Embedded RF Packaging Via Ceramic 3D Printing and Printed Electronics Additive Manufacturing

The demand for advanced, high-performance radio frequency (RF) systems continues to rise in a wide range of applications, and embedded packaging is becoming a critical enabler for high-density electronics. Traditional RF packaging technologies are manufactured using various wafer fabrication lines, have various input/output (IO) pad metallization types, and/or are designed for probe station testing. As a result, it is often challenging to integrate these devices into a more complex module on a single RF substrate in a high-fidelity, low-parasitic way, which hinders the demonstration of next-generation communications architectures and concepts. In this work, we developed a fully additive manufacturing process for RF die packaging based on 3D printing for quick and flexible prototyping of embedded electronic modules and for improvements in size, weight, power, and cost. First, alumina 3D printing was used to produce a matrix for RF chip embedding and RF transmission line printing. Process conditions were optimized to fabricate small square pockets with lateral dimensions of 1 mm x 1 mm and depth of 150 microns. In addition, through plate holes with diameters as small as 300 microns and aspect ratio of ~2:1 were produced. Secondly, printed electronics methods like micro-dispensing (μDS) and aerosol jet printing (AJP) were employed to fabricate dielectric and conductive components. Custom RF test dies were manufactured and were pick-and-placed inside the pockets previously made in the alumina matrix. A conductive adhesive was micro-dispensed for die attachment, and PDS was also used to build a dielectric ramp bridging the die and the matrix. In the subsequent steps, AJP was used to print coplanar waveguide (CPW) transmission lines on the alumina surface and interconnects between those and the metalized pads on the test die. Printed components and RF die units were tested for mechanical and electrical performance and also for robustness and reliability under thermal cycling (-55°C to 125°C, 100 cycles) and aging (85°C, 85% relative humidity), showing excellent results. For conductive die-attach material, average adhesion strength was 13.5 Kgf before and 16.2 Kgf or 21.5 Kgf after aging or thermal cycling, respectively. Conductive vias in alumina presented a similar improvement in performance, with maximum DC resistance being 0.5 Ohms before and 0.35 Ohms after thermal cycling. CPW RF transmission lines with different geometries were simulated via electromagnetic (EM) modeling and a few variations with different pad sizes were printed for validation. Ink conductivity and 3D printed alumina roughness were used in the simulations, and good agreement between measured (0.22-0.29 dB/mm) and modeled (0.22-0.24 dB/mm) signal attenuation loss was observed. The integration of printed CPW lines with custom-manufactured microstrip lines on embedded silicon dies was also performed. This embedded unit exhibited low RF losses of 0.274 dB/mm at a frequency of 30 GHz. As conclusion, the combination of alumina 3D printing and printed electronic methods enabled highly customizable designs and easier prototyping for embedded RF circuits, as well as a path toward more complex RF multi-chip modules.