Air channel formation in packaging process

A method includes forming a reconstructed wafer including encapsulating a device die in an encapsulant, forming a dielectric layer over the device die and the encapsulant, forming a plurality of redistribution lines extending into the dielectric layer to electrically couple to the device die, and forming a metal ring in a common process for forming the plurality of redistribution lines. The metal ring encircles the plurality of redistribution lines, and the metal ring extends into scribe lines of the reconstructed wafer. A die-saw process is performed along scribe lines of the reconstructed wafer to separate a package from the reconstructed wafer. The package includes the device die and at least a portion of the metal ring.