PCB Copper Thickness

When designing a board for production, the issue of copper thickness comes into play as early as the impedance calculations of the stackup software. While its contributions to the overall board thickness are a performance factor, the resulting processing constraints that shape layout design rules are far more critical. Designers will want to speak to a manufacturer at the earliest possible point pre-layout to optimize the board’s manufacturing.

Conversion Chart for Copper Thickness

Copper weight (oz./sq. ft.)	Thickness (mils/µm)	Recommended minimum air gap/trace width (mils/mm)
1	1.37/34.8	3.5/0.089
1.5	2.06/52.2	Consult with a manufacturer.
2	2.74/69.6	8/0.203
3	4.11/104.4	10/0.254
4	5.48/139.2	14/0.355
5	6.89/174	Consult with a manufacturer.
6	8.22/208.8
7	9.59/243.6
8	10.96/278.4
9	12.33/313.2

.Changing Copper Costs in 2025

Copper’s price increased significantly over the first half of 2024. While prices have leveled and stabilized, they still sit above late 2023 levels after adjusting for inflation. In general, copper is facing a typical low-supply, high-demand squeeze:

Supply	Demand
Existing global supply chain disruptions from COVID-19 fallout Compensation disputes by workers and agencies leading to strikes or stalled mining operations An intensifying focus by locals (workers, governments, etc.) on the ecological and health outcomes of mining operations	An increasing transition from fossil-fuel sources to electrification (solar, wind, EVs, etc.) Charging/electrical energy storage infrastructure Datacenter equipment/devices for computing services, specifically AI developments

While prices are in flux, the safe approach for PCB manufacturing is to bake in at least a modest price increase in raw/processed materials for board fabrication. These cost increases will escalate depending on the total amount of copper used, and on a per-unit basis, the thickness of the copper laminate necessary for the design.

Different PCB Copper Thicknesses For Different Applications

Like the distribution of layers about the center of the board, the copper in the top and bottom halves should be equal to prevent processing issues. The issue lies with etching: exposure to an etching solution removes uncovered copper on the laminate as a time-dependent function. The etchant would continue to eat away at the copper until total removal from the substrate or saturation of the solution, meaning there’s no feasible method to chemically etch simultaneously at different rates on the top and bottom during submersion.

However, the thickness of copper layers doesn’t otherwise have to be uniform – it’s common in high-power applications to use thicker copper on the outer layers to withstand the greater currents (and temperatures) from the associated components. On the other hand, copper thickness above the minimum is hugely detrimental to HDI boards due to the need for many discrete traces for dense component net breakout.  As the copper thickness grows, so does the minimum gap between copper features due to the etching process: the etchant solution must remove all vertical copper from the base substrate to prevent shorts. However, because the etch resist patterns can only protect the copper directly underneath, the etch solution begins to attack the newly revealed copper from the sides, forming the trapezoidal traces designers are familiar with. The longer time available for a side-attack of the traces by the etch solution means the in-plane distance between traces naturally increases.

Manufacturers will also scale the artwork for etch compensation to address the lateral etch of copper features underneath the etch resist application. This compensation factor will increase copper features while decreasing the air gap between them. In this sense, the scaling counteracts the increased air gap for thicker coppers (although scaling occurs for all thicknesses, not just those > 1 oz.) The relationship between the minimum gap and thickness is linear; intuitively, power circuitry typically needs larger area pours than several individual traces routed across the board, so there’s little sacrifice necessary when reducing routability for these board types.