Flip chip package utilizing trace bump trace interconnection

1. A flip chip package, comprising:

a substrate having a die attach surface; and

a die mounted on the die attach surface with an active surface of the die facing the substrate, wherein the die is interconnected to the substrate via a plurality of copper pillar bumps on the active surface, wherein at least one of the plurality of copper pillar bumps has a bump width that is substantially equal to or smaller than a line width of a trace on the die attach surface of the substrate, wherein the at least one of the plurality of copper pillar bumps is jointed to the trace without using a via in the substrate.

2. The flip chip package according to claim 1 wherein at least one of the plurality of copper pillar bumps has a bump length that is at least two times greater than the line width of the trace.

3. The flip chip package according to claim 1 wherein at least one of the plurality of copper pillar bumps is oval-shaped from a plan view.

4. The flip chip package according to claim 1 wherein the line width of the trace is between 10 μm and 40 μm.

5. The flip chip package according to claim 1 wherein the die has a bump pitch between 120 μm and 180 μm.

6. The flip chip package according to claim 1 wherein at least one of the plurality of copper pillar bumps has a bump width between 10 μm and 40 μm and a bump length between 40 μm and 80 μm.

7. The flip chip package according to claim 1 wherein at least one of the plurality of copper pillar bumps has a bump orientation that is directed to a center of the die.

8. The flip chip package according to claim 1 further comprising an underfill between the die and the substrate.

9. The flip chip package according to claim 8 wherein the underfill comprises capillary underfill (CUF), molded underfill (MUF) or a combination thereof.

10. The flip chip package according to claim 1 wherein at least one of the plurality of copper pillar bumps is composed of a metal stack comprising an UBM layer, a copper layer, and a solder cap.

11. The flip chip package according to claim 10 wherein the copper layer has a thickness between 30 μm and 60 μm.

12. The flip chip package according to claim 10 wherein the solder cap has a thickness between 10 μm and 40 μm.

13. The flip chip package according to claim 10 wherein at least one of the plurality of copper pillar bumps further comprises a nickel layer between the copper layer and the solder cap.

14. A semiconductor die, comprising:

a base;

a topmost metal layer on the base;

a stress buffering layer overlying the topmost metal layer, wherein the stress buffering layer has an opening exposing at least a portion of the topmost metal layer; and

a copper pillar bump coupled to the topmost metal layer through the opening, wherein the copper pillar bump has an elongated outline along a lengthwise direction of the copper pillar bump, and wherein the lengthwise direction is directed to a center of the semiconductor die.

15. The semiconductor die according to claim 14 wherein the copper pillar bump is oval-shaped from a plan view.

16. The semiconductor die according to claim 14 wherein the copper pillar bump has a bump width between 10 μm and 40 μm and a bump length between 40 μm and 80 μm.

17. The semiconductor die according to claim 14 wherein the copper pillar bump has a lower stress side and a higher stress side, and the opening is situated closer to the lower stress side and is farther from the higher stress side.

18. The semiconductor die according to claim 14 wherein the copper pillar bump is composed of a metal stack comprising an UBM layer, a copper layer, and a solder cap.

19. The semiconductor die according to claim 18 wherein the copper layer has a thickness between 30 μm and 60 μm.

20. The semiconductor die according to claim 18 wherein the solder cap has a thickness between 10 μm and 40 μm.