In a message dated 5/25/99 10:09:53 AM Pacific Daylight Time,
[log in to unmask] writes:

<< Have you tried removing the pad from the solder side of the panel, or
 making the pad less than 360 degrees? These usually prevent hole filling.
  >>

Yep...Aric is right. There is way to design plated tooling holes that are use
for chassis grounding so that they won't fill during wave and you won't have
to mask them. I've heard them called "UFO" holes...where that name came from
I don't know. They were used on products that I used to build for a major
networking company out here in Santa Clara.

That used to be a big bottle neck in our plant before they went to the hole
design. We had a closed-loop water treatment system and it would take longer
to wait for the mask to cure than it did to build the boards.

What it is that there's a anular pad on the topside, and then via's are
drilled in the circumference of the pad and plated through. The inner barrel
of the tooling hole is not plated. So what you wind-up with is a pad on the
topside where the screw used to secure the board in whatever chassis it's
going into can still make contact and ground the board, the via's will
connect to whatever layer it needs to connect to within the PCB...and since
there's no pad on the bottom, and the barrel isn't plated....VIOLA'! No
masking and no filled tooling hole!

-Steve Gregory-

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