Lead-free Assembly Defects in Plastic Ball Grid Array Packages

Printed circuit boards were assembled at Jabil´s San Jose facility using their qualified surface mount assembly processes. The assembly involved lead-free plastic ball grid array (PBGA) packages (256 I/O) soldered to FR4 and polyimide printed circuit boards. The maximum peak lead-free reflow temperature measured at a PBGA location was 246°C. After the lead-free reflow, the assemblies exhibited solder joint defects. The three defect modes were bridges, oversized solder joints, and insufficient solder joints; in some cases these all occurred within a single PBGA. This was not expected because the PBGAs were rated as moisture sensitivity level 3 (MSL 3) and the floor life restrictions were followed as per JEDEC 020C. This paper discusses the details of the defect phenomenon and the failure analysis, and also proposes the failure mechanism based on modeling and materials characterization data. Based on this study, recommendations are provided to prevent the occurrence of the assembly defects.