A four year project in Germany has developed glass packaging for radar sensors for industrial and process metrology that operates up to 300GHz.
The “Glass Interposer Technology for Implementing Highly Compact Electronic Systems for High-frequency Applications” (GlaRA) project has developed and characterized a reliable interposer technology as a system-in-package (SiP) based on glass for broadband millimetre wave chips. This allows modules that can be used in sensors and communication at frequencies above 100 GHz.
Standard packages do not work because of the frequencies exceeding 100 GHz and must allow for adaptation for specialized sensor ASICs as well as manufacturing in medium-sized quantities at competitive prices.
The technology platform uses various waveguide concepts, high-density micro wiring, and hermetic encapsulation to increase the functions that can be integrated. In addition, it makes applications up to 300 GHz possible within a single material system, glass, through excellent waveguide properties and high-precision micromachining.
The use of glass interposers with electric feedthrough vias provides hermetic packaging able to enclose the components between two glass interposers. The packages are manufactured on 300mm glass wafers, enabling simultaneous processing of many components and alignment accuracy within the narrow tolerances of RF technology. It also uses silicon machining techniques to accelerate commercial implementation and reduce costs and glass is available in large panels, considerably simplifying scaling to large quantities.
The consortium demonstrated a compact radar front end (above) developed at Endress+Hauser for radar fill level sensors with an operating frequency of 160 GHz. The glass package is 5.9 x 4.4 x 0.8 mm and contains a radar ASIC in SiGe technology, all electrical connections to external electronics, test structures for characterization, and a waveguide connection that can also be used as an integrated primary emitter for a lens antenna.
The demos were produced using a new kind of process chain, starting with laser-induced deep etching (LIDE) by LPKF Laser & Electronics that generates microstructures in the glass.
Next: Glass system-in-package process
The Fraunhofer Institute for Reliability and Micro-Integration developed an industrial process for metallizing the glass vias with high aspect ratios. A wafer bonding process is used to hermetically package the assembled components by bonding two glass wafers, each of which have vias and cavities.
The conducting paths on the glass substrates are structured and metallized at PacTech using its SB² process, a laser-supported process for the sequential build-up of solder balls, solder deposits are placed on contact surfaces produced without external current. Different alloys are used to enable staggered assembly at different soldering temperatures. MSG Lithoglas assisted with the implementation of the HF packages by producing cavities used to hold the ASIC and other components. In addition, high-precision spacers made of glass are produced by means of low-temperature coating.
With a high-frequency concept developed for the new package by the Institute for Microwave Technology of Ulm University, the radar signal – at more than 100 GHz – can both illuminate a lens directly via a primary beam and be guided at low loss to a detached antenna via a flexible dielectric waveguide. The different options for emitting radar signals from the package enable a range of applications.
Sentronics Metrology used this for a high-speed 3D sensor with layer resolutions in the sub-nanometer range for quality control. Among other uses, the sensor has been qualified for detecting leaks in the encapsulated, evacuated glass packages.
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