PCB design glossary
Net
AKA: nets
A single electrical connection in a schematic — every pin on the same net is electrically tied together.
A net is a named electrical connection. Every wire and pin that should be at the same voltage belongs to the same net. VCC, GND, SDA, and SCLK are all examples of nets you'd expect on a small I2C sensor board.
Power, ground, and high-speed signal nets often get special treatment during routing: wider traces, dedicated layers, controlled impedance, or differential pairing.
Nets, labels and net classes
In a schematic, a net can be drawn as a wire, or joined by giving two wires the same label. Power symbols such as GND or +3V3 are labels too: every GND symbol on every sheet is the same net. Local labels join wires on one sheet; global or hierarchical labels join them across sheets.
A net class groups nets that share rules. A POWER class might use 0.5 mm traces and wider clearance, while a USB class sets differential-pair spacing and impedance. The layout tool then applies those rules to every net in the class automatically.
Mistakes that create wrong nets
ERC and a look at the netlist catch most of these before layout, when they are cheap to fix.
- Two labels with a typo (SDA and SDA1) that were meant to be one net: the connection silently disappears.
- The same label used for two different signals: they are silently shorted together.
- A pin listed on two nets, which is an outright short between them.
- A wire that visually crosses a pin without actually connecting to it.
Check every connection by name before any copper exists
Describe the circuit in plain words and you get an editable schematic first, with each net labelled, so a wrong connection is fixed on paper rather than on the board.
Describe a circuit