Exposed solderable heat spreader for flipchip packages

1. A flipchip comprising:

a silicon die having a circuit side with solder bumps and a non-circuit side;

a leadframe attached to the solder bumps on the circuit side of the silicon die;

a heat spreader attached to the non-circuit side of the silicon die; and

encapsulation material encapsulating the silicon die, a portion of the leadframe, and all but one exterior surface of the heat spreader,

wherein the leadframe has leads that are longer than 1 mm to which the solder bumps are connected, but that have no straight length portion greater than 1 mm.

2. The flipchip of claim 1 wherein the exterior surface of the heat spreader and the portion of the leadframe that is not encapsulated by the encapsulation material are plated with NiPdAu plating.

3. The flipchip of claim 1 wherein the heat spreader includes a plurality of thermally-conductive sections that are separated by separating material having a coefficient of thermal expansion (CTE) that is between the CTE of the silicon die and the CTE of the thermally-conductive sections.

4. The flipchip of claim 3 wherein the separating material is pliable.

5. The flipchip of claim 1 wherein the heat spreader includes a plurality of thermally-conductive sections that are separated by separating material that is pliable.

6. A flipchip comprising:

a silicon die having a circuit side with solder bumps and a non-circuit side;

a leadframe attached to the solder bumps on the circuit side of the silicon die, wherein the leadframe comprises leads that are at longer than 1 mm and at least one feature that limits a maximum straight length of the leads to 1 mm;

a heat spreader attached to the non-circuit side of the silicon die;

encapsulation material encapsulating the silicon die, a portion of the leadframe, and all but one exterior surface of the heat spreader.

7. The flipchip of claim 6 , wherein the one exterior surface of the heat spreader and an additional portion of the leadframe that is not encapsulated by the encapsulation material are plated with a common plating material.

8. The flipchip of claim 7 , wherein the common plating material is NiPdAu.

9. The flipchip of claim 6 , wherein the at least one feature comprises at least one stress relief locking hole in the leadframe.

10. The flipchip of claim 9 , wherein the at least one feature further comprises at least one half-etched dimple on the leadframe.

11. The flipchip of claim 6 , wherein the at least one feature comprises at least one stress relief locking hole in the leadframe and a plurality of half-etched dimples on the leadframe.

12. A device, comprising:

a circuit die;

a leadframe having a first side that is attached by a plurality of solder bumps to a first side of the circuit die;

a heat spreader attached to an opposing second side of the circuit die; and

at least one surface feature on an opposing second side of the leadframe, the at least one surface feature comprising an opening that extends from the opposing second side of the leadframe at least partially into the leadframe toward the first side of the leadframe, the at least one surface feature configured to limit a straight length of a region between solder bumps or an edge of the leadframe below a length of 1 mm, wherein the total length of the region between solder bumps or an edge of the leadframe is longer than 1 mm.

13. The device of claim 12 , wherein the at least one surface feature comprises a stress relief locking hole that extends from the opposing second side through to the first side of the leadframe.

14. The device of claim 13 , wherein the at least one surface feature comprises a half-etched dimple that extends from the opposing second side partially through the leadframe toward the first side of the leadframe.

15. The device of claim 12 , wherein the at least one surface feature comprises a plurality of half-etched dimples that each extend from the opposing second side partially through the leadframe toward the first side of the leadframe.

16. The device of claim 12 , wherein the at least one surface feature limits a maximum straight length of all leads on the leadframe.

17. The device of claim 12 , further comprising a common coating on exposed portions of leads of the leadframe and on an external surface of the heat spreader.

18. The device of claim 17 , wherein the common coating comprises NiPdAu.

19. The device of claim 12 wherein the heat spreader includes a plurality of thermally-conductive sections that are separated by a separating material having a coefficient of thermal expansion (CTE) that is between the CTE of the circuit die and a CTE of the thermally-conductive sections.

20. The device of claim 19 , wherein the separating material is pliable.