Thermoelectric conversion module

Abstract

To provide a thermoelectric conversion module in which residual voids in a solder material layer are suppressed and bonding of a thermoelectric conversion material chip to an electrode is improved.SOLUTION: A thermoelectric conversion module in which the chips of a P-type thermoelectric conversion material and the chips of an N-type thermoelectric conversion material, which are alternately spaced apart, are joined to electrodes via a solder material includes wall structures spaced apart from each other and arranged outside the entire perimeter of the regions on the electrode that are joined to the chips of the P-type thermoelectric conversion material and the chips of the N-type thermoelectric conversion material, and a distance between at least one wall surface among the inner wall surfaces of the wall structure and each side surface of the chip of the P-type thermoelectric conversion material and the chip of the N-type thermoelectric conversion material facing and closest to the wall surface is 1 μm or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a thermoelectric conversion module.

Background Art

[0002] Conventionally, as one means for effectively using energy, there has been an apparatus that directly converts thermal energy and electrical energy with a thermoelectric conversion module having a thermoelectric effect such as the Seebeck effect or the Peltier effect. As the thermoelectric conversion module, the use of a so-called π-type thermoelectric conversion element is known. The π-type is configured by providing a pair of electrodes spaced apart from each other on a substrate, for example, a P-type thermoelectric element on one electrode and an N-type thermoelectric element on the other electrode, also spaced apart from each other, and connecting the upper surfaces of both thermoelectric elements to an electrode on a substrate facing each other. In such a case, in the manufacture of the thermoelectric conversion module, usually, a P-type thermoelectric element and an N-type thermoelectric element are respectively joined to the electrodes on the substrate via a joining material independently. When using a solder material or the like as the joining material, during joining by heating such as reflow, the P-type thermoelectric element and the N-type thermoelectric element are not fixed on the molten solder and exist in an unstable state respectively. At that time, since the molten solders flow due to surface tension or the like, the P-type thermoelectric element and the N-type thermoelectric element are respectively displaced, and there is a possibility that the adjacent side surfaces of the P-type thermoelectric element and the N-type thermoelectric element that should not be electrically joined come close or contact each other and a short circuit occurs. As a configuration of a thermoelectric conversion module (thermoelectric conversion device) for solving this problem, for example, as shown in FIG. 2 of Patent Document 1, a resin such as an epoxy resin is provided between the side surfaces of a pair of adjacent P-type thermoelectric conversion elements and N-type thermoelectric conversion elements on a common electrode.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the resin in the configuration of the thermoelectric conversion module (thermoelectric conversion device) of Patent Document 1 is provided after forming both types of thermoelectric conversion elements. Even if it is provided before forming both types of thermoelectric conversion elements, when joining both types of thermoelectric conversion elements to the electrodes via a soldering material by reflow or the like, since both types of thermoelectric conversion elements are in direct contact with the resin, a large number of voids remain in the soldering material layer, and the joinability with the electrodes becomes insufficient. As a result, the thermoelectric performance may decrease.

[0005] The present invention has been made in view of such circumstances, and an object thereof is to provide a thermoelectric conversion module in which residual voids in the soldering material layer are suppressed and the joinability of the chip of the thermoelectric conversion material to the electrode is improved.

Means for Solving the Problems

[0006] As a result of intensive studies to solve the above problems, the present inventors have found that in the joining of the chip of the thermoelectric conversion material and the electrode via a soldering material that constitutes the thermoelectric conversion module, at least one wall surface inside the mutually spaced wall structures arranged outside the entire circumference of each region joined to the chip of the P-type thermoelectric conversion material and the chip of the N-type thermoelectric conversion material on the electrode, and the side surfaces of the chip of the P-type thermoelectric conversion material and the chip of the N-type thermoelectric conversion material are set to specific values, thereby suppressing residual voids in the soldering material layer during joining by reflow and improving the joinability of the chip of the thermoelectric conversion material to the electrode, and completed the present invention. That is, the present invention provides the following [1] to [5]. [1] A thermoelectric conversion module in which chips of a P-type thermoelectric conversion material and chips of an N-type thermoelectric conversion material that are alternately spaced apart are each joined to an electrode via a soldering material, Each is provided with a spaced-apart wall structure disposed outside the entire perimeter of each region on the electrode that joins the chip of the P-type thermoelectric conversion material and the chip of the N-type thermoelectric conversion material. A thermoelectric conversion module, wherein the distance between at least one of the inner wall surfaces of the wall structure and the side surfaces of the chip of the P-type thermoelectric conversion material and the chip of the N-type thermoelectric conversion material that face and are closest to the wall surface is 1 μm or more. [2] The thermoelectric conversion module according to [1] above, wherein the shape of the wall structure is independently selected from a hollow rectangular parallelepiped shape and a hollow cylindrical shape. [3] The thermoelectric conversion module according to [1] or [2] above, wherein the material of the wall structure is selected from an acrylic resin, an epoxy resin, a urethane resin, and a polyimide resin. [4] The thermoelectric conversion module according to any one of [1] to [3] above, wherein the height of the wall structure in the thickness direction of the electrode is 1 to 25 μm higher than the height of the bottom surfaces of the chips of the P-type thermoelectric conversion material and the N-type thermoelectric conversion material in the thickness direction of the electrode. [5] The thermoelectric conversion module according to any one of [1] to [4] above, wherein the shape of the inner wall surface of the wall structure follows the shape of each of the side surfaces of the chip of the P-type thermoelectric conversion material and the chip of the N-type thermoelectric conversion material. [Advantages of the Invention]

[0007] According to the present invention, it is possible to provide a thermoelectric conversion module in which residual voids in the solder material layer are suppressed and the bonding property of the chips of the thermoelectric conversion material to the electrodes is improved. [Brief Description of the Drawings]

[0008]

Figure 1

Figure 2

Figure 3

[0009] [Thermoelectric Conversion Module] The thermoelectric conversion module of the present invention is a thermoelectric conversion module in which chips of P-type thermoelectric conversion materials and chips of N-type thermoelectric conversion materials that are alternately spaced apart are each joined to an electrode via a solder material, and are each provided with a wall structure that is spaced apart from each other and is disposed outside the entire periphery of each region that joins the chip of the P-type thermoelectric conversion material and the chip of the N-type thermoelectric conversion material on the electrode, and the distance between at least one of the inner wall surfaces of the wall structure and the side surfaces of the chip of the P-type thermoelectric conversion material and the chip of the N-type thermoelectric conversion material that face and are closest to the wall surface is 1 μm or more. In the thermoelectric conversion module of the present invention, in the joining of the chip of the thermoelectric conversion material to the electrode through the solder material that constitutes the thermoelectric conversion module, each of the joining regions that joins the chip of the P-type thermoelectric conversion material and the chip of the N-type thermoelectric conversion material on the electrode is provided with a wall structure that is spaced apart from each other and is disposed outside the entire periphery of each joining region, and the distance between at least one of the inner wall surfaces of the wall structure and the side surfaces of the chip of the P-type thermoelectric conversion material and the chip of the N-type thermoelectric conversion material that face and are closest to this wall surface is set to 1 μm or more. As a result, when joining the chip of the thermoelectric conversion material to the electrode by reflow, voids generated in the solder material layer can easily escape from the gap between the inner wall surface of the wall structure and the side surface of the chip of the thermoelectric conversion material to the external space, and residual voids can be significantly suppressed. Thereby, the joining interface between the chip of the thermoelectric conversion material and the electrode becomes good, and the joinability of the chip of the thermoelectric conversion material can be improved. In this specification, "chips of P-type thermoelectric conversion material and chips of N-type thermoelectric conversion material" may sometimes be simply referred to as "chips of thermoelectric conversion material". Also, the "bottom surfaces of the chips of P-type thermoelectric conversion material and chips of N-type thermoelectric conversion material" and the "top surfaces of the chips of P-type thermoelectric conversion material and chips of N-type thermoelectric conversion material" mean the surfaces where the chips of P-type thermoelectric conversion material and chips of N-type thermoelectric conversion material are in contact with the solder material (layer). These "bottom surface" and "top surface" naturally mean the opposing surfaces of the chips of thermoelectric conversion material. Furthermore, the "bottom surface" and "top surface" may sometimes be referred to as "one surface" and "the other surface" of the chips of P-type thermoelectric conversion material and chips of N-type thermoelectric conversion material.

