JP3539796B2 - Thermoelectric converter - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a thermoelectric conversion device such as an electronic cooling device or a thermoelectric generator, and more particularly, to a substrate and an electrode for supporting the electrode.
[0002]
[Prior art]
FIG. 7 is a partially enlarged sectional view of a conventional electronic cooling device. A heat-dissipation-side electrode 102 is provided on a heat-dissipation-side insulating substrate 100 made of alumina or the like via a solder layer 101, and a P-type semiconductor layer 103 and an N-type semiconductor layer 104 are disposed on the heat-dissipation electrode 102, respectively. I have. A heat-absorbing electrode 105 is provided so as to connect the P-type semiconductor layer 103 and the N-type semiconductor layer 104, and a heat-absorbing insulating substrate 107 is further provided thereon via a solder layer 106.
[0003]
A large number of the P-type semiconductor layers 103 and the N-type semiconductor layers 104 are provided in parallel between the heat-radiating electrode 102 and the heat-absorbing electrode 105 in pairs, and are electrically connected in series and thermally connected in parallel. It constitutes an electronic cooling element group.
[0004]
By passing a predetermined current through this group of electronic cooling elements, heat is absorbed on the heat absorbing side insulating substrate 107 side, and the surrounding area is cooled. The heat deprived by this heat absorption is radiated on the heat-radiating-side insulating substrate 100 side, and is radiated to the outside by radiating fins or a fan (not shown), whereby heat transfer occurs.
[0005]
[Problems to be solved by the invention]
By the way, conventional thermoelectric converters do not have a sufficient service life, and as they are used repeatedly, the thermoelectric conversion efficiency such as cooling efficiency deteriorates. Sufficient power could not be obtained despite the temperature not dropping or the temperature difference.
[0006]
As a result of intensive studies on this problem, the present inventors have clarified that there is a problem in the configuration of the thermoelectric conversion device. That is, in the conventional thermoelectric conversion device, the insulating substrates 100 and 107 made of ceramics such as alumina are integrally joined to the metal electrodes 102 and 105 by the solder layers 101 and 106.
[0007]
The insulating substrates 100 and 107 made of ceramic and the solder layers 101 and 106 (electrodes 102 and 105 and the semiconductor layers 103 and 104) made of metal have significantly different coefficients of thermal expansion (shrinkage). (That is, if the temperature histories of cold and warm are repeated), the insulating substrates 100 and 107 are deformed such as warpage. Then, a fatigue phenomenon occurs at the boundary between the solder layers 101 and 106 and the electrodes 102 and 105 with the P-type semiconductor layer 103 and the N-type semiconductor layer 104, so that the thermal resistance becomes large, resulting in poor connection or disconnection. This has been a factor in shortening the useful life of the thermoelectric converter.
[0008]
In addition, the insulating substrates 100 and 107 made of ceramic also have high thermal resistance, and deformation such as warping occurs during molding or sintering. The resistance increases.
[0009]
Further, since the insulating substrates 100 and 107 made of ceramic are mechanically fragile, they have defects such as chipping and cracking during handling in a manufacturing process and the like, and poor yield.
[0010]
Conventionally, a method of manufacturing a thermoelectric conversion device as described in Japanese Patent Publication No. 40-11577 has been proposed. In this method, a metal heat conductor such as aluminum is immersed in an electrolyte such as oxalic acid to form an anodic oxide film on the surface. Then, the oxide film is sealed with boiling water or steam for a short time (within 2 minutes), and an electrode is formed on the sealed oxide film by electroplating.
[0011]
However, a substrate in which this anodic oxide film has been subjected to sealing treatment has a low bonding strength with an electrode formed thereon, so that the electrode often peels off from the substrate, which is not practical.
[0012]
SUMMARY OF THE INVENTION An object of the present invention is to provide a thermoelectric conversion device which solves such drawbacks of the prior art, has a good thermoelectric conversion efficiency, and has a long service life.
[0013]
[Means for Solving the Problems]
To achieve the above object , the present invention provides:
For example, on at least one surface of a metal substrate such as aluminum, for example, an oxide insulating film made of, for example, alumite having a large number of pores by anodization or the like is formed, and for example, nickel is formed in the pores without sealing the pores. A metal for bonding such as copper or copper is filled to impart conductivity to the surface of the oxide insulating film, and an electrode made of, for example, nickel or copper is bonded on the oxide insulating film.
[0015]
[Action]
According to the present invention, the heat resistance of the substrate itself can be reduced because the metal substrate on which the insulating film is formed is used instead of using the insulating substrate made of a ceramic such as alumina as in the related art. .
[0016]
This metal base material does not significantly differ from the thermal expansion (shrinkage) coefficient of the solder layer, electrode, semiconductor layer, etc., so even if the thermoelectric conversion device is used repeatedly, the substrate may be deformed or the solder layer, electrode, etc. may become fatigued. Does not occur, the thermal resistance can be kept low, and the useful life of the thermoelectric converter can be extended.
