Solder Paste Inspection
Solder paste inspection is the inline metrology process that measures deposited paste volume, area, and height before component placement - it is a primary early-warning control for preventing downstream solder-joint defects.
What Is Solder paste inspection?
- Definition: SPI uses 2D or 3D optical systems to evaluate each printed pad against limits.
- Key Metrics: Typical checks include volume percentage, height distribution, area coverage, and offset.
- Placement in Flow: SPI runs after stencil printing and before pick-and-place operations.
- Control Role: Results feed printer corrections and immediate containment for print excursions.
Why Solder paste inspection Matters
- Defect Prevention: Catches overprint and underprint before expensive downstream processing.
- Yield Improvement: Strong SPI control reduces bridge, open, and tombstoning defects.
- Process Visibility: Pad-level measurements reveal stencil wear and printer drift quickly.
- Cost Reduction: Pre-reflow correction is far cheaper than post-reflow rework.
- Capability Tracking: SPI trends provide direct evidence of print-process Cpk health.
How It Is Used in Practice
- Threshold Design: Set package-specific upper and lower limits for each critical pad class.
- Closed Loop: Enable automatic printer offset and cleaning responses from SPI feedback.
- Data Governance: Use historical SPI analytics to tune stencil and paste maintenance intervals.
Solder paste inspection is a core front-end quality gate in SMT assembly - solder paste inspection is most effective when coupled to rapid corrective action, not used only as a reporting tool.