Protecting MEMS with Parylene Coatings: No Small Feat
Posted by Sean Horn
Friday, February 27, 2015 1:08
@ 1:08 PM
As engineers continue to seek out the most powerful technologies packed into the smallest footprints possible, the use of microelectromechanical systems (MEMS) are on the rise. At the forefront of progress in miniaturization, MEMS enable small form factors without sacrificing precision and reliability. In many cases, MEMS technologies even offer an increase in performance over their larger, traditional counterparts. MEMS technologies can also be produced at low cost, owing to the use of semiconductor fabrication methods.
Despite the myriad advantages of MEMS, their relatively small scale can expose weaknesses such as sensitivity to environmental factors. Indeed, moisture, corrosion, and dust can all affect the performance and structure of a MEMS device. To combat these hazards, it is necessary to integrate some form of protection into products that feature MEMS technology. The most common method of such protection comes in the form of coating of MEMS products with parylene conformal coating.
Parylene coating presents an optimal choice for MEMS applications due to its range of desirable properties and application process. A vapor deposition process is employed to apply parylene to the substrate. This particular process ultimately produces a uniform and truly conformal coating, eliminating any potential pooling or void areas.
The process is performed at room temperature, so coatings are not subjected to stress that can be induced by exposure to extreme temperatures. The ability to apply parylene in a controlled thickness further minimizes risk of creating stress on the sensitive MEMS substrate. When developing on the micrometer scale, after all, component structures can be so sensitive to stress or change that something as seemingly innocuous as a coating can compromise device performance.
Beyond the process, parylene offers additional advantages such as moisture resistance, chemical resistance, corrosion resistance, and temperature stability; it can even act as an anti-reflective coating for silicon optics.
The conformal coating’s performance and durability, which are essential to protecting sensitive MEMS components, are ensured through rigorous testing. This includes thermal shock tests in which coated products are exposed to temperatures on the scale of -65, 25, and 80 degrees Celsius simultaneously. The coating is then inspected for defects such as bubbles, pinholes, blistering, and cracking. The dielectric constant is also measured to ensure quality along with leakage current. Additional tests to safeguard against MEMS product failure include microorganism, flexibility, and flame resistance, as well as a salt spray test.
Because they combine electrical and mechanical components into single chips, MEMS offer a distinct advantage over many current technologies. By allowing for continued miniaturization of complex devices, MEMS technology is allowing engineers and designers to push the boundaries of innovation in consumer products as well as in the medical, aerospace, defense, automotive, and other markets.
But in order to be a viable, real-world technology, MEMS devices require protection of the sensitive electronics from environmental and other potential threats to product performance. Offering this essential protection—along with a number of additional advantages—parylene will undoubtedly play a critical supporting role in the future development of groundbreaking MEMS-enabled products.
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