A package structure includes a substrate, a first die and at least one second die. The substrate includes a first pair of parallel edges and a second pair of parallel edges. The first die is mounted over the substrate. The first die includes a third pair of parallel edges and a fourth pair of parallel edges, wherein the third pair of parallel edges and the fourth pair of parallel edges are not parallel to the first pair of parallel edges and the second pair of parallel edges, respectively. The at least one second die is mounted over the first die.