Porous Epoxy Film for Low Dielectric Constant Chip Substrates and Boards

Lowering the dielectric constant of interconnect, substrates and boards for electronic devices is needed to achieve faster switching speed and smaller electronic device packages. A feasible way to reduce the dielectric constant of existing material is by introducing porosity within the dielectric film. The density of pores and pore size play an important role in determining the mechanical property and electrical property of the film. An increase in the pore fraction leads to lower dielectric constant. However, higher pore fraction can deteriorate the mechanical properties. Therefore, it is important to achieve a balance between dielectric constant and mechanical properties. In this study, a low molecular weight sacrificial polymer poly(propylene carbonate) was functionalized with epoxide groups to increase its miscibility in an FR4 epoxy resin formulation by cross-linking it with the epoxy matrix. During or after curing, the epoxy resin can be heated to a temperature to generate the porous structure by evolution of the sacrificial polymer products. The mechanical and dielectric properties were measured to show the feasibility of using this modified sacrificial polymer in existing FR4 epoxy formulations to achieve lower dielectric constant interconnect.