for high-current applications, the appropriate trace width must be selected by comprehensively considering factors such as current load, cross-sectional area, heat dissipation requirements, and space constraints. Optimal design decisions require basic electronic and electrical knowledge combined with practical experience.
Two days ago, I designed a power PCB. A trace burned out instantly during power-on due to an overly narrow trace width. To resolve this issue, we had to replace the burned trace with an external flying wire.
Previously, the PCBs used by our company were mostly 6-layer, 8-layer, and 10-layer boards with dense component placement and limited routing space. To route wide traces, we constantly compressed the layout space. However, when space is extremely constrained, we have to appropriately reduce the trace width to complete the routing. Based on past experience, we conclude that a 1mm-wide trace is generally required for 1A current. Can we then infer that a 10mm-wide trace is needed for 10A current? When PCB space is sufficient, the trace width can be designed according to this proportional relationship. However, this 10mm width is often unachievable in multi-layer PCBs with limited space, because internal routing layers of multi-layer PCBs offer restricted area, and wide traces occupy excessive space that may not be available. Therefore, for high-current applications, the appropriate trace width must be selected by comprehensively considering factors such as current load, cross-sectional area, heat dissipation requirements, and space constraints. Optimal design decisions require basic electronic and electrical knowledge combined with practical experience.
Basic Knowledge
Copper thickness of PCBs is measured in ounces (oz). 1oz copper means a uniform copper layer weighing 1 ounce per square foot (ft²), equivalent to a thickness of 35 micrometers (μm) or 0.035 millimeters (mm). Common PCB copper thickness specifications are 0.5oz, 1oz, and 2oz, which are widely used in consumer and communication electronic products. 3oz copper is rare and mainly applied in power products handling extremely high currents and voltages. In standard multi-layer PCBs, the top and bottom layers typically use 1oz copper, while inner layers use 0.5oz copper. Detailed specifications can be confirmed with PCB manufacturers.
PCB Trace Width Calculation
The current-carrying capacity of a PCB trace depends on three key factors: trace width, copper thickness, and temperature rise. Wider traces provide higher current-carrying capability.
The PCB manufacturing standard IPC-2221 specifies formulas to calculate the required trace width by inputting relevant parameters:
- Inner-layer trace: I=0.024×ΔT0.44×A0.725
- Outer-layer trace: I=0.048×ΔT0.44×A0.725
Parameter Definition (IPC-2221)
- I: Maximum allowable current of the trace, unit: Ampere (A)
- 0.024 / 0.048: Correction coefficients (denoted as K); K=0.024 for inner layers, K=0.048 for outer layers
- ΔT: Maximum temperature rise, unit: °C; typical values: 10°C, 20°C
- A: Cross-sectional area of the trace (copper thickness × trace width), unit: square mil (mil²)
Although the trace width can be calculated by substituting these parameters, the computation is complex. It is recommended to use online calculation tools or software algorithms compliant with IPC-2221.
Calculation Using Design Assistant Tools
We tested multiple online trace width calculators and obtained nearly identical results (two tools yielded exactly the same values). Under the following conditions: 10A continuous current, 10°C maximum temperature rise, 25°C ambient temperature, 1oz copper thickness, 10mm trace length, the calculated results are:
- Inner-layer trace width: ~18.71mm
- Outer-layer trace width: ~7.19mm
Manual calculation using the IPC-2221 formulas confirmed consistency with the tool results.
ANSI PCB Trace Width Calculator
ProPCB PCB Design Assistant – Trace Width Calculation
The algorithm of this software complies with the international general PCB manufacturing standard IPC-2221.
ProPCB Via Calculation
Conditions: 10A continuous current, 1oz/35μm copper thickness, 10°C temperature rise, 25°C ambient temperature
- Plated copper thickness: 35μm
- Via inner diameter: 0.15mm (after plating)
- Current-carrying capacity per via: 1.61A
- Number of vias required for 10A: 7
The type and thickness of plated metal directly affect the current-carrying capacity of vias.
It should be noted that even though the calculation results of these tools are highly consistent, practical applications must consider additional factors such as PCB material, insulation thickness, and trace spacing. Therefore, these factors must be comprehensively evaluated in actual production, and professional PCB manufacturers should be consulted to ensure the final PCB meets design requirements.
This concludes the analysis. The core conclusion is: A 1mm-wide trace is required for 1A current under general conditions.
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