Meaning
Metallization of semi-severed plated through-holes along a printed circuit board edge provides conductive pad surfaces for module-to-board attachment. Circuit board designers specify castellation plating when surface-mounting daughterboard modules directly onto a main motherboard without pin headers. The process creates semi-cylindrical plated cavities along the board perimeter that align with corresponding surface pads during reflow soldering.
This interconnect method terminates at the outer boundary of the module circuit board.
Edge Geometry
Fabrication starts with standard drill and copper plating cycles before a secondary routing step severs the holes along their centerlines. Precision routing prevents burrs and copper lifting from the cavity walls. Edge tolerances dictate solder joint height and mechanical alignment during surface mount placement.
Solder Wetting
Molten solder wicks up the vertical inner channel of each castellated hole during surface-mount reflow assembly. Capillary action draws alloy up the plated side wall to form a visible fillet between the module and target printed circuit board pad. Automated optical inspection equipment inspects these external fillets to verify joint integrity without requiring X-ray imaging.
Insufficient copper coverage inside the hole wall causes voiding or solder bridging across adjacent contact pads.
Inspection Protocol
Visual verification standards defined in IPC-A-610 govern acceptance criteria for castellated solder connections. Technicians check fillet height and side overhang during quality audits. A compliant solder joint covers the complete semi-cylindrical wall surface.
