Interconnection Technologies

Fraunhofer Center for Silicon Photovoltaics CSP

© Fraunhofer CSP

The interconnection of crystalline Si solar cells is done by soldering tinned copper ribbons on a cell-sided silver thick film pastes. Ensuring the solderability is essential to guarantee reliable production processes and cell interconnection for high product lifetimes and realibility in photovoltaics up to 25 years.

At Fraunhofer CSP, various materials and methods are available to evaluate the joint formation of the cell to ribbon interconnections. The basis are raw material characterizations, e.g. wetting balance tests as well as contact angle measurements. Theses tests provide information on surface wetting qualities of lead / lead-free solders, fluxing agents or the various types of cell metallizations.

By non-destructive as well as destructive test methods, the varying interconnection technologies for solar cell string assemblies are evaluated and analyzed. Thereby the know-how of the fields of microelectronics, automotive, power electronics, etc. are combined  with the competencies of evaluating the contact reliability of individual component levels in packaging of integrated circuits towards photovoltaics.


  • Solar cell soldering
  • Soldering process characterization
  • Interfacial/material interactions
  • Solder contact reliability

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  • Cross section preparation tools for specimen make for microstructure analyses
  • Cross section analysis by light microscopy, SEM, etc. incl. material compound analysis and formation (DIC; POL, EDX, etc.)
  • Characterization of time and temperature dependant material behavior of interconnection materials (TMA, DMA, DSC, TGA)
  • Contact angle measurement equipment for static / dynamic measurements of contact angles and surface tension
  • Wetting balance tester for logging wetting force time progression
  • Pull-/shear tester for evaluation of the mechanical strength of PV contact structures
  • Ultrasonic microscopy and x-ray scanner for non-destructive analysis of interconnection interfaces and contact formation
  • Assembly and soldering stations for test applications and specimen production on cell and module level
  • Laser profilometer and confocal white light microscope for surface structure analyses of cell metallizations, etc.

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  • ·         Schindler, S., Mueller, M., Wiese, S.; Investigation of the undercooling of SnCu solder spheres, Electronics System-Integration Technology Conference (ESTC), 2014 , vol., no., pp.1,7, 16-18 Sept. 2014

  • Sebastian Schindler, Fraunhofer CSP, Halle, & Michael Volk, SCHMID Group, Freudenstadt; Multi-busbar technology: Increased module power and higher reli-ability at lower cost; Photovoltaics International; March 2014; 23rd Edition

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  • Schindler, S; Schneider, J.; Pönisch, C.; Nissler, R.; Habermann, D., Soldering Process and Material Characterization of Miniaturized Contact Structures of a Newly Developed Multi Busbar Cell Metallization Concept, 28th European Photovoltaic Solar Energy Conference and Exhibition, pages: 480 - 483, 30 September - 4 October, 2013, Paris, France

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  • Klengel, R.; Stephan, T.; Petzold, M.; Schindler, S.; Schneider, J.; Spira K.; A Proper Alternative: Ultra Sonic Bonding for Thin Film Solar Cell Interconnections, 27th European Photovoltaic Solar Energy Conference and Exhibition, pages: 2864 - 2867, 24-28 September 2012, Frankfurt, Germany
  • Schindler, S.; Schneider, J.; Klengel, R.; Petzold, M., The impact of material composition and process parameters on the cSi solar cell interconnection, Electronic System-Integration Technology Conference (ESTC), 2012 4th, vol., no., pp.1,6, 17-20 Sept. 2012

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  • Schindler, S.; Wiese, S., Solidification processes of SnCu, SnAg and SnAgCu solder alloys and interface reactions to charactize solar cell interconnections processes, Microelectronics and Packaging Conference (EMPC), 2011 18th European, vol., no., pp.1,4, 12-15 Sept. 2011
  • Wiese, S.; Kraemer, F.; Meier, R.; Schindler, S., Mechanical problems of manufacturing processes for photovoltaic modules, Microelectronics and Packaging Conference (EMPC), 2011 18th European, vol., no., pp.1,6, 12-15 Sept. 2011
  • Klengel, R.; Härtel, R.; Schindler, S.; Schade, D.; Sykes, B., Evaluation of the Mechanical Strength of Solar Cell Solder Joint Interconnects and Their Micostructural Properties by Developing a New Test and Inspection Equipment, 26th European Photovoltaic Solar Energy Conference and Exhibition, pages: 1507 - 1511, 5-9 September 2011, Hamburg, Germany

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  • Schindler, S.; Wiese, S., Investigation of wettability and interface reactions of Sn-Pb, Sn-Cu, Sn-Ag and Sn-Ag-Cu solders for solar cell interconnections, Electronic System-Integration Technology Conference (ESTC), 2010 3rd, vol., no., pp.1,5, 13-16 Sept. 2010
  • Meier, R.; Krämer, F.; Schindler, S.; Wiese, S.; Bagdahn, J., Thermal and Mechanical Induced Loading on Cell Interconnectors in Crystalline Photovoltaic Modules, 25th European Photovoltaic Solar Energy Conference and Exhibition/ 5th World Conference on Photovoltaic Energy Conversion, pages: 3740 - 3744, 6-10 September 2010, Valencia, Spain

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