How do you decide the trace width for your PCB designs?

Design and Layout Design for Manufacturing
1

We often see questions about trace width selection during layout reviews, so I wanted to start a conversation here on how designers determine trace width in different scenarios.
Trace width determines both current-carrying capacity and impedance (when high-speed is involved). If the trace is too narrow for the expected current, it can overheat and lead to reliability issues. On high-speed nets, incorrect width can also cause unintended impedance deviations.

Trace width and spacing on a PCB
Trace width and spacing on a PCB761×412 31.3 KB

Trace widths were initially calculated using IPC-2221B. However, the IPC-2152 standard supersedes it, taking into account temperature rise, copper thickness, and environmental conditions. Additionally, you need to consider dielectric details to determine an accurate trace width that satisfies both thermal and signal integrity requirements.

1 Like
2

When deciding on a trace width, here are the primary variables you need to define:

  1. Maximum current (I): Determine the peak current the trace will carry.
  2. Allowable temperature rise (ΔT): This is not the ambient temperature, but the local board temperature in the trace’s immediate vicinity. A common design rule is to allow for a 10°C to 20°C rise, but this depends on your overall thermal management strategy and component sensitivities.
  3. Copper weight (thickness): Standard 1 oz/ft² copper (1.4 mil thick) is common, but high-current paths may require 2 oz or more.
  4. Trace location: Internal traces dissipate heat less efficiently than external traces, which affects their current capacity for the same width.
1 Like
3

Furthermore, you can account for advanced board characteristics, such as the board’s size, thickness, proximity of nearby copper planes, and the thermal conductivity of the PCB laminate, which are all factors that influence your final width choice. Always check both current capacity and any impedance requirements early in the design process with your fabrication partner.

To learn more about how trace width and current capacity are determined using the IPC-2152 standard, I recommend checking out this article: How to Optimize Your PCB Trace Using IPC-2152 Standard.
Furthermore, to get instant, accurate results tailored to your specific boards, you can use our free online tool: Trace Width and Current Capacity Calculator.

1 Like