Mauro Ciappa

Selected failure mechanisms of modern power modules

Abstract This paper reviews the main failure mechanisms occurring in modern power modules paying special attention to insulated gate bipolar transistor devices for high-power applications. This compendium provides the main failure modes, the physical or chemical processes that lead to the failure, and reports some major technological countermeasures, which are used for realizing the very stringent reliability requirements imposed in particular by the electrical traction applications.

Thermal component model for electrothermal analysis of IGBT module systems

The insulated gate bipolar transistor (IGBT) modules are getting more accepted and increasingly used in power electronic systems as high power and high voltage switching components. However, IGBT technology with high speed and greater packaging density leads to higher power densities on the chips and increases higher operating temperatures. These operating temperatures in turn lead to an increase of the failure rate and a reduction of the reliability. In this paper, the static and dynamic thermal behavior of IGBT module system mounted on a water-cooled heat sink is analyzed. Although three-dimensional finite element method (3-D FEM) delivers very accurate results, its usage is limited by an imposed computation time in arbitrary load cycles. Therefore, an RC component model (RCCM) is investigated to extract thermal resistances and time constants for a thermal network. The uniqueness of the RCCM is an introduction of the time constants based on the Elmore delay, which represents the propagation delay of the heat flux through the physical geometry of each layer. The dynamic behavior predicted by the thermal network is equivalent to numerical solutions of the 3-D FEM. The RCCM quickly offers insight into the physical layers of the components and provides useful information in a few minutes for the arbitrary or periodic power waveforms. This approach enables a system designer to couple the thermal prediction with a circuit simulator to analyze the electrothermal behavior of IGBT module system, simultaneously.

Lifetime prediction and design of reliability tests for high-power devices in automotive applications

Different procedures are defined and compared to extract the statistical distribution of the thermal cycles experienced by power devices that are installed in hybrid vehicles and operated according to arbitrary mission profiles. This enables both to design efficient accelerated tests tailored on realistic data and to provide the input for lifetime prediction models. Initially, the system lifetime is predicted under the assumption of linear accumulation of the damage produced by low cycling fatigue. Also, a novel prediction model based on some fundamental equations is introduced which takes into consideration the creep experienced by compliant materials when they are submitted to thermal cycles.

Lifetime prediction of IGBT modules for traction applications

Bond wire lift-off caused by low-cycle fatigue is one among the dominant failure mechanisms of modern high power Insulated Gate Bipolar Transistors multichip modules used in traction applications. A model is proposed which is calibrated basing on data from accelerated tests and which predicts quantitatively the lifetime of devices submitted to cyclic loads as they are encountered in current converters of railway systems. It assumes linear accumulation of the thermal-cycle fatigue damage and takes into account the redundancy of the bond wires within a complex multichip module.

Extraction of Accurate Thermal Compact Models for Fast Electro-Thermal Simulation of IGBT Modules in Hybrid Electric Vehicles

Abstract An optimized thermal management is of paramount importance when developing efficient and reliable converters for automotive applications. In this paper, we present a new approach to extract accurate compact models for fast electro-thermal simulations of IGBT modules used in hybrid electric vehicles. It is shown that the proposed methodology brings advantages in terms of increased reliability, reduction of the costs, and shortening of the design cycle.

New Technique for the Measurement of the Static and of the Transient Junction Temperature in IGBT Devices under Operating Conditions

A novel technique is presented, which uses dIce/dt and the transconductance as a thermo-sensitive parameter for the measurement of the static and of the transient average junction temperature in IGBT devices. The paper describes the physics of the signal generation, provides the experimental setup, and discusses the accuracy and the suitability of the technique under operating conditions of the devices.

Lifetime prediction on the base of mission profiles

Abstract Realistic mission profiles represent a challenge for the lifetime prediction of complex devices and systems. This paper proposes several examples where this problem has been solved by proper analysis of the stresses, by dedicated physical modeling, and by efficient calculation tools.

Measurement of the transient junction temperature in MOSFET devices under operating conditions.

Abstract The capabilities of three techniques to measure the transient average junction temperature in power MOS devices based on the electrical thermo-sensitive parameters are assessed experimentally and by compact device simulation. The first two methods make use of the dependency of d I d s /d t on the temperature, while the third one exploits the temperature dependency of the turn ON delay of the device.

Monte Carlo modeling in the low-energy domain of the secondary electron emission of polymethylmethacrylate for critical-dimension scanning electron microscopy

The main scattering mechanisms governing the transport of electrons in PMMA in an energy domain ranging from the energy of the primary electron beam down to few hundreds of meV are identified. A quantitative Monte Carlo model for the emission of secondary electrons is developed to be applied for critical dimensions extraction from high-resolution scanning electron microscopy (SEM) images. Selected results are presented, which demonstrate the accuracy of the proposed approach.

Measurement and modeling of the electron impact-ionization coefficient in silicon up to very high temperatures

In this paper, an experimental investigation on high-temperature electron impact-ionization in silicon is carried out with the aim of improving the qualitative and quantitative understanding of carrier transport under electrostatic discharge (ESD) conditions. Special test devices were designed and manufactured using Infineons SPT5 technology, namely: a bipolar junction transistor (BJT), a static-induction transistor (SIT) and a vertical DMOS transistor (VDMOS), all of them with a cylindrical geometry. The measurements were carried out using a customized measurement setup that allows very high operating temperatures to be reached. A novel extraction methodology allowing for the determination of the impact-ionization coefficient against electric field and lattice temperature has been used. The experiments, carried out up to 773 K, confirm a previous theoretical investigation on impact-ionization, and widely extend the validity range of the compact model here proposed for implementation in device simulation tools. This is especially useful to predict the failure threshold of ESD-protection and power devices.