PCB castellations, also known as castellation holes or half-holes, are specialized plated features located along the edges of printed circuit boards. These semi-circular metallic pads serve as electrical and mechanical connection points, enabling boards to be soldered directly onto other PCBs or carrier boards.
What Are Castellations?
Castellations are plated half-holes that appear along the perimeter of a PCB. When viewed from the side, they resemble the battlements of a medieval castle tower, which is how they earned their name. These features are created by drilling or routing holes at the board edge and then cutting through the center of those holes, leaving semi-circular copper-plated notches.
Each castellation consists of a plated copper surface that wraps around the edge cutout, creating a reliable soldering surface. The copper plating typically ranges from 25 to 35 microns in thickness, ensuring robust electrical conductivity and mechanical strength. This plating extends from the top surface, through the edge profile, and down to the bottom surface, forming a continuous conductive path.
Manufacturing Process
The production of castellations requires precise coordination between drilling, plating, and routing operations. First, holes are drilled at designated positions along the board edge according to the design specifications. These holes undergo the standard plating process, where copper is electroplated onto the hole walls to establish conductivity between layers.
After plating, the board edge is routed or scored precisely through the center of each plated hole. This routing operation must maintain tight tolerances to ensure symmetrical half-holes on both sides of the board. The cutting process exposes the cross-section of the plated hole, revealing the copper barrel that will serve as the soldering surface.
Quality control during manufacturing is critical. The castellations must have uniform copper coverage without voids or cracks. Any defects in the plating can compromise electrical connection or mechanical stability. Manufacturers typically inspect castellations using automated optical inspection systems to verify dimensional accuracy and plating quality.
Types and Variations
Castellations can be implemented in several configurations depending on the application requirements. Standard castellations feature uniform spacing along one or more board edges, with typical diameters ranging from 0.5mm to 1.5mm. The spacing between castellations is determined by the pitch requirements of the target application and the current-carrying capacity needed.
Full castellations extend completely through the board thickness, connecting both top and bottom layers. This configuration is common in double-sided boards where signals must pass between layers. The continuous copper barrel provides low resistance and high reliability for power and signal transmission.
Partial castellations may connect only to specific layers in multilayer boards. These selective connections allow designers to route different signals to different castellations while maintaining a compact edge profile. Advanced designs might incorporate multiple rows of castellations at different distances from the board edge to increase connection density.
Applications and Advantages
Castellations are widely used in module-based designs where smaller PCBs must be integrated into larger systems. Bluetooth modules, WiFi modules, GPS receivers, and sensor boards frequently employ castellations for board-to-board connections. This mounting method eliminates the need for separate connectors, reducing both cost and overall assembly height.
The primary advantage of castellations is space efficiency. Unlike traditional connectors that occupy board area and add vertical height, castellations integrate seamlessly into the board edge. This edge-mount capability is particularly valuable in compact devices where every millimeter matters, such as wearable electronics, IoT sensors, and mobile devices.
Castellations also provide excellent mechanical stability when properly soldered. The solder fillet formed around each castellation creates a strong bond that resists vibration and mechanical stress. This reliability makes castellations suitable for applications subject to harsh environmental conditions or frequent handling.
From a manufacturing perspective, castellations simplify assembly processes. Automated pick-and-place machines can position modules with castellations just like surface-mount components. Reflow soldering creates simultaneous electrical and mechanical connections across all castellations, streamlining production and improving yield.
Castellations represent a mature yet continuously evolving interconnection technology. Their combination of space efficiency, reliability, and manufacturing simplicity makes them indispensable in modern electronics design.
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