Metallic whiskers have been a topic of discussion for the past forty years, ever since Western Electric employees first documented the issue in central office facilities in the 1950s. Since that time, a substantial amount of research has been conducted on tin-plated products, observing the high potential for the growth of tin whiskers and the manufacturing practices required to mitigate those risks.
The concerns are that the zinc coating may act in the same manner as tin. The idea is that the zinc coating surface changes over time and, in some instances, tiny 'whiskers' form microscopically, detach when the product is physically touched, and become airborne. Once airborne, they could land onto a circuit board and short out components without leaving a trace. Very little research and testing have been undertaken to fully understand the current manufacturing practices of zinc-coated steel products and what, if any, actual risk exists. The consensus has been to extend the tin-plated research to the zinc plating process, even though no direct tests of the zinc plating have been conducted. Cable Bridge
Much of the concern about the potential of zinc whiskers is based on Western Electric and NASA documents from the 1950s and 1960s that showed zinc whisker formation in a raised floor application. Careful review of the documents and photos reveals two significant concerns with the conclusion that electroplated products in data centers are not acceptable. The first concern is the statement in the paper/articles that the raised floor panels with zinc whiskers are electroplated zinc. The items shown in the photos have zinc 'spangle' markings that occur only in a hot-dip zinc coating process (HDG or Pre-galv) and not in an electroplating process. A review of the manufacturing methods of raised floor tiles via manufacturers of the floor tiles shows they use pre-galvanized materials, not electroplated zinc. Based on these images, any concerns of zinc whiskers should be directed to pre-galvanized or HDG products, not electroplated products. The second concern with the data presented in the articles is the lack of detail regarding the environment of the panels. There is little information concerning whether the area under the raised floor was used for environmental air or sealed. Sealed floor spaces in a humid environment are dramatically different from the current carefully managed environment in a modern data center. Zinc is a very reactive metal and will respond differently to changes in environmental conditions.
Although the topic of zinc whiskers is often discussed, there is limited research and data available, leading some members of the industry to adopt general rules. In the data center industry, a few have taken a cautious approach, opposing all zinc plating due to concerns about zinc whiskers. On the other hand, some members do not see sufficient evidence to warrant a ban on zinc plating. A close review of "pre-galvanized products" reveals that the bending processes used to form them can cause very tiny bits of the galvanizing to crack and flake off, potentially leading to small, if not larger, issues.
Industry members with a great deal at stake, including server, switch, and other electronic equipment manufacturers, continue to use and promote the use of zinc-plated chassis, hardware, mounting slides, and other components directly inside and outside the very electronic items that zinc whiskers are thought to be able to damage.
Most equipment manufacturers perceive the risk of zinc whiskers to be minimal and, therefore, persist in utilizing zinc plating in their electronic equipment, providing a full warranty for the installation.
Cablofil has provided miles of zinc-plated wire mesh cable tray to the communication industry since the 1970s without any recorded incidents of zinc whiskers. When Cablofil zinc-plated wire mesh is installed, Legrand considers it the correct material for the application, and the maintenance schedule is the same as stated in the NEMA VE2 standard. The tray should undergo a visual inspection annually to check for physical damage, overloading, or loose connections. It is not required nor recommended to wipe down the tray or perform any maintenance on the finish. Legrand is comfortable in recommending Cablofil zinc-plated wire mesh cable tray without hesitation, however if the data center owner or user still has reservations Cablofil does offer an organic powder coat paint as a finish option that can provide additional pear of mind.
Hdg Perforated Cable Tray Bob Crain is Director Marketing/Product Development at Legrand/Cablofil. Contact them to learn more about Cablofil's zinc-plated wire mesh cable tray.