Custom Heavy Copper PCB Quotes: What "Custom" Actually Covers

The word "custom" is an instruction for the supplier to fill in the blanks

You sent out one line: *custom heavy copper PCB, 6 oz, 4 layers, 180 × 120 mm, 100 pcs.*

Three quotes came back at meaningfully different prices. The natural next step is to ask why — cheaper laminate, open capacity, someone buying the job.

All of those are possible. But before investigating any of them, confirm something more basic: the three suppliers may not have quoted the same board.

That one line contains exactly four specified parameters: copper weight, layer count, outline, quantity. A heavy copper board needs far more than four decisions before it can be released to production — whether 6 oz means base or finished copper, which minimum line width tier applies at that copper weight, how solder mask behaves over tall copper features, what dielectric thickness the stackup needs, the minimum drill diameter, surface finish, finished thickness tolerance, routing method, electrical test, and who decides the panel array.

None of those blanks stay blank. To produce a number, engineering has to fill them — using that factory's own standard tier. Those tiers are a product of each shop's equipment, process window, and historical order mix, so they differ from shop to shop.

The result: one phrase became three different process routes, and three prices that each describe a different board. You are not comparing three bids on one job. You are comparing three bids, each on that supplier's own default interpretation.

That is what "custom" does in a heavy copper quote. It carries no specification. It carries one signal — *there are nonstandard requirements here, but I have not said which ones* — and the only thing a supplier can do with that signal is define them in whatever way is most convenient to produce.

> The goal here is not a lower price. It is comparable quotes, and a selected quote that cannot be reinterpreted after the PO. Both depend on the same thing: whether each nonstandard item has been assigned to a bucket.

Three buckets: every nonstandard item lands in A, B, or C

List your nonstandard requirements, then ask one question per item: is this already priced, does it need separate confirmation, or can this supplier not do it at all?

There are only three answers, and they demand completely different follow-up:

The value of this table is that it eliminates a middle state. The dangerous nonstandard items are not the rejected ones — they are the ones neither confirmed nor rejected. The supplier treated the item as "we'll sort that out later"; you read the quote as "that must be included." Nobody acted in bad faith, and you now have a scheduled change order.

The test is blunt: any nonstandard requirement not mentioned verbatim in the quote or the covering email is not bucket A by default. Not "probably included" — assume excluded. The price was calculated against the supplier's own filled-in version, and if your requirement never appeared there, it never entered the calculation.

A practical way to classify B and C: watch the verbs in the reply.

• "We can do that," "standard for us," "within range" → leaning A, but still get it in writing
• "We need to evaluate," "let me confirm," "depends on the structure," "engineering will review" → this is B; the current price excludes it
• "That's difficult," "we don't usually go that far," "possible but needs special processing," "that would be outsourced" → this is C; do not read it as A

"Possible but needs special processing" is the one most often misread as A. What it actually means is: achievable, but off the standard route, therefore off the standard price. The moment those words appear, a C item exists — only the charge has not landed yet.

Where heavy copper requirements actually land in B and C

Heavy copper nonstandard items share a trait: they are rarely independent checkboxes. They are mutually constraining combinations. Each parameter can sit inside the supplier's tier while the combination falls outside it. This is the single most common failure mode in heavy copper RFQs.

Roughly from easier to harder:

1) Line width and spacing, as a function of copper weight

Heavy copper traces are etched down from thick foil. More copper means longer etch time and more sidewall loss. The same minimum line width that is routine at 2 oz may require special etch compensation — or a different process — at 6 oz.

So asking "what is your minimum line width?" on its own is close to meaningless. The answer will describe the supplier's thinnest copper. Bind the two numbers together: *at my copper weight, what is the minimum line width and spacing?*

Typical B case: your copper weight is in range, your line width is in their published range, but the combination needs engineering to calculate compensation before anyone can commit.

2) Finished copper vs. base copper

The most frequent source of genuine misunderstanding in heavy copper quoting. If "6 oz" does not state base or finished, the supplier's reading determines which foil they start from, whether plating is added, and the actual cross-section you receive.

This rarely becomes a C item — most shops can do either. It becomes a basis problem: the two readings cost different amounts, so the quotes differ. Comparing without declaring it means comparing two different things.

3) Solder mask coverage over tall copper features

Thick copper creates tall steps that mask must climb and cover evenly. A single standard mask pass may leave thin sidewall coverage at high copper weight, requiring added thickness, additional passes, or a process change.

High probability of B, because it depends on your specific trace density and copper weight rather than a general capability anyone can pre-commit. It becomes C when you impose a specific thickness or appearance criterion that the supplier's standard flow produces no inspection record for.

