Through-Hole Technology

What Is Through-Hole Technology?

Through-hole technology (THT) is a PCB assembly method where component leads are inserted through plated holes drilled in the circuit board and soldered on the opposite side. While surface mount technology has largely replaced through-hole for most components, THT remains essential for parts that require strong mechanical connections to the board — including connectors, large electrolytic capacitors, power semiconductors, transformers, and components subjected to mechanical stress during use or board-to-board mating.

Through-hole components are typically soldered using wave soldering (where the board passes over a wave of molten solder) or selective soldering (where solder is applied to specific through-hole locations on boards that also contain SMT components). The PCB layout must accommodate through-hole assembly requirements including adequate pad annular rings, proper thermal relief connections for pads connected to copper planes, and sufficient clearance between through-hole components and nearby surface-mount parts to avoid solder bridging during wave soldering.

Mixed-Technology Layout Considerations

Most modern PCB designs use both SMT and through-hole components, creating mixed-technology boards that require careful layout planning to accommodate both assembly processes. AI-driven layout tools can manage the constraints of mixed-technology designs during generation, ensuring that through-hole component placement, pad thermal reliefs, and wave solder clearances are all satisfied alongside the SMT requirements for the rest of the board. This integrated constraint management prevents the assembly process conflicts that commonly arise when SMT and through-hole placement decisions are made independently.

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