3D Freeform Antenna-in-Package Approach for FOWLP

Sensing systems for autonomous driving must be reliable and robust in order to fulfill highest safety demands. Especially in urban environments, this requirement translates into developing sensors with very high angular resolution (less than ± 1°) in the near and medium range (up to 100 meters from the car) and a maximum angular detection range (ideally ± 90°) in horizontal plane. In this way, the separate detection of small targets, such as pedestrians, that are very close to each other is possible. RADAR (RAdio Detection And Ranging) systems compared to LIDARs (Light Detection and Ranging) still exhibit poor resolution and the detection range is typically limited to ± 30°. Therefore, considerable technological effort has recently been dedicated to enhance the detection range of RADAR systems without sacrificing the economical advantage. To address this issue, a project with focus on a scalable and low-cost 79 GHz MIMO Radar-Frontend module for autonomous driving was defined with the goal to develop a 3D antenna concept and a related manufacturing technology to increases the angular detection range to ± 90° and improve the angular resolution with respect to the 1°. This technology approach based on 3D compression molding suitable to be combined with fan-out wafer level packaging (FOWLP) or substrate mold embedding. Compression molding is the standard process for manufacturing of reconfigured wafers with embedded bare dies for FOWLP and PLP (panel level packaging). Typically, planar, large and thin formats as e.g. wafer shapes are manufactured by compression molding. Materials used for encapsulation are highly filled epoxy resins. These epoxy molding compounds (EMC) are very well adapted to microelectronics packaging needs. This technology has now been further developed to manufacture 3D shaped structures. In combination with direct metallization of the EMC 3D shaped antennas can be realized. For functional antennas additionally a ground layer is needed with a defined distance to the antenna layer. Hence, a 3D double molding process in combination with direct metallization on EMC was developed. For metallization a seed layer was sputtered on the molding compound followed by copper plating. Structuring of the Cu was done by subtractive etching. Several types of resists (film and liquid) have been systematically evaluated in combination with laser direct imaging to investigate their suitability for 3D metallization. Laser drilled and metallized
$\mu$
vias are used to connect the antenna to the ground layer and e.g. to the radar front electronics. In addition to the described double mold approach with direct metallization the same 3D molding technology can be also used to embed and shape flexible RF substrates with antenna structures and assembled components. In summary, this paper describes in detail the technology development of 3D compression molding to realize a free form antenna for a 79 GHz MIMO Radar-Frontend module. This also includes the demonstrator manufacturing and electrical characterization of the antenna.