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You have completed your search for an ideal conformal coating chemistry, one that will provide your PCBs the protection and reliability demanded by your industry and customers. After all that work, you probably assume your job is finished. Our apologies for being the bearer of bad news: There is still work to be done. In this basic presentation and discussion, we will talk about the proper choice and implementation of thinners for your coating. In many cases, a mistake in thinner can harm or even completely negate the protective properties of your conformal coating when applied to your PCB.

Have you ever seen your conformal coating look like the pictures above? It is a fairly common report to our technical support group. The appearance is often described as “orange peel” or sometimes “alligator skin.” We would like to offer you a basic explanation of this phenomenon, along with some simple approaches to avoid its occurrence or eliminate it when it appears.

What is orange peel and what is the cause?

In our experience, the uneven appearance that looks like the surface of your garden variety orange is almost always the result of exposing the coating to heat and airflow too quickly.

The electronics industry is exploding with the introduction of innumerable consumer devices designed with ever more complex functions and controls. These range from the relatively mundane such as controlling the temperature in your home to potentially life-saving including deploying airbags in your car or sensing hazardous road conditions. The demand for smarter and more complex electronics is becoming more important in everyday life.

The past few years have seen the introduction of a number of thinner-film circuit board protection products of various chemistries, many of which have been generically termed “nano-coatings” by manufacturers despite confusion regarding what this really means. There is no clear definition of a nano-coating as it relates to printed circuit boards, and the product offerings vary from vacuum-deposited films and microparticles of single digit nanometer thicknesses to more robust performing products with thicknesses in the hundreds of nanometers. It is critical to manufacturers that the properties of true nano-coatings be compared to more traditional protection technologies so an accurate evaluation can be made.

Much time and planning are invested in the choice of the ideal conformal coating material and process to adequately protect your printed circuit boards. This often includes multiple qualification trials. There is also what can be long and detailed testing in areas such as electrical performance, flame resistance, and thermal or mechanical cycling. Unfortunately, the qualification and testing process for conformal coatings is simply a snapshot of the process at the start. In order to maintain consistency, there remains an often-overlooked activity: regular cleaning and flushing of your selective conformal coating equipment.

Xylene and Toluene. Two words that can evoke concern and add to paperwork for environmental health and safety departments and manufacturing professionals. Aromatic solvents have been safely used for decades by employing basic safety equipment including gloves, masks, and proper workplace ventilation. Nevertheless, concerns for maximizing employee safety and minimizing effects on the environment have led electronics manufacturers to seek out alternatives. For over 20 years, HumiSeal® has supplied a wide-ranging group of aromatic-free products across all traditional chemistries to manufacturers for whom these concerns are critical.

The evolution of conformal coatings for protection of PCBs and electronics has accelerated over the past few years. One development in particular has increased in popularity due to a promising array of advantages over its predecessors. These are LED Curable Coatings.

A partial list of existing technologies for conformal coatings would include:

• acrylics (both solvent and water-borne)
• solvent-borne polyurethanes
• silicone-based polymers
• synthetic rubber (solvent-borne)
• Parylene technology
• UV-curable acrylated urethanes (arc and microwave bulb source)

and most recently . . .

Picking a Conformal Coating

You and your organization have spent weeks or months researching conformal coatings to meet the demanding specifications of your customers. These can include factors such as dielectric strength, thermal and mechanical shock properties, processing considerations, and so on. At some point, the critical consideration of price and cost must be added to the equation. The amalgamation of cost and performance could be considered a measure of the true value of any specific coating. 

Conformal coating thickness is one of the most important characteristics to ensure long-term reliability of your electronics. A minimum coating thickness is essential to provide the required function of the conformal coating, but if a conformal coating application is too thick, it can actually have negative effects on your level of protection.

Which conformal coating thickness should be applied to reach optimal protection?

For decades, HumiSeal products have been considered the “gold standard” in electronics protection. As a result, it is no surprise that unscrupulous chemical manufacturers have been continuously trying to profit from this reputation through the production of copycat or counterfeit products. While imitation is considered the sincerest form of flattery, the use of counterfeit materials is a serious danger to the integrity of your electronics production.