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70 SMT007 MAGAZINE I AUGUST 2021 ers are developing this kind of machine. Typ- ically, MBB cells are interconnected by seven to 15 solder coated copper wires with circular cross-section (diameter between 200 and 450 µm) on each side of the solar cell. e wires are soldered by infrared soldering on silver pads printed on the front and back of the cells. MBB offers a number of advantages [2] : 1. MBB modules use copper wires instead of ribbons for interconnection. is allows one to use narrower or no busbars on the cells and, therefore, results in reduced silver paste consumption. 2. Reduced current per finger enables small finger width, and shorter effective current paths in fingers enables an increased homogeneous series resistance distribution. 3. e round shape of the wires generates additional reflection gains from the air/glass interface to the cell which brings on improved light absorption and improved generated current. 4. e large number of wires reduces the requirement for lateral transport which results in lower series resistance. 5. A more homogenous busbar design of the cell leads to higher tolerance to cracks. 6. e large number of homogeneously distributed solder joints leads to an electrical redundancy. A failure in solder joints only affects a smaller area of the solar cell and a finger failure is disconnecting a shorter finger length. 7. Technology gives lower optical intercon- nector shading and higher power on module level. Like standard tabbing and stringing pro- cess, the main challenge for the MBB tech- nology remains soldering. e MBB approach requires the realization and reliability of over 100 solder joints on the front side and a similar large number of solder joints on the back side of each solar cell. From the mechanical point of view this represents a major difference to the continuous soldering of a standard four busbar H-pattern design. Defects caused by thermo- mechanical stress aer temperature cycling according to DIN EN 61215 (-40°C to 85°C, 50 cycles) have been reported [7,8] . Mechanical stress-induced delamination of the metalliza- tion paste, or adhesive fracture between solder and silver paste, is also known. In some cases, combinations of the different defect mecha- nisms can be found. Wire crippling and pulling the wire through the grippers as well as exces- sive flux pollution are also associated defects in MBB soldering. At elevated temperatures, the weaker MBB solder joint connection area subjected to the thermal stress can develop micro-cracks. Pre- vious studies show that the cracks are devel- oped mainly in the contact surface of the strip interconnection and the contact condition can adversely affect the performance of the whole module in terms of power output [9] . e crack developed induces contact resistivity between the Cu ribbon interconnection and cell, result- ing in cell-to-module (CTM) loss, hot spot, and eventually the disconnection of the bus bar line which consequently results in DC arc [9, 10] . is article reviews factors affecting MBB sol- dering and interconnection, and also suggests the ways to obviate the same for optimum sol- dering results. Experimental Soldering All the cells were 156.75 × 156.75 mm 2 12BB mono PERC solar cells (Runergy) with a thickness of 200 µm ± 20 µm. For the MBB front grid, each busbar contains 11 silver pads with 1100 µm (length) × 700 µm (width) which were designed to enhance the quality of con- tact between the wires and fingers. Each pro- cessed cell had 20.4% efficiency. e first phase in a photovoltaic module manufacturing line is joining the solar cells, which is done by a solar tabber and stringer.