A package includes a first die and a second die underlying the first die and in a same first die stack as the first die. The second die includes a first portion overlapped by the first die, and a second portion extending beyond edges of the first die. A first Thermal Interface Material (TIM) is overlying and contacting a top surface of the first die. A heat sink has a first bottom surface over and contacting the first TIM. A second TIM is overlying and contacting the second portion of the second die. A heat dissipating ring is overlying and contacting the second TIM.