Copper Pours & Thermal
How you fill copper and connect pads affects power integrity, heat and manufacturing. Two everyday tools: fill zones (copper pours) and thermal relief.
Fill zones (copper pours)​
A fill zone floods an area of a layer with copper tied to a net (usually GND or a power rail).
- Ground/power planes as pours give a low-impedance return path and supply, and add plane capacitance (a power+ground plane pair acts as a small distributed decoupling cap).
- Stitch pours on different layers together with vias so they act as one plane.
- Avoid thin copper slivers/islands — set a minimum width and remove isolated pour fragments (they're useless and can cause issues).
- Don't pour copper that fragments your reference plane under fast signals — a pour is not an excuse to break the return path.
Thermal relief vs solid connection​
When a pad connects to a large pour, how it connects matters:
| Connection | Looks like | Use for |
|---|---|---|
| Thermal relief | Spokes (a "wagon wheel") | Soldering — the spokes stop the pour from sinking all the heat, so the pad heats and solders properly |
| Solid (direct) | Full copper connection | Current/heat conduction — high-current pins, thermal pads that must dump heat into the plane |
Rule of thumb: thermal relief for hand/most assembly soldering; solid for high-current and thermal-pad connections (where you accept harder rework for better conduction).
Thermal management​
- Put thermal vias under hot parts (regulators, FETs, power thermal pads) to move heat to inner/opposite-side copper.
- Use copper pours as heatsinks; more copper area = lower temperature rise.
- Heavier copper weight (2 oz+) for high-current/high-heat boards.
- Give hot parts breathing room; don't bury them under tall neighbours.
The "cold pad" trap
A high-current pad connected solid to a big ground pour can be nearly impossible to solder by hand — the pour wicks all the heat. Use thermal relief for solderability, or preheat the board.