The significance of low-loss dielectric materials becomes more remarkable for high-performance and miniaturized 5G-millimeter-wave packages. Among a wide variety of dielectric materials, low-loss photo-imageable dielectric (PID) is drawing attention because of the unique properties such as patternability and process simplicity. This paper introduces a new advanced low-loss PID material with low dielectric constant and low dissipation factor. The material also provides sub-10 µm photo-patterning using a standard photolithography process. It also offers superior mechanical properties over the previously-reported PID. The new material shows an elongation of 70%, a tensile strength of 120 MPa, a glass transition temperature of 200°C, and high adhesion to metal trace (5 N/cm) with smooth surface ($\text{Rq} < \mathrm{10}\ \text{nm}$). To show the capability of multi-layer patterning with sub-$-\mathrm{40}-\mu \mathrm{m}$ photo-patterned microvias, daisy-chain structures are fabricated. This paper also discusses the surface roughness impact on signal losses in mm-wave frequency band (10–40 GHz). The results indicate that the mitigated surface roughness of this proposed material minimizes signal losses with precise re-distribution layer patterning.