Hi guys,
Simple question. Given an IC (and LED) would need a large track width for supply, but signals don’t…
Can I make a “SigGnd” net of smaller width (obviously yes so far…),
and connect it to the regular GND net?
And NOT have it propagate the GND track widths into the SigGnd net?
Obvious example provided here: the signal pins of the 7447 do not need a large track width, but the IC itself is sinking the CA current from the display through pin 7 (not shown).
Currently (KiCad V5.1.6) there is no way to specify track width in Eeschema.
DRC check in Pcbnew is also limited. It does not follow the net classes, but just has a minimum copper width which it uses for all tracks.
So currently using correct track widths is at the discretion of the person who routes the board.
KiCad does support (a crude form of) net-ties. These can be used to split a single copper net into pieces, for example for star ground points or for 4-point measurement on a shunt resistor with fat current carrying tracks and thin sense lines.
But why do you need separate net for that in the first place? If it’s ground it’s the part of ground unless it has to be separated for some signal quality reasons, and you can for example fill it with a zone and make it as wide as possibe. Or you can draw a track of any width or change the width of any track afterwards, no matter what the net is and what are the net class values.
Well, I’m still learning this tool.
If there was a big ground plane to tie both signals and power paths to, that would be fine.
In this case, I created a ground plane on the bottom, and then imported the DSN into the FreeRouting tool.
In Eagle, if you have a ground plane, and autoroute, it will “carve out” a portion of the plane to allow a bottom track.
It appeared that the FreeRouting decided it was not allowed remove or cut any of the ground plane to accommodate any trace on the bottom layer.
(Maybe there is a way to get around that, I haven’t seen anything yet… And I know this forum is not the place to get FreeRouting support)
So, now I am routing most if it myself, and all the signal grounds on pins are unnecessarily wide. I’m fine with the power grounds being that wide.
(I have hundreds of nets, and all I wanted was a auto-router to handle most of the 14 or so buses… about 60-70% - that’s the really tedious stuff. I’d do the rest myself.)
Is this double sided or more layers?
In KiCad, you can add the GND plane after the (auto) routing, and it will calculate and use clearances, and fill in the rest, for as far as there is still room for a GND plane.
For this, set up some net classes, and assign your nets to these classes to use different defaults for different nets. It is in:
Pcbnew / File / Board Setup / Design Rules / Net Classes
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