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Date:	Wed, 18 Feb 2015 10:26:39 +0100 (CET)
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Subject:	Re: [geda-user] Star connection points in PCB?
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On Wed, 18 Feb 2015, Kai-Martin Knaak wrote:

>>> Drawbacks:
>>>
>>>   - the same pin numbering and back-annotation problem that you
>>>   have with connectors
>
> @Igor2: Would you mind to elaborate?
>
>
>>>   - the star symbol/footprint will have explicit number of pins,
>>>   you may end up unused pins or will have to replace with the next
>>> bigger if more nets are to be connected
>
> The pads of the star symbol can be 100% overlapping in the footprint.
> So a replacement won't break the layout.

If there's 100% overlap of all pads, and you connect a trace to it, you 
connect it to all pads, not just the one you wanted to. This would require 
another exception. The simplicity of my proposal 3 works only if you have 
a section of the pad which does overlap and a section which doesn't and 
the trace is connected to the non-overlapping section only. This means 
find.c figures the trace is connected to that given pad, pad number N, and 
this is what the netlist wants too, so all fine. The only exception to be 
added is that it should stop checking whether this pad is galvanically 
connected to other pads as well.

Another problem with 100% overlap is that once you connect two traces of 
two different nets to it, the two traces may (under the pad, sort of 
invisible to the user in some cases) also touch. This way find.c would 
detect both traces are connected to the pad(s) but they are also shorted 
together in the same point.

My proposal makes this more explicit because the non-overlapping parts of 
the pads would be sticking out, like bristles of a hedgehog and there is 
an 1:1, visible connection between a pad and nets. Just like with 
connectors now.

Hence the pin-numbering/back-annotation problem I mentioned: when drawing 
the schematics, it's hard to predict what pin number of the star should be 
used for a net. When you do the PCB, you already see swapping two pads 
makes routing easier, but then there's no easy mechanism (that I know 
of) to get this swap back-annotated to the schematics.

Regards,

Igor2

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