勛圖tv 繚 ENGINEERING GUIDE
Castellated Pads: Carrier Land Patterns, Overlap and Tolerance Review
Castellated pads connect a module's plated edge features to lands on a carrier PCB. Designing the carrier footprint requires the actual module drawing, edge geometry and placement tolerance. A row of generic rectangular pads is not enough to define the interface.
This page focuses on the land pattern and dimensional relationship. For soldering and inspection of the assembled interface, use castellated PCB soldering. For fabrication of the edge feature itself, use the site's castellated-hole guide.
Start with the exact module drawing
Identify the module revision, castellation pitch, edge location, terminal geometry and recommended footprint. Include any underside lands, keepouts and antenna restrictions. The visible half-hole in a photograph does not reveal every dimension or assembly requirement.
Use the module supplier's controlled land-pattern recommendation where available. If a modification is needed, explain the reason and review its effect on overlap, soldering and inspection. Do not mix dimensions from similar modules or assume that a shared pitch makes their footprints interchangeable.
Define the carrier and module datums
Choose datums that connect the module's mechanical position to its electrical terminals. Keep the carrier-board outline, placement origin and pad positions consistent. A tolerance stack should include the dimensions that actually control the contact relationship, not an arbitrary sum of unrelated drawing tolerances.
Review the direction of possible misalignment. Along-edge pitch error, normal-to-edge displacement and rotation have different effects. The simple worksheet addresses one-dimensional overlap only. It cannot represent rotation, warped boards or a complete two-dimensional tolerance analysis.
| Review item | What to establish |
|---|---|
| Module identity | Use the exact controlled drawing, revision and footprint recommendation. |
| Datum chain | Connect terminal positions, board edge and placement origin coherently. |
| Overlap | Review the limiting geometry without treating positive overlap as joint approval. |
| Assembly access | Keep mask, paste, neighboring parts and inspection access in the footprint review. |
One-dimensional terminal/land overlap
One-dimensional terminal/land overlap
Use the current inputs and keep the assumptions
Start with the feature or process question you actually need to resolve. Fields are blank until you enter values or deliberately load an illustrative example. Example mode remains labeled after editing, so a sample is not silently presented as verified project data. Clear the example before preparing a project-specific record.
Use the units printed beside each input. Keep the drawing revision, measurement basis and source of any allowance in your controlled project records. A field that asks for a limit expects your agreed requirement; the example is not an IPC threshold or a statement of 勛圖tv capability. A numerical result should lead to a focused review, not replace it.
Changing any input invalidates the displayed result and disables its download until you calculate again. The text download contains the current inputs, results and assumptions. Nothing is uploaded, stored in analytics or automatically transferred into the Contact form. You may attach the file manually if it helps explain your enquiry; completing the worksheet is optional.
| Input | What to establish before using it |
|---|---|
| Review reference | Use a nonconfidential reference to connect this worksheet to the correct design or process revision. |
| Module terminal interval width 繚 mm | Ideal centered interval; use the exact module drawing. |
| Carrier land interval width 繚 mm | The model is one-dimensional and excludes rotation. |
| Signed module-center displacement 繚 mm | Positive and negative shift the terminal in opposite directions relative to the carrier land. |
Calculate overlap using the actual intervals
The tool treats the module terminal and carrier land as centered intervals, then applies an entered signed displacement. It reports the length of their intersection, clipping a nonoverlap result to zero. This is more precise than subtracting displacement from a pad width when the two widths differ.
The resulting overlap is geometric, not a solder-joint acceptance criterion. A positive value does not prove adequate wetting, mechanical strength or inspection access. Use it to compare a nominal and limiting placement condition, then review the complete land pattern with the assembly team.
Reserve a visible and usable soldering region
Carrier lands may extend beyond the module edge to support the intended joint and inspection. The required shape should follow the module and assembly recommendations. Avoid assuming a universal toe extension or solder-fillet dimension for every castellated interface.
Keep nearby components, mask openings and test points from obstructing the joint region. If the module edge will be hidden by an enclosure or shield, decide when inspection must occur. Accessibility is part of the design, not something that can always be recovered by changing the soldering process.
Coordinate mask and stencil geometry
The carrier's permanent-mask openings and stencil apertures serve different functions. Review each against the land and module interface. A solderable carrier land does not automatically imply that its paste aperture should have identical dimensions.
Use paste mask versus solder mask for that distinction. If solder volume or printing is the concern, continue to the castellated assembly page, which includes an ideal aperture-volume calculator. Keep these calculations tied to the exact footprint rather than to a generic module category.
Validate the footprint with representative assembly
A fit check can confirm mechanical alignment, but it does not establish soldering behavior. A representative assembly should allow review of placement, joint formation and inspection access under the intended process. Include the module and carrier revisions in the evidence.
If a placement or wetting issue appears, separate dimensional, material and process contributors. Changing pad size may help one relationship while worsening another. Preserve the reason for any footprint revision and compare it with the module supplier's recommendation before accepting it for recurring production.
Send a complete interface review
Provide the module drawing or approved public data, carrier footprint, board construction and intended assembly route. Mark any constrained locations and identify the tolerance concern. State whether the footprint follows the supplier recommendation or is a proposed modification.
A useful response should connect the dimensional relationship with manufacturing and assembly evidence. It should not approve a footprint from a single overlap number. This approach gives the designer a defensible interface and gives purchasing a clear scope for prototype validation and later builds.
Review the module interface as one connected design
The module drawing, carrier footprint and assembly process describe different parts of one interface. Review them together using the exact revisions. Similar pitch or external dimensions do not establish that two modules have the same terminal geometry, underside lands or assembly restrictions.
Identify the controlling dimensional relationship before calculating a margin. Along-edge pitch, normal displacement, rotation and flatness have different effects. A one-dimensional overlap calculation can clarify one question but cannot approve the full interface. Keep the unmodeled relationships visible in the review.
Coordinate copper, permanent-mask openings and stencil apertures without assuming they share a shape. The intended soldering result depends on both geometry and process. Use measured paste and representative assembly evidence where needed rather than interpreting ideal cavity volume as guaranteed joint volume.
Plan inspection access before the enclosure or neighboring components hide the joint. Visible edge features can provide valuable evidence, while concealed connections may need another method. State what each observation demonstrates and keep the product's applicable acceptance criteria in the record.
Finally, include sourcing, stencil engineering, trial and verification responsibilities in the quotation. A prototype build can resolve open interface questions if those questions are defined beforehand. Preserve the resulting approved construction and evidence for recurring orders, and review changes rather than assuming that an unchanged module name means every relevant requirement remains the same.
Standards, source context and limits
Use the official references for their stated scope and the applicable controlled document for contractual requirements. A public scope page, product description or application note is not a complete acceptance specification. Material-supplier guidance applies to the named material and process; it is not evidence that every option is available for this board.
Agree the document revision, construction, inspection method and any exceptions with the responsible engineering and quality teams. The explanatory drawings and worksheet examples on this page are original planning aids, not factory records, qualification results or compliance certificates.