Package structures and methods of forming them are described. In an embodiment, a package structure includes an integrated circuit die embedded in an encapsulant and a redistribution structure on the encapsulant. The redistribution structure includes a metallization layer distal from the encapsulant and the integrated circuit die, and a dielectric layer distal from the encapsulant and the integrated circuit die and on the metallization layer. The package structure also includes a first under metallization structure on the dielectric layer and a Surface Mount Device and/or Integrated Passive Device (“SMD/IPD”) attached to the first under metallization structure. The first under metallization structure includes first through fourth extending portions extending through first through fourth openings of the dielectric layer to first through fourth patterns of the metallization layer, respectively. The first opening, the second opening, the third opening, and the fourth opening are physically separated from each other.