Trace Current Capacity

Trace Current Capacity (IPC-2221)

How much current can a trace carry before overheating? The IPC-2221 standard provides empirical formulas based on temperature rise.

I = K × ΔT^0.44 × A^0.725

Where:

• I = maximum current (Amps)
• K = 0.048 for external traces, 0.024 for internal traces
• ΔT = allowed temperature rise above ambient (°C)
• A = cross-sectional area of the trace (mils²) — 1 mil = 0.0254 mm

The cross-section area in mils²:

A = (width in mils) × (thickness in mils)

Common trace thicknesses in mils: 1 oz = 1.378 mils, 2 oz = 2.756 mils.

Example: External 10 mil wide, 1 oz trace, 10°C rise:

• A = 10 × 1.378 = 13.78 mils²
• I = 0.048 × 10^0.44 × 13.78^0.725 ≈ 0.048 × 2.754 × 6.68 ≈ 0.884 A

Your Task

Implement traceCurrentCapacity(widthMm, thicknessMm, deltaT, external):

• widthMm, thicknessMm: dimensions in mm
• deltaT: temperature rise in °C
• external: boolean (true = external trace)
• Returns max current in Amps