Thermoelectric conversion module and manufacturing method thereof

Abstract

Provided are: a thermoelectric conversion module which prevents the misalignment of thermoelectric conversion material chips on an electrode derived from a bonding material and which suppresses short circuits between adjacent thermoelectric conversion material chips and bonding defects between the thermoelectric conversion material chips and the electrode; and method for manufacturing a thermoelectric conversion module. The thermoelectric conversion module comprises: a first substrate that has a first electrode; a second substrate that has a second electrode; a thermoelectric conversion material chip including a thermoelectric semiconductor composition; a first bonding material layer that is made of a first bonding material for bonding the first electrode and one surface of the thermoelectric conversion material chip; and a second bonding material layer that is made of a second bonding material for bonding the second electrode and the other surface of the thermoelectric conversion material chip, wherein the melting point of the second bonding material is lower than the melting point of the first bonding material, or the melting point of the second bonding material is lower than the curing temperature of the first bonding material.

Description

[Technical Field]

[0001] The present invention relates to a thermoelectric conversion module and a method for manufacturing the same. [Background technology]

[0002] 2. Description of the Related Art Conventionally, as one of the means for effectively utilizing energy, there has been a device that directly converts thermal energy into electrical energy and vice versa using a thermoelectric conversion module that has a thermoelectric effect such as the Seebeck effect or the Peltier effect. A known thermoelectric conversion module is a so-called π-type thermoelectric conversion element. The π-type is configured by providing a pair of electrodes spaced apart on a substrate, with a P-type thermoelectric element on one electrode and an N-type thermoelectric element on the other electrode, also spaced apart, and connecting the top surfaces of both thermoelectric elements to the opposing electrodes on the substrate. In mounting and assembling thermoelectric elements in a thermoelectric conversion module with such a configuration, when joining one side of a thermoelectric element to the opposing electrode and the other side of the thermoelectric element to the opposing electrode, if the same solder material or solder materials with similar melting points are used as the joining materials, the solder material used to join one electrode may melt when joining one side to the electrode after joining the other side, resulting in misalignment of the thermoelectric elements in the thickness direction or in-plane direction. This can lead to short-circuiting between the side of adjacent P-type thermoelectric elements and the side of adjacent N-type thermoelectric elements, or to poor electrode bonding, which can reduce thermoelectric performance. The thermoelectric conversion module of Patent Document 1 relates to preventing cracks caused by differences in thermal expansion of thermoelectric conversion elements, and discloses that in the first bonding step, the thermoelectric conversion element is bonded to the electrode portion, and in the second bonding step, the thermoelectric conversion element is bonded to the electrode portion at a bonding temperature lower than the bonding temperature in the first bonding step. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-67589 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the thermoelectric conversion module of Patent Document 1, in addition to preventing cracks due to differences in thermal expansion of the thermoelectric conversion elements, the thermoelectric conversion elements (thermoelectric conversion materials: silicide-based, oxide-based) and the electrode parts are joined by brazing [silver (Ag) brazing] in the first joining step, while the thermoelectric conversion elements and the electrode parts are joined by soldering or silver paste in the second joining step, and furthermore, the brazing for joining the thermoelectric conversion elements and the electrode parts in the first joining step is performed by heating, for example, at a joining temperature of 605°C to 780°C and for a joining time of 1 to 10 minutes. Therefore, for example, when the thermoelectric conversion material is composed of a thermoelectric semiconductor composition containing a resin, the composition, shape, etc. of the formed thermoelectric element layer may change at the bonding temperature in the first bonding step, resulting in a significant decrease in thermoelectric performance.

[0005] The present invention has been made in consideration of the above-described circumstances, and aims to provide a thermoelectric conversion module that prevents misalignment of thermoelectric conversion material chips on electrodes caused by bonding materials, thereby suppressing short circuits between adjacent thermoelectric conversion material chips and poor bonding between the thermoelectric conversion material chips and electrodes, and a method for manufacturing the same. [Means for solving the problem]

[0006] As a result of extensive research into solving the above problems, the inventors discovered that by using a bonding material in which the melting point of the second bonding material is lower than the melting point of the first bonding material, or the melting point of the second bonding material is lower than the hardening temperature of the first bonding material, when bonding the thermoelectric conversion material chips to the electrodes that make up the thermoelectric conversion module, it is possible to prevent misalignment of the thermoelectric conversion material chips on the electrodes caused by the first bonding material when bonding the second bonding material, and to suppress short circuits between adjacent thermoelectric conversion material chips and poor bonding between the thermoelectric conversion material chips and the electrodes, thereby completing the present invention. That is, the present invention provides the following (1) to (12). (1) A thermoelectric conversion module including: a first substrate having a first electrode; a second substrate having a second electrode; a chip of a thermoelectric conversion material made of a thermoelectric semiconductor composition; a first bonding material layer made of a first bonding material that bonds one surface of the chip of the thermoelectric conversion material to the first electrode; and a second bonding material layer made of a second bonding material that bonds the other surface of the chip of the thermoelectric conversion material to the second electrode, A thermoelectric conversion module, wherein the melting point of the second bonding material is lower than the melting point of the first bonding material, or the melting point of the second bonding material is lower than the hardening temperature of the first bonding material. (2) The thermoelectric conversion module according to (1) above, wherein the difference between the melting point of the first bonding material and the melting point of the second bonding material is 20° C. or more. (3) The thermoelectric conversion module according to (1) above, wherein the difference between the hardening temperature of the first bonding material and the melting point of the second bonding material is 20° C. or more. (4) The thermoelectric conversion module according to (1) or (2) above, wherein the first bonding material and the second bonding material are solder materials. (5) The thermoelectric conversion module according to (1) or (3) above, wherein the first bonding material is a conductive adhesive material, and the second bonding material is a solder material. (6) The thermoelectric conversion module according to (1) above, wherein the thermoelectric semiconductor composition contains a resin. (7) The thermoelectric conversion module according to (6) above, wherein the resin is a heat-resistant resin, and the thermoelectric semiconductor composition contains a thermoelectric semiconductor material, and one or both of an ionic liquid and an inorganic ionic compound. (8) The thermoelectric conversion module according to (7) above, wherein the heat-resistant resin is a polyimide resin, a polyamide resin, a polyamideimide resin, or an epoxy resin. (9) The thermoelectric conversion module according to (6) above, wherein the resin is a binder resin, and the thermoelectric semiconductor composition contains a thermoelectric semiconductor material, and one or both of an ionic liquid and an inorganic ionic compound. (10) The thermoelectric conversion module according to (9) above, wherein the binder resin contains at least one selected from polycarbonate, a cellulose derivative, and a polyvinyl polymer. (11) A method for manufacturing a thermoelectric conversion module including: a first substrate having a first electrode; a second substrate having a second electrode; a chip of a thermoelectric conversion material made of a thermoelectric semiconductor composition; a first bonding material layer made of a first bonding material that bonds one surface of the chip of the thermoelectric conversion material to the first electrode; and a second bonding material layer made of a second bonding material that bonds the other surface of the chip of the thermoelectric conversion material to the second electrode, (a) forming a first bonding material layer made of a first bonding material on a first electrode on a first substrate; (b) placing one surface of a thermoelectric conversion material chip on the first bonding material layer obtained in step (a); (c) a first bonding step of bonding one surface of the thermoelectric conversion material chip placed in step (b) to the first electrode by heating with the first bonding material layer obtained in step (a) interposed therebetween; (d) forming a second bonding material layer made of a second bonding material on a second electrode on a second substrate; (e) bonding the other surface of the thermoelectric conversion material chip on the first substrate to the second bonding material layer obtained in step (d); and (f) a second bonding step of bonding the other surface of the thermoelectric conversion material chip after step (e) to the second electrode by heating with the second bonding material layer interposed therebetween; A method for manufacturing a thermoelectric conversion module, wherein the bonding temperature in the second bonding step is lower than the bonding temperature in the first bonding step. (12) The method for manufacturing a thermoelectric conversion module according to (11) above, wherein the heating in the first bonding step and the second bonding step is performed by reflow. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a thermoelectric conversion module and a method for manufacturing the same, which prevent misalignment of the thermoelectric conversion material chips on the electrodes caused by the bonding material, and suppress short circuits between adjacent thermoelectric conversion material chips and poor bonding between the thermoelectric conversion material chips and the electrodes. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view illustrating an example of the configuration of a thermoelectric conversion module including a bonding material layer used in the present invention. [Figure 2] 3A to 3C are explanatory views showing an example of a method for joining a chip of thermoelectric conversion material to an electrode in the order of steps in the method for producing a thermoelectric conversion module of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Thermoelectric conversion module] The thermoelectric conversion module of the present invention includes a first substrate having a first electrode, a second substrate having a second electrode, a chip of thermoelectric conversion material made of a thermoelectric semiconductor composition, a first bonding material layer made of a first bonding material that bonds one surface of the thermoelectric conversion material chip to the first electrode, and a second bonding material layer made of a second bonding material that bonds the other surface of the thermoelectric conversion material chip to the second electrode, wherein the melting point of the second bonding material is lower than the melting point of the first bonding material, or the melting point of the second bonding material is lower than the hardening temperature of the first bonding material. In the thermoelectric conversion module of the present invention, the melting point of the second bonding material is lower than the melting point of the first bonding material, or the melting point of the second bonding material is lower than the hardening temperature of the first bonding material, so that displacement of the thermoelectric conversion material chips on the electrodes is prevented, and short circuits between adjacent thermoelectric conversion material chips and poor bonding with the electrodes can be suppressed. In this specification, the "melting point" refers to the solidus temperature when the joining material is, for example, a "solder material" as described later. The "hardening temperature" refers to the joining material when, for example, a "conductive adhesive" as described later contains a hardening resin. Furthermore, in this specification, "one side of a chip of thermoelectric conversion material" and "the other side of a chip of thermoelectric conversion material" refer to, for example, the opposing upper and lower surfaces when the chip of thermoelectric conversion material is shaped like a rectangular parallelepiped or a cylinder, etc., and is viewed from the front.

