When manufacturing a custom PCB, choosing between Surface Mount Technology (SMT) and Through-Hole Technology (THT) is one of the most important decisions you will make. Each method has distinct advantages and use cases.

What is SMT?
Surface Mount Technology (SMT) places components directly onto the surface of the PCB. Components like resistors, capacitors, and ICs have small metal terminals that are soldered to pads on the board. SMT is fully automated using pick-and-place machines and reflow ovens, making it ideal for high-volume production.

What is THT?
Through-Hole Technology (THT) involves inserting component leads through drilled holes in the PCB and soldering them on the opposite side. This method provides stronger mechanical bonds and is commonly used for connectors, transformers, and components that handle high voltage or mechanical stress.

Key Differences:

1. Density: SMT allows much higher component density with smaller packages (0402, 0201, QFN, BGA). THT requires larger pads and drill holes.

2. Cost: SMT is cheaper for volume production due to automation. THT requires manual or selective soldering, increasing labor cost.

3. Strength: THT joints are mechanically stronger and better for connectors and high-stress applications.

4. Repair: THT is easier to hand-solder and rework. SMT small packages require hot air stations.

5. Performance: SMT offers better high-frequency performance due to shorter lead lengths and lower parasitics.

When to choose which:
- Use SMT for high-density, compact, cost-sensitive consumer electronics.
- Use THT for connectors, power components, prototyping, and low-volume builds.
- Many real-world boards combine both: SMT for most chips and THT for connectors.