Plasma-polymerization protects electronics

A defective printed circuit board (PCB) grounds a military helicopter while it’s in action. If the crew does not have a replacement, it must perform in-field maintenance to repair the PCB. Traditionally, that could take days, but officials at Semblant, a manufacturer of protective nano-coating solutions for electronics, say they have developed a process that could get that helicopter back in the air within a day.

Military and aircraft electronics use conformal coatings to protect against environmental factors such as liquid contamination. When an electronic component fails, that coating becomes an impediment to fixing the problem. Engineers must remove the coating before diagnosing the problem; then they have to troubleshoot and fix it; and finally, they have to reapply the coating. Add up all the hours, and that process could take as long as three days.

Steve Lowder, CEO of Semblant, says that unlike other coating solutions, engineers don’t need to remove the company’s coating to diagnose a problem; they can rework right through it. Semblant also provides a small coating chamber, so a new coat can be applied within hours.
 

Plasma process

Plasma polymerization is, essentially, a method for applying a thin coating onto a substrate, says Tim von Wern, the company’s CTO. Standard liquid coatings are usually sold premixed in bottle, and a customer will spray or brush it on a component.

“What we’ve done at Semblant is develop a specific combination of materials and processing equipment that allows us to deposit a thin protective coating on circuit boards, electronic circuits, or electronic assemblies,” he says.

“For us, we take precursor gases and liquids and use those precursors in a plasma to create a coating real-time in the chamber,” Lowder says. “If you decide you’d rather have a different coating or a different level of protection, whether through materials or thickness, Semblant can simply dial-in a new recipe using some of the same precursor gases and you get a new level of protection within the plasma chamber.”

For an operator, the plasma polymerization method is simple: load the parts into one of three different sized chambers, close the door, push start, and let the machine work. Behind that simplicity, however, is a complex process. The machine runs through a pre-programmed recipe developed by Semblant scientists that includes these specially designed precursors to control the chemistry of the final coating.

Immediately after starting, the machine pumps down the atmosphere from the chamber, creating a partial vacuum. Then, the chamber is filled with process gas.

“Depending on the coating chemistry that we’re depositing, we can either start with a gas or we can start with a liquid, which is then vaporized and put into the chamber,” von Wern explains. “But when it reaches the plasma chamber, it’s a gaseous state.”

Next, high-frequency RF energy is introduced into the chamber. At this point plasma is created, clearly evident as it glows at room temperature.

“What is happening is the precursor molecules are decomposing into a range of different activated components, which then reassemble on the surface of the part and react with each other,” he says.

That creates a thin, highly cross-linked polymer, which blocks other chemistry or corrosive gases, von Wern says. Once the target coating thickness is reached, the plasma is deactivated, the chamber returns to normal atmospheric conditions, and the part is coated.
 

A&D benefits

Semblant worked with different leaders in the aerospace field to develop its technology, including both OEMs and supply chain partners. A few years ago, the company released its first process, the Semblant Plasma Finish (SPF) solution, which is a 50nm-thick coating, intended to protect bare PCBs from oxidizing and corrosive environments.

Semblant’s latest offering, PlasmaShield, offers protection at nanometer thickness, allowing for faster reworkability in the field, as well as other benefits.

“If you’re putting on quite a bit of encapsulant or traditional conformal coatings, you’re adding weight to your payload,” Lowder states. “A thin, polymer coating could be able to protect significantly enough for a particular payload or assignment.”
 

‘New kids on the block’

Despite being a relatively young company, Semblant is beyond its nascent stage. “We’re the new kids on the block,” Lowder says. “We’ve been around a few years instead of for decades…We’re the new premium coating.”

The new kids are running neck and neck with the big boys, he says. In addition to the benefits that other coatings don’t offer – such as faster reworkability – Semblant provides traditional protection as well. The coating’s flexible, thin material allows it to cycle through extreme weather conditions, including temperature and humidity fluctuations, “as good or better than you might get out of traditional coatings,” Lowder says.

“It may be a thermal expansion mismatch that might cause other coatings to break down or to crack because they’re a little more rigid in nature. Ours is made to be able to handle those thermal increases and decreases.”

Preventing these cracks is important throughout the conformal coating industry. It’s the product’s main job. Contaminants – such as liquid from condensation – sneak through these cracks, which can lead to anything from delamination to peeling to corrosion underneath the coating.

Semblant has many materials available and is working with them to create additional coating compounds.

“We don’t know the full range of what we can solve yet, but we do have understandings of what these individual materials can do,” Lowder says. “We notice that as we do create these compound structures, we’re able to solve even more problems.”

Semblant
www.semblant.com

About the author: Danny English is an associate editor for AMD and can be reached at 330.523.5354.