1 oz vs 2 oz Copper PCB: Thickness, Current and Design Trade-offs

The approximation is thickness ≈ copper weight in oz/ft² × 34.8 µm. One mil is 0.001 inch, not one millimeter. These values describe nominal copper thickness; acceptance limits must come from the approved drawing and material/process requirements.

Outer-layer traces can receive additional copper during hole and pattern plating. Inner-layer copper is commonly patterned from the starting foil without that same outer-layer buildup. Consequently “1 oz on all layers” can be ambiguous unless the drawing identifies the intended finished values and how they are accepted.

State layer-by-layer copper requirements and distinguish nominal or minimum finished thickness from starting foil. Hole-wall plating is a separate reliability requirement; a thick surface conductor does not prove that a plated hole has sufficient copper. See the PCB manufacturing sequence for where these operations occur.

For a uniform conductor, R = ρL/(w × t). Consider an illustrative 100 mm long, 1 mm wide trace at about 20°C, using copper resistivity 1.72 × 10⁻⁸ Ω·m. At 34.8 µm thickness its calculated resistance is about 49 mΩ; at 69.6 µm it is about 25 mΩ. This neglects etch shape, plating variation, temperature dependence and connections.

At an assumed 2 A, I²R gives roughly 0.20 W versus 0.10 W in that trace. This is a resistance example, not approval to carry 2 A. Temperature rise still depends on surrounding planes, board construction, enclosure, airflow and duty cycle. Neck-downs, connectors and vias may be the limiting features.

A wide external pour and a narrow internal trace with the same copper weight have very different heat paths. Choose a permissible temperature rise, then evaluate the real geometry and thermal environment with a suitable method such as IPC-2152-based guidance, simulation or a representative test. Safety-critical ratings need project-specific validation.

Check the entire current path: component lands, thermal reliefs, neck-downs, via transitions and connectors. Additional copper in a plane will not fix an undersized connector pin. For thermal boards, distinguish heat spreading in copper from heat transfer through dielectric to a heatsink.

Thicker copper generally requires more attention to etch compensation and spacing. Do not copy fine-line rules qualified for thinner copper into a heavy-copper build. Copper distribution can also affect resin fill and pressing; the final stackup may need adjustment.

A change from 1 oz to 2 oz changes trace cross-section and can shift controlled impedance. Recalculate widths and gaps against the approved dielectric construction. Material, etching, lamination and yield all affect cost, so ask for a construction-specific comparison instead of assuming a fixed percentage premium.

Send a layer table with starting or finished copper intent, minimum requirements where necessary, current-path geometry, finished board thickness and impedance groups. Flag fine-pitch regions and request confirmation of line/space rules for the selected copper.

If only power planes need thicker copper, ask whether a mixed-copper stackup is practical. Include thermal limits and the finished board thickness requirement so the quote addresses the whole construction, not only copper weight.