Hi Folks,
I am interested in this exchange and I would like to drop my two
cents. I am not an expert on this but I am under the following
impressions:
- Not ALL RTVs are equal,
- ALL conformal Coatings absorb moisture at some rate,
- There are PROs and CONs for all conformal coatings (ie. Rework, TC,
resistance to Solvents - acrlyics poor, RTV good), therefore each
application is different.
I am interested to know what the moisture absorption rate for Acrylic
is?
Regards,
Brent
>>>>>>>>>>>>>>>>>> Original Message <<<<<<<<<<<<<<<<<<
On 5/26/2000, 3:58:26 AM, Brian Ellis <[log in to unmask]> wrote
regarding Re: [TN] Solder Mask:
> I'm sorry, Jerry, any coating that easily permits the passage of
> moisture cannot have, by definition, good dielectric properties. The
> dielectric constant will increase dramatically, as will the loss
factor,
> if there is moisture absorbed into the coating. Many RTVs even depend
on
> their moisture absorption to polymerise! If you want the best
dielectric
> qualities, some of the acrylics are unbeatable.
> Brian
> Jerry Mosur wrote:
> >
> > Actually we use RTV for its good dielectric properties, and not for
its
> > moisture blocking capabiliteis.
> > The root of this problem lies in insuficient space for a given
electrical
> > characteristics of a circuit. If one can not open up spacing, one must
> > resort to other techniques like routing the board in-between pads and
> > encapsulating.
> > As far as the conventional coatings go, we have found that in order to
> > prevent delamination we have to plasma etch boards as well. With
rework
> > being easier with RTVs, we decided to use them instead.
> >
> > Graham, I will e-mail you for more info on solventless or water based
> > coatins. How easy is the rework?
> >
> > Jerry Mosur
> >
> > Spellman High Voltage
> >
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> Brian Ellis
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