Methods for controlling warpage in packaging

1. A method comprising:

placing a plurality of dummy dies over a carrier, wherein the plurality of dummy dies is placed overlapping a peripheral area of the carrier, with the peripheral area encircling an inner area, wherein none of the plurality of dummy dies is placed to overlap the inner area;

placing a plurality of device dies over the carrier, wherein the plurality of device dies is placed overlapping the inner area of the carrier;

molding the plurality of dummy dies and the plurality of device dies in a molding compound;

forming redistribution line over and electrically coupled to the device dies; and

performing a die-saw to separate the device dies and the molding compound into a plurality of packages.

2. The method of claim 1 , wherein the plurality of packages is free from dummy dies therein.

3. The method of claim 1 , wherein the placing the plurality of dummy dies comprises picking up the plurality of dummy dies one by one, and placing the plurality of dummy dies over the carrier one by one.

4. The method of claim 1 , wherein the placing the plurality of dummy dies comprises:

placing the plurality of dummy dies in recesses of a mold; and

transferring the plurality of dummy dies over the carrier, wherein relative positions of the plurality of dummy dies on the carrier are same as relative positions of the plurality of dummy dies in the recesses of the mold.

5. The method of claim 4 , wherein the transferring the plurality of dummy dies comprises:

simultaneously picking up the plurality of dummy dies from the mold using a vacuum suction plate; and

simultaneously placing the plurality of dummy dies over the carrier.

6. The method of claim 4 , wherein the transferring the plurality of dummy dies comprises:

heating the mold and plurality of dummy dies; and

contacting the plurality of dummy dies to an adhesive die-attach film, wherein the adhesive die-attach film is laminated on the carrier.

7. The method of claim 1 , wherein the peripheral area of the carrier has a width smaller than about 25 mm.

8. A method comprising:

placing a plurality of dummy dies on a die-attach film, wherein the die-attach film is further overlying a carrier;

placing a plurality of device dies on the die-attach film, wherein the plurality of dummy dies overlaps a peripheral region of the carrier, and wherein the plurality of device dies overlaps an inner region of the carrier;

molding the plurality of dummy dies and the plurality of device dies in a molding compound to form a composite wafer, wherein the plurality of dummy dies has a Coefficient of Thermal Expansion (CTE) lower than a CTE of the molding compound;

forming redistribution lines over and electrically coupled to the plurality of device dies;

demounting the composite wafer from the carrier; and

performing a die-saw to separate the composite wafer into a plurality of packages, wherein each of the plurality of packages comprises one of the device dies, and is free from dummy dies therein.

9. The method of claim 8 , wherein the plurality of dummy dies has sizes different from each other.

10. The method of claim 8 , wherein the carrier comprises a glass carrier, and wherein the plurality of dummy dies comprises glass dies.

11. The method of claim 8 , wherein the placing the plurality of dummy dies comprises:

placing the plurality of dummy dies in recesses of a mold; and

transferring the plurality of dummy dies onto the die-attach film, wherein relative positions of the plurality of dummy dies on the die-attach film are same as relative positions of the plurality of dummy dies in the recesses of the mold.

12. The method of claim 11 , wherein the placing the plurality of dummy dies in the recesses comprises:

pouring the plurality of dummy dies over the mold; and

vibrating the mold and the plurality of dummy dies.

13. The method of claim 11 , wherein the transferring the plurality of dummy dies comprises:

simultaneously picking up the plurality of dummy dies using a vacuum suction plate; and

simultaneously placing the plurality of dummy dies over the carrier.

14. The method of claim 11 , wherein the transferring the plurality of dummy dies comprises:

heating the mold and the plurality of dummy dies; and

contacting the plurality of dummy dies to the die-attach film.

15. A method comprising:

placing a plurality of dummy dies in recesses of a mold;

picking up the plurality of dummy dies simultaneously using a vacuum suction plate, wherein the vacuum suction plate comprises a plurality of holes, each aligned to one of the plurality of dummy dies during the picking up;

releasing the plurality of dummy dies picked up by the vacuum suction plate onto a die-attach film, wherein the die-attach film is laminated on a carrier, and wherein the plurality of dummy dies is distributed overlapping peripheral regions of the carrier, with an inner region of the carrier encircled by the peripheral region free from overlying dummy dies;

placing a plurality of device dies overlapping the inner region of the carrier;

molding the plurality of dummy dies and the plurality of device dies in a molding compound to form a composite wafer;

forming redistribution lines over and electrically coupled to the plurality of device dies; and

performing a die-saw to separate the composite wafer into a plurality of packages.

16. The method of claim 15 further comprising, during the releasing the plurality of dummy dies, heating the die-attach film.

17. The method of claim 15 , wherein the placing the plurality of dummy dies in the recesses comprises:

pouring the plurality of dummy dies over the mold; and

vibrating the mold and the plurality of dummy dies.

18. The method of claim 15 , wherein the plurality of dummy dies has a Coefficient of Thermal Expansion (CTE) lower than a CTE of the molding compound.

19. The method of claim 18 , wherein the plurality of dummy dies comprises glass dies.

20. The method of claim 18 , wherein the redistribution lines extend beyond edges of the respective underlying ones of the plurality of device dies.