Incoming Inspection Acceptance Plan for PCB Delivery: Who Sets Sampling, Criteria and Rejection

Receiving is where undefined criteria become someone's loss

A shipment lands. Someone at the dock pulls a few boards, looks at them under a lamp, finds something they do not like — a scratch across a copper area, a rough routed edge, a hole that looks off-centre — and raises a hold. Now two companies start negotiating about a board that is already built, already paid for in part, and already blocking a build slot.

The negotiation is almost never about whether the defect exists. It is about three questions nobody wrote down:

• Against what? Whose criteria decide that this observation is a defect rather than a cosmetic variation?
• How many? Was the conclusion drawn from three boards or three hundred, and was that quantity agreed or improvised?
• Then what? If it is genuinely out of criteria, does the lot get rejected, reworked, sorted, or accepted with a concession — and who has the authority to pick?

None of these can be settled honestly after the fact, because both sides now have money on the table and each will read an undefined word in its own favour. "Clean surface", "no burrs", "good registration" and "cosmetically acceptable" are not criteria. They are placeholders for an argument.

An incoming inspection acceptance plan is the document that fills those placeholders before the boards are manufactured. It is short, it is boring, and it converts a future dispute into a lookup. It is also the cheapest quality document a buyer will ever write, because it costs an hour at PO time and it removes the entire class of "your standard versus my standard" conversations.

One framing point worth being blunt about: this plan is a buyer-side document. It does not replace the fabricator's process controls. PCB168's published quality-control set — AOI on every layer, 100% electrical test by flying probe or fixture, TDR coupon impedance verification, microsection for quality validation, X-Ray for BGA and via-fill verification, and ionic-contamination cleanliness testing per IPC standards, all listed on the PCB168 manufacturing capabilities page — is what happens inside the factory before shipment. Your acceptance plan defines what you verify on arrival and, more importantly, what happens when your result and the supplier's result disagree.

Six attribute families, and what "criteria" means for each

Writing "inspect per IPC-A-600" is a common shortcut and a weak one, because a standard with multiple acceptance classes does not by itself tell anyone which class applies, which attributes were selected, or how disputes get measured. A workable plan walks through attribute families and, for each, names a criteria source and a decision owner.

1. Dimensional and outline attributes. Board size, thickness, hole positions and diameters, and edge condition. Criteria here come from your fabrication drawing with explicit tolerances, not from a standard. If your drawing does not carry a tolerance, you have not specified the attribute — you have expressed a preference. Edge condition in particular is a family where the criteria must be negotiated numerically rather than adjectivally; the parameters involved are covered in PCB edge quality inspection: V-cut, routed edge and burr acceptance criteria, and your plan should reference that agreed set rather than restate adjectives.

2. Conductor and etch attributes. Line width and spacing, conductor integrity, nicks, pinholes, and residual copper. This is where the published capability line matters: /en/capabilities/ lists minimum line width/spacing of 2mil/2mil, while the multi-layer PCB product page lists 3mil/3mil for the multilayer product line. Those are different numbers on different pages, and that difference is exactly why your plan must state which figure your part was quoted against. Do not average them and do not assume the tighter one applies to your job; confirm it in engineering review and write the confirmed value into the drawing.

3. Electrical attributes. Continuity, isolation and controlled impedance. Continuity and isolation are pass/fail and already covered by the supplier's 100% electrical test (/en/capabilities/). Impedance is the one to be careful with, because the tolerance you are entitled to depends on which document you were quoted under: /en/capabilities/ states ±5% with TDR verification, while /en/products/multi-layer-pcb/ states ±8%. A buyer who assumes ±5% while the quote was built on ±8% has created a dispute out of a reading habit. Name the figure, name the page or quotation it came from, and name the artefact it is measured on — for PCB168 that is a TDR coupon.

4. Surface finish and cleanliness attributes. Finish type and condition, solderability, and ionic contamination. /en/capabilities/ lists HASL, ENIG, OSP and immersion tin/silver as available finishes, and lists ionic-contamination cleanliness testing per IPC standards as part of quality control. For your own plan, decide whether you will verify solderability at all on arrival — it is a destructive or semi-destructive test on real product — or whether you will rely on the supplier's testing plus your own first-reflow result. Either answer is defensible. Leaving it unstated is not.

