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Subject:
From:
Brent Alcorn <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 26 May 2000 11:38:58 GMT
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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
> Protonique SA
> PO Box 78
> CH-1032 Romanel-sur-Lausanne, Switzerland
> Voice: +41 21-648 23 34 Fax: +41 21-648 24 11
> E-mail: [log in to unmask]
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