Investigating the cyclic bending of PCB subassembly during board level drop test

The dynamic responses of printed circuit boards (PCBs) mounted with thin-profile fine-pitch BGA (TFBGA) packages under board level drop tests were investigated. Data captured during the tests include accelerations, in-plane strains and in-situ change in solder joint resistance. PCBs were mounted on the drop table using either 4-screw or 6-screw supports. A high-speed charge-coupled device (CCD) camera was used to capture the drop impact process. The PCB bending modes, frequency, velocities before and after impact, impact duration, and deflection were derived from the high-speed photographs. The results are consistent with the measured strain and acceleration. In-situ solder joint resistance is monitored using an oscilloscope. In-situ resistance measurement is important as a solder joint crack may close up again after the impact. For the 4- and 6-screw supports, the in-plane strains are found to be similar, but the flexural frequency and failure rate of the solder joints are different. This is attributed to the bending of the PCB that resulted in solder joint failure