Multiple Shape Designed Sintering Paste And Reliability Test Of WBG Chip Packaging

The third generation of semiconductor chips based on Si C and Ga N can significantly improve the efficiency of energy utilization,with high band gap width and heat resistance,stable service under high voltage and current density.However,chip junction temperature rise caused by high volume power density is high,the corresponding wrapper interconnected materials tested.Sintered silver is used to replace traditional tin-based solder,satisfies the requirement of high temperature power chip and the substrate DBC service,but as a result of the sintered silver cost factor limiting its widely used in the field of chip packaging connection,copper with low cost and good thermal conductivity,It can be used to develop interconnection materials between power chips,but the high temperature of copper sintering is not conducive to the requirements of low temperature connection and high temperature service of chip interconnection structure.In this paper,a composite silver-copper sintered paste is proposed to be applied to the packaging of power devices.The silver-copper composite sintered paste is prepared by using flake silver and spherical silver with an average particle size of 2?m and flake copper and spherical copper with an average particle size of 2 ?m.The mass content of silver in the paste is 60% and 90%.The interconnect joints of the composite paste were sintered at 250 ?,20 MPa and 300 s.The mechanical properties and thermal conductivities of composite pastes sintered to from interconnection joints with different silver content and different particle shape combinations were analyzed,and the influence of shape combination matching and particle content ratio on the properties of paste were studied.The result shows that the paste with 60 wt.% flake silver and 40 wt.% sphere copper composite paste provides the best performance in 60 wt.% composite pastes after sintering,the average shear strength is 47.42 MPa,flake silver spherical copper composite paste in the form of combination of interconnection joint shear strength of spherical silver flake copper composite paste 2 times of interconnection joint shear strength.The average shear strength of the interconnect joint of the composite paste with 90%silver flake and 10% spherical copper reaches 69.79 MPa,which is more than two times of the strength of the interconnect joint of the composite solder paste with 60%silver content.The composite paste of 60% flake silver and 40% spherical copper was used to prepare the interconnection joints.After 1100 cycle tests at-40 ??125 ?,the average shear strength increased by 41% reaching 67 MPa.The analysis of sintered microstructure and fracture surface showed that the densification of sintered microstructure increased with the increase of cycles.Through SEM observation of the fracture,it was found that there were obvious dimples at the fracture position,and creep of silver could be observed at the fracture position.The numerical simulation analysis of composite paste joint under temperature cycle shows that there is reciprocating plastic strain in sintering layer during temperature cycle,and the difference of material thermal expansion coefficient causes reciprocating shear stress in sintering layer during temperature cycle.In summary,it can be concluded that the sintering performance of the composite paste with the mass fraction of 60% flake silver and 40% spherical copper can meet the application requirements,and the joint strength increases by 41% after 1100 cycles,which indicated that the composite paste with flake silver spherical copper displayed high reliability.