Through-Hole Isn’t Old-Fashioned: Where It Still Wins
Through-Hole Isn’t Old-Fashioned: Where It Still Wins
Surface-mount technology transformed electronics manufacturing, but it did not make Through Hole obsolete. For connectors, power components, transformers, rugged assemblies, and many mixed-technology products, the older-looking process can still be the smarter engineering choice.
Through Hole is not a nostalgic alternative to SMT. It is a manufacturing method with a different set of strengths. When a component must carry mechanical load, conduct substantial current, withstand repeated connector cycles, or remain accessible for service, mounting the leads through the board can be exactly what the design requires.
Modern electronics frequently use both methods. Fine-pitch devices and small passives may be placed with SMT, while connectors, relays, transformers, power devices, and selected hardware are completed with Through Hole or other secondary operations.
Where Through Hole still earns its place
The deciding factor is not whether the technology looks newer. It is whether the interconnection and assembly method match the product’s physical, electrical, production, and service requirements.
Connectors and controls
Headers, terminal blocks, switches, and other parts exposed to plugging, pulling, or operator force often benefit from leads anchored through the board.
Power and high-current parts
Larger leads, wider spacing, and robust solder joints can support components whose current, voltage, heat, or mass makes a surface-only connection less attractive.
Large and odd-form components
Transformers, relays, large capacitors, inductors, and specialty parts may be better suited to insertion and secondary assembly than standard SMT placement.
Rugged and serviceable products
Industrial equipment, laboratory instruments, field-serviceable systems, and long-life products may prioritize mechanical retention and repair access over maximum density.
SMT and Through Hole solve different problems
Surface mount usually wins when density, automated placement, fine pitch, low mass, and throughput are the priorities. Through Hole becomes valuable when the assembly must manage mechanical force, larger components, substantial electrical load, or service requirements.
SMT is strongest when the design needs:
- Compact size and high component density
- Fine-pitch ICs, QFNs, BGAs, and small passives
- Fast automated placement and repeatable reflow
- Low component mass and short electrical paths
Through Hole is strongest when the design needs:
- Mechanical anchoring through the PCB
- Large leads, power parts, and odd-form components
- Repeated connector cycles or physical interaction
- Accessible rework, replacement, or field service
Most real assemblies are mixed-technology
Using SMT for density and Through Hole for mechanical or power-critical parts is not a compromise. It is often the most practical architecture. Micron supports connected SMT and Through Hole production paths for mixed-technology builds, including secondary assembly, inspection, test, and documentation.
Six applications where Through Hole remains highly relevant
The method is most valuable where the component or product creates demands that go beyond simply making an electrical connection.
Connectors, switches, and terminal blocks
Parts that users plug into, tighten, press, or pull can transfer force into the PCB. Through-board leads can provide useful retention and distribute that stress more effectively than solder pads alone.
Power supplies and high-current circuits
Power resistors, rectifiers, relays, large inductors, fuse holders, and other components may need larger leads, generous spacing, thermal planning, and solder joints designed for their current and heat profile.
Transformers, relays, and large capacitors
Heavy or irregular components may not fit standard pick-and-place or reflow assumptions. Through Hole insertion, fixturing, and secondary soldering can provide a more controlled manufacturing path.
Industrial and rugged electronics
Equipment exposed to vibration, handling, long field life, or repeated maintenance may benefit from mechanically retained components and a process planned around workmanship, cleaning, and inspection.
Legacy and long-life products
Industrial controls, instruments, and replacement assemblies may remain in production for years. Through Hole can support established designs, lower-volume repeat builds, and component-level service without forcing an unnecessary redesign.
Prototypes and specialized low-volume builds
Some prototypes, laboratory systems, and custom equipment benefit from accessible components, manual installation, and easy engineering changes while the design is still evolving.
A controlled Through Hole build is more than hand soldering
The exact route depends on component mix, volume, solder requirements, cleaning needs, board design, and acceptance criteria. A disciplined process connects documentation, insertion, soldering, inspection, and test.
Review and planning
Confirm BOM, polarity, component height, lead form, hole dimensions, solder type, masking, cleaning, inspection, and test requirements.