[0017]
Further, in the case of an insulating substrate made of ceramic, deformation such as warpage occurs when molded or sintered, and thus the adhesion with a heat conductor is deteriorated. There is no problem and the adhesion to the heat conductor is always good.
[0018]
In addition, the pores in the insulating film are filled with a bonding metal without sealing treatment, and the electrodes are bonded on top of them, so the bonding strength between the substrate and the electrodes must be increased. Can be.
[0020]
【Example】
Next, an embodiment of the present invention will be described with reference to the drawings.
(First embodiment)
The aluminum substrate was immersed in an electrolytic solution consisting of a 0.5% by weight oxalic acid solution, and anodized at a bath temperature of 20 ° C. and a constant voltage of 100 V for 5 minutes to form an aluminum plate as shown in FIG. An insulating film 2 having a thickness of about 10 μm is formed on a substrate 1.
[0021]
Then, the aluminum substrate 1 is immersed in a 5% by weight phosphoric acid solution (solution temperature: 30 ° C.) for a certain period of time to expand the diameter of the fine holes formed in the insulating film 2.
[0022]
The expanded aluminum substrate 1 is immersed in a hydrochloric acid tin chloride solution for 1 to 10 minutes, washed with water, and left standing in distilled water for 10 to 30 minutes to complete the sensitization process. Next, it is immersed in a lead chloride solution for 5 minutes, washed with water, and left standing in distilled water for 10 to 30 minutes to complete the activation treatment.
[0023]
After the sensitization treatment and the pretreatment for the activation treatment are performed in this way, the substrate is immersed in an electroless plating bath having the following composition.
NiSO ₄ .6H ₂ O 2.5% by weight
NaPH ₂ O ₂ · H ₂ O 5.0% by weight
_{Na 4 P 2 O 7 · 10H} 2 O 2.5 wt%
pH value 11 (adjusted with ammonia water)
Bath temperature 40 ° C
By performing the electroless plating in this manner, nickel is deposited and filled in the micropores in the insulating film 2 to impart conductivity to the surface of the insulating film 2.
[0024]
Next, as shown in FIG. 1B, a copper conductive film 3 having a thickness of about 0.3 to 50 μm is formed by electroplating on an insulating film 2 having a surface provided with conductivity according to a conventional method. As shown in FIG. 3C, unnecessary portions of the conductive film 3 are removed and patterned by a technique such as photolithography.
[0025]
In the case of a thermoelectric converter in which a small current flows during driving, the patterned conductive film 3 can be used as an electrode as it is, and P and N semiconductor layers can be provided thereon. As shown in FIG. 3D, a relatively thick electrode 4 having a thickness of about 200 to 1000 μm is joined by soldering onto the patterned conductive film 3 as shown in FIG.
[0026]
FIG. 2 is an enlarged cross-sectional view of a portion X in FIG. 1D, in which pores 5 formed in the insulating film 2 are filled with a bonding metal (Ni in the case of the present embodiment) 6, and irregularities are formed. It is in close contact with the peripheral wall surface of the formed pores 5 and is also in close contact with the conductive film 3, thereby increasing the bonding strength between the substrate 1 and the conductive film 3.
[0027]
(Example 2)
FIG. 3 is a cross-sectional view of an aluminum substrate 1 according to the second embodiment, in which a high purity aluminum (for example, a purity of 97%) is formed on a base material 1a made of inexpensive aluminum or an aluminum alloy having a relatively low purity (for example, 97%). (99.99%) is joined by means such as cladding or thermal spraying. If the overall thickness of the substrate 1 is 3 mm, the thickness of the anodizing thin layer 1b is sufficient to be 0.3 mm, which is 10% of the thickness.
[0028]
An insulating film 2 by anodic oxidation is formed on the anodic oxidation thin layer 1b in the same manner as in Example 1, and a patterned conductive film 3 and electrodes 4 are provided.
[0029]
(Example 3)
FIGS. 4A and 4B are diagrams for explaining the third embodiment. As shown in FIG. 4A, aluminum or aluminum alloy having relatively low purity (eg, 97% purity) is used. A high purity (for example, 99.99% purity) aluminum particles 7 are sintered to a predetermined thickness (for example, about 0.2 to 1 mm) by, for example, a plasma sintering method on the base material 1a to be A sintered layer 8 having countless irregularities and having countless grain boundaries therein is formed.
[0030]
Then, as shown in FIG. 3B, an insulating film 2 is formed on the sintered layer 8 by anodic oxidation in the same manner as in the first embodiment, and a pattern is formed on the insulating film 2 (not shown). The patterned conductive film 3 and electrode 4 are sequentially formed.
[0031]
(Example 4)
FIGS. 5A and 5B are views for explaining the fourth embodiment. As shown in FIG. 5A, the surface of a base material 1a made of aluminum is etched by a mechanical method such as a sand blast method or etched. The rough surface 9 is formed by a chemical method such as the above. Then, as shown in FIG. 3B, an insulating film 2 by anodic oxidation is formed on the rough surface 9 having a myriad of fine irregularities as shown in FIG. A patterned conductive film 3 and an electrode 4 are sequentially formed thereon.
