Zhongguang Wang

A New Approach for the Evaluation of Interfacial Reliability in Micro-scale

Lead-free solder/copper single crystal joints were prepared to reveal the interfacial fatigue damage mechanisms. Under cyclic loading, persistent slip bands (PSBs) were activated in copper single crystal and continuously impinged the interfaces of the lead-free solder/copper single crystal joint. The types of fatigue cracking modes, i.e. interfacial cracking between solder and IMC and fracture within IMC, were observed. Based on the damage modes of the IMC interface, the interfacial reliability can be well evaluated in micro-scale.

Creep rupture of Sn-Ag-Cu Pb-free solder alloy

The eutectic Sn3.8Ag0.7Cu alloy is widely considered a leading Pb-free replacement for the eutectic Pb-Sn solder alloy in electronic packaging where creep deformation and rupture is a major concern. In this study, creep rupture behavior of Sn-Ag-Cu solder alloy was investigated under the isothermal condition. Creep tests were conducted under a range of stresses and temperatures. Creep lifetime data were analyzed by the combined time-temperature equations following the Sherby, Larsen-Miller, and Manson-Haferd approaches. From these analyses, a series of material parameters were obtained from the experimental data. The results showed that the Manson-Hanferd method provided a better correlation with the creep rupture data. The mechanisms of creep deformation and rupture at different time-temperature combinations are discussed.

Microstructural Effects on Low Cycle Fatigue of Sn-3.8Ag-0.7Cu Pb-Free Solder

Low cycle fatigue behavior of Sn-3.8Ag-0.7Cu solder was investigated under fully reversed cyclic loading, with particular emphasis on microstructural effects. The LCF behavior of the solder with equiaxed microstructure was found to differ greatly from that of the solder with a dendrite microstructure. At a given total strain amplitude, the dendrite microstructure exhibited a much longer fatigue life than the equiaxed microstructure. Such a strong microstructural effect on fatigue life arose from the difference in cyclic deformation and fracture mechanisms between the two microstructures. A large number of microcracks along grain boundaries of the equiaxed structure solder developed with increasing cycling, while for the dendrite structure solder, cyclic deformation took place along the direction of the maximal shear stress during fatigue tests and microcracks initiated and propagated along shear deformation bands. Besides, the fatigue behavior of the dendritic microstructure was very sensitive to cyclic frequency whereas the fatigue behavior of the equiaxed microstructure showed less sensitivity to cyclic frequency.