Al modification as indicator of current filaments in IGBTs under repetitive SC operation

Abstract

This work investigates modification on the top-side aluminium (Al) metallisation of 1.2 kV insulated-gate bipolar transistors (IGBTs) under repetitive short-circuit (SC) type-I measurements for two different parasitic inductances of 45 and 380 nH. The presence of current-density filaments starting at the collector side during SC leads to local temperature increase of the emitter metallisation and thus to modification of the top Al surface in the pattern of the current filaments. Here, two techniques thermo-reflectance microscopy, which can detect the surface temperature during repetitive short circuits directly and Al modifications after repetitive SC with analysis under optical microscope after the test have been considered. At 45 nH, with different DC-link voltages from 300 to 600 V, the Al modification pattern is non-uniform and it becomes uniform for V DC >600 V. However, for 380 nH parasitic inductance and for DC-link voltages 300 and 400 V, the Al reconstruction shows a non-uniform pattern and becomes uniform for V DC ≥500 V. The SC simulations were performed by using a simplified front-side IGBT structure using variable DC-link voltages and inductances to reproduce the filament behaviour.

Aluminium modification as indicator for current filaments under repetitive short-circuit in 650 V IGBTs

“…The 1200 V IGBT shows a clearly inhomogeneous aluminium modification as an indicator of current filaments as shown in Fig. 6 at DC-link voltage of 300 V [10]. The results in Fig.…”

“…For 1200 V IGBTs, a clear local Al modification under repetitive SC stress using microscopy has been observed as shown in Fig. 6, and explained through simulation in [9,10]. The SC simulation was performed for 1200 V IGBT class at VDC = 400 V, IC = 235 A, Tstart = 300 K and SC pulse length (tSC) of 4 µs.…”

“…After 2000 SC pulses Fig. 6: Aluminium emitter surface analysis using optical microscope for a 1200 V IGBT at VDC = 300 V, VGE = 40 V, IC = 300 A, tSC = 4 µs, tgap = 1 s, RG = 220 Ω, RG,OFF = 270 Ω, and Lpar = 45 nH [10].…”

“…The current filaments generate a similar pattern imprint visible as local Al modification under repetitive SC conditions. Hence, the optical microscope was used to study the local Al modification as an indicator of current filaments in 1200 V and 1700 V IGBTs [9][10][11]. Generally, for lower DC-link voltages, non-destructive current filaments can be observed under repetitive SC measurement.…”

A Review on IGBT Module Failure Modes and Lifetime Testing

“…This accelerates the process of cracks and voids formation [34,47]. High currents cause electro-migration in bond wires and metallization layers, which leads to creation of voids and hot spots [34,48]. High levels of humidity and corrosive chemicals existing in many industrial applications, e.g., mining, cement, oil and gas, and marine, may result in corrosion of bond wires accelerating their mechanical degradation, and eventually leading to their rupture [24,34,36].…”