A few weeks ago, I shared an article that explained the basics of conformal coatings. The piece described a few of the benefits of coatings. I also mentioned some additional protections they provide, such as protecting solder contacts from thermal and mechanical shock, and corrosion. Additionally, they add strength and insulating properties to component connections. The advantage that most electronics engineers appreciate is the insulating properties, which allows engineers to utilize board space and place components closer, knowing the coating will protect against unintended conduction of heat and voltage on densely populated printed circuit boards. Today I want to go a bit further and share information on how and why coatings are selected and a little about a new and particular type of coating.
How are coating selected
When engineers and designers begin working on a new project, there are many factors they must consider, but for this article, we will focus on printed circuit board protection. Considerations specific to the protection of a printed circuit board may look like this; What are the typical uses of the product? In what environment will the finished product be expected to perform? How can our design make the most of the available space, provide proper functionality and component protection in the anticipated environment? How and where will the board be mounted/secured? How will it be housed?...
In some circumstances, the environment may be an office where the product sits on a desk, it is climate-controlled, and temperature and moisture fluctuations are minimal. These boards require little protection. On the other end of the spectrum are products that have to function in a wide range of temperatures, moisture fluctuation, and exposure to chemicals and environmental debris. They may need to perform in environments as extreme as firefighters fighting fires to disaster relief efforts during a hurricane. These products may often get dropped or bounced around regularly, and their electronic components have to remain functional, or it could cost lives. So, engineers use a lot of data to determine how to best design electronic devices, so they fit well in their environment, and they function correctly for the expected use and life cycle of the product.
What About Resins?
One of the newer and lesser-known printed circuit board coatings is two-part polyurethane and epoxy coatings, typically referred to as resins. PROS - These types of coatings have superior protective qualities. They can be applied just like other more common types of coatings, but they cure without any additional process when used in the proper ratios. They provide excellent protection to boards in harsh environments where the board is not encased in a moisture tight protective housing. However, using resins on boards encased in a watertight protective housing adds a secondary layer of protection. When environments are harsh, and a broken seal could jeopardize product function, a resin coating can be a perfect solution when product failure is not an option. When applied correctly, these coatings are significantly thicker than conventional acrylic, so they provide better protection from chemical exposure and mechanical or thermal shock. CONS – Resins cost considerably more. They also add additional weight to the boards and are nearly impossible to remove without causing harm to the board components. So, repairs usually mean a new board.
There are also a couple of other uses for resins that are outside the normal scope of conformal coating functions. Since removal will cause damage, resins provide tamper prevention—tampering, or removal, voids the warranty, and damage functionality. You can also get colored resins that will protect your intellectual property by hiding components under a mask. It will be interesting to see the continued evolution of coatings and electronics. Companies continue the race to create the most innovative products on the market, and in doing so, often cannibalize their products in the process. I will not be surprised to see small electronic devices that are considered disposable, with the electronics wholly encapsulated in an opaque coating, all to protect intellectual property and slow the rate of obsolescence.