Study On Microstructure Of Electroplated Copper Foil And And Shear Properties Of Solder Joints

Copper(Cu)electroplating technology has been widely applied in the microelectronic industry.With the development of three-dimensional high-density interconnect,the geometrical complexity of the electroplated Cu is getting higher and higher.However,the impurities in the plating solution will inevitably be introduced into the electroplated Cu film during the electroplating process,which leads to an increase in the number of voids at the Sn-based solder joint interface and seriously affects the reliability of the solder joint.In this paper,the organic additives polyethylene glycol(PEG)/3-(2-benzothiazolylthio)-1-propanesulfonsaure(ZPS)and the concentration of ZPS are selected as a point of entry,studying the influence of it on the microstructure of electroplated Cu and the microstructure evolution and shear strength of solder joint.In the experiment,the current density of 5 A/dm2 is used to prepared the electroplated Cu film in a 40℃ water bath.The results of X-ray diffraction(XRD)show that the preferred orientation of the electroplated copper foil is<200>when the PEG is added into the basic plating solution.The preferred orientation of the electroplated copper foil changes from<200>to<111>with the addition of ZPS in the plating solution.When the different contents of ZPS are added into the plating solution containing 200 ppm PEG,the preferred orientation of the electroplated copper foil changes from<200>to<220>.According to the atomic force microscopy(AFM)results,the roughness of Cu film surface increases with the addition of PEG/ZPS in the basic solution.When the different contents of ZPS are added into the plating solution containing 200 ppm PEG,the surface of the electroplated copper foil gradually becomes rough with the increase of the ZPS concentration.The solder joints are prepared on a hot plate at a constant temperature of 260℃for 15 min,and then the aging treatment is performed in an oven at 190℃.The results of shear experiment show that the shear strength of SAC305/Cu solder joints decreases with increasing aging time.In the same aging time,the shear strength of the SAC305/Cu solder joint prepared in the Cl-+ZPS plating solution is lower than that of the SAC305 solder joint prepared in the basic plating solution,but higher than that of the SAC305/Cu solder joint prepared within the Cl-+PEG plating solution.In addition,the shear strength of SAC305/Cu solder joint increases with increasing ZPS concentration when the different content of ZPS is added into the plating solution containing 200 ppm PEG.The fracture modes of solder joints could be classified into three types:ductile fracture,mixed solder/intermetallic compounds(IMC)fracture mode and brittle fracture.In the paper,when the SAC305/Cu joint is soldered at the hot plate for 10 min,the solder joint prepared in the basic solution is fractured within solder matrix and the fracture type is ductile fracture.After the aging process,the fracture position of the solder joint is within the solder matrix and IMC layer,and its fracture mode is the mixed solder/IMC fracture.After adding PEG/ZPS to the basic plating solution,the fracture position and fracture mode of the solder joints did not change.However,when the different contents of ZPS are added into the plating solution containing 200 ppm PEG,SAC305/Cu solder joint aging for 24 h is fractured within the solder matrix and IMC layer and its fracture mode is the mixed solder/IMC fracture.When the aging time is 120 h,240 h and 360 h,the fracture position of the solder joint is within IMC layer,and the fracture mode of the solder joint is brittle fracture.