Embedded Actives Using Additive Manufacturing for High-Density RF Circuits and Systems

This paper presents an additive manufacturing (AM) also known as 3-D printing technique as a new approach to embed active and passive devices for high-density radio frequency (RF) packaging. Three different approaches to embed actives are discussed as: 1) face-up; 2) face-down; and 3) side-mount. The electrical connection to the embedded chip is achieved by fabricating vias using a multilayer AM process and metalized using the sputtering and electroplating techniques. Several tunable RF circuits based on varactor diodes are designed and demonstrated. This includes a T-line resonator, a metamaterial-inspired phase shifter, and a patch antenna. Both dc and microwave characterizations are carried out to test the fabrication reliability and the performance of the circuits. The material used for printing is a high-temperature acrylic photopolymer, and it is characterized in the F-and X-bands. The thermal cycling tests (up to 20 cycles between 22 °C and 90 °C) were performed to demonstrate the integrity of the embedded structures and interconnections. Diode did not show any degradation in the electrical performance after thermal cycling. The key advantages of this process are custom printed substrate, heterogeneous integration compatibility, low parasitics associated with interconnections, and minimal or no misalignment errors. The successful implementation of the embedding process using the multilayer AM technique is essential for the advancement of high-density RF packages for the next generation of compact systems.