Manufacturing Bits: June 22

5G metasurface antennas
At the recent 2021 IEEE 71st Electronic Components and Technology Conference (ECTC), the Institute of Microelectronics of the Chinese Academy of Sciences (CAS) presented a paper on a low-profile broadband metasurface antenna for 5G antenna-in-package applications.

The National Center for Advanced Packaging and the University of Chinese Academy of Sciences also contributed to the work, which is still in R&D. Not long ago, researchers presented a similar paper.

Today, carriers are deploying 5G networks at sub-6GHz frequencies. Some carriers are deploying next-generation 5G networks using the mmWave frequency bands at 26GHz, 28GHz and 39GHz.

The industry is developing new IC packages for 5G mmWave. These packages combine an RF chip and the antenna in the same unit, which is called antenna-in-package (AiP). The idea behind these new integrated antenna schemes is to bring the RF chips closer to the antenna to boost the signal and minimize the losses in systems.

In some cases, packaging houses develop a microstrip patch antenna for a 5G AiP package. Used in different applications besides 5G, patch antennas can be fabricated directly on the package. They are low-cost technologies with low profiles.

“However, the traditional low-profile patch antenna does not satisfy the increasing demands of large bandwidth on ultra-thin substrates,” said Weikang Wan, a researcher from the System Packaging and Integration Research Center at the Institute of Microelectronics of the CAS, in a paper at ECTC. “Stacked patch antenna is one of the good candidates for AiP designs for its ability to increase the impedance bandwidth of patch antenna, while maintaining a small physical aperture size. But it needs to provide an additional substrate with a specified thickness for the parasitic patch. As a result, stacked patch antenna does not contribute to lower the antenna profile.”

In response, the industry has been working on metasurface antennas to overcome those challenges. Metamaterials are artificial materials containing arrays of metal nanostructures or mega-atoms. Some metamaterials are able to bend light around objects, rendering them invisible. But they only interact with light over a very narrow range of wavelengths.

Metasurface materials can be used to improve the performance of the antenna, according to researchers. Several entities are working on the technology.

Metasurface antennas consist of symmetric or asymmetric periodic artificial magnetic conductor (AMC) cells or mushroom type electromagnetic bandgap structures, according to the CAS.

Researchers from the CAS have developed a wideband low-profile metasurface antenna for the 5G 37GHz and 39GHz bands with an overall thickness of only 0.33 mm.

Compatible with mainstream packaging processes, the antenna is composed of a 2×2 closely arranged patch array with a loaded square ring type AMC structure. “Compared with the 3.7% impedance bandwidth and 5.6 dBi maximum gain of the reference patch antenna, the proposed metasurface antenna reaches up to a wide impedance bandwidth of 20.1%, covering the entire 37/39GHz bands with a peak gain of 9.8 dBi,” Wan said in the paper.

3D printed interposers
Using a 3D printer, Boston Micro Fabrication and HRL Laboratories have developed ceramic interposers for use in the 3D integration of microelectronic devices.

Researchers devised 3D printed interposers with slated and curved vias at diameters of less than 10µm. Printed dielectric ceramics with temperature stability and durability is of high interest for packaging applications.

The interposers are made using a new 3D printer from Boston Micro Fabrication. The printer technology, called Projection Micro Stereolithography (PµSL), is capable of printing polymer parts with 2µm resolution. PµSL enables mold-free, ultra-high-resolution structures.

Conventional silicon interposers for packaging require complex processes. Only straight vias can be fabricated using traditional patterning and etch techniques.

The technology from Boston Micro Fabrication and HRL enables 3D printed vias in polymer and ceramic materials with 2µm resolution, allowing for complex routing. The vias are then metallized to connect different devices and integrated circuits.

“We have printed arrays of straight and curved vias with an aspect ratio of at least 200:1. There is still room to increase this ratio using the low-viscosity preceramic resin that we developed in house,” said Kayleigh Porter, an engineer at HRL.

“We are developing this technology to improve 3D integration of microelectronic subsystems, such as infrared cameras and radar receivers,” said Tobias Schaedler, group manager at HRL. “Smaller, lighter, and more power-efficient system designs are currently limited by electrical routing and packaging, but our additive technology could resolve this bottleneck.”

HRL Laboratories’ development effort is currently funded by DARPA’s Microsystems Technology Office under the Focal arrays for Curved Infrared Imagers (FOCII) program. HRL is a joint R&D venture between The Boeing Company and General Motors.