Common Conformal Coating Issues and How to Prevent Them

Conformal coating is an essential process where a thin, cosmetic polymeric coating is applied to a printed circuit board’s (PCB) surface to protect it from water, dirt, dust, and other unwanted elements. This process is vital for maximizing the useful life of the equipment. However, it’s not a fool-proof technique, and issues can occasionally develop. However, with the right solutions, you can limit the impact of malfunctions. Learn more about common conformal coating issues and how you can prevent them from occurring.

Robotic Brush Conformal Coater Introduced at SMTA Dallas

Common Conformal Coating Defects

Copper Dendrites

Copper dendrite is one of the most common issues seen while coating PCBs. These occur when moisture is present on the PCB’s surface or in other locations, like on a ceramic substrate or on the surface of a component located between two terminations. This issue leads to copper ferns that grow from one electrode to another and resemble those found on a Christmas tree. Copper dendrites are a problem because excess moisture causes corrosion and can lead to catastrophic failure if ignored.

The best way to prevent copper dendrites from forming is to carefully clean, dry boards and properly set up equipment before starting the coating process.

White Corrosion on Circuit Board

Another common problem that disrupts the coating process is the formation of white corrosion on the circuit boards and components. This is caused by using improper cleaning tools or chemical techniques. It leads to an environment where the flux isn’t soluble and incompatible. White corrosion on circuit boards can impact the useful life and durability of the equipment. When trying to pinpoint the cause of corrosive residue, look at these three areas:

Contamination: Material changes, purposeful or accidental, can cause unexpected cleaning and residue issues.
Solvent: If the corrosive residue appears as a smooth layer of film, then likely you are using the wrong solvent for that flux.
Process: If it’s not contamination or solvents causing the residue, then it’s likely a process issue that needs to be changed.

Conductive Short

A major problem that causes printed board failure is when conductive shorts form on the inner layers of a multilayer board. This is called Conductive Anodic Filamentation, or CAF failure, and can vary in severity. Preventing CAF failure is a top priority for any conformal coating process, here are some of the causes:

Moisture and humidity: A high water content is required for CAF failure to occur. Minimizing moisture and humidity is essential to preventing this issue.
Acid contamination: Some processes used during fabrication can create acid contaminants and increase the risk of CAF.
Voltage: Bias voltage is the power that drives reactions, a low-voltage bias can increase the chances of CAF failure.
Pre-existing defects: Fractures, voids, wicking, and other pre-existing issues can cause CAF failure. Be careful when drilling holes into a PCB, not exercising caution can create cracks.

Delamination

Delamination is another common issue that degrades PCB quality and occurs when the coating lifts from the surface, leaving an exposed area where moisture and other unwanted debris can enter. Typical causes of delamination include surface-area cleanliness and a poor coating cure degree. However, it’s possible to prevent this issue from developing by following these best practices:

Reduce the thickness of the coating material
Minimize force drying processes
Remove contaminants before conformal coating
Adjust the coating materials to create a more beneficial surface environment.

Bubbles

Bubbles, pinholes, and foam are among the most common conformal coating issues. These develop when air pockets get trapped under a conformal coating layer. Foam is the most extreme example and, when they pop, creates pinholes. Using a coating that’s too thick or viscous can increase the likelihood of bubbles.

If you’re looking to prevent bubbles from forming, here are some helpful tips:

Use a conformal coating material with a lower viscosity
Verify the coating layer is applied at the ideal thickness
Some coating materials are potentially more bubbly than others, check with your coating vendor and different coatings.
Apply coats in thin layers

Conformal Coating on Connector Pins

Conformal coating getting on connector pins, or other keep-out zones, can create malfunctioning equipment. This is especially true for areas that are sensitive to underfilling. Carefully applying the coating material is essential to verify it doesn’t cover unwanted areas.

Download Conformal Coating Inspection Chart

Prevent Conformal Coating Issues With Invention House

User error is a common cause of conformal coating defects. Many processes are reliant on operator experience and poor control can lead to an uneven layer – especially manual brush and manual spray coating processes. Invention House understands the frustrations that come with common problems.

We leveraged our knowledge of coating techniques to create the Raphael 4040, an automated coating robot that combines 3D automation and a robotic brush to streamline coating processes. Operators can increase precise coating while reducing waste by following these steps:

Step One: Board Layout Implementation

The first step in our process is programming the path by implementing a Gerber file or board image into Raphael Suite, our proprietary software program. The operator then sets the PCB’s X, Y, and Z dimensions to set boundaries.

Step Two: Coating Path Creation

The operator uses Raphael’s built-in joystick, keyboard, and easy-to-use click-and-drag actions to create a series of coating segments. This path is completed as a dry-run, allowing the user to make an optimal path without wasting product.

Step Three: Wet Run

After finalizing the preferred path, the operator then selects a single PCB, activates the pumps, and conducts a wet run. We recommend paying attention to flow and brush movement to ensure coating accuracy and making adjustments when needed.

Step Four: Full-Run Production

Full production can begin after successfully completing a series of wet runs. Inspecting early samples allows the operator to make sure it’s meeting their specifications and make the necessary small tweaks.

Automated Conformal Coating - Raphael 4040 Thumb 2

Invention House is proud to serve our clients with industry-leading motor control solutions. Along with our conformal coating robot, our team also offers single-phase, 3-phase, and 400 Hz motor drives that are military-grade and built to withstand extreme conditions in any environment. Contact us today to learn more about how our equipment reduces common conformal coating issues.

Want to Learn More About Common Conformal Coating Issues?

Check out our latest webinar and learn more about conformal coating defects that can impact equipment.

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Common Conformal Coating Issues and How to Prevent Them

Common Conformal Coating Defects

Copper Dendrites

White Corrosion on Circuit Board

Conductive Short

Delamination

Bubbles

Conformal Coating on Connector Pins

Download Conformal Coating Inspection Chart

Prevent Conformal Coating Issues With Invention House

Step One: Board Layout Implementation

Step Two: Coating Path Creation

Step Three: Wet Run

Step Four: Full-Run Production

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