Metal paste and thermoelectric module

Abstract

The present invention relates to a metal paste including: a first metal powder including nickel (Ni); a second metal powder including at least one selected from the group consisting of tin (Sn), zinc (Zn), bismuth (Bi), and indium (In); and a dispersing agent, and to a thermoelectric module which adopts a bonding technique using the metal paste.

Claims

1. A thermoelectric module comprising a plurality of thermoelectric elements comprising: a thermoelectric semiconductor; an electrode which is composed of a metal material and is connected between the thermoelectric elements; and a bonding layer in which a metal paste is sintered to bond the thermoelectric elements and the electrode, wherein the metal paste comprises: a first metal powder including nickel (Ni); a second metal powder including at least one selected from the group consisting of tin (Sn), zinc (Zn), bismuth (Bi), and indium (In); and a dispersing agent, and wherein the first metal powder has an average particle diameter of 0.1 to 3.0 μm and the second metal powder has an average particle diameter of 0.5 to 10 μm.

2. The thermoelectric module of claim 1, wherein the bonding layer has porosity of 10% or less.

3. The thermoelectric module of claim 1, wherein the bonding layer has bonding strength of 1 MPa or more.

4. The thermoelectric module of claim 1, wherein the bonding layer has resistivity of 70 μΩ.Math.cm or less at 50° C. and 80 μΩ.Math.cm or less at 300° C.

5. The thermoelectric module of claim 1, wherein the bonding layer has thermal conductivity of 10 W/m.Math.k or more at 27° C. and 15 W/m.Math.k or more at 300° C.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows a cross-sectional image of a thermoelectric module prepared in Example 1.

(2) FIG. 2 shows a cross-sectional image of a thermoelectric module prepared in Example 2.

(3) FIG. 3 shows a cross-sectional image of a thermoelectric module prepared in Comparative Example 1.

(4) FIG. 4 shows images showing of elemental analysis of the cross-section of the thermoelectric module prepared in Comparative Example 1 through EDX (energy-dispersive X-ray spectroscopy).

(5) FIG. 5 shows a cross-sectional image of a thermoelectric module prepared in Comparative Example 2.

(6) FIG. 6 shows images of elemental analysis of the cross-section of the thermoelectric module prepared in Comparative Example 2 through EDX (energy-dispersive X-ray spectroscopy).

(7) FIG. 7 shows a cross-sectional image of a thermoelectric module prepared in Comparative Example 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(8) Hereinafter, the present invention will be described in more detail by way of examples. However, the examples are provided only for illustration of the invention, and the description of the present invention is not limited by the examples.

Example 1

(9) (1) 27.3% by weight of Ni μm powder (0.6 μm), 66.7% by weight of Sn powder (5-10 μm), 1% by weight of sodium stearate, and 5.0% by weight of dihydro terpineol were mixed to prepare a metal paste.

(10) (2) A thermoelectric module was prepared by using a skutterudite-based thermoelectric semiconductor as a thermoelectric material, and primary heat-drying the metal paste at 110° C. for 10 minutes, subjecting it to pressure (15 MPa) at 400° C. for 30 minutes, and bonding.

(11) (3) At this time, the substrate size of the high-temperature portion of the thermoelectric module thus prepared was 30*30 mm, the substrate size of the low-temperature portion was 30*32 mm, and the size of the element was 3*3*2 mm, and the total number of the thermoelectric module is 32 pairs. The cross-section of the thus-prepared thermoelectric module was analyzed by SEM, and the analysis image thereof is shown in FIG. 1.

Example 2

(12) A thermoelectric module was prepared in the same manner as in Example 1, except that 27.5% by weight of Ni powder (0.6 μm), 67.5% by weight of Sn powder (2.5 μm), 1% by weight of oleylamine, and 4.0% by weight of dihydro terpineol were mixed to prepare a metal paste. The cross-section of the thus-prepared thermoelectric module was analyzed by SEM, and the analysis image thereof is shown in FIG. 2.

Comparative Example 1

(13) A thermoelectric module was prepared in the same manner as in Example 1, except that 26.6% by weight of Ni powder (3 μm), 62.1% by weight of Sn powder (1 μm), 1.5% by weight of ethyl cellulose (binder resin), and 9.8% by weight of dihydro terpineol were mixed to prepare a metal paste.

(14) The cross-section of the thus-prepared thermoelectric module was analyzed by SEM, and the analysis image thereof is shown in FIG. 3. With reference to FIG. 3, the porosity of the bonding layer of Comparative Example 1 was about 24%, confirming that it showed high porosity.

(15) In addition, the elemental analysis image of the cross-section of the thermoelectric module of Comparative Example 1 using EDX (energy-dispersive X-ray spectroscopy) is shown in FIG. 4. Referring to FIG. 4, it was confirmed that there was a considerable portion of residual carbon near the pores of the thermoelectric module of Comparative Example 1, which resulted in deteriorated sinterability of the metal compared to the examples, and accordingly, the bonding strength and the electrical/thermal properties of the bonding layer were not good.

Comparative Example 2

(16) A thermoelectric module was prepared in the same manner as in Example 1, except that 26.5% by weight of Ni powder (3 μm), 60.0% by weight of Sn.sub.97.8Ag.sub.1.9Cu.sub.0.3 powder (2-7 μm), 1.5% by weight of ethyl cellulose (binder resin), and 12% by weight of dihydro terpineol were mixed to prepare a metal paste.

