Package-On-Package (PoP) structures and methods of forming PoP structures are disclosed. According to an embodiment, a structure comprises a first substrate, stud bulbs, a die, a second substrate, and electrical connectors. The stud bulbs are coupled to a first surface of the first substrate. The die is attached to the first surface of the first substrate. The electrical connectors are coupled to the second substrate, and respective ones of the electrical connectors are coupled to respective ones of the stud bulbs.