Sorin Dinculescu

Evaluation of Encapsulation Materials for High-Temperature Power Device Packaging

High-temperature power electronics represent an increasing demand. Higher power density or severe ambient temperature applications become the trend, while silicon carbide components with 250-300 °C Tjmax are emerging. Among materials used in high-voltage power module, soft encapsulants play a significant role in improving both semiconductor die and module package voltage ratings, especially under enhanced electrical and thermal constraints. In operation close to their upper temperature limit, two silicone materials were selected among the most thermally stable soft insulators available today. Up to 300 °C, dielectric properties and their stability under isothermal aging in air ambient tests were characterized. The gel, tested using sandwich structures, exhibits cracking of its exposed-to-air face, at an aging temperature as low as 250 °C after less than 100 h. The elastomer, tested as free films, presents no cracking, no degraded electrical characteristics, and a 6 % relative mass loss, after 500 h aging. Moreover, the elastomer insulating properties, at low and high electric field, remains stable up to 300 °C (short-term tests), contrary to the gel which shows a strong increase in dc electrical conductivity. So the elastomer shows promising properties for improved encapsulation performance at 250 °C, to be further investigated in package configurations.

Dielectric and thermal properties of Polyamide-imide (PAI) films

Polyamide-imide (PAI) materials appear as potential candidates for the encapsulation of wide band gap semiconductor power devices operating at high temperature (>200 °C). However, electrical properties of PAIs are under-known compared to those of polyimides (Pis). We propose to evaluate the dielectric properties of two PAI materials with two different glass transition temperatures Tg. The aim is to observe the benefit of increasing Tg, from 280 up to 335 °C for a novel kind of PAIs. So, the broadband dielectric relaxation spectroscopy has been used for measuring the dielectric parameters versus temperature. This paper highlights the role of the glass transition phenomenon in the dielectric properties evolution of PAIs at high temperature. It appears that the glass transition temperature has a strong influence in both the increase of the permittivity, the loss factor and the dc conductivity of several orders of magnitude, and in the characteristic temperature shift when these increases occur.

Fundamental investigation of dielectric phenomena in epoxy composites during curing process under a uniform electric field

This paper deals with the filler movement and the dielectric properties in epoxy composites during curing process under a uniform electric field. For the base epoxy resin, a bisphenol A type epoxy resin and an alicyclic polyamine hardener were used. A plate-like micro-size Al2O3 powder was used as filler. After fully mixing the base resin, fillers, and hardener, they were vacuum-defoamed, poured into a mold having two parallel electrodes, and subsequently heat-hardened. In-situ optical observation and continuous measurements of viscosity and impedance were performed. Broadband dielectric spectroscopy was also carried out after full hardening process. As a result, the formation of chain-like structures of particles is related to both the magnitude of the electric field and its frequency. The dielectric properties of the fluid also impact the formation of chain-like structures.

Packaging of SiC-SBD for high temperature operation

Using wideband gap semiconductors (SiC, GaN) appears as possible solution to the growing demand for the development of high temperature, high frequencies power electronics. This will help downsizing the current Power Electronics systems and extend their range of operation conditions. The aim of this paper is to present the results obtained concerning the packaging of a full-wave rectifying bridge using SiC Schottky Barrier Diodes, capable to operate above 300°C. The diodes are rated 1200 V and 50 A. The proposed packaging is based on an insulating-gas encapsulation and stacking of the components. The rectifying function was tested by feeding a current trough the bridge at room temperature, and while applying high voltage in an insulating gas-filled heated chamber. Results show that the type of interconnection proposed can withstand at least 10 A and 200 V in rectifying conditions. Gas encapsulation allowed for an operation of the diodes under high voltage conditions up to 350°C even if at this temperature diode leakage current is too high to perform an appropriate rectification.

Non-symmetrical electric response in CaCu3Ti4O12 and La0.05Ba0.95TiO3−δ-SPS materials

Two colossal dielectric permittivity (CDC) materials, CaCu3Ti4O12 (CCTO) issued from conventional sintering with grain sizes between 20 and 30 µm and SPS sintered La0.05Ba0.95TiO3−δ (BTL-SPS) with grain sizes between 50 and 100 nm, are characterized by simple electrical measurements (Sawyer–Tower and I(V)). Whatever the type of measurements performed, the results depend, on the one hand, on the relative position of the sample in the measuring setup and, on the other hand, on the type of surface treatment achieved on the sample. A clear demonstration of the non-isotropic character of the materials under study is achieved. The non-symmetrical electrical response observed in these two different materials seems to be independent of microstructure and composition, and could be related to the overall phenomena at the origin of the colossal values of permittivity.

Development of a new package for next generation power semiconductor devices: Toward high temperature and high voltage applications

This paper deals with I-V characteristics of SiC-SBD and rectifying capabilities of four SiC-SBD using a new package under the temperature up to 300°C. As regards of the I-V characteristics, as the temperature increases, the threshold voltage decreases and the reverse current increases dramatically. This increase of the reverse current of the diodes under study leads to the limitation of the rectifying characteristics of the proposed packaging. This study demonstrates the ability of the later to be used in a harsh environment ones the components problems will have been solved.

Partial discharges monitoring in twisted pair fed with PWM inverter using non-intrusive sensors

This paper deals with partial discharge measurements in twisted pair fed by a PWM inverter. Measurements are carried out using antenna sensors. Both D-Dot sensor and self-made sensors are compared when it comes to detect partial discharge in a PWM environment. High-pass filter performance is tested as well with these sensors. Finally, a innovative noise suppression method is demonstrated using two identical antenna sensors. This method could be a useful and simple mean to improve signal to noise ratio before signal processing.

On-line non intrusive PDs' measurements on aeronautical systems

In aeronautics, the concept of the “more electrical aircraft” emerged during the recent years thanks to the evolution of power electronics, the increase of power density, which has considerably spread the use of power converters for Adjustable Speed Drive (ASD) applications. In parallel, due to the power demand, increasing the voltage of the on-board network has been mandatory. Last but not least, some of these equipments work in depressurized areas of the aircraft. All these conditions put together made possible the existence of Partial Discharges (PD) in systems not designed to endure them. One of the main questions to address is the development of an approach for PD detection in machines supposed to be PD free. Their detection under PWM is therefore a key issue in this new field of applications. Recent advances made in the related different topics i.e on line PD detection under PWM voltage on real industrial test benches will be presented and discussed regarding their consequences.

Temperature measurement method for dielectric layer characterization in a high voltage vacuum prober

During the dielectric characterization of an insulating material the temperature of the sample is of great importance for understanding the underlying behaviors. In the specific context of a vacuum prober some difficulties may arise when direct measurements methods for the temperature are used. Therefore, an indirect method for temperature measurements is proposed and tested hereafter.

Partial discharge inception voltage of pressurized gas insulation encapsulation used for high-temperature and high-voltage power module

This paper deals with the gas pressure and temperature dependence of partial discharge inception voltage (PDIV) of a developed gas-insulated power module as a high temperature and high voltage package. Increasing the gas pressure and temperature in the developed power module increases and decreases PDIV, respectively. Furthermore, the result of decreasing PDIV with increasing temperature is discussed by taking PD light emission image and simulating electrical field around the contact between a springs electrode and Si3N4 dielectric chip which simulates SiC-SBD.