SEM insitu study on high cyclic fatigue of SnPb-solder joint in the electronic packaging

The high cycle fatigue (HCF) cracking behaviors in the SnPb solder joints were investigated experimentally via in situ   observations with scanning electron microscope (SEM). The results indicate that the HCF cracks incubate at the toe of the solder joints and propagate mainly along an angle from 20° to 45° tilted to the applied stress axis differing greatly from the propagation behaviors reported previously for low cycle fatigue (LCF). The HCF crack growth rate is evaluated by the term of σs-max2.4ℓ based on the experimentally measured parameters, i.e. the maximum applied stress σs-maxσs-max and the surface crack propagation length ℓℓ. The finite element analysis (FEA) is carried out and shows that the stress relationship between the components of the chip-substrate-solder can be evaluated quantitatively when the applied loading acts on the substrate. Therefore, for most SnPb solder alloys, the failure threshold value for SnPb-solder joint can also be estimated by this work.