[0010] The thermoelectric conversion module of the present invention includes a thermoelectric conversion module having a π-type thermoelectric conversion element configuration.

[0011] FIG. 1 is a cross-sectional configuration diagram for explaining an example of the configuration of the thermoelectric conversion module of the present invention. The thermoelectric conversion module 1 is composed of π-type thermoelectric conversion elements and has substrates 2a and 2b facing each other. A solder material layer 5a' is included between an electrode 3a formed on the substrate 2a and one surface of each of the chip 4p of P-type thermoelectric conversion material and the chip 4n of N-type thermoelectric conversion material. Also, a solder material layer 5b' is included between an electrode 3b formed on the substrate 2b and the other surface of each of the chip 4p of P-type thermoelectric conversion material and the chip 4n of N-type thermoelectric conversion material. Furthermore, a wall structure 7a and a wall structure 7b are provided on the electrodes 3a and 3b in this order, and inner wall surfaces 7ai of the wall structure 7a and inner wall surfaces 7bi of the wall structure 7b are provided at a specific distance from the side surfaces of each of the chip 4p of P-type thermoelectric conversion material and the chip 4n of N-type thermoelectric conversion material. Note that 7a' is the depth side portion of the wall structure 7a, 7b' is the depth side portion of the wall structure 7b, and 8 indicates the space between the wall structures.

[0012] (Wall structure) The thermoelectric conversion module of the present invention is each provided with wall structures spaced apart from each other outside the entire periphery of each region on the electrodes that joins with the chip of P-type thermoelectric conversion material and the chip of N-type thermoelectric conversion material. By providing spaced-apart wall structures outside the entire perimeters of the regions on the electrodes that are joined to the chips of the thermoelectric conversion material, the displacement of the chips of the thermoelectric conversion material due to the flow of molten solder during joining is more easily suppressed by the presence of the wall structures, and the bottom surfaces of the chips of the thermoelectric conversion material are more easily and accurately joined to the electrodes via the molten solder.

[0013] The distance between at least one of the inner wall surfaces of the wall structure and the side surfaces of the chips of the P-type thermoelectric conversion material and the N-type thermoelectric conversion material that face and are closest to the wall surface (hereinafter sometimes referred to as the "distance between the side surface of the chip of the thermoelectric conversion material and the inner wall surface of the wall structure") is 1 μm or more. When the distance between the side surface of the chip of the thermoelectric conversion material and the inner wall surface of the wall structure is less than 1 μm, when joining the chip of the thermoelectric conversion material and the electrode by reflow, voids generated in the solder material layer are less likely to escape from the gap between the inner wall surface of the wall structure and the side surface of the chip of the thermoelectric conversion material to the external space, and residual voids are more likely to be maintained. The distance between the side surface of the chip of the thermoelectric conversion material and the inner wall surface of the wall structure is preferably 5 μm or more, more preferably 5 to 80 μm, still more preferably 8 to 70 μm, and particularly preferably 10 to 65 μm. When the distance between the side surface of the chip of the thermoelectric conversion material and the inner wall surface of the wall structure is within this range, when joining the chip of the thermoelectric conversion material and the electrode by reflow, voids generated in the solder material layer are more likely to escape from the gap between the inner wall surface of the wall structure and the side surface of the chip of the thermoelectric conversion material to the external space, residual voids can be efficiently suppressed, the joining interface between the chip of the thermoelectric conversion material and the electrode becomes good, and the joinability of the chip of the thermoelectric conversion material can be improved. Note that the residual voids in the present invention are not particularly limited, but can be evaluated, for example, by the residual void ratio defined in the section of <Evaluation of the Residual Void Ratio in the Solder Material Layer> of the examples described later. Also, the residual void ratio is about 5 to 10% in the case of the conventional manufacturing method when there is no barrier such as the wall structure used in the present invention.

[0014] FIG. 2 is a diagram for explaining an example of the shape and arrangement of the wall structure provided on the electrode used in the present invention. (a) is a plan view showing the state after the wall structure is provided on the electrode. The inner wall surface 7i of the wall structure 7 is arranged at a position separated by a specific distance from the entire circumference of the bonding region 6p of the P-type thermoelectric conversion material chip and the bonding region 6n of the N-type thermoelectric conversion material chip on the electrode 3. There is a space 8 between the wall structures 7. (b) is a cross-sectional view taken along the line A-A' in (a), and includes the wall structure 7 (the wall structure 7' (depth side portion)) on the electrode 3.

[0015] The shape of the wall structure is not particularly limited, and each is independently selected as appropriate from the relationship with the shape of the chip of the thermoelectric conversion material, such as a hollow polygonal shape typified by a hollow rectangular parallelepiped shape, a hollow irregular shape, a hollow cylindrical shape, a hollow elliptical shape, etc. Among these, from the viewpoints of ease of manufacturing, versatility, and high integration, a hollow rectangular parallelepiped shape and a hollow cylindrical shape are preferable.

[0016] The material of the wall structure is not particularly limited, but from the viewpoint of contacting the solder material, a solder resist is preferable. As the solder resist, preferably, it is selected from an acrylic resin, an epoxy resin, a urethane resin, and a polyimide resin. Among these, from the viewpoint of heat resistance, an epoxy resin and a polyimide resin are more preferable. The method for forming the wall structure is not particularly limited and can be formed by a known method. For example, a method of processing the wall structure by a known physical treatment or chemical treatment mainly using a photolithography method, or a combination thereof, on the electrode described later, or a method of directly forming the wall structure by a screen printing method, a stencil printing method, an inkjet method, etc. can be mentioned.

[0017] The height of the wall structure is not particularly limited, but is appropriately adjusted according to the thickness of the chip of the thermoelectric conversion material, the thickness of the solder material layer, etc. Usually, it is 1 to 100 μm, preferably 15 to 50 μm. When the height of the wall structure is within this range, manufacturing is easy and stability is high.

[0018] (Bonding of the chip of the thermoelectric conversion material to the electrode) The joining of the thermoelectric conversion material chip to the electrode will be described with reference to the drawings.

[0019] Figure 3 is a schematic cross-sectional view showing an example of the state before and after joining the chip of the thermoelectric conversion material to the electrode via the wall structure and the solder material layer used in the present invention. (a) is a cross-sectional view showing a mode of joining one surface of the chip of the thermoelectric conversion material to the electrode. One surface 9a of each of the P-type thermoelectric conversion material chip 4p and the N-type thermoelectric conversion material chip 4n is placed on the solder material layer (before heating and cooling) 5a along the inner wall surface 7ai of the wall structure 7a provided on the electrode 3a. Note that 7a' is the wall structure (depth side portion), and 8 indicates the space between the wall structures. (b) is a cross-sectional view showing the state after further heating and cooling the solder material layer after placing one surface of the chip of the thermoelectric conversion material. By becoming the state of the solder material layer 5a' after solidification after heating and cooling, the side surfaces of the P-type thermoelectric conversion material chip 4p and the N-type thermoelectric conversion material chip 4n are joined to the electrode 3a while maintaining the distance from the inner wall surface 7ai of the corresponding wall structure 7a, and the voids generated in the solder material layer 5a' efficiently escape to the external space from the gap between the inner wall surface 7ai of the wall structure 7a and the side surface of the thermoelectric conversion material chip, and the residual voids are significantly suppressed. (c) is a cross-sectional view showing a mode of joining the other surface of the chip of the thermoelectric conversion material to the electrode. One surface 9b of each of the P-type thermoelectric conversion material chip 4p and the N-type thermoelectric conversion material chip 4n is placed on the solder material layer (before heating and cooling) 5b along the inner wall surface 7bi of the wall structure 7b provided on the electrode 3b. Note that 7a' indicates the wall structure (depth side portion). (d) is a cross-sectional view showing the state after placing the other surface of the chip of the thermoelectric conversion material and further heating and cooling the solder material layer. By being in the state of the solder material layer 5b' after solidification upon heating and cooling, it is joined to the electrode 3b while maintaining the distance between the side surfaces of the chip 4p of the P-type thermoelectric conversion material and the chip 4n of the N-type thermoelectric conversion material, and the inner wall surface 7bi of the corresponding wall structure 7b. At the same time, voids generated in the solder material layer 5b' efficiently escape to the external space from the gap between the inner wall surface 7bi of the wall structure 7b and the side surface of the chip of the thermoelectric conversion material, and residual voids are significantly suppressed. 7b' indicates the wall structure (depth side part).

