kicad-developers team mailing list archive

[Seth Hillbrand <seth@xxxxxxxxxxxxx>]

Hi Rene-

Am 2019-01-01 11:57, schrieb Rene Pöschl:
> Hi,
>
> 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.

No.

> 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 3.1.5.4 
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.

-Seth