The Study Of Dielectric And Thermal Properties Of Hollow Glass Microsphere And Nitride Filled Polymer Composites

With integrating more electronic components into a single device to increase functionalityand enhance performance, it is crucial to use electronic packaging and substrate materials thatare capable of dissipating the heat generated and hence to maintain the operating temperatures ofthe device at a desired level. Meanwhile, as the working frequency of electronic appliancesincreases, it is also required that packaging and substrate materials have small dielectric constantand low dissipation energy to increase the velocity of signal propagation and decrease the signalattenuation. However, a sole polymer material or single filler filled composite as packaging orsubstrate material is hard to simultaneously satisfy the demand of above multifunctionalproperties. In this study, it is suggested that high thermal conductive nitride particles (AlN or BN)and low dielectric constant hollow glass microsphere (HGM) are filled into polymer-matrixsimultaneously. Furthermore, a specific microstructure, i.e., nitride particles surrounding theHGM and them forming thermal conductive networks in the polymer-matrix by themselves, ishoped to obtain by prefabricating core-shell structured HGM@nitride fillers, and thus thecomposites have optimal high thermal conductivity and low dielectric constant.At first, the epoxy-matrix composites filled with HGMs, having the density of0.125~0.60g/cm~3and volume fraction of0~60%, were prepared. The thermal, dielectric, andcompressive properties of the composites were investigated. The results show that the thermalconductivity, dielectric constant and loss, and compressive modulus and strength of thecomposites show decreased trend with increasing HGM content or decreasing HGM density,which indicates that the properties of the composites are mainly dependent on thecharacteristics of HGM. The minimum dielectric constant of2.2can be obtained at HGMdensity of0.2g/cm~3and HGM content of60vol.%. By comparing the measured thermalconductivity and theoretical predictions, the Agari model is recommended to predict the thermalconductivity of HGM filled composites.In order to synthesize HGM@nitride (HGM@AlN or HGM@BN) filled polymer-matrixcomposites, core-shell structured HGM@nitride fillers were prepared by layer-by-layer (LbL)self-assembly technique. The processing parameters, including the pretreatment of HGM,viscosity of polyelectrolyte, and PH value, were symmetrically investigated. The results showthat absorption of nitride particles on surface of HGM is enhanced by pretreating HGM surfacewith5wt.%coupling agent of KH-570and then using poly (diallyl dimethyl ammoniumchloride)(PDDA) with viscosity of800cps and adjusting PH value of solution with suitable amount of thioglycolic acid (MAA), and thus the core-shell structured HGM@AlN orHGM@BN fillers are synthesized.When HGM@nitride fillers were filled into polymer-matrix [epoxy or low densitypolyethylene (LDPE)], it is found that HGM@nitride filled composites have higher thermalconductivity and keep lower dielectric constant compared with nitride particles and HGM(named as nitride+HGM) filled composites at polymer-matrix of LDPE. For example, at thesame volume fraction of HGM (50%S60HS) and AlN (2.91%) in the composites,HGM@AlN/LDPE composites have the thermal conductivity of0.28W/mK compared with thethermal conductivity of0.23W/mK for (AlN+HGM)/LDPE composite. At the same time,HGM@AlN/LDPE composites keep lower dielectric constant of2.15-2.64, which is far lowerthan that of commonly used substrate or packaging materials. Comparing HGM@AlN andHGM@BN filled LDPE-matrix composites, HGM@BN/LDPE composites have higher thermalconductivity and lower dielectric constant due to the fact that BN has higher intrinsic thermalconductivity and lower dielectric constant than these of AlN.In conclusion, HGM filling into polymer-matrix can effectively decrease the dielectricconstant and loss of the composites but also decrease their thermal conductivity. In order tooffset this deficiency, core-shell structured HGM@nitride filler, prepared by LbL self-assemblytechnique, were filled into thermoplastic polymer. The synthesized composites exhibit higherthermal conductivity than that of nitride+HGM filled composite, and they keep lower dielectricconstant at the same time.