Partial discharges measurements have been performed on 3.3 kV IGBT power modules. Results using both the normalized and a new proposed test are compared. The new test, allowing the detection of partial discharges in all the insulating materials, is detailed. Elementary defect patterns are used to distinguish the main cause (dies or insulating materials) of the observed partial discharges in IGBT modules.

IGBT hybrid power modules used in high voltage applications (ex. railway traction systems) are built using several dielectric materials. This stack may be a source of partial discharges. Up to now these modules are tested as regards partial discharges using a normalized test (EIC 270), which despite its quality is not representative of the real applied stresses endured during normal operating conditions, as it does not stress all the materials present in the stack. A new method for determining partial discharges activity in such power modules has been developed. Application of this test to IGBT modules leads to a PD ignition threshold lower than the one found using the normalized test. In this paper the different results obtained up to now in this field are summarized and discussed. Additionally, the test is modified in order to apply it to different structures in order to identify the possible cause of PD developments in such power modules.

In power electronics, the development of new IGBT power modules allow them to switch kV and kA during /spl mu/s. However, such components need to be cooled and ceramic materials are used as an interface between the electronic devices (the chips) and the cooling. Another key point of the reliability of the packaging of these devices is their encapsulation made of silicone gel to prevent any discharge on the substrate surface and also in the vicinity of the bondings. In order to identify the physical mechanisms involved in these materials, different experiments are performed. The results of conductivity and space charge measurements (using the LIPP method) under HVDC electrical stress at different temperatures are presented and analysed.

In railways applications high voltage IGBT power modules are used to build power converters. Such an approach allows increasing at the same time the reliability, the thermal and electrical performances, to decrease the cost and to achieve an improved design. From a material point of view, such modules have to be considered as a stack of different types of materials. Among them, the dielectric materials, both organic and inorganic, suffer from a lack of knowledge of their properties. This paper describes the step by step method which has been followed to study different ceramic substrates and encapsulation materials in order to get a better understanding of their properties and their ability to be used in such a structure. Choice and dimensioning criteria will be presented.

Aluminium nitride (AlN) is emerging as an attractive substrate material in High Power packaging application because of its good thermal and mechanical properties. It has also to present very high electrical characteristics (to withstand high electric stresses). When used as substrate, it is often considered as the key point of the reliability of the component they are involved in. These high power modules are used as elementary blocks to build the switches used in inverters. In these applications and from an electrical point of view, some parts of the substrate are submitted to a DC electrical field (+E), whereas other parts may be submitted to an unipolar electrical stress (+E,0) at a switching frequency (up to 10 kHz). Some studies have already been published on the dielectric breakdown under AC and DC voltages but little is known on the DC conductivity of such materials. The aim of this study is to analyze the conduction current (J) of AlN samples versus temperature (T) and the magnitude of the DC applied field (E). Experimental results are obtained on 1/40 inch-thick DBC (Direct Bonding Copper) samples. Transient currents J(t) and conduction plots J(E) are analyzed to find the most probable conduction mechanism. All these results are discussed and a possible aging phenomenon is identified