Fatigue Strength of BGA Type Solder Joints between Package and Printed Wiring Board of Portable Device

Solder joints between a package and a printed wiring board (PWB) of a portable electronic device sustain heat cycling as a result of power on-off operations, cyclic bending by key pad operation, and impact bending by dropping. Therefore, heat cycling, cyclic bending, and cyclic impact bending tests were conducted on the ball grid array solder joints between a chip scale package and a PWB. The evaluated solders were Sn-3Ag-0.5Cu and Sn-37Pb. The tests showed that the life cycles of the Sn-3Ag-0.5Cu solder joints for the heat cycling and cyclic bending tests were approximately twice those of the Sn-37Pb solder joints. For the cyclic impact bending test, however, the life cycle of the Sn-3Ag-0.5Cu joint under large strain was smaller than that of the Sn-37Pb solder joint because of interfacial crack growth between the solder and the PWB. Finally, fatigue lives of the joints were compared with crack initiation and failure lives of plain specimens by calculating local strain ranges in the joints by elastic-plastic finite element analysis.