In this article, a new type of Vivaldi antenna with heat dissipation enhancement is proposed and manufactured based on 3-D printing and printed circuit board (PCB) technologies. A longitudinal slot on substrate integrated waveguide (SIW) is employed to feed Vivaldi radiation structure, which replaces the balun structure of traditional Vivaldi antennas. The measured 10 dB bandwidth of antenna element reaches up to 34.48% (21.77-30.39 GHz) and the in-band realized boresight gain is 6.5-8.8 dBi. The <inline-formula> <tex-math notation="LaTeX">1\times 4 </tex-math></inline-formula> Vivaldi antenna array with 28.72% (21.63-28.81 GHz) bandwidth and a gain range of 10.5-12.5 dBi is achieved. The fin-shaped structure of the antenna array further enhances the heat dissipation while increasing the gain up to the range of 13.4-15.5 dBi. The measured results are in good agreement with the simulated ones. The proposed antenna array has important application potential in 5G millimeter-wave systems.