Package lid or heat spreader for microprocessor packages

1. A package for an integrated circuit (IC) die, the package comprising:

a substrate, the substrate having an upper surface facing an interior of the package and a lower surface facing an exterior of the package, the upper surface carrying an IC die, the substrate providing electrical connections from the IC die to the lower surface of the substrate on the exterior of the package;

a lid, the lid comprising an outer lid and an inner lid, the inner lid being positioned over the IC die and in thermal communication with the IC die, the inner lid being formed of a material suitable for conducting heat away from the IC die, the outer lid being attached to the upper surface of the substrate; and

wherein a gap extends between the outer lid and the inner lid, the inner lid and the outer lid being constructed and assembled so that the gap permits the inner lid to move with respect to the outer lid and accommodate differences in thermal expansion between the inner lid and the outer lid.

2. The package of claim 1 , wherein the outer lid has a coefficient of thermal expansion (CTE) that closely matches a CTE of the substrate.

3. The package of claim 1 , wherein the inner lid has a coefficient of thermal expansion (CTE) that closely matches a CTE of the IC die.

4. The package of claim 1 , wherein the outer lid is attached to the upper surface of the substrate using an adhesive.

5. The package of claim 1 , wherein the inner lid is attached to the IC die using a heat conductive adhesive material.

6. The package of claim 1 , wherein the gap between the outer lid and the inner lid contains a compliant material, the compliant material being adhered to edges of the outer lid and the inner lid that face the gap.

7. The package of claim 1 , wherein the outer lid is ring shaped and the inner lid is positioned within a central opening of the outer lid, the gap being an annular region between the inner lid and the outer lid.

8. The package of claim 7 , wherein the gap between the outer lid and the inner lid contains a compliant material, the compliant material being adhered to edges of the outer lid and the inner lid that face the gap.

9. The package of claim 1 , wherein the outer lid is ring shaped and the inner lid is positioned within a central opening of the outer lid, the gap extending at least partially around the inner lid, and furthermore, wherein the gap between the outer lid and the inner lid contains one or more springs for retaining the inner lid in the central opening of the outer lid.

10. A composite lid for a package for an IC die, the composite lid comprising:

an outer lid, the outer lid being ring shaped;

an inner lid, the inner lid being positioned within an opening of the outer lid, the inner lid being sized relative to the central opening such that a gap extends between the inner lid and the outer lid, the gap extending vertically from an exterior of the package to an interior space of the package; and

wherein the inner lid is positioned for thermal coupling with the IC die, the inner lid being formed of a material distinct from a material of the outer lid, the material of the inner lid being suitable for conducting heat away from the IC die, the outer lid having a downwardly extending outer rim for attaching to an upper surface of the substrate.

11. The composite lid of claim 10 , wherein the inner lid is formed from a material that has a coefficient of thermal expansion (CTE) that closely matches a CTE of the IC die.

12. The composite lid of claim 10 , wherein the gap between the outer lid and inner lid contains a compliant material, the compliant material being adhered to edges of the outer lid and the inner lid that face the gap.

13. The composite lid of claim 12 , wherein the gap comprises an annular region extending around the inner lid and the compliant material substantially fills the gap.

14. The composite lid of claim 10 , wherein the gap between the outer lid and inner lid contains at least one spring for retaining the inner lid in the central opening of the outer lid.

15. A package for an IC die, the package comprising:

a substrate, the substrate having an upper surface facing an interior of the package and a lower surface facing an exterior of the package, the upper surface carrying an IC die, the substrate providing electrical connections between the IC die and the lower surface of the substrate on the exterior of the package;

a lid, the lid comprising an outer lid and an inner lid, the outer lid being ring shaped and the inner lid being positioned within a central opening of the outer lid such that the inner lid is positioned over the IC die and is thermally coupled with the IC die, the inner lid being formed of a material suitable for conducting heat away from the IC die, the outer lid being attached to the upper surface of the substrate; and

wherein the outer lid and the inner lid are separated by a gap, the gap being an annular region between the inner lid and the outer lid, the inner lid and the outer lid being formed and assembled with the gap so that the inner lid is movable with respect to the outer lid.

16. The package of claim 15 , wherein the outer lid has a coefficient of thermal expansion (CTE) that closely matches a CTE of the substrate.

17. The package of claim 15 , wherein the inner lid has a coefficient of thermal expansion (CTE) that closely matches a CTE of the IC die.

18. The package of claim 15 , wherein the outer lid is attached to the upper surface of the substrate using an adhesive.

19. The package of claim 15 , wherein the inner lid is attached to the IC die using a heat conductive adhesive material.

20. The package of claim 15 , wherein the gap between the outer lid and inner lid contains a compliant material, the compliant material being adhered to edges of the outer lid and inner lid facing the gap.