[0010] FIG. 1 is a cross-sectional view illustrating an example of the configuration of a thermoelectric conversion module of the present invention. The thermoelectric conversion module 1 is composed of so-called π-type thermoelectric conversion elements and has a first substrate 2a and a second substrate 2b facing each other. The thermoelectric conversion module 1 includes a first bonding material layer 6a made of a first bonding material between a first electrode 3a formed on the first substrate 2a and one surface of each of the chips 4 of P-type thermoelectric conversion material and the chips 5 of N-type thermoelectric conversion material, and further includes a second bonding material layer 6b made of a second bonding material between a second electrode 3b formed on the second substrate 2b and the other surface of each of the chips 4 of P-type thermoelectric conversion material and the chips 5 of N-type thermoelectric conversion material.

[0011] <Joining material layer> The thermoelectric conversion module of the present invention uses a first bonding material layer made of a first bonding material and a second bonding material layer made of a second bonding material. The first bonding material layer electrically and physically bonds one surface of the thermoelectric conversion material chip to the first electrode, and similarly, the second bonding material layer electrically and physically bonds the other surface of the thermoelectric conversion material chip to the second electrode.

[0012] The melting point of the second bonding material used in the present invention is lower than that of the first bonding material. If the melting point of the second bonding material is higher than that of the first bonding material, when the other surface of the thermoelectric conversion material chip is bonded to the second electrode, the previously bonded joint (first bonding material layer) between one surface of the thermoelectric conversion material chip and the first electrode will melt, making it easier for the thermoelectric conversion material chip on at least the first electrode to become misaligned. The difference in melting point between the first bonding material and the second bonding material is preferably 20°C or more, more preferably 30°C or more, and even more preferably 50°C or more. When the difference in melting point between the first and second bonding materials is within this range, even when the second bonding material is heated, that is, when the other surface of the thermoelectric conversion material chip is bonded to the second electrode, the pre-bonded bond (first bonding material layer) between one surface of the thermoelectric conversion material chip and the first electrode is maintained, preventing misalignment of the thermoelectric conversion material chip on the first electrode and suppressing short circuits between adjacent thermoelectric conversion material chips and poor bonding between the thermoelectric conversion material chip and the first electrode. There is no particular upper limit to the temperature difference, but a temperature of 100°C or less is preferred because, for example, the composition, shape, etc. of the formed thermoelectric element layer may change, resulting in a significant decrease in thermoelectric performance. The melting point of the first bonding material is preferably in the range of 220° C. to 350° C., more preferably 220° C. to 300° C., and particularly preferably 220° C. to 250° C. When the melting point of the first bonding material is in this range, it is less likely to damage the substrate and the thermoelectric conversion material chip.

[0013] Similarly, when a curable resin is used as the first bonding material, the melting point of the second bonding material used in the present invention is lower than the curing temperature of the first bonding material. If the melting point of the second bonding material is higher than the curing temperature of the first bonding material, cracks, deformation, etc. may occur in the bonded portion (first bonding material layer) between one surface of the thermoelectric conversion material chip and the first electrode when the other surface of the thermoelectric conversion material chip is bonded to the second electrode, making it more likely that the thermoelectric conversion material chip on at least the first electrode will be displaced or peeled off. The difference between the curing temperature of the first bonding material and the melting point of the second bonding material is preferably 20°C or more, more preferably 30°C or more, and even more preferably 50°C or more. When the difference between the curing temperature of the first bonding material and the melting point of the second bonding material is within this range, even when the second bonding material is heated, that is, when the other surface of the thermoelectric conversion material chip is bonded to the second electrode, the pre-bonded bond between one surface of the thermoelectric conversion material chip and the first electrode (first bonding material layer) is maintained, misalignment of the thermoelectric conversion material chip on the first electrode is prevented, and short circuits between adjacent thermoelectric conversion material chips and poor bonding between the thermoelectric conversion material chip and the first electrode are suppressed. Note that there is no particular upper limit on the temperature difference, but a temperature difference of 100°C or less is preferable because, for example, the composition, shape, etc. of the formed thermoelectric element layer may change, significantly reducing thermoelectric performance. The melting point of the second bonding material is preferably in the range of 100° C. to 200° C., and more preferably 120° C. to 180° C. If the melting point of the first bonding material is in this range, stable mounting of the thermoelectric conversion material chip becomes possible.

[0014] Examples of bonding materials constituting the bonding material layer used in the present invention include solder materials, conductive adhesives, sintered bonding materials, etc. In one embodiment, the first bonding material and the second bonding material are preferably solder materials. In another embodiment, the first bonding material is preferably a conductive adhesive, and the second bonding material is preferably a solder material.

[0015] First Embodiment In the first embodiment of the present invention, a solder material is used as the first bonding material and the second bonding material. When solder materials are used as the first and second bonding materials, the liquidus temperature of the solder material used as the second bonding material is selected to be lower than the melting point (solidus temperature) of the solder material used as the first bonding material.

