Gerber, BOM, and Pick-and-Place File Checklist for PCB Assembly

A usable assembly BOM lists, at minimum: reference designator, manufacturer part number (not just a generic value like “10k resistor”), quantity, package/footprint, and any approved alternates. Generic values without a manufacturer part number force the assembler or sourcing team to guess at tolerance, package, and specific electrical characteristics that a schematic value alone does not capture.

DNP (do-not-populate) lines need to be marked clearly and consistently between the BOM and the assembly drawing—a part listed in the BOM but struck through inconsistently, or marked DNP in one document and not the other, is a common source of a wrongly populated first article. If a line item has approved alternates (for lead-time or obsolescence reasons), list them explicitly rather than leaving substitution decisions to be made verbally during a build.

A centroid file lists each component’s position (X/Y coordinates), rotation, and side (top or bottom) referenced to a defined board origin. The data itself is usually straightforward to export from a layout tool; the problems come from convention mismatches—what counts as zero-degree rotation, where the origin sits, and whether rotation is measured clockwise or counterclockwise can differ between EDA tools and assembly equipment.

State your tool’s rotation and origin convention explicitly in the RFQ rather than assuming it is universal. A polarized part placed 180° out of rotation due to a convention mismatch is one of the most common and most avoidable first-article defects, and it is almost always a documentation gap rather than a process error on the assembly line.

The assembly drawing should mark polarity for every polarized component (diodes, electrolytic capacitors, connectors with a keyed orientation) unambiguously—pin-1 indicators and polarity marks on the silkscreen help, but the assembly drawing is the document of record if silkscreen space ran out or a part was placed after the silkscreen layer was finalized. Mechanical keep-out zones (areas where components, adhesive, or conformal coating must not go) belong here too, along with any special process instructions: press-fit connectors, adhesive dispensing locations, selective solder masking, or conformal coating boundaries.

Include the board revision on the assembly drawing and confirm it matches the BOM and Gerber revision—a mismatch here, even a minor one, is worth catching before a kit is pulled rather than after.

This checklist covers the assembly-specific documents; the bare-board fabrication package (Gerbers, drill files, stackup notes, impedance tables) is covered separately in preparing Gerber files for manufacturing. Both packages travel together on a turnkey RFQ, but they answer different questions—fabrication data describes the board itself, while BOM, centroid, and assembly drawing describe what goes on it and how.