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Subject:
From:
Alan Brewin <[log in to unmask]>
Reply To:
Alan Brewin <[log in to unmask]>
Date:
Fri, 26 May 2000 11:41:51 +0100
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text/plain (117 lines)
Jerry,

It just doesn't make sense (to me anyway) to go to the effort of plasma
etching to get adhesion, and they to use a silicone material. Silicones
generally do not have good adhesion. I feel sure that if you use an acrylic
or urethane material (providing your board is pretty clean) you won't have
to plasma etch.

Your comment about rework surprises me, I may be missing something? It has
always been my experience that acrylics are a lot easier to re-work than
silicones/RTV's. Do you want to chemically remove/rework or are you
soldering straight through the product?

I also agree with Brian about the danger of relying upon reported dielectric
properties of a material measured at STP rather than at higher humidity if
these
conditions will exist in your end application.

Alan Brewin

Concoat Ltd.


-----Original Message-----
From: Brian Ellis <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: 26 May 2000 08:03
Subject: 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
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