PCB Supplier Qualification Guide

Supplier qualification is the work of establishing, before the first production order, that a supplier can make what is required, repeatedly, and that there is a written basis for expecting it to continue. It is often treated as a purchasing formality, and it is more accurately an engineering activity, because the questions that matter are technical: which processes, which capability limits, which controls and which evidence. A supplier that is qualified on price alone will eventually be disqualified by a defect, and the cost of that discovery is usually much higher than the audit would have been.

What Qualification Is Trying to Establish

Qualification answers four questions. Can the supplier make the product at all, can it make it repeatedly within tolerance, can it demonstrate that with data, and will it tell the shop when something goes wrong. The first two are capability questions, the third is an evidence question and the fourth is a relationship question, and a supplier that passes the first three and fails the fourth is a supplier that will cause an unpleasant surprise in a year.

The depth of the assessment should match the risk. A supplier of a standard item that is available from several sources needs only a light check of the documentation and a sample lot, while a supplier of a specialised material or an outsourced process step that cannot be brought back in house needs a full audit of the process, the controls and the traceability. Applying the same routine to both wastes effort on the first and leaves the second unprotected.

The Capability Assessment

A capability assessment establishes the limits of what the supplier can produce rather than asking whether it can produce a particular job. The useful output is a short list: the minimum trace and space, the maximum layer count, the smallest hole, the finishes available, the panel sizes, the tolerance classes and the volume range. That list is what the shop needs in order to know which jobs can be sourced without a discussion.

The assessment should be based on evidence rather than on a declaration. Published capability data is a starting point, but the facility should be able to show coupons, measurements and yields from recent production for the limits it claims. Where a supplier cannot show evidence for a claimed limit, the claim should be treated as unproven and the first order should be watched rather than trusted.

The Supplier Audit

A supplier audit looks at the same things an internal process audit looks at, applied to another company: whether the process control that is described is the process control that is practised. The audit should cover the front end data control, the process steps that drive the critical characteristics, the measurement systems, the traceability, the calibration status of the gauges and the handling of nonconforming material.

The audit should be planned from the risks of the parts being sourced rather than from a generic checklist, because the value of the audit is proportional to its focus. Two people with a short list of specific questions will learn more in a day than five people working through a hundred general ones, and the findings are far more likely to be specific enough to correct. A written report with the findings, the agreed actions and the dates should follow the visit.

Sample Lots and First Articles

A sample lot is where a qualification stops being a conversation and becomes evidence. The supplier produces a batch of the actual product, and the shop inspects it against the full specification including the characteristics that are not normally checked at incoming inspection. That is the first time the supplier’s process meets the shop’s requirements in a measurable way, and the results should be recorded as the baseline for future comparison.

The first article inspection should be repeated when anything significant changes, whether that is a process, a material, a machine or a location. A change of plating line or a change of laminate source can alter results without any change to the drawing, and the only defence is a rule that requires the supplier to notify the change and a repeat inspection to prove it.

The Approved Vendor List

The approved vendor list is the operational output of qualification, and it should carry more than a name. The scope of the approval matters: a supplier approved for four layer boards with a standard finish is not approved for a controlled impedance stackup, and the list should say so. Recording the scope prevents both accidental over sourcing and the pointless re qualification of things that were already established.

The list also needs a maintenance rule. Approval should have a review date, and the review should be based on performance data rather than on a calendar. A supplier with a clean delivery and quality record over the review period keeps its approval, while one with recurring problems should be suspended pending corrective action, and the suspension should be recorded rather than applied informally by the buyers.

The Quality Agreement

A quality agreement sets out the things that are otherwise assumed. The specification and the revision control, the inspection and test responsibilities, the notification requirements for change, the handling of nonconforming material, the traceability and records retention, and the response time for a complaint. All of these are cheap to agree at the beginning and expensive to argue about in the middle of a problem.

The agreement should also define the acceptance criteria for the characteristics that matter, so that both sides measure against the same number. Where a supplier and a shop disagree about whether a result is acceptable, the disagreement is almost always traceable to a criterion that was never written down, and the time to discover that is before the material is ordered rather than after the boards have been built from it.

Practical Rules

Match the effort to the risk, base the capability assessment on evidence, and audit the processes that drive the critical characteristics rather than the whole facility. Use a sample lot to verify, and write the agreement so that both sides measure the same way.

Keep the approved vendor list scoped and current, and review suppliers on performance rather than on the calendar. Record the results with the quality data so that a later decision to keep, restrict or replace a supplier can be made from history, because supplier qualification is not a one off exercise but the beginning of a record that either supports the relationship or ends it. It is also worth reviewing the list whenever a new product family is introduced, since a supplier that is adequate for the current range may not be adequate for the next one.

FAQ

How long does qualification take? It depends on the risk. A standard item may take a few weeks including a sample lot, while a new outsourced process can take several months of audits and trials.

Is a sample lot enough evidence? For a first qualification yes, if it covers the full specification. It is a baseline that later production is compared against.

When should a supplier be re-qualified? After any significant change, or at a scheduled review based on performance. Approval should not be permanent by default.