Integrated circuit package substrate with openings surrounding a conductive via

1. Apparatus, comprising:

a substrate layer having upper and lower surfaces;

a conductive via that extends from the upper surface to the lower surface of the substrate layer; and

at least three metal-free openings in the substrate layer that surround the conductive via.

2. The apparatus defined in claim 1 wherein the at least three metal-free openings include partial height holes which are substantially equal in diameter.

3. The apparatus defined in claim 1 wherein each of the at least three metal-free openings is distributed substantially evenly in the substrate layer surrounding the conductive via to reduce the dielectric constant of the substrate layer.

4. The apparatus defined in claim 1 wherein each of the at least three metal-free openings is filled with air.

5. The apparatus defined in claim 1 wherein each of the at least three metal-free openings is filled with low loss material.

6. The apparatus defined in claim 1 wherein each of the at least three metal-free openings comprises a cylindrical cavity that extends through the upper and the bottom surfaces of the substrate layer.

7. The apparatus defined in claim 1 further comprising:

an integrated circuit die mounted on the upper surface of the substrate layer.

8. Circuitry, comprising:

a substrate;

a signal path on the substrate, wherein the signal path includes a via in the substrate; and

at least one opening in a region of the substrate that is adjacent to the via and that is devoid of metal, wherein the at least one opening reduces signal insertion loss of the via, and wherein the at least one opening and the via have the same length.

9. The circuitry defined in claim 8 wherein the at least one opening surrounds the via.

10. The circuitry defined in claim 8 wherein the at least one opening has a height that is substantially equivalent to a thickness of the via.

11. The circuitry package defined in claim 10 , wherein the at least one opening is distributed substantially evenly in the substrate and surrounding the via.

12. The circuitry defined in claim 8 , wherein the via comprises a plated through-hole via.

13. The circuitry defined in claim 12 , wherein the via further comprises a conductive lining that forms a barrel structure.

14. The circuitry defined in claim 8 , wherein the at least one opening is filled with low loss material.

15. The circuitry defined in claim 8 , wherein the at least one opening is substantially cylindrical.

16. Circuitry, comprising:

a substrate layer with a first dielectric constant, comprising upper and lower surfaces;

a conductive via formed in the substrate layer;

a metal trace coupled to the conductive via; and

an opening in the substrate layer that extends from the upper surface to the lower surface of the substrate layer, that changes the effective dielectric constant of a portion of the substrate layer, and that is filled with a solid medium with a second dielectric constant that is less than the first dielectric constant.

17. The circuitry of claim 16 , wherein the portion of the substrate layer comprises a region between the conductive via and the metal trace, and wherein the opening in the substrate layer has a diameter that changes the effective dielectric constant of the portion to match a first impedance associated with the conductive via and a second impedance associated with the metal trace.

18. The circuitry of claim 16 , further comprising:

another opening that extends from the upper surface to the lower surface of the substrate layer, wherein the another opening is separated from the conductive via by a distance that changes the effective dielectric constant of another portion of the substrate layer in a way such that a first impedance associated with the conductive via matches with a second impedance associated with the metal trace.

19. The circuitry of claim 16 , wherein the portion of the substrate layer comprises a region between the conductive via and the metal trace, and wherein the second dielectric constant lowers the effective dielectric constant in the region to match a first impedance associated with the conductive via and a second impedance associated with the metal trace.

20. The circuitry of claim 16 , wherein the second dielectric constant is configured to reduce parasitic capacitance between the conductive via and the metal trace.

21. The circuitry of claim 16 , wherein the second dielectric constant is configured to tune the impedance of the conductive via.

22. The circuitry of claim 16 , wherein the substrate layer directly contacts the solid medium with the second dielectric constant that fills the opening in the substrate layer.

23. The apparatus of claim 1 , wherein the at least three metal-free openings in the substrate layer extend only from the upper surface to the lower surface of the substrate layer.

24. The apparatus of claim 1 , wherein each of the at least three metal-free openings in the substrate layer is filled with a common medium, and wherein each of the at least three metal-free openings in the substrate layer is uncovered.

25. The circuitry of claim 8 , wherein the substrate has a first dielectric constant, and wherein the at least one opening in the region of the substrate is open-ended, the circuitry further comprising:

a dielectric medium that fills the at least one opening, wherein the dielectric medium has a second dielectric constant that is less than the first dielectric constant.