Hello Technetters
I am hoping that someone might be able to provide some insight into an issue
that I have recently been struggling with, namely really bad wrinkling of
SCC3 (Electrolube DCA), which only becomes apparent during the high
temperature 90°C cure.
I have searched the archives and found some reference to wrinkling, but this
previous case looks more to do with rippling and orange peel rather than
what I am seeing. I have attached an image to my google photos account,
which can be seen here: - https://photos.app.goo.gl/FQ3YLGCMVmEsmGNYA
We have been advised by Electrolube that this is the result of solvent
entrapment, but we have carried out a number of experiments which indicate
that this isn’t the case.
The process is
* We are applying a wet film thickness of 100um, which equates to
approximately 10um dry film.
* We leave 15-20 minutes drying time between each coat. 4 coats are
applied to achieve the required thickness.
* Assemblies are then left for approximately 18 hours (overnight)
prior to demasking.
* Then we apply extra coating around the areas that have been
demasked.
* We then wait an additional 18 hours (overnight) for the touch-up to
dry.
* Finally we put the assemblies in an oven at 90°C for 24 hours (in
accordance with Electrolube’s curing recommendations)
Engineering trials, using coupons and scrap PCB’s as the substrate, are
showing perfect results, but as soon as we coat production assemblies they
wrinkle. I immediately assumed that it was related to the production PCB’s
and issues with the solder resist, but we have also seen this wrinkling on
coupons that have been sprayed alongside the production PCBS.
I have also considered that it could be the coating itself, or even the
equipment, but when spraying the most recent production batch I also coated
a scrap PCB at the same time and this coated perfectly.
Has anyone ever seen this level / type of wrinkling before, particularly
with SCC3 (DCA) or even with any other coating? Any idea what could be
causing it?
Many Thanks
Mark
Mark Austin
Lead Engineer
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