Liquid-Phase reaction sintering behavior at below 200 ^oC and electrical sheet resistance of Sn-58Bi/Cu composite pastes

To fabricate a film with the highest electrical conductivity through liquid-phase reaction sintering below 200 ^oC using composite pastes containing both Sn-58Bi and Cu particles as a filler material, the effects of process parameters, such as the mixing ratio of the fillers, reaction temperature, and reaction time, were evaluated and the parameters were optimized. The lowest sheet resistance of 0.0278 Ω/□ was obtained when the composite paste of Sn-58Bi/40 wt% Cu was sintered at 190 ^oC for 180 s. The reduced resistance was attributed to the increase in the portion of acicular Cu₆Sn₅ phases. The phases were formed by the dissolution and precipitation of Cu, and the three-dimensional linkage of irregular polygonal Cu₆Sn₅ phases using the acicular Cu₆Sn₅ through a Bi phase of the highest electrical resistivity. The reaction time, which was prolonged up to 180 s during the reaction at 190 ^oC, maximized the number of acicular Cu₆Sn₅ and irregular polygonal Cu₆Sn₅ phases, through the formation of fine Cu₆Sn₅ phases by splitting behavior of coarse Cu₆Sn₅ phases.