[0020] It is preferable that the height of the wall structure in the thickness direction of the electrode is 0 μm or more higher than the height of the bottom surfaces of the chip of the P-type thermoelectric conversion material and the chip of the N-type thermoelectric conversion material in the thickness direction of the electrode, more preferably 1 μm or more higher, still more preferably 1 to 25 μm higher, and even more preferably 1 to 20 μm higher. When the difference between the height of the wall structure and the height of the bottom surface of the chip of the thermoelectric conversion material is within this range, displacement of the chip of the thermoelectric conversion material due to the flow of molten solder during joining is likely to be suppressed by the presence of the wall structure, and the bottom surfaces of the chip of the P-type thermoelectric conversion material and the chip of the N-type thermoelectric conversion material are likely to be accurately joined to the electrode via the molten solder. Note that the "height in the thickness direction of the electrode" means the distance from the electrode surface to the upper surface of the wall structure and the distance from the electrode surface to the bottom surface of the chip of the thermoelectric conversion material when a perpendicular line is dropped on the electrode surface and the intersection point with the electrode surface is set to 0. Also, the wall structure may be provided on both the upper and lower electrode substrates constituting the thermoelectric conversion module, or may be provided only on one of the electrode substrates. When the wall structure is provided on both the upper and lower electrode substrates, it is necessary to set the height of the wall structure such that the wall structures provided on the upper and lower electrode substrates do not interfere with each other.

[0021] It is preferable that the shape of the inner wall surface of the wall structure follows the shape of each side surface of the chip of the P-type thermoelectric conversion material and the chip of the N-type thermoelectric conversion material. When the shape of the inner wall surface of the wall structure follows the shape of the side surface of the chip of the thermoelectric conversion material, it becomes easier to suppress the positional deviation of the chip of the thermoelectric conversion material in the rotational direction.

[0022] (Electrode) Examples of the metal material of the electrode of the thermoelectric conversion module used in the present invention include gold, nickel, aluminum, rhodium, platinum, chromium, palladium, stainless steel, molybdenum, or an alloy containing any of these metals. In addition to the metal material, a paste material containing a solvent and a resin component may be used for formation. When using a paste material, it is preferable to remove the solvent and resin component by firing or the like. As the paste material, silver paste and aluminum paste are preferable. The firing temperature is usually 100 to 280 °C for 0.5 to 2 hours.

[0023] The electrode is formed using the above-mentioned metal material of the electrode. As a method for forming the electrode, on a substrate, a known physical treatment or chemical treatment mainly based on the photolithography method, or a method of processing into a predetermined pattern shape by using them in combination, or a method of directly forming a pattern of the electrode layer by the screen printing method, stencil printing method, inkjet method, etc. can be mentioned. Examples of the method for forming an electrode without a pattern include PVD (physical vapor deposition method) such as vacuum evaporation method, sputtering method, ion plating method, or CVD (chemical vapor deposition method) such as thermal CVD, atomic layer deposition (ALD), etc., or various coating methods such as dip coating method, spin coating method, spray coating method, gravure coating method, die coating method, doctor blade method, and wet processes such as electrodeposition method, silver salt method, electrolytic plating method, electroless plating method, lamination of metal foil, etc., which are appropriately selected according to the material of the substrate. The thickness of the electrode layer is preferably 10 nm to 200 μm, more preferably 30 nm to 150 μm, and even more preferably 50 nm to 120 μm. If the thickness of the electrode layer is within the above range, the electrical conductivity is high and the resistance is low, and sufficient strength as an electrode can be obtained.

[0024] (Substrate) The substrate on which the electrode is formed is not particularly limited, and known substrates such as glass substrates, silicon substrates, ceramic substrates, and resin substrates can be used. From the viewpoints of flexibility and thinness, it is preferable to use a plastic film (resin substrate). Among them, from the viewpoints of excellent flexibility and the ability to maintain the performance of the thermoelectric conversion module without thermal deformation of the substrate even when the thin film composed of the thermoelectric semiconductor composition is annealed, and high heat resistance and dimensional stability, as the plastic film, polyimide film, polyamide film, polyetherimide film, polyaramide film, and polyamideimide film are preferable, and further, from the viewpoint of high versatility, polyimide film is particularly preferable.

[0025] The thickness of the plastic film is preferably 1 to 1000 μm, more preferably 10 to 500 μm, and even more preferably 20 to 100 μm from the viewpoints of flexibility, heat resistance, and dimensional stability. Further, the plastic film preferably has a 5% weight loss temperature measured by thermogravimetric analysis of 300 °C or higher, and more preferably 400 °C or higher. The heating dimensional change rate measured at 200 °C in accordance with JIS K7133 (1999) is preferably 0.5% or less, and more preferably 0.3% or less. The linear expansion coefficient in the plane direction measured in accordance with JIS K7197 (2012) is 0.1 ppm·°C -1 ~50 ppm·°C -1 and is preferably 0.1 ppm·°C -1 ~30 ppm·°C -1 and more preferably is.

[0026] (Solder material layer) As a bonding material used for bonding an electrode with a chip of a P-type thermoelectric conversion material and a chip of an N-type thermoelectric conversion material, a solder material is used. The solder material is not particularly limited. However, as a solder material having a relatively low melting point, from the viewpoints of being lead-free and / or cadmium-free, for example, Sn-In-based In52Sn48 [melting temperature: solidus temperature (about 119°C), liquidus temperature (about 119°C)], Sn-Bi-based Bi58Sn42 [melting temperature: solidus temperature (about 139°C), liquidus temperature (about 139°C)], Sn-Zn-Bi-based Sn89Zn8Bi3 [melting temperature: solidus temperature (about 190°C), liquidus temperature (about 196°C)], Sn-Zn-based Sn91Zn9 [melting temperature: solidus temperature (about 198°C), liquidus temperature (about 198°C)], etc. can be mentioned. Also, as a solder material having a relatively high melting point, from the viewpoints of being lead-free and / or cadmium-free, for example, Sn-Sb-based Sn95Sb5 [melting temperature: solidus temperature (about 238°C), liquidus temperature (about 241°C)], Sn-Cu-based Sn99.3Cu0.7 [melting temperature: solidus temperature (about 227°C), liquidus temperature (about 228°C)], Sn-Cu-Ag-based Sn99Cu0.7Ag0.3 [melting temperature: solidus temperature (about 217°C), liquidus temperature (about 226°C)], Sn-Ag-based Sn97Ag3 [melting temperature: solidus temperature (about 221°C), liquidus temperature (about 222°C)], Sn-Ag-Cu-based Sn96.5Ag3Cu0.5 [melting temperature: solidus temperature (about 217°C), liquidus temperature (about 219°C)], Sn95.5Ag4Cu0.5 [melting temperature: solidus temperature (about 217°C), liquidus temperature (about 219°C)], Sn-Ag-Cu-based Sn95.8Ag3.5Cu0.7 [melting temperature: solidus temperature (about 217°C), liquidus temperature (about 217°C)], etc. can be mentioned. In consideration of the heat resistance of the substrate, electrodes, etc. constituting the thermoelectric conversion module, the above solder materials can be appropriately used.

