Das Einbetten von Halbleiterbauelementen stellt einen innovativen Ansatz für die Aufbau- und Verbindungstechnik (AVT) leistungselektronischer Systeme dar. Im Rahmen von zahlreichen Forschungsvorhaben wurde gezeigt, dass im Vergleich zu einer konventionellen AVT geringere parasitäre Induktivitäten und Widerstände [1, 2]und damit geringere Leitungs- und Schaltverluste ermöglicht werden. Auch kann der thermische Widerstand durch den Einsatz von Dickkupfersubstraten und wärmeleitfähigen organischen Isolatoren erheblich reduziert werden [2, 3, 4]. Dadurch lässt sich auf Systemebene eine höher Leistungsdichte erreichen [5], ohne dass dadurch die Lastwechselfestigkeit leidet [6, 3].
Dennoch findet die Technologie bis heute nur im Low-Power Bereich oder zum Chip-Scale Packaging von einzelnen Leistungsschaltern kommerziellen Einsatz.
Dieser Vortrag diskutiert mögliche Hemmnisse und Grenzen der Technologie.
The ever-increasing switching speed of semiconductor devices requires a precise measurement of steep current transients. The M-shunt concept offers high signal fidelity, good cooling, and simple manufacturing. Depending on the resistive material used, temperature as well as skin and proximity effects impede static and dynamic measurements to a different degree. A step forward has been derived from the ideal coaxial shunt, so far, a purely theoretical concept, which is hardly producible due to its sophisticated structure. By transferring this concept to the M-shunt structure with its improved PCB manufacturing technologies it can now be realised in practice. Nevertheless, the calibration and the correct degree of delay compensation remain challenging and are investigated more closely within this paper. Furthermore, it will be discussed why the conventional method of bandwidth determination doesn't work for the M-shunt structure. In addition to the low inductance introduced into the load circuit, the high bandwidth of the shunts could be demonstrated, as well as the possibility to extend this by design rules. Supplemented by the advantages of the lower load inductance, the M-shunt will become the tool of choice for characterising switching transients at least up to 200 MHz required bandwidth eventually. Although it is obviously difficult to improve the 3 dB bandwidth with suitable design rules, the range of nearly entirely unaffected measurement frequencies (e.g. < 1 dB) can be significantly extended by limited coupling. For even higher frequencies, measurements of the current M-shunt models, as well as for the coaxial shunts used as reference, should be corrected by post processing to get precise measurement results.
Most current measurement techniques suffer from temperature impacts, though to a different degree. This is also true for shunt resistors, which are usually improved significantly by using temperature compensated alloy materials like Manganin(r) or by proper calibration and subsequent temperature compensation. The concept of the copper-based PCB M-shunt has already been reported to yield excellent current measurement results at room temperature. However, due to the high-temperature coefficient of copper (3920 ppm/K), the current measurement with those M-shunts showed considerable measurement errors for high temperatures and due to self-heating. This can be improved by the use of Manganin. However, still the connection of the resistor with the copper of the PCB and their respective thermal behavior needs to be considered as further possible sources of error. This paper presents challenges associated with the improvement of PCB-based shunts by temperature-compensated material, while not compromising the critical issue of bandwidth and manufacturing capability. It explicitly addresses the problems and difficulties as reported for previous development stages. In its new version, the M-shunt, represents a low inductance measurement system that can be optimised for much higher energies than the coax shunt, while not increasing the inductance introduced into the circuit. Alternatively, it can be configured for a significantly increased bandwidth and lower inductance compared to its coaxial reference.
PCB embedding is an attractive packaging technology for highly integrated future power systems. Electrical and thermal benefits and limitations are well understood, but only few publications focus on reliability. Here we are addressing high-humidity high temperature reverse bias (H3TRB) tests, which are performed to gain deeper understanding of the limitations of this technology. Cu filament growth is observed on both, PCB embedded samples and silicone potted reference samples. These filaments may form a conductive path and lead to an increased leakage current in blocking mode. Electrochemical corrosion of the Cu-plated guard ring is identified as root cause.
This paper presents design, fabrication, and analysis of a PCB embedded half-bridge. Here, a pre-package that contains a 100 V / 100 A MOSFET half bridge is fabricated and embedded into a converter level power PCB, allowing for two routing layers on top of the semiconductors. This enables to minimize the commutation loop inductance by placing a decoupling capacitor directly on top of the switches. Experimentally a parasitic inductance of 1.4 nH is deducted from the ringing frequency in switching experiments. The second design goal is an optimized thermal
performance. Both, simulation with ANSYS Icepak and experiments indicate a value of 1.77 K/W. Based on the results, a 12 V / 48 V bidirectional converter was implemented and operated with a maximum power of 620 W.
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.
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 embedding of power electronics components into the PCB increases their thermal and electrical performance. Due to lower parasitic inductances and a lower thermal resistance, the overall power density of the system can be increased. However, there is a lack on studies about the reliability of PCB embedded power electronics, especially under humidity stress. This study uses test vehicles with functional diodes embedded into the PCB. The reliability of the test vehicles is studied under HV-H3TRB conditions. A critical leakage current is observed after 200h with a benzoxazine based prepreg and after 600h for an epoxy based prepreg. A rootcause analysis revealed lift-off of the polyimide layer and subsequent electrochemical corrosion as failure mechanism. The delamination is most likely triggered by the Au surface on the chips top metal pad. A second set of test samples was fabricated using an improved surface treatment before lamination. 75% of these samples passed the 1000h H3TRB test successfully.
PCB embedding in combination with direct-bonded copper (DBC) substrates is an attractive approach for packaging of power semiconductors facilitating low-inductive designs while relying on a proven insulating material. However, the CTE mismatch of these materials could cause reliability issues. This study presents an initial reliability screening using simple IGBT prepackages with alumina-based DBC as test vehicles. After -40/150 °C temperature cycles, fracture of the substrate and the chip is observed, resulting in an increased on-state resistance. Literature data suggest that the substrate failure is independent from the embedding. To gain a deeper understanding of the limitations of the technology, further research with optimized DBC substrates is required.
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.