The Mechanism And Application Of Cu₃Sn Induced Film Affecting The Reaction Between Cu Layers And Sn Layers

The microelectronics intergrate technology rapidly develops in today’s era and microelectronic integrated circuits are getting smaller and smaller. Packaging dimensions extend from two-dimensional to three-dimensional packaging and the packaging density is getting higher and higher. The high density package requires smaller solder volume, therefore, the proportion of IMC(Intermentallic Compounds)after long-term service will be larger. But the IMC/ solder interface is easy to be a weak spot in the process of deformation, crack initiation, propagation and fracture of lead-free solder. In order to overcome this limitation, more and more researchers focus on the preparation of “Whole-IMC” solder joint, which is entirelly composed of IMC phase.However, the outstanding problem that hinders the industrial application of Whole-IMC solder joint is how to control the growth of IMC in the solder joints. In this paper, based on the principle of seed crystal in wafer manufacturing, the method of controlling Cu/Sn interface reaction by using induced layer is proposed.In this paper, we first determine how long we need to make the Sn used in the subject under different thickness of the condition completely transformed into Cu3 Sn,which lays the foundation for the following-up work. Secondly, the preparation process of Cu3 Sn induced thin film is introduced, and four different kinds of induced thin film substrates are prepared by the introduction of current and the innovative methods of single crystal copper substrate. By setting the control group, we use electronic backscatter diffraction(EBSD) to characterize the impact of current and single crystal copper substrate on the grain orientation, grain size and other aspects of the induced film. Then the surface treatment process of the induced thin film was studied to obtain a good surface smoothness. Next, the effects of four kinds of induced films on the induced effects were studied. By in situ observation method we studied the growth of new Cu3 sn on the induced thin film’s surface, in order to study the mechanism of phenomenon that elongated grains parcelling near equiaxed grain in the process of inducing.Besides, in the respective of atomic density of crystal plane, we interpreted the orientation law that crystal grains obey when inducing. In the end, the effect of the two phase on the preparation of the solder joints was studied by the combination of the induced thin film and the multilayer thin film.The results of the research show that: current can promote the Cu3 sn crystal grain’s growth along the direction of current flow, promote production of high angle grain boundaries; single crystal copper substrate can promote Cu3 sn growth along a specific direction, promote the generation of small angle grain boundaries. But this two factors do not have a significant effect on the grain orientation distribution. In the inductionprocess, the grain size has inherited rules that is to say generate larger grain size induced larger Cu3 sn grain; misorientation angle does not have inheritance rules, instead, no matter how induced film crystal grains’ misorientation angle distribute, in the course of inducing, the misorientation angle will concentrate to 60 degrees, this is because between the Cu / Cu3 Sn, there is orientation relationship similar to the martensite and austenite N-W orientation relationship. The reason why elongated grains can parcelling the near equeaxis grains is the velocity defference when absorb one Cu6Sn5 grain. No matter before or after inducing, the direction <100> of Cu3 Sn always parallel to the TD direction, which can be explained by plane atomic density.Multi-layers can enhance the development rate of whole-Cu3 Sn solder. The induced layer plays a role of decreasing diffusion path/ increasing diffusion distance,which will depress the growth of Cu3 Sn. Because of the manual processes, multilayer solder joints will break between Cu6Sn5 layer and Cu3 Sn layer if Cu3 Sn and Cu6Sn5 exist simutaneously; but if only the Cu3 Sn rest in solder, the break usually happens in Cu3 Sn layer inside.