Acoustic Emission Analysis for Fatigue Prediction of Lap Solder Joints in Mode Two Shear

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Abstract
This current research method combined the disciplines of Fractography, ConFocal analysis, and Acoustic Emission to discover and identify failure modes of eutectic (62%Sn36%Pb2%Ag) solders (with and without rosin core flux) and lead free (99CSn-Cu) solder under cyclic displacement controlled Mode II shear fatigue. Results show a strong pattern of acoustic emission correlating to stages of failure. Three distinct stages were found: “Stage I” (crack initiation), “Stage II” (nucleation), and “Stage III” (failure and/or propagation). Time domain analysis shows distinct waveforms for each stage of fatigue. The frequency domain analysis shows a distinct pattern in the PSD. The combination of these two trends allows for a basis to predict solder joint fatigue in an acoustical manner utilizing acoustic emissions. Fractographic results support the trends seen in the acoustic emission analysis for each stage of fatigue. Dominant failure modes of specimens appeared to be intermetallic crack growth, grain coarsening, and dislocation energy effects. These failure modes can be explained in both the time and frequency responses of these specimens. The conclusion is that utilizing acoustic emissions with the disciplines of Acoustic Emissions, Fractography, ConFocal analysis has uncovered and identified failure modes of eutectic (62%Sn36%Pb2%Ag) solders (with and without rosin core flux) and lead free (99CSn-Cu) solder under cyclic displacement controlled Mode II shear fatigue.