Parylene and Tin Whiskers
Posted by Sean Horn
Tuesday, November 26, 2013 8:50
@ 8:50 AM
Tin whiskers have long been a frustrating occurrence for those manufacturing and using electronic devices. First discovered in the 1940s, the whiskering of metal has been the cause of serious problems including the damaging of vital and difficult to replace equipment. Finding ways to prevent or slow the growth of whiskers has been a focus of engineers and scientists for quite some time.
What are Tin Whiskers?
The exact mechanism behind the development of tin whiskers is not fully understood. However, the growth of these whiskers is believed to be encouraged by mechanically and thermally-induced stresses. Over time, the tin solder used to assemble electronics will begin to “grow” tiny hair-like appendages. These growths are known to cause short circuits and arcing which can result in devastating damage to electrical devices. Tin whiskers have been responsible for damaging vital equipment including pacemakers, power plants, and even satellites.
How Can Tin Whiskers be Prevented?
Mitigating tin whiskers is necessary to ensure the durability and reliability of electronics. In the past, lead was used instead of tin to avoid whiskering. While still prone to whiskering, lead is known to greatly reduce the growth rate of whiskers. However, using lead in manufacturing has its own drawbacks. Lead is a highly toxic heavy metal, and its use in electronics poses a grave health risk. As such, the use of lead in consumer products is restricted in many places, including an almost outright ban in the European Union. Without the use of lead, electronics manufacturers have had to turn to alternative methods to mitigate tin whiskers. Perhaps the most effective method discovered thus far is parylene coating.
How Does Parylene Coating work?
Parylene helps to mitigate tin whiskers when it is used in a process known as conformal coating. This process is used to protect circuitry from a wide variety of environmental hazards such as water, dust, and extreme temperature. As an added benefit, parylene is one of the only coatings that prevents water molecule penetration. In the context of tin whiskers, conformal coating provides a physical barrier to prevent tin whiskers from damaging equipment. When a conformal coating is applied, a barrier is formed and circuitry is protected as components become physically separated from each other. In doing so, whiskers are prevented from creating a bridge between components and causing shorts. While it is impossible at the moment to completely prevent this phenomenon from occurring, whisker mitigation can dramatically slow down whisker growth and prevent damage to equipment. Traditional coating materials such as acrylic, silicone, and urethane were found to be ineffective as protection against whiskering. However, parylene was found to provide significant resistance to whisker penetration.
What Benefits Does Parylene Coating Have Over Alternatives?
The most obvious benefit of using parylene coating is it allows you to avoid using toxic heavy metals such as lead. Additionally, parylene coating has several beneficial properties that make it uniquely suited for use in electrical equipment. These properties include:
- Lack of a liquid phase, allowing for uniform thickness and preventing pinholes.
- Penetrating spaces as small as 0.01mm wide.
- Can be applied at room temperature, allowing stress free application.
- Transparency to allow use with optical elements.
- FDA Approval.
- High Tensile Strength.
- Stability in a wide range of temperatures.
Where Can Parylene Coating be Applied?
Tin whiskering is a universal occurrence in electrical equipment. The phenomenon is not confined to certain industries or sectors. Whiskering has been observed in a wide range of applications including:
As such, the need for a universal solution exists as well. For obvious reasons, lead is a poor choice for use in medical equipment and restrictions apply on its use in other applications. If you’re in the healthcare sector, you know full well the need for safe and effective equipment. Parylene meets both of these requirements with FDA approval and the resiliency to withstand use in the human body. The lead-free nature of parylene also makes it an obvious choice for consumer electronics. As a manufacturer, you want your products not only to be of high quality and durable, but safe for use. Parylene fulfills this need perfectly. If you’re looking to protect electronics in harsh conditions, parylene is a highly versatile and durable coating. This is a huge benefit to those in the automotive, defense, and aerospace industries.
Why Use Parylene?
Parylene coating is the simple solution to a complex problem. The exact causes behind tin whiskers are still not fully understood and their complete elimination is not yet possible. However, parylene coating provides one of the most effective and safe ways to mitigate this unfortunate phenomenon. Parylene is safe for use, poses no health risks, is extremely versatile, and has shown to be extremely effective at reducing the growth of tin whiskers and preventing penetration.