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Tin Whisker Formation and Impact on PCB Assembly Reliability

Posted by Laura Austin on Sat, Oct 20, 2012 @ 07:00 AM

Considerably different from dendrites or other such shapes in components, tin whiskers can pose a very serious problem for a circuit board and other types of technology if they happen to be found and identified correctly. Tin whiskers are structures of "crystalline" formations that resemble whiskers and are most commonly found in electroplated tin that is used a finish on components, including PCB.

Several different components of PC Board assembly utilize tin for coating, although some measures were made to prevent tin whiskers from forming. One way is to reintroduce lead into the market, which can help stabilize the finish, however the exposure to lead over a long PCB Assembly Componentsperiod of time is still dangerous and most governments still ban its use. Because of this, most companies used special alloys.

Also, some industries are still allowed to use lead in their PCB assembly of technology components and there can be other ways to prevent tin whiskers without it that you can implement. But first, what are other ways these whiskers can form?

  • Stresses from poorly formed components which do not fit well together.

  • The use of intermetallic formation can also cause tin whiskers.

  • Many different outside sources of stress can create tin whiskers to form, which means the entire area of the components need to be checked.

  • Bending, stretching, or scratches from both external and internal problems are another big factor to consider when looking for tin whiskers.

Assembly is at most risk, which automatically means a faulty product if the whiskers begin to grow and interfere with the components. While tin whiskers may seem harmless enough, they pose a very real threat to the product as well as people. One of the most common problems from whiskers in PCB assembly is a short circuit or arcing. Electrical equipment can suffer shortages and even harm people from their arcing, which ultimately means lost time and money.

This impact on global PCB assembly means broken equipment, ruined circuity, and shoddy craftsmanship overall that needs to be addressed. In order to prevent or mitigate tin whisker formation, you can take these precautions:

  • If at all possible, remember to avoid the use of pure tin plated coating and other equipment. Most companies utilize alloys to help stabilize the components to mitigate tin whiskers, but caution still needs to be advised.PCB Assembly

  • Simply replate the areas that are at high risk of whiskers by either outsourcing to a contract manufacturing company or attempting it in-house. However, it is highly advised that you use an outside manufacturer to help strip down the current plating and put on a newer plating to avoid tin whiskers.

  • A foam encapsulating coat or housing can be applied to whisker prone areas, helping prevent any problems in the future. However, it entirely depends on the type of foam encapsulating coat used, how much of it is applied, and how dangerous the whisker prone area is. Fortunately, however, this normally helps prevent short circuits in most cases.

  • Alternatively, you can try to relieve any stress to the area with a hot oil reflow or new soldering job.

Working with a reliable assembly manufacturer who is willing to help with any tin whisker problems is also a very highly recommended route. Most are certified to make sure that no pure tin components are used whatsoever and instead alloys are used to mitigate whisker formation. There is always the risk of faulty and counterfeit parts which could also cause tin whiskers, but working with US-based companies normally means a higher standard of quality overall.

Remember, tin whiskers are much different than dendrites and cause serious damage to circuity! Simply ignoring the issue can result in failures in the components with short circuiting and arcing.

Have you ever experienced tin whiskers in your PCB components? What mitigation measures were put in place?

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