Abstract
This paper describes ultrasonic evaluation of initiation and propagation processes of fine cracks at the bonding interface of Sn alloy solder joints under repeated loading. The specimens were subjected to acoustic microscopy to obtain the acoustic images at bonding interface of the solder joints at required numbers of fatigue cycles during shear fatigue testing. The brightness change was observed in the bonded area. After fatigue failure, the fracture surface of SEM image was compared with the acoustic image. In the part of the brightness change in the acoustic image, many fine cracks were observed in the SEM image. The number of fine cracks on the fracture surface was greater at periphery than those inside the bonded region, and increased with increasing number of the fatigue cycles. It was found that the effective bonding area at the final failure was almost the same for specimens of different fatigue lives.
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