The High Thermal Conductive Composites For Electronic Potting

In this paper, sodium silicate and dimethylsiloxane filled withalumina, aluminum nitride and aluminum were investigated to be used asthe high thermal conductive composites for electronic potting. Thethermal conductivity of composites was measured by the stable method,SEM was used to achieve the phase compositions, morphologies and thethermal change respectively. Moreover, the effects of fillers and contenton the thermal conductivity of composite and the method used to reducethe drying time of sodium silicate were discussed.Change laws of sodium silicate solutions with differentconcentrations added by anhydrous alcohols were investigated, whichwere analyzed by the weight loss, FTRI and1H-NMR. The experimentalresults show that the liquid is stratified with the addition of alcohol. Thesupernatant liquid is clarified alcohol solution and the bottom is acolloidal solution of sodium silicate. It is discovered that the addition ofanhydrous alcohol has a critical value in order to form a stable colloidalsolution of sodium silicate. The colloidal solution is changed into a solidprecipitate over the critical values. A possible mechanism was proposedto explain the alcohol action on the solution of sodium silicate. Alcoholmolecules combine water molecules and narrow the distance between thecolloidal particles of sodium silicate, which benefits removing the excesswater and thus reduces the drying time and energy consumption in theprocess.The addition of alumina and aluminum nitride filler particles into the sodium silicate increased its thermal conductivity, and the thermalconductivity increased rapidly after the critical filler concentration. Whenthe mass fraction of alumina was90%, the thermal conductivity ofalumina/sodium silicate composites came up to3.4358W/m·K. When themass fraction of aluminum nitride was90%, the thermal conductivity ofaluminum nitride/sodium silicate composites came up to4.6295W/m·K.It was founded from the SEM investigation of composites that, more filler,with the high content in the same filler system and with the less sphericityin the different filler system, connected each other, which had helped tosignificantly improve the thermal conductive network and the thermalconductivity. Comparing some typical equation with experimental data offilled thermal conductive composites, and a new model and equationbased on the percolation theory were viable.Filling dimethylsiloxane with alumina also could improve thethermal conductivity of composites, when the mass fraction of aluminawas85%, the thermal conductivity of alumina/sodium silicate compositescame up to3.4826W/m·K. The effects of surface preparation of filler andmixture of hybrid particles were discussed.1.0%of aluminic ester wasthe best surface preparation for alumina/sodium silicate composites, andreplaced aluminum with alumina to fill dimethylsiloxane, the thermalconductivity raised from3.3415W/m K to5.5946W/m K.