The capability extract shows in thirty seconds what runs as standard and what carries a surcharge.
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To the data check →Thicker copper carries more current and spreads more heat. It also etches differently: the acid works from the top down and sideways at the same time, so a 140 µm track comes out with a sloped flank and needs far more room than the 35 µm version you are used to.
Copper weight is usually quoted in ounces per square foot; 1 oz is roughly 35 µm. Heavy copper starts at 2 oz — 70 µm — and runs to 4 oz, 140 µm, in the builds we publish; anything heavier goes through a separate feasibility review. The current-carrying capacity scales with cross-section, so doubling the thickness roughly doubles the current for a given track width and temperature rise.
The design consequence is the etch flank. Etching removes copper downward and sideways at similar rates, so a thick track ends up trapezoidal — wider at the base than at the top, with the difference roughly proportional to thickness. That is why the minimum track and gap grow with copper weight, and why carrying a 35 µm design rule set into a 140 µm layer produces open circuits.
Cross-section is what carries current. 140 µm copper carries roughly four times what 35 µm does at the same width and temperature rise.
Thick copper is a lateral heat spreader in its own right, often removing the need for a separate metal core in moderate-power designs.
Signal layers at 35 µm with power planes at 105 or 140 µm is routine. You pay for thick copper only on the layers that need it.
| Copper weight | Min. line / gap | Typical current | Note |
|---|---|---|---|
| 35 µm (1 oz) | 75 / 75 µm | ~ 1 A per mm | Standard reference; outer-layer values |
| 70 µm (2 oz) | 150 / 200 µm | ~ 2 A per mm | Entry to heavy copper |
| 105 µm (3 oz) | 180 / 300 µm | ~ 3 A per mm | Common power plane weight |
| 140 µm (4 oz) | on request | ~ 4 A per mm | Upper end of the published range; confirmed per design |
| > 140 µm | on request | — | Not a published capability — separate feasibility review |
| Mixed weights | per layer | — | Rules differ per layer, not per board |
| Solder mask | thicker | — | Mask must cover a taller copper step |
Guide values for pre-selection. Binding values are confirmed per project against your data.
The points below are what most often comes back as a query after data review. Settling them before layout freeze saves a loop.
The etch flank widens with thickness. A design rule set written for 35 µm produces shorts and opens at 140 µm — the rules have to be per layer, not per board.
Put heavy copper only on the layers carrying current. Uprating signal layers costs money and forces coarse structures where you do not need them.
Mask has to cover a much taller copper step without thinning at the edge. On heavy copper outer layers this occasionally means two mask passes.
Drilling through 140 µm outer copper and plating the barrel behaves differently from a standard build. Give holes in heavy copper areas a generous diameter.
It depends on width, thickness, allowed temperature rise and whether the track is on an outer or inner layer. IPC-2152 is the reference. The figures in the table above are rough guides for a 20 K rise on an outer layer.
Heavy copper spreads heat laterally and carries current. A metal core conducts heat vertically away from a component. They solve different problems and are often used together.
Yes, and it is common for power planes. Inner layers etch from both sides of the core so the flank geometry differs slightly, but the rule that spacing scales with thickness still applies.
140 µm finished copper is the top of what we publish for rigid builds; rigid-flex runs to 5 oz, about 175 µm, after a special check. Anything heavier — and busbar bonding or embedded copper — is a different construction with its own feasibility review.
Send us your data or a rough sketch. We check feasibility, name the cost drivers and answer within one working day.