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

Abstract

Solder joints between a package and a printed wiring board (PWB) of a portable electronic device sustain thermal cycling as a result of power on-off, cyclic bending by key pad operation, and impact bending by dropping. Therefore, the authors conducted heat cycling, cyclic bending, and cyclic impact bending tests on the ball grid array solder joints between a chip scale package and a PWB. The evaluated solders were Sn-3 Ag-0.5 Cu and Sn-37 Pb. The tests showed that the life cycles of the Sn-3 Ag-0.5 Cu solder joints for the feat cycling and cyclic bending tests were approximately twice those of the Sn-37 Pb solder joints. On the other hand, in the case of cyclic impact bending test, the life cycle of the Sn-3 Ag-0.5 Cu joint under large strain was smaller than that of the Sn-37 Pb solder joint because of interfacial crack growth between the solder and the PWB. These 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.