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From:	"Britton Kerin (britton DOT kerin AT gmail DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
Date:	Thu, 18 Apr 2024 04:11:06 -0700
Message-ID:	<CAC4O8c_2XBpaWFNU9g5EJn0dXU=ZH=avSoFas10xsP+b3jMAJw@mail.gmail.com>
Subject:	Re: [geda-user] Allowing pins/pads with zero clearance to contact polygons
To:	geda-user AT delorie DOT com
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Reply-To:	geda-user AT delorie DOT com

On Thu, Apr 18, 2024 at 3:29 AM Onetmt (onetmt AT gmail DOT com) [via
geda-user AT delorie DOT com] <geda-user AT delorie DOT com> wrote:
>
>
> Il giorno mar, 23/01/2024 alle 20.52 -0900, Britton Kerin (britton DOT kerin AT gmail DOT com) [via geda-user AT delorie DOT com] ha scritto:
>
> A while back there was some discussion here about different ways of
> connecting pins/pads to polygons (e.g. ground pads to ground plane).
> At least some people like to do this by setting the clearance for the
> pin/pad to zero, then simply drawing the ground plane over the part.
> It's a nice way to do it because it removes the need to have little
> hard-to-select traces everywhere to connect e.g. ground pins to ground
> plane (which in turn makes it much less painful to move parts around
> after the fact.
>
>
> Yes, please, keep the zero clearance feature working - my last 10 years projects rely on that :-)

I've fixed this in my private mini-fork but I don't know if there's
any appetite to merge it
into anything official.

Britton

>
>
> This used to work without any DRV violations, but a fix to the polygon
> clearance tests by Charles Parker in de49a513 seems to show that it
> only ever worked by accident.
>
> However the current code in master contains this code that explicitly
> allows zero-clearance vias to contact polygons:
>
>   case VIA_TYPE:
>     if (clearance == 0)
>     {
>       /* Vias with zero clearance are allowed, make sure it's connected. */
>       if (obj_touches_poly(&thing1, polygon, GetLayerNumber(PCB->Data, layer)))
>         break;
>       else
>       {
>         /* not connected to the polygon, raise an error*/
>         new_polygon_not_connected_violation (layer, polygon);
>         break;
>       }
>     }
>
> I think this same condition should apply to PAD_TYPE and PIN_TYPE objects as
> well, because it's essentially correct to take zero to mean zero, and incorrect
> to do otherwise.
>
> What I don't agree with is the subsequent requirement that the object touch the
> nearby polygon, for the following reasons:
>
>   * It adds significantly more meaning to clearance == 0 than that setting
>     explicitly states
>
>   * As implemented it triggers on nearby polygons that aren't meant to be
>     connected
>
>   * As implemented the message doesn't make clear what the problem is (refers
>     only to flag and doesn't mention clearance) and gives a wrong prescription
>     for the case of a nearby polygon that isn't supposed to be connected.
>
>   * It doesn't catch thin connections (as happens for DRC elsewhere) anyway
>
>   * Complete misses with polys that are supposed to be connected are caught by
>     connectivity anyway
>
> Changing this to honor the literal meaning of clearance == 0 while not adding
> any unexpected implicit meaning would be fairly low-risk: it wouldn't change
> any existing board, and would only impact users who have deliberately set
> clearance to zero.  So far as I know none of the available footprint libraries
> ship footprints with clearance set that way by default.
>
> Thoughts?
>
> Britton

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