How to Prepare BOM and Pick-and-Place Files for PCB Assembly
Which columns your BOM needs for a PCBA quote, what the pick-and-place file must contain, and a checklist to prevent substitution, DNP and polarity errors.
Table of contents 6 sections
The accuracy of a PCB assembly (PCBA) quote depends mostly on two files: the BOM, which says which components are used, and the pick-and-place file, which says where each one goes on the board.
In short: each BOM line should include reference designators, quantity, manufacturer part number (MPN), manufacturer and package. The pick-and-place file should include each component’s position, rotation and board side.
What should the BOM include?
| Column | Example | Why it matters |
|---|---|---|
| Reference designator | R1, R2, C5 | Matches the component to its board location |
| Quantity | 2 | Requirement per board |
| Manufacturer part number (MPN) | RC0603FR-0710KL | The most critical information for sourcing the right part |
| Manufacturer | Yageo | Distinguishes products with the same number |
| Description / value | 10 kΩ 1% | For checks and alternative searches |
| Package | 0603 | For the pick-and-place machine and stencil |
| Placement status | DNP | Marks components that will not be fitted |
Alternatives policy
For out-of-stock or long-lead components, manufacturers may suggest alternatives. Substituting passives (resistors, capacitors) is usually fine; for microcontrollers, sensors and power components only the specified part should be used. Adding an “Alternative allowed: Yes/No” column to the BOM makes this explicit.
The pick-and-place (CPL) file
The pick-and-place file tells the assembly machine where and at which angle to place each component. It is usually CSV or text and contains:
- Reference designator: must match the BOM exactly.
- X and Y position: the component centre (units must be stated).
- Rotation: the component’s rotation angle.
- Side (layer): top or bottom.
Zero-rotation definitions in footprint libraries can differ between tools. For polarised components (diodes, electrolytic capacitors, ICs), clear pin 1 and polarity markings on the silkscreen make pre-assembly checks easier.
Board design considerations for assembly
- Fiducials: add at least two or three reference marks at the board corners so the machine can align the board.
- Paste layers: send the top and bottom paste Gerbers for stencil production.
- Component spacing: very dense placement makes rework and optical inspection harder.
- Panel rails: small boards may need panel rails for the assembly line.
Common mistake: reference designators in the BOM that do not match those in the pick-and-place file. After any last design change, export both files again.
Choosing a sourcing model
In full turnkey, the manufacturer sources all components. In consignment, you supply the components. In a hybrid model you supply critical parts and the manufacturer sources the rest. You can choose the sourcing model in the Üret Al quote form.
Checklist
- Each BOM line has MPN, manufacturer and package
- Unfitted components marked as DNP
- Lines where alternatives are and are not allowed are marked
- Pick-and-place file matches the BOM exactly
- Paste layers and fiducials included
- Testing and programming requirements stated
Upload your Gerber, BOM and pick-and-place files to get offers for assembly and component sourcing.