Discrete polymer in fan-out packages

1. A method comprising:

encapsulating a lower-level device die in a first encapsulating material;

forming a redistribution structure comprising:

depositing a dielectric layer over the first encapsulating material;

patterning the dielectric layer to form via openings and a trench simultaneously, wherein the first encapsulating material is revealed through the trench; and

forming a plurality of redistribution lines extending into the dielectric layer, wherein the plurality of redistribution lines extend into the via openings, and wherein the trench is unfilled at a time after the plurality of redistribution lines are formed;

placing an upper-level device die over the redistribution structure; and

encapsulating the upper-level device die in a second encapsulating material.

2. The method of claim 1 , wherein the encapsulating the lower-level device die comprises:

dispensing the first encapsulating material; and

planarizing the first encapsulating material, wherein the second encapsulating material is in contact with a planarized top surface of the first encapsulating material.

3. The method of claim 1 further comprising sawing through the first encapsulating material and the second encapsulating material, wherein kerves of the sawing are away from the dielectric layer.

4. The method of claim 1 , wherein the trench forms a full ring encircling a region directly over the lower-level device die.

5. The method of claim 1 , wherein the trench forms a grid.

6. The method of claim 1 further comprising performing a partial cut on the second encapsulating material to form an additional trench, wherein a portion of the first encapsulating material revealed in the patterning the redistribution structure is directly underlying the additional trench.

7. The method of claim 6 , wherein after the partial cut, a portion of the second encapsulating material directly underlying the additional trench remains.

8. The method of claim 1 further comprising:

forming a metal post over the dielectric layer and electrically coupling to the lower-level device die, wherein the metal post is encapsulated in the second encapsulating material.

9. The method of claim 1 further comprising performing a sawing step to form a discrete package comprising the lower-level device die and the upper-level device die, wherein a portion of the second encapsulating material remains in the discrete package.

10. The method of claim 9 , wherein kerves of the sawing step are laterally spaced apart from the dielectric layer by spaces, with the first encapsulating material and the second encapsulating material filling the spaces.

11. A method comprising:

encapsulating a plurality of device dies in a first encapsulant;

forming a first plurality of dielectric layers over the plurality of device dies and the first encapsulant;

removing portions of the first plurality of dielectric layers between neighboring ones of the plurality of device dies to form a plurality of trenches, with the first encapsulant exposed through the plurality of trenches; and

disposing a second encapsulant, wherein portions of the second encapsulant disposed into the plurality of trenches are in contact with the first encapsulant; and

sawing through the first encapsulant, wherein a kerf of the sawing is narrower than a respective trench in the plurality of trenches.

12. The method of claim 11 , wherein the plurality of trenches in combination form a grid.

13. The method of claim 11 further comprising:

in a common process for forming the plurality of trenches, forming via openings in respective ones of the plurality of trenches; and

forming redistribution lines extending into the via openings, with the plurality of trenches unfilled by the forming the redistribution lines.

14. The method of claim 11 further comprising:

performing a partial cut to cut through an additional trench in the second encapsulant.

15. A method comprising:

encapsulating a first device die and a second device die in a first encapsulating material;

planarizing the first encapsulating material to expose the first device die and the second device die;

forming a first polymer layer over the first encapsulating material;

patterning the first polymer layer to form a first trench and a first via opening simultaneously, wherein the first encapsulating material is exposed through the first trench;

forming a first redistribution line having a portion extending into the first via opening to contact the first device die;

forming a second polymer layer over the first redistribution line and the first polymer layer; and

patterning the second polymer layer to form a second trench joined with the first trench to form a combined trench, wherein the first encapsulating material is exposed through the first trench and the second trench.

16. The method of claim 15 , wherein the first trench is directly over a portion of the first encapsulating material, with the portion of the first encapsulating material being between the first device die and the second device die.

17. The method of claim 15 further comprising:

patterning the first polymer layer to form an additional opening; and

plating a metal post comprising a portion extending into the additional opening.

18. The method of claim 17 further comprising encapsulating the second device die and the metal post in a second encapsulating material, wherein the second encapsulating material fills the combined trench.

19. The method of claim 18 further comprising sawing through the first encapsulating material and the second encapsulating material, wherein a kerf of the sawing passes through a middle portion of each of the first trench and the second trench.

20. The method of claim 15 , wherein the first trench is a part of a trench ring encircling the first device die.