Thick Copper PCB Copy | Layer Separation Done Right

A thick copper PCB copy is doable, but it is not the same job as copying a signal board. The copper on these boards is typically 3 oz and up, the etch profile is steeply trapezoidal, dielectric layers are thicker and unevenly filled, and the wide pours hide via connections that a normal continuity sweep will happily short together. Get layer separation and copper weight measurement right and the rest follows. Get them wrong and you produce a board that looks correct and runs hot.

This page is written for the engineer or buyer who has a working (or dead) heavy copper board in hand, no design files, and needs a manufacturable set of data back.

What makes thick copper PCB copy different from a normal board copy

On a 1 oz board, a trace is roughly a rectangle. At 4 oz or 6 oz, it is not. Etching that much copper leaves noticeable sidewall taper, so the top width and the bottom width of the same conductor can differ by a meaningful amount. If you scan the top surface and call that the trace width, you have understated the cross-section — and cross-section is the entire point of a heavy copper board.

That matters because these boards exist to carry current. IPC-2152 relates conductor cross-section, temperature rise, and current-carrying capacity, and it is the framework the original designer almost certainly worked within. Our job is to recover the geometry the designer chose, not to normalize it into something tidier.

Three other differences show up on almost every heavy copper job:

• Non-uniform dielectric. Thick copper needs extra resin to fill between conductors, so the finished thickness between layers varies across the panel. A single caliper reading is not a stackup.
• Mixed copper weights. It is common to see 6 oz inner power planes with 1 oz outer signal layers, or a hybrid where only two layers are heavy. Assuming one copper weight for the whole board is the most frequent error we see in files customers bring us from elsewhere.
• Thermal mass. Wide copper sinks heat fast. Desoldering a large connector or a bus bar off a 6 oz pour without lifting pads takes real preheat discipline, and that affects both the copy work and any rebuild you plan afterward.

How layer separation works on a heavy copper board

Layer separation is the step where a multilayer board becomes a set of individual copper images. On a thin four-layer board, controlled grinding plus scanning gets you there quickly. On thick copper it takes longer and needs more checking, because the copper itself resists uniform removal and the resin between conductors abrades at a different rate.

Step order we actually follow

1. Document the assembled board first. High-resolution scans of both sides, silkscreen, reference designators, connector orientation, and any hand-added rework wires. Once components come off, this record is all you have.
2. Measure before disassembly. Overall thickness at multiple points, hole diameters, board outline, mounting hole positions, and where possible a copper thickness estimate on exposed pads.
3. X-ray the dense regions. On heavy copper boards, X-ray mostly tells us where buried and blind vias land and whether inner planes are split. Wide copper attenuates strongly, so we adjust exposure per region rather than shooting one image of the whole board.
4. Component removal and identification. Parts come off with logged positions and values. Power components — MOSFETs, shunts, current sense resistors, large inductors — get measured, not guessed.
5. Progressive layer removal and imaging. Each layer is imaged before the next is touched. Alignment fiducials carry through every scan so layer-to-layer registration is preserved.
6. Copper weight determination per layer. Sectioning and measurement on each copper layer separately, top width and base width, so cross-section is real rather than assumed.
7. Netlist reconstruction and comparison. The recovered net list is compared against continuity readings taken from a second sample where one is available, and against the X-ray via map.

The one thing we will not do is skip step 6 to save time. Copper weight is the defining parameter of the board class, and it is also the parameter a manufacturer will ask about before quoting production. If you want the general mechanics of multilayer imaging, our write-up on how layer count changes a multilayer copy covers the baseline process this builds on.

What we look at that a generic PCB copy shop skips

Heavy copper boards fail in specific ways, and the copy has to preserve the features that keep them alive:

• Thermal relief geometry on plated holes. A through-hole pin landing in a solid 6 oz plane is nearly unsolderable without relief. The number, width, and angle of the spokes are design decisions and get recorded as drawn.
• Plane splits and their gap width. Where a pour is divided into separate power domains, the split location relative to switching nodes matters. We map splits per layer rather than treating a plane as one net.
• Via count and pattern in current paths. Designers stitch heavy copper layers with arrays of vias sized for current. Reproducing 12 vias where the original had 20 changes the thermal behavior.
• Copper-free clearance around high-voltage nodes. Creepage and clearance spacing on the original is deliberate. IPC-2221 spacing tables are the reference; we flag any spacing that looks tighter than expected so you can decide, rather than silently “fixing” it.
• Solder mask behavior over wide copper. Mask registration and any deliberately exposed copper for solder reinforcement gets noted, since bare tinned pour is sometimes carrying current on purpose.

Which thick copper jobs are straightforward and which are hard

Honest answer: copper weight alone does not decide difficulty. The combination of copper weight, layer count, and via structure does.

Cases where we will tell you it may not be feasible from a single sample: stepped copper construction where copper thickness changes within one layer, boards where a heavy inner plane has already delaminated or been overheated in service, and boards with embedded copper coins or bus bars laminated into the stackup. Those are not impossible, but they usually need two samples — one to section destructively, one to keep intact as reference. Related classes like ceramic substrate board copy have their own separate constraints and are quoted differently.

What to send us, and what you get back

Send this with your first message

• Clear photos of both sides, whole board in frame, on a dark non-reflective background, even lighting, no flash glare on the copper.
• Board dimensions and total thickness, plus your best estimate of copper weight if you know it.
• Markings from the main control chip or any programmable part, read exactly as printed.
• Layer count if known, and whether the board has blind or buried vias.
• One line on which deliverables you need — Gerbers only, Gerbers plus BOM, full schematic, or a working rebuilt board.

What comes back

First a feasibility assessment: whether we can do it from one sample, what the risk points are, and what we would need to confirm during sectioning. Then a lead time and a price. Pricing on thick copper work is driven by layer count, board size, copper weight, component count, whether BGAs are present, whether firmware work is involved, and the deliverable set — so a quote follows the assessment rather than preceding it.

Deliverables normally include per-layer Gerbers with copper weight called out per layer, drill files with plating status, a stackup drawing with measured dielectric thicknesses, a BOM with power components verified by measurement, and a netlist. Schematic capture and re-layout are separate scopes. If your board also carries a locked microcontroller and you need the code recovered, that runs as a parallel workstream — you hold the rights to the design and the firmware, we work under NDA, and compliance with applicable IP law stays on your side of the table.

How long a thick copper board takes

Longer than the same layer count in 1 oz copper, and the gap widens with copper weight. Sectioning and measurement add real hours, and progressive removal on heavy copper cannot be rushed without destroying the layer underneath.

A two-layer 3 oz power board with modest component count is usually a few days. A four-layer board with 6 oz planes and a fine-pitch control section is meaningfully longer, mostly because each inner layer is imaged and measured separately. Add blind vias, or add a second sample for destructive analysis, and the schedule stretches again. We give a date after we see photos, not before. Boards that need RF section reverse engineering alongside the power section run on two tracks and are scheduled accordingly.

FAQ

Can you tell copper weight from photos alone?

No — photos give us a rough hint at best. Wide pours and heavy solder plating look similar across several copper weights. We can usually estimate from board thickness plus trace taper visible at high magnification, but the number we put on a deliverable comes from sectioning and measuring the actual sample.

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