Fabrication Data Package Review Before Build
The fabrication data package is the only thing the shop has to build from, and every question it leaves open becomes an assumption. A package that is complete and consistent produces a quotation that holds and a board that matches the design intent.
What the Package Contains
The package carries the layer images, the drill file, the stack-up, the solder mask and silkscreen layers, the surface finish, the array and panel requirements, and a readme that resolves the questions the files cannot.
Each item answers a specific question, and a missing one does not stop the build. It moves the decision to the shop, where the default is chosen for the process rather than for the design. Our design release notes describe the review that catches that.
Gerber and Its Format Questions
The layer images define the copper and the mask. The format questions that matter are the units, the number of decimal places, the zero suppression and whether the image is positive or negative.
A file that is read with the wrong zero suppression produces a board that is the right shape and the wrong size, and the error is often caught only at the drill. Our fabrication notes describe how the shop verifies the interpretation before drilling.
The Stack-Up and What It Has to Say
A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the shop price the board against the dielectric and copper weights that will actually be used. A table of finished thicknesses alone is not a stack-up, because it does not say where the thickness comes from.
The stack-up should state the material, the copper weight, the dielectric thickness and the tolerance for each layer, together with the finished thickness and the impedance target where one applies. Our outline tolerance notes describe the outline half of the same drawing.
Drill File and Hole Table
The drill file carries the hole positions and the tool sizes, and the hole table carries the finished size and the plating requirement for each. A file without a table leaves the plating allowance to the shop, and the shop will choose the allowance that suits its process.
Press-fit holes, tooling holes and holes with a different plating requirement all belong in the table, because their finished sizes are not interchangeable. A single note calling everything a plated through hole is a common cause of a press-fit hole that is out of tolerance.
Mask, Silkscreen and Finish
The mask layer defines the openings, and the dam width between them is what the shop has to hold. Where the dam is not stated, the shop applies its process minimum, and the result may be a dam that does not hold paste during reflow.
The silkscreen is a marking rather than a functional layer, and it still matters because a marking that lands on a pad is a defect. The finish is a separate statement, and it should name the chemistry and the thickness rather than a trade name. Our board quality notes describe how the finished article is checked.
Array, Panel and Tooling
Where the shop is asked to design the array, the package states the singulation method, the tooling that the assembly line uses and any keep-out on the panel. Where the customer designs the array, the shop needs to know that the array has been checked against the panel size.
Panel utilisation is decided here, and a request to fit a board that does not divide well into the panel produces a quotation that is either high or wrong. Stating the array count that is expected is a useful check.
The Readme and the Questions It Answers
A readme of half a page removes most of the round trips. It should say which items are critical, which tolerances may be relaxed, what the finish has to be, how the board will be assembled, and who to contact with a question.
Where a value sits close to a process limit, the readme should say so, since the shop can then open the process window rather than working to a nominal figure that carries no tolerance. That single sentence is often the difference between a first article pass and a redesign.
Verification Before Release
Before the package is released, the files are read together rather than separately. The drill is checked against the pads, the mask against the copper, the stack against the impedance target and the outline against the array.
A first article that measures the features named in the readme confirms that the package was interpreted as intended. Without that check the package is a document rather than a specification.
Process Control and Verification
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.
Checks Before Release
The checks that matter are the ones performed on the product rather than on a sample kept for the purpose, because a coupon that travels with the panel is the only evidence about that panel. Where a requirement can be measured, it should be measured at the point of manufacture and recorded against the board or the lot it applies to.
FAQ
Is a stack-up drawing always required? Where the thickness or the impedance matters it is, and where it is not supplied the shop supplies its own and the result may not match what was simulated.
What is the most common omission? The drill table with finished sizes, and a statement of the surface finish and its thickness.
What does gopcb provide for data package review? We provide a read of the files before quotation, a check of drill against pads and mask against copper, stack-up and impedance review, array and utilisation feedback, a documented list of the assumptions we had to make, and first article measurement of the critical features.
