Via Resistance

Via Resistance

A via is a plated hole that connects traces on different PCB layers. Like a trace, a via has electrical resistance due to the thin copper plating on its barrel walls.

The via resistance formula:

R = ρ × H / (π × D × T_plating)

Where:

• ρ = copper resistivity = 1.72 × 10⁻⁸ Ω·m
• H = via height (board thickness), meters
• D = via drill diameter, meters
• T_plating = copper plating thickness on via wall, meters

A typical via:

• Board thickness: 1.6 mm
• Drill diameter: 0.3 mm
• Plating thickness: 25 μm (standard spec)

R = 1.72×10⁻⁸ × 0.0016 / (π × 0.0003 × 0.000025) ≈ 1.17 mΩ

Vias are very low resistance — typically < 5 mΩ — so they rarely cause voltage drop problems.

Your Task

Implement viaResistance(H_mm, D_mm, T_mm) returning resistance in milliohms (mΩ).