Parylene Dimer Comparison (N, C, D & AF-4)

Parylene dimers form the foundation of every Parylene coating, but each type—N, C, D, and the fluorinated family—offers distinct performance characteristics.

In industry, “Parylene F” is sometimes used informally as shorthand for fluorinated Parylenes. The most widely referenced commercial fluorinated grade is AF-4, which is frequently marketed as Parylene HT (supplier naming can vary). Other fluorinated variants (e.g., VT4) may also appear in literature and supplier portfolios, but “F” is not a single, universally standardised designation in the same way as N/C/D.

Selecting the right dimer affects not only coating thickness and adhesion strategy, but also moisture resistance, dielectric behaviour, temperature capability, and (critically for production) throughput per cycle.

This guide compares the main Parylene dimers side by side and clarifies the AF-4 vs “F” naming, so you can choose the best match for your application.

Overview

Although all Parylene coatings share the same deposition principle—sublimation, pyrolysis, and polymerisation—the chemical substitution on the dimer molecule strongly influences electrical behaviour, barrier performance, thermal stability and surface energy.

In practice:

• Parylene N – Base polymer (no halogen). Often chosen for excellent dielectric behaviour and good penetration into fine geometry.
• Parylene C – Monochloro-substituted. Widely used for balanced general protection, including strong moisture/ionic barrier performance.
• Parylene D – Dichloro-substituted. Selected when you need higher temperature stability than C while retaining good barrier behaviour.
• Fluorinated family – Most commonly referenced as AF-4 (often marketed as Parylene HT), with other variants (e.g., VT4) appearing depending on supplier and application. Fluorinated grades are used for very high thermal/oxidative stability, lower dielectric constant and lower surface energy (which can reduce adhesion unless the right surface prep/adhesion strategy is used).

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Chemical Structure Differences

The key distinction between each dimer lies in its substitution (chlorine or fluorine) and where those atoms sit in the molecule. This changes crystallinity, chain mobility and surface energy.

Important: “Parylene F” is often used informally as a family label for fluorinated Parylenes. AF-4 is the most commonly referenced commercial fluorinated grade, but “F” is not always synonymous with AF-4 in supplier literature.

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Parameter	Parylene N	Parylene C	Parylene D	Fluorinated (AF-4 / other “F” family variants)
Dielectric behaviour	Excellent; commonly chosen for electrical insulation at thin builds	Very good; widely used in electronics	Very good	Typically low dielectric constant and low loss; often favoured for RF/high-frequency needs (confirm per supplier)
Moisture / ionic barrier	Good	Excellent (common “go-to” for barrier protection)	Very good	Very good barrier performance, but Parylene C remains the typical first choice when moisture barrier is the primary driver
Thermal / oxidative stability	Good	Very good	High (above C)	Very high (highest of common commercial grades)
Chemical resistance	Good	Very good	Very good	Excellent (common driver for fluorinated selection)
Surface energy / adhesion behaviour	Higher surface energy (generally adhesion-friendly)	Moderate	Moderate	Very low surface energy (can be more “non-stick”; plasma activation and/or adhesion strategy is often required)
Process speed / throughput impact	Typically slower deposition than C; may increase cycle time in production systems	Fastest mainstream commercial grade; often preferred where throughput is critical	Often comparable to C in many systems; confirm per equipment configuration	Typically slower deposition; longer cycle times should be factored into equipment sizing and capacity planning
Typical selection trigger	Electrical insulation, thin dielectric layers, penetration	General electronics / barrier protection	Higher-temperature electronics	Very high temperature, aggressive chemistry, UV robustness, RF-driven dielectric goals

Advanced Process Considerations

If you are selecting a dimer for production (or sizing equipment), these “consultant-level” factors often matter as much as the material properties. Values and behaviour are process-dependent, so treat the notes below as guidance to support specification and qualification planning.

Deposition Rates & Throughput per Cycle

Deposition rate directly impacts cycle time and therefore throughput per chamber. In many systems, Parylene C is the fastest-depositing mainstream grade, while Parylene N and especially AF-4/HT often deposit more slowly. For high-volume environments, this can be a decisive factor in equipment selection (chamber size, pumping capacity, load optimisation) and cost per coated unit.

Crystallinity, Chain Mobility & Post-Deposition Annealing

You will often see references to crystallinity and chain mobility because they influence thermal behaviour, barrier performance and long-term stability. In some applications, controlled post-deposition annealing can increase crystallinity and improve high-temperature performance for grades such as Parylene C or Parylene D. This is not universal and must be validated (substrate limits, stress/warpage risk, adhesion performance, and any downstream assembly constraints).

Surface Energy (Quantitative) & Adhesion Engineering

Low surface energy is a key reason fluorinated grades can be more challenging to bond to or overcoat without activation. Typical directional values reported in literature/supplier data include:

• Parylene C – surface energy often cited around ~25–30 dynes/cm, with water contact angles commonly around ~85–95° (varies with process and measurement method).
• AF-4 / HT – surface energy often cited around ~18–20 dynes/cm, with water contact angles commonly around ~100–110° (varies with process and measurement method).

If adhesion is critical (multi-layer assemblies, bonding, overmoulding, selective soldering), plan on plasma activation, highly controlled cleanliness, and qualification testing on your real substrates and geometry.

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Choosing the Right Dimer

When selecting a Parylene dimer, balance the functional and environmental requirements:

• Electrical Insulation: Often Parylene N for thin-build dielectric performance (confirm against your frequency range and test plan).
• Moisture / Ionic Barrier: Typically Parylene C as the general-purpose barrier workhorse.
• Higher-Temperature Operation: Commonly Parylene D, or fluorinated grades where limits are more demanding (particularly AF-4 / HT).
• Extreme Chemical / UV / Low Dielectric Constant: Consider fluorinated options (most commonly AF-4 / HT), but plan adhesion strategy carefully (plasma activation, fixturing cleanliness, and qualification testing).

If you’re writing a controlled spec, include: dimer grade naming (including supplier designation), thickness range, adhesion promotion method (if any), masking/keep-outs, acceptance criteria, and qualification tests. For production planning, also document expected cycle time and load size assumptions (throughput).

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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.