US Patent 9258892 Circuit materials, circuits laminates, and method of manufacture thereof

A circuit subassembly is disclosed comprising a conductive metal layer and a dielectric substrate layer having a dielectric constant of less than about 3.5 and a dissipation factor of less than about 0.006 at 10 GHz, wherein the composition of the dielectric substrate layer comprises about 5 to about 70 volume percent of borosilicate microspheres that have been treated with an alkaline solution.