A semiconductor device is disclosed. The semiconductor device comprises a redistribution structure, a processor die, and a metal post. The metal post has a first end, and a second end. The metal post is connected to the redistribution structure at the first end. The first end has a first width. The second end has a second width. The metal post has a waist width. The first width is greater than the waist width. The second width is greater than the waist width. The metal post has a side surface. The side surface is inwardly curved or outwardly curved.