Reliability assessment for micro lead-free solder joints in electronics package

The authors have developed a series of isothermal fatigue test methods to improve the estimating. efficiency for the thermal fatigue behavior of BGA solder joints. The isothermal fatigue tests were used to give a proper and accurate estimation of the thermal fatigue life of BGA Sn-Pb solder joints and to study the fatigue modes in Lead-free solder joints. In this study, they have focused their attention to the formation of the intermetallic compound and its effect on the initiation and propagation behaviors of fatigue cracks. and several different lead-free solder alloys, Sn-Ag-Cu, Sn-Ag-Cu-Bi, Sn-Cu and Sn-Zn-Bi were investigated. It was found that are two kinds of fracture mode in lead-free solder joints, one is solder fatigue mode like as in Sn-Pb solder joints, and the other is an interface fatigue mode. On the other hand, based the results of the interface cracks, it was also found that not only is the mode transition of the fatigue crack affected by the properties of the intermetallic layer but also is affected by the tension strength of the solder material.