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Thickness measurement of protective coating on PCB

PCB boards can get influenced by environmental factors such as humidity, which is why it is important to protect the PCBs with a protective clear varnish. This coating is required to be at a specific thickness for some applications. This level of thickness needs to be maintained to perform a measurement without destroying the target. Confocal sensors from Micro-Epsilon can solve this problem without making contact with the target and therefore in a non-destructive manner. They can measure thickness in real-time.

The confocalDT IFS 2405 confocal chromatic displacement sensor is characterised by its small spot size and excellent precision for measuring thin layers. Due to these characteristics, the confocal sensor is used in the thickness measurement of varnish in PCBs. The measurement is performed immediately and quickly at a measuring rate of 1 kHz using the confocalDT IFC2461 confocal controller. Any variation in thickness due to the flow behavior during hardening, can be identified by scanning larger areas. The measurement results do not get affected by changing substrates, passivation layers and PCB surface. 

The measurement is carried out in defined zones, from which a generally valid reading on the thickness can be drawn. Within these zones, the measuring point can be freely selected. To carry out the thickness measurement, the refractive properties of the varnish are initially determined, which depend on the hardening and the solvent content. Accommodating confocal sensors in the production line can help save the cost of micrographs and save rejects, along with serving the requirements of the customer.