Where are most SMT defects introduced?

At paste printing. Insufficient or misplaced paste accounts for more rework than placement errors, which is why printers, stencils and paste are controlled together and why SPI sits directly after printing on our lines.

When does through-hole work happen?

After SMT reflow, so the heat of the SMT profile does not disturb the through-hole parts. Selective solder or wave solder then fills the barrels, followed by cleaning if the flux requires it.

Blog

The PCB Assembly Process in Order

Every defect has a stage where it could have been caught. Knowing the sequence is the first step in reading a yield report.

Hitech Circuits Engineering Desk

Shenzhen, China · PCB fabrication and assembly

2 min read

Published: 2018-05-28

Last updated: 2026-10-18

Technical review: Process figures checked against our published capability sheet. View capability sheet

A Quick Intro Guide to the PCB Assembly Process

1. Solder paste printing

Paste is printed through a stencil; SPI measures volume and alignment. This is the highest-leverage control point.

2. Placement

Pick-and-place mounts SMDs from feeders. Feeder setup and component verification decide whether the right part lands in the right place.

3. Reflow

The profile follows the paste alloy. Too little heat leaves cold joints; too much damages parts and the laminate.

4. Inspection

AOI checks placement and solder fillets; X-ray examines hidden joints such as BGAs and QFNs.

5. Through-hole and test

Selective or wave solder, cleaning where required, then ICT, flying probe or functional test according to the test plan.

6. Final

Depanel, clean, inspect against IPC-A-610, pack with traceability records.

Technical Specifications

SMT capacity: 6,000,000 chips per day across four lines
Quality gates: IQC · IPQC · QC · QA
Acceptance: IPC-A-610 workmanship

Frequently Asked Questions

Where are most SMT defects introduced?
At paste printing. Insufficient or misplaced paste accounts for more rework than placement errors, which is why printers, stencils and paste are controlled together and why SPI sits directly after printing on our lines.
When does through-hole work happen?
After SMT reflow, so the heat of the SMT profile does not disturb the through-hole parts. Selective solder or wave solder then fills the barrels, followed by cleaning if the flux requires it.

← Blog

Related engineering notes

Request a customer quote

Free engineering review and quote for PCB manufacturing, PCB assembly, component sourcing and box build.

Request a Quote Explore Capabilities