Size effects on segregated growth kinetics of interfacial IMC between Sn solder and Cu substrate

Abstract

For this research, the interfacial reaction between Cu substrate and the pure Sn solder ball was studied in this research with the solder ball diameter of 1700 µm, 1400 µm, 1000 µm, 800 µm and 500 µm. The size effect on morphology evolution behavior and the segregated growth kinetics of Cu6Sn5 in thermal and cooling stage is researched for the spherical solder joints. The different spreading rate due to utilization of different size solder ball, the ratio of base diameter (W) and the height (H) of the solder ball after spreading are changed with the solder ball volume. The finite element analysis for Cu concentration in relation to the magnitudes of W and H show that edge part of solder ball with smaller H is responsible for enhancement of Cu supersaturation in liquid solder, which can enhance the ripening behavior of Cu6Sn5 at the interface of solder joint. For the cooling stage, for the screw dislocation growth mechanism of the Cu6Sn5, the Cu precipitation promote the growth of prismatic Cu6Sn5. As the ripening at isothermal stage and precipitation at cooling stage contribute to the gross growth behavior of Cu6Sn5 intermetallic compounds layer growth, the combined size effect of base diameter and height of the solder specimen renders solder corresponding to the edge part of solder ball to have the overall thickest intermetallic.