An integrated circuit package assembly includes a first integrated circuit package and a second integrated circuit package. The first integrated circuit package includes a first integrated circuit die mounted on a first substrate. The second integrated circuit package includes a second integrated circuit die mounted on a second substrate. The second integrated circuit package is disposed under the first integrated circuit package. Solder bumps are disposed between the first integrated circuit package and the second integrated circuit package and provide electrical signal connections between the first integrated circuit die and the second integrated circuit die. A buffer layer is disposed between the first substrate and the second integrated circuit die to facilitate thermal conduction between the first integrated circuit package and the second integrated circuit package.