Conformal coating, the applications that use it, and the methods and equipment that apply it have changed considerably. Conformal coatings have long been used to protect printed circuit boards in harsh environments in the automotive industry. In most cases, the areas to be coated were wide and could be covered by spraying the coating over the surface of the board. Now, coating is needed on boards with increased component density, on small parts, and for boards that need a combination of precision coating and spraying.
Advanced electronics in automobiles, and printed circuit boards (PCBs) with a high density of electronic devices to power them, are playing a large role in keeping drivers and passengers safe, comfortable, and technologically connected. These electronics are often placed in areas of the automobile that are subject to chemicals, vibration, and a host of harsh conditions, creating the need to protect the boards or specific components on them. Conformal coatings provide the protective layer between the environment and the electronics.
The precise positional placement and volumetric accuracy of fluids dispensed on circuit boards becomes more challenging as component density increases. For most applications, higher density packaging means smaller keep-out zones for dispensed fluids, smaller pad geometries and pitches to target for electrical connections, and increased gaps between PCB surface and dispense nozzle tip. As components get closer to each other, the more difficult it is to ensure that fluids stay dedicated to the specific device for which they are intended. At the same time, production rates and yields need to increase to stay competitive.
Having a conformal coating system that just sprays a large fan width of fluid is no longer functional on these dense, multipurpose boards. Yes, there still are areas and applications that need a broad coating, but there are others that need a nozzle that can provide edge definition, and still others that need extremely small amounts of fluid dispensed precisely, accurately, and of course, repeatably.
In the automated world, there are several techniques for applying coating, and they usually depend on the coating type and application specifications. Advanced spray valves have the ability to operate in multiple modes (bead, monofilament, and swirl) by adjusting air assist pressure. Software-controlled pneumatic regulators enable all three modes to be used on the same PCB, which often eliminates the need for multiple valves on the coating platform.
Low Air Assist Pressure
Low air assist pressure keeps the coating as a fluid and dispenses a bead of fluid on the PCB. In this bead mode, a stream of material is applied to the circuit board in areas where components are very close to non-coating or keep-out areas. The bead may also be used as a spot command for a single component.
Medium air-assist pressure causes the bead of fluid to eject in a circular motion causing a large area coat with thicker film build in a looping pattern. This monofilament pattern is used for dispensing broad pattern widths. It provides good edge definition and faster cycle times.
High air assist pressure atomizes the coating fluid so that it operates as a spray valve. Air pressure is increased and flow settings lowered. Angled jets impinge air upon the pressurized material exiting the nozzle creating a conical, swirling pattern. The swirling action helps maintain pattern shape resulting in excellent width control. Because the air jets cause slight atomization of the material, extremely thin film builds are possible. This mode works for applications where moderate selective coating and thin-film builds are required.
Traditional conformal coating applicators couldn't coat component sides or underneath components on a PCB, but new applicators come with a tilt accessory to coat four sides of a part or other areas not accessible when using the standard vertical approach. The mechanism can be tilted 30° from vertical position to the left, right, front or back.
On boards with increased component density or surface mount components exposed to harsh environments, traditional coating technologies don't have the speed or precision required to apply coating materials. Using jetting technology expands the capability of conformal coating equipment for use with these applications. Used alone or in conjunction with conventional technology, jetting can provide higher levels of precision, repeatability, and speed, and improve quality and productivity
In jet technology, small droplets of fluids are ejected onto the PCB. Jet deposition offers the advantage of ultra-precise component coating. Individual shots of coating fluid can be used to coat even the smallest electrical components without contaminating neighboring components. Single shots are used for coating extremely small areas while multiple shots can be deposited side-by-side for larger coating areas. High frequency actuation, up to 200 shots per second, enable the coating process to keep pace in high-speed production environments.
Conformal coating and fluid dispensing equipment manufacturers are constantly developing innovative software, process control features, tools, and equipment in addition to new coating compounds — all in response to emerging applications and customer requirements. The adaptation of conformal coating and dispensing valves and applicators and the application of jetting technology are some of the technologies that have enabled manufacturability of advanced automotive electronics.
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