HEAVY COPPER SPECIFICATIONS
Heavy Copper PCB Capabilities: 3–10 oz, Trace/Space and Tolerances
Fabrication limits APTPCB works to for heavy copper PCBs, listed by copper weight: finished copper, minimum trace and space, annular ring, drill-to-copper clearance and lamination rules. Use the tables to check a layout before release. For copper-weight selection, quoting and assembly, see the heavy copper PCB manufacturer page.
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What are the heavy copper PCB capabilities at APTPCB?
Heavy copper trace, space and etch compensation by copper weight
| Finished copper | Thickness | Min trace | Min space | CAM etch compensation (per side) |
|---|---|---|---|---|
| 3 oz | 105 µm | 10 mil (0.25 mm) | 10 mil (0.25 mm) | +2.5 mil |
| 4 oz | 140 µm | 12 mil (0.30 mm) | 12 mil (0.30 mm) | +3.5 mil |
| 6 oz | 210 µm | 18 mil (0.45 mm) | 18 mil (0.45 mm) | +5.0 mil |
| 8 oz | 280 µm | 22 mil (0.55 mm) | 24 mil (0.60 mm) | +7.0 mil |
| 10 oz | 350 µm | 22 mil (0.55 mm) | 25 mil (0.63 mm) | +9.0 mil |
Values are design minimums for production. Where this page and older documents differ, the wider value in this table applies until confirmed at DFM.
Heavy copper drill, annular ring and lamination rules
| Rule | Limit | Why it matters |
|---|---|---|
| Annular ring allowance | +4 mil (3–5 oz); +5–6 mil (6–10 oz) over standard | Drilling thick copper deflects the bit and widens the hole position error. |
| Inner-layer drill-to-copper | ≥ 18 mil up to 4 oz; ≥ 25 mil from 6 oz | Prevents copper smear and shorts at the hole wall. |
| Copper balance between paired layers | Within ±15% area | Unbalanced copper bows the board during lamination and reflow. |
| Prepreg | High-resin 1080 / 2116 class; multi-ply for 6 oz and above | Resin has to fill the full height between thick traces without voids. |
| Thermal stress check | Microsection after solder float at 288 °C, 10 s | Confirms barrels and pads survive soldering heat. |
| Solder mask | 2–3 pass liquid photoimageable | One pass does not cover the edge of a thick trace. |
Board thickness, layer count and copper weight interact; extreme values in several rows on one board are confirmed only at DFM.
Heavy copper design limits to plan around
Heavy copper PCB capabilities FAQ
What is the minimum trace and space on heavy copper?
10/10 mil at 3 oz, 12/12 mil at 4 oz, 18/18 mil at 6 oz and 22/24 mil at 8 oz finished copper. Use the row for the finished weight, not the starting foil.
Can heavy copper and fine-pitch signal traces be on the same board?
Yes, on different layers. Heavy copper goes on power layers and standard 1 oz copper on signal layers in a mixed stackup. Fine-pitch parts cannot sit on a 6 oz outer layer because the minimum space is too wide.
How much larger should annular rings and drill clearances be on heavy copper?
Add about 3–5 mil to the standard annular ring for 6–10 oz copper, and keep inner-layer drill-to-copper clearance at 18 mil or more up to 4 oz and 25 mil or more from 6 oz.
How are voids between thick traces prevented?
High-resin prepreg is selected against copper height and pattern density, then lamination is checked by microsection. Spacing below the table values makes resin fill harder.
Why does the drawing need finished copper instead of base foil weight?
Plating adds copper on outer layers, so 2 oz base foil can finish near 3 oz. The trace/space rules and the current rating depend on the finished value.
Check your heavy copper layout against these limits
Send Gerber files and the stackup with finished copper per layer. Engineering returns DFM comments on spacing, drilling and resin fill with the quote.