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Castellated holes are conductive edge features

Castellated holes are plated holes intersected by the final board edge to leave conductive recesses. They are also called plated half-holes, although the finished geometry need not retain exactly half of a circle. The recesses can form solderable connections between a module and a host board. The important feature is the intended conductive edge interface, not merely a semicircular shape in a photograph.

This page owns castellated-hole fabrication and quotation requirements: hole-to-edge geometry, connected lands, plating intent, edge processing and inspection. The related castellated-pad background introduces module-to-board connections. Keep the host footprint, paste and assembly decisions connected to the manufactured module, but do not treat those two design tasks as the same specification.

For a fabrication review, send the module outline, drill data, copper layers and a section or detail identifying the intended half-holes. Include quantity, material, thickness, finish and the proposed host interface. 吃瓜tv can review these requirements as part of PCB manufacturing; exact construction and inspection conditions must be agreed before release.

Make the fabrication note unambiguous

Do not describe a castellation as an ordinary mounting hole with half its outline missing. The fabrication route has to preserve the required plated edge feature. Drilling, metallization, copper build, imaging, profiling and finishing must be sequenced appropriately for the construction. The manufacturer should confirm that sequence and its controls rather than receiving a generic instruction to cut any plated hole in half.

The pad's electrical intent must also be explicit. Name the net connections and any layers that must remain isolated. Copper near the outline can be intentional at the half-hole and unintended elsewhere. A drawing should distinguish those regions so a broad copper-to-edge exception does not hide a different clearance problem.

Explore edge-to-hole geometry in plan view

The calculator uses an ideal circle with a fixed finished diameter. Its center is x = 0; positive x points into the retained board. The final edge is x = e, and the board retains x 鈮� e. A positive edge offset removes more of the circular hole. The relative allowance represents your combined edge/hole positional uncertainty, not a default machine capability.

The opening chord is `2鈭�(r虏 鈭� e虏)`, and the inward recess extent is `r 鈭� e`. The retained circular-hole area fraction follows the circular-segment relationship shown in the output. These are plan-view geometric quantities. Retained hole area is not plated-wall area, solder-joint strength, current capacity or an IPC acceptance threshold. Diameter tolerance, land registration and actual copper thickness are outside this simple model.

Why 鈥渉alf-hole鈥� does not settle the tolerance

For a 1.00 mm fixed hole centered on the final edge, the ideal opening chord is 1.00 mm and half the circular hole area lies on the retained side. If the edge can move by 卤0.05 mm relative to the hole, the minimum chord is approximately 0.995 mm. The inward recess extent and retained fraction also change, and they do not change in the same way as the chord.

That distinction matters when reading a drawing. A chord that changes very little can coexist with a meaningful change in how much of the hole lies inside the module. Checking only the visible width can therefore miss a different geometric concern. Use the dimensions relevant to the electrical and assembly interface, and agree how they are measured on the finished feature.

The example is an original geometry demonstration, not a recommended diameter or edge tolerance. If the edge interval reaches or passes beyond the circle, the tool rejects the half-hole model rather than extrapolating a convenient result. A hole-diameter interval or a noncircular recess needs an expanded analysis and an appropriate fabrication review.

Review the plated wall and the processed edge together

The final conductive wall must remain continuous where the drawing requires it. Edge processing can introduce local burrs, copper damage or irregularities that a top-view pad image does not reveal. The production review should address how the feature will be supported, processed and inspected, including the relationship between the panel arrangement and the half-hole locations.

Plating and surface finish are related but different requirements. A gold-coloured pad does not prove the hole-wall copper thickness, the finish system or solderability after storage. State the required finish and its applicable acceptance basis in the purchase package. If the interface depends on a particular finish, discuss it with both the fabrication and assembly teams before treating it as interchangeable with another surface treatment.

For conventional rigid-board requirements, use the agreed drawing and applicable performance and acceptability documents. The helps identify the relevant documents, but this page does not invent a universal castellation diameter, land width or plating thickness. A project requirement should name its source, revision and inspection method.

Use CAD properties to express intent, then verify the export

CAD software can distinguish a deliberate castellated pad from an unintended copper-to-edge violation. For example, describes the castellated-pad property, its edge-related rule behavior and its effect on Gerber X2 output. That is a useful way to communicate intent; it is not automatic manufacturing approval.

Inspect the exported outline, hole coordinates, plating declaration and copper layers together. Verify units and origin in an independent viewer. A pad property can be correct while an exported edge is shifted or a drill file belongs to an older revision. If a format does not preserve a needed attribute, the drawing and accompanying notes must make the requirement explicit.

Include a detail view showing the finished edge and the hole relationship. If the hole center is intentionally offset from the outline, dimension that offset rather than relying on a viewer to infer it. Keep the complete module outline intact so the manufacturer can review panelization and support without guessing which line is the delivered perimeter.

Connect the manufactured feature to the host interface

The host land pattern must fit the finished module rather than a nominal sketch. Review pad overlap, module placement tolerance, solder access, paste pattern, standoff behavior and any parts on the underside of the module. An exposed recess can help make a solder joint visible, but visibility alone does not establish complete wetting or the quality of every connection.

The module's edge profile and finish can influence assembly, while the host footprint can influence the solder shape observed during inspection. Keep both drawings available during a joint review. Do not correct an assembly problem by changing the half-hole dimensions without considering the resulting plating, profile or electrical implications.

Read the related castellated-pad and module-connection background alongside the approved host footprint. If the module will be delivered in panels, also coordinate the panelization and separation plan. Temporary breakaway features must not be confused with the permanent conductive half-holes.

Compare quotations using an explicit feature scope

A castellation quotation depends on more than the number of edge recesses. Construction, thickness, diameter, relative tolerances, edge length, panel support, finish, quantity and inspection can change the manufacturing scope. A rate copied from ordinary drilled holes does not capture those requirements. Complex combinations should go directly to engineering review rather than being assigned a generic multiplier.

The worksheet uses only allowances that you enter. Count identical quoted half-holes per board and identify whether the allowance includes plating, profiling, finish or measurement. Choose incremental-feature scope or a full-board scope with an explicit base-board allowance. The subtotal is quantity times the entered per-board amount plus setup and additional lot inspection. It is an uncalibrated planning record, not a market price or a binding 吃瓜tv quote.

For illustration, 100 boards with two quoted features at 0.50 currency units each, plus 60 setup and 40 inspection, produce an incremental subtotal of 200. The number is arithmetic only. Real rates must come from a matching quote; an allowance for one simple recess must not be multiplied across dissimilar edge features without review. Freight, tax and unlisted qualification work are not silently added.

What to include in a castellated PCB enquiry

Send the native or released manufacturing outputs, module dimensions, finished thickness, layer stack, surface finish, required quantity and the intended host interface. Highlight every castellated region and its connected lands. State tolerances and acceptance requirements that affect fit or soldering. If the design is still preliminary, identify which dimensions may change and which come from fixed mating hardware.

Ask the quotation to identify unresolved engineering questions and the evidence included with delivery. The useful result is a defined fabrication scope linked to the approved files. You can contact 吃瓜tv directly with those files; the geometry and budget worksheets simply provide optional briefs that can be downloaded or attached manually.

Castellated-hole PCB questions