Process for forming package-on-package structures

A device comprising:

• an inter-layer dielectric;
• a first device die under the inter-layer dielectric;
• a first die-attach film attaching the first device die to the inter-layer dielectric, wherein a top surface of the first die-attach film contacts a bottom surface of the inter-layer dielectric;
• a first plurality of redistribution lines comprising first portions level with the die-attach film, and second portions in the inter-layer dielectric;
• a first plurality of Z-interconnects under the first plurality of redistribution lines, and electronically coupled to the first device die and the first plurality of redistribution lines;
• a first polymer-comprising material under the inter-layer dielectric, wherein the first device die, the first die-attach film, and the first plurality of Z-interconnects are disposed in the first polymer-comprising material;
• and
• a second plurality of redistribution lines under the first plurality of Z-interconnects, wherein the first and the second plurality of redistribution lines are on opposite sides of, and are electrically coupled through, the first plurality of Z-interconnects.

A device comprising:

• an inter-layer dielectric;
• a first device die under the inter-layer dielectric;
• a first die-attach film over and attached to the first device die;
• a first plurality of redistribution lines comprising first portions level with a portion of the die-attach film, and second portions in the inter-layer dielectric and contacting the first die-attach film;
• a first plurality of Z-interconnects under the first plurality of redistribution lines and electronically coupled to the first device die and the first plurality of redistribution lines;
• a first polymer-comprising material under the inter-layer dielectric, wherein the first device die, the first die-attach film, and the first plurality of Z-interconnects are disposed in the first polymer-comprising material;
• a second plurality of redistribution lines under the first plurality of Z-interconnects, wherein the first and the second plurality of redistribution lines are on opposite sides of, and are electrically coupled through, the first plurality of Z-interconnects;
• a second device die over and bonded to the second portions of the first plurality of redistribution lines;
• and
• a third device die under and bonded to the second plurality of redistribution lines, wherein the second and the third device dies are at opposite surfaces of the device.