Component preparation
Verify parts, form leads if required, prepare hardware, and establish insertion or fixture instructions that protect orientation and spacing.
Insertion and retention
Install components to the drawing and control stand-off, seating, polarity, clinching, support, or temporary fixturing as the assembly requires.
Soldering
Use the appropriate hand, wave, selective, drag, or partner-supported process based on board design, volume, thermal mass, and component limitations.
Trim, clean, and inspect
Control lead trim, residue removal, solder fillets, hole fill, bridges, damage, orientation, spacing, and workmanship acceptance criteria.
Test and final release
Complete electrical or functional test as specified, confirm labels and records, and protect the assembly with appropriate ESD-safe packaging.
Through Hole quality begins in the PCB and documentation
A robust assembly depends on the relationship among the lead, plated hole, pad, copper connection, board thickness, solder process, and surrounding geometry. These details are easier to address before release than on the production floor.
Hole size, plating, lead shape, tolerance, and board thickness must support insertion and the intended solder process.
Land size and surrounding copper should support soldering, inspection, rework, and the board’s reliability requirements.
Large planes can draw heat from the joint. Thermal design should support consistent wetting without overheating the component or PCB.
Provide room for insertion, fixtures, soldering tools, inspection, lead trimming, connectors, hardware, and enclosure interfaces.
Assembly drawings, silkscreen, BOM data, and work instructions should agree—especially for diodes, capacitors, relays, and keyed connectors.
Identify temperature-sensitive parts, no-wash areas, masking requirements, lead-free or leaded solder, coating, and cleaning limitations.
Large components may need brackets, adhesive, hardware, stand-offs, or additional retention rather than relying on solder joints alone.
Make important joints visible where possible and preserve access for probes, fixtures, measurements, repair, and final system verification.
Where Through Hole is usually not the first choice
Through Hole remains useful, but it should not be specified by habit. SMT is normally better for dense digital designs, fine-pitch packages, miniaturization, high automated placement counts, and products where board area and component height are tightly constrained.
Through-board leads and pads consume board area and can complicate routing on multilayer designs.
Modern processors, memory, QFNs, and BGAs are designed around surface-mount production.
Insertion and secondary operations can add labor, setup, handling, or additional process stages.
SMT generally supports thinner assemblies and lower component mass.
What to send for a mixed SMT and Through Hole quote
Clear assembly data helps Micron identify which components require secondary operations, what soldering path is appropriate, and where tooling, inspection, cleaning, or test assumptions need to be confirmed.
Include manufacturer part numbers, reference designators, approved alternates, and DNI/DNP notes.
Provide fabrication data, drill information, board revision, and any stackup or special-process notes.
Show polarity, connector orientation, hardware, stand-offs, component height, special spacing, and lead-form requirements.
Include centroid or pick-and-place data so the complete mixed-technology flow can be planned.
State lead-free, leaded, no-clean, aqueous-clean, masking, coating, and temperature-sensitive component needs.
Share IPC class, customer workmanship requirements, test procedures, fixtures, programming, reports, and acceptance criteria.
Identify prototype, pilot, or recurring production quantities and any required delivery milestones.
Clarify whether the project is turnkey, consigned, or hybrid and identify any customer-controlled components.
Workmanship requirements should be defined—not assumed
Through Hole acceptance can involve solder fillet, wetting, lead protrusion, hole fill, component seating, cleanliness, and other customer- or class-specific criteria. Micron supports IPC-A-610 and J-STD-001 Class 2 or Class 3 requirements when specified. For broader context, the Global Electronics Association’s IPC standards overview explains how industry standards clarify expectations for electronics quality, reliability, and consistency.
Explore the complete mixed-technology build path
The best assembly may use the newest technology—and the proven one
A reliable PCB does not earn extra credit for being entirely surface mount or entirely Through Hole. It succeeds when every component is assembled with a process suited to its electrical, mechanical, thermal, manufacturing, and service requirements.
Micron supports SMT, Through Hole, mixed-technology, prototype, NPI, production, test, programming, and electromechanical integration from our Norwood, Massachusetts facility.