Gina

The most usual causes of blisters under conformal coating are:
1. some contaminating substance on the substrate which prevents adhesion (e.g. any type of
oily residue, esp. silicones)
2. uncleaned and incompatible flux residues
3. any form of hygroscopic contaminant which will absorb atmospheric moisture through the
coating, creating an osmotic pressure which will lift the coating from the substrate. This
is strictly called vesication and may take the form of myriad submicroscopic to large
blisters, depending on the size of the contaminated areas. (this is largely explained and
illustrated in my book)
4. not priming the surface if the coating type requires it.

Hope this helps

Brian

gina wrote:

> I mean conformal coating........
>
> Thanks
>
> *********** REPLY SEPARATOR ***********
>
> On 05/08/2000, at 3:44 PM, Brian Ellis wrote:
>
> >Gina
> >
> >What do you mean by blisters? Under laminate surface (multilayer???), solder mask or
> >conformal coating?
> >
> >Brian
> >
> >gina wrote:
> >
> >> Dear Technetters,
> >>
> >> I need help regarding items to be considered in order
> >> to reduce or eliminate blister occurence.
> >>
> >> Thank you very much and I look forward for your response.
> >>
> >> Regards,
> >>
> >> Gina
> >>
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