Methods/structures of joining package structures are described. Those methods/structures may include forming a metal formate on a surface of a first solder interconnect structure disposed on a first package substrate at a first temperature, and attaching a second solder interconnect structure disposed on a second package substrate to the first solder interconnect structure at a second temperature. The second temperature decomposes at least a portion of the metal formate and generates a hydrogen gas. The generated hydrogen gas removes an oxide from the second solder interconnect structure during joint formation at the second temperature.