The limit, stated plainly
Heavy copper at Hitech Circuits runs from 0.5 oz to 20 oz on outer layers and 0.5 oz to 10 oz on inner layers, on boards 1–38 layers and 0.1–6.0 mm thick. Twenty ounces is about 700 µm per side.
Above that, the process does not simply take longer. It changes at several steps at once, and each change costs yield.
What changes above it
| Step | What changes |
|---|---|
| Prepreg and lamination | Resin-rich grades fill a deeper copper step; extra lamination cycles may be required |
| Drilling | More bit wear and firmer stack support; hole position and aspect ratio stay inside the same limits |
| Plating | Several cycles rather than one pass, each calculated from the racked area |
| Etching | Multi-pass removal to keep the top and bottom of the trace even |
| Solder mask | Two prints to cover the step without skips and trapped air |
| Handling and flatness | Heavier panels scratch and bow more easily; bow and twist still held to 0.7 % |
The order matters. Lamination and drilling limit the build before the plating bath does, which is why an ultra-heavy request is quoted from the stack-up rather than from a copper weight alone.
Three alternatives worth comparing
Copper inlay. A machined or pressed copper slug set into the laminate carries very high current in a defined area without thickening the whole layer. It is a common answer for battery terminals and high-current pads.
Parallel layers. Two 10 oz layers tied together with a full via field carry the same current as one 20 oz layer in most geometries, and each layer stays inside the standard process.
A busbar. Where the conductor leaves the board, a busbar is cheaper, cooler and mechanically stronger than any laminate. Heavy copper planes feeding a busbar is the usual architecture in converters and traction hardware.
None of these is a workaround for a badly specified design; they are standard ways of moving current that a laminate alone should not carry.
How to quote an above-limit request
Send the current per net, the permitted temperature rise, the run length and the termination — a connector, a stud, a welded tab. With those, the answer is a stack-up, an inlay, a busbar or a combination, and it can be priced honestly.
What does not work is quoting 40 oz as if it were a heavier version of 20 oz. The production impact lands on lamination, drilling, etching and mask, and a supplier who quotes it without saying so has not priced the build. The published range is on the heavy copper PCB page and the capability page; for the current paths themselves, the industrial control page covers the application.
