Emmanuel Dutarde

A Study of Mechanisms of Poly (PhenyleneSulfide) Thermal Degradation in Air

Because of its special properties and commercial significance, Poly(phenylene sulfide) (PPS) has been the subject of many research efforts since its commercial introduction in 1967. Intensive work has been done on its crystalline structure and morphology and its thermal behaviour. But fewer investigations have been carried out to understand long term behaviour in high temperature environments. Always anticipating industrial needs linked to power integration, we have launched an extensive study on thermal aging in air of PPS at 250°C. This study has shown that PPS thermal degradation in air happens by intermolecular branching reaction, similar to crosslinking. This phenomenon was already known for temperature above 300°C. This crosslinking is evidenced by rheometry where the relative position of G’ and G’’ above melting temperature changes with aging. IR spectroscopy confirms that para substituted benzene in PPS molecule is transformed in 1,2,4 trisubstituted benzene. DSC measurements evidence both an elevation of melting temperature and a change in melting endotherm showing significant changes in crystalline morphology along aging, which tends to indicate that crosslinking occurs in crystalline phase. Then degradation implies drastic loss of mechanical properties leading to destruction of the sample.

Contribution to the stress grading in integrated power modules

Power electronics packaging, like integrated power modules, constitute an advanced technology leading to power density increase, weight and volume decrease and enhancing the reliability level. However, the continuous increase of the voltage lead to questions regarding power device environment. We discuss in the following different solutions able to achieve the electric stress gradation.

On some electrical characteristics of AlN and Al/sub 2/O/sub 3/

In power electronics, the development of new IGBT power modules allows them to switch kV and kA during us. However, such components need to be cooled and ceramic materials like AlN and Al/sub 2/O/sub 3/ are used as an interface between the electronic devices (the chips) and the cooling. Such materials have to present very well known electrical and thermal characteristics since the reliability of the inverters these components are used in is strongly dependant on them. In order to increase the knowledge of the physical mechanisms involved during aging of these materials, we present in this paper the very first results obtained in this field. Finally, all these results are discussed and analyzed in view of power electronics applications.

Stress grading in integrated power modules

Power electronics packaging, like integrated power modules, constitute an advanced technology leading to power density increase, weight and volume decrease and enhancing the reliability level. However, the continuous increase of the voltage lead to questions regarding power device environment. We discuss in the following different solutions able to achieve the electric stress gradation.

High temperature behaviours of aluminium nitride

One of the most attractive ways to increase power handling capability in power modules is to increase the operating temperature. Aluminium nitride based ceramics are claimed to be the ideal candidates to be used as substrates. However, depending on the elaboration process a decrease of the AlN dielectric strength may be observed. These results are discussed in the following paper.