Alignment mark design for packages

1. A method comprising:

forming a first dielectric layer;

performing a plating to form a metal post and an alignment mark over the first dielectric layer;

placing a device die over the first dielectric layer, wherein the device die comprises integrated circuits therein, and an electrical connector at a surface of the device die;

encapsulating the metal post and the alignment mark in an encapsulating material;

performing a planarization to reveal the electrical connector of the device die, the metal post and the alignment mark, wherein top surfaces of the device die, the metal post, and the alignment mark are coplanar after the planarization; and

forming a first plurality of redistribution lines electrically connecting to both the metal post and the alignment mark.

2. The method of claim 1 , wherein the placing the device die is performed using the alignment mark for alignment.

3. The method of claim 1 further comprising forming a first opening in the first dielectric layer, wherein an extension portion of the metal post is filled into the first opening.

4. The method of claim 3 further comprising forming a second opening in the first dielectric layer when the first opening is formed, wherein an additional extension portion of the alignment mark is filled into the second opening.

5. The method of claim 3 , wherein the alignment mark has its entire bottom surface in contact with a top surface of the first dielectric layer.

6. The method of claim 1 further comprising:

before the forming the first plurality of redistribution lines, forming a second dielectric layer to cover the encapsulating material, the metal post, and the alignment mark; and

forming an opening exposing the metal post, wherein one of the first plurality of redistribution lines extends into the opening to connect to the metal post, and wherein the forming the opening is performed using the alignment mark for alignment.

7. The method of claim 6 , wherein at a time after the first plurality of redistribution lines is formed, the alignment mark in the encapsulating material is overlapped by the second dielectric layer, and a top surface of the alignment mark is in contact with the second dielectric layer.

8. The method of claim 6 further comprising forming an additional opening in the second dielectric layer to expose the alignment mark.

9. The method of claim 1 further comprising performing a sawing process to separate the encapsulating material into a plurality of packages, with the alignment mark and the metal post in a same one of the plurality of packages.

10. The method of claim 1 , wherein the forming the first plurality of redistribution lines comprises:

forming a seed layer comprising portions contacting the metal post and the alignment mark; and

plating a metallic material on the seed layer.

11. The method of claim 1 , wherein the alignment mark and one of the first plurality of redistribution lines form a distinguishable interface, and the distinguishable interface is level with a top surface of the encapsulating material.

12. A method comprising:

forming a first redistribution line and a second redistribution line;

forming a metal post and an alignment mark over and electrically connected to the first redistribution line and the second redistribution line, respectively;

encapsulating a device die, the metal post, and the alignment mark in an encapsulating material;

performing a planarization on the encapsulating material to expose the metal post, the alignment mark, and conductive features of the device die;

forming a dielectric layer over the encapsulating material, the device die, the metal post, and the alignment mark;

patterning the dielectric layer to form openings, wherein the alignment mark is used to align the openings to respective ones of the metal post and the conductive features of the device die; and

forming a plurality of redistribution lines to electrically couple to the conductive features of the device die and the metal post, wherein the plurality of redistribution lines are on an opposite side of the encapsulating material than the first redistribution line and the second redistribution line, and wherein at a time after the plurality of redistribution lines is formed, the alignment mark is fully covered by the dielectric layer.

13. The method of claim 12 further comprising:

forming a solder region electrically coupling to the first redistribution line, wherein a first side of the second redistribution line is electrically connected to the alignment mark, and a second side of the second redistribution line opposite to the first side is fully in contact with a dielectric material at a time after the solder region is formed.

14. The method of claim 12 , wherein one of the plurality of redistribution lines is electrically coupled to the alignment mark.

15. The method of claim 12 further comprising sawing the encapsulating material to form a package, wherein in the package, the alignment mark is electrically floating.

16. The method of claim 12 comprising forming a plurality of metal posts, wherein each of the plurality of metal posts electrically interconnects features on opposite sides of the encapsulating material, and wherein the plurality of metal posts defines a rectangular design area in a top view of the metal post and an alignment mark, with the device die being in the rectangular design area, and the alignment mark is outside of the rectangular design area.

17. A method comprising:

forming a metal post and an alignment mark in a patterned photo resist;

removing the patterned photo resist in which the metal post and the alignment mark are located;

encapsulating a device die, the metal post, and the alignment mark in an encapsulating material;

forming a first dielectric layer over and contacting the device die, the metal post, and the alignment mark; and

forming a plurality of redistribution lines over the encapsulating material, wherein the plurality of redistribution lines comprise a portion extending into the first dielectric layer to contact a top surface of the metal post, and after the plurality of redistribution lines are formed, an entire top surface of the alignment mark is in contact with a bottom surface of the first dielectric layer.

18. The method of claim 17 further comprising, before the metal post is formed:

forming a first redistribution line;

forming a second dielectric layer covering the first redistribution line; and

forming a first via in the second dielectric layer, wherein opposite sides of the first via are in contact with the first redistribution line and the metal post.

19. The method of claim 18 further comprising:

forming a second redistribution line, wherein the second dielectric layer further covers the second redistribution line; and

forming a second via in the second dielectric layer, wherein opposite sides of the second via are in contact with the second redistribution line and the alignment mark.

20. The method of claim 18 , wherein the metal post and the alignment mark are formed simultaneously, and no via is formed in the second dielectric layer to connect to the alignment mark.