| During deep space exploration,some precision electronic components of spacecraft need to be exposed to extreme deep space environments,which puts forward higher requirements for the reliability of electronic packaging interconnection structures.Adding nano particle reinforcement phase to solder is an effective way to improve the reliability of micro solder joints.In this paper,Sn-3.0Ag-0.5Cu-xTiO2(SAC305-xTiO2,x=0,0.05,0.1,0.15,0.2)composite solder was prepared by mechanical mixing method.The evolution law of solder matrix and interface microstructure of SAC305-xTiO2 micro solder joints under extreme temperature environment was studied by-196 ℃～150 ℃ thermal shock test,and the shear properties and fracture behavior of micro solder joints were characterized The growth behavior and mechanical properties of interfacial intermetallic compound(IMC)are studied.Research has found that adding 0.05 wt.%and 0.1 wt.%TiO2 nanoparticles to the solder can refine the microstructure of the solder and effectively inhibit the growth of the IMC layer,which can be attributed to the surface adsorption effect of TiO2 nanoparticles and Ag3Sn particles;with the increase of thermal shock times,the shear force of all micro solder joints generally showed a decreasing trend,and their fracture modes changed from ductile fracture to mixed ductile brittle fracture.However,due to the peeling phenomenon of interface IMC,the thickness of interface IMC in SAC305-0.2TiO2 micro solder joints significantly decreased after 250 cycles,and its fracture mode changed back to ductile fracture.Adding appropriate amount of(0.05 wt.%and 0.1 wt.%)TiO2 nanoparticles into SAC305 solder can improve the shear strength performance of micro solder joints and inhibit the transition from fracture behavior to brittle fracture during Thermal shock,of which 0.05 wt.%TiO2 nanoparticles have a better effect.The interfacial microstructure evolution,crack initiation and propagation of Cu/SAC305/Ni and Cu/SAC305-0.05TiO2/Ni micro solder joints under Thermal shock at196℃～150 ℃ were explored,and their failure modes and failure mechanisms were explored,and the impact mechanism of TiO2 nanoparticles addition on the reliability of micro solder joints was futher clarified.The results showed that after 200 times of Thermal shock,a new phase(Ni,Cu)3Sn4 was formed between the(Cu,Ni)6Sn5 compound layer at the SAC305/Ni interface and the Ni substrate;The addition of 0.05 wt.%TiO2 nanoparticles inhibited the growth of IMC at the interface,and the thickness of IMC at SAC305-0.05TiO2/Ni interface was always lower than that at SAC305/Ni interface during Thermal shock;After 200 times of Thermal shock,the Cu/SAC305/Ni micro solder joint cracks in the layer(Cu,Ni)6Sn5 on one side of the Ni pad and continues to expand,resulting in brittle failure of the micro solder joint after 250 cycles;After 250 times of Thermal shock,short cracks were found in the(Cu,Ni)6Sn5 layer on the side of the Ni pad for Cu/SAC305-0.05TiO2/Ni micro solder joints;The addition of 0.05wt.%TiO2 nanoparticles effectively improves the reliability of SnAgCu leadfree micro solder joints in extreme temperature environments. |