[0027] The thickness of the solder material layer containing the solder material (after heating and cooling) is preferably 10 to 200 μm, more preferably 20 to 150 μm, still more preferably 30 to 130 μm, and particularly preferably 40 to 120 μm. When the thickness of the solder material layer is within this range, it is easier to obtain the bonding property between the chip of the thermoelectric conversion material and the electrode.

[0028] As a method of applying the solder material onto the substrate, known methods such as stencil printing, screen printing, and dispensing method can be mentioned. The heating temperature varies depending on the solder material, substrate, etc., but usually, it is carried out at 100 to 280 °C for 0.5 to 20 minutes.

[0029] Examples of commercially available solder materials include the following. For example, 42Sn / 58Bi alloy [manufactured by Tamura Seisakusho Co., Ltd., product name: SAM10-401-27, melting temperature: solidus temperature (about 139 °C), liquidus temperature (about 139 °C)], 96.5Sn3.0Ag0.5Cu alloy [manufactured by Nihon Handa Co., Ltd., product name: PF305-153TO, melting temperature: solidus temperature (about 217 °C), liquidus temperature (about 219 °C)], Sn / 57Bi alloy [manufactured by Nihon Handa Co., Ltd., product name: PF141-LT7H0, melting temperature: solidus temperature (about 137 °C)], etc. can be used.

[0030] (Solder acceptance layer) In the bonding of the chip of the thermoelectric conversion material to the electrode, a solder acceptance layer may be provided in advance on the chip of the thermoelectric conversion material. The solder acceptance layer has a function of improving the bonding property of the solder material layer on the electrode side facing the chip of the thermoelectric conversion material, and it is preferably directly laminated on one surface and the other surface (upper and lower surfaces) of the chip of the thermoelectric conversion material.

[0031] The solder acceptance layer contains a metal material. The metal material is preferably at least one selected from gold, silver, rhodium, platinum, chromium, palladium, tin, nickel, and alloys containing any of these metal materials. Among these, more preferably, it is a two-layer structure of gold, silver, nickel, or tin and gold, nickel and gold. From the viewpoints of material cost, high thermal conductivity, and bonding stability, silver is even more preferable. Furthermore, in addition to the metal material, the solder-receiving layer may be formed using a paste material containing a solvent and a resin component. When using a paste material, it is preferable to remove the solvent and resin component by firing or the like as described later. As the paste material, silver paste and aluminum paste are preferable.

[0032] The thickness of the solder-receiving layer is preferably 10 nm to 50 μm, more preferably 50 nm to 16 μm, still more preferably 200 nm to 4 μm, and particularly preferably 500 nm to 3 μm. When the thickness of the solder-receiving layer is within this range, the adhesion to the surface of the chip of the thermoelectric conversion material and the adhesion to the surface of the solder material layer on the electrode side are excellent, and a highly reliable joint can be obtained. Also, not only the conductivity but also the thermal conductivity can be maintained at a high level, so as a result, the thermoelectric performance of the thermoelectric conversion module does not decrease but is maintained. The solder-receiving layer may be formed by directly depositing the above-described metal material as a single layer, or may be used in multiple layers by laminating two or more metal materials. Also, it may be formed as a composition in which the metal material is contained in a solvent, resin, or the like. However, in this case, from the viewpoint of maintaining high conductivity and high thermal conductivity (maintaining thermoelectric performance), it is preferable to remove the resin component including the solvent by firing or the like as the final form of the solder-receiving layer.

[0033] The formation of the solder-receiving layer is performed using the above-described metal material. As a method for forming the solder-receiving layer, after providing a solder-receiving layer without a pattern on the chip of the thermoelectric conversion material, a known physical treatment or chemical treatment mainly using a photolithography method, or a combination thereof, is used to process it into a predetermined pattern shape, or a method of directly forming a pattern of the bonding material receiving layer by a screen printing method, a stencil printing method, an inkjet method, or the like can be mentioned. As a method for forming a solder-receiving layer without a pattern, there are vacuum deposition methods, sputtering methods, PVD (physical vapor deposition methods) such as ion plating methods, or CVD (chemical vapor deposition methods) such as thermal CVD and atomic layer deposition (ALD), etc. vacuum film-forming methods, or various coating methods such as dip coating method, spin coating method, spray coating method, gravure coating method, die coating method, doctor blade method, etc. and wet processes such as electrodeposition method, silver salt method, electroplating method, electroless plating method, lamination of metal foils, etc., and are appropriately selected according to the material of the bonding material receiving layer. From the viewpoint of maintaining thermoelectric performance, since high conductivity and high thermal conductivity are required for the solder-receiving layer, it is preferable to use a solder-receiving layer formed by screen printing method, stencil printing method, electroplating method, electroless plating method or vacuum film-forming method.

[0034] (Chip of thermoelectric conversion material) The chip of the thermoelectric conversion material is not particularly limited, and may be made of a thermoelectric semiconductor material or a thin film made of a thermoelectric semiconductor composition. From the viewpoints of flexibility and thinness, it is preferably made of a thin film composed of a thermoelectric semiconductor composition containing one or both of a thermoelectric semiconductor material (hereinafter sometimes referred to as "thermoelectric semiconductor particles"), a resin, an ionic liquid and an inorganic ionic compound.

[0035] (Thermoelectric semiconductor material) The thermoelectric semiconductor material, that is, the thermoelectric semiconductor material constituting the chip of the P-type thermoelectric conversion material and the chip of the N-type thermoelectric conversion material is not particularly limited as long as it can generate a thermoelectromotive force by applying a temperature difference. For example, bismuth-tellurium-based thermoelectric semiconductor materials such as P-type bismuth telluride and N-type bismuth telluride; telluride-based thermoelectric semiconductor materials such as GeTe and PbTe; antimony-tellurium-based thermoelectric semiconductor materials; zinc-antimony-based thermoelectric semiconductor materials such as ZnSb and Zn3Sb 2、 zinc-antimony-based thermoelectric semiconductor materials such as Zn4Sb3; silicon-germanium-based thermoelectric semiconductor materials such as SiGe; bismuth selenide-based thermoelectric semiconductor materials such as Bi2Se3; β-FeSi2, CrSi2, MnSi 1.73, silicide-based thermoelectric semiconductor materials such as Mg2Si; oxide-based thermoelectric semiconductor materials; Heusler materials such as FeVAl, FeVAlSi, FeVTiAl, and sulfide-based thermoelectric semiconductor materials such as TiS2 are used. Among these, bismuth-telluride-based thermoelectric semiconductor materials, telluride-based thermoelectric semiconductor materials, antimony-telluride-based thermoelectric semiconductor materials, or bismuth selenide-based thermoelectric semiconductor materials are preferred.

[0036] Furthermore, it is more preferably a bismuth-telluride-based thermoelectric semiconductor material such as P-type bismuth telluride or N-type bismuth telluride. The P-type bismuth telluride has holes as carriers and a positive Seebeck coefficient. For example, Bi X Te3Sb 2-X represented by is preferably used. In this case, X is preferably 0 < X ≦ 0.8, more preferably 0.4 ≦ X ≦ 0.6. When X is greater than 0 and less than or equal to 0.8, the Seebeck coefficient and electrical conductivity increase, and the characteristics as a P-type thermoelectric element are maintained, which is preferable. Also, the N-type bismuth telluride has electrons as carriers and a negative Seebeck coefficient. For example, Bi2Te 3-Y Se Y represented by is preferably used. In this case, Y is preferably 0 ≦ Y ≦ 3 (when Y = 0: Bi2Te3), more preferably 0 < Y ≦ 2.7. When Y is 0 or more and 3 or less, the Seebeck coefficient and electrical conductivity increase, and the characteristics as an N-type thermoelectric element are maintained, which is preferable.

