The objective of the proposed research is to address two challenges in heterogeneous integration solutions for RF/mmWave and high-speed microelectronic systems: (1) for through-silicon via (TSV)-based integration platforms, significant RF losses arise due to dielectric losses, and crosstalk effects may affect signal integrity; (2) current RF packaging solutions like wirebonds suffer from parasitic inductance and limited bandwidth. Low-loss, low-reflection, and highly-customizable interconnect solutions are essential to drive performance and functionality. To address these challenges, we propose an advanced packaging platform with (1) enhanced low-loss shielded TSVs and (2) impedance-matched, height difference-compensating off-chip transitions. The low-loss shielded TSVs, which are 10 μm wide and 50 μm deep, feature a deep annular air trench that reduced measured capacitance and conductance at 50 GHz by 38.4% and 51.6%, respectively. Simulation results indicate that the shielding configuration reduces coupling. The second part of the integration platform is termed 3D stitch-chip for its ability to electrically stitch across components of different heights. To cover a 10-100 μm step height range, a monolithic connector chip with a sloped sidewall formed by KOH etching is proposed. For greater step heights, vertical connectivity is established by a small chip containing TSVs, while the lateral connectivity is enabled by a coplanar waveguide (CPW) trace on a fused silica chip. Gold stud bumps were used to bond the two components. Simulation results indicate better than 1 dB insertion loss (IL) and better than 17 dB return loss (RL) up to 50 GHz. Measurements up to 50 GHz will be performed, comparing the 3D stitch-chip to wirebonds. In addition, mechanical shear strength testing will be performed to verify the reliability of the assembly. An RF front-end module (FEM), such as a Ka band (26.5-40 GHz) low-noise amplifier (LNA) will be integrated to demonstrate the functionality of the stitching technology. Lastly, the design methodology will be extended to optimize the 3D stitch-chip for W band (75-110 GHz).