Release film as isolation film in package

1. A method comprising:

forming a release film over a carrier;

attaching a device over the release film through a die-attach film;

encapsulating the device in an encapsulating material;

performing a planarization on the encapsulating material to expose the device;

forming redistribution lines to electrically couple to the device;

detaching the device and the encapsulating material from the carrier while the die-attach film remains attached to the device;

after the detaching of the device and the encapsulating material from the carrier, removing the die-attach film to expose a back surface of the device; and

applying a thermal conductive material on the back surface of the device.

2. The method of claim 1 further comprising:

dispensing an underfill to contact the thermal conductive material.

3. The method of claim 1 , wherein after the die-attach film is removed, a recess is formed to extend into the encapsulating material, and the thermal conductive material is filled into the recess.

4. The method of claim 3 , wherein the thermal conductive material laterally extends beyond the recess.

5. The method of claim 1 , wherein the thermal conductive material has a thermal conductivity higher than about 1 W/k*m.

6. The method of claim 1 , wherein the thermal conductive material is selected from the group consisting of solder, silver, copper paste, and combinations thereof.

7. The method of claim 1 further comprising:

forming a metal post over the carrier, wherein the metal post is encapsulated in the encapsulating material, wherein in the removing the die-attach film, a portion of the encapsulating material is removed, and the metal post protrudes out of the encapsulating material.

8. The method of claim 1 , wherein after the removing the die-attach film, the die-attach film is fully removed.

9. A method comprising:

coating a release layer on a carrier;

forming a metal post over the release layer;

attaching a device die over the release layer through a die-attach film;

encapsulating the device die and the metal post in an encapsulating material;

projecting a light on the release layer to decompose a portion of the release layer;

lifting off the carrier from the encapsulating material, the device die, and the metal post;

etching the die-attach film to reveal a back surface of the device die;

applying a thermal conductive material on the back surface of the device die;

bonding a package to the metal post; and

dispensing an underfill, wherein a portion of the underfill is disposed between the device die and the package.

10. The method of claim 9 further comprising:

curing the thermal conductive material, wherein the underfill contacts the thermal conductive material.

11. The method of claim 9 , wherein the underfill contacts the back surface of the device die.

12. The method of claim 9 , wherein when the die-attach film is etched, the encapsulating material is also etched to result in the metal post to protrude out of the encapsulating material.

13. The method of claim 9 , wherein the etching the die-attach film results in a recess to be formed extending into the encapsulating material.

14. The method of claim 13 , wherein the underfill is filled into the recess.

15. A package comprising:

an encapsulating material;

a through-via penetrating through the encapsulating material;

a device encapsulated in the encapsulating material, wherein the device comprises a semiconductor substrate with a back surface;

a package component over and bonded to the through-via;

a thermal conductive material over and contacting the back surface of the semiconductor substrate in the device; and

an underfill between the encapsulating material and the package component, wherein the underfill is in contact with the encapsulating material.

16. The package of claim 15 , wherein the underfill is further in contact with the back surface of the semiconductor substrate in the device.

17. The package of claim 16 , wherein the underfill further comprises a portion extending into the encapsulating material, wherein the portion of the underfill contacts a sidewall of the semiconductor substrate in the device.

18. The package of claim 15 , wherein the through-via comprises a portion protruding higher than a top surface of the encapsulating material.

19. The package of claim 15 , wherein the thermal conductive material further comprises a portion extending into the encapsulating material, wherein the portion of the thermal conductive material contacts a sidewall of the semiconductor substrate in the device.

20. The package of claim 15 further comprising a solder region bonding the through-via to the package component, wherein the solder region contacts sidewalls of the through-via.