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Start with the approved manufacturer part number and the package drawing in its datasheet. Identify the electrical symbol, terminal numbers and any stated polarity mark together. A body mark that resembles a familiar cathode indicator can mean something different in another family. Multi-die, RGB, addressable and integrated-driver LEDs need particular care because a two-terminal anode/cathode assumption may not apply to the complete package.

For a concrete example, the Kingbright AA3528MGC datasheet, revision V.15B, shows a polarity mark on the package diagram and a circuit symbol with terminal 1 at the cathode and terminal 2 at the anode. That is an example for the named part and drawing, not a rule for every 3528 outline. The manufacturer鈥檚 recommended soldering pattern is another drawing with its own dimensions and purpose. Do not infer pad numbering from the body photograph alone.

If a supplier offers an alternate LED with the same nominal dimensions and color, compare its terminal map as well as the electrical and optical requirements. Forward voltage, current, binning, luminous distribution and handling conditions can also affect the design. Identical outside dimensions do not establish electrical interchangeability, and a renamed purchasing line should not silently change the approved assembly orientation.

In the schematic, identify which numbered device pin represents the anode and which represents the cathode. In the footprint, check which physical pad has each number. Finally, view the package drawing and the board from the stated side and compare the resulting physical placement. This chain is more reliable than asking whether the stripe 鈥渓ooks right鈥� beside a copper pad.

Create a short reference detail for any ambiguous device: reference designator, manufacturer part number, cathode pad number, anode pad number, board side and a recognizable package mark. Include the source drawing revision. For a two-terminal LED, the two terminals cannot map to the same pad. The tool highlights that conflict, but it cannot validate that your chosen pad numbers correspond to the actual design.

Distinguish electrical orientation from optical orientation. A side-view LED may be electrically correct while facing away from a light pipe or enclosure opening. A right-angle indicator also has a mechanical viewing direction that belongs in the assembly drawing. Show the board edge, connector or mounting datum that fixes this direction so that optical intent survives a rotation or a change in the drawing viewport.

An angle is incomplete without a reference. The component library has a zero orientation, the CAD export has its coordinate conventions, and the placement system has its own component definitions. A value of 90 degrees is therefore not a universal physical instruction. The assembly team should reconcile a known reference component and a small placement preview before applying a convention to a complete job.

Bottom-side interpretation is a frequent source of confusion. A drawing viewed through the board is different from a drawing viewed directly at its underside. Mirroring about one axis and then rotating is not generally equivalent to rotating first and then mirroring. State the viewing convention rather than adding a handwritten angle correction that another operator has to guess how to apply.

The interactive diagram on this page uses an explicit teaching convention: begin in a top-view coordinate frame, rotate counterclockwise, then mirror left to right for the selected underside view. It shows where the labeled terminals move. This is a conceptual transformation, not a conversion utility for any particular CAD export or placement machine. Use the pick-and-place file guide when preparing the production handoff.

Keep the reference designator and useful orientation cue outside the installed component where practical. If the board is crowded, use an enlarged assembly detail that includes the part outline, relevant pad numbers and a board datum. An outline printed under the LED can help during layout review but may be hidden at the moment inspection needs it most.

Avoid relying on a single generic triangle or bar unless its meaning is defined in the project鈥檚 drawing convention. An 鈥淎鈥� or 鈥淜鈥� label is often more explicit, but it still needs to agree with the datasheet and library. Check that the production silkscreen remains legible after clearances are applied around exposed pads. A correct source drawing can become less clear when printed features are clipped in fabrication preparation.

Include exceptional orientations as deliberate design information. Repeated LEDs may be arranged with alternating polarity because of circuit topology, or rotated because of optical and mechanical constraints. Do not let a visually regular array cause an operator to overlook one intentionally different device. A component-reference list and highlighted assembly detail can communicate these exceptions without placing excessive text on the PCB.

Polarity is only one part of a successful LED assembly. The chosen package also has handling, moisture, reflow, cleaning and mechanical constraints. Check the current manufacturer instructions for the specific series and the agreed assembly process. Do not transfer a soldering profile from a visually similar LED or treat the maximum ratings table as a recommended operating condition.

The nozzle contact area matters for packages with a soft lens or other sensitive optical surfaces. Mechanical pressure, unsuitable cleaning chemistry or rough handling can damage a correctly oriented device. Kingbright鈥檚 SMD application notes discuss handling considerations; use them alongside the exact part datasheet rather than replacing the part-specific requirements. Keep the approved packaging and storage instructions with customer-supplied material.

