Parylene Chemistry and Production Requirements
ParyIene's unique vapor-phase polymerization differs considerably from the application processes of other coating materials. More complex, the technique deposits the substance directly onto the material being coated in a manner that penetrates deeper into the substrate surface. Implemented in a specialized vacuum chamber, parylene's application process does away with the intermediate liquid deposition procedure common to competing coatings.
Chemically, the various parylenes' main-chain phenyl group generates reliable molecule-to-molecule interaction, while possessing high levels of in-plane electronic polarization capabilities. Because these molecular layers are room temperature and chemical vapor deposited (CVD),
- no specialized surface treatment is required, resulting in
- a chemically stronger consistency than conventionally assembled monolayers.
Thus, parylene's molecular layers are particularly valuable for microelectomechnical systems (MEMS) and nanotechnology driven applications, which emphasize simplifying component manufacturability.
Unfortunately, compared to other coating options, more time is generally needed to assure parylene's superior conformal coating of targeted substrates, a consideration that needs to be an integral component of manufacturing strategies. For instance, the fact that coating thicknesses from 0.10 micron to 76 microns can be applied in a single operation enhances the quality of completion of manufacturing processes. In general, however, slower production time leads to:
- smaller product batches,
- delayed delivery to customers or retail markets, and
- more cost to both manufacturer and customer.
Parylene Deposition Rates and Process Duration
Parylene's application process is rather different and, in consequence, slower and more expensive than the traditional wet chemistry coating methods used for acrylic, silicone and other substances. The parylene process is multifaceted, involving several steps. Unlike many competing application processes, parylene deposition is not line-of-sight. Rather, the gaseous monomer uniformly encapsulates all sides of the object being coated simultaneously.
While CVD generates the truly conformal nature of parylene coating, it can be considerably slower to implement. In addition, appropriate cleaning, activation and masking precede CVD coating in the deposition chamber. Deposition rates for parylene conformal coating vary, often significantly, according to:
- the surface material of the selected substrate,
- the type of parylene coating applied,
- its deposition rate,
- the character of the coating project (large/small batch, etc.), and
- the assembly's required surface thickness.
At Diamond MT, our processes are explicit, both in terms of the sequenced-procedures applied to every customer order, and adaptation of those procedures to precise customer specifications throughout the coating process. This may add to completion time, but the quality of results is unsurpassed and verifiable. Individual processes are enacted following inspection of incoming materials, including appropriate component cleaning and masking; at all times results of our in-house procedures are measured against customer diagrams to assure compliance with specification requirements. Adhesion management is also implemented, as necessary, before the coating cycle begins.
Because of these factors, processing time similarly varies, from less than an hour to 24 hours or more, figured at a standard deposition rate of about .2 mils-per-hour, a slower speed compared to the liquid application technique employed by the majority of other coating materials. Special care is taken to match parylene thickness to the product's specified coating requirements. Time to completion of the coating process varies according to deposition rates: coating of lesser thickness will require less time to complete; thicknesses in excess of .2 mils-per-hour will require more time to complete, according to the desired thickness.
Biologically and chemically inert, parylene responds well to the CVD process. Not requiring the liquid phase application standard from most competing coating materials, parylene provides an authentically conformal covering. The excellent barrier strength is characterized by a completely pinhole-free and uniform thickness. Coating application is controllable at thicknesses > 0.5µ, while effectively penetrating product spaces as narrow 0.01mm, making parylene highly relevant to MEMS/nano uses.
Confirmation of these standards is as important to Diamond as it is to our valued customers, and contributes to production time. However, the attention paid to quality throughout all stages of the parylene coating process engenders enhanced delivery of client expectations. It simultaneously generates substrate coatings guaranteed to maintain component protection and performance for the duration of its expected operational life.