Yeah, that is certainly one big ugly can of worms. As I say, "adhesion is
in the eye of the beholder". The beholder being the customer. We apply the
conformal coating as a service and we rarely are requested to conduct any
sort of adhesion testing. If we do, it is almost always on the parylene
side and using the ASTM D3359 method B with a grade of 3 or better. (I have
one now for a space application.) Once or twice for liquids but usually the
same test. The question is always the same: If the coating adheres great to
the solder joints but not to the solder mask (which is usually the test
coupon) is that bad? Aren't the metallics what you are trying to protect
the most?

Lloyd Duso
General Manager
Diamond-MT
(814) 535-3505
www.Diamond-mt.com


On Fri, Jun 26, 2020 at 8:29 AM GRIVON Arnaud <[log in to unmask]>
wrote:

> Hi TechNet,
>
> I know that, contrarily to PCB solder mask adhesion tests, adhesion tests
> for conformal coatings are not standardized or covered by shared/uniform
> practices.
>
> Without willing to open a new can of worms, I would be interested by the
> detailed adhesion test protocol/methodologies from those who are
> successfully performing this kind of test in qualification and/or
> production.
> For both acrylics and silicone conformal coatings, say 1B73 for acrylics
> and 1-2577 or RTV-3140 for silicones if coating references can help driving
> responses.
>
> Questions in particular :
>
> -          What reference standards are used for the adhesion test
> methodology (e.g. IPC-TM-650 - method 2.4.28 for the tape test) ?
>
> -          What types and references of tapes ? This may differ between
> the two considered kinds of coatings.
>
> -          For adhesion tests with cross-hatching : tools and blade
> spacings (1mm vs. 2mm) specified
>
> -          Acceptance criteria with the related reference standard (e.g. :
> grade xx as per EN ISO 2409 or ASTM D3359)
>
> Thanks in advance for your inputs.
>
> Have a nice week-end.
>
> Arnaud Grivon
>