Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration IZM

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  • Publication
    Sporadic Early Life Solder Ball Detachment Effects on Subsequent Microstructure Evolution and Fatigue of Solder Joints in Wafer-Level Chip-Scale Packages
    ( 2020)
    Schambeck, S.
    ;
    Hutter, M.
    ;
    Jaeschke, J.
    ;
    Deutinger, A.
    ;
    Schneider-Ramelow, M.
    The combination of continuous miniaturization of electronics and the demanding reliability requirements for industrial and automotive electronics is one big challenge for emerging packaging technology. One aspect is to increase the understanding of the damage under environmental loading. Therefore, the solder joints of a wafer-level chip-scale package assembled on a printed circuit board (PCB) have been analyzed after a temperature cycling test. In the case of the investigated package, a limited number of joints did not form a proper mechanical connection with the PCB copper pad. Although not intended in the first place, these circumstances cause a detachment of those joints within the first few thermal cycles. However, this constellation offers a unique opportunity to compare the solder joint microstructure after thermomechanical loading (connected joints) with pure thermal loading (detached joints) located directly next to each other. It is shown that microstructure aging effects can be directly linked to regions in the joint with increased loading. This is particularly the case for detached joints, which could almost retain their initial microstructure up to the effect of the high-temperature part of the thermal profile. By means of finite element simulation, it is further possible to quantify the increased loading on adjacent joints if isolated solder balls detach from the board. In one case presented, the lifetime of the corner joint was calculated to reduce up to 85% only.
  • Publication
    Ferrites in Transfer-Molded Power SiPs: Challenges in Packaging
    ( 2020)
    Thomas, T.
    ;
    Dijk, M. van
    ;
    Dreissigacker, M.
    ;
    Hoffmann, S.
    ;
    Walter, H.
    ;
    Becker, K.-F.
    ;
    Schneider-Ramelow, M.
    Transfer-molding process is enjoying growing interest when aiming for novel high-power density system-in-packages (power SiPs), where not only transistors and diodes but also drivers, passives, coils, and transformers are supposed to be integrated in one package. Encapsulating modules in a transfer-molding process induces higher mechanical load onto module components compared with conventional silicone potting. Previous investigations have shown that integration of delicate components as ferrite cores into molded packages is not as trivial as integration of conventional surface-mount devices or power semiconductors; the brittle ferrites tend to fracture during the encapsulation process, resulting in higher ferrite core loss. The current study aims to identify main root causes for ferrite core cracking during manufacturing of molded power SiPs. The test vehicle is a symmetrical printed circuit board-based package with three pairs of E-shaped ferrite cores. The epoxy molding compound deployed here is characterized to enable filling simulations. Because technical datasheets of ferrites typically lack specifications of mechanical properties, ferrite materials are analyzed in more detail. Filling simulations and thermomechanical simulations are performed to gain insight into process-induced stress, which may induce cracks in the ferrites. In addition, different ferrite designs are evaluated regarding core losses and mechanical stability and, thus, their tendency to fracture.
  • Publication
    A numerical study on mitigation of flying dies in compression molding of microelectronic packages
    ( 2019)
    Dreissigacker, M.
    ;
    Hoelck, O.
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    Bauer, J.
    ;
    Braun, T.
    ;
    Becker, K.-F.
    ;
    Schneider-Ramelow, M.
    ;
    Lang, K.-D.
    Compression molding with liquid encapsulants is a crucial process in microelectronic packaging. Material properties of highly filled systems of reactive epoxy molding compounds depend on process conditions in a complex manner, such as shear-thinning behavior, which is superimposed by a time- and temperature-dependent conversion rate, both strongly affecting viscosity. The focus is set on forces exerted on individual dice during encapsulation in fan-out wafer-level packaging (FOWLP). The presented framework consists of an analytical approach to calculate the melt front velocity and simulations carried out to capture the nonlinear kinematics, chemorheology, and to extract forces exerted on individual dice. It offers separate evaluation of pressure and shear contributions for two cases, 0° and 45° between the dice' frontal area and the melt front. Process parameters, such as compression speed, thus cycle time, and process temperature, are determined to keep the forces on the dice below the critical level, where drag forces exceed adhesive forces. As a result, process parameters are determined to minimize flying dice and thereby maximize yield. The approach is easily transferable to arbitrary geometries and is therefore well suited to face the challenges that come with the current efforts toward the transition from FOWLP to larger substrates.
  • Publication
    Transfer molding technology for smart power electronics modules: Materials and processes
    ( 2012)
    Becker, K.-F.
    ;
    Joklitschke, D.
    ;
    Braun, T.
    ;
    Koch, M.
    ;
    Thomas, T.
    ;
    Schreier-Alt, T.
    ;
    Bader, V.
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    Bauer, J.
    ;
    Nowak, T.
    ;
    Bochow-Ness, O.
    ;
    Aschenbrenner, R.
    ;
    Schneider-Ramelow, M.
    ;
    Lang, K.-D.
    In recent years, within power electronics packaging, there has been a trend toward compact power electronics modules for automotive and industrial applications, where a smart integrated control unit for motor drives is replacing bulky substrates with discrete control logic and power electronics. Most recent modules combine control and power electronics, yielding maximum miniaturization. Transfer molding is the method of choice for cost-effective encapsulation of such modules due to robustness of the molded modules and moderate cost of packaging. But there are challenges with this type of package. Typically, these packages are asymmetric, and thus a substrate with single sided assembly is overmolded on the component side and the substrate backside is exposed, providing a heat path for optimized cooling. This asymmetric geometry is prone to yielding warped substrates, preventing optimum thermal contact to the heat sink and also putting thermomechanical stress on the encap sulated components, possibly reducing reliability. Such packages are truly heterogeneous, combining power ICs, wire bonds, SMDs, control ICs, substrate, and lead frame surfaces. As a result, the encapsulant used needs to adhere sufficiently to all surfaces present. Additionally, those packages need to operate at elevated temperatures for extended time periods, for example, at 150°C for 2000 h and more, so high thermal stability is of prime importance. Within this paper, a reference application is described integrating power and control logic inside a lead frame based molded package. Taking into account the challenges mentioned above, a detailed description of material selection for this module will be given, including material analysis, such as rheology, reactivity, and change in εr; and thermomechanical properties, in initial stage as f(t,T) and after media storage. Process development tools for module molding are used to ensure manufacturability and usability.