Additively Manufactured Flexible Materials, Interconnects and Transmission Lines for Flexible Wearable 5G/mmWave Applications
Kexin Hu, Charles Lynch, Yi Zhou, Manos M. Tentzeris, and Suresh K. Sitaraman
The recent development and deployment of 5G/mmWave technologies have enabled the explosive growth of high-data rates and next-generation data-driven Internet of Things (IoT) systems. In particular, wearable 5G/mmWave technologies are highly desirable for various applications such as ubiquitous health monitoring or activity tracking. However, these wearable systems require compact, conformal form-factors with performance that is resilient and adaptable to bending and on-body effects from an RF perspective. Additionally, due to the widespread adoption of 5G/mmWave systems, the designs need to be highly scalable to meet manufacturability requirements. Thus, to meet the needs of the development of scalable, conformal, wearable 5G/mmWave systems, this paper introduces the development of a next-generation System-on-Package (SoP) design with on-demand customizable flexible "smart packaging" structures utilizing additive manufacturing techniques (3D, inkjet printing). The main requirements for components and modules designed for future 5G/mmWave System-on- Package (SoP) integration are reliable performance within broad operational bandwidth, low parasitic losses at mmWave frequencies, and high volumetric utilization so that more functionality can be packed into a compact module. For 5G/mmWave antenna array designs, wideband performance, miniaturization, and high gain are required to support high data rate and high spatial efficiency so that more users and throughput can be supported at the same time.
Thus, flexible die-to-die and die-topackage interconnection topologies with 10x smaller losses and parasitics compared with conventional wire-bonding and via are proposed. Furthermore, 3D structural designs providing important functionalities such as microfluidic thermal management and environmental sensing are proposed for integration within a flexible hybrid package. Finally, the integration of these individual components, including interconnects, antennas, and supporting 3D architecture (microfluidics, frequency selective surfaces for Electromagnetic Interference and Compatibility (EMI/EMC) suppression), is going to be thoroughly discussed to provide a proof-of-concept demonstration of a flexible wireless wearable electronics platform for high-speed data transmission for commercial and military uses utilizing rapid, low-cost additive manufacturing tools. In this paper, numerous different 3D printed flexible materials for FDM and SLA printers are evaluated for both mechanical and electrical properties.
Dielectric constants and loss tangents are measured using Transmission/Reflection method through waveguides up to 40GHz. Two types of conductive inks: nanoparticle (SNP) ink (EMD5730) from Suntronic Chemical and a particle-free silver ink (PFS) from Electroninks are considered to compare the conductivity and printability. The surface roughness of substrates varies with different 3D printed materials and significantly affects the printability of the ink. This can be improved by sanding the surface, printing SU8 layers before the ink and applying UVO treatment. To further investigate the performance of inkjet printed circuits on these substrates, microstrip lines are designed and printed with SNP ink and measured by Vector Network Analyzer. Measurements of transmission loss are also reported over the 24-40GHz frequency band, while the electrical/mechanical impact of different bending radii is thoroughly characterized, providing practical reliability guidelines for real-world conformal and flexible implementations.
