Conformal coating Inspection

The uncured conformal coatings are clear, transparent liquids with viscosities of 700 to 1400 cp at 25°C. A typical composition which has a viscosity of 820 cp at 25°C consists of 43 wt % of a high viscosity urethane acrylate oligomer, 49 wt % of a low viscosity monoacrylate diluent, 5 wt % of a polyfunctional thiol, 2 wt % of benzopinacol and 1 wt % of alpha, alpha-dimethoxy-alpha-phenylacetophenone. A trace amount of a fluorescent dye may be added, if desired, to facilitate inspection of the finished coating. 

The final step in the soldering process is the removal of flux residues from the completed circuit board. No-clean fluxes, as the name implies, produce residues that need not be removed from the assembly after soldering. The corrosive activators are locked up in a hard, polymerized residue. However, no-clean flux residues can potentially interfere with in-drcuit testing (probes) and inspection, degrade cosmetic appearance, inhibit rework activities, and lessen the adhesion of conformal coatings. In the event that any one of these factors becomes critical, it is best to switch to a cleanable flux than to develop a cleaning process for a no-clean flux. 

Paint components, or raw materials, must be carefully eontrolled to produce coatings of consistent quality. A close inspection of incoming raw materials for conformance to preset quality standards is an important aspect of quality control. 

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