Steve,

Currently I bring the mask up on the via pad, enlarged by
.006 over finished hole size.

Via open from both sides.

I have used this method since 1996 on .050, 1mm, .8mm
BGAs  up to 1200 pins with success. Up to 5000 boards
a year.



Hope this helps,
dave







Steve Gregory wrote:

>Mornin' All!
>
>I have a question about solder masking via's in a BGA pattern, and want to
>see if I'm thinking correctly about this.
>
>I think it's a bad idea to leave the via's free from solder mask on the
>topside of the board beneath the BGA, and tent the bottomside via's. To me, you're
>just asking for trouble down the road because you'll trap flux residue and all
>kinds of stuff in the via's that won't be able to be cleaned out well. This
>is a 676 ball 1.0mm pitch BGA pattern. Am I wrong about this?
>
>Thanks!
>
>-Steve Gregory-
>
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--
Dave Seymour, CID+
Catapult Communications Inc.
800 Perimeter Park Dr, Suite A
Morrisville, NC 27560

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