1. Basic Calculation Methods
The current-carrying capacity of a PCB trace primarily depends on three key factors: trace width, copper thickness, and allowable temperature rise. Common calculation methods include:
1.1 Cross-Sectional Area Method
- Standard copper thickness: 1 oz = 35 μm (0.035 mm)
- Cross-sectional area (mm²) = Trace width (mm) × Thickness (mm)
- Current capacity (A) = Cross-sectional area × Current density (15–25 A/mm²)
1.2 IPC Standard Formula
[ I = K \times \Delta T^{0.44} \times A^{0.75} ]
Where:
- K: Correction factor (0.024 for inner layers, 0.048 for outer layers)
- ΔT: Allowable temperature rise (°C)
- A: Cross-sectional area (in square mils)
- I: Maximum allowable current (A)
2. Design Reference Data
2.1 Typical Current Capacity (1 oz Copper, 10°C Temp Rise)
- 10 mil (0.254 mm): ~1 A
- 50 mil (1.27 mm): ~2.6 A (nonlinear increase)
- 100 mil (2.54 mm): ~4.2 A
2.2 Impact of Copper Thickness
- 2 oz copper provides ~1.8× the current capacity of 1 oz.
3. Design Considerations
3.1 Nonlinear Relationship
Current capacity does not scale linearly with trace width. For example:
- 10 mil → 1 A
- 50 mil → ~2.6 A (not 5 A)
3.2 Practical Design Factors
- Voltage drop due to trace length
- Thermal dissipation conditions
- Permissible temperature rise range
- Safety margin (recommend 70–80% of calculated value)
3.3 Special Treatments
- Tinning (solder coating) can increase current capacity but:
- Solder thickness is difficult to control
- Typically improves capacity by only 20–30%
4. Design Recommendations
- Perform thermal simulations for critical traces.
- For high-current traces, consider:
- Using thicker copper (≥2 oz)
- Minimizing trace length
- Parallel routing on multiple layers
- Include test points for real-world validation.
Note: The above data is for reference only. For critical applications, consult your PCB manufacturer for precise current-carrying specifications and validate through testing.