How Are Conformal Coating Thicknesses Controlled in Circuits Assembly?

Conformal Coating Thicknesses Controlled in Circuits Assembly

Conformal coating is a thin protective layer of polymer applied to the surface of printed circuit boards (PCBs). This layer prevents moisture, extreme temperatures, chemical contamination and salt sprays from damaging or shorting out the electrical components and circuitry. The choice of coating material is critical for the long-term reliability and durability of the electronics. It also has specific effects on repairability, toughness and dielectric strength. The conformal coating must be applied properly to ensure quality. This requires careful coordination between the PCB design and coating materials, and adherence to cleaning protocol.

The best conformal coatings for a particular application are determined by the operating environment and the sensitivity of the equipment. IPC class 3 products that perform mission critical services are more likely to be conformally coated because they must withstand high levels of moisture, temperature and corrosive chemicals.

Coating materials are typically selected according to their electrical and thermal properties, processing and application methods and life expectancy. They also have different effects on circuits assembly repairability, toughness, dielectric strength and insulation resistance. In addition, the material’s thickness needs to be balanced against other key factors such as cost and processing time.

A conformal coating is usually applied in one of several ways; brushing, spraying, dispensing or dip coating. The process should be performed in a clean and controlled environment to minimize contaminants that could contaminate the circuit board’s copper surface or cause pinholes in the film.

How Are Conformal Coating Thicknesses Controlled in Circuits Assembly?

In order to avoid these problems, the surface of the circuit board should be thoroughly cleaned using a highly repeatable industrial process such as vapor degreasing or semi-aqueous washing. These procedures can also improve the adhesion of the conformal coating to the substrate, ensuring that it is not lifted during processing and that the coating is well-formed around the component leads.

When a conformal coating is applied, it must be applied to the exact thickness required for the operation of the circuit board. Thick coatings can increase the risk of mechanical stress, heat entrapment or wrinkling. Thin coatings can be less expensive but they may not provide sufficient protection from moisture or other harsh environmental conditions.

Conformal coating thickness is typically measured using a non-destructive, wet film gauge. This technique is used to measure the thickness of a conformal coating while it is still wet, and is particularly effective for applications where thicker coatings cannot be removed and dried. It is also much faster and more accurate than dry film measurements, and can be used to ensure that the conformal coating is not over-applied.

SCH’s Positest Conformal Coating Thickness Measurement system provides an instant, repeatable and highly reliable measurement of the thickness of a conformal coating. The test probe is placed directly against the surface of the coating, and a reading is displayed within seconds. The measurements are then stored as a record for future reference. By applying the coating to a test coupon at the same time as the circuit board, it is easy to establish an accurate comparison between the results of the two tests.

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