Lead-free conductive paste composition and semiconductor devices made therewith
View Patent ↗A lead-free conductive paste composition contains a source of an electrically conductive metal, a fusible material, an optional additive, and an organic vehicle. An article such as a high-efficiency photovoltaic cell is formed by a process of deposition of the lead-free paste composition on a semiconductor substrate (e.g., by screen printing) and firing the paste to remove the organic vehicle and sinter the metal and fusible material.
1. A paste composition comprising in admixture:
(a) a source of electrically conductive metal;
(b) a fusible material comprising:
50-90 wt. % Bi 2 O 3 ,
8-15 wt. % Al 2 O 3 ,
2-26 wt. % SiO 2 ,
0-9 wt. % B 2 O 3 , and
wherein the weight percentages are based on the total fusible material, and wherein some or all of at least one of the oxides is optionally replaced by a fluoride of the same cation in an amount such that the fusible material comprises at most 5 wt. % of fluorine, based on the total fusible material; and
(c) an organic vehicle, and
wherein the paste composition is lead-free.
2. The paste composition of claim 1 , wherein the fusible material comprises:
60-90 wt. % Bi 2 O 3 ,
8-12.5 wt. % Al 2 O 3 ,
2-19 wt. % SiO 2 , and
0.5-7 wt. % B 2 O 3 .
3. The paste composition of claim 1 , wherein the fusible material comprises:
70-90 wt. % Bi 2 O 3 ,
8-10 wt. % Al 2 O 3 ,
2-12 wt. % SiO 2 , and
1-5 wt. % B 2 O 3 .
4. The paste composition of any of claims 1 to 3 , wherein the fusible material further comprises at least one of:
0-6 wt. % ZnO,
0-3 wt. % P 2 O 5 ,
0-5 wt. % Li 2 O,
0-5 wt. % Na 2 O,
0-2 wt. % TiO 2 , or
0-2 wt. % ZrO 2 .
5. The paste composition of claim 1 , wherein the fusible material comprises 0-2 wt. % Li 2 O, 0-3 wt. % Na 2 O, and 0.5-4 wt. % F, with the proviso that the total amount of Li 2 O and Na 2 O present is at least 0.5 wt. %.
6. The paste composition of claim 1 , wherein the fusible material consists essentially of:
71-90 wt. % Bi 2 O 3 ,
8-11 wt. % Al 2 O 3 ,
2-13 wt. % SiO 2 , and
1-5 wt. % B 2 O 3 .
7. The paste composition of claim 1 , wherein the paste composition is zinc-free.
8. The paste composition of claim 1 , wherein the fusible material comprises 0.5 to 10 wt. % of the total paste composition.
9. The paste composition of claim 1 , wherein the source of the electrically conductive metal is an electrically conductive metal powder.
10. The paste composition of claim 1 , wherein the electrically conductive metal comprises Ag.
11. The paste composition of claim 10 , wherein the Ag comprises 75 to 99.5 wt. % of the solids in the composition.
12. A paste composition comprising in admixture:
(a) a source of electrically conductive metal;
(b) a fusible material comprising:
50-90 wt. % Bi 2 O 3 ,
6.5-15 wt. % Al 2 O 3 ,
2-8 wt. % SiO 2 ,
0.5-9 wt. % B 2 O 3 , and
wherein the weight percentages are based on the total fusible material, and wherein some or all of at least one of the oxides is optionally replaced by a fluoride of the same cation in an amount such that the fusible material comprises at most 5 wt. % of fluorine, based on the total fusible material; and
(c) an organic vehicle, and
wherein the paste composition is lead-free.
13. The paste composition of claim 12 , wherein the fusible material is substantially free of Ni.
14. The paste composition of claim 12 , wherein the fusible material is substantially free of Zn.