5. Laminate and structural attributes. Delamination, blistering, haloing, plating voids in hole walls, and layer-to-layer registration. Most of these cannot be judged from the outside of a board. They are microsection findings, and microsection is destructive. If you want structural evidence, you must decide in advance whether you are asking the supplier for its own microsection results as part of shipment documentation, or destroying boards from your own received quantity to generate them — and if the latter, who pays for the destroyed boards.

6. Marking, packaging and documentation attributes. Legend legibility, date and lot identification, panel or single-board delivery format, vacuum sealing, desiccant, and which documents travel with the shipment. These are the cheapest attributes to specify and the most frequent source of avoidable friction, because they are usually assumed rather than written.

The point of enumerating families is not completeness for its own sake. It is that each family has a different natural criteria source — drawing, standard, published capability, quotation, or mutual agreement — and a plan that treats them all as "per IPC" collapses those distinctions and reopens them at the dock.

The sampling question you must answer before the boards ship

Sampling is the part buyers most often skip, and it is the part that decides whether an inspection result means anything. Four decisions have to exist on paper.

Who inspects. Your own receiving team, a third-party inspector, or the supplier under a witnessed protocol. Each has different cost and different evidential weight. If a third party will make a call that can reject a lot, the supplier needs to know that at quotation time, because it changes the risk the supplier is carrying.

On what quantity. You must state the sampling basis, not a vague intent. The honest options are: 100% inspection of a named attribute, a statistically defined sampling scheme drawn from a published standard such as ISO 2859-1, a fixed agreed sample count per lot, or first-article-only for a named subset. Choose the standard by name; do not invent sample sizes and do not copy acceptance numbers out of a standard into your PO without confirming which inspection level and which quality level you are actually invoking. If you are not prepared to specify those, use a fixed agreed count instead and say so plainly — a small honest number that both sides agreed to is stronger than a standard reference nobody applied correctly.

Per what unit. A "lot" needs a definition. Is it one purchase order, one shipment, one production panel batch, or one manufacturing date code? Buyers and fabricators routinely use the same word for different things, which means a rejection can cover ten times more or less product than either side pictured.

With what escalation. State what happens when the initial sample shows a finding: does the inspection expand to a larger sample, move to 100% screening, stop immediately and quarantine, or trigger a joint review before any further inspection? Undefined escalation is how one scratched board becomes a held shipment with no agreed path forward.

A practical note on destructive attributes: any sampling plan that includes microsection, solderability or cleanliness testing on received product is consuming boards you paid for. Write down how many boards may be consumed and whose account they come out of. This single sentence prevents a surprisingly common argument.

Method, not just limit: how each attribute is measured

Two parties measuring the same board with different methods will get different numbers and both will be right. A limit without a method is not a criterion, and this is the most under-specified part of most buyer documents.

For each attribute you intend to verify, the plan should name three things: the instrument or technique, the location on the board, and the conditions.

• Technique. Visual at a stated magnification is a different test from AOI, and a surface reading is a different test from a microsection. For copper thickness specifically, surface-versus-section is exactly the distinction that produces mismatched numbers, and the basis has to be settled in the drawing rather than at receiving — the full specification sequence for that product family is in heavy copper PCB purchase specification and acceptance.
• Location. "Board thickness 1.6mm" without a measurement location invites two readings. Thickness over a copper plane and thickness in an open area are not the same value. Hole diameter measured before and after surface finish is not the same value. Impedance measured on a coupon and on a live trace are not the same value — PCB168 publishes TDR coupon verification as the method (/en/capabilities/), so the coupon is the artefact of record.
• Conditions. Ambient temperature and humidity matter for dimensional checks on thin or large boards. /en/capabilities/ publishes a maximum board size of 600mm × 1100mm and a thickness range of 0.2mm to 6.0mm; at the thin-and-large end of that envelope, handling and conditioning affect what you measure more than the process does.

The general rule: for every number in your acceptance plan, someone should be able to hand the plan to a person who has never seen your product and get a repeatable reading. If two competent people can follow your plan and disagree, the plan is not finished. Method detail for the individual inspection technologies themselves — optical, X-Ray, electrical, microsection — is covered in PCB quality inspection methods; this article is about which of them you invoke, on what, and with what authority.

