A package structure according to the present disclosure includes a package substrate, an interposer bonded to the package substrate, a first die and a second die bonded to the interposer by way of micro bumps, an underfill surrounding the micro bumps, disposed between the first die and the interposer as well as between the second die and the interposer, a metal layer interfacing the interposer, the underfill, sidewalls of the first die, and sidewalls of the second die, a molding material over the metal layer, and a thermal interface material disposed over the molding material, the metal layer, the first die, and the second die.