Thermal conductivity of polyimide/boron nitride nanocomposite films

The thermal conductivity of polyimide/boron nitride (PI/BN) nanocomposite thin films has been studied for two sizes of BN nanofillers (40 and 120 nm) and for a wide range of content. A strong influence of BN particle size on the thermal conduction of PI has been identified. In the case of the largest nanoparticles (hexagonal‐BN), the thermal conductivity of PI/h‐BN (120 nm) increases from 0.21 W/mK (neat PI) up to 0.56 W/mK for 29.2 vol %. For the smaller nanoparticles (wurtzite‐BN), PI/w‐BN (40 nm), we observed two different behaviors. First, we see a decrease until 0.12 W/mK for 20 vol % before increasing for higher filler content. The initial phenomenon can be explained by the Kapitza theory describing the presence of an interfacial thermal resistance barrier between the nanoparticles and the polymer matrix. This is induced by the reduction in size of the nanoparticles. Modeling of the experimental results allowed us to determine the Kapitza radius a_K for both PI/h‐BN and PI/w‐BN nanocomposites. Values of a_K of 7 nm and >500 nm have been obtained for PI/h‐BN and PI/w‐BN nanocomposite films, respectively. The value obtained matches the Kapitza theory, particularly for PI/w‐BN, for which the thermal conductivity is expected to decrease compared to that of neat PI. The present work shows that it seems difficult to enhance the thermal conductivity of PI films with BN nanoparticles with a diameter <100 nm due to the presence of high interfacial thermal resistance at the BN/PI interfaces. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42461.     

Electrical Conductivity of Parylene F at High Temperature

The electrical conductivity of both as-deposited and annealed poly(α,α,α′,α′-tetrafluoro-p-xylylene) (PA-F) films has been investigated up to 400°C. The static conductivity (σ _DC) values of PA-F measured between 200°C and 340°C appear to be ∼2.5 orders of magnitude lower for annealed films than for as-deposited ones. This change is attributed to a strong increase in the crystallinity of the material occurring above 340°C. After annealing at 400°C in N₂, the σ _DC value measured at 300°C, for instance, decreased from 3.8 × 10⁻¹² Ω⁻¹ cm⁻¹ to 7.5 × 10⁻¹⁵ Ω⁻¹ cm⁻¹. Physical interpretations of such an improvement are offered.     

Investigations on high temperature polyimide potentialities for silicon carbide power device passivation

The operation of silicon carbide (SiC) power devices under severe conditions requires the development of thermally, electrically and chemically stable package. Passivation layer provides electrical insulation and environmental protection for the SiC die. As higher junction temperature and higher electric field can be reached within SiC component, consideration must be given to the thermal stability of the dielectric properties of the material in the die surrounding. Due to their supposed high operating temperature and dielectric strength, spin coated polyimide materials appear as a possible candidate for such passivation and insulation purposes. In this paper, we study the potentialities of a high temperature polyimide from HD Microsystems, for SiC power device passivation, at temperature up to 300 °C.