Conformal Coating

1. 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 adhesion.
2. Select the Conformal Coating: There are various types of conformal coatings available, such as acrylic (AR), silicone (SR), and urethane (UR). Choose a coating that suits your specific application and environmental conditions.
3. Choose the Application Method: Conformal coatings can be applied using different methods, including spraying, dipping, brushing, or dispensing. The method you choose depends on the type of coating and your equipment's capabilities.
   Spraying: Suitable for large-scale production. It requires a specialized spray booth and spray gun to evenly apply the coating.
   Dipping: Involves immersing the entire PCB into a reservoir of conformal coating. This method provides uniform coverage but may trap air bubbles.
   Brushing: Manual application using a brush is suitable for small-scale production or touch-ups.
4. Masking Uncoated Areas (optional): If certain components or areas on the PCB should remain uncoated (e.g., connectors, switches, or heat sinks), use a masking material (e.g., Kapton tape or liquid latex) to protect those areas during the coating process.
5. Dispensing: Applying the coating using a controlled dispensing system, which is useful for selective coating on specific areas. Make sure to apply a thin and even layer, avoiding excessive buildup, which could lead to uneven coating thickness or encapsulation of sensitive components.
6. Curing and Drying: Allow the applied conformal coating to cure and dry as per the manufacturer's instructions. This typically involves leaving the coated PCB in a controlled environment, such as an oven, for the recommended duration.
7. Post-Coating Inspection: After the coating has cured, inspect the PCB to ensure proper coverage and to check for any defects, such as bubbles, pinholes, or insufficient coating.

The drying and curing time of conformal coatings can vary depending on the type of coating used and the environmental conditions. Conformal coatings are applied to protect electronic components from moisture, dust, chemicals, and other contaminants. Acrylic (AR) coatings typically dry quickly, and the initial tack-free time can be anywhere from a few minutes to an hour. However, the full curing time can range from 24 to 72 hours, depending on the thickness of the coating and environmental conditions like temperature and humidity. Silicone (SR) coatings usually have a longer tack-free time, which can take several hours. The complete curing time can vary from 12 hours to a few days. Urethane (UR) coatings have a relatively fast drying time, often within a few minutes. However, full curing may take 24 to 48 hours.

Full cure is when it meets all the final specifications. There might be some out-gassing, but it will be as hard as it is going to be, and adhesion is as good as it gets.  Tack-free is as the name suggests, not sticky so you can move it along the assembly process.

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

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, so allow some amount of moisture through. Conformal coating can, however, prevent current leakage or corrosion due to ambient moisture. To truly waterproof electronics, you either need gasketing to seal the electronics within the packaging or cover the electronics with a waterproof encapsulant or potting compound.

No, conformal coatings are non-conductive, or insulative. The job of conformal coating is to isolate the PCB or components from the environment and even components (i.e. high voltage or high heat) from the rest of the board. To do that properly, a coating must have electrically insulating properties with as high of a dielectric withstand voltage (or strength) as possible.

Measuring the thickness of conformal coating is essential to ensure proper application and adherence to the specified requirements. There are several methods used to measure the thickness, and the choice of method may depend on the type of conformal coating and the level of accuracy required. Here are some common methods:

• Calibrated Thickness Gauges: These are handheld devices that use non-destructive methods to measure the thickness of the coating. They typically use magnetic induction or eddy current principles to determine the distance between the probe and the substrate, which correlates to the coating thickness.
• Cross-Sectioning and Imaging: This method involves cutting a sample of the coated surface and examining it under a microscope. The thickness can be determined by measuring the height of the coating in the cross-sectional view.
• Ultrasonic Testing: Ultrasonic thickness gauges use sound waves to measure the thickness of the coating. The device emits ultrasonic pulses, and the time taken for the waves to bounce back from the substrate-coating interface is used to calculate the thickness.
• X-ray Fluorescence (XRF): XRF can be used to measure the thickness of conformal coatings. It involves analyzing the intensity of X-rays emitted from the coating material due to bombardment by X-rays. The thickness is determined based on the X-ray penetration depth.
• Electrical Capacitance Method: This method utilizes the change in capacitance between electrodes positioned on opposite sides of the coated surface. The coating's thickness affects the capacitance, allowing for indirect measurement.
• Weight Difference Method: For some applications, the thickness can be estimated by measuring the weight difference of a substrate before and after coating. This method is more suitable for thicker coatings.

Before choosing a specific method, it is important to consider factors like the type of coating material, the size and shape of the substrate, the required measurement accuracy, and whether destructive or non-destructive testing is acceptable for your specific application. Additionally, it is essential to calibrate the measurement equipment and follow any manufacturer's guidelines for accurate and reliable results.

Yes, all our coatings meet IPC-CC-830 standards. IPC-CC-830 defines the requirements for electrical insulating compounds, commonly known as conformal coatings, used to protect printed circuit boards and electronic assemblies from environmental factors such as moisture, dust, chemicals, and temperature extremes. The standard outlines the testing methods and performance criteria for these insulating compounds to meet industry requirements. It includes specifications for material properties, application procedures, and performance testing for conformal coatings. You might see IPC-CC-830B, 830C, etc. The extra letter refers to the revision. The changes between revisions general do not affect all types of coatings, so coatings are often not retested to the latest standard.

Every organization using hazardous chemicals within their facility has the responsibility to equip their facility and personnel to maintain exposure levels below the TLV. Personal monitoring badges can be used to measure exposure of a specific material. Then, depending on the threshold limit and the application, exposure can be controlled with PPE like masks, face shields, respirators, and even coveralls. If they don’t reduce exposure below the recommended limit, you will need to consider a special ventilation hood or even containment booth. As you can see, as the exposure limit gets down to a certain level, the equipment required to safely use the solvent can get impractical. At that point, your best option is to consider a safer alternative.

The dielectric strength is material intrinsic property and withstand voltage is surface property which depend on thickness of the material. They can be slightly different for thicker materials, but for conformal coating, the two numbers should be very close or the same. That is because we test coating at 3-5 mils thickness, calculate, then report the value per mil.

Conformal coating with UV tracer can be inspected with any typical UV lamp which has wavelength of 320-380 nm.

Techspray offers the TraceTech Conformal Coating Remover Pen that allows you to remove a tight area of coating around a repair area without affecting the rest of the PCB. You first saturate the tip by tapping it lightly on a surface, which opens the valve and releases solvent. Holding the tip down may oversaturate it, which could lead to solvent flowing into unintended areas.