[0037] The content of the thermoelectric semiconductor material or thermoelectric semiconductor particles in the thermoelectric semiconductor composition is preferably 30 to 99% by mass. More preferably, it is 50 to 96% by mass, and still more preferably, it is 70 to 95% by mass. When the content of the thermoelectric semiconductor material or thermoelectric semiconductor particles is within the above range, the Seebeck coefficient (absolute value of the Peltier coefficient) is large, the decrease in electrical conductivity is suppressed, and only the thermal conductivity decreases, so it exhibits high thermoelectric performance, and a film with sufficient film strength and flexibility can be obtained, which is preferable.

[0038] The average particle size of the thermoelectric semiconductor particles is preferably from 10 nm to 200 μm, more preferably from 10 nm to 30 μm, still more preferably from 50 nm to 10 μm, and particularly preferably from 1 to 6 μm. If it is within the above range, uniform dispersion becomes easy and the electrical conductivity can be increased. The thermoelectric semiconductor particles used for the chip of the thermoelectric conversion material are preferably those obtained by pulverizing the above-described thermoelectric semiconductor material to a predetermined size using a fine pulverizer or the like. The method for pulverizing the thermoelectric semiconductor material to obtain thermoelectric semiconductor particles is not particularly limited, and it may be pulverized to a predetermined size using a known fine pulverizer such as a jet mill, a ball mill, a bead mill, a colloid mill, a roller mill or the like. The average particle size of the thermoelectric semiconductor particles is obtained by measuring with a laser diffraction particle size analyzer (Master Sizer 3000, manufactured by Malvern), and is taken as the median of the particle size distribution.

[0039] Further, the thermoelectric semiconductor particles are preferably those subjected to annealing treatment (hereinafter sometimes referred to as "annealing treatment A"). By performing annealing treatment A, the crystallinity of the thermoelectric semiconductor particles is improved, and further, the surface oxide film of the thermoelectric semiconductor particles is removed, so that the Seebeck coefficient or the Peltier coefficient of the thermoelectric conversion material is increased, and the thermoelectric performance index can be further improved. Annealing treatment A is not particularly limited, but before preparing the thermoelectric semiconductor composition, in an inert gas atmosphere such as nitrogen or argon, a reducing gas atmosphere such as hydrogen, or a vacuum condition in which the gas flow rate is controlled so as not to adversely affect the thermoelectric semiconductor particles. It is preferably carried out, and more preferably carried out in a mixed gas atmosphere of an inert gas and a reducing gas. Specific temperature conditions depend on the thermoelectric semiconductor particles used, but usually, it is preferably carried out at a temperature below the melting point of the particles and at 100 to 1500 ° C for several minutes to several tens of hours.

[0040] (Resin) The resin has the effect of physically bonding between the thermoelectric semiconductor materials (thermoelectric semiconductor particles), can enhance the flexibility of the thermoelectric conversion module, and facilitates the formation of a thin film by coating or the like. Examples of the resin include a heat-resistant resin or a binder resin.

[0041] (Heat-resistant resin) When a thin film made of a thermoelectric semiconductor composition is annealed to cause crystal growth of thermoelectric semiconductor particles, the heat-resistant resin maintains various physical properties such as mechanical strength and thermal conductivity as a resin without being impaired. The heat-resistant resin is preferably a polyamide resin, a polyamideimide resin, a polyimide resin, or an epoxy resin from the viewpoints of higher heat resistance and no adverse effect on crystal growth of thermoelectric semiconductor particles in the thin film. From the viewpoint of excellent flexibility, a polyamide resin, a polyamideimide resin, or a polyimide resin is more preferable. As described later When a polyimide film is used as the first substrate or the second substrate, a polyimide resin and a polyamideimide resin are more preferable as the heat-resistant resin from the viewpoint of adhesion to the polyimide film. In the present invention, the polyimide resin is a general term for polyimide and its precursor.

[0042] The heat-resistant resin preferably has a decomposition temperature of 300°C or higher. If the decomposition temperature is within the above range, as described later, even when a thin film made of a thermoelectric semiconductor composition is annealed, the function as a binder is not lost and flexibility can be maintained.

[0043] Further, the heat-resistant resin preferably has a mass reduction rate at 300°C by thermogravimetric measurement (TG) of 10% or less, more preferably 5% or less, and even more preferably 1% or less. If the mass reduction rate is within the above range, as described later, even when a thin film made of a thermoelectric semiconductor composition is annealed, the function as a binder is not lost and the flexibility of the chip of the thermoelectric conversion material can be maintained.

[0044] The content of the heat-resistant resin in the thermoelectric semiconductor composition is 0.1 to 40% by mass, preferably 0.5 to 20% by mass, more preferably 1 to 20% by mass, and still more preferably 2 to 15% by mass. When the content of the heat-resistant resin is within the above range, it functions as a binder for the thermoelectric semiconductor material, facilitating the formation of a thin film, and a film with both high thermoelectric performance and film strength can be obtained. There is a resin part on the outer surface of the chip of the thermoelectric conversion material.

[0045] The binder resin also facilitates the peeling from substrates such as glass, alumina, and silicon used in the production of the chips of the thermoelectric conversion material after firing (annealing) treatment (corresponding to the "annealing treatment B" described later, and the same applies hereinafter).

[0046] The binder resin refers to a resin in which 90% by mass or more decomposes at a firing (annealing) temperature or higher, more preferably a resin in which 95% by mass or more decomposes, and particularly preferably a resin in which 99% by mass or more decomposes. Also, a resin that maintains various physical properties such as mechanical strength and thermal conductivity without being impaired when crystal growth of thermoelectric semiconductor particles is performed on a coating film (thin film) composed of a thermoelectric semiconductor composition by firing (annealing) treatment or the like is more preferable. When a resin in which 90% by mass or more decomposes at a firing (annealing) temperature or higher, that is, a resin that decomposes at a lower temperature than the above-described heat-resistant resin, is used as the binder resin, the binder resin decomposes by firing, so the content of the binder resin, which becomes an insulating component contained in the fired body, decreases, and crystal growth of the thermoelectric semiconductor particles in the thermoelectric semiconductor composition is promoted. Therefore, the voids in the thermoelectric conversion material layer can be reduced and the filling rate can be improved. Whether a resin decomposes by a predetermined value (for example, 90% by mass) or more at a firing (annealing) temperature or higher is determined by measuring the mass reduction rate (the value obtained by dividing the mass after decomposition by the mass before decomposition) at the firing (annealing) temperature by thermogravimetric measurement (TG).

[0047] As such a binder resin, a thermoplastic resin or a curable resin can be used. Examples of the thermoplastic resin include polyolefin resins such as polyethylene, polypropylene, polyisobutylene, and polymethylpentene; polycarbonate; thermoplastic polyester resins such as polyethylene terephthalate and polyethylene naphthalate; polyvinyl polymers such as polystyrene, acrylonitrile-styrene copolymer, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyvinyl chloride, polyvinyl pyridine, polyvinyl alcohol, and polyvinyl pyrrolidone; polyurethane; cellulose derivatives such as ethyl cellulose; and the like. Examples of the curable resin include thermosetting resins and photocurable resins. Examples of the thermosetting resin include epoxy resins and phenolic resins. Examples of the photocurable resin include photocurable acrylic resins, photocurable urethane resins, and photocurable epoxy resins. These may be used alone or in combination of two or more. Among these, from the viewpoint of the electrical resistivity of the thermoelectric conversion material in the thermoelectric conversion material layer, a thermoplastic resin is preferable, cellulose derivatives such as polycarbonate and ethyl cellulose are more preferable, and polycarbonate is particularly preferable.

[0048] The binder resin is appropriately selected according to the temperature of the firing (annealing) treatment for the thermoelectric semiconductor material in the firing (annealing) treatment step. It is preferable from the viewpoint of the electrical resistivity of the thermoelectric conversion material in the thermoelectric conversion material layer to perform the firing (annealing) treatment at a temperature equal to or higher than the final decomposition temperature of the binder resin. In this specification, the "final decomposition temperature" refers to the temperature at which the mass reduction rate at the firing (annealing) temperature by thermogravimetric measurement (TG) becomes 100% (the mass after decomposition is 0% of the mass before decomposition).

