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Subject:	Re: [geda-user] PCB, 2 parts physically in the same place
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	<20201026155510 DOT 23661 DOT qmail AT stuge DOT se>
From:	"Richard Rasker (rasker AT linetec DOT nl) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
Message-ID:	<7df63bf7-7216-c15f-0b56-2b712705cc90@linetec.nl>
Date:	Tue, 27 Oct 2020 11:20:18 +0100
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Op 26-10-20 om 16:55 schreef Peter Stuge (peter AT stuge DOT se) [via 
geda-user AT delorie DOT com]:
> gene glick (geneglick AT optonline DOT net) [via geda-user AT delorie DOT com] wrote:
>> I want to do this on purpose. One part, a 2X16 character display has 10
>> connections to the PCB. Problem is, they are just holes. It is meant to
>> have a 10 pin header on the PCB, and then the display gets positioned over
>> the header and soldered in place.
> Rather than having to deal with two footprints on top of each other I'd
> recommend this:
>
> Create one 2X16LCD footprint which has no electrical connections but
> only silk lines+text and any mounting holes (Pin with attribute "hole").
> I'd recommend to draw silk lines around where the electrical connections
> will go.
>
> Then place one 1x10 header footprint for the electrical connections.
>
> That way you can have both parts in schematic and BOM without having
> redundant connections in the netlist and layout, and no problems with
> two footprints with electrical connections on top of each other.

This had occurred to me as well, but the major caveat here is alignment: 
even a minute unnoticed nudge of either part may spell very serious trouble.

At the very least, I'd recommend combining the connector pins and 
mounting holes in the same footprint when adopting this approach. After 
all, a slightly shifted silk screen symbol isn't much of a problem, but 
mounting holes in the wrong place usually boil down to an unusable board.

> In addition to local simplicity I can imagine that fabs might be unhappy
> or at the very least confused with two drills on top of each other..

Yes, that might indeed be an issue, depending on the fab house.

My standard approach here is actually to NOT use a separate header 
symbol in the schematic, but simply put a warning in the display 
symbol's comment attribute to manually add the header to the bom afterwards.

My final boms (LibreOffice spreadsheet files) contain lots of other 
parts that aren't entered in the schematic anyway, e.g. mounting studs, 
washers, screws, and nuts, bezels, brackets etcetera. So manually adding 
this header is a minor issue.

But it is interesting to see that PCB allows these overlapping parts.

Richard

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