Over-molded IC packages with embedded voltage reference plane and heater spreader

A microelectronic device package assembly, comprising:

• a package substrate or one or more metal redistribution layers;
• an integrated circuit (IC) chip including circuitry on a first side of the IC chip facing the package substrate or the metal redistribution layers, the circuitry coupled to the package substrate or the metal redistribution layers;
• a package material surrounding the IC chip, wherein an interior portion of the package material is located over a second side of the IC chip, opposite the first side, and wherein a peripheral portion of the package material extends beyond an edge of the IC chip and over the package substrate or the metal redistribution layers;
• one or more first metal-filled vias or trenches passing through a thickness of the peripheral portion of the package material, the first metal-filled vias or trenches in contact with the package substrate or at least one of the metal redistribution layers;
• one or more second metal-filled via or trenches passing through a thickness of the interior portion of the package material, in contact with the second side of the IC chip, and electrically connected to the one or more first metal-filled vias or trenches by one or more first metal traces extending between the interior portion and the peripheral portion of the package material.