Zinc Whiskers

Question:

Our company zinc plates steel computer cabinets. Recently one of our customers expressed concern about zinc whiskers and wanted to know if there is a process available to minimize this problem? What are zinc whiskers and where do they come from? C.P.

Answer:

Zinc whiskers are a real problem in the world of computers. The whiskers grow on sheet metal that is zinc plated. It is thought that the whiskers grow because of the compressive stresses that are associated with the zinc electrodeposits. In a typical zinc deposit, “pushing” zinc from the surface of the coating to form zinc whiskers relieves this compressive stress. The whiskers are small—2 microns in diameter and up to a couple thousand microns in length.

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These zinc whiskers can and do fall off the zinc electrodeposit and end up being blown about by the airflow that is necessary for cooling of the components in a computer. These whiskers can lodge almost anywhere within the “guts” of a computer, causing bridging between circuits and ultimately causing voltage and signal changes. When this happens, you often have a computer glitch or failure.

Zinc whiskers were not much of a problem earlier in the computer age because the geometry of components was larger, and the whiskers were not big enough to cause bridging.

Filters on the air circulation system within a computer system are not effective. Using a suitable filter that will trap the airborne whiskers will reduce the airflow to unacceptable levels.

Zinc whisker growth seems to be related to zinc electroplated surfaces only. Zinc galvanized surfaces do not seem to grow whiskers. Another suggested solution is to replace zinc plating with tin-nickel or zinc-tin deposits. As you might guess there are a number of organizations actively investigating this phenomenon.

One of the few papers that discuss zinc whiskers is by Jay R. Downs and R. Michael Francis in Metal Finishing, 92, August, 23-25, 1994.