Role of Plastic Behaviors of Ni3Sn4 Intermetallic Compound on Solder Joint Reliability

The study aims at investigating the influences of the elastoplastic behaviors of the micrometer-thick Ni
₃
Sn
₄
intermetallic compound (IMC) observed in the Cu/Ni/Sn3.5Ag solder joints of 3-D chip stacking package on the solder joint reliability under accelerated thermal cycling (ATC). The IMC's elastoplastic properties are characterized through the developed forward-reverse analysis algorithm, which integrates parametric finite element analysis (FEA) of instrumented indentation, dimensional analysis, and an experimental instrumented indentation test. The algorithm is first applied to characterize the elastoplastic behaviors of an electrodeposited Cu thin film, the results of which are compared with the known data, followed by a test on the thin Ni
₃
Sn
₄
IMC. The predicted elastoplastic properties are input to the ATC FEA model of the package to simulate the solder joint mechanical response, by which the corresponding fatigue life is assessed using a Coffin-Manson model. The simulation is validated against the experimental data. Besides, the prediction is compared with that without the plastic effect. Results show that despite bulk IMCs being normally elastic, brittle, and hard, the thin Ni
₃
Sn
₄
IMC possesses a highly ductile (plastic) and strain-hardening behavior. Moreover, taking the plastic behavior of the thin Ni
₃
Sn
₄
IMC into account helps improve the prediction of the solder joint fatigue life of the package.