Yes, absolutely.
Speaking from many years of experience dealing with many types of adhesives, it is very common for filler materials to separate around the edges of an epoxy or adhesive, including certain types of conformal coating. The clear coating is completely visible around the edges under normal light and even with the unaided vision it is easily visible, but when the normal lighting is reduced and replaced with UV lighting the clear portions around the edges or in the thinner areas of the coating where the filler separated turn invisible, thus making it appear as a skip.
Coating skips seen under UV need to be validated by supplementing with visual inspection under normal light. 99% of the time, the "skips" are simply areas where the filler is not present in the material. The filler is what shows up under UV, not the actual resin.
One good example of this is Armstrong C7 with Hardener "W" with Cabosil filler added. The Cabosil filler is nothing more than silica (ground up glass). The silica likes to agglomerate inside of the clear Armstrong C7 resin, leaving unfilled areas around the edges of the staking. The clear C7 resin and hardener cannot be seen under the UV lighting because of the separation or lack of the ground silica. The ground silica is glass, and the refraction of the UV light is what causes it to be visible. The clear portions of the epoxy where the separation of silica took place is easily visible under normal lighting, but cannot be seen under UV.
Another example of this phenomenon can be seen in Plating applications. If there are fingerprints on the basis or primary metal prior to plating, and the fingerprints get plated-over, the ridges of the fingerprints break up and refract under UV lighting, and it appears as if there is a fingerprint on the SURFACE of the plating, not underneath. No amount of scrubbing with any solvent can remove the plated-over fingerprint, and under normal lighting it is totally invisible, but turn on the UV and presto!, there is that pesky fingerprint again.
Thus speaketh Odin.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
Sent: Thursday, September 22, 2016 8:56 AM
To: [log in to unmask]
Subject: [TN] Fwd: coating complaint
I am in over my head. I have little to no experience with conformal coating. Can anyone with more experience comment?
thanks,
Guy
---------- Forwarded message ----------
From: Guy Ramsey <[log in to unmask]>
Date: Thu, Sep 22, 2016 at 9:51 AM
Subject: Fwd: coating complaint
To: [log in to unmask]
I sent this message on to a friend who posts images for review by members of the IPC technet.
We are looking for technical support and user experiences with this material.
If we inspect at 5x-10x magnification we can observe the conditions that our customer is complaining about.
But, our application process seems well controlled and the condition does not exist when the material is first dispensed. The material flows as it cures and becomes thin at the edges of the components. Thin enough so that is does not glow under UV light. In some instances components appear to have no coating (when viewed under UV). However under normal light it is easy to see the parts are coated.
Is this normal behavior for the material? Can we expect normal performance from the the coating?
Guy Ramsey
---------- Forwarded message ----------
From: Guy Ramsey <[log in to unmask]>
Date: Thu, Sep 22, 2016 at 9:41 AM
Subject: coating complaint
To: Steve Gregory <[log in to unmask]>
Hi Steve,
Can you post these images on your homestead page for the group please?
The images are of acrylic coating Humiseal 1B31. We are applying a thinned mix using a dispenser through a fine needle (25AWG).
Under room lighting we can see coating. Under UV light, at this magnification our customer is complaining about skips. I don't have enough experience with the material to know if this is normal or not.
Notice how the resistor appears to have no coating under UV, but in normal light it is clearly coated.
Also notice how the coating flows off of the components at the edges, leaving only a thin coating that may not glow under UV light.
Are these normal attributes of this type coating.
We do not see this with Urethane spray coatings.
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