Loan,

What we do is design with 2mil per side opening with a solder mask note:
     No finished solder mask over pad edge.  Annular ring of exposed board material around pad edge to
be .001 min, .003 max.
     Maintain  a solder mask bridge of .004 min. wide between fine pitch solder pads.

Also the pad can not be wider then .012 with this approach.  Do not allow for ganged soldermask
relief.  We had all
rework problems with that approach.
Have not had problems since this note.

Greg Scott
Cray Inc.
Seattle, WA.

"Tempea, Ioan" wrote:

> Hi technos,
>
> what would be a reasonable requirement for the registration of the solder
> mask on boards with 20 mils fine pitch having solder mask dams. We asked for
> 0.002" and it almost comes over the edges of the pads.
>
> Is 0.001" doable, with no impact on the price?
>
> Thanks,
> Ioan
>
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