Study Of Preparation And Properties Of AlN/epoxy Composites

AlN has been used as a thermally conductivity filler in thermal conductive composites to enhance the heat dissipation capability of component packages in recent years,due to its high thermal conductivity(320 Wm^-1K^-1 theoretical value),low dielectric constant and matched thermal expansion coefficient of Si.To improve the thermal conductivity of the epoxy,the high content of AlN powder fillers is always needed,which usually results in poor mechanical and processing properties.What's worse,the thermal conductivity is improved limited by traditional method.Firstly,AlN/epoxy composites were prepared by dispersing AlN powder into epoxy with alcohol as the dispersion medium.The effect of the AlN content on the rheological properties of the slurry,the microstructure of the material,the mechanical properties of the material,the thermal conductivity and the dielectric properties of the material were investigated.It was found that the viscosity and shear stress of AlN/epoxy mixed system increase significantly with the increase of AlN filler content and the shear-thinning behavior become more obvious also.Micron-sized AlN filler could be uniformly dispersed in the epoxy matrix without obvious agglomeration,even when the AlN filler content reaches 45 vol%.The compressive strength of the composites increase first and then decrease with the increase of AlN filler content,but all test results are much larger than the compressive strength of the epoxy matrix.The higher the AlN filler content,the higher the thermal conductivity of the composite.When the AlN filler content is 45 vol%,the thermal conductivity of the composite reaches 1.1 Wm^-1K^-1,which is 5.1 times higher than that of the pure resin.Comparing the test results of the thermal conductivity with the thermal conductivity model,it was found that the experimental results fit the Maxwell-Eucken model best when the AlN filler content is less than 20 vol%.When the AlN filler content is higher than 20 vol%,Hamilton-Crosser model can better predict the thermal conductivity of the composites in this experiment.Although the problem that the filler can not be uniformly dispersed in the epoxy matrix was solved by using the alcohol as the dispersion medium.The AlN filling content greatly increased without affecting its processing performance,but the thermal conductivity of the composite material is limitedly increased,and it still cannot meet the needs of some high heat dissipation occasions.For this reason,a new idea of preparing AlN/epoxy composites that AlN foam replace the AlN powder as filler is proposed.XRD and pH results reveled that polyurethane and tetraethylenepentamine have good anti-water effect on AlN powder.The AlN foam skeleton prepared by injection molding combined with mechanical foaming.The porosity of the AlN foam increased with the increasing of the amount of the foaming agent EMAL-TD,and decreased with the increasing of the solid content of the slurry.By adjusting the solid content and the amount of the foaming agent,a series of AlN open-cell foam ceramics with a porosity of 72%-82%were obtained.The compressive strength of the composites were higher than that of the pure resin,but decreased with the increasing of AlN volume fraction.The thermal conductivity of the composites increased with the volume fraction of AlN skeleton,when the volume fraction of AlN reached 27.9 vol%,the thermal conductivity of the composite was 19.02 Wm^-1K^-1,which is 106 times than the pure epoxy(0.18 Wm^-1K^-1)and 25 times higher than that using AlN powder as reported by other researchers.