Gerber Files and Prototype Data: What to Send a Fabricator

Most delays on a prototype order are not caused by the fabrication itself. They are caused by a file package that needs clarification, and every question from the fabricator costs a day. Sending a complete, self-consistent set of Gerber files with the supporting documentation removes that delay and usually removes a cost premium as well.

The Core File Set

The minimum package is one file per layer: copper on each side, solder mask, legend and the board outline. Every copper layer must be present, including planes, because a missing plane is not obvious in the artwork until the board arrives.

Format matters less than consistency. Whether the data is RS-274X or a modern alternative, the files should come from the same export so that the layer order, units and origin agree across the set rather than being assembled from different runs.

Layer Names, Polarity and Mirroring

Ambiguous names cause real mistakes. A layer called top or bottom is clear, while a layer called layer2 requires the fabricator to infer whether it is an inner signal or a plane. Naming files by function and by order removes the guesswork.

Two export settings deserve explicit attention. Legend and mask files should be supplied positive, not inverted, and no layer should be exported mirrored unless the convention is stated. A mirrored solder mask produces a board that is plausible and completely wrong.

<img src="https://www.gopcba.com/wp-content/uploads/2026/08/773604150_122204755928591289_8347654747047466302_n.jpg" alt="Drill file and stackup drawing accompanying a fabrication package” />

Drill Files and the Hole Table

The drill file has to cover plated and non-plated holes, and if the two are combined, the distinction should be given in the fabrication notes rather than inferred from the diameters. Tool sizes, finished hole diameters and tolerances belong in the table that accompanies the file.

Slot and routed features should be identified, since a slot that is drilled rather than routed has a different tolerance. Where a hole is to be filled or capped, that requirement has to be stated here as well as on the drawing.

Stackup and Impedance Data

If the board requires controlled impedance, the package must include the stackup drawing with dielectric thicknesses and copper weights, together with the target impedance for each structure and the tolerance to be held.

The latitude allowed to the fabricator should also be stated. Most suppliers will adjust trace width, spacing or dielectric thickness within a stated band to hit the target, and confirming that band up front avoids a query and a re-quote partway through the order.

Fabrication Notes

The notes carry everything the artwork cannot express: material, glass transition temperature, finished thickness, copper weight per layer, surface finish with thicknesses, solder mask colour and legend colour. They also carry the applicable standard and the class of build.

Special requirements belong in the same document, including flatness limits, edge plating, countersinks and any restriction on glass weave or laminate supplier. A note that says what is not acceptable is as useful as one that says what is.

Board Outline and Mechanical Data

The outline is best supplied as a closed contour on a dedicated layer, with the dimensions and any internal cutouts defined by the same geometry rather than by a separate drawing. Mechanical features such as tooling holes, mounting holes and mounting keepouts should be visible on the outline or clearly referenced.

Where the board fits a housing, a dimensioned drawing helps. The fabricator does not need the full enclosure model, but knowing which edges are critical prevents a tolerance decision from being made arbitrarily.

Assembly Data and the Bill of Materials

For a turnkey assembly order, the package has to include the paste layer, the component placement file with rotations and references, and a bill of materials with manufacturer part numbers and acceptable alternatives.

Rotation convention is a frequent source of error. The zero orientation used by the CAD library must match the orientation assumed by the assembly house, and stating the convention in the notes is quicker than discovering the mismatch after the first article is built.

Special Processes and Approvals

Anything outside the standard flow needs an explicit instruction: heavier copper, blind or buried vias, edge plating, impedance control, non-standard finishes, or a requirement for coupons and test reports with the shipment.

Regulatory or customer-specific requirements belong here as well, particularly for medical, automotive or aerospace work where material declarations and traceability records are part of the deliverable rather than a courtesy.

Checking the Package Before Sending

A short review catches most problems. Open every file set in a viewer and confirm that each layer appears where expected, that the drill file lines up with the pads, and that the outline is closed and matches the copper extents.

Then read the notes as though you were the fabricator. If any sentence could be interpreted in two ways, the board is at risk of being built to the wrong one, and clarifying it now costs a minute rather than a week.

Units, Origin and Aperture Data

Units and origin should be consistent across the whole set. A mix of metric and imperial, or a drill file referenced to a different origin from the artwork, produces a board where the holes sit a fraction of a millimetre away from their pads, which is subtle enough to pass a quick look.

Aperture tables belong with the Gerber data, and embedded apertures should be confirmed as present. An aperture list that has to be supplied separately is a file that can be lost between the quotation and the build.

Revisions and Version Control

Every revision should be identifiable inside the data as well as in the file name. A revision marker on the copper or the legend lets the fabricator and the assembly house confirm which version they are working from, which matters when two revisions are in circulation.

The file name should carry the project, the revision and the date, and the package should contain one revision only. Mixing files from two exports in one archive is the most common cause of a board that almost matches the design.

What the Supplier Should Return

A useful order produces more than boards. An engineering query or a set of fabrication questions confirms that the data was read, a first article report gives measured values for the critical parameters, and the certificate of compliance records the standard that was applied.

For impedance controlled boards, ask for the measured results from the test coupon. That record is what proves the stackup behaved as designed, and it is the evidence needed if the assembly process later raises a question about the board.

Before the Next Order

Keep the package that produced a good board as the baseline for the revision that follows. Archiving the data, the notes, the stackup and the supplier’s report makes the next order repeatable, and it removes the temptation to re-export everything and reintroduce a setting that was previously corrected.

A short checklist saved with the project, covering the file set, the note items and the review steps, turns a task that depends on memory into one that depends on a document, which is the difference between a consistent supplier relationship and a series of avoidable questions.

FAQ

Can I send native CAD files instead of Gerber? Some suppliers accept them, but Gerber remains the neutral format that is reproduced exactly. Native files introduce a version dependency that is best avoided on a first order.

What is missing most often? The stackup with impedance targets, and the drill distinction between plated and non-plated holes. Both cause a query that delays the start of the order.

Do I need a fabrication drawing for a simple board? A short note is usually sufficient if there is no controlled impedance and no special finish. As soon as either appears, a drawing removes the ambiguity.