Argggh Steve, we know ye to be a pirate anyways......

I had the same question come to mind as Lloyd asked.  Pinholes or
dewetting?  Pinholes can be due to moisture coming out of the board, but is
most often point sources of contamination, like droplets of oil or some
other adulterating contaminant in the coating.  A picture would help.


Doug Pauls
Principal Materials and Process Engineer
Rockwell Collins

On Tue, Feb 28, 2017 at 2:20 PM, Steve Gregory <[log in to unmask]> wrote:

> Hi all,
>
> I'm not trying to hijack this thread, but since we're talking conformal
> coating here, what could cause an acrylic to appear that there are tiny
> little fisheyes in the coating, but when you hold the board at an angle,
> you can clearly see that the area is coated. I know pictures would help,
> I'll see if I can get some....
>
> Steve
>
> On Tue, Feb 28, 2017 at 12:59 PM, lduso - Diamond-MT.com <
> [log in to unmask]> wrote:
>
> > We do not pre-bake as an internal rule and never a complaint. Obvious
> > exceptions: We are washing or cleanliness testing the boards. Then we
> will
> > bake them dry before masking and coating. Or the customer specifically
> > requires a pre-bake on the drawing. (I always then ask the question; "How
> > long after the bake do I have to coat them before they need to be baked
> > again?" Strangely, only a few have an answer for that.)
> >
> > I have visited many facilities that conformal coat and I have witnessed
> it
> > both ways but mostly on the "no pre-bake" side. One customer even
> pre-baked
> > their boards before coating with a water based acrylic.
> >
> > Lloyd Duso
> > Plant Manager
> > Diamond-MT
> > (814) 535-3505
> > www.Diamond-mt.com
> >
> > On Tue, Feb 28, 2017 at 2:39 PM, Douglas Pauls <
> > [log in to unmask]> wrote:
> >
> > > Lee,
> > > It Depends.
> > >
> > > We have one facility that has never baked prior to coating application.
> > No
> > > evidence of any conformal coating related problems.  We have several
> > > facilities that bake religiously prior to coating application, also for
> > > acrylic.  No evidence of any conformal coating related problems.
> > >
> > > I think the biggest factor is how much residual water you have.  I
> don't
> > > think your assemblies have to be bone dry before coating.  We do a lot
> > with
> > > in-line aqueous cleaners, which have heated air knifes that remove the
> > bulk
> > > of the water.  Now, there might still be some entrapment areas, but if
> > so,
> > > we find them and then blow out those entrapment areas with ionized air.
> > >
> > >
> > > Doug Pauls
> > > Principal Materials and Process Engineer
> > > Rockwell Collins
> > >
> > > On Tue, Feb 28, 2017 at 10:20 AM, Lee Hitchens <
> > > [log in to unmask]
> > > > wrote:
> > >
> > > > Hi all
> > > >
> > > > I've recently been asked about baking pcbs before conformal coating
> and
> > > > whether there is any quantified data on the effect on coating
> > > performance.
> > > >
> > > > Does anyone know of any public studies on this or can shed some light
> > on
> > > > its effectiveness beyond anecdotal experience ? I would be very
> > grateful
> > > to
> > > > you on this.
> > > >
> > > > Best Regards
> > > >
> > > > Dr Lee Hitchens
> > > >
> > > > SCH Technologies is a Division of SCH Services Limited
> > > >
> > > > www.conformalcoating.co.uk
> > > > Skype: leehitchens
> > > >
> > >
> >
>
> --
>
>
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