In order to take the full advantage of the high-temperature SiC and GaN operating devices, package materials able to withstand high-temperature storage and large thermal cycles have been investigated. The temperature under consideration here are higher than 200 °C. Such temperatures are required for several potential applications such as down-hole oil and gas industry for well logging, aircrafts, automotive, and space exploration. This review focuses on the reliability of a selection of potential components or materials used in the package assembly as the substrates, the die attaches, the interconnections, and the encapsulation materials. It reveals that, substrates with low coefficient of thermal expansion (CTE) conductors or with higher fracture resistant ceramics are potential candidates for high temperatures. Die attaches and interconnections reliable solutions are also available with the use of compatible metallization schemes. At this level, the reliability can also be improved by reducing the CTE mismatch between assembled materials. The encapsulation remains the most limiting packaging component since hard materials present thermomechanical reliability issues, while soft materials have low degradation temperatures. The review allows identifying reliable components and materials for high-temperature wide bandgap semiconductors and is expected to be very useful for researchers working for the development on high-temperature electronics.

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.

Recent aircraft designs increasingly use electrical systems with higher voltages. This can lead to the occurrence of partial discharges. Testing for these phenomena is relatively poorly documented in comparison with other standardized tests available for aerospace components. After having investigated the effect of temperature, pressure, and moisture on the partial discharge inception voltage as well as the discharge characteristics, we focused on the effect of these environmental parameters on the behaviour of the energy dissipated by the discharges and on polyimide film endurance during aging under partial discharge. The results show two different behaviours for the variation of energy dissipation along aging time related to environmental conditions. In fact, when a semi-conducting layer is formed in wet conditions due to the interaction between the gaseous by-products and the water molecules, a decrease in the energy measured was revealed. In addition, the relationship between the measured dissipated energy and the polyimide lifetime was investigated and did not present constant trends for the different aging conditions. While it is clear that the material endurance was energy dependent in dry conditions, it was shown that, even when the discharge energies were higher, an increase in the endurance of the dielectric was observed when the superficial semi-conducting layer was formed.