Jerry,

I am about to order our first PCB's with thermal via holes filled with
Silver epoxy. This process is carried out while the PCB is being
manufactured and prior to the plating process. We haven't done this in
practice before, so we're unsure what the actual results will be, but it
seems to be a mature process (i.e. not an experimental one) and the vias
can be plated over to form a pad if required.

You can then specify solder mask for both sides as normal.

Solder mask on one side and not on the other - are you wave soldering to
fill the vias? If you have solder mask on the side facing the wave, and you
get the wave height wrong (too high), you'll run the risk of making a bit
of a mess of the top side of your board. I'm no scientist in these matters,
so I can't tell you specifically how much extra stress is placed on the
through-plating by solder-filling the vias, but there are gurus on this net
who will be able to say.

Pete Duncan
Asst Principal Engineer
ST Aerospace





                    Jerry Mosur
                    <jmosur@SPELL        To:     [log in to unmask]
                    MANHV.COM>           cc:
                    Sent by:             Subject:     [TN] Masking Vias
                    TechNet
                    <[log in to unmask]
                    ORG>


                    04/10/01
                    10:03 PM
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                    Jerry Mosur






Hello,

Have anyone specified via solder mask on top and not on bottom? I am trying
to fill-in vias as much as I can. What pitfalls in term of assembly,
reliability, etc.. I can expect?

Thanks,

Jerry

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