Which document wins when three of them disagree

By the time boards arrive, at least three documents describe what was supposed to be built: your fabrication drawing and notes, the supplier's quotation or order acknowledgement, and whatever standard both sides referenced. A fourth often appears — a published capability page someone read during sourcing.

They will not agree perfectly, and the disagreement is not usually anyone's fault. It is a versioning and scope artefact. PCB168's own published pages illustrate the pattern: /en/capabilities/ states minimum line width/spacing 2mil/2mil and impedance control ±5% (TDR verified), while /en/products/multi-layer-pcb/ states 3mil/3mil and ±8%. Both are real published figures for different scopes. A buyer who quotes the more favourable one at a dispute meeting is not making an argument, only picking a page.

So your plan needs an explicit order of precedence. A defensible one looks like this:

1. The fabrication drawing at the named revision referenced on the purchase order, including its notes.
2. Written engineering clarifications and deviation approvals issued against that revision, in date order.
3. The supplier's order acknowledgement, to the extent it does not contradict items 1 and 2 — and where it does contradict them, the contradiction must have been resolved in writing before production, not discovered at receiving.
4. The referenced standard at its named revision and class, for attributes the drawing does not address.
5. Published capability pages and marketing material: context only, never a criterion.

That last line does the most work. Capability pages describe what a supplier can do across its business; they are not a commitment about your specific part. Anything from a capability page that you actually need has to be pulled into your drawing and confirmed in engineering review, and combinations that sit at the edge of multiple published ranges should be marked as requiring engineering confirmation rather than assumed.

Also state a version discipline: the PO references the drawing by number and revision, and a drawing change after order placement is a change event with its own approval, not a silent update. Without that, the precedence list has nothing stable at the top.

Rejection, rework, use-as-is: naming the decider in advance

Suppose the finding is real and genuinely outside criteria. Four dispositions exist, and they have very different consequences:

• Reject and replace. Cleanest outcome, worst schedule impact. The lot goes back or gets scrapped and remade.
• Screen and sort. The lot is 100% inspected for the failing attribute and the conforming subset is accepted. Cheap on schedule if the defect is detectable without destruction, useless if it is not.
• Rework. Only viable for attributes that can be corrected without compromising others. Rework has to be defined and approved, not improvised, and it must state what gets re-verified afterwards.
• Use-as-is concession. The nonconformance is accepted for this lot only, with the reason recorded. This is a legitimate engineering decision and a terrible habit — a concession granted twice without a documented reason becomes a de-facto relaxed specification nobody agreed to.

The plan must answer four questions about these four options:

Who can authorise each one? Receiving inspection can reject. It should not be able to grant a use-as-is concession on a functional attribute, because that is an engineering judgement about whether the product still meets its intent. Name the role, not the person.

On what basis? A concession needs a stated reason tied to the attribute's function. "Schedule pressure" is a reason to escalate, not a reason to accept.

Is it lot-limited? Every concession should carry an explicit scope — this lot, this quantity, this date code — and an explicit statement that it does not modify the drawing. Without that sentence, the next lot arrives built to the concession.

What gets re-verified? Any rework or sort has to name the re-verification step. Rework without re-verification just moves the risk downstream into your assembly line.

Two boundaries worth stating so this plan stays in its lane. First, if the supplier has already issued a defect notification and is proposing a disposition, you are past the planning stage and into report review — that process, including how to read distribution data and require revalidation, is covered in how to review an outer layer PCB etching defect report. Second, if the disposition involves a permanent change to the drawing rather than a one-lot concession, it is a change event, and change events need their own approval path; the same principle applies on the assembly side with component substitutions, as described in turnkey PCBA BOM risk and alternate part approval.

A PO attachment you can adapt

Keep this to one page. A long quality document that nobody reads protects nobody. The fields below are the minimum that makes an acceptance plan operable:

Scope. Part number, drawing number and revision, PO number, and the definition of a lot for this order.

Criteria and precedence. The order of precedence listed above, stated explicitly, with the drawing revision named.

Attributes table. One row per attribute you will actually verify. Columns: attribute, criteria source (drawing note, standard by name and class, or written agreement), measurement technique, measurement location, and disposition authority. Rows you will not verify should be omitted rather than listed aspirationally.

