Why does cleaning improve the adhesion of the conformal coating?


In general it is important that conformal coatings have good adhesion in order to be effective. However, there is no single theory that describes the property of adhesion for conformal coatings.

There are three basic mechanisms for conformal coatings that are known to help with good adhesion.

They are:

  1. Adsorption
  2. Chemical Bonding
  3. Mechanical Interlocking
There are three basic mechanisms for conformal coatings that are known to help with good adhesion. They are adsorption, chemical bonding and mechanical Interlocking
There are three basic mechanisms for conformal coatings that are known to help with good adhesion. They are adsorption, chemical bonding and mechanical Interlocking

Adsorption

This is where the molecules in the conformal coating wet or flow freely over the substrate and make intimate contact with the substrate. This forms interfacial (electrostatic) bonds with van-der-Waal forces.

Any contamination between the two will weaken the adsorption. Any de-wetting (prevention of wetting) will also hinder the adsorption.

Cleaning the surface of contamination will help with adsorption.

Chemical bonds

The bonds are formed at the interface between the conformal coating and the substrate.

Good bonding gives strong adhesion of the conformal coating to the substrate. If bonding cannot be achieved due to contamination then poor adhesion may result.

Cleaning the surface of contamination will help the chemical bonding process.

Mechanical interlocking

The conformal coating film penetrates the roughness on the substrate surface and is achieved once the coating dries.

If the surface is smooth then the mechanical bonding is less effective. If the surface can be cleaned, leaving a rough surface, then more effective bonding can be achieved.

Cleaning the surface of contamination will help.


Achieving the best conformal coating adhesion

Surface contamination can be critical when considering conformal coating and the process. If you can clean the contamination from the surface then the adhesion of the conformal coating should improve.

All three mechanisms do not have to occur to form good adhesion. Depending on the specific conformal coating system, substrate, and application method, different mechanisms could work.

However, good wetting or adsorption is normally required for good bonding.

So, if in doubt clean the surface of the substrate to achieve good conformal coating bonding.


Need to know more about conformal coating adhesion?

Contact us now and we can discuss how we can help you.

Give us a call at (+44) 1226 249019 or email your inquiries at sales@schservices.com

What is plasma cleaning?


Plasma cleaning is a process of using plasma energy to clean and modify the surface of a substrate like a circuit board assembly.

It is a highly effective surface cleaning and treatment process before application of conformal coatings and is gaining more popularity due its highly effective performance.

Plasma cleaning is a process of using plasma energy to clean and modify the surface of a substrate like a circuit board assembly. It is a highly effective surface cleaning and treatment process before application of conformal coatings and Parylene.
Plasma cleaning is a process of using plasma energy to clean and modify the surface of a substrate like a circuit board assembly. It is a highly effective surface cleaning and treatment process before application of conformal coatings and Parylene.

What is Plasma?

Plasma is the energy-rich gas state (also known as the fourth state of matter) that can be used to modify the surface of a product to improve its performance.

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, plasma is created.

This modification can be improving the adhesion of a conformal coating or change the surface characteristics of the board.


How is Plasma used for improving the performance of coatings with printed circuit boards?

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

That is it can:

  • Clean the surface of the circuit board. The surface will be free of residues and 100% contamination free including release agents and additives.
  • Activate the surface of the circuit board assembly. This will allow easier bonding and better adhesion of conformal coatings.

These properties make it an interesting technique for improving the surface performance of an electronic circuit board.

In fact, 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 circuits, plasma treatment can be used in two highly effective ways. First, it can clean the surface of the circuit board. Second, it can activate the surface of the circuit board assembly to allow easier bonding and better adhesion of conformal coatings and materials like Parylene.

For electronic circuits, plasma treatment can be used in two highly effective ways. First, it can clean the surface of the circuit board. Second, it can activate the surface of the circuit board assembly to allow easier bonding and better adhesion of conformal coatings and materials like Parylene.

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.


How is the plasma applied to a circuit board to clean and activate the surface?

For materials like liquid conformal coatings then atmospheric pressure plasma is an excellent process for cleaning surfaces and improving adhesion and surface energy performance of circuit boards for conformal coatings.

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

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

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.

For Chemical Vapor Deposition (CVD) coatings like Parylene then low-pressure plasma can be used in the chamber before application.

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


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

Contact us now to discuss what we can offer you in terms of cleaning fluids from our Surclean range of materials.

Give us a call at (+44) 1226 249019 or email your inquiries at sales@schservices.com