An inquiry regarding printed circuit board (PCB) failures that were becoming increasingly prevalent after the SMT (surface mount technology) manufacturing process. The failures were detected by electrical testing, but were undetermined as to the location and specific devices causing the failures. The failures were suspected to be caused predominately in the BGA (ball grid array) devices located on specific sites on this 16 layer construction. Information that was provided on the nature of the failures (i.e., opens or shorts) included high resistance shorts that were occurring in those specified areas.
The surface finish was a eutectic HASL (hot air solder leveling) and the solder paste used was a water soluble Sn/Pb (tin/lead). The diagnostic approach that followed included an examination of both the quality of the manufacturing process and the materials used for assembly.
• SMT Process - determine any obvious manufacturing issues
• Reflow Profile - assess the profiling techniques to assure proper application of recommended parameters
• Bare Board Inspection - look for unusual surface anomalies
• XRF (X-Ray Fluorescence) Analysis - determine correct solder and pad metallurgy
• X-Ray Analysis - proper placement of components, opens or shorts • Endoscopic Analysis - assess proper BGA collapse
• Wetting Balance - determine acceptable soldering surfaces
