Integrated Fan-Out Structure with Openings in Buffer Layer

A package includes a molding compound, a through-via penetrating through the molding compound, a device die molded in the molding compound, and a buffer layer on and contacting the molding compound. An opening is through the buffer layer to the through-via. The buffer layer has ripples in a plane parallel to an interface between the molding compound and the buffer layer and around a circumference of the opening. Other embodiments contemplate an additional package bonded to the package, and methods for forming the package.