Conformal Coating Questions Answered

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.

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. Conformal coating is typically required when electronics will be exposed to moisture, condensation, dust, chemicals, or temperature extremes — common in automotive, aerospace, industrial, outdoor, and medical applications. For consumer electronics in controlled environments, coating may be optional depending on the product's reliability specification.

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. Specifying an IPC-CC-830 compliant coating ensures the product has been tested and qualified against the industry standard for electronic assembly protection.

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 over time. For applications requiring full submersion protection, epoxy encapsulation (potting) is the appropriate solution rather than a standard conformal coating.

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 and should not be relied upon as a substitute for a proper ESD control program. Grounding, static-dissipative materials, and ESD-safe handling procedures remain the correct approach to ESD protection.

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.

Applying conformal coating to a PCB involves five steps:

1. Prepare the PCB: Ensure the PCB is clean, dry, and free from contaminants. Clean using an appropriate PCB cleaning solution or isopropyl alcohol to remove flux residues or other impurities that could interfere with adhesion.
2. Select the coating: Choose acrylic (AR), silicone (SR), urethane (UR), or a specialty type based on your operating environment. Mask any components or areas that should remain uncoated using Kapton tape or liquid latex.
3. Choose the application method: Spraying (large-scale production), dipping (uniform full-board coverage), brushing (small-scale or touch-ups), or machine dispensing (selective coating on specific areas).
4. Cure and dry: Allow the coating to cure per the manufacturer’s instructions, typically in a controlled environment or oven for the recommended duration.
5. Post-coating inspection: Inspect for proper coverage and check for defects such as bubbles, pinholes, or insufficient coating. UV inspection is the standard method — see below.

Five methods are used to measure conformal coating thickness:

• 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.

Conformal coating with UV tracer can be inspected with any typical UV lamp (black light) at 320–380 nanometers. Full coverage glows bright under UV illumination; shadowed areas, pinholes, and gaps show up as dark areas. This is the fastest and most practical method for production inspection and is the industry standard for verifying coating coverage before a board ships.

Removal method depends on the coating type and the scope of the rework:

• Spot removal: The Techspray Trace Tech Conformal Coating Remover Pen removes a tight area of coating around a repair area without affecting surrounding components.
• Full removal: Soak in Techspray’s Conformal Coating Remover or Conformal Coating Remover XT and scrub as necessary.

Note: Acrylic coatings are the easiest to remove with solvents. Urethane coatings are significantly more difficult due to their solvent resistance. Silicone coatings typically require mechanical removal or specialized solvents.