This paper presents the first hybrid-integration assembly of a power amplifier (PA) monolithic microwave integrated circuit (MMIC) and a beam-steering leaky wave antenna (LWA) using an ultra-precise deposition (UPD) printed coplanar waveguide (CPW) interconnect operating in a broad sub- THz range of 220 GHz to 325 GHz. The hybrid assembly uses an InGaAs PA with a saturated output power of up to 14.5 dBm and an InP LWA with a peak antenna gain of up to 13.5 dBi and a beam-steering range from -60° to 35°. The hybrid assembly employs a submount that compensates for the height difference of $\approx 300 \mu \mathrm{m}$ between the PA MMIC and LWA substrates. The PA MMIC and LWA are positioned at an edge-to-edge distance of just $11 \mu \mathrm{m}$ on the submount using a die bonder with sub-micrometer accuracy. The small gap between the PA MMIC and LWA is filled with a polymer that provides a stable dielectric constant in the target sub-THz range. The UPD-printed CPW interconnect is optimized to maintain a characteristic impedance of $50 \Omega$ by analyzing the dielectric properties and thickness of the various materials on which the printing is performed. Moreover, the surface topology is measured using a white light interferometer, to enable fully conformal printing. The electromagnetic simulation results of the CPW interconnect show an insertion loss of 1.1 dB to 1.7 dB, which includes the RF pads of the PA MMIC, LWA, and the short segments of CPW designed on the PA MMIC and LWA substrates. A separate UPD-printed CPW test assembly is manufactured on a single polymer substrate, and custom through-reflect-line calibration standards are printed on the same substrate to experimentally validate the insertion loss of a UPD-printed CPW in the 220 GHz to 325 GHz range. A probe-based measurement setup is used to characterize the hybrid assembly. The hybrid assembly achieves a reflection coefficient of less than -10 dB and a peak gain of up to 26 dBi across the sub- THz range. The beamsteering functionality of the hybrid assembly is successfully validated only in the forward quadrant due to measurement restrictions in the backward quadrant. In the forward quadrant, the measured beam-steering angle of the hybrid assembly varies from 0° to 37°, which is in good agreement with the standalone LWA.