Boards & wires calculator, part of Premium
PCB trace width
A trace is a flat wire: thinner copper must be wider to stay cool.
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The example, worked out
Given
- Current
- 2 A
- Temperature rise allowed
- 10 °C
- Copper weight
- 1 oz (35 µm)
- Layer
- Outer
- Trace length
- 50 mm
- Board temperature
- 25 °C
Working
- IPC-2221: the copper section for the rise (k = 0.048 outside, 0.024 inside)
- 1 oz of copper is 1.378 mil (35 µm) thick
- copper warm, at the trace temperature
Results
The formulas
- A = (I / (k × ΔT^0.44))^(1/0.725)the copper section, k = 0.048 outside, 0.024 inside
- w = A / t1 oz of copper is 1.378 mil (35 µm) thick
The usual traps
- Inner traces need twice the width of outer ones.
- A trace sized for the heat may still drop too much on a 3.3 V rail.
Questions
How wide must a PCB trace be for my current?
A = (I / (k × ΔT^0.44))^(1/0.725): the copper section, k = 0.048 outside, 0.024 inside. w = A / t: 1 oz of copper is 1.378 mil (35 µm) thick.
What does it give for typical values?
0.781 mm for 2 A at +10 °C on 1 oz outer copper. Width needed: 0.7814 mm.
What are the usual mistakes?
Inner traces need twice the width of outer ones. A trace sized for the heat may still drop too much on a 3.3 V rail.
In the app
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The part you can buy
Results rounded to standard values (E12, E24, E96) and power ratings.
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Into your notebook
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Open the calculatorOpens in the app on 1 December, with Circuit Notebook 1.0
Also in Boards & wires
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- Microstrip impedance Z0 of a trace over a ground plane, or the width for 50 Ω.
- Differential pair Zdiff of two coupled traces, or the width for 90 or 100 Ω.