Abstract: The failure mode and mechanism of BGA packages were explored by drop tests of PCB packages. Furthermore, the initiation mechanism and expanding features of cracks were analyzed in this work. Results showed that, cracks in the solder joints and structural fractures of PCB are the main reasons that cause the failure of BGA packages. There are two main kinds of cracks in solder joints which distribute on the joint top and bottom, and the initiation mechanism of them are different. Micro gaps between the solder joint and solder resist film that caused by gravity contribute to the cracks on the top. Cracks on the bottom are caused by the gaps on both sides of the remained solder flux that existed between the solder joint and the solder resist film under drop-impact load. The expanding of cracks has a relationship with the original location, orientation and stress conditions of the crack sources. Relative position of solder joint and pad also have important influence on the expanding of cracks.