PCB Cold Solder Joint — Failure Analysis & 8D Correc...

Symptoms Dull/grainy joint vs shiny proper joint Intermittent connection; joint R > 50 mΩ Cracks at pad-lead interface under microscope Affected Components PCBA for automotive, industrial, consumer electronics SMT/TH solder joints; BGA, QFN, SOIC components ENIG, HASL, OSP, immersion tin pad finishes Detection Methods Visual 10–40×: Dull appearance, incomplete wetting X-Ray: Hidden cold solder under BGA/QFN AOI: Shape, color, reflectivity anomalies ICT/Flying Probe: Joint resistance, intermittent detection Cross-section + SEM: IMC layer thickness Possible Causes Insufficient heat: peak temp too low or TAL too short PCB contamination: copper pad oxidation preventing wetting Component lead oxidation; thermal mass imbalance from copper planes Vibration during cooling; incorrect flux activity 5-Why Example Problem: QFN-32 intermittent after 500 thermal cycles Why intermittent? → Cold joint pin 15 — incomplete IMC Why incomplete? → Peak temp 225°C vs 235°C required Why low temp? → Large ground plane heat sink effect Why unaccounted? → Profile from standard test PCB, not production board Why not validated? → NPI didn't require production board profiling TRC: Low temperature from PCB thermal mass effect MRC: NPI reflow profiling used non-representative test boards Fishbone (6M) Man: Conveyor speed adjusted without re-profiling Machine: Zone 3 TC offset 5°C Method: 6-month profile check...