A package includes a device die, and an encapsulating material encapsulating the device die therein. The encapsulating material has a top surface coplanar with a top surface of the device die. A coil extends from the top surface to a bottom surface of the encapsulating material, and the device die is in the region encircled by the coil. At least one dielectric layer is formed over the encapsulating material and the coil. A plurality of redistribution lines is in the at least one dielectric layer. The coil is electrically coupled to the device die through the plurality of redistribution lines.