The diffusivity and solubility of gold into silicon substrate increases with rising bonding temperatures. Table 2 shows density, diffusivity and viscosity for typical liquids, gases and supercritical fluids. Viscosity and surface tension of water drop and diffusivity increases with increasing temperature. This value of equivalent conductivity corresponds to a diffusivity of 4,75*10 cms. Thermal mass is also related to thermal diffusivity, heat capacity and insulation. Where K is the eddy diffusivity. The rate of transport is governed by the diffusivity and the concentration gradient. Thermal diffusivity is often measured with the flash method. Subscript AB denotes diffusivity of species A diffusing into species B. Transport properties such as diffusivity describe how rapidly molecules move through the polymer matrix. This quantity is called the thermal diffusivity of the medium. The ratio of thermal diffusivity to mass diffusivity is the Lewis number (Le). The higher the thermal diffusivity of the sample, the faster the energy reaches the backside. The Schmidt number describes the ratio of momentum diffusivity to mass diffusivity. Whereas with large values, , the momentum diffusivity dominates the behavior.