Re: gEDA-user: new footprint guidelines

[DJ Delorie <dj@xxxxxxxxxxx>]

> >Mask should be 3 mil away from copper, and slivers should be at least
> >6 mil wide.  That means, if there's less than 12 mil between pads you
> >go with a gang-opening.
> 
> Where did you get these numbers?  Did a manufacturer give this as 
> their capability limit?

Yes.  I've found this to be the "usual" rules for prototype services.
I suspect you can pay more for better accuracy :-)

> >Silk should not overlap the *mask opening* and should be 3 mil away at
> >least.  5 mil min silk lines.
> 
> Same here, who's rules are these?

Many fabs automatically delete silk that overlaps mask holes.  The 3
mil rule comes from the mask rules.  Fabs I've talked to say the
mask placement is +- 3 mil.

> >Origin and license should be stored in element attributes, not file
> >comments, so they're copied into schematics.
> 
> IPC has developed a set of rules for designing footprints to match 
> parts of all sorts and has even provided a library of data for 
> this.  They provide three standard sets, Most, Nominal, Least which 
> differ in the amount of land protrusion.  Armin's footprint is likely 
> a "Most" catagory footprint from his description.  IPC-7351 seems to 
> be very widely adopted and would be a great starting point for any 
> footprint library.

We have IPC footprints in the ~geda library.  Not all, but some.

> I don't bother with putting the refdes in any particular location for 
> a library part.  The times a default location would work out is so 
> seldom, that it just isn't worth the effort. I put the refdes in the 
> middle of the library part and move it to suit the design.

Agreed.  I think middle of the part, despite being bad for the *final*
board, is the best starting point.

*Size* of the refdes should be considered when making a footprint
 though.
 


_______________________________________________
geda-user mailing list
geda-user@xxxxxxxxxxxxxx
http://www.seul.org/cgi-bin/mailman/listinfo/geda-user