Ben,  See my comments below.      Bill Dieffenbacher
> ----------
> From:         Davis Ben[SMTP:[log in to unmask]]
> Reply To:     DesignerCouncil Mail Forum.;[log in to unmask]
> Sent:         Thursday, January 08, 1998 2:13 PM
> To:   [log in to unmask]
> Subject:      [DC] Question on Plated holes
>
> Greetings fellow designers...
>
> A question has come up concerning the need for pads on both sides of
> the
> board for a plated via.  We have slipped and let a via get placed
> under
> a metalized part (big OOPS).  Now we are in the fix it phase and would
> rather not take the time or money to scrap and re-layout the board.
> What we would rather do is remove the pad on the top side of the
> board.
>
> I have always believed the need for pads on both sides of the board is
> mostly a fabrication issue to insure good/complete plating on the hole
> wall (at least on vias).
>
> My questions are:
>
> 1) What problems arise if the top pad is removed from the artwork?
You run the risk of etching out the hole during copper etching if the
resist does not cover the hole well.

> 2) What problems would there be if the pad was removed after
> fabrication?
> It may depend upon where your connection is to the pth.  If the
> connection is near the top of the pwb you may damage it internally
> when you slice off the pad.  You might also make the copper plating
> pull away from the drilled hole wall due to mechanical forces during
> pad removal causing some reliability concerns.
> 3) Any other suggestions.
For a quick fix you might apply a drop of epoxy to the hole to cover it
on existing pwbs.  The epoxy should provide some dielectric material and
separation between the pth and the component.  An adhesive label might
do the same however you may be compromising heatsinking of the part.
For a final fix if you cannot move the pth try applying some solder mask
over the hole.  (I'm assuming you have no lead in the hole and that it
is no larger than .020 inch dia.)


> Thanks in advance for your help and responses.
>
> Ben Davis
> [log in to unmask]
>
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