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AUGUST 2021 I SMT007 MAGAZINE 71 e cells are joined to each other by wire to form the typical strings that then go to form the photovoltaic module. An automated tab- bing and stringing machine (Lead Xi Auto- mated machine) was used for soldering. is comes with contactless IR soldering so that stress is not generated in the cell. e infrared soldering system focuses the light beams on the wire lines for a constant welding process. e motorized ribbon unwinding system and the new stretching system permit positioning of the wire on bus bars avoiding bowing and possible misalignment. e process parame- ters are described in Table 1. Stringed cells were cut in between to get sin- gle cells and then bus ribbons were soldered by hand soldering. Some cells were used to do functional characterization like peel strength analysis, microscopic analysis etc. and some cells were laminated at 140 o C using standard ethyl vinyl acetate (EVA) laminating materi- als. Single cell panels were then used for vari- ous electrical and reliability studies. Characterization Digital Microscope A Keyence microscope (VHX-5000 and VHX-2000) was used to get higher magnified images. MBB cells were analyzed closely for surface smoothness and topology using higher magni- fied microscope. From the topol- ogy, surface variation was esti- mated. e nature of soldering charac- teristics was evaluated by scan- ning electron microscopy. Sam- ples were cut and cold mounted. e metallographic preparation of these cross-sections included grinding and polishing using SiC (silicon carbide) abrasive pads to flatten the sections and remove damage from cutting. An argon ion polisher (Hitachi made) was use in its flat milling mode. A field emission scanning electron microscope (FESEM) from JEOL (model 7800F PRIME) was used for imaging, whereas the qualitative identification of the IMC (intermetallic compound) compo- sition was done using energy dispersive spec- troscopy (EDS) analysis. Peel test e mechanical strength of the soldered joints was assessed by a peel test according to DIN EN 50461 [11] . Tests were done at 180 o C using an Imada force measurement unit. All cells were peeled at a speed of 50 mm/min. e force is recorded over the interconnected distance and normalized to the width of the interconnection. A peel strength of 1 N/mm is deemed necessary according to DIN EN 50461, explicitly for soldered interconnec- tions. All force data was exported into Excel. Approximately 204 data points were collected for a 156.75 mm cell on both sides. Fractured cell surface and ribbon was analysed aer peel test to see the solder joint nature and adhesion using the Keyence microscope. Wetting Wetting was measured by wetting balance (Rheska) test as per JIS Z 3198 standard. Stan-