Interface Design And Thermal Conductivity Of Diamond/Cu Composites

Continuously increasing power density in electronic technology results in high operating temperature of electronics.Efficient heat removal has become a crucial issue for the development of electronic technology.The traditional thermal management materials can't satisfy the development requirements of electronic packaging.It's imperative to develop advanced thermal management materials with higher thermal conductivity?TC?and tailorable coefficient of thermal expansion?CTE?.Diamond reinforced Cu composites featured of excellent resistances from corrosion and heat,high TC and low CTE have been a hotspot nowadays.Unfortunately,diamond particles are incompatible and non-wetted with Cu matrix,resulting in non-bonding at the interface and low TC if directly incorporated in Cu matrix without interface modification.Introducing interface layers through alloying of Cu matrix or surface metallization of diamond particles has been confirmed effective to solve this problem.Due to the diversity of elements adopted for interface modification,differences in layer thickness and the complicated factors in experiments,it's difficult to pick out desirable interface layers according to the TC from references.In terms of the interface design and interface modification of diamond/Cu,the present work optimized the direction of interface modification through theoretical calculation and confirmed the effectiveness of interface modification by coating diamond with W through sol-gel method.The effects of coating microstructure on interfacial bonding state and TC of composites were also discussed.The major results are listed as below:1.A physical model of interface layer was developed based on the acoustic mismatch model?AMM?,extended diffusion mismatch model?DMM?and differential effective medium?DEM?scheme.The effects of various interface layers on the TC and interfacial thermal conductance?ITC?of diamond/Cu composites were systematically evaluated.The result shows that interface layers featured of nanoscale thickness,high intrinsic TC,high phonon velocity and low solubility in Cu matrix are more desirable.With interface layer thickness increasing,the TC of composites shows a decrease,especially for layers with low intrinsic TC,i.e.ZrC,TiC,Mo₂C,Cr₃C₂ and Cr₇C₃.The carbide transformation of interface layers affects TC of composites.Possessing both high intrinsic TC of non-carbides and large phonon velocity of carbides,interface layers with partial carbide formation show great superiority,while carbide transformation should be carefully controlled for layers consisting of carbides with low intrinsic TC,i.e.Mo and Cr.With an overall consideration,W-WC interface layer is the most promising candidate to develop diamond/Cu composites with high TC.2.The microstructure of interface layers is one of key factors influencing the TC of composites and it's still a challenging problem to take both integrity and thickness into consideration.Taking surface metallization of diamond with W by sol-gel method for example,the present work optimized the microstructure of interface layer based on the surface state of diamond.The diamond was preheated in vacuum atmosphere before coating to introduce defects on its surface.W coating on diamond with good uniformity and nanoscale thickness was prepared by sol-gel method.The TC of composites was also revealed.The result shows that preheat treatment introduced many etch pits on diamond surface and changed its bonding state.The percentage of sp² increased,indicating an increase of defects.It showed positive effect on improving TC of diamond/Cu composites through coating diamond with W by sol-gel method after preheat treatment.The highest TC of diamond/Cu composites reached 453 W/mK,improved 59.5%compared with diamond/Cu composites without interface modification.