What Is a Solder Paste Inspection Machine?
A solder paste inspection (SPI) machine is an automated 3D measurement system that inspects solder paste deposits immediately after the printing process and before component placement. SPI systems measure the volume, area, height, and positional accuracy of every paste deposit on every board, providing the data needed to identify print defects and correct process deviations in real time.
SPI is widely recognized as the single highest-ROI inspection investment in SMT assembly. The industry rule of thumb is that approximately 60–70% of end-of-line defects originate at the solder paste printing stage. Catching those defects before component placement, when rework is as simple as washing the board and reprinting, avoids the compounding cost of placing components, reflow soldering, and post-reflow diagnosis on a board that was destined to fail from the start.
SPI Machine Buyer’s Checklist
When evaluating SPI equipment, consider each of the following criteria against your current and anticipated production requirements:
1. Measurement Technology (True 3D vs. 2D). 2D SPI cannot measure paste volume, it captures only area. True 3D SPI using multi-directional projection captures volume, area, height, and shape for every deposit. Volume measurement is essential for meaningful process control. Verify the system uses full 3D measurement, not 2D with pseudo-3D interpolation.
2. Accuracy and Repeatability (Gage R&R). Gage Repeatability and Reproducibility (Gage R&R) quantifies measurement system variation. For SPI, industry benchmarks target Gage R&R below 10% at 6 sigma. Height accuracy should be specified at 1 μm or better. These metrics determine whether the system can reliably distinguish between acceptable process variation and genuine defects.
3. Resolution and Field of View. Resolution (XY pixel size) determines the finest paste feature that can be measured. Common SPI resolutions range from 10 μm to 25 μm. Higher resolution is required for fine-pitch components (0.3–0.4 mm pitch) and small deposits (down to 0201 metric / 008004 inch). FOV determines throughput, larger FOVs capture more deposits per image but must be balanced against resolution requirements.
4. Inspection Speed. SPI throughput must exceed your fastest printer’s cycle time. Speed is measured in cm²/sec and varies by resolution. At 20 μm resolution, mid-range systems should achieve at least 30 cm²/sec; high-end systems can exceed 80 cm²/sec.
5. Z Measurement Range and Resolution. The system must accommodate your paste deposit heights, including any intentional step stencil variation. Typical maximum heights range from 300–450 μm for metrology-grade systems, with Z resolution of 0.37 μm or better.
6. Software and Integration. Look for real-time SPC, automated printer feedback (closed-loop control), support for IPC-2591 (CFX), and integration with MES and factory monitoring platforms. The SPI system should communicate bidirectionally with your printer to adjust parameters automatically based on measurement data.
7. Support for Advanced Materials. If your production uses WFMI (Water-Soluble Flux Media Inspection), conductive glue, or sinter paste, verify that the SPI system supports these material types with appropriate illumination and measurement algorithms.
Koh Young SPI Machine Portfolio
The KY8030-2 best-selling SPI system is the industry’s most popular SPI solution. With a 4M camera at resolutions from 10–25 μm, speeds from 11.1 to 59.5 cm²/sec, Z resolution of 0.37 μm, and Gage R&R below 10% at 6 sigma, it has earned its reputation as the benchmark for mainstream SMT solder paste inspection. Available in M, L, and XL configurations to suit different board sizes.
The KY8030-3 high-speed SPI is the industry’s fastest SPI solution, approximately twice as fast as its predecessor. With 8M or 12M camera options at 10–20 μm resolution and speeds up to 81.85 cm²/sec, it supports long boards up to 1,300 mm in single pass (1,800 mm optional), WFMI, conductive glue, and sinter paste inspection. Runs on Windows 11 IoT Enterprise LTSC 2024.
The aSPIre 3 metrology-grade SPI is the highest-performing SPI solution in the Koh Young lineup, delivering metrology-grade measurement accuracy. With 8M or 12M camera options at 10–15 μm, speeds up to 77.9 cm²/sec, and 03015M component support, it represents the highest standard in 3D solder paste inspection. Gage R&R below 10% at 6 sigma across all standard configurations.
Integrating SPI into Your Production Line
SPI data is most valuable when it drives real-time process correction. Through the KSMART process control platform platform, SPI measurement data feeds into KPO Printer for automatic solder paste process optimization. KPO Printer detects printer setup defects, recommends optimal printing parameters through automated design of experiments, and adjusts parameters in real time as environmental and process conditions change, achieving up to 47% higher productivity.
For a detailed SPI evaluation tailored to your production requirements, read our optical inspection systems guide covering SPI, AOI, and DPI, or contact Koh Young America to speak with an applications engineer and schedule a demonstration.
