|Ask the Experts|
February 11, 2021
Coating Scored Panels Prior to Separation
We have received our first order for conformal coated assemblies. We will be applying an acrylic by hand from aerosol cans.
Are there any considerations to be made for coating scored panels prior to board separation?
|Expert Panel Responses|
Well, the answer to this, like any good engineering answer, is "It Depends".
Principal Materials and Process Engineer
This depends on the thickness and uniformity of the panels...
To properly conformal coat this assembly, we would recommend a selective coating system. This reduces variation, minimizes environmental impact and EHS training, and improves application method and yield.
If you are manually coating these assemblies, you will want to avoid the score line, and any chassis grounds etc. The coating in the score line, when separated will be prone to peel, pending the thickness of the acrylic.
Also, care should be taken to review all the components, for compatibility of being 'sealed'. Electrolytic Capacitors, for example, are vented and sealing the vent will cause them to prematurely fail over time.
Conformal coating will "wet" to specific thickness based on formulation, and controlling the coating application can be difficult with aerosol cans. If you do spray them,it would be best to separate them first. If that is not an option, you might consider masking the scorelines with a peelable masking.
As another option,you could use a scoring machine for routing/scoring after coating. This will require a cleaning to remove dust and foreign material, and is generally done with high volume assembly.
Capital Equipment Operations Manager
Specialty Coating Systems
The only important issue to consider is the areas which are to be coated and the areas that are to be protected. As for spraying over the V-grove, my only concern would be when the boards are separated that the conformal coating does not crack and break off edges.
Please review IPC-610 section 10.8.2 Conforma Coating - Coverage and review the Acceptable Class 1, 2, 3, conditions and I would suggest checking for any cracks or flaking of the coating along the edges of the boards where they were separated from each other.
Vice President, Technical Director
This is quite commonplace practice.Providing that the coating has good adhesion to the PCB surface it will not delaminate duringde-panelisation.
Adhesion can be influenced by the type of coating, residues left on the board surface and type or solder resist. A surface energy test made on the board surface is the simplest method to gauge how well a coating will wet and adhere to a surface. This can be carried outwith a set dyne pens. 38 dynes or greater is recommend for coating.
Just a note on hand spraying, at least 3 coats should be applied sprayed in different direction across the board to attain the required thickness for full protection.
If you have a scored panel and the coating gets into the V-score, my first question would be how effective is the depanel process and can it be done as initially designed as you are adding material there.
If the V-score designed is correct it will match your equipment (type of blade, angle,etc). The material in the V-score can create a condition where the panel pulls apart and you may experience pulled fibers from the internal layers.
On the other hand like another expert mentioned - are there customer requirements for the depaneled sides to be coated?
Extra inspection will be necessary to ensure that the coating material does not peel off the board.
Engineering and Operations Management
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