4) Mixed copper weights across layers

Outer layers at 6 oz with inner layers at 2 oz, or a single thickened layer. Extremely common on power boards — and from a process standpoint it is not "a 6 oz board" at all. It is a structure requiring a reworked stackup and lamination plan.

This is almost always B. It cannot be conveyed by one copper-weight field. List copper weight per layer. This is also exactly why single-value "6 oz" heavy copper RFQs get kicked back at engineering review.

5) Dielectric thickness against finished board thickness

Heavy copper consumes vertical space. Fitting a given layer count and copper weight inside a fixed finished thickness compresses the dielectric. When your finished thickness is pinned by a mechanical constraint — a slot, a card guide, a mating connector — that constraint collides directly with copper weight.

B when engineering must propose a stackup to confirm feasibility. C when your thickness and copper weight combination cannot be built from the materials they stock.

6) Minimum drill diameter in a thick board

Heavy copper boards tend to be thicker overall, which raises aspect ratio and makes plating distribution in small holes harder. "We can drill that diameter" and "we can drill that diameter in *your* board thickness" are two different statements.

7) High-current structures

Embedded copper coins, bonded bus bars, selective plating, integrated heat spreaders. At many shops these are unambiguous C items — not impossible, but not inside the standard heavy copper line, requiring a separate process arrangement.

If your design contains one, it belongs in the first sentence of the RFQ, not buried in one layer of an attached drawing. Undiscovered means unpriced; unpriced means a change order after the PO.

8) Surface finish interactions

Some finishes carry extra conditions at high copper weight, over large exposed copper areas, or where subsequent joining is planned. The finish alone is usually A — but combined with "large bare copper thermal area" or "bus bars will be soldered later," it converts to B.

9) Test and inspection requirements

Electrical test, cross-section coupons, specific inspection records and report formats. This is the item buyers drop most often, because it is not a property of the board — it is a property of acceptance.

A standard quote includes that supplier's routine testing. It does not include anything you specified beyond it. Any non-routine inspection, report format, or retained-sample requirement is B or C by default.

10) Routing and panel array

Non-rectangular outlines, internal slots, castellated edges, beveling, tightened tolerances. Plus one item that is almost always overlooked: who decides the array. If the supplier panelizes for best material yield while your assembly line needs a specific array format and rail geometry, that is an undeclared nonstandard requirement.

Writing the RFQ so "custom" becomes quotable

What those ten items have in common is that none of them can travel inside the word "custom." Replace it.

Step one: turn the adjective into fields.

Not "custom heavy copper PCB, 6 oz, 4 layer." Instead:

```

Layer count:

Copper weight per layer (list each; state BASE or FINISHED):

Finished board thickness + tolerance:

Outline dimensions + routing requirements:

Minimum line width / spacing (at the copper weight above):

Minimum hole diameter + tolerance:

Dielectric thickness requirement (state the source if mechanically constrained):

Solder mask: type / color / coverage requirement over heavy copper steps:

Surface finish + any large bare copper area or later joining operation:

Special structures (copper coin / bus bar / selective plating / heat spreader): YES / NO

-- if YES, attach a location drawing

Electrical test requirement:

Inspection and documentation requirements (incl. report format, retained samples):

Panel array: SPECIFIED BY US (drawing attached) / SUPPLIER'S CHOICE

Quantity + required delivery:

```

Every field does the same job: it converts a blank the supplier would have filled with an invisible default into a known value you supplied. Fill it, and they quote your version. Leave it, and they quote their default — which is not visible to you when the price arrives.

Step two: ask for the bucket assignment explicitly in the RFQ.

The highest-leverage sentence here, and the one almost nobody writes. Add it at the end of the RFQ:

> Please classify each nonstandard requirement in your quotation as: (A) included in this quotation; (B) quotable only after engineering confirmation — state what must be confirmed and when a conclusion will be available; (C) outside your standard process range — state whether a special process can achieve it and what that changes. Any item not classified will be treated by us as (A), included in the current quoted scope.

That last sentence carries all the weight. It reverses the burden of proof: without it, silence means "not priced." With it, silence means "priced." A supplier who wants to exclude something must actively mark it B or C — which is precisely the information you were missing.

Step three: require a conclusion date on every B item.

The real risk in a B item is not the surcharge. It is that it stays open. It sits at "engineering is still reviewing" until schedule pressure forces you to place the PO without an answer. So each B item needs two fields: what is being confirmed, and when the answer arrives. A B item with no date is a deferred C item.

Step four: reference the scope basis in the PO.

After the comparison is done, the PO should not reference "your quotation dated X." It should reference "your quotation dated X, together with the bucket-A confirmed scope list and the bucket-B supplemental pricing conclusions."

