PCB Fabrication Specifications: Writing a Sheet That Binds the Quote

The quote did not become non-binding. It was never written down tightly enough

A familiar sequence. You send a package, a price comes back, you release the order. Weeks later something is different: the surface finish is not what you pictured, the copper reads thinner than expected on a cross-section, a hole size sits outside what you assumed, or a cosmetic mark is called acceptable by the supplier and unacceptable by you. You go back to the quote. The quote references your files. Your files contain a number, and nothing else.

Almost every dispute of that shape traces to the same root, and it is usually not bad faith. It is that the specification named a value without naming how the value is measured, what document decides pass or fail, and which file wins if two files disagree. A supplier quoting against an incomplete sheet has to fill the gaps with its own defaults in order to produce a price at all. Those defaults are legitimate. They are simply not yours, and you never saw them.

There is a second, quieter version of the same problem. Online estimating is explicit about its own limits. PCB168's quote page says a calculator gives an instant estimate, that Gerber upload is what produces a precise quote, and in plain words that "final price depends on Gerber file review. This is an estimate only." Read that as a design statement rather than a disclaimer. The estimate prices a geometry. The engineering review prices your requirements. Whatever your requirements do not say, the review will resolve on your behalf.

So the practical question is not how long the specification should be. Long sheets full of restated defaults are common and change nothing. The question is what has to be present in each field for a price quoted against it to be traceable afterwards.

The four things every field needs

For each requirement you care about, write four items. Not four sentences necessarily, but four decisions.

1. The value. A number or a named option, with units and the stage it refers to. "1oz copper" does not say whether that is base foil or finished thickness after plating. "0.2mm hole" does not say finished or drilled. Stage ambiguity is the single most common source of a legitimately different delivered board.

2. The method. How the value gets measured or judged, and where. A copper thickness measured on a coupon is not the same measurement as one taken in a cross-section of a plated through hole wall, and neither is the same as an average across a panel. Impedance is a good case in point: PCB168's capabilities page publishes ±5% impedance tolerance and states TDR-verified. The tolerance alone is a number. "TDR-verified" is the method that makes the number checkable. Your sheet needs both, including whether the measurement is on a coupon travelling with the lot.

3. The criterion document. Which document decides acceptable versus not, at what class or level, and what happens to conditional cases. This is where most sheets stop short by writing a standard's name without a class, which is close to writing nothing. It also covers who dispositions a borderline part, and whether a waiver for one lot creates a precedent for the next one.

4. The priority. Where this field sits if two of your own documents disagree. You will have a fabrication drawing, a Gerber set, a drill file, possibly an assembly drawing and a PO. They will not agree forever. Declaring the order of precedence once, in the specification, removes the whole class of argument.

Any field that carries all four is a field the supplier can price and you can later verify. A field missing item 2 or 3 is a field where two parties can both be right.

Field by field: what a bindable line looks like

The pattern is easier to read as examples. Each pair below is a real field, written weakly and then written so it binds.

Copper thickness.

Weak: 1oz copper, 2oz inner.

Bindable: base foil weight and required finished thickness stated separately, by layer position, with the measurement location named, and the acceptance document and class cited. The reason this field deserves care is that finished copper on an outer layer is the result of plating added to base foil, so a sheet that names only one of them has named half a requirement. PCB168 covers the declaration mechanics for exactly this field in finished copper thickness versus base copper in a PO. For heavy copper work the heavy copper page publishes 3oz to 20oz across 1-16 layers, which tells you the band available, not which convention your line is written in.

Layer count and stackup.

Weak: 6 layer, 1.6mm.

Bindable: the layer count, the dielectric and copper sequence, whether the supplier may substitute an equivalent construction to hit thickness, and if so what has to stay fixed. Thickness is an outcome of the build. If you fix thickness and leave the build open, you have authorised substitution without saying so. The capabilities page publishes 1-40 layers and 0.2-6.0mm thickness as the outer envelope; inside that envelope, the specific construction is your call or theirs.

Hole sizes and tolerances.

