PCB Copper Thickness: A Practical Guide for Your Board's Performance

Beyond the Default: An Engineer’s Guide to PCB Copper Thickness

If you’ve ever opened your EDA tool and blindly accepted the default “1 oz” copper setting, you aren’t alone. For many digital designs, that standard works just fine. But as a senior engineer who has seen plenty of boards fail due to thermal issues or poor yield, I can tell you that copper weight is a variable you need to actively manage—not just for signal integrity, but for the PCB manufacturing process and overall cost.

Whether you are a layout engineer trying to keep a power rail cool or a procurement manager analyzing a Bill of Materials (BOM), understanding the nuance of copper thickness is essential.

Decoding the "Ounce" in PCB Stack-Up

It’s one of the quirks of our industry that we measure thickness by weight. When we say "1 oz copper," we mean one ounce of copper rolled out over one square foot.

In practical terms for your PCB stack-up:

• 1 oz ≈ 1.37 mils (35 µm)

• 0.5 oz ≈ 0.7 mils (17.5 µm)

• 2 oz ≈ 2.8 mils (70 µm)

This copper foil is bonded to the core (often FR4) and prepreg layers. While 1 oz is the industry workhorse—offering a great balance between cost, etching precision, and current capacity—it isn’t a silver bullet.

When to Go Heavy: Current and Heat

The most obvious reason to increase copper weight is current handling. If you are designing a power supply or a motor controller, standard 1 oz traces might turn into unintentional fuses.

Thicker copper (2 oz, 3 oz, or even higher) reduces resistance, minimizing voltage drop and heat generation. It acts as a heatsink, spreading the thermal load across the board. However, this decision has a ripple effect on PCBA assembly.

When soldering components on heavy copper boards, the thermal profile changes. The board sucks the heat away from the soldering iron or reflow oven rapidly. This is where the debate of SMT vs through-hole becomes relevant; achieving a proper solder fillet on a heavy-copper through-hole pin requires significantly more thermal energy than a standard SMT pad. If your manufacturer isn't prepared for this, you risk cold solder joints.

When to Stay Thin: Flexibility and Fine Pitch

More copper isn't always better. If you are designing a rigid-flex PCB or a board that will endure high mechanical stress, thinner copper (like 0.5 oz) is often superior because it is more ductile and less prone to cracking during bending.

Furthermore, from a DFM (Design for Manufacturability) perspective, heavy copper limits your layout geometry. The etching process involves chemicals eating away unwanted copper. With a thick layer, you get an effect called "undercutting," where the etchant eats sideways as well as downwards.

This makes it nearly impossible to have fine lines and spaces. If your BOM includes a fine-pitch BGA or tiny 0201 passives, stick to standard or thin copper to ensure the layout is printable.

PCB Layout Best Practices for Copper Weight

To ensure your design survives both the fabrication house and the test bench, keep these PCB layout best practices in mind:

1. Calculate, Don’t Guess: Use an IPC-2221 calculator to determine the required trace width based on your current and acceptable temperature rise.

2. Mind the Spacing: If you specify 2 oz copper, you generally need to increase your clearance (spacing between traces). A good rule of thumb is 8 mils space for 2 oz copper, whereas you might get away with 4-5 mils on 1 oz.

3. Thermal Reliefs are Critical: For heavy copper boards, ensure your ground pads have thermal relief spokes. Without them, the heat will dissipate too fast during assembly, leading to difficult rework or bad joints.

4. Balance the Stack-Up: Try to keep copper weights symmetrical (e.g., if top is 2 oz, bottom should be 2 oz). Asymmetrical stacks can cause the board to warp or bow during the reflow oven process.

The Procurement Angle: Cost vs. Performance

For the procurement managers reading this: thicker copper costs more. Not only is the raw material more expensive, but the processing time increases. Etching takes longer, and lamination cycles can be more complex.

However, spending more on the bare board might save you money on the BOM by eliminating the need for external heatsinks or fans. It’s a trade-off that engineering and purchasing should evaluate together.

Partner with Omini for Your Next Build

Choosing the right copper weight is just one piece of the puzzle. At Omini, we bridge the gap between complex design requirements and manufacturing reality. Whether you need high-power heavy copper boards or high-density rigid-flex designs, our team handles everything from the initial layout review to final box-build. Let us help you optimize your stack-up for performance and price.