Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration IZM

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  • 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.