Drop impact reliability of edge-bonded lead-free chip scale packages

This paper presents the drop test reliability results for edge-bonded 0.5 mm pitch lead-free chip scale packages (CSPs) on a standard JEDEC drop reliability test board. The test boards were subjected to drop tests at several impact pulses, including a peak acceleration of 900 Gs with a pulse duration of 0.7 ms, a peak acceleration of 1500 Gs with a pulse duration of 0.5 ms, and a peak acceleration of 2900 Gs with a pulse duration of 0.3 ms. A high-speed dynamic resistance measurement system was used to monitor the failure of the solder joints. Two edge-bond materials used in this study were a UV-cured acrylic and a thermal-cured epoxy material. Tests were conducted on CSPs with edge-bond materials and CSPs without edge bonding. Statistics of the number of drops-to-failure for the 15 component locations on each test board are reported. The test results show that the drop test performance of edge-bonded CSPs is five to eight times better than the CSPs without edge bonding. Failure analysis was performed using dyepenetrant and scanning electron microscopy (SEM) methods. The most common failure mode observed is pad lift causing trace breakage. Solder crack and pad lift failure locations are characterized with the dye-penetrant method and optical microscopy.