Bob,
It is possible for normal vias to be filled. We have had FR4 boards from a
well known pcb manufacturer with 0.4 to 0.3 mm diam drilled vias which have
been epoxy filled and then surface metallised (sorry do not know what process
was used) with Cu track and Ni/Au finish.  The holes were filled to slightly
sub-surface. No evidence, after a couple of years in the field, of reduced
reliability due to the construction of the bare pcb.

Best of luck
Barry Bates
BAE SYSTEMS


-----Original Message-----
From:   Brian Ellis [SMTP:[log in to unmask]]
Sent:   26 September 2000 07:37
To:     [log in to unmask]
Subject:        Re: [TN] Via in SMT

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This is a valid technique with microvias, which are necessarily blind and of
small
diameter. They are left open and cause no subsequent soldering problems
because the
volume of solder 'robbed' in filling the hole is so small that there remains
largely
sufficient for the real solder joint. Frankly, I know of no reliable way of
doing this
with drilled through-vias. FWIW

Brian

Bob Dube wrote:

> We are a PWB fab house.
>
> We' ve recently come across a requirement to fab boards with vias located in
> SMT pads. The requirement is to have these vias completely shut and as close
> as possible to flush with the pad surface. Initial thought was given to
> copper plating completely shut but have CTE concerns. Thought is also being
> given to epoxy fills and then metallization.
>
> Does anyone have any thoughts on the best way to achieve this condition? Are
> there any reliability pitfalls?
>
> Thanks in Advance,
>
> Bob Dube
> ES&D
>

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