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Conformal coating is generally the last step in the PCB manufacturing process and the method of protection for all those valuable functional components, but it's not always that simple. Let's look at a fairly common scenario.

Everything was moving along fine through the design and testing process. You have begun production spraying and suddenly there are wisps of translucent webs floating in the air. Your taller components look like a scene from the movie Arachnophobia. This is the oft-dreaded cobwebbing effect; and while it may appear confounding and a little scary, it is often one of the simplest problems to eliminate when conformal coating.

In this brief article, we will discuss the likely causes of this odd situation and provide some simple solutions to get you back to applying your coating in a defect-free manner.   Let's begin by exploring the phenomena in more detail.

Bubbles. They can be a real challenge in any adhesive or coating, but they are particularly undesirable when covering electronics and printed circuit boards (PCBs) with fluid conformal coating material. The technical support engineers at Humiseal have over five decades of experience in support of PCB manufacturers. They report that bubbles within the finished film are the most commonly reported technical issue they receive.

In this brief article, we will discuss many of the causes as well as many potential solutions to the problem of entrapped bubbles.

Conformal coatings have a long and storied history with printed circuit boards. A good conformal coating protects PCB components from moisture, corrosion, contaminants, and additional PCB threats like vibration and thermal shock. Coatings are a complicated science, and there isn’t one best coating or application method for every job. These choices are dependent on the design, use case, and assembly of the PCB. For instance, manual brushing PCB coating material is a slow, tedious process; but for small batch applications, it’s quite cost-effective.

Regardless of the chosen method, there are fundamental application errors that can occur, leading to defects forming in the coating which ultimately limit the functional service life of the PCB.

We at HumiSeal are no strangers to conformal coatings; and if you’re reading our blogs, it’s likely you’re familiar with these coatings as well. The word “conformal” is descriptive of the function of the coatings which are expected to spread and conform evenly across all surfaces that are to be protected. This uniform and even distribution is necessary to protect delicate electronic components from things such as humidity, water, vibrations, and thermal damage (to name a few).

Does your conformal coating not wet properly? Do you struggle with craters, fish-eyes, or film separation? The culprit could be that the surface energy of your PCB is lower than the surface tension of the conformal coating.   The above defects are discussed frequently with customers on our technical support line, and any time we receive a technical enquiry regarding poor wetting or loss of adhesion, we ask “what is the surface energy of your substrate?” In this blog, we will explain surface energy, surface tension, and how to quickly troubleshoot defects resulting from low surface energy.