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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.
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 demand for highly compact power converters in many applications such as on-board power supplies and motor drives leads to high power loss densities. Typically, thermal management components and filters take the biggest part of the converter volume. To reduce the size, embedding technology can be used. Embedding of power semiconductors enhances the electrical performance of such devices due to reduced interconnection length. This leads to lower inductance which enables higher switching frequencies and allows more compact filter elements [1]. Direct cooling strategies pursue ways to enhance heat transfer to a coolant while reduce the heat sink size. Products like the “Danfoss ShowerPower”[2] and “Infineon Hybrid Pack”[3] show examples where cooling structures are attached directly on the backside of the power module. By omitting the thermal interface between power module and heat sink, the thermal resistance is significantly reduced. Due to superior thermal properties, water-glycol is usually applied as coolant. However, using a dielectric coolant enables some unique benefits: First, no electric insulation layer to coolant is required, which reduces the thermal resistance, second, corrosion problems are avoided, as dielectric coolants are typically inert, and third, the system stays safe for users in case of coolant leakage. Our approach combines these strategies to create an ultra-compact PCB embedded power module with integrated dielectric cooling. This paper is focused on the experimental thermal performance evaluation of the developed heat exchangers. It continues the theoretical work, which was presented as paper at the CIPS 2018 [5].