[0049] The final decomposition temperature of the binder resin is usually 150 to 600 °C, preferably 200 to 560 °C, more preferably 220 to 460 °C, and particularly preferably 240 to 360 °C. If a binder resin having a final decomposition temperature within this range is used, it functions as a binder for the thermoelectric semiconductor material and facilitates the formation of a thin film during printing.

[0050] The content of the binder resin in the thermoelectric semiconductor composition is 0.1 to 40% by mass, preferably 0.5 to 20% by mass, more preferably 0.5 to 10% by mass, and particularly preferably 0.5 to 5% by mass. When the content of the binder resin is within the above range, the electrical resistivity of the thermoelectric conversion material in the thermoelectric conversion material layer can be reduced.

[0051] The content of the binder resin in the thermoelectric conversion material is preferably 0 to 10% by mass, more preferably 0 to 5% by mass, and particularly preferably 0 to 1% by mass. If the content of the binder resin in the thermoelectric conversion material is within the above range, the electrical resistivity of the thermoelectric conversion material in the thermoelectric conversion material layer can be reduced.

[0052] (Ionic liquid) The ionic liquid that can be contained in the thermoelectric semiconductor composition is a molten salt formed by combining a cation and an anion, and refers to a salt that can exist in a liquid state in any temperature range from -50°C to less than 400°C. In other words, the ionic liquid is an ionic compound having a melting point in the range of -50°C to less than 400°C. The melting point of the ionic liquid is preferably -25°C or higher and 200°C or lower, more preferably 0°C or higher and 150°C or lower. Since the ionic liquid has characteristics such as an extremely low vapor pressure and being non-volatile, excellent thermal stability and electrochemical stability, low viscosity, and high ionic conductivity, as a conductive auxiliary agent, it can effectively suppress the reduction of the electrical conductivity between thermoelectric semiconductor materials. In addition, the ionic liquid exhibits a high polarity based on its aprotic ionic structure and has excellent compatibility with heat-resistant resins, so it can make the electrical conductivity of the thermoelectric conversion material uniform.

[0053] Known or commercially available ionic liquids can be used. For example, nitrogen-containing cyclic cation compounds such as pyridinium, pyrimidinium, pyrazolium, pyrrolidinium, piperidinium, imidazolium, and their derivatives; tetraalkylammonium-based amine cations and their derivatives; phosphine-based cations such as phosphonium, trialkylsulfonium, tetraalkylphosphonium, and their derivatives; cation components such as lithium cation and its derivatives, and Cl - , Br - , I - , AlCl4 - , Al2Cl7 - , BF4 - , PF6 - , ClO4 - , NO3 - , CH3COO - , CF3COO - , CH3SO3 - , CF3SO3 - , (FSO2)2N - , (CF3SO2)2N - , (CF3SO2)3C - , AsF6 - , SbF6 - , NbF6 - , TaF6 - , F(HF) n - , (CN)2N - , C4F9SO3 - , (C2F5SO2)2N - , C3F7COO - , (CF3SO2)(CF3CO)N - and the like composed of anion components can be mentioned.

[0054] Among the above ionic liquids, from the viewpoints of high-temperature stability, compatibility with thermoelectric semiconductor materials and resins, suppression of the decrease in electrical conductivity in the thermoelectric semiconductor material gap, etc., it is preferable that the cation component of the ionic liquid contains at least one selected from pyridinium cation and its derivatives, imidazolium cation and its derivatives.

[0055] As an ionic liquid in which the cation component contains a pyridinium cation and its derivatives, 1-butyl-4-methylpyridinium bromide, 1-butylpyridinium bromide, and 1-butyl-4-methylpyridinium hexafluorophosphate are preferable.

[0056] Also, as an ionic liquid in which the cation component contains an imidazolium cation and its derivatives, [1-butyl-3-(2-hydroxyethyl)imidazolium bromide] and [1-butyl-3-(2-hydroxyethyl)imidazolium tetrafluoroborate] are preferable.

[0057] Moreover, the above ionic liquid preferably has a decomposition temperature of 300 °C or higher. If the decomposition temperature is within the above range, as described later, even when a thin film composed of a thermoelectric semiconductor composition is annealed, the effect as a conductive auxiliary agent can be maintained.

[0058] The content of the ionic liquid in the thermoelectric semiconductor composition is preferably 0.01 to 50% by mass, more preferably 0.5 to 30% by mass, and still more preferably 1.0 to 20% by mass. If the content of the ionic liquid is within the above range, a decrease in electrical conductivity can be effectively suppressed, and a film having high thermoelectric performance can be obtained.

[0059] (Inorganic ionic compound) The inorganic ionic compound that can be contained in the thermoelectric semiconductor composition is a compound composed of at least a cation and an anion. Since the inorganic ionic compound exists as a solid in a wide temperature range of 400 to 900 °C and has characteristics such as high ionic conductivity, it can suppress a decrease in electrical conductivity between thermoelectric semiconductor materials as a conductive auxiliary agent.

[0060] The content of the inorganic ionic compound in the thermoelectric semiconductor composition is preferably 0.01 to 50% by mass, more preferably 0.5 to 30% by mass, and still more preferably 1.0 to 10% by mass. If the content of the inorganic ionic compound is within the above range, a decrease in electrical conductivity can be effectively suppressed, and as a result, a film with improved thermoelectric performance can be obtained. In addition, when an inorganic ionic compound and an ionic liquid are used in combination, the total content of the inorganic ionic compound and the ionic liquid in the thermoelectric semiconductor composition is preferably 0.01 to 50% by mass, more preferably 0.5 to 30% by mass, and still more preferably 1.0 to 10% by mass.

[0061] (Method for preparing thermoelectric semiconductor composition) The method for preparing the thermoelectric semiconductor composition is not particularly limited. For example, by a known method such as an ultrasonic homogenizer, a spiral mixer, a planetary mixer, a disperser, a hybrid mixer, etc., the thermoelectric semiconductor particles, the ionic liquid, the inorganic ionic compound (when used in combination with the ionic liquid), the heat-resistant resin, and if necessary, the other additives, and further a solvent are added and mixed and dispersed to prepare the thermoelectric semiconductor composition. Examples of the solvent include solvents such as toluene, ethyl acetate, methyl ethyl ketone, alcohol, tetrahydrofuran, methylpyrrolidone, and ethyl cellosolve. These solvents may be used alone or in combination of two or more. The solid content concentration of the thermoelectric semiconductor composition may be any viscosity suitable for coating the composition, and there is no particular limitation.

[0062] The chip of the thermoelectric conversion material composed of the thermoelectric semiconductor composition is not particularly limited. For example, it can be formed by applying the thermoelectric semiconductor composition on a substrate such as glass, alumina, or silicon, or on a substrate on the side where a sacrificial layer described later is formed, to obtain a coating film and drying it. In this way, a large number of chips of thermoelectric conversion materials can be obtained simply and at low cost by forming them. Examples of the method for applying the thermoelectric semiconductor composition to obtain a chip of the thermoelectric conversion material include known methods such as screen printing, flexographic printing, gravure printing, spin coating, dip coating, die coating, spray coating, bar coating, and doctor blade coating, and there is no particular limitation. When forming the coating film in a pattern, a screen printing method, a slot die coating method, etc. that can easily form a pattern using a screen plate having a desired pattern are preferably used. Next, by drying the obtained coating film, a chip of the thermoelectric conversion material is formed. As the drying method, conventionally known drying methods such as hot air drying method, hot roll drying method, and infrared irradiation method can be adopted. The heating temperature is usually 80 to 150 °C, and the heating time varies depending on the heating method, but is usually several seconds to several tens of minutes. Also, when a solvent is used in the preparation of the thermoelectric semiconductor composition, the heating temperature is not particularly limited as long as it is within the temperature range capable of drying the used solvent.

