SMT lines are fast but sensitive to design, materials, and environment. Below are defect classes we see most often in reviews, with practical countermeasures.
Tombstoning
Common on 0402/0201 parts, often tied to asymmetric pads, aggressive ramp rates, or unequal paste on both terminations. Responses include pad redesign, profile tuning, and nitrogen reflow where available.
Solder balls and bridging
Stencil thickness and aperture design, squeegee pressure, and paste type (lead-free vs. leaded) must match. Peak temperature and time above liquidus matter; SPI catches excessive or insufficient paste before placement.
Insufficient solder and BGA voids
BGAs/LGAs need adequate venting and defined X-Ray sampling. Profiles should be measured on production boards, not copied from generic templates.
Offset and polarity errors
Increase pick-and-place calibration frequency, enforce first-article and patrol checks, and use barcode or AVL checks on error-prone lines.
PCBA PARTNER correlates AOI defects with SPI, reflow, and material lots to close the loop—moving customers from reactive rework to proactive prevention.