Via Current Capacity (IPC-2221)

Formula

Description

The same IPC-2221 empirical formula applies to via barrels, where A is the cross-sectional area of the copper plating in the via barrel (not the via drill area). The via barrel is a hollow cylinder of plated copper, so A = π × d × t, where d is the drill diameter and t is the plating thickness (typically 0.7-1.0 mil for standard plating). A single standard via can typically handle 0.5-1A depending on temperature rise and plating thickness. For higher currents, use multiple vias in parallel.

Variables

• I — Maximum current (A)
• k — Constant (0.048 for external, use same as outer trace)
• ΔT — Allowable temperature rise (°C)
• A — Via barrel cross-section area (mil²)

Practical Notes

Via barrel area for a 12 mil drill with 1 mil plating: A = π × 12 × 1 ≈ 37.7 mil². Multiple vias in parallel share current; use 3-5 vias per amp as a conservative rule of thumb. Via-in-pad designs improve thermal performance but require filled and capped vias for surface mount components. Thermal vias under power components should be arrayed in a grid pattern.