Grain refinement by precipitate formation in PB-free alloys of tin
View Patent ↗Micro-addition of a metal to a Sn-based lead-free C4 ball is employed to enhance reliability. Specifically, a metal having a low solubility in Sn is added in a small quantity corresponding to less than 1% in atomic concentration. Due to the low solubility of the added metal, fine precipitates are formed during solidification of the C4 ball, which act as nucleation sites for formation multiple grains in the solidified C4 ball. The fine precipitates also inhibit rapid grain growth by plugging grain boundaries and act as agents for pinning dislocations in the C4 ball. The grain boundaries enable grain boundary sliding for mitigation of stress during thermal cycling of the semiconductor chip and the package on the C4 ball. Further, the fine precipitates prevent electromigration along the grain boundaries due to their pinned nature.
1. A metallic ball comprising:
at least one metal selected from Pd, and Pt and having an atomic concentration greater than 0% and less than 5%; and
Sn at an atomic concentration of at least 95%, wherein Sn comprises a balance composition of said at least one metal and said at least one metal includes Pd or Pt at an atomic concentration greater than 0% and less than 3.0%.
2. The metallic ball of claim 1 , wherein said at least one metal includes Pd at an atomic concentration greater than 0% and less than 3.0%.
3. The metallic ball of claim 2 , wherein an atomic concentration of Pd in said metallic ball is greater than 0.22% and less than 1.0%.
4. The metallic ball of claim 1 , wherein said at least one metal includes Pt at an atomic concentration greater than 0% and less than 3.0%.
5. The metallic ball of claim 4 , wherein an atomic concentration of Pt in said metallic ball is greater than 0.10% and less than 1.0%.
6. A metallic ball comprising:
at least one metal selected from Au, Pd, and Pt and having an atomic concentration greater than 0% and less than 5%;
Sn at an atomic concentration of at least 95%; and
at least another metal at an atomic concentration less than 3.4%.
7. The metallic ball of claim 6 , wherein said at least another metal includes Ag at an atomic concentration from about 0.1% to about 2.3%.
8. The metallic ball of claim 6 , wherein said at least another metal includes Cu at an atomic concentration from about 0.1% to about 1.0%.
9. A metallic ball comprising:
at least one metal selected from Au, Pd, and Pt and having an atomic concentration greater than 0% and less than 5%; and
Sn at an atomic concentration of at least 95%, wherein said at least one metal is present in said metallic ball as fine precipitates in grain boundaries between Sn-containing regions.
10. The metallic ball of claim 6 , wherein Sn comprises a balance composition of said at least one metal.
11. The metallic ball of claim 10 , wherein said at least one metal includes Au at an atomic concentration greater than 0% and less than 3.0%.
12. The metallic ball of claim 10 , wherein said at least one metal includes Pd at an atomic concentration greater than 0% and less than 3.0%.
13. The metallic ball of claim 10 , wherein said at least one metal includes Pt at an atomic concentration greater than 0% and less than 3.0%.
14. The metallic ball of claim 6 , wherein said at least one metal is present in said metallic ball as fine precipitates in grain boundaries between Sn-containing regions.
15. The metallic ball of claim 9 , wherein Sn comprises a balance composition of said at least one metal.
16. The metallic ball of claim 15 , wherein said at least one metal includes Au at an atomic concentration greater than 0% and less than 3.0%.
17. The metallic ball of claim 15 , wherein said at least one metal includes Pd at an atomic concentration greater than 0% and less than 3.0%.
18. The metallic ball of claim 15 , wherein said at least one metal includes Pt at an atomic concentration greater than 0% and less than 3.0%.
19. The metallic ball of claim 9 , further comprising at least another metal at an atomic concentration less than 3.4%.
20. The metallic ball of claim 19 , wherein said at least another metal includes Ag at an atomic concentration from about 0.1% to about 2.3% or Cu at an atomic concentration from about 0.1% to about 1.0%.