(17) The cross-section of the thus-prepared thermoelectric module was analyzed by SEM, and the analysis image thereof is shown in FIG. 5. Referring to FIG. 5, it was confirmed that the bonding layer of Comparative Example 2 exhibited high porosity of about 41%.

(18) In addition, the elemental analysis image of the cross-section of the thermoelectric module of Comparative Example 2 using EDX (energy-dispersive X-ray spectroscopy) is shown in FIG. 6. Referring to FIG. 6, as in the case of Comparative Example 1, the thermoelectric module of Comparative Example 2 also showed poor bonding strength and electrical/thermal properties of the bonding layer compared to the examples, due to a considerable amount of residual carbon present near the pores.

Comparative Example 3

(19) A thermoelectric module was prepared in the same manner as in Example 1, except that 27.4% by weight of Ni powder (0.3 μm), 64.6% by weight of Sn powder (1 μm), 1.4% by weight of ethyl cellulose (binder resin), and 6.6% by weight of dihydro terpineol were mixed to prepare a metal paste.

(20) The cross-section of the thus-prepared thermoelectric module was analyzed by SEM, and the analysis image thereof is shown in FIG. 7. Referring to FIG. 7, the bonding layer of Comparative Example 3 exhibited porosity of about 2.6%, similar to that of the examples, but it was confirmed through an experimental example described below that the bonding strength and the electrical/thermal properties of the bonding layer were not good compared to the examples not using a binder resin.

Comparative Example 4

(21) A thermoelectric module was prepared in the same manner as in Example 1, except that 73% by weight of Ag powder (0.3 μm), 10.0% by weight of Sn powder (1 μm), 2.6% by weight of methyl methacrylate (binder resin), and 14.4% by weight of isophorone were mixed to prepare a metal paste.

(22) A cross-sectional photograph of the thus-prepared thermoelectric module was printed out by using SEM, and the porosity of the bonding layer measured by analyzing particles using an image analysis program (Image J) was about 2.4%, showing a value similar to those obtained in the examples. However, it was confirmed through an experimental example described below that Comparative Example 4 had poor bonding strength of the bonding layer compared to those of the examples not using a binder resin.

Comparative Example 5

(23) A thermoelectric module was prepared in the same manner as in Example 1, except that 73% by weight of Ag powder (0.3 μm), 10.0% by weight of Zn powder (6-9 μm), 2.6% by weight of methyl methacrylate (binder resin), and 14.4% by weight of isophorone were mixed to prepare a metal paste.

Experimental Example

(24) The bonding layer resistivity, bonding strength, and bonding layer thermal conductivity of the thermoelectric modules prepared in Examples 1 and 2 and Comparative Examples 1 to 5 were measured by the following methods, and the results are shown in Tables 1 and 2 below.

(25) (1) Bonding strength: Instantaneous shear strength when the device ruptures from the electrode by applying a shear force to the thermoelectric device while the thermoelectric device is attached to the substrate through the metal paste was measured using a bond tester (Nordson DAGE 4000).

(26) (2) Porosity of bonding layer: Cross-sectional image of the bonding layer obtained by SEM was measured by analyzing particles using an image analysis program (Image J).

(27) (3) Resistivity of bonding layer: Resistivity value according to temperature was measured by bringing the electrode into contact with the bonding material having a predetermined standard using a resistivity measuring device (Linseis LSR-3).

(28) (4) Thermal conductivity of bonding layer: Thermal diffusivity and thermal conductivity according to temperature were each measured by irradiating the bonding material having a predetermined standard with a laser using a thermal conductivity measuring device (Netzsch LFA457).

(29) TABLE-US-00001 TABLE 1 Average bonding strength (MPa) Porosity (%) Example 1 39 1.8 Example 2 22 2.7 Comparative Example 1 12 24 Comparative Example 2 10 41 Comparative Example 3 18 2.6 Comparative Example 4 11 2.4 Comparative Example 5 6 —

(30) TABLE-US-00002 TABLE 2 Resistivity Thermal conductivity of of bonding layer (μΩ.Math.cm) layer (W/m.Math.k) 50° C. 300° C. 400° C. 27° C. 300° C. 400° C. Example 1 61 76 85 12.4 16.6 17.2 Example 2 49 60 72 16.6 21.7 21.6 Comparative 75 91 98 10.1 13.7 14.3 Example 1 Comparative 77 98 109 11 14.3 14.6 Example 2

Example 2

(31) Referring to Table 1, it was confirmed that, since the thermoelectric modules prepared in the examples had a high average bonding strength of 22 MPa and 39 MPa, they showed sufficient bonding properties compared to the thermoelectric modules of the comparative examples having a low bonding strength of 12 MPa, 10 MPa, 18 MPa, 11 MPa, and 6 MPa.

(32) Further, referring to Table 2, it was confirmed that, since the thermoelectric modules prepared in the examples had a low bonding layer resistivity of 61 μΩ.Math.cm, 76 μΩ.Math.cm, and 85μΩ.Math.cm or less at 50° C., 300° C., and 400° C., respectively, they showed excellent electrical conductivity compared to the thermoelectric modules of the comparative examples having high resistivity.

(33) Furthermore, it was confirmed that the thermoelectric modules of the examples had bonding layer thermal conductivity of 12.4 W/m.Math.k, 16.6 W/m.Math.k, and 17.2 W/m.Math.k or higher at 27° C., 300° C., and 400° C., respectively, which were higher thermal conductivities compared to the thermoelectric modules of the comparative examples.