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Technical Article

PCB Fabrication: How Conformal Coating Protects PCBs

Time:2017-05-16 15:41:08 Click:

Salt sprays, moisture, fungi, corrosion and other forms of contamination caused by wet or harsh environments can damage printed circuit boards (PCBs). To prevent damage and avert costs incurred by replacement or repair, non-conductive conformal coating is applied to PCBs during the assembly process. 

Conformal coating is commonly applied on PCBs used in consumer electronics, appliances and mobile phone products that may be exposed to wet, humid, dusty or other harsh environments. 

How does conformal coating protect PCBs? 
The conformal coating process inserts a layer of protection between the PCB board-level parts and the outside environment. This layer of protection functions like a one way street: it permits moisture contained beneath the layer to be travel across the conformal coating layer, but does not allow contaminants in the ambient environment to transit across the conformal coating to the board-level parts. 

Does conformal coating have any other benefits? 
Yes. Since conformal coating is made from lightweight material, it allows the PCB to maintain a small footprint. In addition, conformal coating provides a support bridge between the conductors thereby increasing overall strength. Conformal coating not only protects a PCB to ensure reliability, its layer of protection expands the working life of the board which will keep your costs low. 

Are there different kinds of conformal coating? 
Yes. The most common types of conformal coating are silicone, acrylic, urethane and Paraxlylene. The choice of a specific type depends on the level of protection needed. The final choice is based on the chemical and physical properties of the coating material. 

How is conformal coating applied to PCBs? 
There are four primary processes by which conformal coating is applied to PCBs: dipping, selective robot coating, spraying and brushing. Each of these alternatives achieve the same goal: to completely cover the PCB including sharp edges and all board contours. 

After the conformal coating is applied to a PCB, the coating must be cured. The curing process can be accomplished via air drying, thermally via an oven, or by UV light. 
In summary, there are six necessary steps to apply conformal coating. They are:
▪ Clean the PCB board.
▪ Remove all terminal pins and connectors.
▪ Select a type of conformal coating and apply it to the board.
▪ Select a curing type and cure the board.
▪ Put re-install parts back onto the board.
▪ Test the board to ensure it functions normally.

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