Additively Manufactured Flexible Material Characterization and On-demand "Smart" Packaging Topologies for 5G/mmwave Wearable Applications

Additively manufactured materials are key components in Flexible Hybrid Electronic (FHE) designs. Accurate characterizations of electrical and mechanical properties for these emerging flexible materials are critical for future wearable 5G/mmWave technologies. This paper investigated 6 types of 3D printed flexible materials including both SLA printed and FDM printed materials. The dielectric constant and loss tangent of these materials over 26-40GHz were extracted from measurements of material samples using Transmission/Reflection method through WR28 waveguide. Universal testing machine and 2D digital imaging correlation (DIC) system were also performed to obtain mechanical properties such as elastic modulus, percent elongation at break,nominal tensile strength and Poisson's ratios. Among all the tested materials, Polypropylene (PP) demonstrates a very low loss tangent of 0.001, with an elastic modulus of 230 MPa, and a Poisson's ratio of 0.40, making it an excellent candidate for mmWave flexible and wearable SoP modules. In addition, Silver Nano Particle (SNP) ink and Particle Free Silver (PFS) ink were evaluated for their conductivity and inkjet printability on the 3D printed flexible materials. Inkjet printed microstrip line samples were fabricated on PP substrates with different metallization thickness to measure the insertion loss. With 6 layers of SNP ink, the average deembedded insertion loss is less than 0.1dB/mm. Finally, based on the characterized results and previous work, a "smart" packaging topology including phased array antenna and microfluidic channel with flexible encapsulation is proposed, providing a proof-of-concept demonstration of a flexible wireless wearable electronics platform for high speed data transmission utilizing rapid, low-cost additive manufacturing tools.