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JULY 2022 I SMT007 MAGAZINE 59 Results and Discussion ALPHA® OM550 HRL1 has a melting point significantly lower than standard SAC305 (tin-silver-copper) alloy. A peak temperature of only 165°C is also equivalent to most ECA curing temperature. is reduces energy con- sumption in the PV application process and stress build-up on the cells. e solder paste is lead-free which means there is no environ- mental hazard and it can be snap reflowed like ECAs. e alloy is specifically designed to improve reliability of the solder joint. In a back contact cell, due to moderate adhesion between silicon and silver paste, soldering is difficult and standard soldering fluxes may not Experimental Low temperature lead-free solder paste was used in this study. is is non-eutectic tin-bis- muth paste, namely, OM550 ® HRL1 from Mac- dermid Alpha (Table 1). N-type monocrystalline M6-IBC cells were used. Efficiency was 23% with thickness 170±20 micron. Scheme 1 shows the complete test matrix. Typically, print optimization and reflow optimization were carried out to eval- uate a paste's wetting characteristics on the metallization pad. During interconnection, reflow optimization work was thoroughly con- ducted, and bond strength and other reliability aspects were investigated. In the last set, once the minipanels were prepared, they were ana- lyzed for IV-curve values, EL (electrolumines- cence) and accelerated aging tests. Test condi- tions are given in Table 1 and Scheme 1. e idea of doing the DOE was to optimize print- ing as well as reflow optimization for solder paste to achieve good wetting on the metalli- zation pad and form reliable bond with the sil- ver paste as well as ribbon or wire. Scheme 1: Schematic of back-side soldering of structured ribbon using solder paste. Table 2: Solder paste IBC assemblies: Process parameters.