Compact Power Electronics System Fabrication by Sintering and Lamination of Components into Build-up Layers of the Printed Circuit Boards

Power electronic systems equipped with wide band gap semiconductors like SiC and GaN are attracting increasing attention due to the superior functionality of these materials. Especially for automotive, aerospace and energy grid applications a large market potential is expected, which is reflected in massive investments in respective semiconductor development and fabrication. In order to make full use of the semiconductor properties, however, not only the single components but the whole system has to be taken into account. Major aims in system optimization is the reduction of dc voltage link inductance, optimization of heat dissipation and an overall miniaturization and robustness of modules. Thus, the shortening of interconnect length, the integration of thermal dissipation structures and a compact three-dimensional build-up of systems are at the core of ongoing developments in power electronics. During the past decade, embedding of electronic components into printed circuit board has proven to be a highly promising technology for large-scale fabrication that can meet these requirements. In this paper we present a fabrication approach that is applicable in any printed circuit board fabrication, since only standard equipment is used. As basic building blocks, pre-packaged power semiconductors were used. The fabrication of these will be described briefly. Power components of this type are now commercially available from some suppliers. For the module fabrication, first a typical insulated metal substrate is fabricated. Onto the copper structures, sinter paste is printed to mount pre-packages and vertical resistors. A prepreg-layup is then assembled which surrounds the components. The final layer of the stack is a two-layer power core for electrical routing, which is equipped with sinter depots for top side connection of the components. The stack is laminated with an initial pressure and temperature overshoot in order to facilitate the sintering process. Subsequently the profile resumes conventional parameters in order to cure the prepreg and finalize the lamination process. Surface mounted ceramic capacitors soldered to the top complete the low-impedance dc-link buffer circuit. Damping resistors were embedded into the PCB module, which besides compactness enables an excellent cooling of the module. This technology pushes the fast-switching SiC and GaN power semiconductors to the next step. The drastic reduced switching overvoltage of only 4%, demonstrated for 950 V operation, enables a significantly improved utilization of the semiconductors.