Heavy Copper PCB Cost: How to Compare Quotes That Differ by Two to One

Why a heavy copper price spread is not one number

Treat any quote comparison as three separable layers.

Layer one is scope. Did all suppliers price the same physical product? If one assumed base copper where you meant finished copper, or assumed no dielectric filling between thick traces, it is not cheaper — it is quoting something else.

Layer two is process route. Two shops both meeting your spec may reach it differently: different copper build strategy, different etch approach, different lamination sequence. These are real cost differences and legitimately shoppable.

Layer three is commercial. Panel utilisation, tooling amortisation, minimum order handling, freight, and margin.

Most buyers compare layer three while the spread actually lives in layer one. Normalise scope first, and the remaining spread becomes a real decision instead of a guess.

The six places heavy copper quotes silently diverge

Each item below is one your supplier must resolve to produce a number. If your documents do not resolve it, they resolve it for you, and they are not obliged to tell you how.

1. Finished copper versus base copper

The most expensive ambiguity in heavy copper procurement. Plated copper adds to starting foil, so a requirement stated as a bare number without a measurement basis can be read two ways. The supplier reading it the cheaper way wins your comparison and ships thinner copper than you designed for.

It is also the easiest to close: state the copper requirement per layer, name the basis explicitly, and say where it is measured. This is covered in detail in finished copper thickness versus base copper in the PO.

Ask every supplier to restate copper by layer and by basis in their quote. Any quote that will not restate it has not been normalised.

2. Trace geometry tolerance and etch allowance

Thick copper cannot be etched with the same sidewall behaviour as thin foil. As copper gets heavier, the etched edge becomes less vertical, and the manufacturer must compensate by adjusting the artwork or widening the spacing envelope.

If your drawing gives nominal widths without telling suppliers how much compensation is acceptable or which dimension is critical, each shop applies its own house rule. Those rules differ enough to change both price and whether the board passes your own electrical checks.

What to normalise: state which conductors are current-carrying and dimensionally critical, and which are routing you will accept compensation on.

3. Spacing and dielectric filling between thick conductors

Heavy copper conductors leave deep gaps that resin must fill during lamination. Filling them reliably can require extra resin content, different prepreg selection, or an additional lamination step. A supplier who assumes your gaps are wide enough to fill with a standard stack will quote low; one who plans for a filling strategy quotes higher and is often the one who has read your drawing properly.

This is the item where the cheapest quote most often turns into a change request after engineering review.

4. Layer construction and how thick copper stacks

Putting heavy copper on inner layers is a different manufacturing problem from putting it on outers, and the number of heavy layers changes the construction options available. Constraints here are structural rather than negotiable, and they are laid out in thick copper multilayer layer count limits.

For quote comparison, the question is narrower: did each supplier price the copper distribution you actually asked for, layer by layer, or did they price a simplified version? Ask for the layer-by-layer copper assignment back in writing.

5. Holes, plating and thermal features

Thermal vias, large plated holes, via arrays under power devices, and any structure intended to move heat all carry process cost that a generic hole count does not capture. A quote built from hole count alone has not priced your thermal intent.

If your board relies on copper structures for heat removal, those features need to appear as requirements rather than as geometry the supplier infers. The interface side of this is covered in defining the high-current connection interface in your RFQ.

6. Surface finish and mask over heavy copper

Solder mask behaves differently over tall copper features, and finish choice interacts with how the board will be joined — bolted, pressed, or soldered. Leaving finish as "supplier standard" invites the cheapest option, which may not survive your assembly or field conditions.

Normalising quotes: the requote pass

Do not compare until the quotes describe one product. A short, structured requote round is cheaper than a post-award change.

Send every supplier the same clarification request and ask them to confirm in writing:

• Copper weight per layer, with basis stated and measurement location named
• Which conductor dimensions they treat as critical and what compensation they applied
• Whether their flow includes a dielectric filling strategy for the specified gaps, and if so what it adds
• The layer-by-layer construction they priced, including heavy layer placement
• Which holes and thermal features they priced as special process
• Surface finish and mask treatment assumed
• Any item they flagged as needing feasibility review before the number is firm

Then rebuild the comparison. Quotes that shift upward when asked to restate scope were never comparable. Quotes that hold steady and answer specifically are the ones carrying real information.

The general mechanics of forcing a quote onto a fixed document basis appear in the fabrication specification sheet that binds a quote.

Reading the spread after normalisation

Once scope is level, a remaining spread tells you something useful.

A narrow spread means the board sits inside everyone's comfortable range. Decide on lead time, communication quality and acceptance terms.

A wide spread with consistent scope usually means the board sits at the edge of some suppliers' process window. The high quotes are pricing risk they can see. Ask the low bidder which step they consider hardest — a specific answer is reassuring, a dismissive one is not.

An outlier low quote that survives requoting deserves one more question: what does their process do by default that makes this board easy? Sometimes the answer is a genuinely good fit. Sometimes it reveals they are still pricing a simplified version.

What cheap actually costs later

An underscoped heavy copper order does not fail at the quote stage. It fails at engineering review, at first article, or at incoming inspection — and by then you have lost schedule, not just price.

Two places to close the loop: define what evidence you require before parts ship, per heavy copper PCB purchase specification and acceptance evidence, and agree the incoming criteria in advance, per the incoming inspection acceptance plan.

If you also need the shortlist stage covered, requesting process evidence up front is described in heavy copper supplier process evidence requests.

Where copper weight itself comes from

This guide assumes copper weight is already fixed. If it is not — if you are still working from current and temperature rise — that derivation is a separate exercise and is covered in deriving copper weight from current and temperature rise. Do not attempt to settle copper weight during a price comparison; you will end up negotiating an engineering input, which is how underspecified boards get ordered.

To start a comparison on a fixed basis, submit the package through our quote request and review the heavy copper PCB product page for the declaration fields to fill in.

FAQ

Why do heavy copper quotes vary more than standard PCB quotes?

Because heavy copper touches more process decisions. Copper weight interacts with etching, spacing, resin filling, construction and plating, so each unstated requirement becomes a supplier assumption, and assumptions differ.

Is the cheapest heavy copper quote always underscoped?

No. It can reflect a genuinely good process fit or better panel utilisation. The test is whether the number holds when the supplier is asked to restate copper basis, filling strategy and construction in writing.

What single document change reduces quote spread the most?

Stating copper per layer with an explicit measurement basis. That one ambiguity produces the largest and most consequential differences.

Should I tell suppliers what other quotes came in at?

Sharing numbers invites matching rather than explaining. Sharing the clarification questions is more useful, because it forces every supplier onto the same scope.

How many suppliers should I compare for heavy copper?

Enough to see a pattern, few enough to run a real requote round with each. A normalised comparison of three beats an unnormalised comparison of eight.

Can a heavy copper quote be firm without feasibility review?

Sometimes, but not when the board sits near a process limit. A supplier who flags an item for review before firming the number is describing their process honestly, which is information worth having.