Research On AMB Process And Mechanism Of Thermally Conductive Ceramics Brazed With Copper

Al₂O₃,Al N and Si₃N₄ ceramics are widely used as packaging materials for components such as IGBT modules and ceramic relays in significant fields such as rail transportation,new energy vehicles and LED lighting because of their excellent thermal conductivity,mechanical properties and high voltage resistance.To meet the increasingly demanding requirements for the use of ceramic-to-metal sealed components in these applications,ceramic-to-metal sealing technology is increasingly in demand.This paper presents a systematic study of the connection between the above three thermally conductive ceramics and Cu materials with the AMB process to address the technical challenges of ceramic-to-metal connection.Firstly,based on Al₂O₃ceramic metallization,the mechanism and sealing effect of Al₂O₃ ceramic AMB process were comparatively studied.Secondly,the enhancement mechanism of Zn on Al₂O₃ ceramic AMB process was proposed and explained.The influence of brazing process conditions on the interfacial microstructure and sealing performance of Al₂O₃/Cu brazed joints was investigated through XRD,SEM and EDS tests.In addition,high thermal conductivity Al N and Si₃N₄ceramic copper-clad substrates were successfully prepared by the AMB process,and the effects of brazing temperature and active element content on the brazing interface structure were investigated.The main findings are as follows.(1)The metallization of Al₂O₃ ceramics and the AMB process differ significantly in mechanism and sealing performance.The metallization method using the activated Mo-Mn method mainly involves the inter-migration of the molten glass phase in the Al₂O₃ ceramic and the metallization paste,which generates products such as Mn Al₂O₄ with a spinel-type structure at the sealing interface.The mechanism of Al₂O₃ ceramic AMB process is mainly the reduction reaction between the active element Ti in the liquid brazing filler and Al₂O₃ ceramic,which forms 0.64?m thick layer I(Ti O)and 1.03?m thick layer II(Cu₃Ti₃O)on its surface in turn.The sealing strength of the Al₂O₃/Cu joints made by the metallization method((60.2±7.7)MPa)was better than that of the AMB process((43.1±6.9)MPa),and the gas tightness of both was around 2.3×10^-11 Pa·m~3·s^-1.(2)The volatile behavior of Zn effectively optimizes the morphology of the Ag-Cu eutectic structure in the brazing interface.It reduces the surface tension?_lv of the liquid brazing filler,which facilitates the spreading and wetting of the liquid brazing filler on the surface of Al₂O₃ceramics.The tensile strength of Al₂O₃/Cu joints brazed at 900°C for 20 min using Ag-Cu-Ti+Zn composite brazing filler(20.89 MPa)was 67.6%higher than that of the joint without Zn brazing filler under normal conditions,and the fracture path of the brazed joints was"right-angle"inside the Al₂O₃ ceramic.The Ag-Cu eutectic structure in the brazing interface gradually became shorter and thinner with the increase of brazing temperature.The thickness of Ti O layer also gradually decreased and discontinuity appeared.The Ag-Cu eutectic structure in the brazed joints with Ag-Cu-Ti+Zn composite brazing filler was uniformly dendritic.In contrast,the Ag-Cu eutectic morphology without Zn was unevenly flattened and spherical,and the width of the interface was significantly lower than the former.(3)The mechanism of copper cladding on Al N ceramics mainly involves the reduction of Ti on the surface of Al N ceramics to produce a Ti N layer on its surface.The thickness and continuity of Ag-Cu eutectic structure in the brazing interface tend to increase and then decrease with the increase of brazing temperature.Its thickness value reaches the highest(33.66?m)at880?.The mechanism of copper cladding on Si₃N₄ ceramics is mainly the reduction of Ti on the surface of Si₃N₄ ceramics to produce Ti N and Ti₅Si₃ layers on the surface in turn.The thickness of the Ti N reaction layer in the Si₃N₄/Cu interfacial structure increases with the increase of Ti content up to 1.7?m.