The Influence Of Microstructure And Grain Orientation On Lead-free Solder Joint's Reliability

Solder joints in the chip pack age not only protect the chip, but also play a role in the formation of electrical connection between the chip and the external circuit. Along with the development of integrated circuit technology, the chip packaging forms improve continuously, and the flip chip interconnect technology has become a major way of chip packaging. With the miniaturization of electronic components, the current density of the solder joints is larger than before. When the current density reaches a certain value, electromigration will occur in the solder joint. Electromigration can lead to the formation of compound and crack, which will affect the life of the solder joint. At the same time, due to the high current density, the higher temperature of the solder joints are generated in the solder joint, which will lead to increase the thickness of the solder joints. The high temperature also causes the Ag3 Sn IMC to be thicker, which will make the brittleness of the solder joint higher.In this paper, I first designed a flip chip structure, which used 300?m SAC305 solder balls to interconnect. At the same time, this paper improve d the experimental platform of the reflow soldering and the electromigration, which provided a guarantee for the welding of the flip chi p interconnection and the research of the electr omigration.Secondly, I used the large current to make the solder joints melt, and the effect of current on the solidification process of the solder joints was studied. Electromigration experiments were carried out on single crystal solder joints, and the migration of single crystals was mainly controlled by Sn grain orientation, the diffusion rate of Cu atoms and Ni atoms along the c axis of Sn grains was much faster than a and b axis. With the increase of ti me, the grain size of the solder joint could be rotated, which was caused by the difference of the vacancy concentration in the grain boundary.Finally, in the aging process of the solder joints, the(Cu,Ni)6Sn5 IMC became thicker, the Ag3 Sn particles in the solder joints were coarser than before, which formed the mesh organization at the grain boundaries. Th e electromigration experiment was carried out after aging of the samples, the IMC migration of the solder joint was less than the original sample, this is because Ag3 Sn particles and the internal organization became more coarse, which blocked the atoms migration path. In addition, this paper also did the Vivtorinox hardness measuremen t, the intermetallic compounds we re accumulated in the anode, which l ed to the high hardness of the anode interface and made the plasticity drop in the region.