[0016] The solder material is selected taking into consideration not only the melting point but also the heat resistance temperature of the resin contained in the substrate and the thermoelectric conversion material chip, as well as the electrical conductivity and thermal conductivity. The solder material is not particularly limited, but examples of solder materials with relatively low melting points that are lead-free and / or cadmium-free include Sn-In-based In52Sn48 [melting temperature: solidus temperature (approximately 119°C), liquidus temperature (approximately 119°C)], Sn-Bi-based Bi58Sn42 [melting temperature: solidus temperature (approximately 139°C), liquidus temperature (approximately 139°C)], Sn-Zn-Bi-based Sn89Zn8Bi3 [melting temperature: solidus temperature (approximately 190°C), liquidus temperature (approximately 196°C)], and Sn-Zn-based Sn91Zn9 [melting temperature: solidus temperature (approximately 198°C), liquidus temperature (approximately 198°C)]. Furthermore, as solder materials with a relatively high melting point, from the viewpoint of being lead-free and / or cadmium-free, for example, Sn-Sb based Sn95Sb5 [melting temperature: solidus temperature (approximately 238°C), liquidus temperature (approximately 241°C)], Sn-Cu based Sn99.3Cu0.7 [melting temperature: solidus temperature (approximately 227°C), liquidus temperature (approximately 228°C)], Sn-Cu-Ag based Sn99Cu0.7Ag0.3 [melting temperature: solidus temperature (approximately 217°C), liquidus temperature (approximately 226°C)], Sn-Ag based Examples include Sn97Ag3 [melting temperature: solidus temperature (approximately 221°C), liquidus temperature (approximately 222°C)], Sn-Ag-Cu based Sn96.5Ag3Cu0.5 [melting temperature: solidus temperature (approximately 217°C), liquidus temperature (approximately 219°C)], Sn95.5Ag4Cu0.5 [melting temperature: solidus temperature (approximately 217°C), liquidus temperature (approximately 219°C)], and Sn-Ag-Cu based Sn95.8Ag3.5Cu0.7 [melting temperature: solidus temperature (approximately 217°C), liquidus temperature (approximately 217°C)]. The first and second bonding materials are appropriately combined with the solder materials described above based on the provisions of the present invention. Preferably, the second bonding material is Bi58Sn42 or In52Sn48, and the first bonding material is Sn96.5Ag3Cu0.5 or Sn95Sb5. More preferably, the second bonding material is Bi58Sn42, and the first bonding material is Sn96.5Ag3Cu0.5.

[0017] Commercially available solder materials include the following: 42Sn / 58Bi alloy [manufactured by Tamura Corporation, product name: SAM10-401-27, melting temperature: solidus temperature (approximately 139°C), liquidus temperature (approximately 139°C)], 41Sn / 58Bi / 1.0Ag alloy [manufactured by Nippon Handa Co., Ltd., product name: PF141-LT7HO, melting temperature: solidus temperature (approximately 136°C), liquidus temperature (approximately 138°C)], and 96.5Sn3.0Ag0.5Cu alloy [manufactured by Nippon Handa Co., Ltd., product name: PF305-153TO, melting temperature: solidus temperature (approximately 217°C), liquidus temperature (approximately 219°C)].

[0018] 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, even 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, adhesion between the thermoelectric conversion material chip and the electrode can be easily obtained.

[0019] Methods for applying the solder material to the electrodes include known methods such as stencil printing, screen printing, and dispensing. The heating temperature varies depending on the solder material and substrate used, but is typically 100 to 350°C for 0.5 to 20 minutes. When using a solder material with a relatively high melting point, heating is preferably performed at 200 to 280°C for 0.5 to 10 minutes, more preferably 230 to 280°C for 0.5 to 8 minutes. When using a solder material with a relatively low melting point, heating is preferably performed at 110 to 210°C for 0.5 to 20 minutes, more preferably 110 to 195°C for 1 to 20 minutes.

[0020] In this embodiment, the first bonding material is a Sn-Ag-Cu-based solder material, Sn96.5Ag3Cu0.5 [melting temperature: solidus temperature (approximately 217°C), liquidus temperature (approximately 219°C)], and the second bonding material is a Sn-Bi-based solder material, Bi58Sn42 [melting temperature: solidus temperature (approximately 139°C), liquidus temperature (approximately 139°C)].

[0021] Second Embodiment In the second embodiment of the present invention, a conductive adhesive material is used as the first bonding material, and a solder material is used as the second bonding material.

[0022] The conductive adhesive is not particularly limited, but examples thereof include conductive pastes containing metal particles as a conductive material such as silver, copper, nickel, etc. Examples of the conductive paste include silver paste, copper paste, and nickel paste, and examples of the binder include epoxy-based thermosetting resins, acrylic-based thermosetting resins, and silicone-based thermosetting resins. Among the conductive pastes, silver paste is preferred from the viewpoint of electrical conductivity and versatility. Methods for applying the conductive adhesive onto the electrode include known methods such as screen printing, dispensing, etc. The heating temperature varies depending on the conductive adhesive used, the substrate, etc., but is usually 100 to 280°C for 0.5 to 20 minutes, preferably 100 to 220°C for 10 to 20 minutes.

[0023] The thickness of the conductive adhesive layer containing the conductive adhesive is preferably 10 to 200 μm, more preferably 20 to 150 μm, even more preferably 30 to 130 μm, and particularly preferably 40 to 120 μm.

[0024] Commercially available conductive adhesives include the following: Conductive adhesive (manufactured by Nihon Handa Co., Ltd., ECA300, conductive material: silver particles, resin: epoxy resin, curing temperature: 200°C), conductive adhesive (manufactured by Muromachi Chemical Co., Ltd., EPS-110A, conductive material: silver particles, resin: epoxy resin, curing temperature: 180°C), conductive adhesive (manufactured by Muromachi Chemical Co., Ltd., K-72-1 LV, conductive material: silver particles, resin: epoxy resin, curing temperature: 150°C), etc.

[0025] In this embodiment, a conductive adhesive (manufactured by Nihon Handa Co., Ltd., ECA300, conductive material: silver particles, resin: epoxy resin, curing temperature: 200°C) was used as the conductive adhesive of the first bonding material, and a Sn-Bi based Bi58Sn42 [melting temperature: solidus temperature (approximately 139°C), liquidus temperature (approximately 139°C)] was used as the solder material of the second bonding material.

[0026] The sintering bonding material may be used as the first bonding material. The sintering bonding material is not particularly limited, but may include a sintering paste. The sintering paste is made of, for example, micron-sized metal powder and nano-sized metal particles, and, unlike the conductive adhesive, directly bonds metals by sintering. The sintering paste may contain a binder such as an epoxy resin, an acrylic resin, or a urethane resin. Examples of the sintering paste include silver sintering paste and copper sintering paste. Methods for applying the sintering bonding material onto the electrode include known methods such as screen printing, stencil printing, dispensing, etc. Sintering conditions vary depending on the metal material used, but are usually 100 to 300°C and 30 to 120 minutes. Commercially available sintered bonding materials include, for example, a silver sintering paste (manufactured by Kyocera Corporation, product name: CT2700R7S) and a sintered metal bonding material (manufactured by Nihon Handa Co., Ltd., product name: MAX102). The thickness of the sintered bonding material layer containing the sintered bonding material is preferably 10 to 200 μm, more preferably 20 to 150 μm, even more preferably 30 to 130 μm, and particularly preferably 40 to 120 μm.

[0027] <Thermoelectric conversion material chip> The thermoelectric conversion material chip used in the thermoelectric conversion module of the present invention comprises at least a thin film made of a thermoelectric semiconductor composition, preferably a thin film made of a thermoelectric semiconductor composition containing a thermoelectric semiconductor material (hereinafter sometimes referred to as "thermoelectric semiconductor particles"), a resin described below, and one or both of an ionic liquid and an inorganic ionic compound described below.

