Monday, December 18th
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We recently authored a post that discussed the use of stackups in multi-layer PCB design. But another factor to consider when designing single-layer and multi-layer PCBs is trace width. As with other design factors for PCBs, requirements for a good trace width can impact the size and layout of a PCB. Reducing PCB size may reduce costs, but there’s still a need to ensure you have sufficient space for effective trace widths.

Why Does Trace Width Matter?
An effective trace width ensures that the trace, whether for signal or power, is operating effectively and providing optimal PCB function.

Top 5 Considerations
PCB trace width can be determined after considering several considerations including:

  1. Purpose: power trace or signal trace?
  2. Amperage: or, current, through the trace.
  3. Location: top or bottom layer, or, inner layer, where heat can’t escape as quickly.
  4. Thickness: how thick is the copper on the layer?
  5. Length: how long is the trace?

Standard Practices

Width – In general, trace widths used to carry signal can be smaller than traces used to carry current. For a trace optimized for current a good range of widths might be from 0.010” for 0.3 amps up to 0.150” for 6.0 amps.

Shape A trace can be laid out on a PCB layer in a horizontal or vertical direction, or at an angle (45 degrees). Right or acute angle turns are not recommended for trace widths of 0.012” or less. Try to keep the traces as short and direct as possible. If using a trace along the edge of a layer, ensure there is enough space between the trace and the edge of the layer, typically 10 to 15 mils.

Spacing Traces too close to each other or to other components could produce a risk of a potential short in the board during operation. While 0.003” can be a common minimum spacing between traces; recommended spacing for most trace widths should be at least 0.010”. Spacing for higher voltage traces should be larger.

Checking Trace Width Using Design Tools
Most design tools offer functionality to perform a basic check of the trace width in a design. We also recommend using InstantDFM, our free, fully-automated, web-based tool to verify that trace widths are optimal for the PCB design.

 

Additional Resources

Design Considerations with Heavy Copper

Controlled Impedance for Printed Circuit Boards

What is Controlled Impedance and How Is It Measured?

Also check out our PCB Design Guidelines for additional help.

 

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