How to Set PCB Castellated Holes Requirements

Quick Answer: PCB castellated holes requirements should state finished half-hole size, pad geometry, plating expectation, routing quality, panel support, surface finish, assembly use, and inspection evidence. The goal is a solderable module edge, not simply a row of cut-through vias.

Key takeaways – Define the castellated edge from the assembly interface backward. – Finished hole, copper wrap, pad width, and edge quality should be checked together. – Panelization and routing sequence can decide whether half-holes are clean or damaged. – Use DFM approval before production when the module will be soldered to another PCB.

Castellated holes look simple in a finished module, but they combine drilling, plating, routing, surface finish, and assembly fit. A buyer may ask for “half holes” and expect a solderable side terminal. A factory needs the dimensions, copper condition, and acceptance level that make the side terminal reliable.

This topic is useful for RF modules, IoT modules, small daughterboards, and test adapters that solder onto a carrier board. The risk is not only whether the board can be fabricated. The risk is whether the finished edge matches the carrier footprint and creates repeatable solder joints. Start with the normal PCB fabrication quote files, then add the castellated-hole requirements below.

Decision path

1. Confirm the assembly role
2. Define geometry and copper
3. Control routing and panel support
4. Decide finish and inspection evidence
5. Close DFM questions before production
6. Send a quote-ready package
7. Practical approval path for castellated modules

Start with the module assembly role

A castellated edge exists because the module will connect to something else. That carrier board, socket, fixture, or soldering process should drive the requirement. If the module is hand-soldered for prototypes, the acceptance may be different from automated assembly. If it carries RF, power, or dense signal nets, pad geometry and wetting are more sensitive.

The buyer should state whether each half-hole is an electrical terminal, a mechanical alignment point, a test point, or a mix of these roles. A row that looks identical on the PCB may contain power pins, ground pins, RF nets, and no-connect mechanical features. Treating all of them as the same can create unnecessary risk.

For early supplier screening, use the broader PCB manufacturer capability check to confirm whether the supplier is comfortable with small plated half-holes, clean routing, and inspection expectations before a production schedule is promised.

Define hole size, pad geometry, and copper wrap

The finished half-hole size should match the mating footprint and solder process. State finished size rather than only drill tool size when the assembled fit matters. Plating reduces the hole diameter, routing removes half the barrel, and final edge quality decides how much copper remains available for solder wetting.

Pad geometry matters as much as hole size. The land around the half-hole should support solder fillet formation and survive routing. If copper is too close to the cut, the half-hole may chip or expose uneven copper. If the pad is too small, the module may be hard to solder even if the board passes a basic visual check.

When a drawing and Gerber disagree, the supplier should stop and ask. That is a normal CAM-control issue, not a nuisance. The production record should say whether the drawing or data file controls the final half-hole geometry.

Requirement	Why it matters	Typical evidence
Finished half-hole size	Controls mating footprint and solder volume	Drawing and drill table alignment
Pad width	Supports wetting and routing survival	Gerber review and DFM note
Copper wrap condition	Confirms solderable side terminal	Visual inspection or sample photo
No-connect features	Avoids unnecessary plating assumptions	Netlist and drawing note

Control routing, tabs, and panel support

Castellated holes are usually drilled and plated before the board is routed through the holes. The panel must support the small module while the cut is made. If the panel design is weak, the routed edge can tear, burr, or leave uneven copper on the half-hole wall.

A buyer does not need to design the factory panel in detail, but should tell the supplier which edge must remain clean and whether small tab remnants are acceptable. For very small modules, discuss rail location, breakaway method, and whether array shipment is better for assembly.

Do not place mouse bites through functional castellations unless the supplier has explicitly confirmed the method. A small tab that is harmless on a rectangular FR-4 board can damage the most important feature on a castellated module.

Match surface finish and inspection to soldering risk

The surface finish should support the assembly method and shelf-life expectation. ENIG is often discussed for fine module edges, but the right answer depends on soldering process, cost, and reliability needs. The important point is to state whether the half-hole edge must be solderable and what evidence the buyer expects.

