Wafer-level interconnect for high mechanical reliability applications

1. An interconnect structure positioned between two electrical contacts including a first metal contact and a second metal contact, the interconnect structure comprising:

a solder alloy comprising nickel (Ni) and tin (Sn), wherein the nickel (Ni) is in a range of 0.01 to 0.20 percent by weight (wt %); and

an intermetallic compound (IMC) layer having a top surface in contact with the solder alloy and a bottom surface in contact with the first metal contact, the IMC layer comprising a compound of copper and nickel.

2. The interconnect structure of claim 1 , wherein the interconnect structure is incorporated in a flip-chip package.

3. The interconnect structure of claim 1 , wherein the first metal contact comprises nickel.

4. The interconnect structure of claim 1 , wherein the solder alloy consists essentially of nickel (Ni), tin (Sn), silver (Ag), and copper (Cu).

5. The interconnect structure of claim 1 , wherein the first metal contact and the second metal contact are each located on a respective substrate, and the respective substrate of the first metal contact is a semiconductor die comprising an integrated circuit electrically coupled to the second metal contact.

6. The interconnect structure of claim 1 , wherein the first metal contact comprises a top layer comprising copper.

7. The interconnect structure of claim 6 , wherein the first metal contact further comprises an intermediate layer underlying the top layer, and the intermediate layer comprises nickel.

8. The interconnect structure of claim 1 , wherein the compound of copper and nickel promotes smoothness of the top surface of the IMC layer.

9. An interconnect structure, comprising:

a semiconductor substrate comprising an integrated circuit;

an under bump metallurgy (UBM) on the substrate, the UBM comprising nickel and the integrated circuit electrically coupled to the UBM;

an intermetallic compound (IMC) layer on the UBM, the IMC layer comprising a compound of copper and nickel; and

a bulk solder body on the IMC layer, the bulk solder body comprising nickel (Ni) and copper (Cu), wherein the nickel (Ni) is in a range of 0.01 to 0.20 percent by weight (wt %).

10. The interconnect structure of claim 9 , wherein the bulk solder body comprises:

greater than 94.5 percent by weight (wt %) tin (Sn);

less than 4.0 percent by weight (wt %) silver (Ag); and

less than 2.0 percent by weight (wt %) copper (Cu).

11. The interconnect structure of claim 9 , wherein the bulk solder body comprises less than 2.0 percent by weight (wt %) of copper (Cu).

12. The interconnect structure of claim 9 , wherein the under bump metallurgy (UBM) is a film having a top layer of copper and an underlying layer of nickel.

13. The interconnect structure of claim 9 , wherein the IMC layer has a thickness of less than 2.0 microns.

14. The interconnect structure of claim 9 , wherein the under bump metallurgy (UBM) is a film composed of one or more alloys selected from the group consisting of:

aluminum (Al)-nickel vanadium (NiV)-copper (Cu);

titanium (Ti)-nickel vanadium (NiV)-copper (Cu);

titanium (Ti)-nickel (Ni)-copper (Cu);

titanium tungsten (TiW)-copper (Cu);

titanium tungsten (TiW)-nickel (Ni)-copper (Cu);

titanium tungsten (TiW)-nickel vanadium (NiV)-copper (Cu);

chromium (Cr)-nickel (Ni)-copper (Cu); and

chromium (Cr)-nickel vanadium (NiV)-copper (Cu).

15. The interconnect structure of claim 9 , wherein the UBM has a structure selected from the group consisting of:

aluminum (Al)-nickel vanadium (NiV)-copper (Cu); and

titanium (Ti)-nickel vanadium (NiV)-copper (Cu).

16. An interconnect structure positioned between two electrical contacts, the interconnect structure comprising:

a solder alloy attached through an intermetallic compound (IMC) layer to an under bump metallurgy containing copper on a top surface, the under bump metallurgy being disposed between the two contacts, and the solder alloy comprising nickel (Ni), tin (Sn), silver (Ag), and copper (Cu);

wherein the nickel (Ni) content is in a range of 0.01 to 0.20 percent by weight (wt %), and the IMC layer comprises a compound of copper and nickel.