SMD vs through-hole: how to choose PCB components

Nearly every component you place on a PCB is either surface-mount (SMD/SMT) or through-hole (THT). The choice shapes your board's size, cost, mechanical strength, and how easy it is to assemble — so it's worth understanding before you commit a layout to a fab.

Short answer: Use SMD for almost everything — it's smaller, cheaper at volume, and machine-friendly. Reach for through-hole where you need mechanical strength or high power: connectors, large electrolytic caps, terminal blocks, and parts that take physical stress. Most real boards mix both, and that's completely normal.

What are SMD/SMT and through-hole?#

Surface-mount devices (SMD) sit directly on the surface of the board and solder to flat copper pads. There are no leads passing through the board. The process of assembling them is called surface-mount technology (SMT) — the terms get used interchangeably, but strictly, SMD is the part and SMT is the method. SMD parts can populate both sides of a board and range from tiny 0201 resistors to QFN and BGA chips.

Through-hole technology (THT) components have wire leads or pins that pass through drilled, plated holes and solder on the opposite side. Think of the classic axial resistor, a DIP chip, a barrel jack, or a pin header. The leads anchor the part mechanically as well as electrically.

Pros and cons of SMD#

Advantages:

• Size and density. SMD parts are far smaller and mount on both sides, so you fit more circuitry in less area — essential for compact, modern designs.
• Cost at volume. Most SMD passives cost fractions of a cent, and because assembly is automated, the per-board labor is minimal at scale.
• Automation. Pick-and-place machines place thousands of SMD parts per hour, then a single reflow pass solders them all at once. This is the backbone of cheap, high-volume manufacturing.
• High-frequency performance. Shorter leads mean lower parasitic inductance, which helps with high-speed and RF designs.

Trade-offs:

• Mechanical strength. SMD joints rely on the solder alone, so parts under physical stress (connectors, ports) can lift pads or crack.
• Hand-soldering difficulty. Small passives and leadless packages (QFN, BGA) are hard or impractical to solder by hand and often need hot air or a stencil and reflow.
• Rework. Replacing a fine-pitch or leadless SMD part is fiddlier than desoldering a through-hole pin.

Pros and cons of through-hole#

Advantages:

• Mechanical strength. Leads through the board create a strong physical bond — ideal for connectors, switches, and anything that gets plugged, pressed, or pulled.
• Power handling. Larger leads and lugs handle higher current and dissipate more heat, so many power components stay through-hole.
• Hand-soldering and prototyping. THT is forgiving with a basic iron, easy to inspect, and easy to rework — the friendliest choice for breadboarding, learning, and one-off prototypes.

Trade-offs:

• Size. Bigger footprints and drilled holes eat board area and block routing channels on inner layers.
• Cost and speed. Automated through-hole insertion exists but is less common; many THT parts end up wave-soldered, selectively soldered, or placed by hand, all of which add time and money.
• Density limits. Holes on both sides restrict double-sided placement.

SMD vs through-hole at a glance#

When should you mix SMD and through-hole?#

Most production boards are a mix, and mixing is the right call whenever each technology plays to its strength. A typical design uses SMD for all the logic, passives, and ICs, then through-hole for:

• Connectors and headers that take repeated mating stress.
• Power components — large electrolytic capacitors, inductors, terminal blocks.
• Mechanical parts — mounting posts, relays, big switches.

The main thing to watch when mixing is assembly cost. A board that is otherwise pure SMD, plus a handful of through-hole parts, still needs a second soldering process for those few parts. If you can find a surface-mount equivalent for a connector or cap that isn't load-bearing, doing so can eliminate an entire assembly step. Consolidating on SMD where it's safe is one of the reliable levers to reduce PCB manufacturing cost.

What does this mean for assembly cost?#

Assembly economics come down to how many processes your board needs. A pure-SMD board runs through one automated line: solder paste, pick-and-place, reflow, inspect. Add through-hole and you tack on wave or selective soldering — or, for small runs, manual labor charged per joint.

For a hobby build or a handful of prototypes, that hardly matters — through-hole is often the easier path and hand assembly is free if you're doing it yourself. At volume, though, every extra process step multiplies across thousands of boards, so designers lean SMD-first and keep through-hole parts to the ones that genuinely need it. Thinking about placement, package choice, and process count early is the essence of designing for assembly, and it pays off directly in your quoted per-board price.

Getting the details right#

Whichever mix you land on, the manufacturer needs an accurate, consistent package for every part — the right footprints, a clean bill of materials, and a pick-and-place file that matches your actual placements. Package mismatches and stale BOMs are a common cause of assembly delays, which is why disciplined BOM management matters as much as the SMD-vs-THT decision itself.

That's where an automated pipeline helps. Connect a KiCad project to GoForFab and every push regenerates the full manufacturing package with kicad-cli — Gerbers, drill files, BOM, and a CPL/pick-and-place file — so your outputs always reflect the components you actually placed, SMD and through-hole alike. It's free forever to get started, so you can wire up a reproducible output pipeline before your first order and stop hand-exporting files every revision.

Pick the technology each part deserves, keep your outputs honest, and the SMD-versus-through-hole question stops being a dilemma and becomes just good engineering.