Gerber, BOM and Pick-and-Place Files: What a PCBA Supplier Needs
A practical guide to the files a PCBA supplier reviews before quotation and SMT assembly, including Gerber, BOM, placement data, drawings, and test notes.
Quick answer
A PCBA supplier needs files that define the PCB, the parts, the component positions, assembly notes, and testing scope. Gerber files control PCB fabrication, the BOM controls component sourcing, pick-and-place data controls SMT placement, and assembly drawings clarify polarity, connectors, and special instructions before production.
Core PCBA files at a glance
| File type | What it controls | Why it matters | Common issue |
|---|---|---|---|
| Gerber and drill files | PCB layers, copper, mask, silkscreen, holes | Defines PCB fabrication | Missing drill or outdated revision |
| BOM | Components, quantities, MPNs, designators | Drives sourcing and kitting | Generic part descriptions or missing MPNs |
| Pick-and-place / centroid | Component coordinates, side, rotation | Supports SMT programming | Rotation or side mismatch |
| Assembly drawing | Polarity, connectors, manual assembly notes | Reduces build ambiguity | No polarity mark or unclear connector direction |
| PCB specifications | Finish, thickness, copper, color, panel notes | Confirms fabrication requirements | Specification differs from Gerber notes |
| Test requirements | Firmware, fixture, acceptance criteria | Defines functional test scope | Test expected but not documented |
Gerber defines PCB fabrication data
Gerber and drill files describe the physical PCB: copper layers, solder mask, silkscreen, board outline, holes, slots, and related fabrication data. For turnkey PCB assembly, this data is reviewed together with assembly and sourcing information so the whole PCBA scope is clear.
Common delays happen when the Gerber package is missing a drill file, conflicts with the drawing, or does not match the latest revision. Clear revision control helps both the buyer and supplier avoid quoting or building the wrong board.
BOM and placement data define assembly preparation
The BOM defines which components must be purchased and mounted. It should include reference designators, quantity, manufacturer part number, manufacturer name, package, value, rating, and approved alternatives where available.
The pick-and-place or centroid file defines component coordinates and rotation. Without it, SMT preparation may need manual reconstruction from design data, which adds review time and increases the chance of orientation errors. For overseas buyers comparing China PCB assembly suppliers, complete BOM and placement data make quotes easier to compare.
Assembly drawings and test notes reduce ambiguity
Assembly drawings help clarify polarity, connector direction, board side, mechanical restrictions, hand-soldered parts, labels, and special instructions. They are especially useful when the silkscreen is crowded or when a connector can be installed in more than one direction.
Test notes should explain what must be checked after assembly. Functional testing depends on customer-provided firmware, fixtures, procedures, or acceptance criteria. If testing is not defined before quotation, the supplier cannot accurately include it in the production scope.
FAQ
What is the difference between Gerber and BOM?
Gerber files define the bare PCB fabrication data, while the BOM defines the components that must be sourced and mounted on the board. A turnkey PCBA quote needs both.
Why does a PCBA supplier need pick-and-place data?
Pick-and-place data tells the SMT process where each component is located, which side it is on, and how it is rotated. This helps machine programming and review before assembly.
Can assembly start without centroid data?
Sometimes the supplier can review the project without centroid data, but SMT preparation may be delayed or require extra engineering work. Providing it early reduces ambiguity.
What should be included in a BOM?
Include designator, quantity, manufacturer part number, manufacturer name, package, value, tolerance or rating where relevant, and approved alternatives if available.
How can overseas buyers reduce file review delays?
Send the latest Gerber, BOM, pick-and-place file, assembly drawing, quantity, and test requirements together. If something is missing, note it clearly when you send the files for review.