A comparative study of microstructure during solidification within ultrafine interconnects of different sizes and geometries

Microstructures in ultrafine interconnects are needed to be considered when the size of the interconnects has shrunk down to as small as a few microns. In this work, a phase field model is used to simulate the dendritic microstructure formation during solidification in solder joints of 8-24 μm standoff heights. The influences of the size and geometry of the joints on the microstructural features are investigated. It is found that the widths of the dendrites in the joints with different standoff height are similar. However, the dendrites occupy the joint more quickly in a smaller joint. The geometry of the joints is found to influence the microstructural formations. A 90° primary arm that present in the rectangular joint is not found in the hourglass-shaped joint. The geometry effects are also found when two or three nuclei are placed in the joints. In addition, a mechanical modeling on the simulated microstructure is carried out to investigate the geometry effects on the mechanical properties. It is found that the stress distributions in the joints with microstructure included are not as homogeneous as those of the joints that ignore microstructure. Therefore, microstructures, as well as size and geometry of the joints, are recommended to be taken into consideration to enable reliable ultrafine interconnects.