RAYPCB · ENGINEERING GUIDE
PCB Component Polarity and Orientation: From Pin One to Placement Files
Correct component orientation connects electrical terminal identity to the component's physical position on the board. The schematic pin, CAD pad number, package marker, placement rotation and inspection image must agree. A part can be centered perfectly on its footprint and still be electrically reversed.
This guide helps resolve orientation across documents. The angle worksheet illustrates a declared rotation or mirror operation only. It does not convert arbitrary CAD output into a placement-machine program, because exporter zero angles and bottom-side conventions must be agreed with the assembler.
Start with terminal identity
Use the exact manufacturer part number and package drawing to identify pin one, anode/cathode, positive/negative terminal or keyed mechanical orientation. Do not infer meaning from the presence of a stripe or dot alone. Different component families use different marking conventions, and a photograph of a similar part may show a different package variant.
Check the chain from schematic symbol pin number to PCB pad number and then to the physical terminal. A correct rotation cannot repair a footprint whose pad numbering is wrong. For a substitute part, verify pin assignment and marking as well as body dimensions; matching package size does not establish electrical interchangeability.
Distinguish top view from bottom view
A package drawing may show the component from above or from the terminal side. An assembly drawing may show the bottom side as viewed from below or as a transparent view from above. Label these conventions explicitly and use an asymmetric reference to prevent accidental interpretation as a rotation.
Reflection and rotation are different transformations. In the worksheet, mirroring about the Y axis changes the sign of the X direction, then an optional counterclockwise rotation is added. A 30-degree vector becomes 150 degrees after that mirror. This is a geometric illustration, not a statement that every bottom-side placement export uses this rule.
| Review item | What to establish |
|---|---|
| Identity | Physical marker resolves to a terminal on the exact part. |
| Mapping | Symbol pins, footprint pads and board nets agree. |
| Convention | Side, view, angle direction and zero reference are declared. |
| Verification | The regenerated export and first-article reference show the intended orientation. |
Agree on the placement-file convention
Record coordinate units, origin, side labels, angle direction and zero-angle reference for the export. Ask the assembler how the data will be interpreted for the actual machine library. Package orientation in a tape pocket is another relationship and must not be confused with board placement rotation.
Use the placement preview and assembly drawing to reconcile at least one asymmetric component on each populated side. Compare the actual pin-one location, not only a numeric rotation column. A file full of angles that look consistent can still have the wrong source zero convention.
Make inspection marks survive assembly
Place readable polarity and pin-one indicators where they remain useful after the component is fitted. Keep markings clear of pads, mask openings and critical mechanical features. If the finished part hides the board marker, the assembly drawing or inspection documentation must provide another unambiguous reference.
Do not rely on silkscreen to override electrical design data. Silkscreen can be omitted, clipped or interpreted incorrectly, while the machine uses the placement program. The release should agree before production, with visual marks serving as a corroborating check rather than the sole source of truth.
Drawing-view orientation transform
Drawing-view orientation transform
Use the current inputs and keep the assumptions
Choose the question you want to resolve before entering numbers. The fields start blank. Load example deliberately if you want to understand the calculation, and keep that example separate from your project record. The example label remains visible after editing; reset the tool before preparing a record from your own data.
Use the displayed units and identify the source of each input. A dimension should refer to the same layer, reference plane and design revision as the other dimensions in the model. An entered limit is your review requirement, not an IPC value supplied by this website. Where a value is unknown, obtain it or preserve the question as open instead of guessing a familiar number.
Read the assumptions with the result. A negative margin is retained so a conflict remains visible. A positive margin only answers the stated mathematical question. It does not establish process capability, compliance, electrical performance or production yield. Checklist statuses are self-reported and do not imply that the underlying evidence has been inspected.
