A heatsink assembly including a substrate having an active circuitry, at least one cavity located adjacent to at least one heat producing element of the active circuitry, at least one vessel sealably coupled to said substrate in fluid communication with the at least one cavity, and a phase change material (PCM) contained inside the vessel. The vessel and at least one cavity are configured to facilitate migration of the PCM from the vessel into the at least one cavity for absorbing heat produced by the at least one heat producing element of the active circuitry.