| As the key thermal and electrical interconnection components in high-temperature power modules,the chip connection layer and substrate connection layer play an important role in effectively reducing thermal resistance and improving long-term reliability.However,relatively little research has been conducted on large-area connection materials applied to substrate connections.Traditional substrate connection materials,such as grease,gel,and brazing compound,limit the high-temperature applications of packaged modules due to their higher thermal resistance and high-temperature reliability issues.To address these shortcomings,this paper proposes a copper foam-silver composite material that can be used for large-area connections by homogeneously mixing a copper foam solid skeleton with a micron silver paste.The main findings of this paper are as follows:First,the shear strength of the composite was increased to 52.46 MPa by optimizing the preparation and sintering processes,which is much higher than the29.49 MPa before optimization,and higher than the 50.04 MPa of sintered silver by the same process.The fracture of the composite joint was determined by SEM to include internal fracture of the sintered silver,fracture of the copper skeleton,and fracture of the sintered silver and copper skeleton connection.It was also found that the joint quality of the sintered composite joints gradually improved with increasing copper foam thickness and porosity.As the thickness of copper foam increased(60μm,80 μm,120 μm),the joint deformation rate increased in sequence(3.13%,7.33%,20.23%),the porosity of sintered silver in sintered composites decreased in sequence(23.05%,11.9%,2.42%),and the shear strength increased in sequence(34.8 MPa,48.6 MPa,59.7 MPa).When the porosity of copper foam increases,the change trend is basically the same.Secondly,the material properties of the composites were determined for the thermal performance evaluation of the connecting layers and modules.The Young’s modulus of 20.3 GPa and the thermal conductivity of 192 W/(m·K)were determined for the sintered composite layer prepared from copper foam with a thickness of 120μm and 85% porosity by uniaxial tensile experiments and laser thermal conductivity tests.The simulation model of the sintered composite was simplified and the correctness of the model was verified by the simulation of Young’s modulus,based on which the Poisson’s ratio of 0.42 and the thermal expansion coefficient of 17.6 E-6/℃were determined after simulation.The model thermal characteristics of Pb92.5Sn5Ag2,sintered silver and sintered composite materials as the substrate connecting layer were simulated respectively.It was found that when the substrate joining layer material was sintered composite,the model maximum junction temperature was 8.03% lower than that of Pb92.5Sn5Ag2.5,the thermal resistance was reduced by 19.62%,and the maximum stress of the substrate joining layer was reduced by 26.42%;compared with sintered silver,the model maximum junction temperature increased by 0.58%,the thermal resistance increased by 1.57%,and the maximum stress of the substrate joining layer was reduced by 4.55%Finally,based on the substrate connection process of copper foam-silver composite material,this chapter proposes a packaging strategy for a double-sided direct-cooled heat dissipation Si C MOSFET module and establishes a packaging integration process for a 750V/150 A MOSFET chip.By comparing the leakage characteristics and forward characteristics of the chip and module before and after the package,the feasibility of the packaging strategy of the double-sided direct cooling Si C MOSFET module and the composite material for the substrate connection is verified.Meanwhile,the thermal resistance of the junction-heatsink of the double-sided direct cooling module is reduced by 69% and the maximum junction temperature is reduced by 14.7℃ compared to the conventional single-sided heat sink package module.By analyzing the thermal resistance distribution,it can be found that the thermal resistance of the substrate and substrate connection layer in the single-sided heat sink module is 48.98%,so the significance of eliminating these two layers of the structure is very important. |
