PPAP and APQP for PCB Assemblies: What the Documents Contain
Automotive and medical customers ask for documents that a consumer customer never mentions, and the requests arrive with abbreviated names. Understanding what each document contains makes the difference between a routine submission and a month of rework.
What PPAP Is For
PPAP, the production part approval process, is the evidence package that a supplier submits to demonstrate that the production process can make the part to the drawing, at the required rate, reproducibly. It is a submission for approval, not a test report.
The approval is tied to a specific part, a specific drawing revision and a specific manufacturing location. Moving production to another site or changing a material invalidates the approval and triggers a new submission.
The content scales with the risk. A new part on a new process requires the full package, while a minor change on a mature part may require only the changed elements.
The Documents in a Submission
The core elements are the design records, the process flow diagram, the process failure mode analysis, the control plan, the measurement system analysis, dimensional results, material and performance test results, and the initial process study.
The design record is the drawing and the specification at the revision being approved, and every other document refers back to it. A submission that references a different revision than the drawing is the commonest reason for rejection.
Our fabrication notes checklist describes the manufacturing information that feeds the process documents.
The Control Plan and the Flow Diagram
The flow diagram lists every step of the process in sequence, from incoming material through to packing. The control plan lists, for each step, the characteristic controlled, the specification, the measurement method, the sample size, the frequency and the reaction when the result is out of specification.
The two documents must agree with each other and with the process that actually runs on the floor. A control plan that describes a check that nobody performs is worse than no control plan, because it documents a false claim.
Our quality notes describe how the in-process checks are structured for a board.
The FMEA and Its Logic
The process failure mode and effects analysis examines each step and asks what can go wrong, how severe the effect would be, how likely the cause is, and how likely the existing controls are to detect it before the part leaves.
The output is a ranking of risks, and the ranking drives the control plan. Where a risk scores highly and the existing detection is weak, the analysis requires an action, which the control plan must then reflect.
The analysis is a living document. Repeating it after a defect escapes, and recording what changed, is the practice that turns it from paperwork into a control.
Measurement System Analysis
Before a measurement can be used as evidence, the measurement system itself must be shown to be adequate. The analysis typically separates the variation in the parts from the variation introduced by the gauge and the operator.
For a board, the measurements that need this treatment are the ones used to accept or reject: dimensional checks, plating thickness, impedance and solderability results where they are measured in house.
A gauge that is not capable turns a capable process into one that appears to fail intermittently, and the resulting investigation wastes time because the true cause is the measurement.
Initial Process Study and Capability
The initial process study takes a run at production rate and calculates the capability of the characteristic against its specification. The capability index expresses how much of the tolerance the process consumes.
The required index depends on the customer and on the characteristic. On a special characteristic where a failure creates a safety risk, the requirement is higher than on a general dimension.
Where the index is inadequate, the response is to widen the specification, improve the process, or accept containment with agreed inspection. Choosing the first without engineering justification is a decision that will be revisited.
Traceability Through the Production Chain
Traceability means that a finished assembly can be linked to the boards, the components and the process conditions that produced it. That requires a lot code on the board and records that connect the code to the panel, the material and the date.
Our industrial assembly notes describe the traceability practice used for control equipment, which is similar in structure to the automotive requirement.
The practical test of a traceability system is a recall exercise: pick a serial number and reconstruct the material and process history without assistance. A system that fails that test fails the audit.
APQP and the Sequence
APQP, advanced product quality planning, is the framework that produces the PPAP submission. It is a sequence of phases: planning, product design and development, process design and development, product and process validation, and feedback and corrective action.
The PPAP package is the output of the validation phase. Seeing the two as one process rather than as two documents avoids the situation where the planning was done informally and the submission has to be reconstructed afterwards.
Our design release checklist notes describe the inputs that the design phase must produce for the later phases to work.
Common Reasons Submissions Are Returned
The list is short and repetitive. Documents that disagree with each other, a control plan that does not match the process, capability results that fall below the requirement without an action, a measurement system that has not been analysed, and material certificates that do not cover the lots used.
Each of these is a documentation failure rather than a manufacturing one, and each is preventable by reviewing the package against the requirement list before submission rather than after.
The first article inspection results, which are the dimensional evidence, are frequently incomplete: a sample of features rather than all of the specified characteristics. The requirement is the specified characteristics, and the drawing determines which those are.
Process Control and Verification
On a design of this kind, APQP is the item that decides how the rest of the board is arranged. The process window is set by the narrowest step in the flow, so an improvement anywhere else shows up as margin rather than as yield until that step is addressed. A short note on the drawing about handling, storage or packaging is often worth more than an extra decimal place on a tolerance.
Process Control and Verification
On a design of this kind, APQP is the item that decides how the rest of the board is arranged. The process window is set by the narrowest step in the flow, so an improvement anywhere else shows up as margin rather than as yield until that step is addressed. A short note on the drawing about handling, storage or packaging is often worth more than an extra decimal place on a tolerance.
FAQ
Does every part need a full PPAP? No. The submission level is agreed with the customer and can range from a warrant only to a full package with samples.
How long does approval take? It depends on the completeness of the submission and on the customer’s review queue, and a complete submission removes the most common cause of delay.
What does gopcb provide for an approval submission? We provide process flow diagrams, control plans, capability studies at production rate, measurement system analysis for the gauges used, first article inspection results against the drawing, material certificates traceable to the lots, and lot level traceability from the finished assembly back to the panel.
