JP3617506B2 - Thermoelectric module and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thermoelectric module in which a plurality of thermoelectric elements are connected in series or in parallel by a plurality of upper electrodes and a plurality of lower electrodes, and a method for manufacturing the same .
[0002]
[Prior art]
FIG. 4 is a diagram showing a conventional thermoelectric module 10. A plurality of P-type and N-type thermoelectric elements 11 are alternately arranged in one direction between the upper substrate 12 and the lower substrate 13. A plurality of upper electrodes 14 are formed on the lower surface of the upper substrate 12, and a plurality of lower electrodes 16 are formed on the upper surface of the lower substrate 13. A P-type thermoelectric element 11 and an N-type thermoelectric element 11 are arranged on one lower electrode 16, and are adjacent to the P-type thermoelectric element 11 on one lower electrode 16 and the one lower electrode 16. Each of the thermoelectric elements 11, the upper electrode 14, and the lower electrode 16 is connected to the adjacent N-type thermoelectric element 11 disposed on the lower electrode 16, by the upper electrode 14. The thermoelectric module 10 is assembled by joining the thermoelectric elements 11 to the upper electrode 14 and the lower electrode 16 with solders 15 and 17, respectively. Thus, P-type and N-type thermoelectric elements are alternately connected in series by the upper electrode 14 and the lower electrode 16.
[0003]
When a current is passed through the thermoelectric module in which the P-type and N-type thermoelectric elements are alternately connected in series, heat is generated or absorbed by the Peltier effect at the dissimilar metal connection portion. A thermoelectric module serving as the heat absorption side of the lower substrate 13 is configured.
[0004]
The solder 15 and 17 are prevented from diffusing into the thermoelectric element 11 on the joint end face with the electrode of the thermoelectric element 11, and the thermoelectric element is prevented from being deteriorated by long-time use. In order to improve the above, a nickel alloy plating film is formed. This nickel alloy plating film is generally formed by electroless plating a Ni-P alloy or a Ni-B alloy.
[0005]
[Problems to be solved by the invention]
However, in the above-described conventional thermoelectric module, in order to prevent the diffusion of solder, an electroless plating film of Ni-P or Ni-B alloy is formed between the thermoelectric element and the electrode. Because of the high resistivity of the electroless plating film, when each thermoelectric element is energized, resistance heat is generated in this plating film and the heat absorption side also generates heat. As a result, the performance as a thermoelectric module is the physical property of the thermoelectric element material. There is a problem that it falls below the theoretical value determined from Moreover, since the resistivity of the electroless plating film is high, even when a predetermined voltage is applied between the electrodes at the end of the series connection body when the series connection body of the thermoelectric element is energized, Due to the voltage drop, the potential difference applied to each thermoelectric element becomes low, and as a result, the efficiency of the current flowing through each thermoelectric element decreases. Due to these factors, the conventional thermoelectric module has a problem that the obtained thermoelectric characteristics are low.
[0006]
This invention is made | formed in view of this problem, Comprising: It aims at providing the thermoelectric module with low electrical resistance of the electrode junction end surface of a thermoelectric element, and high current efficiency, and its manufacturing method .
[0007]
[Means for Solving the Problems]
The method for manufacturing a thermoelectric module according to the first invention of the present application is a method for manufacturing a thermoelectric module in which a plurality of thermoelectric elements are connected in series or in parallel by a plurality of upper electrodes and a plurality of lower electrodes, and the temperature is 5 to 6 and the temperature is 5 to 6. Immersing in an electroless plating solution at 80 to 90 ° C. to form a nickel electroless plating film containing phosphorus or boron on the end face joined to the upper electrode or the lower electrode of the thermoelectric element; And a step of joining the nickel electroless plating film and the upper electrode or the lower electrode with solder. The main component of the plating solution is, for example, sodium hypophosphite and nickel sulfate, or a dimethylamine boron and nickel sulfate. The thermoelectric module according to the second invention of the present application is the thermoelectric module according to any one of claims 1 to 3, wherein a plurality of thermoelectric elements are connected in series or in parallel by a plurality of upper electrodes and a plurality of lower electrodes. The resistivity of the nickel electroless plating film obtained by the module manufacturing method and formed on the end face joined to the upper electrode or the lower electrode of the thermoelectric element is 10 to 60 μΩ · cm. .
[0008]
In this thermoelectric module, the nickel electroless plating film is, for example, a phosphorus-containing nickel-based alloy or a boron-containing nickel-based alloy. The nickel electroless plating film is preferably formed in a nickel electroless plating solution having a temperature of 80 to 90 ° C. and a basicity pH of 5 to 6.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 shows an enlarged portion of a thermoelectric element of a thermoelectric module 1 according to an embodiment of the present invention. The structure of the thermoelectric module itself is the same as that of the conventional thermoelectric module shown in FIG. That is, the thermoelectric module 1 is configured by sandwiching the thermoelectric element 3 between the upper substrate 6a and the lower substrate 6b. An upper electrode 2a is formed on the lower surface of the upper substrate 6a, and a lower electrode 2b is formed on the upper surface of the lower substrate 6b. Then, two thermoelectric elements 3 (P-type thermoelectric element and N-type thermoelectric element) are arranged for one upper electrode 2a and one lower electrode 2b, respectively. The arrangement of the thermoelectric element 3 and the upper electrode 2a and the lower electrode 2b is, for example, arranged so that the thermoelectric elements 3 are alternately connected in series with the P-type and the N-type, as in FIG. .
