Microelectronic packages formed by using novel fluxing agents are disclosed. In one aspect, a microelectronic package may include a microelectronic device, a substrate, and an interconnect structure including a solder material coupling the microelectronic device with the substrate. Underfill material may be included around the interconnect structure between the microelectronic device and the substrate. The underfill material may include an organic rosin acid moiety derived from an anhydride adduct of a rosin compound that was used as a fluxing agent. Methods of making such microelectronic packages using anhydride adducts of rosin compounds are also disclosed.