Does Parylene Adhesion Decrease with Coating Thickness?

When it comes to Parylene coatings, adhesion is everything. A coating may offer exceptional barrier protection, but if it delaminates or peels from the substrate, performance and long-term reliability are immediately compromised. One of the most common technical questions in Parylene processing is whether adhesion decreases as coating thickness increases.

The short answer: thickness alone is not the root cause. Adhesion performance depends primarily on surface preparation, substrate chemistry, and process control.

Understanding Parylene Deposition

Parylene is applied using a vapour deposition process (CVD), where the coating polymerises directly onto the substrate at a molecular level. This produces a pinhole-free, highly uniform film that conforms perfectly to flat surfaces, sharp edges, and recessed geometries.

Unlike brush, spray, or dip-applied conformal coatings, Parylene does not rely on surface tension or solvent evaporation. However, like all coatings, its adhesion is still governed by surface energy, cleanliness, and interfacial bonding.

Parylene Thickness vs Adhesion Performance

In general, thinner Parylene coatings (typically 2–5 µm) exhibit excellent adhesion because internal stresses within the polymer layer remain low. As coating thickness increases—sometimes to 25–50 µm or more—internal mechanical stress within the film can increase.

If surface preparation is inadequate, this stress can contribute to adhesion loss. However, when substrates are properly prepared, even thick Parylene coatings can achieve outstanding adhesion and long-term durability.

Key influencing factors include:

• Smooth or low-energy surfaces can limit adhesion at any thickness
• Contamination (oils, flux residues, moisture) dramatically reduces bond strength
• Surface activation significantly improves adhesion across all thickness ranges

Best Practices to Maintain Adhesion at Any Thickness

To ensure reliable Parylene adhesion—whether applying thin or thick coatings—the following best practices are essential:

• Use plasma cleaning or chemical surface activation to increase surface energy
• Apply adhesion promoters where required for challenging substrates
• Select coating thickness based on functional need, not assumption
• Validate adhesion using recognised standards such as cross-hatch testing (ISO 2409)

Parylene Adhesion Expertise at SCH Services Ltd

At SCH Services Ltd, we understand how coating thickness, substrate preparation, and process control interact to determine Parylene adhesion performance. Our Parylene processes combine controlled surface preparation with optimised deposition parameters to deliver reliable adhesion across both ultra-thin and high-build coatings.

Whether your application requires thin Parylene films for medical sensors or thicker layers for aerospace and defence electronics, we ensure adhesion performance is never compromised.

Learn more about our capabilities:
Parylene Coating Solutions