[0010]
Ni plating films 5a and 5b are formed on the electrode joint end faces of the thermoelectric elements 3, respectively. Between the plating films 5a and 5b and the upper electrode 2a and the lower electrode 2b, respectively, solder 4a, Joined by 4b. The plated films 5a and 5b prevent the components of the solder 4a and 4b from diffusing into the thermoelectric element 3 when the thermoelectric module is assembled or used, and improve the solderability of the thermoelectric element 3. is there.
[0011]
Examples of the constituent material of the thermoelectric element 3 include Bi-Te (bismuth-tellurium), Bi-Te-Sb (bismuth-tellurium-antimony). Further, an insulating substrate such as a ceramic substrate can be used as the upper substrate 6a and the lower substrate 6b. Examples of the ceramic substrate include alumina (Al ₂ O ₃ ) and aluminum nitride (AlN). Furthermore, examples of the solder 4a and 4b include SnSb and SnPb.
[0012]
Thus, in the present embodiment, the Ni plating films 5a and 5b are formed by electroless plating of Ni. The resistivity of the plating films 5a and 5b is 10 to 60 μΩ · cm. Since the conventional Ni plating film has a resistivity of 70 to 100 μΩ · cm , the resistance heat generation at the joint portion including the Ni plating film is large and the thermoelectric characteristics are deteriorated. Since the resistivity at 5a and 5b is 10 to 60 μΩ · cm, it is possible to avoid the influence of resistance heat generation at the joint including the plated films 5a and 5b.
[0013]
Such low resistivity electroless plating films 5a and 5b can be formed by appropriately setting the temperature and pH of the Ni electroless plating solution. When forming the Ni electroless plating films 5a and 5b on the joining end face of the thermoelectric element 3, first, the thermoelectric element 3 is degreased with an alkaline solution, washed with water, and then pickled with, for example, a 10% hydrochloric acid aqueous solution. Thereafter, it is washed with water, and a dilute hydrochloric acid solution of tin chloride or palladium chloride is alternately attached to the surface of the thermoelectric element 3 as a catalyst. Thereafter, the substrate is washed with water and immersed in a nickel electroless plating solution to perform Ni plating. For example, in the case of a phosphorus-containing nickel-based alloy, this Ni electroless plating solution is mainly composed of nickel sulfate and sodium hypophosphite. In the case of a boron-containing nickel-based alloy, nickel sulfate and dimethyl The main component is amine borane. In this case, conventionally, the temperature of the plating solution is 70 to 80 ° C. and the basicity pH is 4 to 5, and the resistivity of the plating film obtained by plating under these conditions is 70 to 100 μΩ · cm. However, in this embodiment, Ni is electrolessly plated under higher temperature and higher pH treatment conditions than before, that is, under conditions of a temperature of 80 to 90 ° C. and a basicity pH of 5 to 6. Thus, by adjusting the temperature and basicity pH of the plating solution, the resistivity of the obtained plating film can be made 10 to 60 μΩ · cm.
[0014]
Next, a method for measuring the resistivity of the Ni electroless plating film will be described. On the glass substrate, a Ni film serving as a plating nucleus is formed by sputtering to a thickness of about 0.1 μm. Thereafter, a Ni electroless plating film is formed on the Ni film by Ni electroless plating. The thickness of this Ni electroless plating film is about 4 μm. Then, the resistivity of the Ni electroless plating film is measured by a four-terminal method. Thereby, the resistivity of the plating film in the Ni electroless plating process conditions (the temperature of the plating solution, the basicity pH, etc.) is obtained.
[0015]
Therefore, in plating the thermoelectric element, Ni is electrolessly plated under a plating condition in which the resistivity obtained as described above is 10 to 60 μΩ · cm. Thereby, the electroless plating films 5 a and 5 b having a desired resistivity can be formed on the joining end face of the thermoelectric element 3.
[0016]
In the case of pure Ni, the resistivity is the lowest, but pure Ni cannot be formed by electroless plating. If an Ni film is formed by electroless plating, impurities or components such as P and B will enter. When a large amount of P and B are mixed as impurities, the resistivity exceeds 70 μΩ · cm as in the conventional case. However, by electroless plating under the conditions of the present invention, a Ni electroless plating film having a resistivity of 10 to 60 μΩ · cm can be formed.
