PCB Hole Selection Guide: PTH, NPTH, Through, Blind, Buried and Special Holes
A practical way to classify PCB holes by conductivity, layer connection and function, with design details that should be made explicit for manufacturing.
PCB holes should be described by both electrical function and physical construction. Clear classification helps prevent ambiguity in drill data, fabrication drawings and assembly requirements.
Plated through holes (PTH)
A PTH has conductive copper on the hole wall and connects copper features on two or more layers. It may be used for component leads, connectors, test points or interlayer vias.
Non-plated through holes (NPTH)
An NPTH has no conductive barrel and is commonly used for mounting, alignment or mechanical clearance. The drawing should identify it as non-plated, especially when it sits near copper.
Through vias
A through via crosses the full board thickness. It is generally straightforward to fabricate, but its finished diameter, annular ring, aspect ratio and unused stub still need review.
Blind vias
A blind via connects an outer layer to one or more inner layers without passing through the entire board. Its construction depends on the stack-up and lamination sequence, so the connected layers must be specified.
Buried vias
A buried via connects inner layers only and is not visible from the board surface. It adds lamination and process complexity and must be designed together with the stack-up.
Microvias and HDI structures
Laser-drilled microvias are used in HDI designs. Stacked, staggered, filled and capped structures have different reliability and process implications. The via structure should be defined, not inferred from pad geometry alone.
Slots, castellations and other special holes
Plated or non-plated slots, edge castellations, counterbores and controlled-depth holes should be called out in the fabrication drawing with dimensions, plating status and tolerance.
Common review points
- Finished hole size versus drill size and plating allowance
- Pad diameter and annular ring after tolerance
- Hole-to-copper and hole-to-edge clearance
- Aspect ratio, board thickness and material system
- Via filling, plugging, capping or planarization requirements
- Consistent definitions across Gerber, drill, stack-up and drawing files
Choose the simplest structure that meets the design
A more complex via structure can increase routing density, but it also changes cost, risk and lead time. Confirm the electrical need, then have the proposed structure reviewed against the actual manufacturing route.
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