SMT vs. Through-Hole Assembly: Which Is Right for Your PCB?

Oct 19,2026

Choose surface mount technology (SMT) for small, dense boards built in volume. Choose through-hole technology (THT) for parts that face vibration, repeated plugging, or high current. Most products use both.

This guide compares SMT vs through-hole by strength, cost, and design, so you can pick the right method for your PCB.

Surface Mount Technology vs. Through-Hole: What Is the Difference?

SMT mounts parts on the board surface. Through-hole parts have leads that pass through drilled holes.

SMT is the assembly process. SMD (surface mount device) is the component it places, so SMD vs THT compares the same two methods.

Factor	SMT (Surface Mount)	Through-Hole (THT)
How parts attach	Soldered to pads on the surface	Leads soldered through drilled holes
Board size and density	Smaller; parts fit on both sides	Larger; holes block routing
Assembly method	Automated: stencil, pick-and-place, reflow	Wave, selective, or hand soldering
Mechanical strength	Good for small, light parts	Better for heavy or frequently handled parts
Heat and current	Relies on copper area and thermal vias	Handles higher power; can bolt to heatsinks
High-speed signals	Better; shorter leads, lower inductance	Longer leads add inductance
Prototype rework	Needs rework station and steady hands	Easy with a standard soldering iron
Cost at volume	Lower; machines place the parts	Higher; more labor per board

What Is SMT?

SMT places components directly onto copper pads. Assembly runs in four steps: solder paste printing, pick-and-place, reflow soldering, and AOI inspection.

Advantages

Smaller, lighter boards
Fast automated placement and low cost in volume
Better high-speed and RF performance

Disadvantages

Tall or heavy parts stress surface joints
Small passives can tombstone during reflow
Fine-pitch rework needs skill and equipment

What Is Through-Hole?

Through-hole parts have leads that go through plated holes. The solder anchors the joint through the board thickness.
Parts are placed by hand or insertion machines, then soldered by wave, selective, or hand soldering.
Advantages

Stronger joints for connectors, switches, and heavy parts
Better for high-current power parts
Easy hand assembly and repair

Disadvantages

Holes take up routing space on every layer
More handling and labor per board
Larger, heavier boards

SMD Components vs. Through-Hole Components: Which Parts Use?

SMD vs through-hole components come down to the part's size, weight, and job.

Component type	Common choice	Why
Resistors, small capacitors	SMD	Tiny, cheap, fast to place
Microcontrollers, FPGAs, memory	SMD	Many come only in SMD packages (QFP, QFN, BGA)
Board-to-board and I/O connectors	Through-hole or mixed	Plugging puts repeated force on joints
Large electrolytic capacitors	Through-hole	Height and weight need extra anchoring
Transformers, relays, inductors	Through-hole	Weight and current need mechanical support
Power transistors and regulators	Both	TO-220 parts bolt to heatsinks; D2PAK and DPAK use copper pours

SMD vs. Through-Hole LED: Which Should You Use?

Use SMD LEDs for indicator arrays, backlighting, and lighting boards. Use through-hole LEDs for panel indicators, prototypes, and replaceable parts.

SMD LEDs sit flat and pack densely. High-power types shed heat into the board, so lighting designs often use a metal-core substrate.
Through-hole LEDs have bendable leads and can stand off the board to line up with an enclosure hole.

Is SMT Cheaper Than Through-Hole Assembly?

Usually yes at medium and high volumes, because machines place the parts. Through-hole can cost less on very small runs or boards full of large power parts.

Quantity. SMT setup (stencil, feeders, programming) spreads thin over large runs but weighs heavily on a run of three.
Part mix. A board with 300 SMD parts and 4 connectors is mostly an SMT job.
Drilling. Each through-hole lead needs a drilled and plated hole.
Labor. Manual insertion and hand soldering add time per board.

The surest way to compare is to quote both versions. Our online quote calculator takes SMT and through-hole part counts separately.

How Do You Choose Between SMT and Through-Hole?

Match your product to the closest row below.

Your situation	Likely best choice
Wearable, IoT, or handheld product	SMT
High-volume consumer electronics	SMT
Very small enclosure	SMT, both sides
Power supply, motor controller, or industrial drive	Mixed: SMT logic, through-hole power parts
Aerospace, defense, or rugged equipment	Mixed: through-hole connectors and heavy parts
Prototype debugged by hand	Through-hole or mixed
Large connectors or frequent plug cycles	Through-hole connectors, SMT for the rest

Can You Use SMT and Through-Hole on the Same PCB?

Yes. Most modern boards are mixed technology: SMT for logic, through-hole for connectors and power parts. Our mixed technology PCB assembly service covers both.
Three design tips make it smoother:

Keep through-hole parts on one side to avoid a second soldering pass.
Leave clearance around through-hole joints for selective soldering nozzles.
Check that every part is rated for the heat cycles it will see. SMT goes first, then through-hole soldering.

What Mistakes Should You Avoid When Choosing?

Choosing by habit. Teams often keep through-hole because the first prototype used it, then pay for it in volume.
Ignoring availability. Some through-hole parts are being discontinued in favor of SMD versions.
Skipping assembly review. A layout that looks fine can still cause wave soldering shadows or paste problems.

Why Choose Sierra Assembly for Your PCB Project?

Sierra Assembly provides SMT, through-hole, and mixed-technology PCB assembly backed by 30+ years of experience, ISO 9001:2015 and AS9100D certifications, and U.S.-based engineering support. From prototypes to production, we help you select the right assembly approach for your design, performance, and budget. Request a quote for your PCB assembly project.

Frequently Asked Questions

1. Can I hand-solder SMD components?
Ans: Yes, for larger parts like 0805 resistors, SOIC chips, and many QFPs. Use a fine tip, flux, and magnification. Tiny passives, QFNs, and BGAs need paste and reflow.

2. Can through-hole parts go through reflow with SMD parts?
Ans: Sometimes. This is called pin-in-paste: paste is printed in the hole, the lead is inserted, and the part reflows with the SMD parts. Check the datasheet first, because many connectors cannot handle reflow heat.

3. Can I convert a through-hole design to SMD?
Ans: Often, but it is a redesign, not a swap. You need new footprints and SMD versions of each part with the same ratings. Connectors and large power parts are the usual exceptions.

4. Is through-hole technology obsolete?
Ans: No. Through-hole is still the standard for connectors, transformers, relays, and large capacitors. Many other parts have moved to SMD, but strength and power handling keep through-hole in use.

5. How can I tell if a part is SMD or through-hole?
Ans: Check the package name on the datasheet. 0603, SOIC, QFN, and BGA are SMD, while DIP, TO-220, and axial or radial parts are through-hole. The footprint also shows it: SMD uses flat pads, and through-hole uses drilled holes.

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