Effects Of Active Elements On Microstructure And Properties Of The Brazed Joint Between High Thermal Conductivity Graphite Film And Copper

With the high-speed development of the microelectronics manufacturing process,electronic components are developing towards high integration,miniaturization,and lightweight.The heat dissipation problem of high-power devices has become increasingly prominent.However,the traditional heat dissipation structure and gluing technology cannot meet the heat dissipation requirements.Light,flexible,and high thermal conductivity graphite film has the advantages of high thermal conductivity,low density,low thermal expansion coefficient,lightweight,and good flexibility,but it is easy to damage,which limits its application range.In this study,in order to solve the problem of heat accumulation in high-power chips and broaden the application range of graphite film,active Ag Cu filler was used to reliably bonding between graphite film and copper to obtain the brazed joint of graphite film/copper with high thermal conductivity.The wetting and spreading behavior of Ag Cu active filler on graphite film were systematically studied,and the effects of Ti and Cr on wetting behavior were compared.Based on the results of the wettability study,the brazing bonding between graphite film and copper was carried out.Combined with the change of interfacial microstructure and the difference of thermal conductivity of different brazed joints,the relationship between microstructure and thermal conductivity of the joint was established,and the heat transfer mechanism of graphite film and copper brazed joint was explained.The spreading behavior of active filler metal was compared and analyzed.It was found that Ag Cu-Cr filler metal had a more incubation period than Ag Cu-Ti filler metal.The active elements reacted with the graphite film at the solid/liquid interface to generate carbides,thereby reducing the surface tension of the filler and the adsorption energy at the solid/liquid interface,and improving the wettability of the filler on the graphite film.Ti reduced the wetting angle of Ag Cu on graphite film from 137.6°to 20.9°.Under the action of 2%Cr,the minimum wetting angle of Ag Cu-Cr on graphite film is 40.4°.With the increase of Ti or Cr content,the solid phase(Ti₃Cu₄ or Cr)in the melt increased,which increased the viscosity of the melt and inhibited the spreading behavior of the filler.The spreading activation energies of Ag Cu-Ti and Ag Cu-Cr on the graphite film were219.06 k J/mol and 206.90 k J/mol,respectively.During the spreading process of filler,the active elements were enriched at the solid/liquid interface under the adsorption mechanism,and the spreading behavior of filler on the graphite film was promoted under the combined action of interfacial reaction.After holding for 10 minutes at 900?,the graphite film and copper were successfully bonding with Ag Cu-4Ti filler.The typical interface structure of the joint was as follows:Cu/diffusion layer/Ag(s,s)+Cu(s,s)+/Ti C/graphite film.When the active filler metal containing 2%Cr was used for brazing copper with graphite film at950°C for 10 min,the typical interface microstructure of the joint was as follows:Cu/diffusion layer+Ag(s,s)+Cu(s,s)/Ag(s,s)+Cu(s,s)/Cr₇C₃/graphite film.When the Ti content or Cr content is 2%,the brazing joints with different active elements had achieved maximum thermal conductivity,respectively from 214.82 m^-1·K^-1,216.60 m^-1·K^-1.The thermal conductivity of the joint decreases with the increase of active element content,and the existence of brazing defects is extremely unfavorable to the thermal conductivity of the joint.The thermal conductivity of the joint decreased with the increase of active element content,especially the existence of brazing defects was extremely unfavorable to the thermal conductivity of the joint.In the process of heat transfer,the carbide layer not only realized the good interface bonding between the graphite film and the metal,but also improved the phonon transfer coefficient between the graphite film and the metal as a transition layer,bridging the acoustic mismatch between the materials,thus effectively improving the thermal conductivity of the joint.