Revision Control: Documentation Discipline for PCB Projects
A printed circuit board is a document as much as it is a product, and the quality of the documentation determines whether the board can be built again in three years. The disciplines that make that possible are simple and they are usually the first to be dropped under schedule pressure.
The Drawing Set and What Each Part Does
The fabrication drawing describes the bare board: the outline, the stack, the holes, the finish and the tolerances. The assembly drawing describes the populated board: the component positions, the polarity, the height limits and the process notes. The bill of materials lists what is fitted.
The three must agree, and a change to any one of them triggers a check of the other two. That is the whole discipline, and it is the one that is most often missing. Our fabrication notes guidance lists the entries for the first.
Revision Control
Every document carries a revision, and the revisions move together. A package in which the fabrication data is at revision C and the assembly drawing at revision B is a package that will produce a board that matches neither document.
The revision should appear in the file names, in the readme and on the documents themselves, so that a shop receiving two versions on the same day can tell them apart without opening them.
Data Formats and Compatibility
The fabrication data is delivered in a standard format, and the assembly data in the format the machine expects. Both should be generated from the same source rather than exported by hand, because a manual export is a step where an error can be introduced without a trace.
Where a customer supplies data generated by a tool the shop does not use, the shop may need to convert it, and the conversion should be verified against the original. Our data review notes describe the checks.
Assumptions and Their Recording
Every design contains assumptions: the current a trace will carry, the temperature the product will see, the tolerance the assembly can hold. Those assumptions belong in a document, because they are what a future change has to be checked against.
Where an assumption is not recorded, a later reviewer will make a different one, and the change will be evaluated against the wrong premise.
Test and Inspection Documentation
The test plan states what is tested, by what method and with what acceptance criterion. It also states what is not tested, which is the part that is usually omitted and the part that matters when a defect escapes.
The inspection requirements belong with the drawings rather than in a separate standard, because the drawing is the document that reaches the machine operator.
Supplier and Process Records
The material certificates, the process parameters and the coupon results are part of the product record, and they allow a failure to be traced back to a batch. Without them, an investigation can identify a mechanism but not its cause.
The records should be retained for the period the product may be in service, which for an industrial product is measured in decades. Our traceability marking notes describe how the link is made.
What to Do When the Package Is Incomplete
Where a document is missing, the shop has to infer the intent, and the inference will be made for the shop’s convenience. That is why an incomplete package produces boards that are buildable and not necessarily correct.
The response is a query rather than an assumption. The query costs an hour and the assumption costs whatever the difference turns out to be.
Reviewing the Package Before Release
The review is a checklist applied by the same person every time: are the three documents present, do they carry the same revision, do the reference designators agree, is the stack on the drawing, are the drill sizes finished or drilled, are the tolerances stated where they matter.
Every item on that list corresponds to a query that has been raised before. The list is short and it removes most of the delay from a job. Our design release checklist is structured that way.
Process Control and Verification
On a design of this kind, revision control is the item that decides how the rest of the board is arranged. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used. Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design.
The measurements that matter are the repeatable ones: conductor width and spacing, annular ring, finished hole size, plating thickness and surface finish are all verifiable on a coupon that travels with the panel. Running a first article through the same checks as the production panel confirms that the two agree, and that comparison is the cheapest form of process control available at prototype stage.
Keeping a sample from the panel turns a dispute into a measurement, because the same coupon can be re-examined by both parties without rebuilding the batch. Reviewing the design before the data is released is cheaper than correcting it after the panel is in the tank, because every step downstream inherits the decision made at the front end.
Process Control and Verification
On a design of this kind, revision control is the item that decides how the rest of the board is arranged. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used. Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design.
The measurements that matter are the repeatable ones: conductor width and spacing, annular ring, finished hole size, plating thickness and surface finish are all verifiable on a coupon that travels with the panel.
Process Control and Verification
On a design of this kind, revision control is the item that decides how the rest of the board is arranged. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used. Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design.
FAQ
Is a single document package possible? It is possible where the tool allows the notes to be embedded in the data, and it is not yet universal. Until it is, the drawings remain the document that carries the intent.
Who owns the package? The design authority, because the contents are engineering decisions. The assembler and the fabricator may propose additions, and the approval belongs to the design.
What does gopcb do with an incomplete package? We raise a query and hold the job rather than making an assumption, unless the assumption is trivial and can be recorded in the review. Every query and its resolution is recorded against the job so that the history is available later.