[0028] (Thermoelectric semiconductor materials) The thermoelectric semiconductor material used in the present invention, i.e., the thermoelectric semiconductor material constituting the chips of P-type thermoelectric conversion material and N-type thermoelectric conversion material, is not particularly limited as long as it is a material that can generate thermoelectric power when a temperature difference is applied, and examples thereof include 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; ZnSb, ZnSb 2、 Zinc-antimony thermoelectric semiconductor materials such as Zn4Sb3; silicon-germanium thermoelectric semiconductor materials such as SiGe; bismuth selenide thermoelectric semiconductor materials such as Bi2Se3; β-FeSi2, CrSi2, MnSi 1.73 Examples of thermoelectric semiconductor materials that can be used include silicide-based thermoelectric semiconductor materials such as Mg2Si, oxide-based thermoelectric semiconductor materials, Heusler materials such as FeVAl, FeVAlSi, and FeVTiAl, and sulfide-based thermoelectric semiconductor materials such as TiS2. Among these, bismuth-tellurium-based thermoelectric semiconductor materials, telluride-based thermoelectric semiconductor materials, antimony-tellurium-based thermoelectric semiconductor materials, and bismuth selenide-based thermoelectric semiconductor materials are preferred.

[0029] Furthermore, it is more preferable that the material be a bismuth-tellurium 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 Zener coefficient. For example, Bi X Te3Sb 2-X 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 Zener coefficient and electrical conductivity increase, and the characteristics as a P-type thermoelectric element are maintained, which is preferable. In addition, the N-type bismuth telluride has electrons as carriers and a negative Zener coefficient. For example, Bi2Te 3-Y Se Y 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 between 0 and 3, the Zener coefficient and electrical conductivity increase, and the characteristics as an N-type thermoelectric element are maintained, which is preferable.

[0030] The blending amount 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. If the blending amount of the thermoelectric semiconductor particles is within the above range, the Zener 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.

[0031] The average particle size of the thermoelectric semiconductor particles is preferably 10 nm to 200 μm, more preferably 10 nm to 30 μm, still more preferably 50 nm to 10 μm, and particularly preferably 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-mentioned thermoelectric semiconductor material to a predetermined size using a pulverizer or the like. The method for pulverizing the thermoelectric semiconductor material to obtain thermoelectric semiconductor particles is not particularly limited, and the material may be pulverized to a predetermined size using a known fine pulverizing device such as a jet mill, ball mill, bead mill, colloid mill, or roller mill. The average particle size of the thermoelectric semiconductor particles was obtained by measurement using a laser diffraction particle size analyzer (Malvern, Mastersizer 3000) and was taken as the median value of the particle size distribution.

[0032] The thermoelectric semiconductor particles are preferably annealed (hereinafter, sometimes referred to as "annealing treatment A"). Annealing treatment A improves the crystallinity of the thermoelectric semiconductor particles and removes the surface oxide film of the thermoelectric semiconductor particles, thereby increasing the Seebeck coefficient or Peltier coefficient of the thermoelectric conversion material and further improving the thermoelectric figure of merit. Annealing treatment A is not particularly limited, but is preferably performed before preparing the thermoelectric semiconductor composition in an inert gas atmosphere such as nitrogen or argon, a reducing gas atmosphere such as hydrogen, or under vacuum conditions with a controlled gas flow rate, so as not to adversely affect the thermoelectric semiconductor particles. Annealing treatment A is more preferably performed in a mixed gas atmosphere of an inert gas and a reducing gas. The specific temperature conditions depend on the thermoelectric semiconductor particles used, but it is usually preferable to perform the annealing treatment at a temperature below the melting point of the particles, at 100 to 1500°C, for several minutes to several tens of hours.

[0033] (resin) The resin used in the present invention has the effect of physically bonding the thermoelectric semiconductor material (thermoelectric semiconductor particles) together, which can increase the flexibility of the thermoelectric conversion module and also makes it easier to form a thin film by coating or the like. The resin is preferably a heat-resistant resin or a binder resin.

[0034] The heat-resistant resin maintains its physical properties such as mechanical strength and thermal conductivity without being impaired when the thin film made of the thermoelectric semiconductor composition is annealed or otherwise treated to cause crystal growth of thermoelectric semiconductor particles. The heat-resistant resin is preferably a polyamide resin, a polyamide-imide resin, a polyimide resin, or an epoxy resin, because it has higher heat resistance and does not adversely affect the crystal growth of the thermoelectric semiconductor particles in the thin film, and more preferably a polyamide resin, a polyamide-imide resin, or a polyimide resin, because it has excellent flexibility. When a polyimide film is used as the first substrate or the second substrate described below, polyimide resins and polyamide-imide resins are more preferred as the heat-resistant resin in terms of adhesion to the polyimide film, etc. In the present invention, polyimide resins collectively refer to polyimides and their precursors.

[0035] The heat-resistant resin preferably has a decomposition temperature of 300° C. or higher. If the decomposition temperature is within the above range, the resin will not lose its function as a binder and will be able to maintain flexibility even when a thin film made of the thermoelectric semiconductor composition is annealed, as will be described later.

[0036] Furthermore, the heat-resistant resin preferably has a mass loss rate of 10% or less, more preferably 5% or less, and even more preferably 1% or less at 300°C as measured by thermogravimetry (TG). If the mass loss rate is within the above range, as will be described later, even when a thin film made of the thermoelectric semiconductor composition is annealed, the resin does not lose its function as a binder and the flexibility of the thermoelectric conversion material chip can be maintained.

[0037] 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 even 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, making it easier to form a thin film, and a film that achieves both high thermoelectric performance and film strength is obtained, and a resin portion is present on the outer surface of the chip of the thermoelectric conversion material.

[0038] The binder resin also facilitates the separation of the thermoelectric conversion material from the substrate, such as glass, alumina, or silicon, used in the production of chips after the firing (annealing) treatment (corresponding to "annealing treatment B" described below, and the same applies below).

[0039] The binder resin refers to a resin that decomposes at 90% by mass or more at a baking (annealing) temperature or higher, more preferably a resin that decomposes at 95% by mass or more, and particularly preferably a resin that decomposes at 99% by mass or more. Furthermore, a resin that maintains various physical properties such as mechanical strength and thermal conductivity without being impaired when a coating film (thin film) made of a thermoelectric semiconductor composition is subjected to a baking (annealing) treatment or the like to cause crystal growth of thermoelectric semiconductor particles is more preferred. When a resin that decomposes at 90% by mass or more at temperatures equal to or higher than the firing (annealing) temperature, i.e., a resin that decomposes at a temperature lower than the heat-resistant resin described above, is used as the binder resin, the binder resin is decomposed by firing, and therefore the content of the binder resin, which serves as an insulating component in the fired body, is reduced, and crystal growth of the thermoelectric semiconductor particles in the thermoelectric semiconductor composition is promoted, thereby reducing voids in the thermoelectric conversion material layer and improving the filling rate. Whether or not a resin decomposes to a predetermined extent (e.g., 90% by mass) at or above the baking (annealing) temperature is determined by measuring the mass loss rate (the value obtained by dividing the mass after decomposition by the mass before decomposition) at the baking (annealing) temperature using thermogravimetry (TG).

[0040] Thermoplastic resins and curable resins can be used as such binder resins. Examples of thermoplastic resins 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, vinyl chloride, polyvinylpyridine, polyvinyl alcohol, and polyvinylpyrrolidone; polyurethane; and cellulose derivatives such as ethyl cellulose. Examples of curable resins include thermosetting resins and photocurable resins. Examples of thermosetting resins include epoxy resins and phenolic resins. Examples of photocurable resins include photocurable acrylic resins, photocurable urethane resins, and photocurable epoxy resins. These resins may be used alone or in combination. Among these, from the viewpoint of the electrical resistivity of the thermoelectric conversion material in the thermoelectric conversion material layer, thermoplastic resins are preferred, polycarbonate and cellulose derivatives such as ethyl cellulose are more preferred, and polycarbonate is particularly preferred.

