Molecular basis of the interphase dielectric properties of microelectronic and optoelectronic packaging materials

High frequency microelectronic and optoelectronic device packaging requires the use of substrate and encapsulation materials having a low dielectric constant, low dielectric loss and high volume resistivity. Most packaging materials are polymer-ceramic composites. A clear understanding of the broadband dielectric properties of composite materials is thus of great current importance for the effective development of high frequency packaging materials and optimized package design. Toward this goal, a general framework for understanding the dielectric properties of packaging materials was recently developed in which the dielectric constant of polymer-ceramic composite materials is characterized by the electrical properties of the polymer phase, the filler phase and an interphase region within the composite system. However, for this framework to be a viable tool for tailoring the dielectric properties of packaging materials, one must understand the dielectric properties of the polymer-filler interphase region, which represents a region of polymer surrounding and bonded to the surface of each filler particle having unique dielectric and physical characteristics. This work presents a model to explain and predict the dielectric properties of the composite interphase region based on dipole polarization theory. Our results show that a) the interphase region surrounding the filler particles of polymer-ceramic composites possess a dielectric constant less than that of the bulk polymer matrix; b) the value of the dielectric constant of the interphase region can be explained by the change in chemical polarizability of the polymer caused by the chemical bonding of the polymer to the filler particle surface; c) the change in the dielectric constant of the interphase region can be calculated through the use chemical polarizability equations. These results are fully consistent with experimental evidence and lay the groundwork for a comprehensive explanation and determination of the overall effective dielectric properties of packaging materials for a wide range of electrical, electronic, and RF applications.