If shipment evidence matters, align the request with PCB quality documents before shipment. A small prototype may only need visual confirmation. A production module for a customer audit may need outgoing photos, sample inspection, or lot-level records.

Inspection should look at edge copper condition, burrs, breakout, finish coverage, and obvious plating defects. The supplier should not promise perfect cosmetic edges on an aggressive geometry unless the drawing and panel plan make that realistic.

Risk	Buyer control	Supplier evidence
Poor side wetting	State solderable edge requirement	Sample photo or visual record
Copper tear-out	Review panel and routing approach	DFM approval before tooling
Burrs on module edge	Define acceptable edge quality	Outgoing inspection note
Misfit to carrier	Share carrier footprint	First-article fit check

Close DFM questions before production starts

Castellated holes often trigger useful DFM questions: whether the pad is wide enough, whether the finished half-hole is achievable, whether the route line cuts through the correct hole center, and whether the surface finish is suitable. These questions are easier to solve before production than after a batch of modules is packed.

Use the PCB CAM questions process to classify each answer. A minor clarification can be answered quickly; a changed half-hole size, pad width, carrier footprint, or finish should become a controlled revision.

The buyer should also watch for silent substitutions. If the supplier proposes a simpler plated slot or edge pad instead of true castellated holes, decide whether that still fits the assembly requirement. The alternative may be valid, but it should not happen invisibly.

Build the quote-ready castellated-hole package

A useful package includes the PCB data, fabrication drawing, finished half-hole dimensions, carrier-board footprint or mating requirement, surface finish, quantity, inspection expectation, and whether the modules should ship as individual boards or panels. If assembly will be performed later, state how the modules will be handled.

The best RFQ language is specific without over-prescribing the factory process. Say what the finished edge must do, which features are functional, what evidence is needed, and which file revision controls the order. Let the supplier propose panel details and raise DFM issues early.

When the data is ready, send it through QueenEMS contact and ask for a castellated-hole manufacturability review before quotation lock. That gives purchasing a comparable quote and gives engineering a safer release record.

Package item	Why it belongs
Carrier footprint	Confirms assembly fit
Finished half-hole dimensions	Prevents drill/tool ambiguity
Surface finish	Controls solderability expectation
Shipment format	Protects small modules during handling

Practical approval path for castellated modules

Start from the carrier board, not the module alone

A castellated module is only successful when it works with the board it will be soldered onto. That means the buyer should review the module edge and carrier footprint together. Pad pitch, pad length, exposed copper, solder mask opening, stand-off expectation, and assembly process all influence whether the final joint is repeatable. If the module supplier sees only the module Gerbers, the quote may miss a fit issue that appears later at assembly.

For a new product, send the carrier footprint or at least the critical landing pattern. The supplier does not need the whole system design if it is confidential, but they need enough information to judge whether the half-hole geometry supports the solder joint. This is especially important when the castellated edge carries RF or high-current nets, because solder volume and ground continuity are part of the product performance.

Treat edge quality as an acceptance item

Castellated holes can be electrically connected and still look rough. The buyer should decide what edge quality is acceptable for the product. A development sample used for bench testing may tolerate more cosmetic variation than a module sold to a customer or assembled by automation. If the edge will be inspected by the end customer, sample photos or a first-article approval step can prevent a dispute.

Acceptance language should be practical. “Perfect half holes” is not a useful manufacturing requirement. Better wording identifies unacceptable conditions: broken copper that affects soldering, heavy burrs, loose laminate, missing plating in functional half-holes, or edge damage that prevents module seating. The supplier can then quote and inspect against visible risk rather than guessing the buyer’s cosmetic threshold.

Keep prototype decisions from leaking into production

Many castellated modules begin as urgent prototypes. A buyer may approve a wider tolerance, different panel method, or visual workaround to get samples quickly. That can be reasonable, but the approval should be marked as prototype-only when production will later require a cleaner edge. Otherwise the prototype shortcut becomes the silent production standard.

