What Files Do You Need to Send a PCB for Fabrication?

Detailed Explanation

A complete fabrication package needs to describe the board fully enough that a fab house with no other context can build exactly what was designed. At minimum that means: Gerber files (one per copper layer, solder mask layer, and silkscreen layer), an NC drill file (hole positions and sizes), and a document specifying the stack-up (layer order, copper weight, and dielectric), since Gerber files alone don't inherently convey how layers stack vertically.

For assembly, two more files matter: a pick-and-place (centroid) file giving each component's position, rotation, and reference designator, and a bill of materials (BOM) listing every part, its footprint, and ideally a manufacturer part number. Without both, an assembly house has the bare board and a schematic but no machine-readable instructions for where each component actually goes.

For KiCad users, the complete export workflow (Gerber plot layer selection, drill file generation, coordinate origin alignment, and pre-submission verification in GerbView) is covered in How to Export Gerber Files from KiCad for PCB Fabrication.

Fabrication Package Reference

Solder Paste and Assembly Drawing Files

Two commonly overlooked files sit alongside the core fabrication package once assembly, not just bare-board fabrication, is part of the order:

• Solder paste (paste mask) layer: defines the stencil apertures used to print solder paste onto pads before reflow. It's a separate layer from the solder mask (which defines where copper is exposed, not where paste goes), and most EDA tools export it automatically when Gerbers are generated, but it's easy to leave out when manually picking which layers to include, since a board with no paste layer still looks visually complete in a Gerber viewer. Some assembly houses cut a stencil directly from this layer; others require a separately submitted, laser-cut stencil order.
• Assembly drawing: a PDF showing component placement, reference designators, and orientation markers (pin 1 indicators, polarity marks, connector keying) at a scale a human assembler or inspector can actually read. This matters most for orientation-sensitive parts and for hand-assembly or low-volume runs where a human, not just a placement machine, is making the final call on part orientation. It's not strictly required by every assembly house, but its absence is the single most common cause of a reversed polarized component on a first-article build.

Practical Examples

A two-layer board with simple through-hole and SMT parts can typically ship with just Gerbers, a drill file, and a basic stack-up note (it's usually obvious from "2 layers, standard 1.6 mm FR4"), so the fab house has little ambiguity to resolve.

A four-layer board with controlled-impedance traces needs its stack-up specified explicitly and unambiguously, because the fab house's actual dielectric thickness and copper weight directly determine whether the delivered board meets the impedance target the design assumed. A vague or missing stack-up drawing here isn't just an inconvenience: it can silently change the board's electrical behaviour.

Design Considerations

• Always include an explicit stack-up drawing for anything beyond a basic two-layer board. Don't rely on the fab house guessing layer order or copper weight correctly.
• Generate the BOM and pick-and-place file directly from the same design database as the Gerbers, not a hand-maintained spreadsheet: manual BOMs drift out of sync with the actual layout far more often than generated ones.
• Confirm units and format conventions with your specific fab house before sending files. Gerber format variants and unit conventions (metric vs imperial) have historically been a source of silent misinterpretation.
• Run a final design rule check immediately before generating output files, not before some unrelated later change. Output should always reflect the layout's final, DRC-clean state.
• End-to-end fabrication support: If you're navigating a first board submission or a new fab house relationship, a rapid prototyping partner can manage the output package, submission, and first-article review on your behalf.

Common Mistakes

• Sending Gerber files without a stack-up drawing and assuming the fab house will infer the correct layer order and copper weight.
• Maintaining the BOM by hand in a separate spreadsheet instead of generating it from the design database, leading to mismatches between what's documented and what's actually on the board.
• Generating output files before the final DRC pass, then having to regenerate everything after a late layout fix.
• Assuming every fab house interprets Gerber conventions (units, layer naming, aperture format) identically: confirming this in advance avoids a misfabricated first article.
• Omitting the solder paste layer from an assembly order because the board "looks complete" in a Gerber viewer without it: the missing layer only becomes apparent once the stencil doesn't print paste correctly.
• Skipping the assembly drawing on a first-article build with polarized or keyed parts, then discovering a reversed component only after reflow.