Drop reliability performance assessment for PCB assemblies of chip scale packages (CSP)

Drop impact reliability assessment of solder joints on the chip scale packages is critical for use in miniature handheld products. Replacement of lead-based with lead-free solders requires the need of evaluating its compatibility with existing printed circuit board surface finishes. A 15 /spl times/ 15mm fine-pitch BGA with solder ball compositions of 36Pb-62Sn-2Ag and Sn-4Ag-0.5Cu on surface finishes of organic solderability preservative, electroless nickel immersion gold and immersion tin were tested. The results revealed a strong influence of different intermetallic compound formation on soldered assemblies drop durability. The lead-based solder supersedes the lead-free composition regardless of the types of surface finish. Joints on organic solderability preservative were found to be strongest for each solder type. Other factors affecting drop reliability such as component location on the board and drop orientation are reported.