Ensuring the proper PCB conformal coating thickness

Ensuring the proper PCB conformal coating thickness

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Working with a printed-circuit board (PCB) requires following stringent PCB quality control methods to ensure the component performs as desired and has the expected lifespan. One of the important things to check is the appropriate PCB conformal coating thickness.

A correctly applied conformal coating can protect delicate parts from water, dust, and other things that could damage the PCB. Here are some actionable ways to achieve consistent quality assurance regarding this critical step.

Give employees thorough and ongoing training to improve quality control

The people who apply the conformal coating need in-depth training to ensure they know the right procedures. The specifics will vary depending ON the type of application method used and the conformal coating applied.

In addition to on-the-job training that happens internally, managers can consider sending employees to conferences that offer intensive training within the event schedule. One conformal coating conference in Texas had at least two professional development boot camps available.

Investing in employee education tends to positively affect PCB quality control. However, workers must adapt and update the content as required, especially if a company changes processes or products.

Understand the application-specific PCB coating thickness needs

Meeting PCB quality control goals also means knowing whether there are requirements for the industry or application that will use the finished PCB. Products with waterproof features have ingress protection codes within their specifications that explain how effectively they can keep water out. They range from 0 to 8, and associated ratings provide performance benchmarks.

People who apply conformal coatings can follow established parameters in their work, too. Doing that should raise the overall PCB quality control levels. For example, MIL-I-46058 is a widely used military standard for conformal coatings. There’s also a more recent standard called IPC-CC-830.

Besides detailing the specifics for different types of conformal coatings, the standards explain what people should do to give their PCBs the best chance of passing internal tests or those that a customer requires.

Coat flat test coupons to test PCB quality control

The IPC A 610 standard has ranges for various types of conformal coatings and the ideal thickness. The best practice is to compare the information in its documentation with what the manufacturer recommends.

People should also treat thickness ranges as averages rather than absolute values. Factors such as the liquid’s surface tension and the board’s design will mean it’s not always possible to stay within the recommended PCB coating thickness range in all cases.

However, the IPC A 610 standard suggests coating flat test coupons while following the company’s internal process. Then compare the outcome to the standard to check for any discrepancies.

Rely on advanced technologies to improve coating consistency

It’s becoming more common for people to depend on automation when building PCBs. One such system makes more than a dozen product types each day. Companies also install robotic cells specifically to handle conformal coating steps. That’s often a wise step to take when a process is already well-established.

Automated equipment won’t experience the things that could make humans fall short, such as boredom, distractions, or fatigue. Plus, leaving robots to do some of the tasks that people once did allows those employees to focus on duties that are more rewarding for them, valuable to the company, or both.

Another possibility is to utilize a coating solution that works with artificial intelligence. One product on the market combines AI with machine-vision inspection to accelerate PCB quality control and allow operators to validate what the technology finds.

It can tell if the PCB thickness is insufficient or overapplied. The technology also creates logs, letting managers track trends. This solution can also cut the average inspection time to 20 seconds and reduce false-positive and escape rates to less than 5%.

Implement reliable techniques to measure PCB coating thickness

How someone applies a conformal coating is only part of the resulting PCB coating thickness. Staying on top of quality assurance in a production facility means using various measurement options at different stages of the overall process.

One possibility is to use a wet-film gauge to check that the thickness is correct before the coating cures. This device has machined combs that contain markings showing different thicknesses. The operator places the tool into the coating and checks to see if at least one of the comb teeth remains unsubmerged.

Alternatively, a person can do a dry-film measurement with calipers by checking the PCB coating thickness at several points. This is a low-cost option with limited accuracy. The caliper measurements happen before and after the PCB gets coated. People then take averages to estimate the coating thickness.

These are just two of the many avenues to take. The goal is to find at least one measurement technique that helps a company maintain tight PCB quality control.

The correct PCB coating thickness matters

Failing to use enough conformal coating could result in the component not getting the expected protection. However, trying to overcompensate by using too much comes with its own set of potential problems. These include cracking, wrinkling, and bubbling. Another thing to be mindful of when improving PCB quality control is that some parts of the board may not need coating.

The tips here will help production managers stay abreast of quality control related to conformal coating. However, it’s also useful to gather metrics of failure rates and check if process improvements reduce them.

About the author

Emily Newton is a technical writer and the editor-in-chief of Revolutionized. She enjoys researching and writing about how technology is changing the industrial sector.