For the next-generation printed circuit boards with a fine pattern, low power consumption and high-speed propagation with low variation of signal propagation must be satisfied. In order to meet such requirements, we investigated a dielectric material for printed circuit boards which has three superior features: low dielectric constant (permittivity), low dielectric loss, and a flat surface with sufficient adhesion force for plating metal. The propagation loss of a microstrip line on the developed material is about 40% of the conventional material at 10 GHz. Significant reduction of the manufacturing fluctuation of the developed materials is achieved due to the flat surface. We adopted a distributed constant model to the propagation results and revealed that the significant reduction of the propagation loss is caused by the flat surface and low dielectric loss. This technology greatly contributes to the next generation of printed circuit boards.