Materially, parylene is the most distinctive of the major conformal coatings. But just how does it differ from liquid coatings -- acrylic, epoxy, silicone and urethane??
Liquid coatings are just that, wet; they begin as liquid and are applied to substrates in that format, by brushing, dipping or spraying the fluid material onto the substrate.
A common generic name for Poly-para-xylylene, parylene forms a protective plastic film when applied to substrate surfaces, through a chemical vapor deposition (CVD) process. In contrast to liquid coatings, parylene begins in a solid format, as a white powdered dimer, requiring specialized equipment to enact CVD in a vacuum. Transformed to a gas, the parylene is applied as uniform, pinhole-free conformal coating to targeted substrate surfaces.
A green polymer chemistry without the need for catalyst or solvent, parylene requires neither an initiator nor termination group. Commonly used precursors include paracyclophane, paraxylylene and di-paraxylylene. During CVD:
- the dimer (for Parylene C, Parylene N, Parylene D, Parylene AF-4, or other variants), solid at room temperature, is placed into a loading boat, inserted into the vaporizer, heated between 100-150º C, drawn under vacuum into the furnace, and heated again to much higher temperatures (550 °C or more),
- generating sublimation, which pyrolizes the substance into a monomer on a molecule-by-molecule basis, further transported by vacuum one molecule at a time onto the designated substrate at ambient temperatures in the coating chamber, where it polymerizes forming the conformal parylene film
- Cooling in the cold trap to temperatures ranging from -90º to -120º C removes residual parylene materials pulled through the coating chamber leaving the finished coating product.
The CVD process is far more complex than the general brushing, dipping and spraying procedures used for wet coatings. The result is a range of conformal films without peer or functional versatility. Parylene films are very adaptable, protecting substrates with a wide range of advantages, compared to liquid coatings. Chemically inert parylene provides:
- dependable barrier protection against acids, caustic solutions, dust, humidity, moisture, salts, solvents, and numerous other contaminants,
- exceptional electrical insulation,
- low dielectric constancy,
- high tension strain,
- pinhole-free coverage,
- complete conformal coating of substrate surfaces characterized by crevices, exposed internal areas, or sharp edges,
- the thinnest available coating, measured in microns,
- suitability for MEMS/Nano applications, and
- resistance to extremes of physical stress and temperature, among many other coating benefits.
Where to Buy Parylene
When purchasing parylene it is important to use a qualified vendor like Diamond MT (DMT), whose in-depth understanding of the CVD process accurately controls film coverage and thickness, ensuring a successful coating cycle. Based on our experience and expertise, we recommend you use these criteria when evaluating vendors for parylene conformal coating:
- Experience developing solid procedures and processes for conformal coating. Unlike many newer vendors who lack the background to enact first-class parylene coating, DMT has been providing conformal coating services to the aerospace, defense, electronics, life sciences, and MEMS/nano markets since 2001.
- Compare vendors’ background as well as their typical weekly, monthly, quarterly and annual project-volume to determine their profile within the industry.
- Also, if warranted by the organization’s project-volume, visit vendors’ facilities, for a better assessment of their abilities regarding your coating requirements.
- Check into the types of conformal coating vendors provide. Those offering only liquid conformal coatings (acrylic, urethane, etc.) services will be ill-equipped to meet your parylene needs, Equally, vendors specializing in parylene will lack the experience to complete your wet coating assignments. It is generally preferable to select a vendor who offers all varieties of conformal coatings.
DMT is well-positioned to satisfy clients standardized or custom-designed parylene or liquid conformal coating projects. As necessary, we can quickly develop a custom solution, ensuring your specialized conformal coating requirements are expertly achieved. Fifteen-plus years’ experience with multiple mediums further supports our ability to handle any unexpected developments that might arise during the coating process. You’ll be assured the essential degree of parylene or liquid conformal coating attention and proficiency your project needs.
To learn more about parylene, download our introductory whitepaper now: