Split the BOM
Classify SMT, THT and press-fit parts; confirm DNP and consigned vs turnkey lines.
PCB assembly
Mixed-Technology PCB Assembly (SMT + Through-Hole)
Most real products mix surface-mount and through-hole parts. XFPCB builds mixed-technology PCBA with a clear sequence: SMT reflow first, then THT soldering chosen to protect nearby fine-pitch packages.
Why Mixed-Technology Needs Its Own Plan
A mixed board fails when SMT and THT are quoted as afterthoughts. XFPCB reviews both together: which side is SMT, where THT pins land, whether selective solder is required, and how AOI/X-ray plus fillet checks combine into one inspection plan.
Share a single BOM, CPL for SMT parts, and an assembly drawing that flags THT-only reference designators.
Mixed-Technology Process Flow
SMT complete
Print, place and reflow all SMT; AOI (and X-ray if needed) before THT heat is applied.
THT soldering
Wave, selective or hand solder through-hole parts with fixtures for tall connectors.
Final inspection
Combine optical checks on SMT with fillet/seating checks on THT before pack-out.
Controls Unique to Mixed PCBA
- Never assume wave solder is safe if SMT parts sit in the wave path - selective solder is planned instead.
- Double-sided SMT with THT needs an explicit side/sequence note in the traveler.
- Odd-form parts get fixture or hand-place callouts before the lot starts.
- One revision-controlled assembly drawing covers both technologies.
Mixed Assembly Quotation Focus
| Project Area | XFPCB Guidance |
|---|---|
| BOM structure | Clear SMT / THT / press-fit flags per line |
| Heat exposure | Minimize extra reflow cycles on fine-pitch SMT |
| Solder method | Wave only when layout allows; else selective/hand |
| Inspection mix | AOI/X-ray for SMT + visual fillet for THT |
Mixed-Technology DFM Checklist
Technology Split
Every BOM line is tagged SMT, THT or mechanical so labor and solder method are quoted correctly.
Keep-Out Review
We check clearance between THT solder joints and nearby SMT packages before choosing wave vs selective.
Unified Traveler
One build traveler lists stencil, reflow, THT method and inspection gates for the whole board.
Useful Terms
- Mixed technology
- SMT and through-hole parts on the same PCB.
- Process sequence
- Order of reflow and THT soldering steps.
- Odd-form
- Parts that need fixtures or hand placement.
- Traveler
- Shop-floor document controlling each build step.
Related XFPCB Pages
Mixed-Technology PCB Assembly (SMT + Through-Hole) FAQs
How should I mark SMT vs THT on the BOM?
Add a column for mounting type (SMT/THT/press-fit) or note it in the description. Include CPL only for SMT parts and show THT orientation on the assembly drawing.
Will wave solder damage SMT parts?
It can, if SMT packages sit in the wave path. We recommend selective or hand solder when clearance is tight.
Can one quote cover both technologies?
Yes. Mixed builds are quoted as a single PCBA job with stencil, SMT, THT and inspection itemized.
What causes the most delays on mixed boards?
Missing THT orientation drawings, unclear press-fit vs soldered connectors, and BOMs that do not separate consigned parts.
Request a Quote for Mixed-Technology Assembly
Send one BOM that flags SMT and THT parts so we can plan sequence and solder method correctly.
- Attach CPL for SMT and orientation drawing for THT.
- Call out press-fit connectors separately from soldered pins.
- State required inspections for both technologies.