PCB Embedding Technology for 5G mmWave Applications

Along with the large scale implementation of 5G networks a number of crucial technical challenges are still under development. Some of these are concerning the packaging and module developments, where the implementation of a large number of signal connections compatible with high data rates, the use of novel RF materials and finally new process approaches are the main issues to be tackled. Within the European funded project SERENA, an integration platform based on printed circuit board (PCB) embedding technology was developed. The technology enables the reduction of module size, system power consumption, design time, and complexity. At the same time improved performance and transmitted output power were achieved. In particular, by PCB embedding integrated RF electronic modules containing ICs for RF signal generation in very close proximity to the antennas were realized in a single package, thus minimizing the signal path losses. In the framework of the project, new materials suitable for the embedding of RF-components are used in combination with high gain GaN and SiGe dies. In this way a scalable System-in-Package operating at 39 GHz was ultimately implemented. In the course of the project a low and a high power module have been investigated. A functional low power module was fabricated at Fraunhofer IZM. Two process technologies had to be adopted (1) a combination of novel RF laminate and high-end prepreg materials to embed the dies into the build-up of the PCB and (2) the electrical connection of 3 µm Au contact pads by laser drilling and electroplating. Electrical test structures were fabricated in parallel to assess the electrical performance of package configuration and technology. Package interconnects and integrated patch antenna arrays were designed based on simulations with a 3D full-wave EM simulator (AnsysEM HFSS). The simulated structures were fabricated and measured using a network analyzer. The very short interconnection signal path between the passive and active elements realized in the PCB embedding technology achieve very low insertion (less than 0.4 dB) and return loss (better than 20 dB).The antennas in the package designed and fabricated using the PCB embedding technology achieved a wide bandwidth (3.1 GHz) with a peak gain of 8.8 dBi. Mutual coupling less than - 20 dB is obtained over the entire frequency range of interest between the elements of the antenna, thus making it suitable for beamforming. The approach proved to be well suited for the fabrication of 5G System-in-Package RF modules. The paper will give a detailed description of the fabrication processes and will discuss the technological approaches in depth. A brief overview of the electrical results will be given.