Zinc Whisker Remediation

Zinc Whisker Remediation

As often happens, an invention designed to solve a bizarre problem in a highly technical field has other applications in many other fields. The mathematical equations, developed from research funded by the American Military,  that govern a tin whisker trying to puncture an elastomer film on an electronic circuit board also explain how a nail punctures a tire and then its inner tube. Before we cover the zinc whisker remediation story, lets look at the area where zinc whiskers present the biggest problem.

Zinc Whiskers in the Data Centre

There are other areas that have metal whisker problems besides tin plated RoHS compliant parts on circuit boards. While zinc whiskers were not a problem with the earliest computers, it became one when computers began to be built in large arrays of many racks, filling rooms. These computers had air cooled cards in them, stacked side by side in layer after layer. These are typically filled with boards covered with those microcircuits typically having leads spaced 2 to a millimetre.

These rooms are the Data Centres, and they store and handle the information and records of every medium and large company, of every State and many local Governments. They are owned and used by the companies that memorise the Internet and store it for easy access and searching, by the telecommunications companies that handle and connect calls and manage all the billing for everyone for each call. All of that needs lots and lots of computers that fill warehouses and those are the Data Centres.

Data centres are also where The Cloud is, physically; it’s in huge buildings, on millions of square metres of floor. Our modern civilisation is utterly dependant upon the data centre. It has come to pass in the last ten years or so that individual computers and components in these data centres began to malfunction, entirely too often.

The culprit turned out to be not so much tin whiskers on the electronic components on the air cooled circuit boards, but zinc whiskers. These were not on the circuit boards at all, but were actually growing in the cooling air distribution system in between the floor and the sub floor, a metre further down. Data Centre floors have a metal structure of steel frames in which the floor tiles rest, and vertical supports that carry the weight loads of the racks of equipment to the sub floor. The under faces of all those floor tiles are covered with steel sheet, and the supporting structure of the floor is similarly made of steel frames and posts. To prevent it from rusting all the steel is galvanised (zinc plated). As Bell Labs discovered three generations ago, zinc grows whiskers that look similar to tin whiskers.

The scale of the problem of electrical failures caused by Zinc Whiskers is illustrated in this NASA presentation.

Here is a photograph of a sample of a galvanised floor tile with zinc whiskers.

Zinc whisker remediation needed on this data centre floor tile sample
Galvanised floor tile with Zinc whiskers. Click to enlarge

Zinc Whisker Distribution in data centres

Zinc whiskers are really light which means when they break off they can travel in the cooling air. The cooling air is designed to cool the computers, so the whiskers get pumped right to where they cause most harm. They collect just like dust, except that they are conductive and can cause short circuits. Not only can air flow break off those whiskers, but swarms of them can be detached when floor tiles are removed. Incidences of failures can increase after performing some work, running additional cabling or any other task that moves galvanised surfaces. The metal whiskers get blown into the electronics, shorting out power supplies and electrical signals and then things quit working, intermittently or permanently, and maybe with a flash of light and a cloud of smoke.  You can see these whiskers and get an idea of their scale in this picture:

Zinc whisker remediation problem whisker scale ruler
Ruler graduations 0.25mm. Click to enlarge.

Zinc Whisker Remediation – Redundant Systems

The random failures of the computer cards are frequent enough that these systems are designed often with multiple redundancy. Multiple redundancy means that even with many parts failed the whole system can still work.  Good (and costly) design ensures that each plug in card that fails can be removed, even while everything is running, and a new one plugged in. This is an expensive solution but the only one that is practical when there are thousands and millions of such replaceable circuit cards and they are all handling information whose reliable flow is necessary to keep a busy civilisation humming along.

Zinc Whisker Detection

How do you know if you have zinc whiskers in your Data Centre?  Well, you could just run your finger over the floor tile undersides or the galvanised steel parts below. If you find yourself saying “Ouch”, or some more colourful word, and feel a sharp pain in your finger, then you have just found a zinc whisker. How many zinc whiskers would you find if you do have them? Millions, based on some NASA investigations of floor tiles. Whiskers are sharp pointy things; and while some are curly, some are dagger straight. You may need a magnifier to see them since they are so thin. You don’t have to see them to feel them stick you; the straight ones will get you every time.

A more conservative method of whisker detection is to shine a strong LED flashlight on the surface, from the side, moving the angle around. Illuminating the surface from the side and viewing it against a dark background is recommended here. Seeing a forest of sparkling points of light means you are looking at a field of zinc whiskers. Any magnification will make them clearer, and you will then be able to appreciate the threat safely.

Zinc Whisker Remediation by Conformal Coating

Historically there never was a good solution to containing the zinc whiskers and preventing their electrical failures because there never was a paint or coating that could be applied to encapsulate them.  The whiskers would just grow through any paint or coating. The reason for that is that the science of the situation, the physics of failure of coatings in that circumstance, was entirely unknown. The people working in that field did not have the scientific background to develop the physics of failure of such coatings. That was then…

Dataguardian™

The tin whisker captivation work funded by the American military, described here, yielded the mathematical equations that govern the captivation of any kind of metal whiskers by an elastomeric coating.

whisker encapsulation peelback of conformal coating
High magnification optical view of the Whisker-Tough conformal coating peel-back during tin whisker growth prior to whisker collapse

This allowed the definition of the polymer properties required of a conformal coating capable of captivating tin whiskers on electronic circuit-card assemblies.

Those same equations defined the polymer properties required to captivate zinc whiskers in the environment of Data Centres.

Such a coating has now been designed. It is a waterborne “high tech” emulsion (latex) type coating, called Dataguardian™, and is offered for application by Data Centre owners, operators and maintenance organisations. Dataguardian™ is suitable for application to new or old galvanised surfaces requiring protection from zinc whiskers.

Please click here for more information on how Dataguardian™ can offer you permanent zinc whisker remediation, reducing your downtime and maintenance requirements thus boosting up-time and profits. Alternatively Contact us for pricing and availability.