Boron nitride silicone rubber composite foam with low dielectric and high thermal conductivity

Silicone rubber（SR） is widely used in the field of electronic packaging because of its low dielectric properties. In this work, the porosity of the SR was improved, and the dielectric constant of the SR foam was reduced by adding expanded microspheres（EM）. Then, the thermal conductivity of the system was improved by combining the modified boron nitride（f-BN）. The results showed that after the f-BN was added, the dielectric constant and dielectric loss were much lower than those of pure SR. Micron-sized modified boron nitride（f-m BN） improved the dielectric and thermal conductivity of the SR foam better than that of nano-sized modified boron nitride（f-n BN）, but f-n BN improved the volume resistivity,tensile strength, and thermal stability of the SR better than f-m BN. When the mass ratio of f-m BN and fn BN is 2:1, the thermal conductivity of the SR foam reaches the maximum value of 0.808 W·m-1·K-1,which is 6.5 times that before the addition. The heat release rate and fire growth index are the lowest,and the improvement in flame retardancy is mainly attributed to the high thermal stability and physical barrier of f-BN.