[0017]
In FIG. 2, the horizontal axis represents the resistivity (μΩ · cm) of the Ni electroless plating film formed on the joining end face of the thermoelectric element, and the vertical axis represents ΔTmax of the thermoelectric module incorporating the thermoelectric element. It is a graph which shows the relationship. The symbol ○ indicates a case where a phosphorus-containing nickel-based (Ni-P-based) Ni plating film is formed, and the symbol ■ indicates a case where a boron-containing nickel-based (Ni-B-based) Ni plating film is formed. Both of the plating films have a thickness of 4 μm. In measuring ΔTmax, an electric current was applied so that the temperature difference generated by energizing the thermoelectric module was maximized. However, the end of the thermoelectric module on the low temperature side was kept at 27 ± 0.1 ° C. The thermoelectric module has a width of 6 mm, a length of 10.2 mm, and a thickness of 1.65 mm, and 29 pairs of thermoelectric elements are arranged on an alumina substrate. The thermoelectric element has a square shape with a side length of 0.64 mm and a thickness (height) of 0.8 mm.
[0018]
As shown in FIG. 2, when the resistivity is 60 μΩ · cm or less, ΔTmax is 70.0 K or more, indicating extremely excellent thermoelectric characteristics. On the other hand, when the resistivity is 70 μΩ · cm or more as in the prior art, ΔTmax of 70.0 K or more cannot be obtained.
[0019]
FIG. 3 is a graph showing the relationship between the thickness of the Ni plating film on the horizontal axis and ΔTmax on the vertical axis. The plating film is a Ni-P plating film, and the resistivity of the plating film is 30 μΩ · cm when the film thickness is 4 μm, and similarly, the resistivity is 85 μΩ · cm when the film thickness is 4 μm. Two types of thermoelectric elements were prepared. The plating process conditions are the same for the four data having a resistivity of 30 μΩ · cm, and the same for the 4 k data having a resistivity of 85 μΩ · cm. And (DELTA) Tmax was measured about the thermoelectric module incorporating this thermoelectric element. The sizes of the thermoelectric module and the thermoelectric element are the same as those in FIG.
[0020]
As shown in FIG. 3, ΔTmax was substantially constant regardless of the thickness of the Ni plating film, regardless of whether the resistivity was 30 or 85 μΩ · cm. As described above, the dependency of ΔTmax on the thickness of the Ni plating film is not recognized (when the plating film thickness is the smallest, ΔTmax is slightly higher) than the resistance of the plating film itself with respect to the thermoelectric characteristics. This is probably because the interface resistance between the thermoelectric element and the plating film and the interface resistance between the plating film and the solder are more influential. Note that the resistivity measured by the four probe method also includes the influence of the interface resistance as a result.
[0021]
As described above, as a result of reducing the interface resistance between the Ni electroless plating film, the thermoelectric element, and the solder, the thermoelectric module of the present embodiment can increase ΔTmax and improve the thermoelectric characteristics.
[0022]
【The invention's effect】
As described in detail above, according to the thermoelectric module of the present invention, attention is paid to the resistivity of the Ni electroless plating film formed in order to prevent solder diffusion and improve solderability on the joining end face of the thermoelectric element. However, by suppressing the resistivity low, the thermoelectric characteristics can be improved, and the thermoelectric characteristics, in particular, ΔTmax is significantly improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing a portion of a thermoelectric element in a thermoelectric module according to an embodiment of the present invention.
FIG. 2 is a graph showing the relationship between resistivity and ΔTmax.
FIG. 3 is a graph showing the relationship between the thickness of a Ni plating film and ΔTmax.
FIG. 4 is a diagram showing a structure of a conventional thermoelectric module.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1, 10: Thermoelectric module, 2a, 2b, 14, 16: Electrode, 3, 11: Thermoelectric element, 4a, 4b, 15, 17: Solder, 5a, 5b: Ni electroless plating film, 10: Thermoelectric module

Claims (4)

In a method for manufacturing a thermoelectric module in which a plurality of thermoelectric elements are connected in series or in parallel by a plurality of upper electrodes and a plurality of lower electrodes, the thermoelectric module is immersed in an electroless plating solution having a pH of 5 to 6 and a temperature of 80 to 90 ° C. Forming a nickel electroless plating film containing phosphorus or boron on an end face joined to the upper electrode or the lower electrode of the thermoelectric element; and the nickel electroless plating film and the upper electrode or the lower electrode. A method of manufacturing a thermoelectric module, comprising: joining each of them with solder. Method for manufacturing a thermoelectric module according to claim 1, the main component of the plating solution is characterized in that it is a sodium hypophosphite and nickel sulfate. The method for manufacturing a thermoelectric module according to claim 1, wherein the main components of the plating solution are dimethylamine boron and nickel sulfate. A thermoelectric module in which a plurality of thermoelectric elements are connected in series or in parallel by a plurality of upper electrodes and a plurality of lower electrodes, obtained by the method for manufacturing a thermoelectric module according to any one of claims 1 to 3, wherein A thermoelectric module characterized in that a resistivity of a nickel electroless plating film formed on an end face joined to the upper electrode or the lower electrode of an element is 10 to 60 μΩ · cm.

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