Parylene and Wearable Devices

Estimated reading time: 3 minutes

Wearables are no longer emerging technology—they are here. Whether a wearable item is a medical device like an insulin pump, a smart watch or even a finely woven piece of smart fabric, they all have one basic fact in common. All of them contain technologies that need protection from the outside world and, in just about every case, Parylene is the most appropriate choice for protection.

Parylene is the most different of all conformal coating compounds. While others deposit as a liquid, Parylene deposits as a vapor. Most coatings need to applied in thicknesses measured in mils, while Parylene is effective at thicknesses measured in microns. Finally, many conformal coatings are especially good at one or two things while Parylene is great at just about everything.

The wearable challenge

The life of a wearable device is harder than it might seem. After all, it goes everywhere that its wearer goes. At first glance, these conditions might not seem that extreme. After all, the places that we go usually don't harm or kill us. However, from the perspective of a device, consider the many challenges that it faces:

• A wearable device could be exposed to summer in Phoenix (115°C) and winter in Minneapolis (-25°C), giving it a 140° range.
• Wearables need to be small and light enough to be comfortably worn. Generally, they also need smooth surfaces for comfort, especially where they are to touch the skin.
• A user with an outdoor-based job could easily expose their device to eight to 12 hours of direct sunlight—filled with UV rays.
• Wearable devices get exposed to corrosive spray when they are taken to the beach or on a boat.
• Household cleaning chemicals—that are likely to end up landing on a wearable device—contain harsh compounds and powerful solvents.
• Between office equipment, wireless personal devices, and high-tension power lines, wearable devices are constantly bombarded with RF and EMF signals of varying strength.
• Wearable devices are in a constant state of vibration and motion and are at risk of abrasions and impacts at any time.
• The human body itself exudes gases, liquids and maintains a constant temperature that is almost 30°F above room temperature.

The Parylene solution

Parylene offers a solution to just about every challenge posed by a wearable device. Point by point, here is what Parylene brings to the table:

• Parylene withstands temperatures as high as 80°C with no degradation and can go as low as -200°C. At body temperature, it can last forever.
• Because its coating is so thin, Parylene adds almost no perceptible weight or size increase to the item that it coats. It is comfortable and non-irritating against the skin (or, for that matter, inside the body) thanks to its high level of biocompatibility and its dry film lubricating capability.
• Parylene resists water, corrosives, chemicals and solvents, making it a great coating in real world applications.
• Of all coatings, Parylene is one of the most effective dielectrics in a thin coat, blocking EMF and RF interference.
• While it doesn't have the cushioning properties of a thick coat of silicone, Parylene is tough and able to withstand impact and abrasion.
• Parylene forms a truly conformal coat that also blocks gasses from entering the coated item.

Parylene and two wearable challenges

Wearables can pose two unique challenges, and Parylene can handle both of them. First, many wearables carry sensors that report back on either what they are doing or what the person wearing them is doing. Microelectronic mechanical sensors, especially, are fine and finicky items that require protection, but not so much of it that it blocks their proper functioning. Parylene's ability to conformally coat even the smallest and most complicated item makes it the best choice for protecting wearable MEMS.

The dielectric properties of Parylene are usually desirable, but if a wearable device needs to take measurements of the world around it (or of its wearer), those properties could prevent the device from functioning. Luckily, wearable devices can be masked before coating. The masking can prevent the Parylene from depositing on the sensors, allowing them to properly function while the rest of the device still gets the benefits of being conformally coated.

To learn more about how Parylene, as an enabling technology, can significantly increase the performance of sensors as they become increasingly integrated into our daily lives, click here.