[0041] The binder resin is appropriately selected depending on the temperature of the annealing treatment of the thermoelectric semiconductor material in the annealing treatment step. From the viewpoint of the electrical resistivity of the thermoelectric conversion material in the thermoelectric conversion material layer, it is preferable to perform the annealing treatment at a temperature equal to or higher than the final decomposition temperature of the binder resin. In this specification, the term "final decomposition temperature" refers to the temperature at which the mass reduction rate at the firing (annealing) temperature determined by thermogravimetry (TG) is 100% (the mass after decomposition is 0% of the mass before decomposition).

[0042] 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 with a final decomposition temperature within this range is used, it functions as a binder for the thermoelectric semiconductor material, making it easier to form a thin film during printing.

[0043] The content of the binder resin in the thermoelectric semiconductor composition is 0.1 to 40 mass%, preferably 0.5 to 20 mass%, more preferably 0.5 to 10 mass%, and particularly preferably 0.5 to 5 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.

[0044] The content of the binder resin in the thermoelectric conversion material is preferably 0 to 10 mass %, more preferably 0 to 5 mass %, and particularly preferably 0 to 1 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.

[0045] (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 liquid form at any temperature range from -50°C to less than 400°C. In other words, an ionic liquid is an ionic compound with 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 to 200°C, more preferably 0°C to 150°C. Ionic liquids have characteristics such as extremely low vapor pressure and nonvolatility, excellent thermal and electrochemical stability, low viscosity, and high ionic conductivity. Therefore, as a conductive additive, they can effectively suppress a decrease in electrical conductivity between thermoelectric semiconductor materials. Furthermore, ionic liquids exhibit high polarity due to their aprotic ionic structure and excellent compatibility with heat-resistant resins, thereby enabling the electrical conductivity of thermoelectric conversion materials to be uniform.

[0046] The ionic liquid may be a known or commercially available one. For example, a nitrogen-containing cyclic cationic compound such as pyridinium, pyrimidinium, pyrazolium, pyrrolidinium, piperidinium, or imidazolium, or a derivative thereof; a tetraalkylammonium-based amine-based cation and a derivative thereof; a phosphine-based cation such as phosphonium, trialkylsulfonium, or tetraalkylphosphonium, or a derivative thereof; a lithium cation and a derivative thereof; or a mixture of a cation component and a Cl cation. - , 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 an anion component such as the above.

[0047] Among the above-mentioned ionic liquids, from the viewpoints of high-temperature stability, compatibility with thermoelectric semiconductor materials and resins, and suppression of a decrease in the electrical conductivity of the gaps between thermoelectric semiconductor materials, it is preferred that the cationic component of the ionic liquid contains at least one selected from pyridinium cations and derivatives thereof, and imidazolium cations and derivatives thereof.

[0048] Specific examples of ionic liquids whose cationic component contains a pyridinium cation and its derivatives include 4-methyl-butylpyridinium chloride, 3-methyl-butylpyridinium chloride, 4-methyl-hexylpyridinium chloride, 3-methyl-hexylpyridinium chloride, 4-methyl-octylpyridinium chloride, 3-methyl-octylpyridinium chloride, 3,4-dimethyl-butylpyridinium chloride, 3,5-dimethyl-butylpyridinium chloride, 4-methyl-butylpyridinium tetrafluoroborate, 4-methyl-butylpyridinium hexafluorophosphate, 1-butylpyridinium bromide, 1-butyl-4-methylpyridinium bromide, 1-butyl-4-methylpyridinium hexafluorophosphate, etc. Among these, 1-butyl-4-methylpyridinium bromide, 1-butylpyridinium bromide, and 1-butyl-4-methylpyridinium hexafluorophosphate are preferred.

[0049] Specific examples of ionic liquids in which the cation component contains an imidazolium cation or a derivative thereof include [1-butyl-3-(2-hydroxyethyl)imidazolium bromide], [1-butyl-3-(2-hydroxyethyl)imidazolium tetrafluoroborate], 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium chloride, 1-octyl-3-methylimidazolium chloride, 1-decyl-3-methylimidazolium chloride, and 1-decyl-3-methylimidazolium chloride. Examples of the imidazolium bromide include 1-dodecyl-3-methylimidazolium chloride, 1-tetradecyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-methyl-3-butylimidazolium methyl sulfate, and 1,3-dibutylimidazolium methyl sulfate. Among these, 1-butyl-3-(2-hydroxyethyl)imidazolium bromide and 1-butyl-3-(2-hydroxyethyl)imidazolium tetrafluoroborate are preferred.

[0050] The above ionic liquid has an electrical conductivity of 10 -7 If the electrical conductivity is in the above range, the conductive additive can effectively suppress a decrease in electrical conductivity between thermoelectric semiconductor materials.

[0051] The ionic liquid preferably has a decomposition temperature of 300° C. or higher. If the decomposition temperature is within the above range, the ionic liquid can maintain its effect as a conductive additive even when a thin film made of the thermoelectric semiconductor composition is annealed, as described below.

[0052] Furthermore, the ionic liquid preferably has a mass loss rate of 10% or less, more preferably 5% or less, and even more preferably 1% or less at 300°C as measured by thermogravimetry (TG). If the mass loss rate is within the above range, the ionic liquid can maintain its effectiveness as a conductive additive even when a thin film made of the thermoelectric semiconductor composition is annealed, as described below.

[0053] The amount of the ionic liquid in the thermoelectric semiconductor composition is preferably 0.01 to 50 mass%, more preferably 0.5 to 30 mass%, and even more preferably 1.0 to 20 mass%. When the amount of the ionic liquid is within the above range, a decrease in electrical conductivity is effectively suppressed, and a film with high thermoelectric performance is obtained.

[0054] (inorganic ionic compounds) The inorganic ionic compound used in the present invention is a compound composed of at least a cation and an anion. The inorganic ionic compound is solid at room temperature, has a melting point somewhere in the temperature range of 400 to 900°C, and has characteristics such as high ionic conductivity, so that it can suppress a decrease in electrical conductivity between thermoelectric semiconductor particles as a conductive additive.

[0055] As the cation, a metal cation is used. Examples of metal cations include alkali metal cations, alkaline earth metal cations, typical metal cations and transition metal cations, with alkali metal cations and alkaline earth metal cations being more preferred. Examples of alkali metal cations include Li + , Na + , K. + , Rb + , Cs + and Fr + etc. Examples of alkaline earth metal cations include Mg 2+ , Ca 2+ , Sr 2+ and Ba 2+ etc.

[0056] Examples of anions include F - , Cl - , Br - , I - , O.H. - , C.N. - , NO3 - , NO2 - , ClO - , ClO2 - , ClO3 - , ClO4 - , CrO4 2- , HSO4 - , SCN - , BF4 - , PF6 - etc.

[0057] The inorganic ionic compound may be a known or commercially available one. For example, a compound containing a cationic component such as potassium cation, sodium cation, or lithium cation and Cl - , AlCl4 - , Al2Cl7 - , ClO4 - Chloride ions such as Br - bromide ions, such as I - Iodide ions such as BF4 - , PF6 - Fluoride ions such as F(HF) n - Halide anions such as NO3 - , O.H. - , C.N. - and an anion component such as the above.

