Evaluation of Parylene-HT as Dielectric for Application in Advanced Package Substrates

Polymer dielectrics having low dielectric constants are necessary for next-generation package substrates to achieve lower losses and higher bandwidth densities. Conventional silica-filled dielectrics have higher dielectric constants due to the silica fillers. Therefore, it is important to explore novel dielectric materials for next-generation package substrates that have lower dielectric constants. Parylenes have a unique set of properties such as- very low moisture absorption, low gas permeability, conformal deposition, and heat resistance. Some parylenes also have a very low dielectric constant, low dielectric dissipation losses and low roughness that make them attractive as dielectrics for application in advanced package substrates. Amongst all parylenes, Parylene-Hthas the lowest dielectric constant
$(\mathrm{D}_{k})$
of 2.17 and dissipation factor
$(\mathbf{D}_{f})$
of 0.001 at 1 MHz, thus making it attractive for high-frequency applications. However, there are several challenges associated with the use of polymer dielectrics in package substrates such as- adhesion to Cu, via formation ability, processability, mechanical reliability and electrical reliability. This paper evaluates Parylene- Htwith respect to all these challenges.