Two files answer different questions
Here, CPL means component placement list in a PCB assembly package. Acronyms may be used differently in other procurement systems; name the required fields explicitly when exchanging data.
The bill of materials identifies what is to be fitted. A component placement list, often called CPL, centroid or pick-and-place data, identifies where the components belong. They work together, but one cannot substitute for the other. A valid coordinate does not identify the exact orderable part, and an accurate part number does not define its orientation on the board.
Use the same released design and assembly variant to generate both outputs. The common reference designator, such as R12 or U3, connects the BOM item, placement row and assembly drawing. If those identifiers differ, the assembler must resolve the discrepancy rather than infer the intended build.
Check the BOM as a procurement document
For each fitted item, provide the manufacturer and complete orderable part number, quantity and reference designators. Include package or footprint information where it helps verification, plus any approved alternate rules. A description such as “10 k resistor” does not establish tolerance, power rating, package and other application constraints.
Make do-not-populate positions and variant differences explicit. Separate customer-supplied parts from purchased parts. If several reference designators share a row, their count must agree with the quantity for that variant. Record the approval needed before a buyer substitutes an apparently equivalent item.
Check placement as geometry and orientation
- Declare coordinate units, origin and whether coordinates refer to the component’s placement center.
- Identify the board side for every fitted component.
- Confirm the CAD rotation convention, including bottom-side interpretation.
- Compare pin one, polarity and connector orientation with the exact manufacturer drawing.
- Identify items placed manually, installed after soldering or excluded from the automatic-placement dataset.
The assembly drawing provides a useful human-readable cross-check. Include clear views and reference designators, especially around polarized or asymmetric components. Do not “correct” every bottom-side rotation with a blanket rule without knowing how the CAD exporter and assembly system interpret it.
Reconcile the package before kitting
Compare the sets of reference designators: fitted items in the BOM should have an appropriate placement or installation instruction, and placed items should have an approved identity. Then review quantities, duplicate designators, missing sides and unexpectedly identical coordinates.
When a component library or footprint changes, re-export the relevant files and check the physical fit as well as the data. Archive the BOM, CPL, fabrication revision, assembly drawing and approval record together. This makes a repeat build reproducible and gives both engineering and purchasing the same basis for answering questions.