Conformal Coating Questions Answered

Nicole Bass, Product Manager for Techspray Conformal Coatings, takes us through the most common questions received from customers setting up a coating process. For a complete guide to conformal coating selection, application, and PCB protection, visit our Conformal Coating & PCB Protection Resource Hub.

A conformal coating is a thin layer of polymer applied to electronic components or circuit boards to protect them from environmental factors like moisture, dust, chemicals, and mild mechanical stress. The goal is to increase durability and improve reliability of electronic devices, extending their life in harsh environments. They are commonly used in electronics, automotive, aerospace, medical electronics, and many more industries.

What Are the Main Types of Conformal Coatings?

Conformal coatings are categorized by their base resin — the material left behind once the carrier solvents evaporate. The chemical composition of each conformal coating determines its main attributes and protective properties. The best coating for your application is determined by the operational requirements of your electronics.

Acrylic Resin (AR) is the most economical conformal coating option and provides good general protection. Generally, acrylic coatings have high dielectric strength, and fair moisture and abrasion resistance. They are easily and quickly removed by a variety of solvents, often without scrubbing, making rework and field repair very practical.

Silicone Resin (SR) provides excellent protection in a very wide temperature range, with good chemical resistance, moisture resistance, and high flexibility. Silicone conformal coating is not abrasion resistant because of its rubbery nature, but this property makes it resilient against vibrational stresses.

Urethane Resin (UR) has excellent moisture and chemical resistance, and can withstand abrasion better than other types of coatings. Because urethanes are solvent resistant, they can be very difficult to remove. Urethane conformal coatings are commonly specified for aerospace applications where exposure to fuel vapors is a concern.

Others are used for specialized applications:

• Epoxy Conformal Coating is common for encapsulating or “potting” electronics, often required when a device will be fully submerged in water.
• Parylene Conformal Coating is applied using vapor phase deposition — top-of-the-line, most expensive, and most difficult to rework.
• Thin Film / Nano Coatings provide a water repellant layer for “good enough” protection needed for some consumer electronics.

When Is Conformal Coating Necessary?

Whether or not conformal coating is required depends on the environment the electronic device will operate in, the reliability requirement of the device, and the cost of failure.

Does Your Conformal Coating Meet IPC-CC-830?

Yes, all Techspray coatings meet IPC-CC-830 standards. IPC-CC-830 defines the requirements for conformal coatings used to protect printed circuit boards and electronic assemblies from environmental factors such as moisture, dust, chemicals, and temperature extremes.

Is Conformal Coating Waterproof?

While conformal coatings can offer a moisture resistant layer of protection, most cannot be considered waterproof. Even if applied heavily, most coatings are semi-permeable and will allow some amount of moisture through.

Does Conformal Coating Protect Against ESD?

While conformal coatings can offer some level of protection against ESD by providing a barrier between sensitive electronic components and the surrounding environment, they are not specifically designed as ESD control measures.

How Long Does Conformal Coating Take to Cure?

The drying and curing time of conformal coatings varies depending on the type of coating, thickness, and environmental conditions. Acrylic coatings typically dry quickly with tack-free time from a few minutes to an hour and full cure from 24–72 hours. Silicone coatings usually have a longer tack-free time of several hours with complete cure from 12 hours to a few days. Urethane coatings have a relatively fast tack-free time, often within a few minutes, but full cure may take 24–48 hours.

How Do You Apply Conformal Coating to a PCB?

Prepare the PCB

Ensure the PCB is clean, dry, and free from any contaminants. Clean it using an appropriate PCB cleaning solution or isopropyl alcohol to remove any dirt, flux residues, or other impurities that could interfere with the coating's adhesion.

Select the Conformal Coating

Choose a coating that suits your specific application and environmental conditions — acrylic (AR), silicone (SR), urethane (UR), or specialty types. If certain components or areas should remain uncoated, use a masking material such as Kapton tape or liquid latex to protect those areas.

Choose the Application Method

• Spraying: Suitable for large-scale production using a specialized spray booth and spray gun.
• Dipping: Involves immersing the entire PCB into a reservoir of conformal coating for uniform coverage.
• Brushing: Manual application using a brush — suitable for small-scale production or touch-ups.
• Machine dispensing: Applies coating using a controlled dispensing system for selective coating on specific areas.

Curing and Drying

Allow the applied conformal coating to cure and dry as per the manufacturer's instructions, typically in a controlled environment or oven for the recommended duration.

Post-Coating Inspection

After the coating has cured, inspect the PCB to ensure proper coverage and check for any defects such as bubbles, pinholes, or insufficient coating.

How Do You Measure the Thickness of the Final Coating?

• Caliper: Measure the PCB thickness before and after coating.
• Calibrated Thickness Gauges: Handheld devices using magnetic induction or eddy current principles.
• Cross-Sectioning and Imaging: Cut a sample and examine under a microscope.
• Ultrasonic Testing: Ultrasonic pulses bounce off the substrate-coating interface to calculate thickness.
• X-ray Fluorescence (XRF): Analyzes X-ray intensity emitted from the coating material.

How Can You Double-Check Your Conformal Coating Coverage?

Conformal coating with UV tracer can be inspected with any typical UV lamp (black light) at 320–380 nanometers. Full coverage glows bright; shadowed areas, pinholes, and gaps show up as dark areas.

How Do You Remove Conformal Coating When Repairing or Reworking a PCB?

Techspray offers the Trace Tech Conformal Coating Remover Pen for removing a tight area of coating around a repair area. Coating can also be removed completely by soaking in Techspray's Conformal Coating Remover or Conformal Coating Remover XT, and scrubbing as necessary.

Watch in Video Format

Related Resources: For our complete guide to conformal coating types, application methods, masking, and PCB repair, visit our Conformal Coating & PCB Protection Resource Hub. For soldering and rework resources, see our Soldering, Desoldering & Rework hub.