Before moving to production, review whether the prototype process, finish, panelization, and inspection method will remain the same. If the supplier plans to change the array, routing method, or shipment format, the buyer should ask whether the half-hole edge will look and solder the same. This is a small conversation compared with the cost of discovering that production modules no longer assemble like the approved sample.

Questions that separate real capability from a quick yes

Before accepting a quote, ask how the supplier will protect the half-hole edge during routing, whether the finished half-hole size is quoted from the drawing or inferred from drill data, whether the panel method can support the module size, and what evidence will show edge quality. These questions turn a broad capability claim into a production plan.

Also ask whether the supplier sees any conflict between the carrier footprint and the module edge. If the supplier cannot review the carrier footprint because it was not provided, record that limitation. A quote can still proceed, but the buyer should understand that the assembly fit has not been fully reviewed. For modules that will be sold as products, that limitation matters.

How to compare two castellated-hole quotations

Two quotes may differ because one supplier includes first-article photos, tighter edge-quality control, or array shipment while another assumes individual boards with minimal evidence. The buyer should not force both suppliers into the same price box without understanding scope. A cheaper price may be fine for a prototype, but production modules need repeatable solderability and edge quality.

Compare the finished half-hole requirement, panel/shipment method, surface finish, inspection scope, and DFM assumptions. If a supplier suggests a different pad size or route path, ask whether the change affects the carrier footprint. If it does, engineering should approve it before purchasing treats the quote as final.

What QueenEMS should confirm before draft production

A good review should confirm that the castellated edge is visible in the data, that half-hole size and pad geometry are not contradictory, that functional edges are protected in panel planning, and that the requested evidence matches the order risk. If questions remain, QueenEMS should raise them before tooling rather than smoothing over the uncertainty.

Wording that prevents a weak production release

Use RFQ wording that names the finished module function. For example, “castellated edge for soldering to carrier PCB, finished half-hole geometry per drawing, supplier to confirm routing and edge quality before production” is stronger than “make half holes.” If the assembly house needs modules shipped in panel, include that requirement before quotation. If the carrier footprint is preliminary, label it preliminary so the supplier does not treat it as frozen production data.

The final release should also say what happens to open DFM questions. If the supplier asks to change pad size, route position, or finish, the order should hold until engineering approves the effect on assembly. This keeps the module, carrier board, and production record aligned.

Approval record for reorders and supplier comparison

For a first build, buyers often focus on getting the quotation back quickly. For the second and third build, the bigger value is repeatability. Keep the final PCB castellated holes requirements decision with the released files: what was quoted, what was clarified during DFM, what evidence was accepted, and which assumptions should carry forward. This prevents a repeat order from being treated like a fresh interpretation of the same ambiguous data.

The same record also helps compare suppliers without forcing an unfair price match. One supplier may include engineering review, file-control questions, sample evidence, and shipment documentation; another may quote only the base fabrication step. The lower number is not automatically wrong, but the buyer should know what risk has been removed and what risk remains with the buyer. When the requirement affects assembly, fit, signal behavior, or customer acceptance, the extra review may be cheaper than one remake.

Before releasing production, ask one final internal question: if the boards arrive exactly as the supplier understood the RFQ, will engineering and purchasing both agree that the requirement was met? If the answer is uncertain, the RFQ package needs one more clarification before the purchase order is locked.

FAQ

Is PCB castellated holes requirements always required?

No. Use it when the feature or evidence changes assembly, reliability, or quotation risk. Low-risk prototypes may need a simpler review.

Can purchasing approve a change by email?

Purchasing can approve commercial scope, but engineering should approve geometry, finish, tolerance, or signal-integrity changes.

What should QueenEMS review before quoting?

QueenEMS should review the controlled data package, drawing notes, risk evidence, quantity, lead time, and any supplier questions before quotation lock.

Ready to quote this requirement? Send the controlled files, drawing, quantity, target lead time, and evidence request through QueenEMS contact. Ask for a DFM review before production release so the quotation reflects the real requirement rather than a hidden assumption.