Optical inspection for conformal coating: Page 6 of 6

September 03, 2018 //By Francesco Argentiero
Optical inspection for conformal coating
One of the main challenges in the production of printed circuit boards (PCB) in the electronic industry is the protection against harsh environments with high humidity, strong temperature changes and dust or chemical contamination. Since the ‘60s, the conformal coating process has been proposed as a solution for these problems.

Below are given two concrete examples of conformal coating inspection, obtained with white light LED illumination and with UV LED illumination using the Dragonfly Next> series system.

Figures 8a and 8b show a PCB featuring through-hole and SMD components. In the area which contains the SMD components, a lacquer for conformal coating has been applied. The protective coating film contains an ultraviolet tracer, clearly visible in figure 8b (right), with light-blue fluorescent illumination.

The printed circuit board has been illuminated with ultraviolet and red LEDs, the first ones activate the ultraviolet responsive tracer contained in the lacquer for conformal coating, while the second ones outline the structures of the printed circuit, to facilitate the orientation of the user on the image. The intensity variances seen in the image correlate directly with the coating film thickness variances on the printed circuit. Furthermore, some areas which are not perfectly covered can be seen, as well as some “splashes” outside of the given areas, and some sprays in areas which should not be coated.

Therefore, we can state that the CCI (Conformal coating Inspection), taking advantage of a model to analyze the fluorescence intensity of ultraviolet light projected on the PCBs, and an appropriate calibration, appears to be an effective, reliable and fast method to measure the quality and consistency of the conformal coating lacquer.


About the author:

Francesco Argentiero works at Automatic Test Equipment (ATE) manufacturer SEICA Spa - www.seica.com

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