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December 1997

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Subject:
From:
annie laberge <[log in to unmask]>
Reply To:
TechNet Mail Forum.
Date:
Fri, 5 Dec 1997 15:20:22 -0500
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Hi every one,


We design and assemble PCBs and I have a question regarding soldermask
clearance, plug vias, etc,  for VIAS UNDER BGAs.

Actually, we have .015" vias with .030"pads and .012" vias with .028" pads
under .050"pitch BGA.  One of our design rule is "min .006" from pad to pad
(edge to edge)". We do not have any X-ray machine.

I was wondering if  there is exisiting standards in the industry for those
vias (in term of solder mask coverage)?

Does the solder mask need to cover the entire surface of the pad (on
componant side),  including that it might or probably will run down the hole ?
If yes do we need to put a clearance in the soldermask smaller than the
finish hole diameter or will the PCB Fab (all of them?) will automatically
do it  to prevent air entrapment ?

On solder side we presently plug the vias with SR 1000 (plug is .002"larger
tha pad size).

Any suggestions and/or comments are welcome.


Thanks in advance

ALaberge

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