The Metal Embedded Chiplet Assembly for Microwave Integrated Circuits (MECAMIC) technology utilizes RF GaN transistor chiplets integrated into passive interposer wafers using a metal electroplating embedding approach. Chiplets in Wafers (CiW) enable high level of integration between the transistor chiplets and the packaging circuitry, resulting in high RF performance. In this paper, we present the detailed process flow, the development of a MECAMIC Process Design Kit (PDK) for mm-wave RF Integrated Circuits (ICs), and its application to the design, simulation, fabrication and measurements of heterogeneously-integrated multi-stage W-band Low Noise Amplifiers (LNAs) using state-of-the-art mm-wave GaN transistor chiplets and low-cost silicon interposer packaging with 16 dB gain and 4dB noise figure at 77 GHz.