Method for manufacturing a thermoelectric conversion module

Abstract

In the case where a paste containing metal nanoparticles is used in the manufacture of a thermoelectric conversion module, due to the influence of special fluid properties such as thixotropy, it is difficult to apply a controlled amount of paste on the thermoelectric conversion element, and it is difficult to obtain a high output density as a thermoelectric conversion module due to disconnection or short circuit, etc. The manufacturing method of the thermoelectric conversion module of the present application manufactures a thermoelectric conversion module in which a first conductive member, a thermoelectric conversion element, and a second conductive member are joined by a joining member, and includes the following steps: after applying a first paste containing metal particles on the first conductive member, arranging the thermoelectric conversion element on the first paste, and compressing and spreading the first paste; after applying a second paste containing metal particles on the thermoelectric conversion element in a controlled amount, arranging the second conductive member, and compressing and spreading the second paste; and manufacturing the joining member by sintering the first and second pastes.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a thermoelectric conversion module, which utilizes waste heat as a heat source to directly convert thermal energy into electrical energy. Background Technology

[0002] In recent years, in order to reduce energy consumption, research has been conducted on recovering waste heat from boilers, incinerators, and automobiles in an electrical form. Patent Document 1 discloses the structure of a thermoelectric conversion module that recovers heat in an electrical form. It has a structure in which electrodes (conductive members) are connected to both sides of multiple thermoelectric conversion elements, and discloses the following process: assembling the module by printing a bonding material containing copper particles as metal particles using a metal mask or the like.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: International Publication No. 2019 / 082932 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] As with existing sinterable metal particles, particles containing the following characteristics are referred to as metal nanoparticles: a particle size of 1000 nm or less, designed to achieve a sintering temperature below the melting point of the metal. When coating a paste containing these metal nanoparticles, it is difficult to achieve a controlled amount on the thermoelectric conversion element due to the influence of its characteristic fluid properties. If the coating amount is miscontrolled, it is difficult to obtain a high output density as a thermoelectric conversion module due to issues such as wire breaks or short circuits.

[0008] The purpose of this invention is to provide a method for manufacturing a thermoelectric conversion module with high output density.

[0009] Technical means to solve the problem

[0010] One embodiment of the manufacturing method of the thermoelectric conversion module of the present invention involves manufacturing a thermoelectric conversion module in which a first conductive member, a thermoelectric conversion element, and a second conductive member are joined together by a bonding member, and the manufacturing method of the thermoelectric conversion module includes the following steps:

[0011] After coating the first conductive component with a first paste containing metal particles, the thermoelectric conversion element is disposed on the first paste, and the first paste is compressed and unfolded.

[0012] After applying a second paste containing metal particles to the thermoelectric conversion element in a controlled amount, the second conductive member is disposed, and the second paste is compressed and unfolded; and

[0013] The first paste and the second paste are sintered to form a joint component.

[0014] Furthermore, the first and second pastes preferably contain dispersants and thickeners to maintain dispersion during sedimentation tests.

[0015] Furthermore, in the relationship between shear rate and viscosity, the slope of the first and second pastes is preferably smaller on the side with a higher shear rate than on the side with a lower shear rate.

[0016] Furthermore, a mechanical dispensing machine is preferably used to apply the first and second pastes in controlled amounts.

[0017] Furthermore, it is preferable that the first and second pastes extend to the mating surface of the thermoelectric conversion element, excluding at least a portion of the corners.

[0018] The effects of the invention

[0019] According to the present invention, a method for manufacturing a thermoelectric conversion module with high output density can be provided. Attached Figure Description

[0020] Figure 1 This is a three-dimensional diagram showing the overall structure of the thermoelectric conversion module.

[0021] Figure 2 This is a cross-sectional schematic diagram of a manufacturing process based on the manufacturing process.

[0022] Figure 3 This is a magnified cross-sectional diagram of a portion of the thermoelectric conversion module.

[0023] Figure 4 A graph showing the relationship between the coating amount and screw speed of a mechanical dispensing machine.

[0024] Figure 5 A graph showing the relationship between pressing load and the contact area ratio of a paste containing metal nanoparticles.

[0025] Figure 6 To indicate Figure 15 A three-dimensional image taken from the microscope.

[0026] Figure 7 A scanning electron microscope image of the cross-section of the joint component.

[0027] Figure 8 A perspective view illustrating an example of the shape of a joining member.

[0028] Figure 9 A perspective view illustrating an example of the shape of a joining member.

[0029] Figure 10 A perspective view illustrating an example of the shape of a joining member.

[0030] Figure 11 This is a magnified microscope image of a portion of the thermoelectric conversion module of the comparative example.

[0031] Figure 12 This is a photo of a settlement test.

[0032] Figure 13 This is a diagram showing the relationship between the cycle and output in the thermal cycle of the thermoelectric conversion module.

