Mail Archives: geda-user/2015/09/11/21:32:04
> Usually solder mask is a little bit larger to not cover any of the
> pad. I guess you will be able to solder the part even if "visible" pad
> is a little bit smaller because of tolerance problem with solder mask.
>
Yes, I agree with you.
Presumably, you've designed your pads to meet some guidelines (maybe
manufacturers recommendation). That gets you a nice heel and toe solder,
and maybe some solder on the sides of the pad. As you say, you don't
want to cover the pad with soldermask, and I'd say because you don't
want to shrink the exposed pad geometry and compromise your solder
joint. In a perfect world, 0.0 gap from pad to mask is okay. But,
because the board manufacturer cannot guarantee this precision, they
like to add a gap such that under worst case the mask doesn't cover the
pad.
A good fab house will adjust a lot of things on your design in order to
maintain it's internal design rules. I suppose not all places would do
this. I also suspect some folks want ultimate control of the board so
that what they get exactly matches the gerber. In those cases, maybe the
fab process is iterative, so the fab house suggests changes in the
layout until it meets their design rules.
As I said before, the place that my company uses will increase or
decrease mask clearance in order to make their design rules work. That's
why setting 0.0 mask clearance is okay - in this case. Like you,
however, I prefer to set the clearance to around 10 mil in my designs.
If your design house has no checks, and no feedback to you, then maybe
they do something to your design, maybe they don't. It would be nice to
know for sure.
gene
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