Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration IZM

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Now showing 1 - 10 of 11
  • Publication
    Determination of Lemaitre Damage Parameters for Al H11 Wire Material
    ( 2023)
    Kuttler, Simon
    ;
    Abali, Bilen Emek
    ;
    Wittler, Olaf
    The quality of wirebond interconnects is characterized by shear and pull tests. For such a simulation we need an adequate damage model, since a purely elasto-plastic model fails to give the full picture [1]. For the description of damage, the Lemaitre damage model is selected, because this model is already used in comparable blanking simulations [2]. In addition, the main damage-driving factor of this damage model is the equivalent plastic strain, which is known to be the suitable failure criteria for ductile materials. The model, introduced by Lemaitre in 1985, is for isotropic ductile damage [3]. It has been used and extended in many other works. Still, more than three decades later, modelling free evolving multiaxial damage is often a more scientific topic and has not yet been proven a sufficient engineering tool to investigate destructive tests by numerical simulation. Reducing the amount of tests has been and still is a demand to save time in the design process. Therefore, it is needed to further investigate the capabilities of such damage models on complex applications. Indeed, the damage parameters first need and will be determined in this study for the material used in the application.
  • Publication
    Finite Element-Based Monitoring of Solder Degradation in Discrete SiC MOSFETs
    ( 2023)
    Kilian, Borja
    ;
    Gleichauf, Jonas
    ;
    Maniar, Youssef
    ;
    Wittler, Olaf
    ;
    Schneider-Ramelow, Martin
    Many of the reliability methods used in power electronics require extensive experimental data, resulting in long product design cycles. This work focuses on developing a simulation-driven approach to assess the reliability of a discrete silicon carbide MOSFET by monitoring 2nd level solder degradation under power cycling in the thermal and thermo-mechanical domains. Active power cycling tests are performed to determine the loading condition at which end-of-life is reached due to a 20% increase in thermal resistance. Numerical analysis using finite element simulations is conducted to gain a physical understanding of the failure criterion from a mechanical point of view. The proposed methodology aims to accelerate the quality assurance and product qualification processes of discrete power electronic devices.
  • Publication
    Warpage of Fan-Out Panel Level Packaging - Experimental and Numerical Study of Geometry and Process Influence
    ( 2023)
    Stegmaier, Andreas
    ;
    Hölck, Ole
    ;
    Dijk, Marius van
    ;
    Walter, Hans
    ;
    Wittler, Olaf
    ;
    Schneider-Ramelow, Martin
    In order to reduce waste and cost, the trend in Fan-Out Packaging is the move to rectangular panels instead of circular wafers [1]. These panels can be made in larger formats and better utilize the space due to the rectangular shape. However, with the larger format, warpage of the panels increases and remains a challenge in Fan-Out Panel Level Packaging (FOPLP) production. Warpage occurs mainly due to the multitude of materials that undergo multiple production steps at different temperatures, which leave residual stresses induced by mismatch of thermal strains and strains due to chemical processes (e.g. cure shrinkage). These superimposed effects and the complex material behaviour still make it challenging to predict warpage numerically and control warpage during production [2], [3]. In this work, warpage of nine different variants of a 300 × 300 mm2 panels with dummy dies have been investigated experimentally and numerically. It has been shown that the numerical model can replicate warpage of the panels and the potential for numerically supported warpage adjust steps in the fabrication of the panels has been demonstrated.
  • Publication
    Modification of Prony Series Coefficients to Account for Thermo-Oxidative Ageing Effects within Numerical Simulations
    ( 2023)
    Dijk, Marius van
    ;
    Wittler, Olaf
    ;
    Wagner, Stefan
    ;
    Schneider-Ramelow, Martin
    Ageing effects potentially limit the lifetime of electronic device and systems. To prevent failure during the desired lifetime, knowledge about the used materials is of key importance. Moreover, the change of the used materials during the expected lifetime and its impact on the functionality of the product needs to be considered.In this study, a simulation approach is discussed that can consider ageing effects caused by oxidation at elevated temperature of a printed circuit board material used for radio-frequency applications. By state-of-the-art thermomechanical material characterization, the properties are derived of samples that were stored at elevated temperature (175°C) for up to 1000 hours.Within the simulation workflow, the properties of the different aged states are defined by modifying the pristine properties. Four exponential functions are derived modifying the initial modulus, the characteristic time constants, the shift function and the coefficient of thermal expansion, all in dependency of ageing time.This new approach is compared with an approach where for each aged state a different material set is defined. The deviation between experiment and simulation becomes larger with this new approach, which was expected, since much less detailed information about the material properties are being used. However, the new approach has a major benefit of opening up the opportunity to, for example, perform sensitivity analyses in a very simple manner. Additional benefits are the gained knowledge on how the material is changing over time and the possibility to extract material properties for aged times that are not being measured.
