Fraunhofer-Publica
The Fraunhofer-Publica has been successfully documenting the research results of the Fraunhofer-Gesellschaft for over 30 years. The platform enables the collaborative linking of research-relevant objects and disseminates within the international scientific community.
The Fraunhofer-Publica thus fulfils its responsibility to promote the transfer of knowledge and know-how to industry and society.
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Research outputs
As an application-oriented research organisation, Fraunhofer aims to conduct highly innovative and solution-oriented research - for the benefit of society and to strengthen the German and European economy.
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Projects
Fraunhofer is tackling the current challenges facing industry head on. By pooling their expertise and involving industrial partners at an early stage, the Fraunhofer Institutes involved in the projects aim to turn original scientific ideas into marketable products as quickly as possible.
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Researchers
Scientific achievement and practical relevance are not opposites - at Fraunhofer they are mutually dependent. Thanks to the close organisational links between Fraunhofer Institutes and universities, science at Fraunhofer is conducted at an internationally first-class level.
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Institutes
The Fraunhofer-Gesellschaft is the leading organisation for applied research in Europe. Institutes and research facilities work under its umbrella at various locations throughout Germany.
Recent Additions
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PublicationDeutschlandticket - Impulsgeber für nachhaltige Mobilität?( 2024)
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PublicationAutomated classification of electroluminescence images using artificial neural networks in correlation to solar cell performance parameters( 2023-09-15)The quality control in solar cell production relies on the acquisition of quantitative performance data (I-V-data) together with imaging diagnostics such as electroluminescence (EL) imaging. The classification of the solar cells into different quality groups based on the performance parameters or the identification of specific defects in the EL-images, such as cracks, is rather straightforward and well established. These techniques are extended in our work as we analyze the quantitative correlation between the two approaches. As a specific example, a quality issue related to the contacting of the solar cells during the solar simulator measurement is considered. We demonstrate that a reliable and fully automated classification of the images with respect to the considered quality issue can be achieved by our artificial intelligence (AI) approach. This approach is different from the majority of state-of-the-art approaches as it does not consider specific image objects or features, such as cracks or spots, but rather predicts an image category for the entire image. The performance of the developed supervised image classification approach based on a neural network is analyzed quantitatively. We show that a clear quantitative correlation between cell I-V-data and AI-predicted EL-image classes can be established. In this way, an early-warning procedure can be implemented to detect this performance related issue using the AI-analysis of the EL-images even when its appearance is rather weakly pronounced and before it can be discovered in the I-V-data. We also present results on the impact of the training data set on the performance of the neural network and key parameters describing the quality of the network.
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PublicationInfluence of micro- and macrostructure when determining the contact resistivity of interconnects based on electrically conductive adhesives( 2023-09-15)The contact resistivity of interfaces in solar module interconnects has a direct impact on the series resistance of the entire module and fill factor. Thus, this impacts the performance of entire photovoltaic systems. Accurate measurement of the contact resistance is a key component of optimizing the performance of such interconnects. However, this is difficult for electrically conductive adhesive (ECA) based interconnects. This work shows that transmission line method (TLM) test structures based on ECA display non-negligible inhomogeneities leading to inaccuracies when determining the contact resistivity. Seven methods based on two models - the front- and end-contact TLM models (or a combination of both) - were investigated for four commercially available ECAs used in solar modules and their impacts on the extrapolation of the contact resistivity were quantified. It was determined that even when macroscale inhomogeneities (e.g., variations in the thickness of the ECA) are not present, microscopic structural effects influence the sheet and contact resistance. In particular, variations in the distribution of fillers significantly alter the bulk resistivity of the composites and this variability is also clearly correlated with differences in the geometry of the fillers. It is concluded that the best approach to reduce inaccuracies in the determination of the contact resistivity of ECA-based interconnects is to calculate the sheet and contact resistance locally (using three consecutive contacts) employing a redundant and modified test structure. Afterwards, the contact resistivity ought to be computed using the end-contact TLM model and the median should be assigned as the contact resistivity of the sample.
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PublicationValidation of methodology to determine the contact resistivity of ECA-based bonds grounded on end-contact resistance measurements using redundant and modified TLM test structures( 2023-09-05)Accurate determination of the contact resistivity between electrically conductive adhesives (ECAs) and solar metallization paste is a key component of optimizing the electrical performance of bonds based on ECAs, such as shingled joints. This work proposed and validates a methodology that accounts for non–negligible inhomogeneities of test structures based on ECAs and silver screen-printed metallization, such as changes in width of the ECA, to improve the accuracy in the calculation of the contact resistivity. The proposed validation uses statistical theory based on the central limit theorem and the law of large numbers showing that the contact resistivity of bonds based on two different commercially available ECAs can be clearly differentiated with a minimum confidence level of 95% and a maximum error margin of 5%. Moreover, the necessary sample size to achieve such requirements is calculated and shown to be equal to 24 test structures. The validation was done using an acryl-based adhesive loaded with silver flakes (∼10-4 Ω cm), which was compared to an epoxide-based ECA filled with silver-coated copper particles (∼10-3 Ω cm). The validated methodology indicates that the contact resistivity when using the acrylic conductive adhesive is 0.1791 ± 0.0766 mΩ cm2 while when using the epoxide-based adhesive is 0.5025 ± 0.1218 mΩ cm2. Additionally, it is shown that the standard deviation of the contact resistivity is highly dependent on the composition of the conductive adhesive. Hence, the sample size varies depending on the ECA. It is expected that the presented methodology will be a powerful instrument for developers and researchers in the improvement and optimization of ECAs and ECA bonding processes.
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PublicationQualitative evaluation of flip chip solder bumps produced by stencil printing of solder paste on various electroless nickel/gold metallizations( 2006)Stencil printing of solder paste in conjunction with electroless Ni/Au UBM on Al metallization offers the most economical method for wafer bumping either for Flip chip applications or for WLCSP packages. This paper deals in detail with the bumping process of 6? wafers at 300µm and 200µm pitch and investigates the bump interface integrity for different Au flash thicknesses on 5µm Ni. The bump height produced is 108±5µm with Sn63Pb37 and Sn4Ag0.5Cu compositions. Bumped chips have undergone high temperature storage at 150oC and up to 10 multiple reflow passes. Interesting results show that the shear strength of bumps with 5µmNi/26nmAu/Sn4Ag0.5Cu interface is about 97.1±8.3 MPa; very close to the standard 5µmNi/80nmAu UBM used so far in electroless processes. Furthermore, Sn4Ag0.5Cu bumps with only 5µm Ni UBM (without flash Au) has shown significant shear strength of about 80.4 ± 8.9 MPa which corresponds to about 17% reduction in strength. The prevailing shear fracture mode for all bumped chips is solder bulk fracture. The results imply that a possible reduction in Au flash thickness or a complete absence of Au can be potentially applied without any compromise in the mechanical integrity and robustness of the bumps.
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PublicationAlgorithm for the Automatic Verification of Complex Mixed-Signal ICs regarding ESD-Stress( 2005)In this publication, an algorithm is described which automates the verification of a com¬p¬lex integrated circuit (IC) with regard to the behavior under transient high voltage impulses (e.g. ESD). Here, the complexity of the whole circuit diagram is being reduced in a first step in order to carry out a transient simulation with high current simulation models time-efficiently in a second step. The nowadays usual manual extraction of the relevant circuit parts for such a transient analysis is then automated and therefore, the error susceptibility of this process is minimized as well. The algorithm is embedded in a commercial design frame¬work for IC-design and uses the data structures already existing.