Crack Area Analysis of SnPb and SnAg Solder Joints in Plastic Ball Grid Array Packages From Dye Penetration Studies

Crack growth in solder joints caused by thermal cycling is a critical issue for reliability in electronic packages. This study presents experimental data on crack growth in SnPb and SnAg solder joints of 357-joint PBGA packages attached to PWBs and subjected to 30-minute, 0°C to 100°C temperature cycles. The board assemblies were exposed to three process conditions upon exiting the solder reflow furnace—air cooled to room temperature, quenched at 0°C, and aged at 150°C (SnPb) or 160°C (SnAg) for 1008 hours—prior to the accelerated thermal cycle testing. At scheduled intervals, the packages were dye-penetrated, removed from the board, and the joint crack areas in several regions measured. The experimental data and statistical analysis of 9000 joints show that SnAg solder joints have half the crack areas of their SnPb counterparts for all regions, cycles and aging conditions. For both solders, the joints located under the die edge have the largest cracks of any region, and the three adjacent joints at each of the four corners under the die edge are the joints most likely to have the largest crack areas. Comparing aging conditions, the differences in the means of % crack area for SnPb packages were not statistically different, but for SnAg packages, the aged joints had 50% smaller crack areas than non-aged joints (air and quench).