Sampling. Inspector, sampling basis (100%, named standard scheme, or fixed agreed count), unit of sampling, escalation rule on first finding, and the allowance for destructively consumed boards including whose account they fall to.

Documentation required with shipment. State what must travel with the boards for the lot to be inspectable at all. Ask only for what you will read: typically lot and date identification, the supplier's electrical test confirmation, impedance verification records where impedance is specified, and any first-article documentation agreed for the part. PCB168 publishes AOI on every layer, 100% electrical test, TDR coupon impedance verification, microsection, X-Ray and ionic-contamination testing as part of its quality control (/en/capabilities/); which of those results are reported to you, in what format, is a commercial agreement to settle at quotation — do not assume a report format or a turnaround time that was never discussed.

Dispositions. The four options, the authority for each, the requirement that concessions be lot-limited and reasoned, and the re-verification requirement for rework and sort.

Contacts and clock. Named quality and engineering contacts on both sides, and the window within which you will complete incoming inspection and raise findings. A buyer who inspects eight weeks after delivery has weakened their own position regardless of what the plan says.

Send this attachment with the RFQ, not with the PO. A supplier that sees your acceptance plan before quoting can price and plan against it, or tell you which line is unworkable while it is still cheap to change. Sending it after award converts it into a surprise. If you are assembling the wider quotation package at the same time, the document-completeness side is covered in PCBA quote comparison and scope boundaries, and for questions about whether your specific combination of attributes is within published ranges, raise it through /en/quote/ or /en/contact/ and get the answer in writing before the drawing is frozen.

FAQ

Is an incoming inspection plan still necessary if the supplier already does 100% electrical test and AOI?

Yes, but for a different reason than most buyers assume. Supplier-side controls reduce the probability that nonconforming product ships; they do not define what you and the supplier will do if your receiving result disagrees with theirs. PCB168 publishes AOI on every layer and 100% electrical test (flying probe or fixture) as standard quality control (/en/capabilities/). Your plan is not a second opinion on those tests — it is the agreed procedure for resolving disagreement and for the attributes their tests do not cover, such as dimensional conformance to your drawing tolerances and packaging and documentation requirements.

Can I just write "inspect per IPC-A-600" and be done?

Not usefully. A standard with multiple acceptance classes requires you to name the class, and it does not select attributes, define sampling, specify measurement locations, or assign disposition authority for your part. Referencing the standard by name is correct and worth doing for the attributes it genuinely governs; treating the reference as a complete plan is what leaves the dock argument intact. Name the standard, then add the class, the attribute selection, the sampling basis and the disposition authority.

How many boards should I inspect per lot?

This article deliberately does not give you a number, because a sample size only means something in combination with an inspection level, a quality level and a lot-size band from a published scheme such as ISO 2859-1, and copying digits out of context produces a plan that looks statistical and is not. Two honest paths: invoke a named scheme correctly with its parameters stated, or agree a fixed count per lot with the supplier and write that count down. The second is common, defensible for low volumes, and far better than an unstated intent.

What if the capability page says my requirement is possible but the quotation says something different?

The quotation and the drawing govern; the capability page is context. Published capability describes the range a supplier operates across, not a commitment for your part, and different pages on the same site can legitimately state different figures for different product scopes — PCB168's /en/capabilities/ gives 2mil/2mil minimum line width/spacing and ±5% impedance with TDR verification, while /en/products/multi-layer-pcb/ gives 3mil/3mil and ±8%. If you need the tighter figure, it has to be confirmed in engineering review and written into your drawing before the order, not cited afterwards.

Who decides between rejection and use-as-is?

Whoever your plan names, which should not be receiving inspection alone for any functional attribute. Rejection can be a receiving-level call because it is the conservative outcome. Accepting nonconforming product is an engineering judgement about whether the part still meets its intent, so it belongs to a named engineering role, with the reason and the lot scope recorded. The critical clause is that the concession applies to that lot only and does not amend the drawing.

Does this plan cover assembled boards as well as bare boards?

The structure transfers, but the attribute families and criteria sources do not. Assembled product adds component identity and placement, solder joint condition, and BOM conformance, which are governed by different documents and different approval paths — component substitution in particular is a pre-build approval question rather than a receiving question, covered in turnkey PCBA BOM risk and alternate part approval. If you are buying assembled boards, write two plans, or one plan with clearly separated bare-board and assembly sections.