When a printed circuit board needs to be assembled, one of the first decisions an engineer makes is how the components will be attached. Two mounting methods dominate the industry: surface mount technology (SMT) and through-hole technology (THT). Both place electronic parts onto a PCB, but they go about it in very different ways, and each brings its own trade-offs in size, strength, cost, and performance.
This article explains the difference between SMT and through-hole components, compares their advantages and limits, and outlines when a mixed approach makes the most sense. If you are planning a project, the information here will help you brief a contract manufacturer with the right questions.
Surface mount technology places components directly onto the surface of the board. Small solder pads are printed with solder paste, the parts are set down on those pads by automated pick-and-place machines, and the whole board then passes through a reflow oven where the solder melts and forms the joints. No holes are drilled for the leads to pass through.
Because the components are small and both sides of the board can be populated, SMT supports very dense layouts. It is the standard method for smartphones, wearables, IoT modules, communication boards, and most high-speed digital circuits, where short connections keep parasitic inductance and capacitance low and signal integrity high.
In through-hole assembly, components have wire leads that are inserted into plated holes drilled through the board and soldered on the opposite side. This can be done by hand or, at higher volumes, with wave soldering, where the board travels over a wave of molten solder that wets each joint. The leads lock mechanically into the PCB, which is exactly why the method survives vibration, shock, and temperature cycling so well.
Through-hole is still the sensible choice for connectors that are plugged and unplugged repeatedly, for power transistors, relays, transformers, and the larger current-carrying parts found in industrial controls and power supplies. Those leads also make components easier to ｒｅｐｌａｃｅ with basic soldering tools, which is a real advantage for maintenance and rework.
Although the goal is the same, SMT and THT differ in several practical dimensions:
Component size and board space. SMT parts are small, sit flat on the board, and permit double-sided placement, so designers can pack far more functionality into a small area. Through-hole parts are bulky, occupy both sides of the board, and block routing space on inner layers because of the drilled vias.
Electrical performance. SMT joints are short, which keeps parasitic effects low and suits high-frequency and high-speed designs. Through-hole leads are longer, so the technology is better suited to power circuits and applications where very high frequency performance is not the priority.
Mechanical strength. Through-hole leads form a strong physical anchor, making the design more resistant to vibration and mechanical stress. SMT relies on surface solder joints; over time, large packages under heavy stress may benefit from underfill or adhesive reinforcement.
Heat handling. Through-hole power devices can transfer heat through larger leads and, if needed, connect to external heat sinks. SMT power parts depend on copper areas, thermal pads, and thermal vias, so heat is managed through layout rather than the package itself.
Production speed and cost. SMT is highly automated, which makes it very economical as volumes grow. Through-hole involves more manual or separate wave-soldering operations, so it tends to be more appropriate for prototypes, lower volumes, and products that must be repaired easily in the field.
For many real-world products, especially automotive, industrial, and communication systems, the answer is not one technology but both. Dense parts such as microcontrollers, sensors, and communication ICs are placed on the board with SMT, while connectors, terminal blocks, relays, and power devices are inserted as through-hole. The board is typically assembled SMT-first, then the through-hole parts are processed with wave soldering.
A processor that can handle this mixed process from a single supplier saves a lot of coordination. Handling a true one-stop SMT assembly service together with a through-hole soldering service under one roof means boards move from solder-paste printing through placement, reflow, wave soldering, lead cutting, cleaning, and testing without being handed between several contractors.
Choosing the right process is only half the job; the quality of the shop that runs it determines whether boards survive in the field. Farway Electronic, an electronics manufacturing services provider based in LongGang, Shenzhen, supports the full chain from PCB board making and component sourcing through SMT, DIP plug-in welding, conformal coating, and finished-product assembly.
On the SMT side, two production lines run Yamaha medium- and high-speed placement machines and Jintuo ten-zone reflow ovens, with the capability to place components down to 01005 size and BGAs at 0.2 mm pitch. The DIP department operates two plug-in lines, two wave-soldering machines, 24 rear-welding stations, and a board-washing line. Boards up to 510 mm by 460 mm can be handled at PCBA stage, and orders are accepted from a single prototype unit through medium and large batches.
Quality controls follow IPC standards, with checkpoints including solder-paste inspection, AOI optical inspection, first-article inspection, X-ray inspection, ICT, and functional testing. The company operates under ISO 9001, ISO 13485, IATF 16949, and ISO 14001 systems, which matters when boards are headed into automotive, medical, or industrial equipment that cannot tolerate early failures.
SMT wins on size, density, speed, and signal performance; through-hole wins on mechanical strength, power handling, and easy repair. Neither is universally better, and a well-planned mixed assembly often delivers the best balance of both. Discussing these trade-offs with a contract manufacturer early, and confirming how SMT, DIP, and testing are handled together, goes a long way toward predictable quality and on-time delivery.
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