[0032]
(Example 5)
6 (a) to 6 (d) are views for explaining Example 5, and as shown in FIG. 6 (a), the surface of a substrate 1a made of aluminum is heated to be soft, Is embedded in the vicinity of the surface by applying high pressure to hard particles 10 of about 50 to 150 μm made of alumina, aluminum nitride, or the like. By embedding the hard particles 10, the surface of the substrate 1a is slightly raised.
[0033]
Next, as shown in FIG. 3B, only the hard particles 10 are eluted from the substrate 1a without eroding the substrate 1a to make the surface of the substrate 1a rough, and as shown in FIG. The insulating film 2 is formed on the rough surface 9 by anodic oxidation in the same manner as in the first embodiment.
[0034]
Thereafter, as shown in FIG. 2D, a layer of the bonding metal 6 is formed on the insulating film 2 by electroless plating, and the pores in the insulating film 2 are filled with the bonding metal 6 (Ni). At least, although not shown, the patterned conductive film 3 and the electrode 4 are sequentially formed on the bonding metal 6.
[0040]
In Examples 1 to 5, the oxalic acid method was used as the anodic oxidation method. However, the present invention is not limited to this method. For example, other anodic oxidation methods such as a sulfuric acid method, a hard anodic oxidation method, and a chromic acid method. It is also possible to apply
[0041]
In the above embodiment, the case of the electronic cooling device has been described, but the present invention is also applicable to a thermoelectric generator.
[0042]
【The invention's effect】
According to the first aspect of the present invention, since the metal substrate on which the insulating film is formed is used instead of using the insulating substrate made of ceramic such as alumina as in the related art, the thermal resistance as the substrate itself is reduced. Can be lower.
[0043]
This metal base material does not significantly differ from the thermal expansion (shrinkage) coefficient of the solder layer, electrode, semiconductor layer, etc., so even if the thermoelectric conversion device is used repeatedly, the substrate may be deformed or the solder layer, electrode, etc. may become fatigued. Does not occur, the thermal resistance can be kept low, and the useful life of the thermoelectric converter can be extended.
[0044]
Further, in the case of an insulating substrate made of ceramic, deformation such as warpage occurs when molded or sintered, and thus the adhesion with a heat conductor is deteriorated. There is no problem and the adhesion to the heat conductor is always good.
[0045]
In addition, the pores in the insulating film are filled with a bonding metal without sealing treatment, and the electrodes are bonded on top of them, so the bonding strength between the substrate and the electrodes must be increased. Can be.
[0047]
Further, as claimed in claim 4, wherein, if it is composed of an oxide film of high-purity metal oxide insulating film is substantially free of impurities (e.g., purity of 99.99 wt%), a high electric insulation even in extremely thin And reliability can be improved.
[0049]
As described above, a thermoelectric conversion device having good thermoelectric conversion efficiency and a long service life can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a manufacturing process of a substrate according to a first embodiment of the present invention.
FIG. 2 is an enlarged sectional view of a portion X in FIG. 1 (d).
FIG. 3 is a sectional view of a substrate used in a second embodiment of the present invention.
FIG. 4 is a cross-sectional view illustrating a step of manufacturing a substrate according to Example 3 of the present invention.
FIG. 5 is a cross-sectional view illustrating a step of manufacturing a substrate according to Example 4 of the present invention.
FIG. 6 is a cross-sectional view illustrating a step of manufacturing a substrate according to Example 5 of the present invention.
FIG. 7 is a partially enlarged cross-sectional view of a conventional electronic cooling device.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 aluminum substrate 1a base material 1b thin layer for anodizing 2 insulating film 3 conductive film 4 electrode 5 pore 6 bonding metal 7 aluminum particle 8 sintered layer 9 rough surface 10 hard particle 11 electrode body 12 insulating layer 13 for solder bonding Metal layer 14 Laminated electrode 14a Heat absorbing side laminated electrode 14b Radiation side laminated electrode 15 Cooling side heat conductor 16 Radiation side heat conductor 17 P-type semiconductor layer 18 N-type semiconductor layer

Claims (4)

An oxide insulating film having a large number of pores is formed on at least one surface of the metal substrate, and the pores are filled with a bonding metal in the pores without sealing to impart conductivity to the surface of the oxide insulating film. A thermoelectric conversion device wherein electrodes are bonded on the oxide insulating film. 2. The thermoelectric conversion device according to claim 1, wherein a conductive film is patterned on the oxide insulating film provided with the conductivity, and the electrode is bonded on the conductive film . 2. The thermoelectric conversion device according to claim 1, wherein a conductive film is patterned on the conductive oxide insulating film, and the conductive film is used as the electrode . 2. The thermoelectric conversion device according to claim 1, wherein the oxide insulating film is formed of a high-purity metal oxide film containing almost no impurities.

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