Laser-Enhanced Direct Print Additive Manufacturing (LE-DPAM) for Low-Loss, Low-Parasitic Heterogeneous Integration of MMICs

This paper presents an innovative additive manufacturing approach leveraging an organic interposer for low-parasitic and low-loss heterogeneous integration of monolithic microwave integrated circuits (MMICs) at RF and millimeter-wave (mm-wave) frequencies. The methodology involves precise fabrication of patterned cavities within the interposer to seamlessly embed MMICs. Conductive inks, micro-dispensed and cured to form lateral interconnections and integrated chip carriers, are further refined by pico-second pulsed laser micromachining to achieve micrometer-scale accuracy. This laser refinement significantly improves reflection coefficients, facilitating wideband impedance matching. Experimental validation through simulation and measurement of S-parameters for an embedded MMIC distributed amplifier demonstrates superior performance as compared to traditional wire-bonded quad flat no-lead (QFN) packages, with low interconnect attenuation (0.028 dB/mm at 5 GHz, 0.187 dB/mm at 20 GHz, and 0.512 dB/mm at 30 GHz). A system-in-package (SiP) protoype, comprising a cascaded MMIC amplifier and filter as a receiver module, achieved return losses below 10 dB and low package loss. Enhanced laser trimming and de-embedding techniques further reduced return losses beyond 27 dB and decreased insertion losses by 0.5-0.8 dB up to 30 GHz, significantly improving fabrication tolerance and performance consistency. Also, this study introduces and validates an equivalent circuit model for ground-signal-ground (GSG) probe pads up to 40 GHz repeatedly fabricated by laser-enhanced direct-print additive manufacturing (LE-DPAM) for several devices under test (DUTs). The findings offer critical insights for future development and verification of LE-DPAM foundry-compatible process design kits (PDKs), highlighting transformative potentials of additive manufacturing for advanced heterogeneous integration of MMICs, RFICs, and mixed-signal circuits.