Fan-out package structure and methods for forming the same

A package comprising:

• a device die comprising a first plurality of metal pillars at a top surface of the device die;
• a die stack comprising:
• a plurality of dies bonded together;
• and
• a second plurality of metal pillars at a top surface of the die stack;
• a polymer region molding the device die and the die stack therein, wherein a top surface of the polymer region, top ends of the first plurality of metal pillars, and top ends of the second plurality of metal pillars form a first planar surface;
• a dielectric layer over the polymer region, wherein edges of the dielectric layer are aligned to respective edges of the polymer region;
• and
• redistribution lines in the dielectric layer, wherein the redistribution lines are electrically coupled to the first and the second plurality of metal pillars, and wherein bottom surfaces of the redistribution lines and the dielectric layer form a second planar surface in contact with the first planar surface.

A method comprising:

• placing a device die over a carrier, wherein the device die comprises a first plurality of metal pillars;
• placing a die stack over the carrier, wherein the die stack comprises a second plurality of metal pillars;
• dispensing a polymer to mold the device die and the die stack therein;
• performing a planarization on the polymer until the first and the second plurality of metal pillars are exposed;
• and
• forming a plurality of redistribution lines over the device die and the die stack, wherein the plurality of redistribution lines is electrically coupled to the first and the second plurality of metal pillars.