PCB Embedding Technology for 5G mmWave Applications

The roll out of 5G networks has already started worldwide and in the near future it is expected to dramatically reshape the wireless communication landscape. Nevertheless, a number of technical challenges still need to be addressed in the most recent packaging development approaches, such as the implementation of a large number of connections at high data rates, exhibiting high gain to compensate for the high free space loss at millimeter wave frequencies. Within the European funded project SERENA, partners from academia, research and industry are collaborating to address these topics and develop an integration platform, based on PCB embedding technology, capable of reducing size, power consumption and design time and complexity, while at the same time achieving increased performance, energy efficiency and transmitted output power. In particular, PCB embedding technology offers the potential to realize an integrated RF electronics module containing ICs for RF signal generation and antennas with very short interconnects in a single package, thus minimizing the signal path losses. In the framework of the SERENA project, new RF materials suitable for the embedding of components are applied in combination with high gain GaN and SiGe dies for the first time to implement a scalable System-in-Package operating at 39 GHz. Different concepts for the realization of RF modules with embedded GaN and SiGe dies were outlined and first demonstrators are currently being fabricated at Fraunhofer IZM to develop a process technology which allows 1) using RF laminate and prepreg materials to embed the dies for modularization and 2) handle non-standard die pad metallization, such as 3 μm thick Au pads, within the embedding process sequence. Test structures were also fabricated for the electrical assessment of the package configuration and the applied technology. Specifically, package interconnects and integrated patch antenna arrays were designed, simulated with the aid of a 3D full-wave simulator and measured after fabrication. It was shown that the interconnects realized in the PCB embedding technology have good RF properties in terms of insertion loss and return loss and are well suited for System-in-Package RF modules. The antennas also exhibit good radiation characteristics in terms of the gain and efficiency. The paper will give a detailed description of the fabrication process development and will discuss the technological approaches in depth.