Preparations,Microstructures And Properties Of The Graphite Flakes/Cu Matrix Composites

Extremely wide application of the electronic information technology in military and aerospace industries has been promoting development of the electronic packaging towards high performance,high integration,light weight and miniaturization.Graphite flakes/Cu matrix composites,which combine excellent properties of the Cu matrix and the reinforcements,have excellent comprehensive properties than each component of the composites,and therefore act as one of the most potential new electronic packaging materials.However,unfortunately,problems of that uneven and anisotropy distribution of the graphite flakes in the Cu matrix and poor interface combination between the graphite flakes and the Cu matrix are not solved well so that the performance of the graphite flakes/Cu matrix composites is far from developed.Therefore,it is valuable for optimizing the technology and microstructure of the composites in order to improve the properties of the composites to a large content,aiming at satisfying the demand of modern electronic packaging technology.In this study,the graphite flakes of an average diameter of 60?m and a thickness of 200nm were used to fabricate the graphite flakes/Cu matrix composites through a pressureless sintering technique.When the content of the graphite flakes is 3wt%and below,the agglomeration of the graphite flakes is weak,and the interface combination between the graphite flakes and the Cu matrix is tight.However,as the graphite flake content increased,the graphite flakes in the composites turn to be overlapped and aggregated,resulting in decrease of the relative density and also deterioration of the graphite flake/Cu interface of the composites.The 1wt.%graphite flakes/Cu matrix composites have a relative density of 93.6%,a hardness value of HB49.2,TCs of 327.7W/(m·K)in the X-Y direction and 223.6W/(m·K)in the Z direction,and a CTE of14.1×10^-6/K in the X-Y direction.After the thermal-mechanical treatment of cold-rolling of 55%reduction and final annealing at 400?,the graphite flakes/Cu matrix composites are nearly fully dense,the orientation of the graphite flakes is more apparent,the graphite flakes turn to be linear,and the disaggregation of the graphite flakes takes place too.However,the density of the composites is lower,the interface combination between the graphite flakes and the Cu matrix is weaker,moreover,crack of the composites happens during rolling,as for the composites of the graphite content of 5wt.%and more.The 1wt.%graphite flakes/Cu matrix composites after the thermal-mechanical treatment have a relative density of 99.2%,a hardness value of HB58.6,TCs of 380.4W/(m·K)in the X-Y direction and 179.3 W/(m·K)in the Z direction and a CTE of 13.6×10^-6/K.The composites have higher comprehensive properties,compared with the as-sintered graphite flakes/Cu matrix composites.High fraction graphite flakes/Cu matrix composites were produced employing a hot-pressing technique.The relative displacement of graphite flakes is promoted,through increasing the sintering pressure.It is beneficial to elimination of the agglomeration of the graphite flakes and thus the increase of the relative density of the composites.On the contrary,the density,flexural strength and CTE of the high fraction graphite flakes/Cu matrix composites decrease with the increase of the graphite flake content.The 20 wt.%graphite flakes/Cu matrix composites hot pressed at 55MPa have a TC of 288.5W/(m·K),a CTE of 8.9×10^-6/K,and a flexural strength of 35MPa in the X-Y direction.