Solder holes and through holes are two common via structures in PCB pads, with essential differences in structural characteristics, functional positioning, manufacturing processes, and application scenarios, and confusing the two will lead to poor soldering quality and circuit performance defects. A through hole is a full-through hole that penetrates all layers of the PCB, including the top layer, substrate dielectric layer, and bottom layer. It is designed for interlayer electrical connection, with metal plating on the hole wall to realize circuit conduction between different layers. Its core function is signal and power transmission, and it is widely used in multi-layer PCB interlayer wiring and component pin penetration welding.

A solder hole, also known as a soldering relief hole or pad hole, is a partial hole opened on the surface pad or local layer, which does not penetrate the entire PCB board in most cases. Its main purpose is to assist soldering and improve soldering reliability, rather than realizing interlayer conduction. Solder holes are mostly set on SMT pads or plug-in pads to solve problems such as solder accumulation, virtual soldering, and solder balling. During the soldering process, the solder hole can discharge excess solder gas and redundant solder, make the solder paste distribute evenly on the pad, and enhance the bonding force between the component pin and the pad.

There are also obvious differences in process requirements and application limitations between the two. Through holes require strict hole wall metallization, with high requirements for hole position accuracy and plating thickness, and they will introduce parasitic inductance and capacitance, which are not suitable for high-speed signal paths. In contrast, solder holes generally do not need metallization, with lower process difficulty and cost, and they only act on the surface soldering process without affecting interlayer circuit transmission. In practical PCB design, through holes are used for electrical interconnection, while solder holes are used for soldering optimization, and standardized distinction and layout can effectively improve PCB soldering yield and long-term service stability.