Abstract
Dielectric liquids are incompressible, able to fill voids and have selfhealing effect and hence are being considered as alternative encapsulation materials to
establish power electronics at ambient high pressure at subsea conditions. In a long-term
endurance test, insulated-gate bipolar transistor (IGBT) chips subjected to 6.5 kV DC
stress in dielectric oil environment was reported to have failed after less than one week in
operation. A critical look at the failed objects revealed contamination fibres at the surface
and around the high field regions. This paper presents the numerical simulation of field
distribution around a conducting fibre at the surface of the IGBT chip. It also evaluates the
influence of the nature of the encapsulation material on the integrity of power electronic
modules using a long-term experiment at a medium elevated temperature for high and
low relative humidity operated close to service load using IGBT relevant chips. Finite
element method (FEM) calculations show how the high field region can be shielded from
impurities that can easily trigger partial discharge (PD) and breakdown. The simulation
suggests that coating the surface of the module with a thin polymer layer with a thickness
of 20 µm or more could be sufficient to improve the reliability of the encapsulation system.
Additional polymer coat with thickness 27 µm on the chip made the system survive without
failure for 67 weeks under test and dry operating condition. Meanwhile, thick coating such
as silicone gel protected the object longer under higher relative humidity.
establish power electronics at ambient high pressure at subsea conditions. In a long-term
endurance test, insulated-gate bipolar transistor (IGBT) chips subjected to 6.5 kV DC
stress in dielectric oil environment was reported to have failed after less than one week in
operation. A critical look at the failed objects revealed contamination fibres at the surface
and around the high field regions. This paper presents the numerical simulation of field
distribution around a conducting fibre at the surface of the IGBT chip. It also evaluates the
influence of the nature of the encapsulation material on the integrity of power electronic
modules using a long-term experiment at a medium elevated temperature for high and
low relative humidity operated close to service load using IGBT relevant chips. Finite
element method (FEM) calculations show how the high field region can be shielded from
impurities that can easily trigger partial discharge (PD) and breakdown. The simulation
suggests that coating the surface of the module with a thin polymer layer with a thickness
of 20 µm or more could be sufficient to improve the reliability of the encapsulation system.
Additional polymer coat with thickness 27 µm on the chip made the system survive without
failure for 67 weeks under test and dry operating condition. Meanwhile, thick coating such
as silicone gel protected the object longer under higher relative humidity.
