FATIGUE-CRACK INITIATION IN SOLDER JOINTS

A backface strain technique is introduced to examine fatigue crack ini tiation in solder lap joints. The technique detects the fatigue crack initiation by monitoring the backface strain at the end of the overlap . Variation of the backface strain with the development of a crack was simulated by finite element method. The simulation indicated that the backface strain at the end of the overlap reached a peak value when a fatigue crack initiated. Experimental verification was carried out in 63Sn-37Pb solder joints. The backface strain was recorded as a functi on of stress cycle to demonstrate the applicability of this technique. Experimental results showed that fatigue crack initiation took about half of the fatigue lifetime of the solder joints.