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Re: Cost of different courtyard elements for the closed outline and DRC algorithms


Hi Rene-

Am 2019-01-01 11:57, schrieb Rene Pöschl:

Right now we have a few contributions for the library that use arcs
quite extensively on the courtyard layer.

I would therefore like a bit of input.

Are arc generally more expensive than lines?

Yes. Arcs are generally computed as a series of segments, so they are up to 64x more computationally expensive. BUT... This is the difference between a tiny fraction of a millisecond and 64 tiny fractions of a millisecond. In other words, you wouldn't notice the difference in the DRC runtime even with a modest computer.

Is there a difference if the arc is a multiple of 90 degree compared
to any other angle.


Is there a difference if the endpoints of two neighboring endpoints
meed exactly vs they being within the tolerance range for counting as
a closed outline (If i remember correctly then the tolerance was
0.01mm. I assume this is the radius of the tolerance circle.)

Right now this is hard-coded with a magic number to be 0.05mm. This seems to be a reasonable number and probably won't change without specific reason.

Personally, I don't see any reason to prohibit arcs in the courtyard. While one use of the layer is to provide mechanical keepout as others have mentioned, it serves other purposes as well and IPC 7351 explicitly states that it is to be used as a starting point for the minimum area of the component + landing pads. Therefore if a manufacturer wants to only use rectangles, they will simply convert each to a bounding box and add their specific manufacturing allowance. Designers will need to modify the courtyards in their designs based on the DFM feedback, so the initial courtyard should be considered a minimum suggestion.


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