8.0.6
I’m a noob and trying to understand Netclasses to route a 4x4mm with 0.4mm pitch QFN28
(similar to Kicad default QFN-28-1EP_4x4mm_P0.4mm_EP2.6mmx2.6mm footprint)
I’ve tried different net class settings but I am still in violation somewhere and unable to route properly.
I get green alternate green PCB pads when trying to connect.
Can some point me in the right direction.
The goal is to route the QFN28 to a .1" set of headers.
You don’t give much information, which makes it a bit of guesswork to where you got stuck. I’ll assume you can put nets into net classes. (You do this in the schematic editor, but you set properties such as track width and clearance in **PCB Editor / File / Board Setup / Design Rules / Net Classes).
From there, it’s just a few numbers. Clearances can overlap with other clearances, but a clearance may not overlap with copper (Track or pad) from another net. As a result, the sum of the Clearance and the Track Width in the net class setup must be equal (or slightly smaller) then the pitch of your IC. Another limit is because of the pad size of the footprint. These also get the same clearance rules as your net class (They can be overridden with custom rules, but that’s another topic).
The QFN you have chosen has a pitch of 0.4mm, and a pad width of 0.2mm. A logical choice is to use a clearance of 0.18mm (0.2mm clearance probably works too, but I like to give KiCad some room for tolerances) Keeping the track width the same as the pad width (0.2mm) is also a logical choice.