October, 2022


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Page 59


Implementing Quality Control in the Conformal Coating Process


By Wilson Chen, Insituware T


he entire conformal coating process has several key steps that should be regu-


larly inspected and controlled to


orifice is observed, the time is stopped. The measured flow time can


then be used in a lookup table to determine the coating viscosity. There are various types of flow cups (ISO 2432, DIN 53211, Ford, Zahn, etc.) that can be used depending on the specific appli- cation.


1 A viscometer can also be 3/9/22 12:13 PM


used to provide a greater degree of precision and reproducibility if required. Various types of vis- cometers are available, but the most common for measuring the viscosity of coatings are rotation- al viscometers. Rotational vis- cometers use either a rotating spindle or a cup-and-bob system


with a rotating bob. The viscome- ter measures the amount of torque required to rotate a spin- dle or bob at a specific rate that is proportional to the viscosity of the coating.


Thinning Conformal Coating The thinning process of con- Continued on next page


Vision MARK-1 with E-Chem insight and probe.


ensure continued reliability in its application and environmen- tal protection. These include: incoming inspection; thinning conformal coating; conformal coating thickness; and coating adhesion.


Implementing process con-


trol into all these steps is critical to producing consistent and reli- able coated PCBs. To aid in process control in some of these key steps, Insituware has devel- oped the Vision MARK-1 and the CC-100 conformal coating thick- ness tester.


Incoming Inspection It is advised upon purchas-


ing conformal coating that an incoming inspection test be con- ducted to ensure that the coating from the manufacturer is consis- tent and reproducible. Some con- formal coating manufacturers have been known to make small adjustments in the formulation without notifying their users. In solvent-based coating


systems, an easy and low-cost test involves measuring the vis- cosity. Two ways that coating viscosity can be measured are by using flow-cups or a viscometer. A flow-cup measures the


flow time (or efflux time), which is the time required to empty a vessel of known dimensions. The cup is submerged into the coat- ing and as soon as the cup breaks the surface of the coating, the time starts. When the first inter- ruption in flow out of the bottom


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