Thieving patterns

[Alex Tom]

I'm new to PCB stuff so don't kill me right away.
I've picked up a project someone was working on
and I was curious as the thieving was stated they
would prefer not to use cross hatching but then
they went on and did it!? If they didn't want
cross hatching is there a good reason why. If
cross hatching isn't an option then what kind
of thieving patterns are typically used?

[Tom]

Alex,

Here are the standard Thieving Fab notes:

Thieving:
A) Supplier may add thieving to compensate for high copper density areas on this design.
B) The following guidelines must be adhered to in order to maintain electrical and mechanical integrity of the design:
1. Thieving to card edge spacing 2.5 minimum.
2. Thieving to Fiducial spacing 5 minimum.
3. Thieving to non-plated through holes 5 minimum.
4. Thieving to all other features 0.25 minimum.
5. There shall be no exposed thieving in any areas free of solder mask or internal copper plane.

The normal Thieving pattern is 1mm squares that do not touch each other. Crosshatching (waffle pattern) is a manufacturing hassle. It creates potential acid traps. It's also harder to remove the little squares from a crosshatch pattern.

We don't use crosshatching because it consists of a continuous piece of etch that runs all over the board. If anything shorted to it, it would create a giant antenna and or EMI problems. Where as if you were to short to a small (unattached) square that was not joined together it would not cause a problem.

And we do not use ROUND thieving because it can be confused as a fiducial.