Ordering PCBs and SMT Assembly From a Fab: A Practical Checklist

Online PCB fabs have made it possible for a student to upload a zip file and receive professional boards in about a week or two, including shipping. The order form, however, is full of options that can raise the price, delay the order or ruin the boards if chosen carelessly. Assembly services add another layer: matching parts, checking orientations and approving a placement preview.

This article explains the common order options and then gives a checklist you can follow every time, from final design check to approving the assembly preview.

Understanding the Order Form

OptionCommon choicesHow to choose
Layers1, 2, 4, 6Must match your design exactly
DimensionsRead from the outlineCheck against your Edge.Cuts size
Thickness0.8, 1.0, 1.2, 1.6 mm1.6 mm unless the enclosure or a connector needs otherwise
Copper weight1 oz, 2 oz1 oz unless you sized tracks for 2 oz
Solder mask colourGreen, black, blue, red, whiteGreen is cheapest and easiest to inspect
Surface finishHASL, lead-free HASL, ENIGHASL for simple boards; ENIG for fine-pitch and flat pads
Via coveringTented, untented, pluggedTented is usual; plugged under BGA or thermal pads if needed
PanelisationSingle boards or panelSingle for prototypes
Remove order numberDefault, specify location, removeSome fabs print an ID on the board unless told otherwise

Surface finish deserves a note. HASL (hot air solder levelling) coats pads with solder; it is cheap and very solderable but slightly uneven, which can make fine-pitch QFN and 0402 parts harder to place. ENIG (electroless nickel immersion gold) gives a flat, long-lasting finish at a higher price. Choose lead-free HASL or ENIG if your product must be RoHS compliant.

Checklist Before Uploading

  1. ERC in the schematic and DRC in the PCB Editor both report zero errors, with schematic parity enabled.
  2. Every footprint has been checked against the datasheet of the exact part you will buy, especially connectors, regulators and transistors whose pinouts vary.
  3. Design rules match the fab's published capabilities for your chosen layer count and copper weight.
  4. The board outline is a single closed shape on Edge.Cuts, and internal cutouts are also closed.
  5. Mounting holes are the right size for your screws, for example 3.2 mm for M3.
  6. Silkscreen shows the revision, polarity marks and connector labels.
  7. Gerbers and drill files were reloaded in the Gerber Viewer and look correct.
  8. The output zip contains copper, mask, silkscreen, paste, Edge.Cuts and drill files, and nothing stale from an earlier revision.

Adding SMT Assembly

With assembly, the fab also buys parts, applies paste through a stencil, places parts by machine and reflows the board. You upload the BOM and component position (centroid) file along with the Gerbers.

  • Part matching: each BOM line must map to a part the assembler stocks or will source. Put the assembler's part number or a manufacturer part number in a symbol field so matching is automatic.
  • Basic vs extended parts: some assemblers charge a setup fee for each unique part not already loaded on their machines. Using common resistor and capacitor values in the same package keeps costs down.
  • Rotation check: footprint zero orientation in KiCad does not always match the assembler's convention. The online preview shows each part on the board; check every IC, diode, LED and polarised capacitor and correct rotations before approving.
  • Sides: confirm whether you ordered top-side only or both sides; parts in the position file for the other side may be ignored.
  • Through-hole parts: often cheaper to solder yourself. Mark them do-not-populate in the BOM.
  • Quantity: assemble only a few boards from the batch for the first revision. If there is a design error, fewer assembled boards are wasted.

If You Assemble Yourself: Stencils

For hand assembly of SMD boards, order a stainless steel stencil with the boards. It is made from the F.Paste layer. A frameless stencil is cheaper and adequate for small batches; tape the board and two spare boards around it to keep the stencil flat. Spread paste in one firm pass with a card, lift the stencil straight up, place parts with tweezers, and reflow on a hot plate or in a reflow oven.

After You Order

  • Watch for an engineering query from the fab. They may ask about an ambiguous outline, missing drill file or unusual features, and the order waits until you answer.
  • Order the parts you will hand-fit while the boards are being made, so you can start bring-up on arrival.
  • Keep a copy of the exact zip you uploaded with the revision number. If the board has a fault, you need to know precisely what was built.

Summary

Choose layers, thickness, copper weight and surface finish to match your design, and leave the rest at the fab's defaults. Before uploading, confirm clean ERC and DRC, verified footprints, matching rules and checked Gerbers. For assembly, map every BOM line to a real part, verify rotations in the preview, and assemble a small quantity first. A careful checklist turns a first order into a working board instead of an expensive lesson.