Zinc Whisker Detail
For over 50 years, the electronics industry has been aware of the threat posed by Zinc Whisker growth on surfaces with a zinc-electroplated passivation coating. During recent years, growing concern has developed in computer rooms where these conductive contaminants form on the bottoms of some access floor tiles and are distributed to hardware where they cause failures or degraded performance.
Frequently Asked Questions
What are Zinc Whiskers?
Metal surfaces are coated with Zinc in a galvanization process to help protect them from corrosion. While several techniques are used, such as hot-dip or spraying, whisker growth appears to be limited to electroplated samples. Several industry studies have shown that whisker growth is dependent on internal stresses during the plating process. The whiskers are Zinc (Zn) filaments extending from the treated surface. They are normally only a few microns in width but can be several hundred to over a thousand microns long. Under proper lighting they can be visible to the naked eye on surfaces.
Where are Zinc Whiskers found?
Zinc Whisker growth has been found on sub-racks, switches, card cages, floor tiles, and other electroplated surfaces. The whisker growth can occur on surfaces within the hardware, or can be carried to the hardware from outside sources. Not all electroplated surfaces exhibit whisker growth and not all develop the problem at the same rate. The influencing factors are not fully understood at this point, though environmental factors are suspected.
Whisker growth on access floor tiles is a particular concern. These tiles have large surface areas and are often disturbed during normal activity in the computer room. Since the subfloor void of most computer rooms is used as a duct, the susceptible surfaces of these tiles are within the supply airflow. The Zinc Whiskers can easily be dislodged and carried to the hardware. Floor tiles are often dragged across the top of each other as they are removed from the floor grid, spreading the contamination throughout the room.
How do Zinc Whiskers cause failures?
The Zinc Whiskers are conductive contaminants. They can cause shorts on IC cards, power supplies or other electronic components. Identification of the source of such a failure can be extremely difficult. Often the contaminant will be dislodged during handling and shipping and the component will function normally when tested at the lab. In some cases, the contaminant will not cause a short but will cause voltage variances that can interrupt service without damaging the component. At sites with an identified Zinc Whisker problem, field technicians have had short-term success in reusing parts by blowing compressed air on the surface of a failed circuit board.
Why have I not heard of Zinc Whiskers before?
While the electronics industry has been aware of the threat of these conductive whiskers for many years, older electronic designs were less susceptible. As technology evolved, circuitry became much denser and operated at lower voltages. The growth of Zinc Whiskers is not new but its ability to impact hardware reliability has been increased by the denser geometry of the newer technologies.
What do the hardware manufacturers say about Zinc Whiskers?
Several hardware manufacturers and industry groups have published warnings regarding the potential impact of Zinc Whiskers on the reliability of electronic components. The IBM AS/ 400 Physical Planning Reference V4R1 states that, "Raised floor tiles that have a Zinc-electroplated passivation coating have the potential to grow Zinc Whiskers. IBM believes that Zinc Whiskers cause intermittent AS/400 operational problems." In its NUMA-Q™ Systems Site Planning Guide, Sequent Computer Systems cautions that Zinc Whiskers, "can break off and become airborne particles. If Zinc Whiskers land in power supplies or electronic equipment with dense circuitry the shavings can cause a short that damages the system." In its customer services documentation, Amdahl warns that, "Accumulations of contaminants within the computer room can adversely affect equipment availability," and lists among these, "Zinc extrusions on floor tiles." This problem has also been documented by FUJITSU, Bellcore and numerous industry groups.
What can I do if I suspect a Zinc Whiskers problem?
The presence of Zinc Whiskers can be verified by experts using specialized field and laboratory tests. An inspection of your site can identify the source and degree of any conductive contaminant problems. If Zinc Whisker growth is identified on your floor tiles, extreme caution must be used in addressing it to avoid making matters worse by spreading it throughout the room. The most appropriate action is the replacement of all floor tiles with the selective encapsulation of inaccessible tiles. This is an extremely delicate and labor-intensive procedure involving specialized high efficiency decontamination and encapsulation of appropriate air plenum surfaces to trap residual contaminants. The project must employ appropriate monitoring and must be planned with proper regard to contaminant isolation and conditioned air distribution to minimize the possibility of impacting hardware up-time. Such drastic measures are not always necessary and consultation with experienced specialists is strongly recommended. Worldwide Environmental Services can help determine the solutions that are right for your site.
Contact a WES representative if you have any questions on Zinc Whiskers or if you would like to learn more about our decontamination services.
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Zinc Whiskers collected on
Sample wipe as viewed by
Scanning Electron Microscope. |
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Zinc Whiskers shown on back of access floor tile.
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