Thin Foil, Big Impact: Designing PCBs for Current and Heat

In printed circuit board (PCB) design, copper foil thickness is one of the most important 
element. At first glance, it may seem like just the “thickness of the wiring,” but it directly affects the current capacity, heat generation, and voltage drop, greatly influencing the reliability and lifespan of the circuit.

What is Copper Foil Thickness?

The thickness of copper foil used in PCBs is generally expressed in μm (micrometers) or oz 
(ounces).

• 1 oz ≈ 35 μm
• 0.5 oz ≈ 18 μm
• 2 oz ≈ 70 μm

These conversions are often listed in the specifications of board manufacturers as 
“Copper foil thickness: 18 μm / 35 μm / 70 μm,” etc.

How Copper Thickness Affects Current Capacity

The current capacity that can flow through a trace is mainly determined by the following factors:

• Copper foil thickness (thicker means a larger cross-sectional area, allowing for 
  higher current)
• Trace width (wider means a larger cross-sectional area)
• Allowable temperature rise (how much heat the board can tolerate)
• Whether the trace is on an inner or outer layer (outer layers dissipate heat more 
  easily, inner layers less so)

For example, a 35 μm thick copper foil and a 1 mm wide outer layer trace, the general standard is 1A to 2A. If you use 70 μm thickness, the current capacity for the same trace width roughly doubles.

Things to Watch for in PCB Design

• Use simulation and design tools:
  There are easy-to-use tools that help you figure out how much current a PCB trace can handle based on its width and copper thickness. Many of these tools follow global standards like IPC-2221 or IPC-2152, which are helpful guides during the design process.
  
• Include a safety margin:
  The calculated values are estimates. The actual temperature rise will vary depending on the heat generated by mounted components and how well the board cools down. To stay safe, always design with some extra allowance.
• Consider special designs for high current applications:
  For high-current applications, it’s not enough to just increase copper thickness. You may also need to use wider traces, add extra layers, or include bus bars and external wiring. These methods help handle more current safely and keep the board stable.
  

Copper Foil: Cost vs. Capacity

Copper foil thickness is a factor that directly affects board cost and but also a fundamental parameter for determining current capacity. By keeping these distinctions in mind and combining them with trace width and heat dissipation conditions, stable board design becomes possible.

Ready to Finalize Your PCB Design?

If you're preparing a custom PCB order, choosing the right copper foil thickness is key—not just for cost, but for current capacity and overall reliability. 
Upload your files here, and our team will take a close look to ensure your copper specs, trace widths, and thermal conditions are optimized for a stable and efficient board.