Can Parylene be used as a Standalone Enclosure?

Parylene polymer conformal films are recognized for their wide array of advantageous functional traits when it comes to coating printed circuit boards (PCBs) and similar electronics. These films offer valuable properties like biocompatibility, resistance to chemicals and solvents, reliable dielectric and insulation characteristics, and ultra-thin, pinhole-free film thicknesses ranging from 1 to 50 μm. Furthermore, they boast complete surface adaptability, irrespective of the substrate design, surpassing the coating capabilities of liquid conformal materials such as acrylic, epoxy, silicone and urethane.

Despite these advantages — which allow Parylene to effectively encapsulate virtually all surfaces with durable protective conformal film – one question about its performance cannot be satisfied: Can Parylene be used as a standalone enclosure?

Parylene can effectively enclose any object or form fitting in the deposition chamber; however, it cannot stand alone. Parylene requires a surface to adhere to before it can be successfully applied as a conformal film.

Standalone Enclosures

For a device or object to stand alone, structural independence is required to support the maintenance of an upright posture, either horizontal or vertical, and ongoing functionality without peripheral assistance or subsequent addition. In this regard, a standalone object sustains and preserves its operational purpose, as a separate entity, exclusive of external support or power.

An enclosure is a physical construction that circumscribes an object, surrounding its structure and defining its internal spatial limits by its material boundaries. By this definition, a standalone enclosure is a manmade (basement, courtyard) or natural (cavern, tree trunk) structure that requires no secondary aid to maintain and protect its position. This basic condition eliminates Parylene’s standalone abilities. Much has to do with Parylene’s chemical vapor deposition (CVD) method of film application.

Parylene CVD

While the chemical vapor deposition (CVD) techniques generate a versatile platform for a wide range of Parylene coating applications, its procedural requirements also eliminate the chance of using Parylene to create independent standalone enclosures. Completely excluding the liquid phase of pre-synthesized wet coatings, CVD polymerization synthesizes truly conformal protective film in-process. It does so by

• Transforming powdered, solid Parylene dimer into a gas at the molecular level
• Heating the material to 100ºC – 150ºC
• Heating the material further to 680ºC and sublimating the vaporous molecules
• Splitting each into a monomer
• Directing monomers by vacuum into the coating chamber,
• Depositing the monomers homogeneously onto the substrate surface
• Creating a truly conformal, pinhole-free film both below and above the targeted surface

These procedures are followed by rapid cooling, to between -90ºC and -120ºC, helping to solidify the coating while removing residual Parylene materials from the substrate. The result is uniform film thickness conforming completely to the substrate, regardless of substrate topography, with excellent chemical, dielectric barrier and moisture protection, among many other performance benefits.
CVD processes can compel Parylene to provide complete and conformal encapsulation of three-dimensional objects. Parylene does this by attaching to the targeted surfaces, including those already assuming a standalone enclosure format.

Parylene cannot be used as a standalone enclosure. To adhere to a substrate and provide ultra-thin conformal protection, Parylene must undergo the CVD process, converting the powdered dimer into a vaporous state. Parylene acquires its coating capacity after infiltrating a substrate’s surface in a gaseous form, providing protection both below and above the substrate’s surface. As a vapor, Parylene can completely cover and encapsulate the flattest surface or larger structures of virtually any shape. In doing so, it encloses the targeted surface and form. However, it cannot stand alone because it must be applied as a vapor and, as such, simply lacks the physical constitution to provide a stable stand-alone molecular structure and shape.