PCB Via Current Calculator
Design vias for current handling based on IPC-2221.
What is a PCB Via?
A Via (Vertical Interconnect Access) is a plated hole in a Printed Circuit Board used to connect copper traces on different layers. It is essentially a tiny tube of copper.
While traces are flat, vias are cylindrical. Calculating their current capacity is critical because a via that is too small for the current can act like a fuse, blowing open and destroying the connection (and potentially the board).
Via Current Formula (IPC-2221)
We model the via as a cylinder of copper plating. The effective cross-sectional area is the ring of the plating, not the hole itself.
Area ≈ π × (d × t)
Imax = k × ΔT0.44 × Area0.725
Where:
- d: Finished Hole Diameter (mm or mils).
- t: Plating Thickness (standard is 25µm or 1 mil).
- k: 0.048 (Outer layers) or 0.024 (Inner layers).
Practical Applications
- Power Planes: Connecting a voltage regulator's output on the Top Layer to a VCC Internal Plane. Usually, a single via isn't enough; designers use "via stitching" (arrays of vias) to share the current.
- Thermal Vias: Placing vias under a hot component (like a QFN chip) to conduct heat to the bottom ground plane.
- Layer Transition: Moving a high-speed signal from Top to Bottom to cross over other traces.
FAQ
What is the "Aspect Ratio"?
It is the ratio of Board Thickness ÷ Via Diameter. For most standard fabs, you should keep this below 10:1 (e.g., a 1.6mm board should have vias no smaller than 0.16mm). Exceeding this makes it hard to plate the hole reliably.
Should I tent my vias?
"Tenting" means covering the via with soldermask. This is generally good practice to prevent accidental shorts and corrosion. However, for test points or high-current thermal vias, you might leave them exposed.
How much current can a 0.3mm via handle?
A standard 0.3mm (12 mil) via with standard plating (1 mil) can handle about 0.5 Amps to 0.8 Amps with a 10°C temperature rise. For 2 Amps, you would need 3 or 4 of them in parallel.