Reducing Risk of Field Failures: Benefits of Conformal Coating and Potting

By Jeff Brattrud, Burton Industries’ Engineering Manager

Anyone who has spilled a cup of coffee on a keyboard or dropped a cell phone in water understDSC05352ands the negative effects that moisture can have on the operation of electronic products. Products used in harsh environments with regular exposure to temperature extremes, water, humidity, sand or salt spray can also have performance issues. One way to mitigate that risk is to either coat or encapsulate all or part of the printed circuit board assembly (PCBA).

Conformal coating is the most widely used method and acrylics are among the most popular conformal coating material. Acrylics are easy to apply and easy to rework. Silicone is also popular. However, it is harder to remove for rework. Rework on silicone-coated PCBAs requires use of solvents unless only a small area of the product will undergo rework. The main advantage of silicone is that it is stable at higher temperatures up to 200 degrees C, which makes it appropriate for high heat applications. The team at Burton Industries uses a one-part silicone formula. Both acrylics and silicone provide good protection from moisture, fungus, dirt, dust and salt spray. Silicone provides better protection in environments that include chemicals or solvents and vibration.

Potting provides additional protection in harsh environments by encapsulating sensitive electronics. When used on a single component in a process known as “glob top,” it can protect ICs from damage or strain. Some companies use potting compounds as a means to prevent theft of proprietary data. Potting may be a better solution than conformal coating for protecting products in environments that have a lot of vibration because it provides total encapsulation. It can also help with heat dissipation, since encapsulation spreads heat more evenly. Other harsh environmental conditions it can protect against include chemical or gas exposure, shock and drops.

In selecting an appropriate potting compound, it is important to consider environmental factors and potential component stress issues. For example, a softer compound will put less stress on components, particularly when there are temperature extremes.

Both potting and conformal coating add cost to the product, although prevention of field failures can eliminate a much higher cost. Once a product is potted, it generally can’t be reworked. Products incorporating potting must either be designed with an enclosure that won’t allow seepage during cure or a mold must be made to hold the compound during cure. Curing time with potting can be longer than that of conformal coating and the curing process requires control, since heat and humidity can affect cure time.

Both coating and potting require a clean substrate for the coating or potting to adhere properly. When no clean flux is used, it must be tested to determine if an additional step is required to clean the substrate prior to coating or potting. Use of non-wettable components will add cost. At a minimum they need to be masked or protected with a fixture if dipping or spraying is used. Thickness of the coating must be controlled to stay within the design specification including the thickness tolerance.

Conformal coating and potting offer viable options for protecting products from harsh environmental conditions. The team at Burton Industries is experienced with a wide range of options and can help with both the design and selection process.