Can a board carry 10 oz outside and 5 oz inside?

Yes. Keep one weight per layer — a single layer should not mix 10 oz and 5 oz copper — and apply each layer its own rules. Hitech Circuits quotes up to 20 oz on outer layers and 10 oz on inner layers, so a 10/5 split sits inside the published range and is a normal power-board stack-up.

Do through-holes follow the heaviest layer in the board?

A plated through hole follows the heaviest layer it actually passes through: 0.15 mm mechanical minimum, 0.1 mm by laser, 15:1 aspect ratio, with the annular ring sized for that layer. A hole that only crosses 1 oz layers is not held to the 10 oz rules, and blind or buried vias are judged by the layers they cross rather than by the heaviest layer on the board.

Where does mixing weights help most?

Power on the outside, signals inside. Outer layers take the wide current paths and the thermal connection to the enclosure; inner layers keep 1 oz or 2 oz for fine routing and controlled impedance. The result is a lighter, flatter and cheaper board than a uniform heavy build, with the same current capacity.

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Mixing Copper Weights in One Stack-Up

A power board rarely needs the same copper everywhere. Mixing weights works, as long as each rule follows the right layer.

Hitech Circuits Engineering Desk

Shenzhen, China · PCB fabrication and assembly

2 min read

Published: 2016-05-24

Last updated: 2026-10-18

Technical review: Process figures checked against our published capability sheet. View capability sheet

What mixing buys

A uniform heavy stack-up is expensive to build and hard to keep flat. It also solves a problem the design may not have: only a few nets carry the current, and only a few layers need the thermal path.

Mixing weights lets the copper follow the function. Heavy outer layers carry current and spread heat; thin inner layers hold fine routing and, where needed, controlled impedance. The published range accommodates this directly — 0.5–20 oz outside, 0.5–10 oz inside — so the choice is a design decision rather than a special request.

Three rules that follow the thickest layer

Plated through holes. A barrel that crosses a heavy layer is drilled, plated and cleared for that layer. The minimum finished hole is 0.15 mm mechanically or 0.1 mm by laser, and the aspect ratio stays at 15:1. The annular ring is sized against the copper weight, because the etch takes more of the pad on a heavy layer.
Clearance and mask dams. The gap between two conductors on the heavy layer, and the mask dam that sits in it, follow the heavy layer's minimum. A 1 oz layer next to it can hold a much finer gap; do not apply the fine rule to the heavy layer just because it is on the same board.
Balance and flatness. Copper is balanced across the stack-up, not per layer. Heavy copper on the outer layers and thin copper inside is acceptable if the lay-up is mirrored; heavy copper on one side only is what bows the panel, and bow and twist are held to 0.7 %.

What stays per layer

Minimum feature size. 0.075 mm line and space remains available on fine-feature layers; the heavy layer is quoted against its own limit.
Conductor tolerance. The ±20 % band applies per layer, because plating thickness and etch undercut depend on the weight of that layer.
Thermal relief. Pads on a heavy layer need relief sized for the heat the copper sinks; the same pad on a 1 oz layer does not.

Writing the stack-up table

Quote documents should list layer number, copper weight and dielectric thickness for every layer, plus the current each net carries and the permitted temperature rise. That table is what the fabricator prices and what DFM reviews; a note saying "heavy copper, 10 oz" leaves the most expensive decisions open.

The published range is on the heavy copper PCB page, and the design consequences of a mixed stack-up are covered in the design guide.

Technical Specifications

Outer layers: 0.5–20 oz
Inner layers: 0.5–10 oz
Layer count: 1–38 layers
Fine-feature minimum: 0.075 mm line / space
Aspect ratio: 15:1

Frequently Asked Questions

Can a board carry 10 oz outside and 5 oz inside?
Yes. Keep one weight per layer — a single layer should not mix 10 oz and 5 oz copper — and apply each layer its own rules. Hitech Circuits quotes up to 20 oz on outer layers and 10 oz on inner layers, so a 10/5 split sits inside the published range and is a normal power-board stack-up.
Do through-holes follow the heaviest layer in the board?
A plated through hole follows the heaviest layer it actually passes through: 0.15 mm mechanical minimum, 0.1 mm by laser, 15:1 aspect ratio, with the annular ring sized for that layer. A hole that only crosses 1 oz layers is not held to the 10 oz rules, and blind or buried vias are judged by the layers they cross rather than by the heaviest layer on the board.
Where does mixing weights help most?
Power on the outside, signals inside. Outer layers take the wide current paths and the thermal connection to the enclosure; inner layers keep 1 oz or 2 oz for fine routing and controlled impedance. The result is a lighter, flatter and cheaper board than a uniform heavy build, with the same current capacity.

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