A SiC Double-Sided Stacked Wire-Bondless Power Module for High-Frequency Power Electronic Applications

This article reports a double-sided stacked wire-bondless power module package for silicon carbide (SiC) power devices to achieve low parasitic inductance and improved thermal performance for high-frequency applications. The design, simulation, fabrication, and characterization of the power module are presented. A half-bridge module based on the SiC power MOSFETs is demonstrated with minimized parasitic inductance. Double-sided cooling paths are used to maximize heat dissipation. Besides conventional packaging materials used in the power module fabrication, a low-temperature cofired ceramic (LTCC) and nickel-plated copper balls are used in this module package. The LTCC acts as an interposer providing both electrical and thermal routings. The nickel-plated copper balls replace bond wires as the electrical interconnections for the SiC power devices. The electrical and thermo-mechanical simulations of the power module are performed, and its switching performance is evaluated experimentally.

An Anti-Interference Online Monitoring Method for IGBT Bond Wire Aging

Due to the constant changes of the environment and load, the insulated-gate bipolar transistor (IGBT) module is subjected to a large amount of junction temperature (Tj) fluctuations, which often leads to damage to the bond wires. The monitoring parameters of IGBTs are often coupled with Tj, which increases the difficulty of monitoring IGBTs’ health status online. In this paper, based on the collector current (Ic) and collector-emitter on-state voltage (Vce_on) online monitoring circuit, an online monitoring method of IGBT bond wire aging against interference is proposed. First, the bond wire aging model is established, and the Vce_on is selected as the monitoring parameter. Secondly, taking a three-phase inverter circuit as an example, the Vce_on and Ic waveforms of the IGBT module are monitored in real time, and the process of online monitoring is introduced accordingly. Finally, the experimental results indicate that the method proposed in this paper can accurately identify the aging state of IGBT bond wires under different conditions.

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

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.

Thermo-Mechanical Stress Comparison of a GaN and SiC MOSFET for Photovoltaic Applications

Integrating photovoltaic applications within urban environments creates the need for more compact and efficient power electronics that can guarantee long lifetimes. The upcoming wide-bandgap semiconductor devices show great promise in providing the first two properties, but their packaging requires further testing in order to optimize their reliability. This paper demonstrates one iteration of the design for reliability methodology used in order to compare the generated thermo-mechanical stress in the die attach and the bond wires of a GaN and SiC MOSFET. An electro-thermal model of a photovoltaic string inverter is used in order to translate a cloudy and a clear one-hour mission profile from Arizona into a junction losses profile. Subsequently, the finite element method models of both devices are constructed through reverse engineering in order to analyze the plastic energy. The results show that the plastic energy in the die attach caused by a cloudy mission-profile is much higher than that caused by a clear mission-profile. The GaN MOSFET, in spite of its reduced losses, endures around 5 times more plastic energy dissipation density in its die attach than the SiC MOSFET while the reverse is true for the bond wires. Potential design adaptations for both devices have been suggested to initiate a new iteration in the design for reliability methodology, which will ultimately lead to a more reliable design.