Heavy copper boards are built for current, not for signals. Increasing the copper thickness increases the cross-section of every trace, so the same trace width carries more current with less temperature rise, and the copper spreads heat sideways under the components. Copper conducts heat at 401 W/m·K, an order of magnitude above the laminate around it, which is why these boards turn up wherever a converter, motor or power stage has to survive its own losses.
Where heavy copper is used
- Power supplies and converters — primary and secondary sides of switch-mode supplies, bus bars and shunt paths.
- Motor drives and inverters — three-phase output stages in industrial control and pump drives where the current has to reach a connector without a cable.
- Automotive — 48 V systems, battery management, starter-alternator and charging hardware under IATF 16949:2016, described further on the automotive PCBs page.
- Renewable energy — solar micro-inverters, string converters and storage interfaces, where heat and current have to be handled on the same board; see renewable energy.
- Welding, plating and traction equipment — industrial current paths, covered on the industrial control page.
From 0.5 oz to 20 oz
One ounce of copper is about 35 µm, so the range runs from thin inner-layer foil up to roughly 700 µm on outer layers. Heavy copper normally means 3 oz (105 µm) and above per layer. Where a stack-up mixes a power layer with a fine-feature signal layer, the signal layer is held to the plant's 0.075 mm minimum line and space while the heavy layer's minimum is set by its copper weight and confirmed in the DFM review — etching a 20 oz layer is not the same process as etching a 1 oz layer.
What changes in the design
Copper weight affects more than resistance. Creepage and clearance distances grow, thermal reliefs have to be sized so a heavy pad can still be soldered by hand or by reflow, solder mask openings and via treatment are adjusted, and copper balance across the panel decides whether the finished board bows during lamination and reflow. The 15:1 aspect ratio and 0.15 mm mechanical hole minimum are the same as for standard boards, and impedance can be held to ±10 % on layers that need it.
Assembly, test and documentation
Heavy copper panels run through four SMT lines at six million chips per day and three DIP lines at 1.6 million pieces per day, with reflow profiles set for the additional thermal mass. X-ray inspection covers joints under connectors, BGA rework and re-balling are handled in-house, and boards are fabricated to IPC-6012B and IPC-A-600H with UL recognition under file E354070.
Getting a quotation
Send the Gerber set with the copper weight per layer, the current each net has to carry, the permissible temperature rise, board thickness and quantity. Prototypes come back in 1–3 days and medium volume in 4–10 days; the capability page holds the process limits and the certifications page the issued certificates.
Heavy copper boards that go on to assembly are covered on the China PCB assembly page, together with component sourcing and box build.
