A Study on the Effect of Bond Wires Lift-Off on IGBT Thermal Resistance Measurement

Abstract

Bond wire lift-off will cause an increase of remaining wires’ power dissipation, which usually is ignored for healthy modules. However, only partial wires’ power dissipation transfers through thermal path from junction to case, which will lead to overestimate the whole power dissipation from collector to emitter pole and underestimate the calculated thermal resistance using the proportion of temperature difference to power dissipation. A FEM model is established to show the change of heat flow after bond wires were removed, the temperature of bond wires increases, and the measured thermal resistance decrease after bond wires lift-off. It is validated by experimental results using open package Insulated Gate Bipolar Transistor (IGBT) modules under different current conditions. This conclusion might be helpful to indicate the bond wires lift-off and solder fatigue by comparing the change of measured thermal resistance. Using the Kelvin setup to measure thermal resistance will cause misjudgment of failure mode due to the ignoring of wires’ power dissipation. This paper proposed that the lift-off of bond wires will lead to underestimating the thermal resistance measurement, which will overestimate the lifetime of IGBT module and misjudge its state of health.

Improved Temperature Monitoring and Protection Method of Three-Level NPC Application Based on Half-Bridge IGBT Modules

“…3. It should be noted that the bonding wires in power modules have an influence on the temperature distribution [22], [23], but for the sake of simplicity and speeding up the FEM simulation, these geometric features are typically ignored. In the FEM software, the IGBT module is thermally simulated by setting different boundary conditions and thermal loads, so that we can obtain the temperature change curves of the power chips inside the IGBT module under different step power inputs.…”

“…When it comes to the boundary condition, it refers to the specific heat transfer coefficient for the heatsink. As shown in [22], a convection coefficient of 3000W/m 2 •K is defined on the bottom to simulate as forced air cooling [17] and the rest surfaces are defined as 12.5 W/m 2 •K in the FEM simulation. This is the boundary setting of merely IGBT module, however, when it comes to the whole FEM model of IGBT module and real heatsink with fans, there is no need to directly give the convection coefficient on the bottom to simulate as forced air cooling.…”

A Fault Detection Method of IGBT Bond Wire Fatigue Based on the Reduction of Measured Heatsink Thermal Resistance

“…Our previous study [22,23] proposes that the heat flow of bond wires is different from the die, which transfers to both the die side and the emitter side at the same time, as in Figure 3a. Hence, the power loss of bond wires could be divided into two parts based on the direction of heat flow, which transfers through the die side P WB _ D and emitter side P WB _ E , as in Equation (5).…”

“…Although the measured thermal resistance of heatsink seems to show a notable change during cycling, it shows a significant decrease after bond wires fault, which is shown in Figure 18b, where the brown wave is normalized conduct voltage and the blue wave is normalized measured thermal resistance of heatsink. Previous research proposed that the thermal resistance will decrease after bond wires failed [23], which is shown in Figure 18a, where the brown wave is normalized conduct voltage and the blue wave is normalized measured thermal resistance of the IGBT module. The measured thermal resistance of the IGBT module could be measured in this test due to the special custom circuit test circuit; however, it is nearly impossible to measure the thermal resistance of the module during operation in a normal power converter.…”