[0058] Among the above inorganic ionic compounds, from the viewpoints of high-temperature stability, compatibility with thermoelectric semiconductor particles and resin, and suppression of a decrease in the electrical conductivity of the gaps between thermoelectric semiconductor particles, it is preferable that the cation component of the inorganic ionic compound contains at least one selected from potassium, sodium, and lithium. Also, it is preferable that the anion component of the inorganic ionic compound contains a halide anion, and Cl - , Br - , and I - It is more preferable that the composition contains at least one selected from the following:

[0059] Specific examples of inorganic ionic compounds in which the cationic component contains potassium cations include KBr, KI, KCl, KF, KOH, K2CO3, etc. Among these, KBr and KI are preferred. Specific examples of inorganic ionic compounds in which the cationic component contains a sodium cation include NaBr, NaI, NaOH, NaF, Na2CO3, etc. Among these, NaBr and NaI are preferred. Specific examples of inorganic ionic compounds in which the cationic component contains lithium cations include LiF, LiOH, LiNO3, etc. Among these, LiF and LiOH are preferred.

[0060] The above inorganic ionic compounds have an electrical conductivity of 10 -7 S / cm or more is preferable, and 10 -6 If the electrical conductivity is in the above range, the conductive additive can effectively suppress a decrease in electrical conductivity between thermoelectric semiconductor particles.

[0061] The inorganic ionic compound preferably has a decomposition temperature of 400° C. or higher. If the decomposition temperature is within the above range, the effect as a conductive additive can be maintained even when a thin film made of the thermoelectric semiconductor composition is annealed, as described below.

[0062] Furthermore, the inorganic ionic compound preferably exhibits a mass loss rate of 10% or less, more preferably 5% or less, and even more preferably 1% or less at 400°C as measured by thermogravimetry (TG). If the mass loss rate is within the above range, the compound can maintain its effectiveness as a conductive additive even when a thin film made of the thermoelectric semiconductor composition is annealed, as described below.

[0063] The amount of the inorganic ionic compound in the thermoelectric semiconductor composition is preferably 0.01 to 50 mass %, more preferably 0.5 to 30 mass %, and even more preferably 1.0 to 10 mass %. When the amount of the inorganic ionic compound is within the above range, a decrease in electrical conductivity can be effectively suppressed, resulting in a film with improved thermoelectric performance. 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 mass%, more preferably 0.5 to 30 mass%, and even more preferably 1.0 to 10 mass%.

[0064] (Method for preparing thermoelectric semiconductor composition) The method for preparing the thermoelectric semiconductor composition used in the present invention is not particularly limited, and the thermoelectric semiconductor composition may be prepared by, for example, mixing and dispersing 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 a solvent, using a known method such as an ultrasonic homogenizer, a spiral mixer, a planetary mixer, a disperser, or a hybrid mixer. Examples of the solvent include toluene, ethyl acetate, methyl ethyl ketone, alcohol, tetrahydrofuran, methylpyrrolidone, ethyl cellosolve, etc. These solvents may be used alone or in combination of two or more. The solids concentration of the thermoelectric semiconductor composition is not particularly limited as long as the composition has a viscosity suitable for coating.

[0065] The thermoelectric conversion material chip made of the thermoelectric semiconductor composition is not particularly limited, and can be formed, for example, by applying the thermoelectric semiconductor composition to a substrate such as glass, alumina, silicon, or a substrate on which a sacrificial layer (described later) is formed to obtain a coating film, and then drying the coating film. By forming the thermoelectric conversion material chip in this manner, a large number of thermoelectric conversion material chips can be obtained easily and at low cost. Methods for applying the thermoelectric semiconductor composition to obtain chips of thermoelectric conversion material include, but are not limited to, known methods such as screen printing, flexographic printing, gravure printing, spin coating, dip coating, die coating, spray coating, bar coating, doctor blade, etc. When forming a coating film in a pattern, screen printing, slot die coating, etc., which allow for easy pattern formation using a screen plate having a desired pattern, are preferably used. The resulting coating film is then dried to form chips of the thermoelectric conversion material, and any conventionally known drying method can be used as the drying method, such as hot air drying, hot roll drying, infrared irradiation, etc. The heating temperature is typically 80 to 150°C, and the heating time, which varies depending on the heating method, is typically several seconds to several tens of minutes. When a solvent is used in preparing the thermoelectric semiconductor composition, the heating temperature is not particularly limited as long as it is within a temperature range that allows the solvent used to be dried.

[0066] The thickness of the thin film made of the thermoelectric semiconductor composition is not particularly limited, but from the viewpoint 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.

[0067] The thermoelectric conversion material chip in the form of a thin film made of the thermoelectric semiconductor composition is preferably further subjected to an annealing treatment (corresponding to the firing (annealing) described above, hereinafter sometimes referred to as "annealing treatment B"). By performing annealing treatment B, the thermoelectric performance can be stabilized and the thermoelectric semiconductor particles in the thin film can undergo crystal growth, thereby further improving the thermoelectric performance. Although there are no particular limitations on annealing treatment B, it is usually performed in an inert gas atmosphere such as nitrogen or argon, in a reducing gas atmosphere, or under vacuum conditions with a controlled gas flow rate, and is performed at 100 to 500°C for several minutes to several tens of hours, depending on the heat resistance temperature of the resin and ionic compound used.

[0068] The sacrificial layer can be made of 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. By using the sacrificial layer, the chip of the thermoelectric conversion material formed on the substrate such as glass can be easily peeled off from the glass or the like after the annealing treatment B. The method for forming the sacrificial layer is not particularly limited, and can be performed by a known method such as flexographic printing or spin coating.

[0069] <Substrate> The substrates of the thermoelectric conversion module used in the present invention, i.e., the first substrate and the second substrate, are not particularly limited, and known substrates such as glass substrates, silicon substrates, ceramic substrates, and resin substrates can be used independently. It is preferable to use a plastic film (resin substrate) that has flexibility and does not affect the decrease in electrical conductivity or the increase in thermal conductivity of the thermoelectric conversion material chip. Among these, polyimide films, polyamide films, polyetherimide films, polyaramid films, and polyamideimide films are preferred as plastic films from the viewpoints of excellent flexibility, the ability to maintain the performance of the thermoelectric conversion module without thermal deformation even when a thin film made of a thermoelectric semiconductor composition is annealed, and high heat resistance and dimensional stability, and further, polyimide films are particularly preferred from the viewpoint of high versatility.

[0070] The thickness of the plastic films used for the first substrate and the second substrate 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. The plastic film preferably has a 5% weight loss temperature of 300°C or higher, more preferably 400°C or higher, as measured by thermogravimetric analysis. The thermal dimensional change rate measured at 200°C in accordance with JIS K7133 (1999) is preferably 0.5% or lower, more preferably 0.3% or lower. The linear expansion coefficient in the planar direction measured in accordance with JIS K7197 (2012) is 0.1 ppm·°C.-1 ~50 ppm·℃ -1 and 0.1 ppm °C -1 ~30 ppm·℃ -1 It is more preferable that:

[0071] <Electrode> Examples of metal materials for the first electrode and the second electrode of the thermoelectric conversion module used in the present invention include, independently, gold, nickel, aluminum, rhodium, platinum, chromium, palladium, stainless steel, molybdenum, and alloys containing any of these metals. The thickness of each layer of the first electrode and the second electrode is preferably 10 nm to 200 μm, more preferably 30 nm to 150 μm, and even more preferably 50 nm to 120 μm. When 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.

