Partial Discharges in Ceramic Substrates - Correlation of Electric Field Strength Simulations with Phase Resolved Partial Discharge Measurements

Abstract

High voltages and the edges of the metallization on ceramic substrates (AMB, DBA, DBC, HTCC, LTCC) lead to high electric field strengths. In the vicinity of the metal edges these high electric field strengths induce partial discharges in the ceramic insulation and in the potting and thereby represent one key degradation mechanism of power modules. In this work the correlation of the simulated electric field strength with phase resolved partial discharge (PRPD) measurements has been investigated. For the simulation of the electric field strength a new method was used to bypass numerical artifacts. The simulated values show that it is possible to reduce the electric field strength by an adaption of the metallization structure. There the distance of the upper and the lower metallization to the rim of the ceramic was changed relative to each other. Due to this variation a reduction of the electric field strength of about 30% can be reached by choosing the optimum distance compared to state of the art design. In PRPD measurements for insulating ceramic substrates (AlN/Al 2 O 3 by DCB) we examined whether the electric field strength reduction leads to higher partial discharge inception voltages (PDIV). The measurements were executed on layouts with different dimensions of the upper and lower metallization relative to each other as well as for 3 different thicknesses of the ceramic insulation layer. An increase from 20% to 35% of the PDIV was measured for layouts designed according to the findings from the simulation with respect to electric field strength reduction. Finally, the calculated electric field strength and the measured PDIV were correlated.

Electrical Insulation Weaknesses in Wide Bandgap Devices

“…in Figure 11a, the PDIV was plotted as shown in Figure 11b as a function of the geometric mean of E values at ML1-ML4. A fitted equation as "PDIV (kV) = 20.4-0.25E (kV/mm)" was also reported for Figure 11b [21].…”

“…However, as shown in Figure 10 [21,30,31] for the same metalized ceramic embedded in silicone gel, PD was found at a phase between zero and the maximum voltage, between 0-90° and 180-270°. Since the number and magnitude of the PDs strongly increase with rising voltage, it was argued that the origin of this discharge phenomenon is due to discharges at the interface between the silicone gel and the substrate and not due to locally restricted cavities in the gel.…”

“…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.…”

“…In [21] the calculated electric field intensity and the measured PDIV were correlated. Combining the calculated electric field intensity in four measuring points ML1-ML4 shown…”

PD measurements, failure analysis, and control in high‐power IGBT modules

“…However, identifying the critical spots with the maximum electric field magnitude due to only sharp edges can be useful to develop strategies to reduce the electric field magnitude peaks due to the effect of one contributing factor. Electrostatic electrical field simulations for determining the electrical field distribution inside a power module were carried out in [8–17].…”