Abstract: Technological advancements and the emphasis on reducing the use of hazardous materials, such as Pb, have led to the widely use of Sn-based Pb-free solder in advanced packaging technology. With the miniaturization of solder joints, Sn-based micro solder joints often contain single or limited β-Sn grains. The strong anisotropy of β-Sn, which is significantly correlated with the reliability of the micro solder joints during service, requires the development of methods for controlling the orientations of these β-Sn grains. In this review, we focus on the anisotropy of the β-Sn grains in micro solder joints and the interactions between β-Sn grain orientation and reliability issues concerning electromigration (EM), thermomigration (TM), EM + TM, corrosion process, tensile and shear creep behavior, thermal cycling (TC) and cryogenic temperature. Furthermore, we summarize the strategies for controlling the β-Sn orientation in micro solder joints. The methods include changing the solder joint size and composition, adding additives, nucleating on specific substrates and interfacial intermetallic compounds, with the aid of external loads during solidification process and introducing heredity effect of the β-Sn texture during multi-reflow. Finally, the {101} and {301} twinning models with ～60° rotations about a common 〈100〉 are adopted to explain the mechanism of β-Sn grain nucleation and morphology. The shortcomings of the existing methods and the further potential for the development in the field are discussed to promote the application of Pb-free solders in advanced packaging.

Key words: Advanced packaging, Pb-free solder joints, Anisotropy, Reliability, β-Sn grain orientation, Nucleation mechanism