I have previously worked with KiCad 5, but I jumped over multilayer work in v6 entirely.
I’ve started a multilayer (just 4) board and I’ve muddled through the workflow in v7. It seems like the interface (etc) in v7 has changed significantly. I tried to assign a Net-class to each of the power layers (e.g., GND to one layer, and Vcc to another) before doing any routing whatsoever, but there does NOT seem to be a way to do this. It seems that the best I can do is to use these dialogues in PCB Editor: Board Setup/Board Stackup/ Board Editor Layers, and then choose from {signal, power plane, mixed, jumper}. No obvious way to assign a net-class. Am I missing something?
Does anybody have a step-by-step accounting of the workflow to set-up a multilayer board and make preliminary (pre-routing) net-class assignments to the layers in this way?
Ah…now, I tried putting zones like this in place, but seem to have not hit upon the step of assigning a net-class to that zone. Thanks, I will give that a try!
Just to note, you assign a net to a zone (i.e. a particular node in your schematic), and not a netclass (which is just set of rules for multiple nets).
I just recalled why I stopped adding the copper zone: this is a board for RF (sub-GHz) and I am concerned about adding an excessive amount of “stray” capacitance. Any thoughts?
Why you’re concerned about a ground plane? It’s a standard feature even for RF, just make sure to follow the rules for Microstrip depending on your board’s parameters.
Otherwise, I dont understand what would you like to achieve, without using copper planes.
Thanks for your patience. I admit to being not-well-versed in RF PCB design. I understand the basics of microstrip design calculations (e.g., under KiCad Calculator Tools). Does it make much, if any difference (viz stray capacitance) whether a ground or DC power-plane is immediately next to an RF signals plane (i.e., should the DC layers be on the two layers of the “back”, as far as possible from the signal layers)?
When I’m doing 4-layer, I put my RF tracks on Top, and just below RF there’s my continuous GND then Power then secondary signals. And that’s quite common stackup.
Ah, so you are keeping the signals on the outer surfaces and the DC internal. Thanks for the advice.
Now, my question is: If I have the ability to do so, is it better to use a simple microstrip line, OR, is a co-planar wave-guide arrangement (with the ‘co-planar’ being a grounded copper zone) preferable? If you can point me to an accessible (PDF, download-able) summary of the rules-of-thumb for the various RF options, that would be appreciated!
Microstrip lines are more commonly used, however I do sometimes arrange a co-planar waveguide. Google for “optimized rf board layout”, there’s tons of info available.
Good starting point would be the documentation for the IC you have chosen for your application. They usually provide some dedicated design and layout tips.