Changing a field invalidates the result and disables its download until you calculate again. The text download contains the current inputs, result and limitations. No CAD file is read, no project data is uploaded and nothing is automatically inserted into Contact. Attach the record manually if useful. You can request a review directly without using the worksheet.
| Input | What to establish before using it |
|---|---|
| Review reference | Connect this worksheet to a nonconfidential design/revision reference. |
| Source angle · degrees | Illustrative vector angle, counterclockwise from +X. |
| View transform | Mirror about Y changes x to -x; this is a declared drawing operation, not a machine bottom-side convention. |
| Added rotation · degrees | Applied after any mirror. Obtain the actual exporter and assembler convention separately. |
Resolve a conflicting orientation before building
Suppose an LED symbol identifies anode and cathode correctly, but the footprint's polarity graphic contradicts the part drawing. First verify pad numbers and net connectivity. Next correct the library graphic or symbol mapping as required. Then regenerate the placement and assembly outputs and recheck the physical orientation against the exact part.
Do not fix the symptom by adding an unexplained 180-degree rotation in a spreadsheet. Such a correction can be lost on the next export or applied twice by another operator. If a production-specific transform is necessary, document its owner, scope and verification method in the controlled release.
Review variants and substitutions separately
Different fitted options can use different component markings or require different machine-library entries. Preserve the approved part identity and variant context so the first-article review uses the right reference. A substitute with a rotated internal pin assignment must be treated as an electrical design change, not a purchasing convenience.
An orientation investigation should retain the observed condition, component lot or identity where available, board revision, placement data and the corrected result. These records help distinguish a design-library error from a programming or handling problem without blaming the wrong stage.
Hand off a specific question
Provide RAYPCB the affected reference designator, exact part number, relevant datasheet view, current assembly view and placement convention. The SMT footprint guide helps check the associated land pattern. Clear evidence lets the review focus on the actual mismatch and prevents a generic statement such as rotate the component from becoming an ambiguous manufacturing instruction.
Run a short cross-file release rehearsal
Choose a small set of references that exposes the likely ambiguities: one polarized component, one bottom-side component, one optional part and one mechanical attachment. Trace each through the BOM, drawing and placement data. Use the actual exports that will be sent for production, rather than relying on the CAD view alone.
For each reference, ask what is fitted, where it is fitted, which side receives it and what identifies the correct orientation. Where a special operation applies, locate the instruction and its owner. If the answer requires an undocumented conversation, improve the release package before it leaves the design team. This exercise is short enough to repeat after a consequential revision.
Next, compare identifiers across the files. The bare-board revision, assembly revision and product variant may legitimately differ, but their relationship must be explicit. Filenames can help, yet a filename alone should not be the only evidence of the intended build. Keep a concise manifest that identifies the files actually released and the unresolved questions, if any.
Assign a decision owner for proposed substitutions or manufacturing changes. The person who uploads a package is not necessarily authorized to approve a pin-compatible replacement, a copper change or a different inspection scope. Making that responsibility visible avoids a production delay being resolved through an assumption that later becomes a product problem.
After a correction, regenerate the affected outputs and re-run the representative checks. Preserve the superseded package as a historical record, while making the approved package unambiguous to the receiving team. Do not distribute two apparently current versions and expect the assembler to decide which one is authoritative.
The enquiry can contain the current package plus a short list of decisions that need help. Keep commercial details such as quantity, delivery constraints and customer-supplied materials separate from engineering exceptions, but include both where they affect the scope. A reviewer should be able to identify the next useful action without interpreting an entire email history.
Standards, source context and limits
The references below support the stated package, design or process context. Apply a component manufacturer's guidance to its named device or family and confirm the exact drawing revision. A supplier application note is not a universal manufacturing rule, and a public standards scope is not the complete controlled standard.
Agree the governing documents, revision basis, acceptance requirements and exceptions with the responsible engineering and quality teams. The official IPC revision table is useful for checking document status; it does not by itself resolve a project's contractual requirements. This page does not reproduce paid normative tables or claim certification.
Archive photographs illustrate relevant boards, components or assembly activity. They are not proof of the current equipment inventory or a completed qualification for your project. The explanatory drawings and worked examples are original teaching aids. Confirm actual process availability and the proposed inspection scope during the project review.