Design,Fabrication And Thermal Properties Of High Thermal Conductive Graphite Film/Aluminum Composites

With the ever-increasing power density and continuing miniaturization of semiconductor devices in the electrical industry,effective thermal management is becoming increasingly important for the reliability and lifetime of electronic components.Therefore,it is essential to develop lightweight thermal management materials with high thermal conductivity?TC?and low coefficient of thermal expansion?CTE?.Among the materials nowadays being considered in thermal management,graphite/Al composites have attracted much attention due to their excellent thermal properties.A novel graphite film/aluminum composite with excellent and tailorable thermal properties was developed.Based on the thermodynamics and diffusion dynamics of Al/C system,the effects of fabrication parameters of vacuum hot pressing?VHP?process on interfacial microstructures and TC of the composites were studied.Effective interfacial modification methods were investigated and TC of composites was improved.Graphite/aluminum composite with different architecture structures and thermal properties were designed and fabricated.The major results are listed as follows:1.The VHP parameters were optimized according to the effects of them on interfacial microstructures and TC of the composites.The results show that oxide films on the Al foils are interfacial diffusion barriers.The in-plane and out-of-plane TC of the composites can be improved by 9.4%and 38.6%after eliminating these oxide films,respectively.The optimized VHP parameters are 655oC/45 MPa/100 min,which can fabricate graphite film/Al composites with well-distributed,well-oriented graphite films.Graphite film/Al composites with graphite volume fraction of 17.4-69.4%possess high in-plane TC of 380-940 W/mK and out-of-plane TC of 28.7-7.2 W/mK.2.During the VHP process,the formation and evolution process of the graphite/Al interface is as follows:At the beginning,a nanoscale amorphous intermediate layer was formed at the graphite/Al interface.As the sintering time increased,Al₄C₃ interfacial reaction product was formed at the interface.The amount of Al₄C₃ increases while the sintering time increases.Interface with diffusion intermediate layer is favorable to the improvement of TC of the composites.On the contrary,Al₄C₃ is harmful for the TC of the composites.3.The effects of W coating and Cu coating on the graphite films on interfacial bonding,interfacial thermal conductance?ITC?and TC of the composites were investigated.The results show that W coating fabricated by sol-gel process was discontinuous.Cracks and interfacial debondings are very easily formed at the interface of graphite film/W/Al composites,which is harmful for the TC.Cu coating fabricated by physical vapor deposition?PVD?process is dense,uniform and integrated.Fine interface with good interfacial bonding was obtained between Cu and graphite.Gr/Cu/Al composites fabricated at 400°C/30 min have fine interfacial microstructures with high ITC.Cu coating is effective to improve the ITC,in-plane and out-of-plane TC of 17.4-53.2vol%graphite film reinforced Al composites by more than 20 times,3-4.5%and 14-25%,respectively.4.Graphite/Al composites with different architecture structures were designed and fabricated.The theoretical models and finite element models were established.The results show that architecture design is effective to tailor the TC of the composites.The TC values of the composites with different architecture structures can be predicted by combining these two models,which can guide the architecture design of these composites.5.Architecture structure-TC relationships of graphite/Al composites were studies.The results show that composites with lamella structures possess in-plane TC,out-of-plane TC and CTE of 380-940 W/mK,<40 W/mK and 20.2-3.4×10^-6 K^-1,respectively.The composites with perforated lamella or heterogeneous structures have in-plane TC,out-of-plane TC and CTE of 290-670 W/mK,10-70 W/mK and 23.4-8.5×10^-6 K^-1,respectively.The composites with discontinuous structures have in-plane TC,out-of-plane TC and CTE of 200-500 W/mK,30-100 W/mK and 23.2-17.5×10^-6 K^-1,respectively.This research developed a novel graphite film/aluminum composite with excellent and tailorable thermal properties.The in-plane TC of the as-fabricated graphite film/Al composites is 940 W/mK,which is more than twice of the TC of Cu.Also,high thermal conductive graphite film/Al composites with different thermal properties were fabricated,which can be effective thermal management materials for microprocessor,phased-array radar and so on.This research provides a theoretical foundation and technical method for the development of composites with high TC for thermal management.