[0033] Figure 14 The graph shows the correlation between the shear rate and viscosity of the paste.

[0034] Figure 15 A microscope image showing the unfolded shape of a paste containing metal nanoparticles.

[0035] [Explanation of Symbols]

[0036] 10: Thermoelectric conversion module

[0037] 20: Thermoelectric conversion element

[0038] 201: P-type thermoelectric conversion element

[0039] 202: N-type thermoelectric conversion element

[0040] 30: Second conductive component

[0041] 40: Ceramic wiring board

[0042] 401: Ceramic substrate

[0043] 402: First conductive component

[0044] 403: Metallic layer

[0045] 50: Anti-diffusion layer

[0046] 61: Ointment containing metal nanoparticles

[0047] 62: Joining components

[0048] 70: Observation direction under a microscope

[0049] 71: Not joined

[0050] 72: Engagement

[0051] 73: Corner Detailed Implementation

[0052] The following describes embodiments of the invention, but in the description below, "first" and "second" are designated according to the manufacturing sequence. In this embodiment, as an assembly process, the assembly process is performed sequentially from a stationary state, stacking in the opposite direction of gravity. Therefore, with the thermoelectric conversion element as the center, "first" is described below and "second" is described above. Regarding the paste, it is also basically the same that the paste used to connect the lower side of the thermoelectric element to the first conductive member is designated as "first," and the paste used to connect the upper side of the thermoelectric element to the second conductive member is designated as "second." Furthermore, even if there are multiple elements, they can be interchanged. In addition, all the metal nanoparticles described in this invention are metal particles.

[0053] Figure 1 The image shows the thermoelectric conversion module 10 obtained by the present invention. In the thermoelectric conversion module 10, thermoelectric conversion elements 20 are arranged between the second conductive member 30 and the ceramic substrate 40 with the first conductive member. Next, Figure 2 In the diagram, a cross-sectional schematic diagram of a process-based manufacturing process is shown as one embodiment of the manufacturing method of the present invention. Figure 2 (a) in the figure is a cross-sectional view of the prepared ceramic substrate with the first conductive member. In this embodiment, the following example will be used for illustration: a first conductive member 402 is provided on the upper surface of the ceramic substrate 401, and a member with a metal layer 403 is provided on the lower surface of the ceramic substrate 401. By providing the metal layer 403 in this way, the contact thermal resistance when placed in a heat source can be reduced, which is therefore preferred. Regarding the ceramic substrate 401, an insulating ceramic substrate can be used. For example, by using ceramic materials such as alumina, aluminum nitride, or silicon nitride, it can be used in a wide temperature range from low to high temperatures, which is therefore preferred. The first conductive member 402 only needs to have a surface that can bond with metal nanoparticles. For example, nickel plating can also be applied to the surface.

[0054] Figure 2 (b) describes the process of applying a paste 61 (first paste) containing metal nanoparticles to the first conductive member 402. In the following description of the paste 61 containing metal nanoparticles, terms such as "configuration" are used, but configuration includes not only simple placement but also the following action: compressing the paste 61 to unfold it into a predetermined shape and placing it in contact with each member.

[0055] The metal nanoparticles are metals with a melting point higher than the temperature at which the thermoelectric conversion element is bonded to the conductive component. A paste 61 (first paste) containing metal nanoparticles is coated onto the first conductive component 402. The coating of the paste 61 (first paste) containing metal nanoparticles onto the first conductive component 402 does not necessarily require a mechanical dispensing machine; other printing or dispensing machines can be used to coat the required amount and shape.

[0056] Figure 2 (c) describes a process in which a thermoelectric conversion element is placed on a paste containing metal nanoparticles using a mounter, and the paste 61 (first paste) containing metal nanoparticles is compressed and unfolded via the thermoelectric conversion element. Here, the thermoelectric conversion elements may also be connected in series with the P-type thermoelectric conversion element 201 and the N-type thermoelectric conversion element 202 to increase the voltage. Figure 2 Examples of the described situation are shown below. Furthermore, in the following description, when referred to as thermoelectric conversion elements, it means P-type thermoelectric conversion element 201 and / or N-type thermoelectric conversion element 202. Each thermoelectric conversion element can be spread by the load during configuration of the paste 61 containing metal nanoparticles. Thus, the spread metal nanoparticle paste 61 (first paste) can be used to ensure the bonding area between the first conductive member 402 and the thermoelectric conversion element, which is therefore preferred.

[0057] Figure 2 Step (d) in the text describes the process of applying a paste 61 (second paste) containing metal nanoparticles to the thermoelectric conversion element in a controlled amount using a mechanical dispensing machine after the thermoelectric conversion element has been configured. When using a mechanical dispensing machine, the paste 61 (second paste) containing metal nanoparticles can be applied to the thermoelectric conversion element without contacting it. Therefore, it prevents positional displacement of the thermoelectric conversion element, which is preferable. Furthermore, the paste containing metal nanoparticles, described later, can be applied in a controlled amount.

