Devices employing thermal and mechanical enhanced layers and methods of forming same

1. A method comprising:

attaching a first first-level device die and a second first-level device die to a dummy die;

encapsulating the first first-level device die and the second first-level device die in a first encapsulating material;

forming first through-vias, wherein the first through-vias comprises a through-via grown from a metal pad in a first portion of the first first-level device die;

attaching a second-level device die comprising a first portion overlapping the first first-level device die and a second portion overlapping the second first-level device die;

encapsulating the first through-vias and the second-level device die in a second encapsulating material, wherein the encapsulating the first first-level device die and the second first-level device die and the encapsulating the first through-vias and the second-level device die are separate encapsulation processes; and

forming redistribution lines over and electrically coupled to the first through-vias and the second-level device die, with the dummy die, the first first-level device die, the second first-level device die, the first encapsulating material, the second-level device die, and the second encapsulating material being parts of a composite wafer.

2. The method of claim 1 further comprising:

before the attaching the first first-level device die, attaching the dummy die to a carrier, wherein the dummy die is a blanket die free from active devices and passive devices; and

after the redistribution lines are formed, de-bonding the carrier from the dummy die.

3. The method of claim 1 , wherein the dummy die is a part of an un-sawed dummy wafer, and the method further comprises:

thinning the un-sawed dummy wafer, with the first first-level device die attached to the dummy die in the thinned un-sawed dummy wafer; and

sawing the composite wafer into a plurality of packages, with the thinned dummy wafer sawed into a plurality of dummy dies, wherein the plurality of dummy dies comprises the dummy die.

4. The method of claim 1 , wherein the dummy die is a discrete die, and the method further comprises sawing the composite wafer to form a package comprising the dummy die, wherein edges of the dummy die are spaced apart from respective closest edges of the package.

5. The method of claim 1 , wherein the dummy die is formed of a homogeneous material.

6. The method of claim 1 , wherein the dummy die comprises silicon, and is free from active devices, passive devices, and conductive lines.

7. The method of claim 1 , wherein the dummy die comprises a blanket metal plate or a blanket dielectric plate.

8. The method of claim 1 further comprising:

forming second through-vias over and electrically coupled to the first first-level device die and the first through-vias;

attaching a third-level device die over the second-level device die; and

encapsulating the second through-vias and the third-level device die in a third encapsulating material, wherein the redistribution lines are formed over the third encapsulating material.

9. A method comprising:

attaching a dummy wafer over a carrier, wherein the dummy wafer is free from integrated circuit devices;

thinning the dummy wafer;

attaching first-level device dies to the thinned dummy wafer, wherein the first-level device dies comprises a first first-level device die and a second first-level device die;

stacking second-level device dies over the first-level device dies, wherein one of the second-level device dies comprises a first portion overlapping the first first-level device die and a second portion overlapping the second first-level device die;

forming through-vias electrically coupled to the first-level device dies, wherein the through-vias comprise a through-via grown from a metal pad in a portion of the first first-level device die;

forming redistribution lines over and electrically coupled to the through-vias and the second-level device dies; and

performing a die saw to separate the dummy wafer, the first-level device dies, and the second-level device dies into a plurality of packages, with each of the plurality of packages comprising a dummy die in the dummy wafer, one of the first-level device dies, and one of the second-level device dies.

10. The method of claim 9 further comprising:

encapsulating the first-level device dies in a first encapsulating material;

forming a dielectric layer over the first encapsulating material and the first-level device dies; and

encapsulating the second-level device dies and the through-vias in a second encapsulating material, wherein the second encapsulating material is over the dielectric layer.

11. The method of claim 9 further comprising:

before the attaching the first-level device dies, attaching the dummy wafer to a carrier, with the thinning performed after the dummy wafer is attached to the carrier; and

after the redistribution lines are formed, de-bonding the carrier from the dummy wafer.

12. The method of claim 9 , wherein the dummy wafer is formed of a homogeneous material.

13. The method of claim 9 , wherein the dummy wafer comprises silicon, and is free from active devices, passive devices, and conductive lines.

14. The method of claim 9 , wherein the dummy wafer comprises a blanket metal plate or a dielectric plate.

15. The method of claim 9 , wherein the dummy wafer is free from conductive traces.

16. A method comprising:

attaching a dummy wafer over a carrier;

thinning the dummy wafer;

attaching a first first-level device die and a second first-level device die to the thinned dummy wafer;

encapsulating the first and the second first-level device dies in a first encapsulating material;

stacking a second-level device die over the first and the second first-level device dies, wherein the second-level device die overlaps a first portion of each of the first and the second first-level device dies;

forming first through-vias overlapping a second portion of each of the first and the second first-level device dies;

encapsulating the second-level device die and the first through-vias in a second encapsulating material;

stacking a third-level device die over the second-level device die, wherein the third-level device die overlaps a portion of the second-level device die;

forming second through-vias overlapping a portion of the second-level device die;

encapsulating the third-level device die and the second through-vias in a second encapsulating material; and

forming redistribution lines over and electrically coupled to the second through-vias and the third-level device die.

17. The method of claim 16 , wherein the dummy wafer is formed of a homogenous material, with the dummy wafer free from active devices, passive devices, and conductive lines.

18. The method of claim 16 , wherein the first and the second first-level device dies are attached to the dummy wafer through adhesive films.

19. The method of claim 16 , wherein the dummy wafer is free from conductive traces.

20. The method of claim 16 further comprising de-bonding the carrier from the dummy wafer.