Heavy Copper PCB
The engineer's workbench for high-current boards. Size traces with IPC-2221, convert copper weights from 1 to 30 oz, check voltage drop and heat — then send it straight to fabrication.
Copper cross-section
8.27 mil
0.209 mm
Drag to feel why high current needs heavy copper. Thicker foil = more cross-section = the same amps in far less trace width.
Copper thick enough to carry power
A Heavy Copper PCB uses copper layers of 3 oz/ft² (≈105 µm) or more instead of the 1 oz standard. That extra metal carries tens to hundreds of amps, spreads heat away from hot components, and shrugs off the thermal cycling that cracks thin traces. It is the backbone of power supplies, motor drives, EV systems, and welding gear — anywhere current is the design constraint.
Engineering calculators
Four tools that do the math behind every heavy copper layout. Everything updates live — change an input and read the result.
IPC-2221: I = k·ΔT⁰·⁴⁴·A⁰·⁷²⁵, with k = 0.048 external, 0.024 internal. A is in mil²; width = A ÷ thickness. A planning model — verify against your stack-up and standard.
1 oz/ft² of copper = 1.378 mil = 34.8 µm = 0.035 mm. Each ounce stacks the same thickness, so converting between weight and physical thickness is linear.
R = ρ·L⁄A with copper ρ = 1.724×10⁻⁸ Ω·m, temperature-corrected at 0.393%/°C. Heat in the copper raises resistance, which raises drop — size with margin.
Copper weight → thickness, 0.5 to 30 oz
The full ladder from standard foil to extreme copper. Print it, pin it, or pull the exact numbers into your stack-up notes.
| oz/ft² | mil | micron (µm) | mm | Class |
|---|
Class is a common convention: ≤2 oz standard, 3–10 oz heavy copper, 12 oz+ extreme / ultra-heavy. Definitions vary slightly between fabricators.
Get the layout right the first time
Heavy copper rewrites a few rules you take for granted on signal boards. The big ones:
Size by ampacity, not habit
Run the current and your ΔT budget through IPC-2221 every time. Heavy copper buys the width back — a trace that needs 7 mm at 1 oz can shrink dramatically at 6 oz.
Budget your temperature rise
Pick a ΔT and stick to it. Internal layers shed heat poorly, so they run hotter for the same copper — design inner power traces with more margin than outer ones.
Allow for etch factor
Thick copper undercuts during etching, leaving a trapezoid. Widen traces, open up spacing, and confirm the fabricator's heavy-copper trace/space rules for your weight.
Voltage clearance is separate
Current sets trace width; voltage sets spacing. Use IPC-2221B clearance and creepage tables for your working voltage and altitude — don't let ampacity sizing decide gaps.
Use copper as a heatsink
Thick planes pull heat out of hot parts. Pair heavy copper pours with thermal vias and exposed copper to move that heat into the board and out.
Mix copper weights to save cost
Step or mixed copper puts heavy foil only where current flows and keeps signal areas thin. It cuts material cost and eases fine-pitch routing on the same layer.
Typical heavy copper fabrication envelope
A representative capability set for heavy and extreme copper builds. Confirm exact limits for your design with the fab.
Where heavy copper earns its place
If current, heat, or ruggedness drives the design, heavy copper is usually the answer.
Power supplies & converters
High-current rails and dense thermal paths.
EV & automotive
Traction power, on-board chargers, busbars.
Motor drives & inverters
Industrial and renewable power stages.
Battery & energy storage
BMS, pack interconnects, solar inverters.
Welding & industrial
Surge currents and harsh thermal cycling.
Aerospace & defense
Rugged power distribution and backplanes.
Heavy Copper PCB, answered
What counts as a Heavy Copper PCB?
How thick is one ounce of copper?
How do I pick a trace width for high current?
Why is heavy copper more expensive?
Can heavy copper and fine-pitch parts share a board?
From calculator to copper
You sized it here — now build it. PCBSync fabricates Heavy Copper PCBs from 1 to 30 oz, prototype to production.