Customized 0.5-15OZ Heavy Copper PCB Manufacturer What is Heavy Copper PCB? A Heavy Copper PCB is a printed circuit board that contains copper conductors 3 oz/ft² (≈ 105 µm) or thicker on any layer; the term is usually reserved for boards with ≥ 4 oz (≈ 140 µm) and can go up to 20 oz (≈ 700 µm) or more. The thick copper carries high continuous currents (tens to thousands of amps), provides low resistance and excellent thermal conductivity, and acts as an integral heat-sink.