Hasn’t anyone here used Altium before?? Not that im saying altium is the be-all-end-all standard but it does (and other packages too) do a lot of things rights. One of which being net classes…
Defining them in the schematic is just good practice, simply put. To me schematics are like code, it should be well documented no matter who is looking at it. These net classes should be transferable to/from the pcb design. The net classes should be able to define a myriad of things/rules for the DRC/Fills/etc. as guides to follow.
I personally use net classes and rules everywhere i can. I primarily use them for length matching, differential pairs, clearance, widths, layers, and even vias.
Altium for sure is a good inspiration source but i would not copy it fully. After all kicad can at best be as good as a software it copies.
I am not so sure i would define manufacturing specific things inside the schematic (absolute minimums of width, clearance, …).
However, a way to define the requirements for potential classes (increased clearances) would definitely fall in the responsibility of the schematic designer.
But even here i would not really burden the schematic designer with directly setting the clearance in “mm”. It does not only depend on the voltage but also the materials used in pcb manufacturing (and the layer the trace ends up in). All the layout side really needs to know is what the voltage is of a specific net and then the manufacturing parameters are used to derive what clearance is required.
Similarly, for width and via size as these can be derived from the current, maximum voltage drop and temperature rise. Here again the manufacturing parameter “layer thickness” comes into play as well as trace length and of course the layer. (All these things are not known to the schematic designer.)
Agreed, and I wouldn’t want it any other way. That’s also not what I was after with my comment. Just merely pointing out that other tools offered some facility to transfer information from schematic to the pcb layout.
Also agreed. However I still think some minimal information still needs to be transferable to the PCB designer. Things like differential pairs and impedance controlled signals just to label a few. This information could at the very least be carried by net classes which pre-groups them. Which in Kicad’s current state (as far as I can tell) can not create net classes in the schematic for transfer. It currently seems to be a manual step for the PCB designer to find and select the correct nets (if they were even labeled correctly) to be classed. Which IMO, could/should fall under the practice of an schematic designer.
For the majority of us, nearly all of the circuitry in a schematic will perform quite acceptably when manufactured according to the “standard” (or “routine”, “common”, etc) board parameters. There ARE exceptions - such as controlled impedance, high current, high voltage, etc. I agree that KiCAD should plan for identifying the exceptions, and capturing the details of the exceptional requirement (spacing, width, impedance, isolation, etc) at the schematic level. This could be done with “Net Classes”, or by attaching parameters on a connection-by-connection basis, or by creating a new type of net which has these all the special parameters specified, or some other way that is intuitively obvious to software developers but inscrutable to us mere mortals.
Of course, eventually this information should propagate into PCBNew where it gets acted on and implemented. For now, making a well thought-out provision for the information in the data structure seems like a reasonable first step, even if the full feature doesn’t get implemented until two or three major revisions in the future.
Is there a Feature Request in Bug Tracker that already addresses this?