These crystalline growths are known as whiskers. In the case of access flooring, the zinc electro-passivation coating on the steel sheet used to form the bottom pan of certain wood-core panels can have just the right makeup of zinc to promote whiskering of the zinc finish.

Because whiskering happens at the molecular level, the specific molecular make-up of the metal finish can literally prevent or exacerbate the problem. Moreover, the problem is not affected by environmental conditions such as temperature and humidity. If your panels are destined to grow whiskers, they will grow regardless of the environmental conditions.

WHY NOW?
Two things are happening in computer rooms to cause zinc whiskers to be noticed now. One, the floors are now old enough in many facilities. The floors have simply been in place long enough to grow reasonably sized whiskers and enough have broken off the panels, floated around and landed inside equipment. Your floor may have been growing whiskers for years and not known it because they weren't that large.

"We had analog card problems on our old 3090 systems and then we lost 10 power supplies on our new CMOS processors." Fort James Corp.

Second, is the continually shrinking size of electronic assemblies. The lead pitch (lead to lead spacing) on integrated circuits and other components has shrunk dramatically. A whisker has a much better chance of causing a short on today's electronics versus 1980s vintage equipment. Even a small whisker has a chance of shorting two leads.

"We were changing to SP/2 equipment and started having a lot of errors", Manpower, Inc.

The same issue is true for tapes. The bit density continues to increase and therefore contamination can more easily obliterate a large portion of data.

On the human side, zinc whiskers are not known to cause any threat to people. Zinc is actually necessary in our bodies and is contained in most mineral supplements. Overexposure is not a factor since the concentrations in the room extremely small. And the whiskers themselves are not toxic like lead or asbestos.

WHAT SHOULD YOU DO?
First, determine if you are at risk. If you don't have wood-core access panels, you don't need to worry about your raised floor giving you zinc whisker problems.

If you don't know what kind of panels you have, follow these steps:
1) Look at the bottom of the panel. If its smooth and flat, its probably wood core. If it has dimples or cutouts, it's definitely NOT wood core.
2) If the bottom is smooth and flat, confirm that it's wood-core by looking at a cut tile along the perimeter or at a cable cutout. Looking at the cut edge, you should see the core - particleboard.

Note: Zinc whiskers only grow on panels that utilize electroplated steel. These panels have a uniform dull, or slightly shiny, gray appearance. Zinc plating can also be applied using Hot Dipped Galvanization (HDG). This process yields a bright mottled finish like on a metal wash tub. HDG plating does not grow whiskers. So even if you have wood-core panels, you are not at risk if they have HDG plating.

DO YOU HAVE ZINC WHISKERS?
If you've got wood-core flooring panels and the metal on the bottom has electroplated zinc, you need to check for whiskers. The simplest and most straightforward method of detection is good old visual inspection. Rest the tile on its edge and sight down the plane of the tile and view the bottom pan with a flashlight. Whiskers will appear as small shiny or glittering protrusions from the metal. (A darkened room helps) Remember, whiskers are typically only 3-10mm in length. You should review several panels to get a good perspective of your situation.

Be Careful! This is the time to exercise caution! Zinc whiskers break off the panels easily. Sliding, or scuffing the panels will cause them to break off. Rubbing your hand over the panel will cause them to break off!

If you see whiskers, you now have proof. However, if you don't see whiskers, you can't automatically assume you are safe. You may not have checked the right panels, or the whiskers may not have grown enough to see.

An indirect but accurate testing method is wipe sampling of surfaces. If zinc whiskers are inside your equipment, they are also everywhere else in your computer room. With wipe sampling, a wet wipe is used to wipe a small defined area in the room The wipe is sealed in a plastic bag and sent to an environmental lab. The lab will then test for the presence of zinc on the wipe. The laboratory analysis typically costs less than $20 per sample with a 3-5 day turnaround. The lab won't be able to see individual zinc whiskers but they will be able to give you the concentration of zinc in the sample. If your wipe tests turn out positive, you've got whiskers!

More sophisticated microscope testing can be conducted to identify actual whiskers on specific components, such as a failure power supply. Although more expensive than wipe tests, Scanning Electron Microscopy (SEM) is essential in conducting failure analysis.

GETTING RID OF WHISKERS
If you determine you have a zinc whisker problem, the big question is what to do about them. In the short term you can and should do nothing! Literally nothing. If the whiskers are undisturbed, they will generally remain attached to the panels. However, this means that you can't move the panels to facilitate equipment moves and rearrangements or even repairs. This is not a reasonable solution for most facilities.

In the long term, you don't have any option other than to replace the affected floor panels. The panels can be cleaned but the whiskers will grow back! You could seal or paint the bottoms of the panels but research has shown whiskers will grow right through most coatings. Moreover, the cost of painting would most likely exceed the cost of replacement panels.

Replacement is no simple task either. The more zinc related equipment problems you've had, the more careful you need to be. You first need to determine the extent of your problem. Inspect a number of panels (at least 20) to decide of you need to replace all your panels or just a few. The more you replace the bigger the potential impact of the project. Zinc Whisker remediation is a big deal and should only be undertaken after careful planning. Without proper equipment, personnel and procedures, the likelihood of success is low. The following outlines the general procedure for panel replacement.

Step 1. - Power down and REMOVE from the environment any and all equipment that you can. If the whole room can be shut down, do it!
Step 2. - Power down as many air conditioning units as you can for the remaining load.
Step 3. - Protect remaining equipment with plastic barrier tents. Create safe envelopes for equipment by sealing plastic sheeting between the ceiling and the floor. If you still have airflow under the floor, you will need to create underfloor barriers as well. This step is critical since these barriers will protect your equipment from zinc-laden airflow during the replacement process.
Step 4. - Remove affected panels by carefully lifting (without sliding or jostling them) and placing them in a plastic garbage bag. Place only one panel in a bag and fold and seal the bag. Remove the panel from the room. Don't reuse the bags!
Step 5 - Clean the underfloor plenum, flooring understructure, and underfloor infrastructure using HEPA vacuums and wet wiping.
Step 6 - Clean the underside of unmovable panels (under equipment that cannot be moved) using wet wiping.
Step 7 - Install replacement panel
Step 8 - Repeat Steps 4 - 7 throughout remainder of affected area.
Step 9 - Carefully remove barriers, reinstall equipment.
Step 10 - Get back to work!

Remember to map or mark panels that were not removed, if any. These panels should be monitored for continued whisker growth and replaced coincident with future equipment moves.

CONCLUSION
Zinc whiskers are real but manageable. Many companies have successfully dealt with the problem and no doubt many more will be forced to deal with it in the coming years. Be proactive! Even if you haven't had problems, check your panels. If you think there may be zinc whiskers in your future, get some money in your budget to replace the floor before you have a problem.


About The Author
Rich Hill is President of Data Clean Corporation. The company has been cleaning computer rooms and other controlled environments since 1979. Data Clean provides consulting and remediation services for Zinc Whiskers and other contamination problems. Rich may be reached at rhill@dataclean.com.

[an error occurred while processing this directive]