Identity comes before interpretation
A dot, stripe, notch or chamfer can mean different things on different component families. Start with the BOM’s exact manufacturer part number and the applicable datasheet or package drawing. Do not infer polarity from a photograph of a similar-looking device.
Confirm that the physical package and markings agree with the supplied part documentation. If identity is uncertain, hold the item for clarification rather than creating a placement rule from appearance. A correct orientation for the wrong component still produces the wrong assembly.
Check the relevant feature for each family
- LEDs and diodes: verify anode and cathode identification and the package view used in the drawing.
- Polarized capacitors: confirm which terminal a marking identifies; conventions are not identical across all capacitor types.
- ICs: verify pin one, numbering direction, package variant and any exposed-pad connection.
- Inductors and magnetic components: distinguish an ordinary two-terminal part from coupled windings or devices with a specified orientation.
- Connectors: confirm pin numbering from the correct mating or mounting view.
Some components are not electrically polarized, but they may still have placement or inspection conventions. Record a required orientation when it matters to the process, without inventing a polarity that the component documentation does not define.
Make every release representation agree
Check the schematic pin numbers, footprint pads, assembly drawing and placement data against one another. A placement-file rotation is meaningful only with its origin, side and convention. Bottom-side interpretation deserves a deliberate check because mirroring and rotation can be confused.
Use clear pin-one or polarity marks where they remain visible and do not interfere with pads. The assembly drawing should resolve any ambiguity that the board legend cannot. Do not ask an operator to choose between contradictory marks, a CAD preview and a supplier package image.
Verify setup before committing the build
During first-off review, compare the actual fitted component with the approved orientation reference. A photograph or inspection record can help preserve the accepted setup for repeat builds, provided it identifies the board and component revision. Review the setup again when a package, alternate manufacturer or placement library changes.
If an orientation defect is found, contain affected units and determine the proper rework and retest scope before power is applied. Electrical behavior alone may not expose every misplaced or overstressed part. Correct both the physical units and the source of the instruction error so the next build does not repeat it.