Solder Paste Inspection (SPI) Machine: 2D vs 3D, and What to Check Before You Buy
Published Time:
2026-01-23
A hands-on SPI machine guide for SMT printing—what SPI measures, 2D vs 3D SPI differences, key specs that matter, and how SPI reduces paste-related defects.
Solder Paste Inspection (SPI) Machine: 2D vs 3D, and What to Check Before You Buy
In SMT, most “reflow problems” actually start earlier—at printing. Once paste volume or alignment drifts, you can’t fix it later by hoping the oven will behave.
That’s why SPI has such a strong reputation in stable production lines: it catches printing issues before you place parts and before defects become expensive.
What an SPI machine really measures
SPI inspects solder paste deposits right after printing and flags problems like:
- offset/misalignment
- insufficient paste
- excessive paste
- inconsistent volume across pads
- paste bridging risk
Think of SPI as a process guardrail. It doesn’t just “find defects”—it tells you printing is drifting while you still have time to correct it.
2D vs 3D SPI (how to choose without overthinking)
2D SPI: good when the job is simple
2D is mainly about top-view imaging. It can do a decent job on area coverage and offset, and it’s often fine for larger pads and easier products.
3D SPI: safer when you care about volume control
3D adds height/volume measurement, which matters when:
- aperture sizes are small
- pitch is tighter
- your defect patterns involve weak joints, tombstoning, or intermittent opens
- you want consistent yield over long production runs
If you’re aiming for stable FPY and fewer “random” defects, 3D tends to be the more future-proof choice.
Where SPI belongs in the line (and why placement matters)
Best practice is straightforward:
Printer → SPI → Pick & Place → Reflow → AOI
If SPI comes late, it loses its value. The goal is to stop bad printing before components are placed.
What to look at when comparing SPI machines (the real checklist)
1) Repeatability and false calls
In production, the worst SPI is not the one that misses defects—it’s the one that screams all day for nothing. Check:
- measurement repeatability
- stability over shifts
- how easy it is to tune thresholds without hiding real issues
2) Resolution vs throughput
High resolution means nothing if it bottlenecks your line. Ask:
- can it match your printer/placement task time?
- does it keep speed when you inspect bigger boards or more pads?
3) Programming effort (recipe time)
If recipe creation takes forever, operators will hate it and skip best practices. You want:
- fast program generation
- good library templates
- smooth data review (so it’s actually used)
4) Process feedback capability
If you care about process control, look for:
- trend charts / SPC outputs
- clear defect classification
- ability to support printer feedback (depending on your setup)
Common printing problems SPI helps you stop early
SPI is especially helpful for problems that “come and go,” like:
- stencil clogging building up after a few prints
- paste slump/smearing on certain pads
- squeegee pressure or speed drifting
- board support issues causing inconsistent deposits
In other words: it’s great for catching the stuff operators don’t see until reflow starts failing.
Quick decision: which SPI fits your factory?
Choose 3D SPI if you have:
- fine pitch / higher density boards
- long-run production where drift matters
- recurring paste-related defects
- stronger yield/quality targets
Choose 2D SPI if you have:
- simpler boards and larger pads
- lower defect risk
- tight budget and you mainly need alignment/area checks
FAQ
We already have AOI—do we still need SPI?
AOI is after reflow. SPI is before placement. If your top defects are paste-related, SPI often gives you the fastest ROI.
Is SPI useful for LED production lines?
Yes, especially in long runs where consistency and throughput matter. Stable printing reduces rework and keeps the line smooth.
No. 739, Zhou Shi Road, Hezhou Community, Hangcheng Street, Baoan District, Shenzhen
Copyright © 2025 Shenzhen ETON Automation Equipment Co., Ltd. ALL Rights Reserve.