  • Publication
    Experimental and simulative study of warpage behavior for fan-out wafer-level packaging
    ( 2022)
    Dijk, Marius van
    ;
    Huber, Saskia
    ;
    Stegmaier, Andreas
    ;
    Walter, Hans
    ;
    Wittler, Olaf
    ;
    Schneider-Ramelow, M.
    Controlling warpage effects in fan-outwafer-level packaging (FO-WLP) is of key importance for realizing reliable and cost-efficient system in packages (SiPs). However, warpage effects can occur during the manufacturing process, caused by a combination of different processing temperatures, different materials, and the changing properties of the materials (e.g. polymerization and related cure shrinkage). One approach to controlling warpage could be realized by assessing a numerical simulation workflow of the FO-WLP process chain, in which the relevant material properties and geometry are used as input. Since there are many different steps included in the FO-WLP process, accompanied by complex material behavior, this workflow is not straight-forward. In the present paper, the first FO-WLP processing steps are investigated in detail by performing extensive thermo-mechanical material characterization, temperature-dependent warpage measurements, and numerical simulations. The investigation focuses on two epoxy mold compound (EMC) materials with completely different physical properties. The warpage measurements of bi-material (EMC and silicon) samples reveal an irreversible effect after passing certain processing temperatures, which are significant for final warpage at room temperature. A new approach to measuring the coefficient of thermal expansion (CTE) is discussed, using a temperature profile based on the temperature in the process, instead of the three identical temperature ramps suggested by the typical standards. This new approach makes it possible to determine possible shrinkage effects. Within the simulation model, the hysteresis effect observed in the experiment is taken into account by adding a shrinkage strain as well as changing the CTE values during the process. A very good agreement between the experiment and simulation is achieved, which is shown for several demonstrators with different epoxy mold compound materials and thicknesses.
  • Publication
    Numerical simulation of transient thermomechanical ageing effects
    ( 2022)
    Dijk, Marius van
    ;
    Huber, Saskia
    ;
    Walter, Hans
    ;
    Wittler, Olaf
    ;
    Schneider-Ramelow, Martin
    Automotive radar and 5G communication systems require for their high frequency functionality substrates with low dielectric constants, which are capable to operate at elevated temperatures for long lifetimes. Special substrates based on laminate Printed Circuit Board (PCB) technology come here into focus due to their cost benefit against ceramic substrates. But the matrix of these substrates is based on polymers like for example PPE (Polyphenylether) or PTFE (Polytetra-floureten). In general, polymers are susceptible to ageing, which may already be initiated at mild conditions and short times (e.g. during the expected usetime) and can have a potential large influence on the reliability as the properties can change massively.To enable the development of reliable electrical components, the behavior during the desired lifetime of the used materials is of importance. In this paper we focus on thermo-oxidative ageing effects of a Radio Frequency (RF) application suitable PCB material and how this effect can be considered transiently in a numerical simulation approach. For this approach, first extensive material characterization was performed on samples aged for different periods of time at 175°C. This temperature was selected as this is the specified maximum operating temperature for the material. These different states of the material were then used within the simulation model, where the ageing process is simulated and a gradual-continuous change of one state to the other is calculated.
  • Publication
    Finite Element Influence Analysis of Power Module Design Options
    ( 2022)
    Dijk, Marius van
    ;
    Wittler, Olaf
    ;
    Hung, P.-C.
    ;
    Lai, W.-H.
    ;
    Hsieh, C.-Y.
    ;
    Wang, T.
    ;
    Schneider-Ramelow, M.
