Selecting the best material/application method for your coating assignment prolongs assembly service-life and promotes optimal performance. The conformal coating industry is highly competitive, with competent providers available throughout the country. Compared to liquid resin coating materials – acrylic, epoxy, silicone and urethane – the polymer parylene generates superior conformal coating, but is more complex and expensive.
Unlike liquid coatings – which are generally brushed, dipped (immersed), or sprayed onto substrates – parylene uses a chemical vapor deposition (CVD) application process. CVD converts powdered parylene dimer into a vapor, on a molecule-by-molecule basis. Enacted in a vacuum, the gaseous parylene seeps deeply into a substrate’s most minute surface crevices. The result is a uniform, pinhole-free coating, offering unsurpassed assembly protection.
However, despite the effectiveness of parylene conformal film, the CVD method has several prominent disadvantages, including:
· greater expense than any liquid technology,
· small batch-size/greater turn-around time, and
· difficulty reworking/repairing coatings.
These conditions highlight the importance of choosing a parylene provider appropriate to your process/product needs.
Look for a provider that has a range of experiences, not just within parylene, but conformal coatings as a whole. While of course you want to choose someone who has experience coating a similar product if possible, by evaluating someone who has experience across multiple mediums you raise the possibility of a cheaper or more effective solution. If the vendor you are considering only applies parylene, you raise the possibility of their interests not being aligned with yours and falling victim to the old adage, “If all you have is a hammer, everything will look like a nail.”
Look for experienced staff and proven processes, capable of accommodating assignments ranging from small custom orders to full production runs. Fast project turnaround (5 - 10 business days) is desirable, so long as QA can be maintained. This is particularly the case for time-sensitive orders; ensure the firm you choose can complete the expedited assignment within QA parameters acceptable to your project needs, regardless of complexity and quantity.
The QA certifications discussed in Chapter 1 as important for parylene application as they are for liquid coatings. Clients seeking conformal coating services are advised to select firms whose commitment to providing QA specifications/standards for conformally coated processes/products has been verified by the industry. QA certs present achievable and necessary performance benchmarks, stipulating appropriate QMS for parylene application.
Attention to QA certification is recommended when selecting a parylene provider. In addition to ISO9001 and NASA-STD-8739.1, important certs for parylene are:
· Both AS9100C and IPC 001:2015 specify QMS guidelines for aviation, space and defense applications, focusing on ongoing systemic improvement, customer support, and compliance with applicable regulatory/statutory requirements.
· IPC-7711/7721 delineates rework/repair benchmarks for parylene/liquid coatings.
· Coating thickness requirements are set by IPC-A-610, according to the coating material/assembly function.
· IPC-CC-830/830B delineates optimal-confidence criteria/ minimum test-redundancy for parylene/liquid coatings; 830B standardizes coating performance for military-grade/ruggedized performance conditions.
· ITAR regulations safeguard your sensitive company/process/ product data.
· NADCAP AC7120 Rev A provides QMS guidelines for audit criteria/circuit card assemblies for aerospace applications.
· RoHS assures parylene dimer/process materials are compliant with European Directive 2002/95/EC.
· USP biological testing requirements for Class VI Plastics assure parylene used for biomedical devices is safe.
When seeking parylene services, look for firms having at least some of these QA certifications, since they establish the firm’s professional QA-reliability, for industry-standard compliance, performance and risk management.
Parylene is available in a variety of formats; prominent parylene types include varieties C, N, F, D, and AF-4. Each has a range of distinctive uses, distinguished by their relatively unique chemical, electrical and physical properties.
Parylene C and N adhere to substrates more quickly than other parylene types, with strong resistance to chemical corrosion. They are more adaptable for a wider range of uses, and display less trace metal contamination. While N is chemically the most fundamental of the parylenes, C is more widely applied as a product/component coating. The deposition rates of the remaining parylenes are slower and costlier than C and N, which are used for most current parylene applications.
Compared to other parylenes, Type F has lesser coating capacitation, operational electrical charge, and dielectric constant. Better thermal stability means F is well-suited for:
- inner layer dielectric (ILD) applications and
- ultra large-scale integration (ULSI) -- one million+ circuit elements positioned on a single chip.
These conditions improve F’s utility for MEMS/nanotech applications.
Parylene D provides effective coating protection at 134° C (273° F), and reliable component protection for 10 years at 100° C, in oxygen-dominated environs.
More costly/lower yield AF-4 exhibits enhanced UV stability and higher oxidative resistance, suitable for specialized applications.
You’ll want a parylene provider capable of providing reliable application services, regardless of parylene type. Provision of certified manufacturer services for parylene AND liquid coatings verifies:
- experience with conformal coatings of all types,
- competitively-priced, consistent quality service,
- focus on meeting/surpassing clients’ QA-expectations, and
- thoroughly fully-documented production/inspection processes.
The capacity to provide liquid coating alternatives to parylene also supports other coating solutions, should your original parylene strategy become unworkable. Diamond MT’s 30 years’ experience combines with its staff of highly-trained personnel, quality materials and process solutions to generate optimal implementation of your conformal coating assignments.
To learn more about selecting a parylene conformal coating vendor, download our whitepaper now: