Choosing the Right Parylene Dimer

Choosing the right Parylene dimer determines how your coating will perform under electrical, thermal, and environmental stress.

The common dimer families are Parylene N, C, D and fluorinated Parylene grades. In industry, “Parylene F” is often used as a shorthand for fluorinated Parylene, but your specification should name the exact fluorinated grade (for example AF-4, sometimes referred to commercially as HT) because different fluorinated chemistries can behave differently in deposition and in-service performance.

This guide helps you make an informed selection based on key performance priorities.

Key Selection Factors

Before choosing a dimer, consider how your end-use environment interacts with coating properties. The following factors should guide your choice:

• Operating temperature & thermal cycling: If the part sees sustained elevated temperature or aggressive thermal cycling, consider Parylene D or a fluorinated grade (e.g., AF-4/HT) and validate performance to your duty cycle and qualification plan.
• Electrical insulation vs RF performance: For high dielectric strength and deep penetration around fine geometries, Parylene N is often preferred. For RF/microwave applications, some fluorinated grades are selected for their electrical characteristics (validate against your frequency band and loss targets).
• Moisture & chemical exposure: For broad protection in humid or corrosive atmospheres, Parylene C is commonly chosen as a balanced barrier grade.
• Adhesion vs low surface energy: Fluorinated Parylene (e.g., AF-4/HT) has lower surface energy, which can improve chemical inertness and “non-stick” behaviour, but may require extra attention to adhesion promotion, printing/bonding, or downstream assembly steps.
• Geometry, gaps and shadowing: Tight gaps, deep cavities and complex assemblies can influence effective coverage and thickness distribution. Select a grade and thickness range that maintains margin in your worst-case features.

Tip: If your drawing/spec currently says “Parylene F”, tighten it to an exact callout (e.g., “Parylene AF-4/HT, thickness X–Y µm, with adhesion-promotion process Z if required”).

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Application-Driven Choices

Each dimer aligns naturally to specific application environments:

• Parylene N – Often selected where dielectric strength, optical clarity, and uniform ultra-thin coverage are priorities (e.g., fine-feature electronics, sensors, some optical assemblies).
• Parylene C – A common baseline choice for automotive, industrial and medical electronics requiring dependable moisture/chemical barrier performance and practical manufacturability.
• Parylene D – Often chosen where higher-temperature capability is required versus C, while maintaining a robust barrier profile (validate to your thermal profile and acceptance tests).
• Fluorinated grades (e.g., AF-4 / “HT”) – Used where very high chemical inertness, low surface energy, and/or specialised electrical performance is required (often aerospace, harsh chemicals, and some high-frequency electronics). Specify the exact grade rather than a generic “F”.

Where component performance must be validated to IPC-CC-830, UL 746E or IEC 60664 PD1/PD2, dimer selection should also reflect compliance with the applicable test regime and film-thickness specification.

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Performance Trade-offs

While no single Parylene type is “best” for all situations, understanding the trade-offs allows optimal engineering compromise:

• N vs C: Parylene N can offer very strong electrical insulation performance and penetration, while C is often preferred when moisture/chemical barrier performance is the dominant driver.
• C vs D: Parylene D is typically chosen when temperature capability needs extra headroom beyond C; confirm performance across your expected thermal profile and thickness range.
• C vs fluorinated (AF-4/HT): Fluorinated grades can surpass C for chemical inertness and low surface energy, but can be more challenging for adhesion, bonding, printing and some downstream assembly steps. Plan adhesion promotion and verification tests if those steps matter.
• Specification clarity: Avoid ambiguous language like “Parylene F” unless you define it. Different suppliers and sectors may use different naming conventions.

For design teams, a practical route is to benchmark Parylene C as the baseline, then validate D or a defined fluorinated grade only where operating limits demand extra headroom.

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Summary Table

The quick-reference table below summarises common pairing of dimer to requirement (always validate with your qualification plan and thickness spec):

Need help defining the correct Parylene type for your product? Our team supports prototype evaluation, coating trials, and qualification testing to identify the optimal dimer and process conditions for your design.

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Note: This article provides general technical guidance only. Final design, safety, and compliance decisions must be verified by the product manufacturer and validated against the applicable standards.