Weak: a drill table with diameters.

Bindable: finished hole size and tolerance separately from drilled size, plated versus non-plated stated per size, and tolerance class cited. Published capability gives you the floor — 0.1mm mechanical and 0.075mm laser on the capabilities page — but a floor is not a tolerance, and a diameter without a stage is the classic case of two documents both being honest.

Surface finish.

Weak: ENIG.

Bindable: the finish plus its thickness ranges, the acceptance document, and whether an alternative may be offered. HASL, ENIG, OSP and immersion tin/silver are published as available on the capabilities page. Which one you get is a choice; the thickness window inside it is a separate requirement that affects both solderability and price.

Impedance-controlled nets.

Weak: 50 ohm controlled impedance.

Bindable: which nets or layers, target and tolerance, whether a coupon is required, how it is measured and whether the report ships with the lot. Without the coupon and report clauses you have specified a target with no evidence path, and the board can be delivered compliant on paper.

Material.

Weak: FR-4.

Bindable: grade and Tg, whether an equivalent is permitted, and if permitted, which properties must match and who approves the swap. FR-4 is a family, not a material. The capabilities page publishes Tg135/150/170/180 among its options, which is the point: naming the family leaves the grade to the person pricing it.

Markings and cosmetics.

Weak: silkscreen per Gerber.

Bindable: what must remain legible, what may be clipped or shifted, whether legend may be moved off pads, and where date or lot codes go. Legend gets adjusted during production more often than buyers expect, and a sheet silent on it has delegated the decision.

Inspection and test.

Weak: 100% tested.

Bindable: which tests, sampling versus full, whether records are delivered, and retention. The capabilities page publishes AOI on every layer, 100% electrical testing by flying probe or fixture, microsection for validation, X-ray for BGA and via fill, and cleanliness testing per IPC. Note what that is: a statement that the operations exist. Whether a record for your lot arrives with your boards is a separate line you write. For the assembly side of defining this, PCBA test and inspection requirements in an RFQ covers scope definition in more depth.

Panel and delivery form.

Weak: silence, or panelise as needed.

Bindable: array or singles, rail treatment, separation method, and edge acceptance. This one is frequently omitted and frequently expensive, because panel form is an assembly input as much as a fabrication one. Edge criteria are covered in board edge depaneling acceptance criteria.

Three phrases that quietly hand the decision back

Some wording looks like specification and functions as delegation. Three are worth naming because they appear in most sheets.

"or equivalent." Attached to a material, a finish or a laminate grade, this transfers the equivalence judgement to whoever is pricing it. Equivalent in what respect? Tg, Td, dielectric constant, loss, CTI, filler system, and thermal reliability are different axes, and a substitute can match one while diverging on another. If you want substitution allowed — often you do, for availability — then say which properties must match and who signs off. "Or equivalent, subject to written approval, matching Tg and dielectric constant" is a usable clause. Bare "or equivalent" is an open option you granted for free.

"per IPC." IPC publishes classes, and the class is the requirement. A citation without a class gives the supplier a legitimate choice between acceptance levels that differ materially in cost and in what gets rejected. If a field references a standard, reference the class as well, and state how conditional or borderline conditions are dispositioned.

"industry standard" / "normal practice" / "as usual." These describe the supplier's own defaults by definition, since they are the one with the practice. Used in a sheet, they are an instruction to apply house rules. Sometimes that is exactly what you want on a field you genuinely do not care about — and in that case, say so explicitly, so that a later surprise is one you knowingly accepted rather than one you discover.

A short sheet where uncontrolled fields are explicitly ceded is stronger than a long one full of soft phrases. The goal is not to control everything. It is that both parties know which fields are controlled.

The precedence clause

Write one paragraph, once, near the top of the specification. It should say which document governs when documents conflict, and what happens when a conflict is found.

A workable version reads: this specification governs; where it is silent, the fabrication drawing governs; where the drawing is silent, the Gerber data governs; the drill file governs hole locations; the PO governs quantity, price and delivery only. On discovering any conflict, the supplier stops and requests written clarification rather than selecting an interpretation, and any resolution is issued as a new revision rather than an email.

