The ABCs of plasma cleaning for conformal coating

Plasma cleaning is a process that is gaining more popularity in thin film applications due its highly effective performance on cleaning and modifying surfaces.

It is also a highly effective surface cleaning and treatment process before application of conformal coatings.

What is Plasma?

Plasma is an energy-rich gas state that can be used to modify the surface of a product to improve its performance. This modification can be improving the adhesion of a conformal coating or changing the surface characteristics.

Plasma technology is based on a simple physical principle.

Matter changes its state when energy is supplied to it. Solids become liquid. Liquids become gas.

If additional energy is then fed into a gas by means of electrical discharge it eventually ionises and goes into the energy-rich plasma state, the fourth state of matter.

Plasma is created.

How can Plasma be used for cleaning printed circuit boards?

Plasma treatment can clean, activate or coat nearly all surfaces. These surfaces include plastics, metals, (e.g., aluminum), glass, recycled materials and composite materials. This means the plasma process can be highly effective on many different products.

For electronic circuit surfaces, plasma treatment can be used in two highly effective ways.

That is it can:

1. Clean the surface of the circuit board to be 100% contamination free. The surface will be free of residues and contamination including release agents and additives.
2. Activate the surface of the circuit board assembly to allow easier bonding and better adhesion of conformal coatings. It can change the surface energy of the surface to ensure complete adhesion is possible and in some cases it can make materials bond where it was previously impossible.
3. These properties make it an interesting technique for improving the surface performance of an electronic circuit board.

What are the typical plasma processes available for surface treatment?

There are traditionally three types of plasma treatment:

1. Low-pressure plasma
2. Corona treatment
3. Atmospheric pressure plasma

Low-pressure plasma

These plasmas are generated in closed chambers in a vacuum (10-3 to 10-9 bar).

They can be used in conjunction with Chemical Vapor Deposition (CVD) coatings like Parylene before application.

Corona treatment

Corona treatment (corona process) is a physical process involving high voltage and is mainly used for treatment of films.

This is normally not suitable for electronic circuit boards.

Atmospheric pressure plasma

Atmospheric plasma is generated under normal pressure. This means that low-pressure chambers are not required.

The plasma is created with clean/dry compressed air (plant air) and does not require forming gases. It is possible to integrate plasma directly into manufacturing processes under normal pressure conditions.

This is an excellent process for improving adhesion and surface energy performance of circuit boards for conformal coatings.

How is the plasma applied to a circuit board to clean it?

Typical plasma components used for cleaning surfaces on circuits are:

• Plasma jets (nozzles) to apply the plasma to the surface of the circuit board. They could be controlled by a robotic system.
• The plasma generators that create the plasma to clean or supply the coatings as required. They provide output power and, in conjunction with complete pretreatment stations, assume various control functions.
• The process monitoring that controls the nozzles, the movement of the system and the quality of the output.
• These three parts form the plasma cleaning process.

What sectors is plasma treatment used?

There are many sectors that plasma cleaning is used for improving conformal coating performance.

They include:

• Automotive
• Telecommunications
• Mobile phone and Tablets
• Aerospace
• Military
• Transport
• Consumer goods
• Life sciences
• LED Coating

Want to know more about plasma cleaning and conformal coating performance?

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