A quotation usually carries only a total. Attaching the bucket list to the PO is what gives that classification contractual force. Otherwise the three-bucket exercise was internal housekeeping and binds nobody.

Asking the right question: tiers, not ceilings

There are two ways to probe a supplier, with very different results.

Ineffective: "How many oz can you run?" "What's your minimum line width?" "What's your smallest hole?"

Each answer is a single-parameter maximum, and single-parameter maximums almost never hold simultaneously. The shop that runs 20 oz is not holding its published minimum line width at 20 oz. The shop with the smallest drill is not holding it at maximum board thickness. You end up with a collection of ceilings that assemble into no buildable board.

Effective: "At my copper weight, board thickness, and layer count, what are your standard tiers for each parameter? For anything outside those tiers, is it special processing or is it a no?"

That question targets the tier structure, which is the actual logic generating the price. The answer sorts your requirements into A, B, and C without further prompting.

Three more structural questions worth asking:

1. "Which revision of my data was this quoted against?" Confirm they priced the current one. Change copper weight or stackup on a heavy copper board and the pricing basis changes with it.
2. "How far does the engineering charge extend?" It typically covers one data preparation pass. Whether your later revisions are rechargeable is a pre-PO question, not a discovery to make mid-revision.
3. "Which items would trigger a change-control process if problems appear after release?" This asks for their own risk register — effectively inviting the supplier to name their B items unprompted.

The short version

"Custom" is not a specification. It is a blank you asked someone else to fill in. Break it into fields, require A/B/C classification, put a conclusion date on every B item, and reference the bucket list in the PO. Those four steps are what turn a quote from a number into a document that binds.

Heavy copper nonstandard items rarely surface during quoting. They surface after the PO, during production, before delivery — under the heading "engineering change." By then there are no longer three quotes to compare.

To organize copper weight, layer count, and structural requirements into per-field form and confirm their bucket assignments, see how specification fields are grouped on the heavy copper PCB product page, or submit a data package with your nonstandard list through the quote request. For mixed-weight multilayer constructions, the multilayer PCB page covers the stackup side. If overall process boundaries still need confirmation, review the capabilities page or raise an engineering question via contact.

FAQ

Q1: The quote says "custom heavy copper PCB" — doesn't that mean my special requirements are included?

No. That line names the inquiry; it does not define the scope. One test applies: was each of your nonstandard requirements mentioned verbatim in the quote or the covering email? Anything absent did not participate in the pricing. The fastest fix is to send your nonstandard list back and ask for item-by-item A (included) / B (needs confirmation) / C (cannot do) classification.

Q2: The supplier said "we can do it, but it needs special processing." Is that in the price?

No. "Special processing" means off the standard route, therefore off the standard price. Those words signal that a C item — or at minimum a B item — already exists, with the charge not yet landed. Immediately ask two things: what the special processing physically involves, and whether it is included in the quoted unit price.

Q3: I wrote "6 oz." Why did engineering come back asking for copper weight per layer?

Because "6 oz" cannot describe a multilayer board. Each layer can carry a different copper weight, and outer-layer and inner-layer heavy copper are realized differently in the first place. From one number, engineering cannot fix the stackup, the lamination plan, or the dielectric configuration. Per-layer copper weight, plus a base/finished declaration, is the minimum viable information for a heavy copper RFQ.

Q4: Why shouldn't I just ask for their minimum line width?

Because that answer will come from their thinnest copper. Heavy copper etches longer and loses more sidewall, so the same line width carries a completely different difficulty at different copper weights. Bind the two together — *at my copper weight, what is the minimum line width and spacing* — and the number you get is valid for your board.

Q5: Can I place the PO with open B items and settle them afterward?

Technically yes; from a risk standpoint, no. Once a B item enters production, your leverage is gone, and if the conclusion is "cannot do," the redesign cost and schedule hit are entirely yours. Set a conclusion date per B item and resolve them pre-PO. When that genuinely is not possible, at minimum state in the PO that the item is unresolved and define what happens if the answer is negative.

Q6: Three quotes are far apart. Is it wrong to start with the lowest?

Start with the source of the spread, not the ranking. The gap may reflect real process cost differences, or it may reflect different assumptions each supplier made about what you left unspecified. Align all three bucket classifications on one sheet and you will often find the lowest bid simply defaulted several items to looser tiers. Compare after the basis is unified — that is when you are comparing the same board.

Q7: Does the panel array count as a nonstandard item?

It does once you have a requirement. If you say nothing, the supplier panelizes for best material yield — fine at the bare board stage, but a problem if your downstream assembly needs a specific array format, rail geometry, or tooling holes. Stating "array specified by us (drawing attached)" versus "supplier's choice" in the RFQ prevents discovering a format mismatch when the first shipment lands.

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