[0072] The first electrode and the second electrode are formed using the above-mentioned metal material. Examples of methods for forming the electrodes include a method of processing a substrate into a predetermined pattern shape by known physical or chemical treatments, mainly photolithography, or a combination of these, or a method of directly forming a pattern of an electrode layer by screen printing, stencil printing, inkjet printing, or the like. Examples of methods for forming electrodes without a pattern include vacuum deposition methods such as PVD (physical vapor deposition) methods such as vacuum deposition, sputtering, and ion plating, or CVD (chemical vapor deposition) methods such as thermal CVD and atomic layer deposition (ALD), or various coating methods such as dip coating, spin coating, spray coating, gravure coating, die coating, and doctor blade methods, wet processes such as electrodeposition, silver halide plating, electrolytic plating, electroless plating, and metal foil lamination, and the like, and these methods are selected appropriately depending on the material of the substrate. In the present invention, electrodes are required to have high electrical conductivity and high thermal conductivity in order to maintain thermoelectric performance. Therefore, it is preferable to use electrodes formed by screen printing, stencil printing, electrolytic plating, electroless plating, or vacuum film formation. Depending on the size and dimensional accuracy of the formed pattern, a hard mask such as a metal mask may be used to easily form a pattern. Furthermore, when forming a film by vacuum film formation, the substrate may be heated to a temperature within a range that does not impair the properties of the substrate, for the purpose of improving adhesion to the substrate or removing moisture. When forming a film by plating, a film may be formed by electrolytic plating on a film formed by electroless plating.

[0073] As is clear from the first and second embodiments, in the thermoelectric conversion module of the present invention, the melting point of the second bonding material constituting the thermoelectric conversion module is lower than the melting point of the first bonding material, or the melting point of the second bonding material is lower than the hardening temperature of the first bonding material. Therefore, it is possible to prevent misalignment of the thermoelectric conversion material chips on the electrodes caused by the first bonding material when bonding the second bonding material, thereby suppressing short circuits between adjacent thermoelectric conversion material chips and poor bonding between the thermoelectric conversion material chips and the electrodes, leading to improved thermoelectric performance.

[0074] [Method of manufacturing thermoelectric conversion modules] The thermoelectric conversion module of the present invention is a method for producing a thermoelectric conversion module including a first substrate having a first electrode, a second substrate having a second electrode, a chip of a thermoelectric conversion material made of a thermoelectric semiconductor composition, a first bonding material layer made of a first bonding material that bonds one surface of the chip of the thermoelectric conversion material to the first electrode, and a second bonding material layer made of a second bonding material that bonds the other surface of the chip of the thermoelectric conversion material to the second electrode, (a) forming a first bonding material layer made of a first bonding material on a first electrode on a first substrate; (b) placing one surface of a chip of thermoelectric conversion material on the first bonding material layer obtained in the step (a); (c) a first bonding step of bonding one surface of the chip of the thermoelectric conversion material placed in the step (b) to the first electrode by heating via the first bonding material layer obtained in the step (a); (d) forming a second bonding material layer made of a second bonding material on the second electrode on the second substrate; (e) bonding the other surface of the thermoelectric conversion material chip on the first substrate to the second bonding material layer obtained in (d); and (f) a second bonding step of bonding the other surface of the thermoelectric conversion material chip after the step (e) to the second electrode by heating via the second bonding material layer; The bonding temperature in the second bonding step is lower than the bonding temperature in the first bonding step. Hereinafter, the step (a) will be referred to as the "first bonding material layer forming step", the step (b) as the "thermoelectric conversion material chip mounting step", the step (c) as the "first bonding step", the step (d) as the "second bonding material layer forming step", the step (e) as the "second bonding material layer bonding step", The step (f) is sometimes referred to as the "second joining step." The steps included in the present invention will be explained in order.

[0075] 2A and 2B are explanatory views showing, in order of steps, an example of a method for joining chips of thermoelectric conversion material to electrodes in a method for manufacturing a thermoelectric conversion module of the present invention, in which (p) is a cross-sectional view after forming a first joining material layer 6a made of a first joining material on a first electrode 3a on a first substrate 2a (not shown), and then placing one surface of each of chips 4 of P-type thermoelectric conversion material and chips 5 of N-type thermoelectric conversion material on the first electrode 3a. FIG. 2C is a cross-sectional view after the step of (p) in which the joining material layer 6a is hardened by heating, and one surface of each of chips 4 of P-type thermoelectric conversion material and chips 5 of N-type thermoelectric conversion material is hardened. FIG. 1(r) is a cross-sectional view showing a state in which a second bonding material layer 6b made of a second bonding material is formed on a second electrode 3b on a second substrate 2b (not shown), and these are then bonded to the other surfaces of the chips 4 made of P-type thermoelectric conversion material and the chips 5 made of N-type thermoelectric conversion material, respectively; and FIG. 1(s) is a cross-sectional view showing a state in which the bonding material layer 6b is hardened by heating after the step of (r), and the other surfaces of the chips 4 made of P-type thermoelectric conversion material and the chips 5 made of N-type thermoelectric conversion material are bonded to the second electrode 3b.

[0076] <First bonding material layer formation process> The first bonding material layer forming step is the step (a) in the method for producing a thermoelectric conversion module of the present invention, and is a step of forming a first bonding material layer on a first electrode using a first bonding material. The first bonding material layer is used to bond one surface of each of the P-type thermoelectric conversion chip and the N-type thermoelectric conversion chip to the first electrode. In the present invention, the first bonding material is, for example, the above-mentioned solder material or conductive adhesive. The thickness of the first bonding material layer, the method of applying it onto the first electrode, etc. are as described above.

[0077] <Thermoelectric conversion material chip mounting process> The step of placing chips of thermoelectric conversion material is the step (b) in the method for producing a thermoelectric conversion module of the present invention, and is a step of placing one surface of a chip of thermoelectric conversion material on the first bonding material layer obtained in the step (a). For example, this is a step of placing one surface of a chip of P-type thermoelectric conversion material and one surface of a chip of N-type thermoelectric conversion material on the corresponding upper surface of the first bonding material layer using a hand such as a chip mounter. In the present invention, from the viewpoint of theoretically obtaining high thermoelectric performance, it is preferable that the arrangement of the chips of P-type thermoelectric conversion material and the chips of N-type thermoelectric conversion material be such that multiple pairs of chips of P-type thermoelectric conversion material and chips of N-type thermoelectric conversion material are arranged with electrodes interposed therebetween. The method for placing the thermoelectric conversion material chip on the bonding material layer is not particularly limited, and any known method can be used, such as handling one or more thermoelectric conversion material chips using the aforementioned chip mounter or the like, aligning them with a camera or the like, and then placing them. From the viewpoints of ease of handling, placement accuracy, and mass productivity, it is preferable that the thermoelectric conversion material chips be placed using a chip mounter.

[0078] <First joining process> The first bonding step is step (c) in the method for manufacturing a thermoelectric conversion module of the present invention, and is a step of bonding one surface of the thermoelectric conversion material chip placed in step (b) to the first electrode by heating via the first bonding material layer obtained in step (a), for example, a step of heating the first bonding material layer to a predetermined temperature, maintaining it for a predetermined time, and then returning it to room temperature. The bonding conditions, such as the heating temperature (bonding temperature) and holding time, are as described above.

[0079] <Second bonding material layer formation process> The second bonding material layer forming step is the step (d) in the method for producing a thermoelectric conversion module of the present invention, and is a step of forming a second bonding material layer on the second electrode using a second bonding material. The second bonding material layer is used to bond the other surfaces of the chip of P-type thermoelectric conversion material and the chip of N-type thermoelectric conversion material to the second electrode. In the present invention, for example, the above-mentioned solder material is used as the second bonding material. The thickness of the second bonding material layer, the method of applying it onto the second electrode, etc. are as described above.

[0080] <Second bonding material layer bonding step> The second bonding material layer bonding step is step (e) of the method for manufacturing a thermoelectric conversion module of the present invention, and is a step of bonding the other surface of the thermoelectric conversion material chip on the first substrate to the second bonding material layer obtained in step (d). The other surface of the thermoelectric conversion material chip and the second bonding material layer can be bonded by a known method such as lamination.

