Parylene Dimer Comparison (N, C, D & AF-4)
Understanding the key differences between Parylene dimers
Parylene dimers form the foundation of every Parylene coating, but each typeโN, C, D, and the fluorinated familyโoffers distinct performance characteristics.
In industry, โParylene Fโ 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 (for example VT4) may also appear in literature and supplier portfolios, but โFโ is not a single, universally standardised designation in the same way as N, C and 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 โFโ naming, so you can choose the best match for your application.
For guidance on selecting the right grade, see our Parylene dimer selection guide. If specifications are not clearly defined, even the correct grade can lead to issues โ see our insight on why Parylene specifications fail.
Comparison chart of Parylene dimers N, C, D and AF-4, showing broad differences in dielectric behaviour, barrier performance, thermal stability, chemical resistance, surface energy and typical use cases.
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Overview
Although all Parylene coatings share the same deposition principleโsublimation, pyrolysis and polymerisationโthe chemical substitution on the dimer molecule strongly influences electrical behaviour, barrier performance, thermal stability and surface energy.
In practice, each grade tends to suit a different balance of electrical, environmental and production requirements.
- Parylene N โ Base polymer with no halogen substitution. Often chosen for excellent dielectric behaviour and good penetration into fine geometry.
- Parylene C โ Monochloro-substituted. Widely used for balanced general protection, including strong moisture and ionic barrier performance.
- Parylene D โ Dichloro-substituted. Selected when you need higher temperature stability than C while retaining good barrier behaviour.
- Fluorinated family โ Most commonly referenced as AF-4 (often marketed as Parylene HT), with other variants such as VT4 appearing depending on supplier and application. Fluorinated grades are used for very high thermal and oxidative stability, lower dielectric constant and lower surface energy, which can reduce adhesion unless the right surface preparation and adhesion strategy is used.
Chemical Structure Differences
The key distinction between each dimer lies in its substitution pattern, such as chlorine or fluorine, and where those atoms sit in the molecule. This changes crystallinity, chain mobility and surface energy.
That molecular difference is what drives the practical changes seen in barrier performance, thermal stability, electrical properties and adhesion behaviour.
Important: โParylene Fโ is often used informally as a family label for fluorinated Parylenes. AF-4 is the most commonly referenced commercial fluorinated grade, but โFโ is not always synonymous with AF-4 in supplier literature.
| Type | Substitution (simplified) | Practical implication |
|---|---|---|
| Parylene N | None | Strong electrical behaviour; good penetration into fine features |
| Parylene C | Monochloro | Very strong general-purpose barrier performance |
| Parylene D | Dichloro | Improved temperature stability versus C; good barrier profile |
| Parylene VT4 | Fluorinated variant (family member; supplier dependent) | Lower dielectric constant; improved thermal and oxidative stability; naming and availability vary by supplier |
| Parylene AF-4 (often marketed as HT) | Highly fluorinated variant (family member) | Very high temperature and oxidative stability; low dielectric constant; very low surface energy, so adhesion strategy is critical |
Performance Comparison Table
The table below gives a practical side-by-side comparison of the most common dimer options. These are directional engineering comparisons rather than a substitute for supplier data or qualification testing.
For controlled specifications, always confirm the final material designation, deposition behaviour and test performance against the exact supplier grade being quoted.
| Parameter | Parylene N | Parylene C | Parylene D | Fluorinated (AF-4 / other โFโ 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 and high-frequency needs, but confirm per supplier |
| Moisture / ionic barrier | Good | Excellent; common first choice for barrier protection | Very good | Very good barrier performance, but Parylene C usually remains the first choice when moisture barrier is the primary driver |
| Thermal / oxidative stability | Good | Very good | High; above C | Very high; highest of the common commercial grades |
| Chemical resistance | Good | Very good | Very good | Excellent; a common reason for fluorinated grade selection |
| Surface energy / adhesion behaviour | Higher surface energy; generally more adhesion-friendly | Moderate | Moderate | Very low surface energy; can be more non-stick, so plasma activation and a defined adhesion strategy are often required |
| Process speed / throughput impact | Typically slower deposition than C, which may increase cycle time in production systems | Fastest mainstream commercial grade; often preferred where throughput is critical | Often comparable to C in many systems, but confirm per equipment configuration | Typically slower deposition, so longer cycle times should be factored into equipment sizing and capacity planning |
| Typical selection trigger | Electrical insulation, thin dielectric layers, penetration | General electronics and barrier protection | Higher-temperature electronics | Very high temperature, aggressive chemistry, UV robustness and RF-driven dielectric goals |
Selecting the right grade is only part of the process. See our guide to specifying Parylene coating to ensure your drawing and process requirements are clearly defined.
Advanced Process Considerations
If you are selecting a dimer for production, or sizing equipment around it, these factors often matter as much as the headline material properties. Values and behaviour remain process-dependent, so the notes below should support specification and qualification planning rather than replace it.
Deposition Rates and 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, including chamber size, pumping capacity, load optimisation and the real cost per coated unit.
Crystallinity, Chain Mobility and 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 against substrate limits, stress or warpage risk, adhesion performance and any downstream assembly constraints.
Surface Energy and 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 and supplier data include surface energy for Parylene C often around 25โ30 dynes/cm, while AF-4 / HT is often cited around 18โ20 dynes/cm.
Water contact angles are also commonly higher for fluorinated grades, reinforcing their more non-stick behaviour. If adhesion is critical for multi-layer assemblies, bonding, overmoulding or selective soldering, plan on plasma activation, tightly controlled cleanliness and qualification testing on your real substrates and geometry.
Throughput, adhesion and qualification risk can change the best dimer choice just as much as raw material properties. A technically โbetterโ grade is not always the right production grade.
Choosing the Right Dimer
When selecting a Parylene dimer, balance the functional requirement, operating environment and production constraints. The best choice is usually the one that gives enough performance without creating unnecessary process complexity.
- Electrical insulation: Often Parylene N for thin-build dielectric performance, subject to confirmation against your frequency range and test plan.
- Moisture and 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 resistance, UV robustness or low dielectric constant: Consider fluorinated options, most commonly AF-4 / HT, but plan adhesion strategy carefully.
If you are writing a controlled specification, include the dimer grade naming, including supplier designation where needed, thickness range, adhesion promotion method, masking and keep-out requirements, acceptance criteria and qualification tests. For production planning, also document expected cycle time and load size assumptions.
For a more decision-led view, see our guide to choosing the right Parylene dimer and our overview of what Parylene dimer is.
Related Pages
Use these pages to move from general comparison into material selection, specification and broader Parylene process planning.
Why Choose SCH Services?
SCH Services supports Parylene projects from early evaluation through to controlled production, helping customers choose the right grade, define the right process and build a supply route that is practical as well as technically credible.
- โ๏ธ Technical Parylene Support โ Guidance on dimer selection, thickness strategy, adhesion control and process fit.
- ๐ ๏ธ Integrated Supply Route โ Support across materials, equipment, coating services, consumables and process inputs.
- ๐ Production-Focused Thinking โ Practical help on throughput, qualification, risk reduction and scale-up planning.
- ๐ Responsive Commercial Support โ Support for development builds, ongoing supply and wider project planning.
- โ Hands-On Experience โ Real-world understanding of coating challenges across electronics and high-reliability applications.
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