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74 SMT007 MAGAZINE I AUGUST 2021 raman shi peak typically appears at around 525 cm -1 . It is known that limiting the oxygen level in the wire improves wettability and thus contact with metallization paste [13] . e MBB interconnection has one unre- solved design/manufacture challenge: the problem associated with the non-homogene- ity of solder coating that is produced around the Cu-wire which can result in weaker sol- der joints [14] . Simulation modeling of the non- homogenous solder coating on round wire used in multi-busbar (MBB) strip intercon- nection of solar PV module may lead to form micro-crack initiation at high temperatures. Rendler, et al. [8, 15] have investigated the defor- mation of cell and thermomechanical stress in both cell and interconnecting wire of MBB PV modules. ey found by using lower diameter of wires and by reducing the Young's modulus or the yield strength of the copper, the thermo- mechanical stress in a solar cell is decreased. ey also recognized that the maximum stress in the wires occurs at the edge of the outermost contact pads on both sides of the solar cell and interconnections. Another challenge is to produce low yield strength wire, which is difficult to process and even make. Changing the shape of cop- per-based wire potentially leads to a signifi- cant change of its mechanical properties. To reshape a wire, a method that enables the pro- duction of wave-shaped wires with adjustable periods and amplitudes has been developed [16] . e authors proposed wave-shaped wire with a diameter of 300 μm, a constant period of 3.1 mm, and various amplitudes for MBB. Another way to improve better contact between the pad and wire is to use thicker solder-coated Cu wires [17] . e authors have reported that increasing solder thickness could help in increasing the efficiency of the panel. is approach, however, requires thicker EVA and it may induce cracks during the lamination. We propose to use wire with periodic solder bumps as shown in Figure 3. Our experiments show that that this design (Figure 3) provides better contact with the sil- ver pad and produces reliable soldering results. e influence of solder joint failures in one interconnector can be mitigated by the neigh- boring interconnectors, as 12BB MBB provides current redundancy. Flux Fluxes are typically liquid and consist of a chemical activator package, additives, a sol- vent system and, optionally, rosin or syn- thetic resin. e solar industry is tradition- ally using alcohol-based flux formulations. For an efficient soldering, the fluxing mechanism requires the right chemistry coupled with a proper initial heat cycle to remove the oxide and surface contamination. Acid number and wetting of a flux are two important characteristics to determine the Figure 2: a) Cross-sectional analysis of solder wire; b) Raman spectrum of wire surface.