The surface energy of the laminate or solder resist can have a huge impact on the ability of the conformal coating to stick or adhere.
Major problems like delamination, de-wetting and coating peeling off a circuit board can be due to the surface energy of the board being too low compared to the circuit board surface.
To achieve the optimum adhesion, it is necessary to ensure that the the surface energy of the substrate is above that of the conformal coating material to be applied.
There are a few ways to determine surface energy and these include the use of Surface Energy Test Pens (Dyne level testing). This is a simple test and easy to do with the right set of Dyne Pens (which are also referred to as Corona Pens).
SCH use these pens in their coating services to check the incoming cleanliness quality of printed circuit boards where a problem is suspected. We also offer them for sale to customers to help them monitor their board cleanliness and surface energy in their conformal coating process.
The Dyne Pen is used like a marker pen to draw a line of ink on the surface to be tested.
When the Dyne pen is applied to the surface of the printed circuit board, the conformal coating will either form a continuous film on the laminate or de-wet (pull back) into small droplets of coating.
If the Dyne fluid remains for three seconds or more then the surface energy of the laminate will be at least as high as the Dyne Pen ink value. This is a good result.
If the liquid de-wets, shrinks or forms droplets in less than a second then the surface energy of the circuit board laminate is lower than the Dyne Pen ink value. This is a bad result.
The exact surface energy of the laminate of the circuit board can be determined by applying a range of increasing or decreasing values of Dyne test pens.
Once the exact energy is determined then the datasheet for the conformal coating can be checked to see if the energy level is high enough to provide good adhesion of the coating to the board.
Conformal Coating dewetted on surface of Printed Circuit Boards
The surface energy of the circuit board can really affect the quality of the conformal coating finish
Defects like delamination, de-wetting and conformal coating peeling off easily in sheets can be realted to poor surface energy
You can measure the surface energy of the board using Dyne Pens