Metal powder sintering paste and method of producing the same, and method of producing conductive material
There is a problem that when a silver powder sintering paste that is substantially free from resin is used, an organic solvent used as a dispersion medium bleeds, which results in contamination and wire bonding defects. In order to solve the problem, provided is a metal powder sintering paste that contains, as a principal component, silver particles having an average particle diameter (a median diameter) of 0.3 μm to 5 μm and further contains an anionic surfactant but is substantially free from resin.
1. A metal powder sintering paste,
the paste comprising, as a principal component, silver particles having a median diameter of 0.3 μm to 5 μm, and
further comprising an anionic surfactant, and
being substantially free from resin,
wherein
the surfactant is one in which when the temperature is increased with thermogravimetric-differential thermal analysis (TG-DTA) from room temperature to 350° C. at 2° C./min, a residue is reduced to not more than 20% by mass with respect to the initial mass, and
wherein
a content of the surfactant is not more than 2% by mass with respect to the paste.
2. The metal powder sintering paste according to claim 1 , wherein
the surfactant is a saturated carboxylic acid represented by Formula (I) below:
R 1 O(CH 2 CH(R 2 )O) n1 CH 2 COOR 3 (I)
wherein R 1 is a linear or branched alkyl group having at least 7 carbon atoms,
R 2 is any one of —H, —CH 3 , —CH 2 CH 3 , and —CH 2 CH 2 CH 3 ,
R 3 is —H or alkali metal, and
n1 is in a range of 2 to 5.
3. The metal powder sintering paste according to claim 1 , wherein
the surfactant is liquid at 25° C.
4. The metal powder sintering paste according to claim 1 , wherein
the silver particles are in a flake form.
5. The metal powder sintering paste according to claim 1 , wherein
in the silver particles, the content of particles with a particle diameter of smaller than 0.3 μm is not more than 5% by mass.
6. The metal powder sintering paste according to claim 5 , wherein
in the silver particles, the content of particles with a particle diameter of smaller than 0.5 μm is not more than 15% by mass.
7. The metal powder sintering paste according to claim 1 , wherein
the metal powder sintering paste further comprises an organic solvent as a dispersion medium.
8. The metal powder sintering paste according to claim 7 , wherein
the organic solvent has a boiling point in a range of 150 to 250° C.
9. The metal powder sintering paste according to claim 1 , capable of being sintered to form a conductive material having an electric resistance of not higher than 6 μΩ·cm.
10. The metal powder sintering paste according to claim 1 , wherein
the content of the silver particles is at least 70% by mass with respect to the paste.
11. A metal powder sintering paste,
the paste comprising, as a principal component, silver particles having a median diameter of 0.3 μm to 5 μm, and
further comprising an anionic surfactant, and
being substantially free from resin,
wherein
a content of the surfactant is not more than 2% by mass with respect to the paste, and
wherein
a bleed ratio is less than 1.70,
wherein the bleed ratio is calculated as a ratio of a diameter after bleeding to an original diameter of the paste
when the paste is applied onto a substrate having a gold electrode with a surface roughness Ra of 0.04 μm on its surface by a stamping method to have a diameter of 170±50 μm, which then is left to stand for 20 minutes, and
the diameter after bleeding is measured by measuring the diameter including a dispersion medium that had bled.
12. The metal powder sintering paste according to claim 11 , wherein
the surfactant is one in which when the temperature is increased with thermogravimetric-differential thermal analysis (TG-DTA) from room temperature to 350° C. at 2° C./min, a residue is reduced to not more than 20% by mass with respect to the initial mass.
13. The metal powder sintering paste according, to claim 11 , wherein
the surfactant is a saturated carboxylic acid represented by Formula (I) below:
R 1 O(CH 2 CH(R 2 )O) n1 CH 2 COOR 3 (I)
wherein R 1 is a linear or branched alkyl group having at least 7 carbon atoms,
R 2 is any one of —H, —CH 2 CH 3 , and —CH 2 CH 2 CH 3 ,
R 3 is —H or alkali metal, and
n1 is in a range of 2 to 5.
14. The metal powder sintering paste according to claim 11 , wherein
the surfactant is liquid at 25° C.
15. The metal powder sintering paste according to claim 11 , wherein
the silver particles are in a flake form.
16. The metal powder sintering paste according to claim 11 , wherein
in the silver particles, a content of particles with a particle diameter of smaller than 0.3 μm is not more than 5% by mass.
17. The metal powder sintering paste according to claim 16 , wherein
in the silver particles, a content of particles with a particle diameter of smaller than 0.5 μm is not more than 15% by mass.
18. The metal powder sintering paste according to claim 11 , wherein
the metal powder sintering paste further comprises an organic solvent as a dispersion medium.
19. The metal powder sintering paste according to claim 18 , wherein
the organic solvent has a boiling point in a range of 150 to 250° C.
20. The metal powder sintering paste according to claim 11 , capable of being sintered to form a conductive material having an electric resistance of not higher than 6 μΩ·cm.
21. The metal powder sintering paste according to claim 11 , wherein
a content of the silver particles is at least 70% by mass with respect to the paste.
22. A method of producing the metal powder sintering paste according to claim 1 , comprising mixing an anionic surfactant and silver particles having a median diameter of 0.3 μm to 5 μm together but substantially not with resin.
23. A method of producing a conductive material, comprising a step of calcining a metal powder sintering paste according to claim 1 .
24. The method of producing a conductive material according to claim 23 , wherein
the calcining is carried out at a temperature in a range of 160° C. to 300° C.
25. The method of producing a conductive material according to claim 23 , wherein
the calcining is carried out in an air oven at 160° C. to 250° C. for 30 to 120 minutes.