Vitec (Germany)

The change to wide bandgap power semiconductors in automotive traction inverters enables higher operation temperature and also higher temperature swings. The existing packaging technology for the bare dies comprising soldering and Al wire bonding cannot withstand the accompanying higher thermo-mechanical loads. This leads to the need of new die-related packaging technologies. Two possible new packaging technologies for silicon carbide and gallium nitride devices - namely, sintering and embedding - and their relevant failure mechanisms will be investigated using power cycling experiments.

The higher operating temperatures of power modules based on wide-bandgap semiconductors demand a better understanding and modeling of the viscoplastic material behavior of the die attach layer, in this case sintered silver (SAG). Within a physics-of-failure approach, the damage caused by viscoplastic and plastic deformation is crucial for the estimation of lifetime and reliability of the power modules. In this study, the viscoplastic Anand model and a newly proposed creep model for SAG will be presented, fitted to data from tensile tests and implemented in finite element simulation by means of a user-programmable feature. Subsequently, the simulational results will be compared.

A large diameter high strength titanium free-hanging catenary riser was evaluated by the Demo 2000 Ti-Rise project, from initiative of the Kristin Field development license. In order to reduce the uncertainties related to the schedule, cost, and special technical issues identified in the work related to a similar riser for future installation on the A˚sgard B semi-submersible platform, a fabrication qualification of a full scale riser in titanium was run. Several full-scale production girth welds were made in an in-situ fabrication environment. The welding was performed on extruded titanium grade 23 (ASTM) pipes with an ID of 25.5″) and wall thickness of 30 mm. The main challenge was to develop a highly productive TIG orbital welding procedure, which produced welds with as low pore content as possible. It is well known that sub-surface pores often are initiation sits for fatigue cracks in high strength titanium welds. This paper describes how a greatly improved productivity was obtained in combination with a high weld quality. NDT procedures were developed whit the main on the reliability to detect and locate possible sub-surface weld defects, volumetric defects such as pores and tungsten particles and planar defects such as lack of fusion. The results from the actual Non Destructive Testing (NDT), the mechanical testing, and the fatigue testing of the subjected welds are presented. The response of the catenary is optimised by varied distribution of weight coating along the riser’s length. A satisfactory weight coating with sufficient strength, bond strength, and wear properties was developed and qualified. The riser is planned to be fabricated from extruded titanium pipes, welded together onshore to one continuous piece. The field coating is added and the riser is loaded into the sea and towed offshore and installed.