[0063] The thickness of the thin film made of the thermoelectric semiconductor composition is not particularly limited, but from the viewpoints of thermoelectric performance and film strength, it is preferably 100 nm to 1000 μm, more preferably 300 nm to 600 μm, and even more preferably 5 to 400 μm.

[0064] The chip of the thermoelectric conversion material as a thin film made of the thermoelectric semiconductor composition is preferably further subjected to annealing treatment (hereinafter sometimes referred to as "annealing treatment B"). By performing the annealing treatment B, the thermoelectric performance can be stabilized, and the thermoelectric semiconductor particles in the thin film can be crystallized and grown, and the thermoelectric performance can be further improved. The annealing treatment B is not particularly limited, but is usually performed in an inert gas atmosphere such as nitrogen or argon, a reducing gas atmosphere, or under vacuum conditions with controlled gas flow rate, and depends on the heat-resistant temperature of the resin and ionic compound used, etc., and is performed at 100 to 500 °C for several minutes to several tens of hours.

[0065] As the sacrificial layer, a resin such as polymethyl methacrylate or polystyrene, or a release agent such as a fluorine-based release agent or a silicone-based release agent can be used. When a sacrificial layer is used, the chip of the thermoelectric conversion material formed on a substrate such as glass can be easily peeled off from the glass etc. after the annealing treatment B. The formation of the sacrificial layer is not particularly limited and can be performed by known methods such as flexographic printing method and spin coating method.

[0066] The thermoelectric conversion module of the present invention can suppress the displacement of the chip of the thermoelectric conversion material with respect to the electrode due to the molten solder flow during bonding, and can also suppress the residual voids in the solder material layer. Therefore, the bonding property between the chip of the thermoelectric conversion material and the electrode is improved, the decrease in thermoelectric performance can be suppressed, and the yield of the manufacturing process can be improved. Furthermore, it can be expected to lead to higher density mounting of the thermoelectric conversion module.

Example

[0067] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0068] The evaluation of the residual void ratio in the solder material layer used for bonding the chip of the thermoelectric conversion material and the electrode in the thermoelectric conversion modules manufactured in the examples and comparative examples was performed by the following method.

[0069] 〈Evaluation of Residual Void Ratio in Solder Material Layer〉 In the thermoelectric conversion modules obtained in the examples and comparative examples, the residual voids present in the longitudinal section of the solder material layer used for bonding each of the chips of the P-type thermoelectric conversion material and the N-type thermoelectric conversion material to the electrode were imaged by CT (Computed Tomography) using an X-ray observation device (manufactured by Ibit Corporation, model name "FX-400tRT"). For the obtained transmission image, binarization processing was performed using Image J (image processing software, ver.1.44P). The dark part in the binarization processing was regarded as the void part, and the bright part was regarded as the solder material part. The residual void ratio defined by the ratio of the area of the residual voids in the area of the longitudinal section of the solder material layer was calculated. The evaluation of the residual void ratio was the arithmetic mean of 12 chips.

[0070] (Example 1) (Fabrication of Thermoelectric Conversion Module) (1) Fabrication of Thermoelectric Semiconductor Composition (Fabrication of Thermoelectric Semiconductor Particles) P-type bismuth telluride Bi, which is a bismuth-tellurium-based thermoelectric semiconductor material 0.4 Te3Sb1.6 (Manufactured by High Purity Chemical Research Institute, particle size: 90 μm) was pulverized in an air atmosphere using a planetary ball mill (manufactured by Fritsch Japan, Premium line P-7) to produce thermoelectric semiconductor particles T1 with an average particle size of 2.5 μm. Also, N-type bismuth telluride Bi2Te3 (manufactured by High Purity Chemical Research Institute, particle size: 90 μm), which is a bismuth-tellurium-based thermoelectric semiconductor material, was used to produce thermoelectric semiconductor particles T2 with an average particle size of 2.5 μm in the same manner as above. Regarding the thermoelectric semiconductor particles T1 and T2 obtained by pulverization, the particle size distribution was measured using a laser diffraction particle size analyzer (manufactured by Malvern, Mastersizer 3000). (Preparation of coating liquid for thermoelectric semiconductor composition) Coating liquid (P) 83.3 parts by mass of the P-type bismuth telluride Bi 0.4 Te 3.0 Sb 1.6 Particles T1 were mixed and dispersed with 2.7 parts by mass of polyamideimide (manufactured by Arakawa Chemical Industries, product name: Composelan AI301, solvent: N-methylpyrrolidone, solid content concentration: 18% by mass) as a heat-resistant resin and 14.0 parts by mass of 1-butylpyridinium bromide as an ionic liquid to prepare a coating liquid (P) composed of a thermoelectric semiconductor composition. Coating liquid (N) 91.6 parts by mass of the N-type bismuth telluride Bi2Te3 particles T2 obtained above were mixed and dispersed with 3.6 parts by mass of polyamideimide (manufactured by Arakawa Chemical Industries, product name: Composelan AI301, solvent: N-methylpyrrolidone, solid content concentration: 18% by mass) as a heat-resistant resin and 4.8 parts by mass of 1-butylpyridinium bromide as an ionic liquid to prepare a coating liquid (N) composed of a thermoelectric semiconductor composition.

[0071] (2) Fabrication of chips for thermoelectric conversion materials As a sacrificial layer on a glass substrate (soda-lime glass) with a thickness of 0.7 mm, a polymethyl methacrylate resin (PMMA) (manufactured by Sigma-Aldrich, trade name: polymethyl methacrylate) dissolved in toluene was spin-coated to form a film with a thickness of 10.0 μm after drying. The resulting solution had a solid content concentration of 10% by mass. Next, through a metal mask, the coating liquid (P) prepared in (1) above was applied onto the sacrificial layer by screen printing, and dried at a temperature of 120 °C for 7 minutes in an air atmosphere (thickness: 350 μm). Thereafter, by applying pressure at 110 MPa for 10 minutes at 250 °C in an air atmosphere, a thin film composed of a thermoelectric semiconductor composition containing particles of a P-type thermoelectric semiconductor material with a thickness of 200 μm was formed. For the obtained thin film, in an atmosphere of a mixed gas of hydrogen and argon (hydrogen:argon = 3 vol%:97 vol%), the temperature was raised at a heating rate of 5 K / min, held at 430 °C for 1 hour, and the thin film was annealed to cause crystal growth of the particles of the thermoelectric semiconductor material, resulting in a P-type bismuth telluride Bi 0.4 Te3Sb 1.6 A chip of a P-type thermoelectric conversion material in the shape of a rectangular parallelepiped with upper and lower surfaces each being 1.15 mm × 1.15 mm and a thickness of 200 μm was obtained. Also, by changing to the coating liquid (N) prepared in (1) above, and under the same method except that the pressure conditions were 37 MPa for 10 minutes at 250 °C in an air atmosphere and held at 360 °C for 1 hour in an atmosphere of a mixed gas of hydrogen and argon for annealing the thin film, a chip of an N-type thermoelectric conversion material in the shape of a rectangular parallelepiped with upper and lower surfaces each being 1.15 mm × 1.15 mm and a thickness of 200 μm (thickness before pressurization: 390 μm) containing N-type bismuth telluride Bi2Te3 was obtained.

[0072] (3) Formation of solder-receiving layer The chips of the P-type and N-type thermoelectric conversion materials after annealing were peeled off from the glass substrate, and by electroless plating, a nickel layer (thickness: 3 μm) and a gold layer (thickness: 40 nm) were laminated in this order as a solder-receiving layer on all surfaces of the chips of the P-type and N-type thermoelectric conversion materials. Next, the solder-receiving layers on the sides of the P-type and N-type thermoelectric conversion material chips were removed using a mechanical polishing method, i.e., using sandpaper (grit number 2000), so that the P-type and N-type thermoelectric conversion material chips would each have dimensions of 0.87 mm × 0.87 mm, and chips of P-type and N-type thermoelectric conversion materials having solder-receiving layers only on the upper and lower surfaces were obtained. In order to completely remove the solder-receiving layer laminated on the side surface, polishing was also performed including a part of the wall structure on the side surface of the P-type and N-type thermoelectric conversion material chips.

