A microelectronic device includes a reflow structure. The reflow structure has a copper-containing member and a solder member, and a barrier layer between them. The barrier layer has metal grains, with a diffusion barrier filler between the metal grains. The metal grains include at least a first metal and a second metal, each selected from nickel, cobalt, lanthanum, and cerium, with each having a concentration in the metal grains of at least 10 weight percent. The diffusion barrier filler includes at least a third metal, selected from tungsten and molybdenum. A combined concentration of tungsten and molybdenum in the diffusion barrier filler is higher than in the metal grains to provide a desired resistance to diffusion of copper. The barrier layer includes 2 weight percent to 15 weight percent of the combined concentration of tungsten, and molybdenum. A bump bond structure and a lead frame package are disclosed.