PTH

A plated through-hole is a drilled opening in a printed circuit board that has been electroplated with copper on its inner walls. The hole passes completely through the board, from top surface to bottom, and the conductive copper plating allows electrical current to flow between components or traces on different layers. This fundamental connection method has remained the dominant assembly technique for decades, even as surface-mount technology has grown.

The manufacturing process for PTH involves drilling the hole first, then running the entire board through an electroplating bath. The copper deposit, typically 25 to 50 micrometers thick, coats all exposed surfaces including the hole walls. After plating, a lead frame or component lead is inserted and soldered; the solder wicks into the hole and bonds to the plated copper, creating a mechanically and electrically reliable joint. Hole diameter ranges from 0.3 mm for fine-pitch work to 2 mm or larger for power connections.

PTH boards remain standard for prototype work, hobbyist electronics, and applications requiring mechanical ruggedness or easy repair. A technician can desolder and replace a PTH component without special equipment. However, PTH fabrication costs more than surface-mount-only boards because drilling and plating add process steps. High-volume manufacturers often use a hybrid approach: PTH for critical connections or components that need rework capability, surface mount for everything else.

Common failure modes and variants

Poorly plated holes develop copper voids or incomplete coverage, allowing corrosion and electrical failure. Thermal cycling can cause the plated copper to crack if the board material and copper coefficient of mismatch is too high. Via holes, which are similar but smaller and used only for internal routing rather than component leads, require more aggressive plating parameters to ensure adequate coverage in smaller diameters. Blind vias and buried vias, which do not exit both sides of the board, require sequential build-up or laser drilling, and are more expensive.

The term PTH distinguishes this through-hole method from surface-mount pads and also from older unplated holes, which had no conductive coating and were used in some early boards with hand-wired connections. Today, PTH remains the reference standard for conventional through-hole assembly, and the acronym appears on nearly all board drawings and assembly specifications.