Simulation of the electric field strength in the vicinity of metallization edges on dielectric substrates

Abstract

High electric field strengths at the edge of the metallization of insulated gate bipolar transistor (IGBT) power modules are, besides defects in the substrate or the potting gel, the main reason for partial discharge. These critical electric field strengths occur at the energized contact where it is bordered by the insulating ceramic and the cover (mostly silicone gel). The reduction of high electric field strengths for increasing the threshold voltage for partial discharge has been studied in several publications based on experiments as well as on simulations. Simulations allow the localization of the critical spots and the quantification of the maximum electric field strength. However, a systematic study of the singularities of the electric field strength at the sharp edges is lacking. Such singularities are investigated in this article. The calculation of an absolute electric field strength value is only possible for finite edge radii. For sharp edges, however, the maximum electric field strength returned by simulation depends on the grid size: Through the finite grid size a virtual edge radius is induced that suppresses the singularity at the edge. To get around this problem, a mesh-independent evaluation procedure is introduced. With this procedure it is possible to quantitatively evaluate the electric field strength in the vicinity of the sharp edge. As an example, the influence of the offset between the top and bottom metallization layer on the maximum electric field strength is studied. Moreover, the influence of the thickness of the involved layers and of the shape of the electrodes is discussed. Also, the impact of the material properties of the involved dielectrics is examined. In addition to electrostatic simulations we have carried out electric transient simulations, which show that the ratio of the conductivities of the involved dielectric materials plays a major role for determining the maximum electric field strength

Metallized ceramic substrate with mesa structure for voltage ramp-up of power modules

“…This approach is proposed because, in this process, we don't want to evaluate the exact maximum field in the triple point but to compare different solutions. The significant changes in geometry did not allow to use some other methods proposed in the literature [22,23]. Figure 3 presents an example of the predetermined mesh used in this study.…”

Electrical Insulation Weaknesses in Wide Bandgap Devices

“…To overcome this difficulty, it was shown in [20,21] that when the distance to sharp edges becomes larger than 20 μm for the assumed geometry and dimensions, the differences between the electric field magnitudes for different meshing sizes are less than 1%. To be on the safe side, measuring points were considered at a distance of 50 μm to sharp edges in [20,21]. In [22], both strategies containing rounded edges and considering measuring points at a distance of 20 μm from edges were benefited.…”

“…Assuming the measuring points defined above, the influence of following geometrical options are studied in [20,22] on reducing the electric field stress values. Among four parameters above, the thickness of the substrate and metal/conductive layer offset have a strong influence on the electric field magnitude.…”

Partial discharges in ceramic substrates - correlation of electric field strength simulations with phase resolved partial discharge measurements

“…10). Further results on the influence of the structure or of the dielectric materials used (ceramic, potting) on the PDIV are given elsewhere [23,24]. Combining the calculated maximum electric field strength in the two measurement points of each edge the PDIV was plotted as a function of the arithmetic as well as the geometric mean ( Fig.…”