Hi Steve,
I'll admit, it has been a long time since I have had to conformal coat, but
my ace in the hole for masking was always 3M#250, which is also one that is
used for adhesion tests (ASTM). At least it used to be....
The property that I always admired it for was the complete lack of transfer
of adhesive, even through my urethane, epoxy, and acrylic coating
processes, baked or not baked.
We monitored shelf life on the rolls to ensure that the bonding system
remained intact. I suspect that is what the issue is in your situation.
I used Caplugs and made custom boots (after all, we did potting in the same
lab) for the higher volume products. The issue with the plugs was
viscosity of the coating so be careful.
Phil
At 01:34 PM 2/5/2007 -0600, Steve Gregory wrote:
>Hi Kenny!
>
>We look at the labor cost of having to mask something vs. just putting
>on a cap before we decide to buy caps. In all cases we save masking
>labor.
>
>As far as ESD issues, there isn't any more risk with caps as there is
>with masking tape. We do all our masking and de-masking under an air
>ionizer.
>
>We reuse them until they get to the point that they can't protect what
>they are supposed to protect...usually it's because of some sort of
>damage.
>
>I've got a picture of one of our more challenging assemblies to coat
>that we use plugs on:
>
>http://stevezeva.homestead.com/files/Masked_Assembly.jpg
>
>As you can see it's a rigid-flex board and we have to mask the flex area
>beside the connectors. We use a masking paper over the flex area so that
>we lessen the chance of tearing it during de-masking. The plugs save a
>lot of masking time. I wish there was an off-the-shelf plug for the
>421-pin connector at the end of the flex, but there isn't. The really
>difficult thing about coating this assembly is getting coating in that
>PCB area beneath the round connectors. All those connectors stand-off
>the board quite a bit, and the area of the pins that are exposed beneath
>the connector shell has to be coated as well which makes things fun...
>
>BTW, I don't have the tape residue problem on this board...it's another
>assembly that I have that problem on. Weird huh?
>
>-Steve Gregory-
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Bloomquist, Ken
>Sent: Monday, February 05, 2007 11:49 AM
>To: [log in to unmask]
>Subject: Re: [TN] Humiseal Masking Tape Residues/latex peelable
>
>Graham/Steve,
>
>I've never used boots for conformal coat masking because I always
>thought it would be expensive. I have a couple questions regarding
>"Boots".
>
>Are you able to use them more than once?
>
>Are there any ESD issues?
>
>If you do use them more than once how do you know when to stop using
>them?
>
>Have you done any cost trade studies?
>
>Thanks,
>
>KennyB
>
>
>-----Original Message-----
>From: Graham Collins [mailto:[log in to unmask]]
>Sent: Monday, February 05, 2007 9:20 AM
>To: [log in to unmask]
>Subject: Re: [TN] Humiseal Masking Tape Residues/latex peelable
>
>Hi Guy
>There is (in addition to CAPLUGS that Steve referred to) Kinnarney
>Rubber Co. They make some standard and will also do custom stuff.
>http://www.kinnarney.com/
>
>regards,
>
>Graham Collins
>Process Engineer,
>L-3 Communications Electronic Systems Inc.
>Halifax
>(902) 873-2000 ext 6215
>
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