Engineering Change Orders in PCB Production
A change order is a small document with a large effect. It invalidates drawings, programs, fixtures, test limits and stock, and it does so in several places at once. The cost of a change is rarely in the change itself.
What a Change Order Contains
The order should identify the item, the revision it applies to, the new revision, the description of the change, the reason and the effective date.
The reason is the part that is most often omitted and most often needed. Without it, a later reader cannot tell whether the change is still required. Our design release notes describe the record that a revision should carry.
What the Change Touches
The change touches every artefact that describes the item: the drawing, the bill of materials, the fabrication data, the assembly data, the test program and the fixture.
It also touches the physical world: stock on the shelf, work in progress, and units already delivered. Each of those needs a decision, and the decision should be recorded rather than assumed.
Effective Date and Cut-in
The effective date can be a date, a serial number, a work order or a stock level. Whichever is used, it must be unambiguous at the point where the board is built.
A change that cuts in by stock level means two revisions exist in the field at the same time. That is sometimes the right answer and it is always a support cost, so it should be deliberate.
Verification of the Change
The change should be verified before it is released, at the level that the change affects. A component change is verified on a sample assembly; a layout change is verified on a first article.
Where the change is made to correct a defect, the verification should reproduce the defect and show that it is gone. Our failure analysis notes describe how the verification is tied to the cause.
Communication
The people who build must know before the first board, and the people who support must know before the first return. The notice should state what changed in terms of what they have to do differently.
A notice that quotes the drawing change without translating it into an action is a notice that will be read and not used. Our training notes describe how the change is carried into the process.
Records
The history of the item should allow a unit to be traced back to the revision it was built to, and forward to the changes it does not include.
Where the traceability is by date code or serial number, the record must be searchable in that direction, not only by revision. Our fabrication notes notes list the records that should be kept.
Verification of the System
The system is verified when an auditor picks a delivered unit and traces it to a revision and to the change orders that apply. If that cannot be done, the records exist but the system does not.
The check should be performed on a sample rather than only when a customer asks, because the exercise is what keeps the records current.
Process Control and Verification
On a design of this kind, revision is the item that decides how the rest of the board is arranged. 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.
Documenting the assumption is part of the design work, and a short note on the drawing prevents a question that would otherwise arrive a day later and cost a day of schedule. 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. Where a value sits close to a process limit, the drawing should say so, since the shop can then open the process window rather than working to a nominal figure that carries no tolerance.
Process Control and Verification
On a design of this kind, revision is the item that decides how the rest of the board is arranged. 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.
Documenting the assumption is part of the design work, and a short note on the drawing prevents a question that would otherwise arrive a day later and cost a day of schedule.
Process Control and Verification
On a design of this kind, revision is the item that decides how the rest of the board is arranged. 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.
A first article check confirms that the process and the drawing agree on the points listed above, and that the coupon data supports the values used in the design.
Where a measurement falls outside the expected window, the sample is retained so that the cause can be established before the balance of the batch is released.
FAQ
Should a change be released as soon as it is approved? It should be released when the affected artefacts are ready and the stock position is known. A drawing change released alone creates a mismatch with the program.
Can several changes be combined? They can, and combining them reduces the number of cut-ins and makes the verification cheaper. They should still be recorded separately.
What does gopcb provide for change control? We provide change records with item, revisions, description, reason and effective date, an impact list covering every affected artefact and the stock position, a defined cut-in method, verification at the level the change affects, translated notices for build and support, and traceability from a delivered unit back to its revision.
