Hole & lead review
Check finished hole sizes against lead diameters, press-fit specs and any odd-form parts that need fixtures.
PCB assembly
Through-Hole PCB Assembly for Strong Mechanical Connections
XFPCB supports through-hole PCB assembly when connectors, terminals, transformers, relays or tall discrete parts need stronger mechanical joints than SMT alone can provide.
When Through-Hole Assembly Is the Right Choice
Through-hole parts insert into plated holes and are soldered from the opposite side - by wave, selective solder or hand soldering. This page covers THT-specific planning: hole size vs lead diameter, solder fillet criteria, press-fit vs soldered connectors and keep-out for tall parts.
Many boards combine SMT and THT. XFPCB sequences SMT first, then through-hole soldering, so heat-sensitive SMT packages are not reflowed twice without a plan.
Through-Hole Process Steps
Insertion planning
Confirm pin-1, keying, height limits and which parts are auto-insertable vs hand-placed.
Wave or selective solder
Choose wave for dense THT fields or selective/hand solder when SMT parts sit close to THT pads.
Trim, clean, inspect
Trim leads to drawing, clean if required, and inspect fillet wetting and connector seating.
THT Build Controls
- Assembly drawings should show orientation, height and which side is soldered.
- Selective solder is preferred when SMT components are near THT pads.
- High-current terminals and transformers get extra attention on hole fill and fillet size.
- Press-fit connectors are handled to the supplier insertion force guidance you provide - not forced as soldered parts.
Through-Hole Quotation Focus
| Project Area | XFPCB Guidance |
|---|---|
| Typical parts | Connectors, relays, transformers, switches, terminal blocks, large electrolytics |
| Soldering options | Wave, selective solder, or hand solder for low volume / odd-form |
| Mechanical checks | Pin seating, keying, lead trim length, strain relief |
| Often paired with | SMT on the same board (mixed-technology PCBA) |
DFM Checklist for Through-Hole Builds
Connector & Terminal Review
We verify keying, pin count and soldering side against your drawing so housings are not installed reversed.
Wave or Selective Solder Plan
Dense THT fields may run wave; boards with nearby SMT usually need selective or hand solder to protect fine-pitch parts.
Lead Trim & Fillet Criteria
Lead length after trim and acceptable fillet wetting are confirmed before operators start a production lot.
Useful Terms
- PTH
- Plated through-hole used for component leads.
- Wave solder
- Molten solder wave used for many THT joints at once.
- Selective solder
- Targeted soldering for THT joints near SMT keep-outs.
- Fillet
- Visible solder joint shape at the lead and pad/barrel.
Related XFPCB Pages
Through-Hole PCB Assembly for Strong Mechanical Connections FAQs
What should I send to quote through-hole assembly?
Send Gerbers, BOM with MPNs, assembly drawing showing orientation and height, and note which parts are wave-soldered vs hand-soldered. Photos of odd-form parts help.
Can XFPCB do wave and selective solder?
We plan wave or selective solder based on board layout. If SMT parts sit close to THT pads, selective or hand solder is usually safer.
Do you support mixed SMT + THT boards?
Yes. Most production boards are mixed. SMT is typically completed first, then through-hole soldering and final inspection.
How do you avoid connector seating issues?
Clear pin-1 / keying marks on the drawing, correct hole sizes, and a first-article check of seating height before the full lot proceeds.
Request a Quote for Through-Hole PCB Assembly
Tell us which parts are through-hole, how they must be oriented, and whether wave or selective solder is preferred.
- List connectors, relays and transformers with MPNs and orientation notes.
- Mark any keep-out zones near SMT components.
- State inspection needs: visual fillet check, continuity, or functional test.