Investigation of the mechanical properties of a connector – silver – enamel – float glass composite Von der Fakultät für Georessourcen und Materialtechnik der Rheinisch-Westfälischen Technischen Hochschule Aachen zur Erlangung des akademischen Grades eines Doktors der Ingenieurwissenschaften genehmigte Dissertation vorgelegt von M.Sc Emmanuel Walch aus Colmar Berichter: Herr Univ.-Prof. Dr. rer. nat. Christian Roos Frau Univ.-Prof. Dr.-Ing. habil. Edda Rädlein Tag der mündlichen Prüfung : 28.07.2020 Diese Dissertation ist auf den Internetseiten der Universitätsbibliothek online verfügbar “Twenty years from now you will be more disappointed by the things that you didn’t do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover.” H. Jackson Brown Jr. Acknowledgment Firstly, I would like to express my sincere gratitude to my advisor Prof. Dr. rer. nat. Christian Roos for his continuous support during this Ph.D. His valuable suggestions have significantly contributed to the success of this work. The collaboration with Saint-Gobain Research Germany has enabled us to benefit from remarkable technical knowledge about the manufacturing process of backlights. I would like to thank Dr. Benjamin Kaplan, Dr. Stefan Uebelacker and Bernhard Reul for their continuous guidance, the beneficial discussions and great interest concerning the research results. Their feedbacks and advices were very valuable since they greatly improved my way of structuring the technical reports and presentations. I would also like to acknowledge Dr. Stefan Droste for his technical support during the thesis. I would also like to express my very profound gratitude to Dr. Klaus Schmalbuch, for his great support and help in creating together the PhD subject, and searching the funding. This accomplishment would not have been possible without his invaluable contribution. I would also like to acknowledge Prof. Dr.-Ing. habil. Edda Rädlein, from the University TU Ilmenau, as the second reader of this thesis, and I am gratefull for her very valuable comments on this thesis. My sincere thanks goes to Dr. Alessandro Benedetto and Dr. René Gy for the access to the laboratory and research facilities in Saint-Gobain Research Paris, as well as their great interest in my work and their remarkable critical thinking skills. I would like to thank Dr. Jalal Bacharouche and André Beyrlé from Saint-Gobain Research Compiègne for their technical support concerning the enamel and silver thick films as well as the firing process. The major part of this work consists in experimentation. Thus, I would like to acknowledge Dr. Philippe Letocart for the FIB tomography, Dr. Paul Leplay for the support concerning the image analysis for the extaction of the pore fraction in the tomography, David Tisiot and Armelle Lany for the screen printing followed with a sintering of the layers onto thin glasses, Frederic Barrieres for his support for the curvature measurement, Ralf Coenen for the SEM analysis, Thierry Cretin for the TOF SIMS analysis, Fahri Kabadayi, François Hermange, Hadi Rastegar and Cynthia Halm for their support concerning the soldering, Petra Cellar and Heiko Bastert for their support concerning the Ring on Ring testing, Dr. Andreas Gioia for his support on the residual stress measurement via XRD sin²Ψ. Additionnaly, I would like to acknowledge Dr. Marco Sebastiani from the Roma Tre University for his support on the residual stress measurement via FIB-DIC. Last but not the least, I would like to thank my parents Joseph and Evelyne Walch for their invaluable emotionnal support throughout the complete thesis and the hard periods during my life. I | Table of contents Table of contents Table of contents ......................................................................................................................... I Abstract .................................................................................................................................... IV Kurzfassung ............................................................................................................................... V Abbreviations ........................................................................................................................... VI Symbols ................................................................................................................................... VII Index of figures ........................................................................................................................ IX Index of tables ....................................................................................................................... XIII 1 Introduction ............................................................................................................................. 1 2 State of the art ......................................................................................................................... 4 2.1 Backlights manufacturing process .................................................................................... 4 2.1.1 Float glass substrate ................................................................................................... 4 2.1.2 Enamel and silver pastes ............................................................................................ 4 2.1.3 Screen-printing ........................................................................................................... 5 2.1.4 Firing and tempering process ..................................................................................... 6 2.1.5 Soldering process ....................................................................................................... 7 2.2 Fracture mechanics of brittle materials ............................................................................ 8 2.2.1 Theoretical resistance ................................................................................................. 8 2.2.2 Defect on glass surface .............................................................................................. 9 2.2.3 Stress concentration factor ....................................................................................... 11 2.2.4 Tempered glass ........................................................................................................ 12 2.2.5 Sub-critical crack growth – stress corrosion ............................................................ 16 2.3 Review on the composite stack ...................................................................................... 17 2.3.1 SLS Float glass ........................................................................................................ 17 2.3.2 Enamel thick film ..................................................................................................... 18 2.3.3 Silver thick film ....................................................................................................... 20 2.3.4 Lead Free Solders .................................................................................................... 23 3 Theoretical background ......................................................................................................... 27 3.1 Ring On Ring biaxial flexure testing .............................................................................. 27 3.2 Nanoindentation.............................................................................................................. 28 3.2.1 Young’s Modulus and Hardness .............................................................................. 28 3.2.2 Apparent fracture toughness .................................................................................... 30 3.3 Curvature measurement .................................................................................................. 31 3.4 Heat capacity and thermal conductivity ......................................................................... 33 3.5 Residual stresses ............................................................................................................. 33 3.5.1 Residual stresses in glass fragments ........................................................................ 34 3.5.2 XRD sin² Ψ method ................................................................................................. 35 II | Table of contents 3.5.3 Residual stresses induced by soldering .................................................................... 37 3.6 Aging tests ...................................................................................................................... 39 4 Experimental methods and sample preparation .................................................................... 40 4.1 Ring On Ring testing ...................................................................................................... 40 4.1.1 Screen-printing and firing conditions ...................................................................... 41 4.1.2 Automatic soldering conditions ............................................................................... 42 4.1.3 Biaxial flexure testing .............................................................................................. 45 4.2 Nanoindentation.............................................................................................................. 45 4.2.1 Young’s modulus and Hardness .............................................................................