High-temperature differential thermal analysis is used to establish that an increase in cobalt concentration in a copper–manganese alloy leads to an increase in the solidus and liquidus temperatures and the expansion of the melting temperature range. The alloy Cu–Mn–Co in the cast state is characterized by a cast dendritic structure. An increase in the amount of cobalt in the copper–manganese alloy contributes to increasing its microhardness. During the spreading of alloys of this system along the Kovar, an increase in the interfacial angle from 8° to 26° is observed with an increase in the cobalt concentration from 0.5% to 4.5%. Local X-ray microspectrum analysis shows that when the brazing filler metal crystallizes on the base metal substrate (under non-equilibrium conditions), a copper-based solid solution structure with inclusions of the dispersed phase enriched in iron is formed.