When planning a new electronics assembly, one of the fundamental decisions is whether to use Surface Mount Technology (SMT), Through-Hole Technology (THT), or a combination of both. Each technology has specific strengths, and the right choice depends on your component selection, volume, mechanical requirements, and budget.
A Brief History
Through-hole assembly was the dominant PCB assembly technology from the 1950s through the 1980s. Components had wire leads that passed through drilled holes in the board and were soldered on the underside — either by hand or by wave soldering machine. The method is reliable and produces mechanically strong joints.
Surface mount technology emerged in the 1970s and became mainstream in the 1990s. Instead of through-holes, SMT components have flat leads or pads that sit directly on the surface of the PCB and are soldered using reflow ovens. SMT allows much smaller components, higher component density, and greater automation — making it the dominant technology for modern mass-produced electronics.
Surface Mount Technology (SMT)
In SMT assembly, the process is:
- Solder paste is applied to pads via a stencil
- Components are placed by automated pick-and-place machines
- The board passes through a reflow oven — the solder paste melts and forms joints
- Boards are inspected by AOI (Automated Optical Inspection)
Advantages of SMT:
- Much smaller component packages (0201, 01005, fine-pitch QFN, BGA)
- Higher component density — more functionality in less space
- Lower cost at medium-to-high volumes due to automation
- Components can be placed on both sides of the board
- Better high-frequency performance (shorter lead lengths reduce parasitics)
Limitations of SMT:
- Smaller components are harder to hand-solder for prototyping or repair
- Mechanical strength of joints is lower — not ideal for connectors subject to repeated stress
- Requires stencil and pick-and-place setup, increasing non-recurring engineering (NRE) cost for small batches
Through-Hole Technology (THT)
THT assembly involves inserting component leads through drilled holes and soldering them — either manually or by wave/selective soldering.
Advantages of THT:
- Mechanically robust joints — ideal for connectors, switches, power components subject to stress
- Easier to hand-solder, prototype, and rework
- Still the best choice for high-voltage, high-power components (large capacitors, transformers, relays)
- No stencil required for low-volume assembly
Limitations of THT:
- Components are much larger — limits board density
- Drilling adds manufacturing cost and reduces available routing space
- Wave soldering is less compatible with mixed SMT+THT boards
Mixed Technology Assembly
Most modern PCBs use a combination: SMT for the majority of components (microcontrollers, passives, ICs) and THT for mechanical connections (USB ports, barrel jacks, large capacitors, through-hole switches). EazyPCB handles mixed-technology assembly in a single production run, using reflow for SMT components followed by selective soldering for THT parts.
Which Should You Choose?
Use this framework:
- High-volume production, compact design? SMT is the answer. Automation drives the cost down at scale.
- Prototype or low-volume (<10 units), hand-assembly acceptable? Consider larger SMT packages (0805, SOT-23) or THT for simplicity.
- Heavy mechanical connectors, high-current components? Use THT for those components regardless of overall assembly method.
- Wearable or miniaturised product? SMT only, with the smallest practical package sizes.
Need advice on assembly strategy for your specific project? Send us your BOM and we’ll recommend the most practical and cost-effective approach. Contact us at op@eazypcb.com.
