Physical Properties

Summary

Co-Authors and contributors
  • Dr Lee Hitchens, Nexus

Conformal coatings have varying physical properties, dependent on the type of chemistry of the coating.

These properties can be subdivided into three key areas.

These are

  • Liquid
  • Process
  • Dry State

They can be further subdivided into many different individual properties that make up the conformal coating.


Liquid properties

The liquid properties are defined for the conformal coating material before it is used in the application process.

So, it is still in its liquid state and stored in the container.

Critical properties for the conformal coating whilst stored include:

  • Flash point
  • Storage Lifetime
  • Appearance and Colour
  • Density
  • Solids Content
  • Viscosity

Click to review more on the liquid properties of conformal coatings.

The physical properties of a conformal coating have a huge impact of the process and the long term reliability of the product.

The viscometer measures the conformal coating viscosity that is an important liquid property for process control

 


Process Properties

The process properties are defined for the conformal coating material whilst it is used in the application process.

So, it is still in its liquid state but being applied in various ways to the circuit board.

Critical properties of the conformal coating during production include:

  • Wetting
  • Capillary
  • Viscosity
  • Wet Film Thickness
  • Surface Tension
  • Pot life
  • Drying and Curing

Click to review more on the process properties of conformal coatings.

The physical properties of the conformal coating can effect the final quality of the finish on the circuit board. In this case the material has been scavenged and shows capillary effects

Dry state properties

When the conformal coating has been applied and is fully dried / cured then it will have reached its full potential physical properties.

This is the dry state.

Critical properties for the dried conformal coating include:

  • Edge loss
  • Refractive index
  • Glass transition temperature (GTT)
  • Coefficient of thermal expansion (CTE)
  • Temperature gradient (Tg)
  • Flammability
  • Flexibility
  • Abrasion resistance
  • Hydrolysis stability
  • Permeability
  • Chemical compatibility
  • Chemical resistance
  • Corrosion resistance
  • Fungus resistance
  • UV stability
  • Outgassing
  • Thermal stability
  • Thermal shock

Click to find out more on the dry state properties of conformal coatings.

Note: The liquid properties may not be relevant to Parylene materials.

These physical properties may be defined by the manufacturer and contained on a data sheet.

Other properties may be required to be monitored by an International Standards.

 

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