Every fabrication job begins long before a drill touches laminate. It begins with a handoff — the moment your design data leaves your CAD environment and lands in the inbox of a board fabricator. What happens next depends almost entirely on how complete and unambiguous that package is. A pcb board maker reads files literally. If a stackup note is missing, if a drill chart conflicts with the Gerbers, or if a via type is implied but never declared, the job stalls while someone asks questions. The purpose of this guide is to walk through the details that matter most: the files themselves, the specifications that define the build, and the design intent that no Gerber layer can capture.
Building the Fabrication Data Package: Gerbers, Drills, and the Fabrication Drawing
The foundation of any quote or build is a complete image set. At minimum, expect to supply one Gerber file per copper layer, soldermask layers for both sides, silkscreen layers, and a clearly defined board outline. Layer names should be self-explanatory rather than cryptic internal labels, and the file format, units, and decimal precision should be stated in a cover note so nothing is guessed at import. If your tool exports ODB++ or IPC-2581, those formats bundle the netlist and stackup relationships into a single package, which reduces interpretation risk — but the drill data still deserves separate scrutiny.
Drill information is where many otherwise tidy packages fall apart. Provide an NC drill file that distinguishes plated from non-plated holes, includes slot features if any exist, and matches the drill chart in the fabrication drawing. If your design mixes mechanical and laser-drilled features, say so explicitly. Holes that appear identical in a drill file may require entirely different processes, and the fabricator needs to know which is which before scheduling.
The fabrication drawing is the written contract that accompanies the images. It should state board thickness and tolerance, copper weight per layer, the finished surface finish by name, and any special processes the design depends on — countersunk holes, press-fit features, castellated edges, cavities, or semi-flex constructions. A stackup diagram, even a simple one, removes guesswork about dielectric thickness and layer sequencing. If impedance control is required, list the target ohms per net group, the reference plane relationship, and the acceptance tolerance; the stated tolerance for controlled impedance work is typically within plus or minus five percent.
Finally, version control deserves a mention. Include a revision identifier in the file names and on the drawing, and confirm that the Gerbers, drill file, and drawing all carry the same revision. Mismatched revisions are a quiet but expensive source of scrap.
Specification Details That Define the Build: Layer Count, Vias, Materials, and Finish
Once the package is legible, the next layer of detail is the construction itself. Layer count sets the manufacturing path, and the range commonly spans from two layers up to fifty-eight layers, with any-layer HDI constructions such as 9+N+9 available where routing density demands it. When you declare a layer count, also indicate whether sequential lamination is implied, because that decision affects tooling, throughput, and how the stackup must be ordered.
Via requirements are equally consequential. State whether the design uses through-hole vias only, or whether blind and buried vias are present, and note whether those vias are mechanically or laser drilled. Microvia structures should be identified as staggered, stacked, or skipped. Where via-in-pad is used, specify the fill expectation — conductive, non-conductive, or copper plug — and whether microvias must be epoxy filled and copper capped. Numerical limits should be checked against capability before release: BGA pitch down to 0.15 mm minimum, minimum trace width and spacing of 0.002″ by 0.002″, and back-drilled holes with a minimum size of 15.7 mils held to a depth tolerance of plus or minus 6 mils. A capable pcb board maker will flag anything outside those boundaries, but catching it in design review is cheaper than catching it in fabrication.
Material selection is the specification most often left vague, and it is the one that most affects electrical performance. For high-frequency and high-speed work, name the laminate family rather than describing it generically. Recognised options include Isola grades such as I-Speed, ASTRA MT77 and I-TERA MT40, Rogers materials including RO4003C and RO4350B, Arlon’s AD series, Taconic’s TLY-5 and RF-35, and Panasonic MEGTRON 6, 7 and 8 for high-speed networking. Polyimide laminates are the standard choice for rigid constructions requiring thermal resilience. Heavy copper builds up to 30 oz. require their own conversation about etch tolerance and pattern integrity.
The finished surface is the last specification most designers touch. Options include ENIG, ENEPIG, hard gold, gold fingers, selective gold plating, wire-bondable gold, OSP, immersion silver and immersion tin. The right answer depends on solderability, contact wear, wire bonding, and whether the assembly will be reflowed more than once.
Design Intent Beyond the Gerbers: Stackup Notes, Assembly Data, and Flex or Rigid-Flex Requirements
If the project includes assembly, the fabrication package is only half the submission. Assembly requires its own documentation set: a bill of materials with manufacturer part numbers and any approved alternates, a centroid or pick-and-place file keyed to the same rotation convention used in your CAD library, and a clear statement of technology mix. Assemblers routinely handle SMT, through-hole, and mixed technology on the same board, fine-pitch micro BGA down to 0.4 mm, and components as small as 01005s, with board sizes up to 20″ by 24″. Specify whether you need IC programming, functional testing, or X-ray inspection — particularly relevant for BGAs and QFN packages where joints are invisible to the eye.
Flexible and rigid-flex designs carry additional file requirements. Beyond the standard image layers, note the substrate — polyimide, PET, PEN, or LCP — along with coverlay openings, stiffener locations, and the intended bend region. If the flex circuit uses thick copper, state it, since thick copper flexible boards extend to 500 µm and change how bending stress is managed. Sculptured flex circuits, castellated holes, and cavity processes all need to be named rather than assumed, because each one alters the tooling path.
Practical order details round out the submission. Quantity, prototype versus production intent, panelization preferences, and delivery expectations all shape how a job is scheduled. When these are captured alongside the technical package, the quotation step becomes straightforward rather than iterative. Many fabricators now provide an online price calculator for prototypes, quick-turn boards, HDI, RF, rigid-flex, flex, and assembly work, which allows you to validate a specification before committing — but the calculator is only as accurate as the details you feed it.
Treat the data package as a deliverable in its own right. A drawing that answers the obvious questions, a set of files that agree with each other, and a specification list that names materials and finishes precisely will move through fabrication with far fewer interruptions than a design that relies on the fabricator to infer intent.
