Failure mode analysis of board-level solder joint under random vibration load

The vibration acceleration failure test platform was set up to complete the failure test. And then, solder joints were observed by electron microscope and failure modes were studied. The results show that the solder joint on the outermost corner of the chip is the key solder joint. The internal solder joints are basically no signs of crack propagation and cracks are concentrated in the outermost corners on the solder joints. Cracks are distributed in the PCB board side and the chip side of the IMC layer area, where the chip side to withstand greater stress, cracks and more. The crack is easily sprouted on the loose parts of the solder joint and extends along the Cu6Sn5 grain in the IMC layer. There are two kinds of extension modes: transgranular mode and intergranular mode. When the crack spread close to the penetration, the crack prone to momentary brittle fracture.