Lead-free and cadmium-free conductive copper thick film pastes
View Patent ↗Thick film conductive copper pastes that are lead-free and cadmium-free. The inventive copper pastes possess desirable characteristics, including good solderability, good wire bondability, a low firing temperature, and a wide temperature processing window, and provide excellent adhesion to a variety of substrates, including alumina and glass coated stainless steel substrates, as well as low resistivity, and a microstructure after firing that is dense and substantially free of pores.
1. A lead-free and cadmium-free conductive thick film paste comprising a solids portion comprising a glass component and a metal component, said glass component comprising:
a. a first glass composition comprising in mole %:
i. about 25 to about 67% BaO,
ii. about 33 to about 70% SiO 2 +B 2 O 3 ,
iii. about 0.1 to about 20% TiO 2 ,
b. a second glass composition comprising in mole %:
iv. about 27 to about 65% ZnO,
v. about 33 to about 70% SiO 2 +B 2 O 3 ,
c. wherein the first and second glass compositions are present in a weight ratio of about 1:40 to about 20:1.
2. The thick film paste of claim 1 wherein the second glass composition further comprises about 0.1 to about 10 mole % TiO 2 +ZrO 2 and about 0.1 to about 15 mole % Li 2 O+Na 2 O+K 2 O.
3. The thick film paste of claim 1 wherein said metal component comprises copper.
4. The thick film paste of claim 1 wherein the second glass composition further comprises 0.1 to 10 mole % Al 2 O 3 .
5. The thick film paste of claim 1 , wherein the glass component further comprises a third glass composition, wherein the third glass composition comprises about 5 to about 80 mole % Bi 2 O 3 .
6. The thick film paste of claim 1 wherein the second glass composition further comprises about 0.1 to about 10 mole % ZrO 2 .
7. The thick film paste of claim 1 wherein the second glass composition further comprises TiO 2 , wherein the total of TiO 2 +ZrO 2 in the second glass composition is about 0.1 to about 10 mole %.
8. The thick film paste of claim 7 wherein the second glass composition further comprises about 0.1 to about 20 mole % Nb 2 O 5 .
9. The thick film paste of claim 8 , wherein the second glass composition further comprises about 0.1 to about 15 mole % Li 2 O+Na 2 O+K 2 O.
10. The thick film paste of claim 5 wherein the third glass composition further comprises about 0.1 to about 25 mole % CuO.
11. The thick film paste of claim 10 , wherein the third glass component further comprises about 0.1 to about 10 mole % NiO.
12. The thick film paste of claim 1 wherein the glass component comprises:
a. a first glass composition comprising in mole %:
vi. about 35 to about 65% BaO,
vii. about 35 to about 66% SiO2+B2O3,
viii. about 0.1 to about 10% TiO2.
b. a second glass composition comprising in mole %:
ix. about 30 to about 60 mole % ZnO,
x. about 40 to about 60% SiO2+B2O3,
xi. about 0.1 to about 10% ZrO 2
c. wherein the first and second glass composition are present in a weight ratio of about 1:40 to about 20:1.
13. The thick film paste of claim 12 further comprising a third glass composition wherein the third glass comprises about 15 to about 65 mole % Bi 2 O 3 .
14. The thick film paste of claim 12 wherein said glass component comprises about 2.5 to about 80 wt % of the first glass composition and about 2 to about 97.5 wt % of the second glass composition.
15. The thick film paste of claim 1 wherein said solids portion comprises by weight from about 80 to about 98% of said metal component and from about 2 to about 20% of said glass component.
16. The thick film paste of claim 1 having subsequent to firing a maximum resistivity of about 20 mOhm/square.
17. The thick film paste of claim 1 further comprising a liquid portion, said paste comprising by weight from about 10 to about 30% liquid portion.
18. An electronic device having a conductive path, said path formed by firing a lead-free and cadmium-free conductive thick film paste, said paste including a glass component, said glass component comprising:
a. a first glass composition comprising in mole %:
xii. about 25 to about 67% BaO,
xiii. about 33 to about 70% SiO 2 +B 2 O 3 ,
xiv. about 0.1 to about 20% TiO 2
b. a second glass composition comprising in mole %:
xv. about 27 to about 65% ZnO,
xvi. about 33 to about 70% SiO 2 +B 2 O 3 ,
c. wherein the first and second glasses are present in a weight ratio of about 1:40 to about 20:1.
19. An electronic device as set forth in claim 18 wherein said electronic device comprises a product selected from the group consisting of a solar panel, a heater and a windshield panel.
20. A method of making an electronic device comprising the steps of:
i. providing the conductive thick film paste of claim 1 and a substrate;
ii. applying said paste upon said substrate;
iii. firing said substrate from said step (ii) at temperature of from about 650° to about 850° C.
21. A method as set forth in claim 20 wherein said substrate is selected from the group consisting of an alumina substrate, a porcelain enamel coated steel substrate, a beryllia substrate, a barium titanate substrate, an aluminum nitride substrate and a silicon carbide substrate.