An Introduction to Conformal Coatings

In the first of a two-part series of articles, AZoM talks to Masterbond about the properties and benefits of conformal coatings.

How do conformal coatings protect electronics from harmful elements?

A thin uniform layer of a specially formulated polymer compound is applied by electronics manufacturers to traces, printed circuit boards and components during the final manufacturing stage.

It is designed to conform to the object contours to which it is applied and acts as a barrier between the environment and the electronics, securing all areas it covers, whilst at the same time strengthening traces and delicate components.

In order to improve reliability, manufacturers add conformal coatings to electronics even if operating conditions are benign.

What are the different chemistries associated with conformal coatings?

Conformal coatings for high-end applications include silicone, epoxy or UV curable compounds, each of which offer unique advantages. The easy-to-apply epoxy-based coatings offer excellent protection against chemicals, moisture, solvents, abrasion, vibration and mechanical shock.

It is very difficult to remove most epoxy-based coatings and some of the more rigid ones may stress delicate components or traces when subjected to extreme thermal shocks. Certain grades can be formulated specially to be retrievable and flexible at the expense of chemical and temperature resistance.

What is the primary advantage of epoxies?

Epoxies are extremely versatile, enabling them to be formulated to exhibit several combinations of electrical, thermal, mechanical and physical properties to suit a variety of coating applications, with each grade offering a different range of properties.

Certain epoxies can have a broad temperature range from 4K to 500°F. Furthermore, fillers can be added to increase their thermal conductivity.

There are some optically clear epoxies that can be used in a range of opto-electronic applications. Formulators also offer grades that meet specific industry standards, such as NASA low outgassing specifications or USP Class VI biocompatibility tests.

There are also grades that are capable of withstanding autoclaving sterilization procedures, as is required for many medical electronics applications.

What do UV curable coatings offer?

The primary benefits of UV curable coatings are:

  • They offer excellent environmental protection, extremely rapid processing, and moderate versatility.
  • These easy to use coatings require no mixing and cure within seconds upon exposure to UV light.

For curing any shadowed out areas, using a dual UV/heat curable compound is required. Many UV curable coatings offer superior electrical properties, good chemical and high-temperature resistance. Specific UV curable coating formulations vary in viscosity, hardness, flexibility, impact resistance, thermal shock and other properties.

What are some of the advantages and trade-offs of silicone conformal coatings?

Silicones offer high temperature resistance and excellent flexibility, but may not be resistant to chemicals and moisture as compared to epoxies. Their flexibility makes silicones suitable for applications that require vibration dampening.

Silicone-based coatings can be applied easily and can be removed by cutting when rework is needed. They can be formulated to be optically clear or to exhibit lower outgassing.

Their viscosity and resistance to shock, vibration, heat, humidity and corrosion can be controlled by formulators. No mix one part silicones cure at room temperature via moisture in the air, while two part systems cure at ambient or elevated temperatures upon addition of a curing agent.

This information has been sourced, reviewed and adapted from materials provided by Master Bond Inc.

For more information on this source, please visit Master Bond Inc.

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