That last sentence is the working half of the clause. Without it, precedence tells the supplier which file to follow, and they follow it silently — which means a conflict you would have wanted to know about gets resolved without you. With it, conflicts surface before production instead of at incoming inspection. The mechanics of running that process once a conflict does appear are covered in the PCB fabrication notes conflict checklist.

Revision control belongs in the same paragraph. Name the specification with a revision identifier, require the quote to cite the revision it priced, and treat any later change as a new revision with a new price confirmation. A quote that cites "your files" is not traceable to anything. A quote that cites "Specification SPEC-1234 Rev C" is.

Three reconciliation steps when the quote comes back

The sheet is half of it. The other half takes about twenty minutes and is skipped more often than it is done.

Check what revision was quoted. The quote should name the specification and its revision, not just a project name or a file bundle. If it does not, ask for it in writing before releasing. This single line is what makes every other clause enforceable later.

Read the exceptions list as the real specification. Any professional quote carries deviations, assumptions and clarifications, sometimes on a second page and sometimes in a short paragraph. Whatever appears there overrides your sheet on those points, because by accepting the quote you accept them. If a field you care about appears in that list, it is no longer specified the way you wrote it. Compare the two documents field by field on the ones that matter.

Confirm what is included versus quoted separately. Coupons, cross-section reports, electrical test records, material declarations, first-article documentation: each either sits inside the quoted price or does not. The quote page states that an engineer reviews the design within two hours, which is the moment to raise these, before a price is set. Documentation added after the order is a change, and changes are priced.

If your requirements are complex enough that the exchange is getting long, the capabilities page is the fastest way to see whether what you are about to specify is inside the published envelope before you write it, and PCB168's stated response time for written enquiries is within 24 hours.

FAQ

Is a quoted price binding?

Commercially that depends on your terms, not on the specification. What the specification determines is something different and more useful: whether the requirement the price was based on can be identified afterwards. A price quoted against a sheet with values but no methods or criteria can be honoured to the letter and still deliver boards you consider wrong. Binding, in the practical sense, means traceable to a stated requirement.

How long should a fabrication specification be?

Length is not the variable. Coverage is. A two-page sheet where every field you care about carries value, method, criterion and precedence, and where uncontrolled fields are explicitly ceded, outperforms a ten-page document that restates defaults and leaves methods open. Write fully on the fields that affect function, cost or acceptance. Cede the rest on purpose.

Do I need this for a prototype?

Less of it, but not none. For a prototype you usually still want copper convention, hole stage, finish, material grade and panel form specified, because those four to five fields are the ones that make a later production quote comparable. If the prototype is priced against unstated defaults, the production quote has no baseline to be compared with.

What if the supplier's quote contradicts my specification?

That is the useful outcome, and it is why the exceptions list matters. A contradiction raised at quote stage costs an email. The same contradiction discovered after delivery costs a lot. Ask for each deviation to be stated as a line item, decide each one, and have the accepted set written into the order.

Can I just cite a standard and stop there?

Only if you cite the class and say who dispositions borderline conditions. A standard names requirements at levels; without the level, you have named a document rather than a requirement. Also state whether a waiver on one lot applies to subsequent lots, because silence there tends to be read as yes.

Does an online instant quote work for a specified build?

It works for what it says it does. Instant estimating prices geometry quickly, which is genuinely useful for budgeting and comparison. PCB168's quote page is explicit that the final price depends on file review. For anything with controlled impedance, a defined stackup, heavy copper, HDI structures or documentation requirements, treat the estimate as a starting figure and get the written quote that cites your specification revision.

Related links

• PCB manufacturing capabilities
• instant quote page
• heavy copper PCB page
• HDI PCB page
• Amber-lit PCB production room with a large panel clamped on an open machine platen, a four-camera alignment display above it, a row of similar tools receding to the left and operators in white cleanroom suits — every field you leave out of the specification gets decided here, by someone else, against a default.