[0073] (4) Formation of electrodes First, a polyimide film substrate (manufactured by Ube Eximer Co., Ltd., product name: Upisel N, polyimide substrate, thickness: 12.5 μm, copper foil, thickness: 12 μm) with copper foil pasted on both sides was prepared, and on only one side of the copper foil of the polyimide film substrate, by an etching method, an outer shape of 3.20 mm × 1.50 mm [bonding region 1 (corresponding to the bonding region of the P-type thermoelectric conversion material chip): 0.87 mm × 0.87 mm, bonding region 2 (corresponding to the bonding region of the N-type thermoelectric conversion material chip): 0.87 mm × 0.87 mm, distance between wall structures in the connection direction between chips: 0.10 mm], a total of 20 sets, 2 rows × 10 columns, of electrode patterns were formed. Further, by electroless plating, a nickel layer (thickness: 3 μm) and a gold layer (thickness: 40 nm) were laminated in this order to fabricate electrodes (hereinafter sometimes referred to as "electrode substrates").

[0074] (5) Formation of wall structures On the electrode substrate obtained in (4), at positions 15 μm apart from each of the four sides of the entire perimeter of each of bonding region 1 (corresponding to the bonding region of the P-type thermoelectric conversion material chip) and bonding region 2 (corresponding to the bonding region of the N-type thermoelectric conversion material chip), openings of 0.90 mm × 0.90 mm (the centers of the openings were made to coincide with the centers of the respective bonding regions), a frame width of 0.015 mm, and a height (thickness) of 25 μm wall structures (hollow rectangular parallelepiped shape) were fabricated. The wall structures were made by bar coating a solder resist (manufactured by Nippon Polytech Co., Ltd., product name: NPR-90 / 305B) on the electrode substrate, drying at 80°C for 30 minutes, repeatedly performing pattern exposure with an integrated light quantity of 600 mJ / cm 2 and then developing, and curing at 150°C for 30 minutes.

[0075] (6) Mounting of chips of thermoelectric conversion material Next, centering on each of the bonding regions 1 and 2 on the electrode substrate, using a metal plate with an opening of 0.50 mm × 0.50 mm and a plate thickness of 100 μm, and a solder material (manufactured by Honghui Co., product name: S3X70 - M500), a solder material layer (thickness before solidification: 100 μm) was formed by stencil printing. One surface having a solder - receiving layer of each of the P - type and N - type thermoelectric conversion material chips obtained in (3) was placed so as to overlap the upper surface of the solder material layer, and heat treatment was performed by reflow at 235°C for 1 minute and then returned to room temperature to solidify the solder material layer (thickness of the solder material layer, height of the bottom surfaces of the P - type and N - type thermoelectric conversion material chips from the electrode surface: 24 μm), thereby bonding to the electrodes, and the P - type and N - type thermoelectric conversion material chips were respectively bonded to the bonding regions 1 and 2 of the electrode substrate. Next, using a pair of opposing electrode substrates each provided with another wall structure of the same specification fabricated in (5), in the same manner as above, the other surface having a solder - receiving layer of each of the P - type and N - type thermoelectric conversion material chips was placed so as to overlap the upper surface of the solder material layer, and the P - type and N - type thermoelectric conversion material chips were respectively bonded to the bonding regions 1 and 2 of the electrode substrate, thereby fabricating a thermoelectric conversion module.

[0076] In accordance with the evaluation of the residual void ratio in the solder material layer described above, the residual void ratio was evaluated. The results are shown in Table 1.

[0077] (Example 2) In Example 1, a thermoelectric conversion module was fabricated in the same manner as in Example 1, except that the opening of the wall structure made of solder - resist was changed to 1.00 × 1.00 mm, and a metal plate with an opening of 0.55 mm × 0.55 mm and a plate thickness of 100 μm was used. For the obtained thermoelectric conversion module, the residual void ratio was evaluated in the same method as in Example 1. The results are shown in Table 1.

[0078] (Comparative Example 1) In Example 1, a thermoelectric conversion module was fabricated in the same manner as in Example 1, except that the opening of the wall structure made of solder resist was set to 0.87 × 0.87 mm, and a metal plate with an opening of 0.45 mm × 0.45 mm and a plate thickness of 100 μm was used. The residual void ratio of the obtained thermoelectric conversion module was evaluated by the same method as in Example 1. The results are shown in Table 1.

[0079]

Table 1

[0080] In Examples 1 and 2, where the distance between each side surface of the chip of the P-type thermoelectric conversion material and the chip of the N-type thermoelectric conversion material and the inner wall surface of the wall structure is within the specified range, it can be seen that the residual void ratio is significantly lower than that in Comparative Example 1 where the distance is 0 outside the specified range.

Industrial Applicability

[0081] In the thermoelectric conversion module of the present invention, a decrease in the bonding property of the chip of the thermoelectric conversion material to the electrode is suppressed, leading to an improvement in thermoelectric performance. Therefore, since the thermoelectric conversion module of the present invention is useful for improving the degradation of thermoelectric performance and improving the yield of the manufacturing process, it is used in known power generation and cooling modules.

Explanation of Symbols

[0082] 1: Thermoelectric conversion module 2a, 2b: Substrate 3, 3a, 3b: Electrode 4p: Chip of P-type thermoelectric conversion material 4n: Chip of N-type thermoelectric conversion material 5a, 5b: Solder material layer (before heating and cooling) 5a’, 5b’: Solder material layer (after heating and cooling) 6p: Bonding region of chip of P-type thermoelectric conversion material 6n: Bonding region of chip of N-type thermoelectric conversion material 7, 7a, 7b: Wall structure 7’, 7a’, 7b’: Wall structure (depth side part) 7i: Inner wall surface of the wall structure 7 7ai: Inner wall surface of the wall structure 7a 7bi: Inner wall surface of the wall structure 7b 8: Space between wall structures 9a: One surface (P-type and N-type, bottom surface) of the chip of the thermoelectric conversion material 9b: The other surface (P-type and N-type, bottom surface) of the chip of the thermoelectric conversion material

Claims

1. A thermoelectric conversion module in which chips of a P-type thermoelectric conversion material and chips of an N-type thermoelectric conversion material that are alternately spaced apart are each joined to an electrode via a solder material, each comprising a mutually spaced-apart wall structure disposed outside the entire perimeter of each region on the electrode that joins to the chip of the P-type thermoelectric conversion material and the chip of the N-type thermoelectric conversion material, and the mutually spaced-apart wall structures are disposed via a void portion formed by the region between the wall structures, a thermoelectric conversion module, wherein the distance between at least one of the inner wall surfaces of the wall structure and the side surfaces of the chip of the P-type thermoelectric conversion material and the chip of the N-type thermoelectric conversion material that face and are closest to the wall surface is 1 μm or more.

2. The thermoelectric conversion module according to claim 1, wherein the shape of each of the wall structures is independently selected from a hollow rectangular parallelepiped shape and a hollow cylindrical shape.

3. The thermoelectric conversion module according to claim 1 or 2, wherein the material of the wall structure is selected from an acrylic resin, an epoxy resin, a urethane resin, and a polyimide resin.

4. The thermoelectric conversion module according to any one of claims 1 to 3, wherein the height of the wall structure in the thickness direction of the electrode is 1 to 25 μm higher than the height of the bottom surfaces of the chips of the P-type thermoelectric conversion material and the chips of the N-type thermoelectric conversion material in the thickness direction of the electrode.

5. The thermoelectric conversion module according to any one of claims 1 to 4, wherein the shape of the inner wall surface of the wall structure follows the shape of each of the side surfaces of the chip of the P-type thermoelectric conversion material and the chip of the N-type thermoelectric conversion material.

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