[0081] <Second joining process> The second bonding step is the step (f) in the method for producing a thermoelectric conversion module of the present invention, in which the other surface of the thermoelectric conversion material chip is bonded to the second electrode by heating via the second bonding material layer obtained in the step (d). For example, it is a step of heating the second bonding material layer to a predetermined temperature, maintaining it for a predetermined time, and then returning it to room temperature. The bonding conditions, such as the heating temperature (bonding temperature) and holding time, are as described above.

[0082] The heating method in the first bonding step and the second bonding step is not particularly limited, but examples include a method of heating part or the whole of the connection structure using a reflow furnace or an oven, and a method of locally heating only the connection portion of the connection structure. When heating by reflow, for example, the connection structure having the first electrode, the first bonding material layer, and the thermoelectric conversion material chip stacked on the first substrate, and the entire connection structure including the second bonding material layer obtained in the bonding process, are placed inside a reflow heating furnace and heated. Examples of devices used for localized heating include a hot plate, a heat gun that applies hot air, a soldering iron, and an infrared heater. In the present invention, the first and second bonding steps are preferably successively heated by reflow, from the viewpoints of heating the connection structure, ease of manufacturing, and shortening of takt time. The heating in the reflow process varies depending on the combination of the first and second bonding materials, but can be performed under the heating conditions for the solder material and conductive adhesive material described above.

[0083] Another example of a method for manufacturing a thermoelectric conversion module includes the following manufacturing steps (i) to (x). (i) forming a first bonding material layer made of a first bonding material on a first electrode on a first substrate; (ii) placing one surface of a chip of a P-type thermoelectric conversion material on the first bonding material layer obtained in the step (i); (iii) a first bonding step of bonding one surface of the chip of the P-type thermoelectric conversion material placed in the step (ii) to the first electrode by heating via the first bonding material layer obtained in the step (i); (iv) forming a second bonding material layer made of a second bonding material on the other surface of the chip of the P-type thermoelectric conversion material after the step (iii); (v) forming a first bonding material layer made of a first bonding material on the second electrode on the second substrate; (vi) placing one surface of a chip of N-type thermoelectric conversion material on the first bonding material layer obtained in the step (v); (vii) a third bonding step of bonding one surface of the chip of the N-type thermoelectric conversion material placed in the step (vi) to the second electrode by heating via the first bonding material layer obtained in the step (v); (viii) forming a second bonding material layer made of a second bonding material on the other surface of the chip of the N-type thermoelectric conversion material after the step (vii); (ix) a step of bonding the second bonding material layer obtained in the step (viii) to the first electrode of the first substrate after the step (iv), and bonding the second bonding material layer obtained in the step (iv) to the second electrode of the second substrate after the step (viii); and (x) a fourth bonding step of bonding the other surface of the chip of the N-type thermoelectric conversion material after the step (viii) to the first electrode of the first substrate after the step (iv) by heating, with the second bonding material layer obtained in the step (viii) interposed therebetween; and a fifth bonding step of bonding the other surface of the chip of the P-type thermoelectric conversion material after the step (iv) to the second electrode of the second substrate after the step (viii) by heating, with the second bonding material layer obtained in the step (iv) interposed therebetween; The bonding temperature in the fourth bonding step and the bonding temperature in the fifth bonding step are lower than the bonding temperature in the first bonding step and the bonding temperature in the third bonding step. In the third bonding step, bonding is performed under the same conditions as the heating temperature (bonding temperature), holding time, etc. described in the first bonding step described above, and the fourth bonding step and the fifth bonding step are performed simultaneously under the same conditions as the heating temperature (bonding temperature), holding time, etc. described in the second bonding step described above. In this method, for example, first, one side of a chip of P-type thermoelectric conversion material is bonded to a first electrode on a first substrate via a first bonding material layer, and then a second bonding material layer is formed on the other side of the chip of P-type thermoelectric conversion material (only chips of P-type thermoelectric conversion material are present on the first substrate), and then a substrate is manufactured in which one side of a chip of N-type thermoelectric conversion material is bonded to a second electrode on a second substrate via the first bonding material layer, and then a second bonding material layer is formed on the other side of the chip of N-type thermoelectric conversion material (only chips of N-type thermoelectric conversion material are present on the second substrate). Next, the surfaces of the obtained substrates having chips of P-type thermoelectric conversion material or chips of N-type thermoelectric conversion material are placed opposite each other, and the substrates are bonded together so that the chips of P-type thermoelectric conversion material and the chips of N-type thermoelectric conversion material are electrically connected in series alternately over each electrode (π-type thermoelectric conversion element configuration), whereby the other surface of the chip of P-type thermoelectric conversion material is bonded to the second electrode of the second substrate via the second bonding material layer, and the other surface of the chip of N-type thermoelectric conversion material is bonded to the first electrode of the first substrate via the second bonding material layer. However, as defined in the present invention, the bonding temperature of the second bonding material layer is set lower than the bonding temperature of the first bonding material layer. Regarding the arrangement of the chips of P-type thermoelectric conversion material on the first electrode of the first substrate and the arrangement of the chips of N-type thermoelectric conversion material on the second electrode of the second substrate, when the two substrates are bonded together, the chips of P-type thermoelectric conversion material and the chips of N-type thermoelectric conversion material are electrically connected in series alternately over each electrode as described above (π-type thermoelectric conversion element configuration).

[0084] According to the method for manufacturing a thermoelectric conversion module of the present invention, it is possible to prevent misalignment of the thermoelectric conversion material chips on the electrodes originating from the first bonding material that occurs when the second bonding material is bonded, and to suppress short circuits between adjacent thermoelectric conversion material chips and poor bonding between the thermoelectric conversion material chips and the electrodes, which leads to improved manufacturing yield and shorter takt time. [Explanation of symbols]

[0085] 1: Thermoelectric conversion module 2a: First substrate 2b: Second substrate 3a: First electrode 3b: Second electrode 4: P-type thermoelectric conversion material chip 5: N-type thermoelectric conversion material chip 6a: First bonding material layer 6b: Second bonding material layer

Claims

1. A thermoelectric conversion module including: a first substrate having a first electrode; a second substrate having a second electrode; a chip of a thermoelectric conversion material made of a thermoelectric semiconductor composition; a first bonding material layer made of a first bonding material that bonds one surface of the chip of the thermoelectric conversion material to the first electrode; and a second bonding material layer made of a second bonding material that bonds the other surface of the chip of the thermoelectric conversion material to the second electrode, the melting point of the second bonding material is lower than the hardening temperature of the first bonding material; The first bonding material is a conductive adhesive material, and the second bonding material is a solder material. Thermoelectric conversion module.

2. The thermoelectric conversion module according to claim 1 , wherein the difference between the hardening temperature of the first bonding material and the melting point of the second bonding material is 20° C. or more.

3. The thermoelectric conversion module according to claim 1 , wherein the thermoelectric semiconductor composition contains a resin.

4. 4. The thermoelectric conversion module according to claim 3, wherein the resin is a heat-resistant resin, and the thermoelectric semiconductor composition contains a thermoelectric semiconductor material, and one or both of an ionic liquid and an inorganic ionic compound.

5. The thermoelectric conversion module according to claim 4 , wherein the heat-resistant resin is a polyimide resin, a polyamide resin, a polyamideimide resin, or an epoxy resin.

6. The thermoelectric conversion module according to claim 3 , wherein the resin is a binder resin, and the thermoelectric semiconductor composition further comprises a thermoelectric semiconductor material, and one or both of an ionic liquid and an inorganic ionic compound.

7. The thermoelectric conversion module according to claim 6 , wherein the binder resin contains at least one selected from the group consisting of polycarbonate, a cellulose derivative, and a polyvinyl polymer.

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