    The electrification trend for the automotive industry (electric- and hybrid electric vehicles EV/HEV) desires the development of application specific power modules with shorter time-to-market for which the reliability is guaranteed over a large time span. Besides the electrical layout of such power modules, numerous variations of the design can be made which include material selection, the used assembly and interconnection technologies and geometrical variations like layer thicknesses and position of certain components.Due to the time efficiency, relative low costs and good possibilities for visualizing thermal and thermomechanical behavior in detail, research and development is focusing nowadays more and more on Finite Element Analysis (FEA). The possibilities of assessing finite element analysis for visualizing influences of certain design choices are discussed in this paper, where the development of a new, low-power automotive power module is used as an example. Moreover, simulation analysis focusses on the complete power module, in order to consider cross influences of design choices.First, a discussion on the static thermal behavior is presented followed by the thermomechanical behavior. As the die attach is prone to show early failure/degradation, a numerical simulation Design of Experiment (DoE) is conducted to visualize the influence of - for example - the heat sink material on die attach reliability. For this purpose, 37 simulation models are evaluated, having different configurations. Additional simulations are performed to investigate the reliability of the electrical connection (ribbon- or wire bond).Special attention is given to the reliability of sintered silver die attach technology. This trend-topic in power electronics is gaining much interest in the recent years where many authors have published results of increasing reliability when the classical soldered die attach is replaced with sintered silver. Experimental tests are performed to investigate the influence of the sintered silver Bond Line Thickness (BLT) and to verify the simulation results. The experiments indicate that even after 2500 thermal shock cycles according to the AQG324 no failure or starting degradation for all bond line thicknesses was observed.
  • Publication
    Potentials of a SiC Fan-out Wafer Level Package for High Power Application
    ( 2022)
    Mackowiak, Piotr
    ;
    Conrad, Janine
    ;
    Wittler, Olaf
    ;
    Schiffer, Michael
    ;
    Braun, Tanja
    ;
    Schneider-Ramelow, Martin
    This paper describes the research on the development of a SiC Fan-out Wafer level Package for high power application. Electronic Packaging for High Power devices needs to address high temperature capability and a low thermal resistance, as thermal power losses impact the reliability of power devices. These in contrast trend towards higher power densities and performances. A comparison between Fan-out Packages with two different Mold compounds and a SiC Wafer Level Package was performed using FEM Simulation. The simulation shows the high potential of the SiC Fan-out package. It is shown that the thermal resistance of the package is reduced by 72%. This allows to package power devices with much higher power losses compared to mold embedded devices (x3.5). Additionally, we propose a manufacturing process for this package using wafer level back-end processes. It uses deep etching of SiC with an electroplated metal mask, wafer bonding and laser release technologies. It also introduces a SiC nanoparticle filled adhesive to improve thermal conductivity of the bond adhesive. The performed experiments show that up to 37.5wt% SiC nanoparticles could be mixed into the adhesive and spincoated with a good homogeneity on the wafer.
  • Publication
    Numerical Simulation of a Wire Bond Shear Test Using Nonlinear Adaptive Remeshing
    ( 2022)
    Kuttler, Simon
    ;
    Wittler, Olaf
    ;
    Schneider-Ramelow, Martin
    The shear test is typically being used to quantify the interconnect quality of wire bonds. Besides the pull test, the shear test is more relevant to quantify the mechanical stability of the interface region of wire bond and chip/substrate metallization. The criteria for these tests are collected in the DVS-2811 [1], [2]. These are widely used in the industry and accepted for common wire materials. Due to higher lifetime requirements of wire bonds especially in power electronics, new materials and material combinations are developed and already in use [3]-[7].The focus of this work is on aluminum wires. Some of these materials show very promising results in lifetime testing (temperature cycling) but do not show reasonable results considering the shear test. Therefore, this work is giving an insight into the shear test method using advanced numerical simulation methods.
  • Publication
    SiC Fan-out Wafer Level Package for High Power Application
    ( 2022)
    Mackowiak, Piotr
    ;
    Wittler, Olaf
    ;
    Braun, Tanja
    ;
    Erbacher, Kolja
    ;
    Schiffer, Michael
    ;
    Schneider-Ramelow, Martin
    The thermal concept of the electronic package for high power devices needs to address the increased temperature of operation and the need to insure the head dissipation of the device. In common Fan-out packages Epoxy Mold compounds (EMC) are used which is not well adopted to high temperature operation as EMC has a low thermal conductivity. In this paper the research on the development of a Fan-Out Wafer Level Package is described. First a FEM simulation comparing a Mold compound and SiC Fan-out Packages was performed. It showed that the thermal resistance of the package can be reduced by 72% allowing up to 20 W/mm2 eight times power loss in a 3.9 mm2 package. Later a manufacturing process was developed for this SiC Fan-out Wafer level Package which suits for high power application addressing. For this package Wafer Level bonding techniques of SiC Wafers are used to embed the active chip, e.g. a Monolithic Microwave Integrated Circuit (MMIC). Through SiC Vias (TSiCV) are used to realize the backside contacts and a SiC nanoparticle filled adhesive is used to inprove the thermal conductivity of the bond interface.