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64 SMT007 MAGAZINE I JULY 2022 angle was found to be 13°C. No silver leach- ing observed. ECA, on the other hand, does not form any IMC and there is pseudo-bond- ing between silver pad and silver flakes in the ECA 3 (Figure 8). e quality of the joints was also analyzed by X-ray. is determines voiding in the joints. e solder paste spread well over the busbar and no solder balls were observed. e voiding was less than 10% (Fig- ure 9) in each assembly which means there is good thermal contact between the joining sur- faces. Many voids reduce the solder joint reli- ability. Voids also reduce the thermal conduc- tivity of the solder joints, and can cause solder bridges and solder transfer between neighbor- ing solder joints during the reflow soldering process. In small solder joints, voids can signif- icantly reduce their current carrying capacity. Soldered cells were analyzed for peel strength at 180°C using an Imada peel tester. e results are presented in Figure 10. Paste gives acceptable peel strength, much above the required 1 N/mm as per DIN EN 50461. e bond strength between paste and silver metallization pad was assessed by die shear strength. e average gram force was about 294 gF. is is excellent bonding without any kind silver leaching. Fracture surface analysis (Figure 10) done at different peak reflow con- ditions showed that, at 190°C and 210°C peak, the maximum peel strength and nice cohesive bond failure can be achieved. Laminated minipanels were exposed to cli- matic testing, conforming to IEC 61215, at 1000 h of damp heat (DH) and 200 tempera- ture cycles (200 TC). Power measurements Figure 8: Silver flaking observed with joints formed with ECA. Figure 9: X-ray analysis evaluating voiding in joints of ECA and OM-550; <10% voids observed for both the pastes. a b