Wave soldering
Use a controlled wave route when the board has a suitable through-hole population and accessible solder side.
PCB Assembly technology / through-hole process
Through-Hole PCB Assembly (THT)
Through-hole PCB assembly service places leaded components through drilled board holes and selects wave, selective or controlled hand soldering around the component mix, board support and required inspection evidence.
THTLeaded components
WaveBatch soldering
SelectiveTargeted joints
InspectionRoute by risk
At a glance
What Is Through-Hole PCB Assembly?
Through-hole PCB assembly installs component leads through plated or non-plated board holes before soldering. The process is often chosen for connectors, relays, transformers, large capacitors and parts that need mechanical retention, but the final route depends on lead geometry, thermal mass, solder access and the rest of the PCBA.
Engineering choices
Choose the THT process from the joint and board access.
Through-hole assembly is not one soldering step. Component geometry, copper area, board thickness, solder access and downstream operations determine the practical route.
Selective soldering
Apply solder to defined joints when SMT, connectors or thermal-sensitive areas make a full wave route unsuitable.
Controlled hand soldering
Use documented hand operations for selected joints, repair, odd-form parts or areas that need operator access.
Connector and power parts
Review hole size, annular ring, lead forming, keepout and insertion force before the line is released.
Technical reference
Through-Hole PCB Assembly Process Reference
These rows describe the information needed to select a THT route; exact soldering, fixture and acceptance limits remain project-specific.
Through-Hole PCB Assembly Process Reference
Send the through-hole component drawings and assembly drawing so engineering can confirm hole, lead and solder-access fit.
| Component families | Connectors, relays, transformers, terminal blocks, large capacitors and odd-form parts by review |
|---|---|
| Board data | Gerber or ODB++, NC drill, fabrication drawing and plated/non-plated hole definition |
| Assembly data | BOM, CPL where applicable, assembly drawing, polarity, insertion direction and no-populate notes |
| Soldering routes | Wave, selective or controlled hand soldering selected by joint access and board population |
| Thermal review | Copper planes, heavy terminals and component temperature limits considered in the solder profile |
| Mechanical review | Lead forming, hole fit, component height, keepouts and enclosure access checked before setup |
| Inspection | Visual, AOI where visible, X-ray where hidden and electrical or functional testing where defined |
| Secondary operations | Programming, coating, cable work, box build or packaging added only when drawings and procedures are available |
Design context
A THT drawing must describe the joint, not only the part name.
A through-hole component can be electrically correct and still be difficult to assemble if the hole, lead form, keepout, solder side or mechanical clearance is undefined. The review connects the component drawing to the fabrication and assembly package.
- Confirm finished hole and lead-form relationship
- Mark solder-side access and keepout zones
- Identify high-mass or heat-sensitive parts
- Define inspection and test access after soldering
Engineering review
What the Through-Hole Assembly Review Should Close
The review turns a mixed list of leaded components into a controlled THT process route.
Hole, lead and annular-ring consistency
Component orientation and polarity
Wave or selective-solder access
Thermal mass and solder-profile risk
Mechanical clearance and enclosure fit
Inspection, rework and functional-test access
Practical fit
Where Through-Hole Assembly Fits
Use THT when mechanical retention, connector strength, high-mass components or serviceable leaded parts matter to the product.
Industrial controls
Terminal blocks, relays, connectors and power components in PLC, gateway and motor-control assemblies.
Power electronics
Large components and current-carrying parts that need defined mechanical and thermal handling.
Interfaces and connectors
I/O, cable, shield and chassis interfaces where insertion or vibration loads affect the joint design.
Frequently asked questions
Questions that shape the through-hole pcb assembly (tht) route
These THT answers help define the soldering route, component data and inspection evidence before quotation.
What is a through-hole PCB assembly service?
A through-hole PCB assembly service inserts leaded components through board holes and solders them using a wave, selective or controlled hand process selected from the component mix and board access.
Can you combine THT and SMT on the same PCB?
Yes. Mixed builds can be evaluated. The SMT, through-hole and secondary-operation sequence is selected from component location, solder access, thermal exposure and inspection requirements.
What files are needed for THT assembly?
Provide fabrication data, NC drill files, BOM, assembly drawing and component drawings where hole, lead form, polarity or mechanical fit is not unambiguous.
How is through-hole solder quality verified?
Inspection is matched to the joint and product risk. Visible joints can use visual or optical inspection, while hidden or electrically critical areas can require X-ray, ICT, flying probe or functional testing.
Related pages
Connect the THT route to the complete PCBA plan.
Compare through-hole with SMT, mixed-technology, testing and turnkey assembly before releasing the build package.
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Turnkey PCB assembly services with component sourcing, PCB fabrication, BOM control, SMT or THT assembly, programming, inspection and agreed test evidence.Review a Through-Hole PCB Assembly Build.
Share the fabrication data, BOM, component drawings, assembly drawing and required soldering or test evidence for a THT review.