For an LED board enquiry, separate the optical requirement, thermal path and assembly requirement. A correct terminal map does not establish junction temperature or light-output consistency. The LED PCB page covers board materials and thermal design considerations. Here, the goal is a clear installation instruction and a traceable review of the device orientation.

Imagine a prototype whose status LED does not illuminate. First compare the physical part and BOM against the released assembly detail. Verify the electrical terminal map and the viewing direction used for placement. Also check the drive circuit, solder joints and supply conditions under an appropriate test procedure; failure to illuminate is not proof that the LED is reversed.

Suppose the component itself is correct, but the assembly drawing was interpreted as a top view even though it was exported from below. Correct the drawing convention and check the other polarized parts on that side for the same ambiguity. Review whether the placement file and machine library require a corresponding correction. A one-off repair to the prototype is not enough if the underlying handoff can recreate the error in production.

Document the resolved mapping with a reference photo or assembly view approved for the job. If a test result is included, state the conditions and the responsible test procedure. Avoid creating a claim that a general visual check verifies brightness, lifetime or operating margin. Those outcomes require their own specifications and evidence, which may involve different equipment and acceptance criteria.

Provide the BOM with exact part numbers, the PCB and assembly drawing revisions, the component references involved and the placement export. Add the relevant datasheet page or a link with the revision clearly identified. If the issue concerns a bottom-side interpretation, include a board datum and explicitly state which side is being viewed.

Use the tool to explore the geometry and prepare a local note if that helps explain the question. Entering your own pad numbers replaces the example values; it does not cause the tool to read or verify your CAD data. Download the regenerated note after your last input change. Contact remains available whether or not you use the tool, and no tool data is automatically transferred to the form.

For a broader review covering polarity, component clearances, file completeness and inspection access, continue to design for assembly. That keeps the LED-specific detail attached to a clear board-level task. An enquiry can then ask for a defined review rather than a general statement that the board is ready to build.

A practical orientation review uses a known, unambiguous reference component to connect the CAD view, placement export and assembly preview. Select a reference with a documented terminal map, then compare its position and angle in each representation. Include a board datum so that the reviewer can distinguish a rotated viewport from a rotated component. Apply the agreed convention to the remaining parts only after this reference is understood.

Check at least one relevant example on each populated board side when the handoff includes both sides. A convention that appears correct for a top-side LED does not automatically establish the underside transformation. Record whether the underside drawing is viewed through the board or directly from below. If a production system applies an additional library offset, that offset belongs in its controlled setup rather than in an unexplained correction to the design drawing.

The first-article record should identify the board revision and exact part actually placed. Where a body mark is difficult to see after soldering, retain a suitable preassembly reference or approved enlarged detail. The record should explain the interpretation without depending on a person remembering which way a reel was loaded. Reel presentation and finished board orientation are related through machine setup, but they are not the same coordinate description.

If an inconsistency appears, review whether it affects one library component or a whole export convention. A local repair may be sufficient for an individual erroneous footprint; a mirroring error may affect many polarized parts. Describe the scope before changing a batch of angles. That avoids fixing the visible LED while leaving a second orientation problem elsewhere on the board.

This approach also keeps the enquiry focused. Instead of asking whether 鈥渢he LED is correct,鈥� provide the terminal map, side, view, reference component and conflicting output. The reviewer can then answer a concrete assembly question and identify the specific file or setup record that needs revision.

Is the flat edge of a round LED always enough? It is a common clue for some through-hole products, but the exact part documentation should establish the terminal definition. Trimming leads, damaged housings or unusual internal constructions make visual shortcuts less dependable.

Can a diode test prove placement is correct? A controlled electrical observation may help diagnose a known part, but it does not reconcile an incorrect footprint or export convention. Do not use an arbitrary meter output on a device without understanding its limitations and the surrounding circuit.

Should all LEDs share one footprint? Only if the full approved package and land-pattern requirements match. Equal body length and width alone do not establish pad geometry, thermal pad arrangement, terminal numbering or optical direction. Maintain distinct verified library entries when those requirements differ.

Will this tool output a machine rotation? No. It explains a named geometric convention and records your mapping. The actual placement system needs a validated library and agreed export interpretation. The first-article review should verify the resulting placement against the released job information.