A group of nets sharing routing rules (track width, clearance). E.g., POWER vs SIGNAL. Freerouting and KiCad respect these.
How it looks
Real geometry: CORE3588 copper, drawn from our board file (2D plan view)
Top copper of CORE3588, whole board. Amber: every net in the two high-speed classes, MIPI_100R (64 camera wires) and USB_90R (8 USB wires). They are the thin, paired lines. The wide grey runs are the power classes.
Real geometry: CORE3588 copper, drawn from our board file (2D plan view)
Zoom: 14 x 9 mm of top copper, drawn from the board file. Three classes side by side; the width difference is set by the class, not by hand.
1POWER_MAIN class: the 4 V main supply, a 1.5 mm wide track.
2Default class: a camera control wire (CAM0_SCL), 0.2 mm wide.
3MIPI_100R class: camera data pairs, 0.12 mm wide.
How it works
Where it fits
A net class is a rule set shared by many nets: track width, clearance, via size and differential pair gap. CORE3588 defines ten in its project file.
Extra rules (maximum length, length match within a pair) are added on top in a custom rules file; see differential pair.