Copper Weight

What Is Copper Weight?

Copper weight is the standard measure of copper foil thickness on a PCB layer, expressed in ounces per square foot (oz/ft²). One ounce copper corresponds to a foil thickness of approximately 35 micrometers (1.4 mils). Common copper weights include 0.5 oz (17.5 μm), 1 oz (35 μm), and 2 oz (70 μm), with specialty applications using 3 oz, 4 oz, or even heavier copper for high-current power electronics. The copper weight selection directly affects trace current carrying capacity, minimum achievable trace width and spacing, thermal dissipation capability, and overall board cost.

Heavier copper enables narrower traces to carry the same current and provides better thermal spreading, but it also increases etching difficulty and limits the minimum trace width and spacing that the fabricator can reliably achieve. A design using 2 oz copper may need wider spacing between traces than the same design on 1 oz copper, consuming more routing area. Multi-layer boards can use different copper weights on different layers — for example, heavy copper on power layers for current capacity with standard 1 oz copper on signal layers for fine routing.

Copper Weight-Aware Design Rules

The interaction between copper weight and achievable trace geometries is a critical constraint that must be reflected in design rules. Physics-driven AI layout tools that incorporate copper weight parameters into their trace width and spacing calculations can ensure that routing decisions are compatible with the actual fabrication capabilities for each layer's copper thickness. When engineers need to evaluate tradeoffs between copper weight and routing density, AI-generated layouts across different copper weight configurations provide concrete data for selecting the option that best balances current capacity, thermal performance, and routing density.

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