Research And Numerical Simulation On Creep Properties Of Lead Free Micro-joints Under Thermomigration

With the development of miniaturization,high performance and high reliability of electronic device,the IC is driven to the higher level of integration.The characteristic size of packaging solder joints is decreasing rapidly,resulting in large current density.Large current density can cause joule heat and introduce greater temperature gradient across the solder joints,which makes the service environment of solder joints more severe.On one hand,the increase of temperature gradient across the solder joints induces thermomigration effect(TM),which leads to the directional migration of atoms.Thermomigration can cause the evolution of microstructure of solder joints.On the other hand,creep deformation and destruction are caused by the change of the thermal stress during the service process because of the different thermal expansion coefficients among the substrate,solder and encapsulating materia ls.Thermomigration and creep are two kinds of failure modes that are common in microelectro nic packaging.Therefore,research on the creep properties of micro-solder joints under TM condition is significant.This research adopts experimental analysis and numerical simulation methods to study the creep behavior of two kinds of interconnect solder joints,including flip chip packaging and through-silicon vias for 3D packaging.ANSYS is used to calculate the creep deformation value which can represent the creep damage.That will provide the theoretical basis for lifet ime evaluation of interconnecting solder joints.Firstly,the creep properties of 800?m Cu/Sn0.7Cu/Cu solder joints are studied.The solder joints are subjected to thermomigration with the temperature gradient of 1046?/cm and shear stress of 1.78 MPa,2.53 MPa and 3.62 MPa,and the creep properties under isothermal conditio ns of 100? and 150? are also studied for the contrast.The creep curve,fracture morphology and fracture position of solder joints are investigated under the two conditions.Experime nt a l results show that the fracture position of the solder joints under TM condition is near the hot end.However,the position of isothermal creep fracture is near the center of the solder joints,and the creep lifetime of the solder joints under TM condition is shorter than isotherma l condition.The creep fracture mechanism is mainly controlled by dislocation climbing.Finite analysis results indicate that the creep deformation value of solder joints under TM conditio n is larger than isothermal condition,and the largest value appears at the hot end.Secondly,the 10?m Cu/Sn/Cu solder joints are subjected to thermomigration with the temperature gradient of 1200?/cm and the shear stress of 3.3MPa,4.4MPa and 5.4MPa,and creep properties of solder joints under isothermal temperature 110? are also studied for the contrast.The creep curve,fracture morphology and fracture position of solder joints are investigated.Experimental results show that the interface IMC has asymmetrical growth under TM condition,and the creep deformation mechanism of solder joints is controlled by dislocation climbing.Due to the large proportion of interface IMC in the whole solder joint,it is necessary to consider the influence of interface IMC on creep performance when caculating the creep deformation of solder joints in ANSYS.Finite analysis results indicate that the large st creep deformation appears between the solder and interface IMC near the hot end,where the creep damage is most serious and vulnerable to fracture.With the increase of the thermomigration time,the creep deformation of the solder joints is increasing and the fracture position is getting closer and closer to the hot end.