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The requirements for power electronic assemblies are continuously increasing and are mainly driven by costs, functionality, and reliability. A novel and promising approach is the embedding of power semiconductor devices into PCB-materials. Benefits are the reduction in size and volume of the system. The embedding of semiconductor devices provides a high degree of miniaturization. Also printed circuit board technology in combination with the use of established processes apparently has the potential for low-cost manufacturing. Further functional advantages are the possibility to place passive components and peripheral circuits close to the switching devices, enabling shorter commutating paths. In consequence, they are expected to produce smaller parasitic effects caused by the package, which results in higher possible frequencies and reduced conduction and switching losses. However, there is a significant challenge regarding package design, processing, and materials selection to make use of this potential even at high operating temperatures. To address only one aspect, generally used materials, like epoxy-glass-substrates (FR4) and solder alloys like PbSnAg or SAC are not suitable for temperatures above 150 °C. This work will introduce and evaluate a concept for double-side Ag-sintered semiconductor chips, which are embedded between two organic high-temperature PCBs. A proof-of-concept will be presented by setting up a 30 kW (600 V, 50 A) power package as a demonstrator.
The increasing demands on power electronics with high currents and high operating temperatures has led to the establishment of ceramic substrates. More efficient heat distribution, as well as increased thermal durability, are two aspects of the superior properties of ceramic substrates compared to conventional Printed Wiring Boards (PWB). Nevertheless, there is an demand to develop new solutions based on PWBs to provide affordable and highly integrated power electronic devices for electromobility. For cost optimization, it would be advantageous to replace the hybrid technology with a single board in order to reduce materials, parts and interconnections. Unfortunately, mounting techniques like pressure-assisted silver sintering lead to damages of epoxy-glass-substrates due to high bonding pressures and high temperatures during bonding. Recent projects led to the development of high-temperature stable benzoxazin-based wiring boards. Investigations on the quality and reliability of sintered assemblies on these PWB-substrates are still pending and were systematically carried out in this work.
PCB embedding is a novel and promising approach for packaging of power semiconductors. Due to the planar construction the technology enables lower conduction and switching losses, an increase switching frequency and ultimately yields a higher power density. Usually embedding is performed during lay-up of the PCB. Here, a novel concept for fabrication of PCB based power devices is proposed. The bare dies are sandwiched between two circuit boards using Ag sintering and simultaneous lamination of prepregs. The technology is discussed with reference to a 600V / 50A IGBT half bridge module. Using high-Tg isolator material in the PCB, a suitable process window is established and laboratory demonstrators are fabricated. An electrical characterization proves the feasibility of the concept.