A Wideband Millimeter-Wave HDI-Based Antenna-in-Package Design and its GSG-Probe-Free Measurement

This article presents a wideband millimeter-wave antenna-in-package (AiP) design using high-density interconnect (HDI) technology for flip-chip-based packaging applications. The proposed AiP design incorporates parasitic elements with multiple resonant modes in a magnetoelectric (ME) dipole, pushing the bandwidth of flip-chip-based AiP beyond 50%. To demonstrate the proposed wideband AiP design, a wideband GSG-probe-free AiP measurement method is also proposed, utilizing the ball grid array (BGA), flip-chip soldering, and a substrate-integrated coaxial line (SICL) transition board. The continuous coaxial transmission structure ensures a wide measurable bandwidth of AiP and also reduces sensitivity to BGA fabrication tolerance. This approach overcomes the limitations of conventional probe-based AiP measurement and closely replicates real flip-chip packaging scenarios. The measurement results demonstrate that the proposed AiP design achieves an impressive impedance bandwidth of 56.8% from 26.7 to 47.9 GHz, a wide 3-dB gain bandwidth of 44.7% from 29.5 to 46.5 GHz, a competitive realized gain of 8.3 dBi, and stable radiation patterns. The narrowed 3-dB gain bandwidth is attributed to HDI fabrication tolerance. The proposed wideband AiP design and GSG-probe-free measurement method are promising for wideband RF integrated circuit (RFIC) packaging applications. © 2025 IEEE.