gEDA-user: Question about footprints in pcb

[Rob Butts]

   I'm a little unclear about the mask dotted line of the pad command.
   In the How to Create Footprints document it says this value is the
   width of the solder mask relief.  Is this value the distance from the
   pad location line to the center  of the clearance measurement?  If I
   double the mask how does it affect the diagram in the document?  I'm
   also wondering why the distance from the pad to other conductors on
   any plane (the clearance) is the clearance value divided by two and
   not just the clearance value.
   Finally, if I'm laying out these boards to be made at home what are
   good values for clearance and mask?
   Thanks


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Re: gEDA-user: Question about footprints in pcb

[DJ Delorie]

 I'm a little unclear about the mask dotted line of the pad command.

The solder mask size is specified as its own width, just like the
copper pad's size is its own width.

 I'm also wondering why the distance from the pad to other conductors
 on any plane (the clearance) is the clearance value divided by two
 and not just the clearance value.

The copper clearance is specified as the amount to add to the pad
size.  So it's a total for both sides

 Finally, if I'm laying out these boards to be made at home what are good
 values for clearance and mask?

Depends on your process.  For toner transfer, 10 mil line/space rules
are normal if you're experienced (up to 20/20 for TT newbies), that
means clearance will always be 20 mil or more (10 on each side).  Most
home-fabs don't do masks, but I set mine to result in a 3 mil gap
between copper and mask, since that's what most commercial fabs want.
The MinMaskGap() action can fix up any stragglers for you.


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