Padstacks

[davepcb]

Tom,
I read somewhere that the reason the soldermask and pastmask was added to the padstacks of the pcbstandards libs as 1:1 was so that the fab houses can take care of ?oversizing?

Should I write them fabrication notes explaining this? Is there a standard spacing from pad or via to soldermask/pastemask?

Thanks,
davepcb

[randychase]

Hi Dave, Tom is out of town right now, not sure if he has computer access.

I have always created pastemasks as 1:1 no matter what. You don't want any overlap.

Soldermasks were historically bigger than the pad to account for tolerances. In the old days, we swelled up pads .010" on the side and it was good. As technology became tighter, that was too much and would allow solder bridging to adjacent pads or traces.

I think the amount of "swell" over the pads for the mask would depend on the board and the technology/spacing being used. So it would be hard to define a standard.

Should you make a note to have the fabricator adjust the pads on the mask artowork? That is a good question. Seems like a good idea. I have not done that.

[davepcb]

Thanks Randy,
I learn something new everyday at pcbstandards!

davepcb