Surface condition is one of the biggest drivers of coating success or failure.

Even when the correct conformal coating is selected, poor adhesion, dewetting and long-term reliability issues often trace back to contamination or low surface energy at the substrate level.

Plasma cleaning provides a controlled way to remove contamination and modify surface energy before coating. It is widely used where conventional cleaning alone cannot deliver consistent adhesion — particularly for difficult substrates and high-reliability applications.

Emerging ultra-thin coating technologies such as hybrid ALD/CVD coatings reduce reliance on traditional masking and surface preparation, but still depend on controlled surface conditions to perform reliably.

What is plasma?

Plasma is often described as the fourth state of matter. When sufficient energy is applied to a gas, it becomes ionised, forming an ऊर्जा-rich environment containing ions, electrons and reactive species.

This reactive environment allows plasma to interact with surfaces at a molecular level.

In coating processes, plasma is used to clean, activate or modify surfaces without mechanical contact or liquid chemistry.

Why plasma cleaning is used before conformal coating

Plasma treatment addresses two key challenges in coating processes:

• Removal of contamination – including organic residues, oils, additives and weak surface films
• Surface activation – increasing surface energy to improve coating wetting and adhesion

This is particularly important where coatings struggle to wet or bond consistently. For the wider context of how cleanliness affects coating reliability, see surface preparation and cleanliness for conformal coating.

Reality check: Plasma does not fix poor process control. If contamination levels are inconsistent or excessive, plasma may improve results but will not stabilise an unstable upstream process.

What plasma does to a PCB surface

When applied to electronic assemblies, plasma treatment can:

• Remove organic contamination at a molecular level
• Increase surface energy to improve wetting
• Promote stronger adhesion between coating and substrate
• Enable bonding on otherwise difficult materials

This makes it particularly useful for Parylene processes and difficult-to-bond substrates where adhesion is a known risk.

Types of plasma processes used

There are three main plasma approaches used in surface treatment:

• Low-pressure plasma: Vacuum-based systems used for high control and uniform treatment. Often used in conjunction with vapour deposition processes such as Parylene.
• Atmospheric plasma: Operates at normal pressure using compressed air. Easier to integrate inline and widely used for PCB surface activation.
• Corona treatment: Primarily used for films and packaging materials. Generally not suitable for complex PCB assemblies.

Atmospheric plasma is typically the most practical option for conformal coating processes due to ease of integration and process flexibility.

How plasma is applied in practice

A typical plasma treatment system consists of:

• Plasma jet or nozzle: directs the plasma onto the PCB surface
• Generator: creates and controls the plasma energy
• Motion system: ensures consistent coverage across the assembly
• Process control: manages power, exposure time and repeatability

These systems are often integrated into automated lines or used as standalone pre-treatment steps.

Where plasma cleaning fits in the process

Plasma is not a universal requirement. It is typically used where standard cleaning and process control are not sufficient.

• Difficult substrates (plastics, low surface energy materials)
• High-reliability coating requirements
• Parylene coating processes requiring adhesion control
• Situations where dewetting or adhesion failure has been observed

For most standard conformal coating processes, stable cleaning and handling control are often sufficient without plasma.

In complex assemblies where adhesion, geometry and coating boundaries interact, plasma is often part of a wider process strategy rather than a standalone solution. See hybrid coating strategies for complex PCB assemblies.

Summary

Plasma cleaning is a powerful surface preparation tool, but it is not a substitute for good process control.

• Improves adhesion and surface energy
• Removes contamination at a molecular level
• Supports difficult coating applications
• Best used where standard processes cannot deliver stability

Used correctly, plasma can significantly improve coating reliability. Used incorrectly, it can mask underlying process problems without resolving them.

Why Choose SCH Services?

SCH Services supports coating processes with practical engineering input — from surface preparation and adhesion control through to coating selection, process development and validation.

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• 🛠️ Process-Led Support
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Note: This article provides general technical guidance only. Final process decisions should be validated against the specific assembly, materials and applicable standards.