[0058] Figure 2 (e) describes the process of applying a paste 61 (second paste) containing metal nanoparticles onto the thermoelectric conversion element, then using a mounting machine to place the second conductive member 30, and compressing and unfolding the paste 61 (second paste) containing metal nanoparticles. The paste 61 (second paste) containing metal nanoparticles can be unfolded by a compression load. Therefore, the unfolded paste containing metal nanoparticles can be used to ensure the bonding area between the second conductive member 30 and the thermoelectric conversion element, which is preferable.

[0059] Figure 2 (f) describes the process of sintering metal nanoparticles to form a bonding member. By heating pastes 61 (first paste and second paste) containing metal nanoparticles, placed between the first conductive member and the thermoelectric conversion element, and between the second conductive member and the thermoelectric conversion element, components other than the metal nanoparticles evaporate, followed by sintering of the metal nanoparticles. Thus, a bonding member 62 is formed between the first conductive member and the thermoelectric conversion element, and between the second conductive member and the thermoelectric conversion element, through the sintering of metal nanoparticles. This facilitates heat conduction to the upper and lower surfaces of the thermoelectric conversion element, thereby enabling the manufacture of a thermoelectric conversion module with high output density.

[0060] Figure 3 To be Figure 1 The diagram shows an enlarged cross-sectional view of a portion of the thermoelectric conversion module 10. The first conductive member 402 is joined to the P-type and N-type thermoelectric conversion elements 201 and 202, respectively, and the P-type and N-type thermoelectric conversion elements 201 and 202 are joined to the second conductive member 30 via joining members 62. The greater the temperature difference between the upper and lower surfaces of the P-type and N-type thermoelectric conversion elements 201 and 202, the higher the output of the thermoelectric conversion module. Without joining members 62, the thermoelectric conversion elements and conductive members are in a simple, non-jointed contact state, resulting in high thermal resistance and a smaller temperature difference generated by the thermoelectric conversion elements. Therefore, the thermoelectric conversion elements are joined to the first conductive member 402, and the thermoelectric conversion elements are joined to the second conductive member 30, respectively, via joining members 62. Furthermore, an anti-diffusion layer 50 can be provided to prevent element diffusion between the joining members 62 and the thermoelectric conversion elements 201 and 202. Figure 3 In this design, the anti-diffusion layer 50 is represented by a single layer structure between the thermoelectric conversion element and the bonding member. The anti-diffusion layer 50 is composed of monomeric metals, alloys, intermetallic compounds, nitrides, etc. To achieve a higher anti-diffusion effect, the anti-diffusion layer 50 may also be composed of multiple layers including monomeric metals, alloys, intermetallic compounds, nitrides, etc. Even when the anti-diffusion layer is composed of a single layer or multiple layers, it can be effectively resisted by using... Figure 2 The thermoelectric conversion module is assembled using the same manufacturing method as the described embodiment. As an anti-diffusion layer, it only needs to be conductive and have the function of preventing elemental diffusion caused by heat; for example, it can be a layer containing nickel, titanium, aluminum, antimony, etc. These can be fabricated, for example, by integral sintering while manufacturing the thermoelectric conversion element.

[0061] The metal nanoparticles are metals with a bonding temperature higher than their melting point. For example, when pastes containing metal nanoparticles are disposed between the first conductive member and the thermoelectric conversion element, and between the second conductive member and the thermoelectric conversion element, and heated to 400°C, it is preferable to use copper (Cu) with a melting point of 1085°C, nickel (Ni) with a melting point of 1455°C, or silver (Ag) with a melting point of 961°C, as these materials do not exhibit fluidity during heating, thus suppressing element movement. The metal nanoparticles can be not only the single metal but also alloys containing one or more of the aforementioned metal elements. It is preferable if the mass concentration of the metal nanoparticles in the paste is 80 mass% or more relative to the total mass of the paste.

[0062] Furthermore, the metal nanoparticles are ideally spherical to promote uniform sintering. Spherical metal nanoparticles with an average particle size of 20 nm or more and 1000 nm or less are preferred, and secondary particles formed by the aggregation of these particles may also be included. Moreover, they do not necessarily have to be aggregated secondary particles; even spherical powder particles of 1 μm to 50 μm are acceptable. Ideally, an organic film layer is formed on the surface of the metal nanoparticles. The organic film layer prevents excessive aggregation, and by reducing the oxide film or similar material formed on the surface of the metal nanoparticles during bonding, sintering is easily achieved. For example, bonding based on sintering can be performed by holding the nanoparticles at 300°C to 400°C for 5 to 60 minutes in a hydrogen atmosphere or a reducing gas atmosphere containing hydrogen.

[0063] The coating of a paste containing metal nanoparticles includes the following steps: coating a first conductive member and bringing it into contact with a thermoelectric conversion element; and applying the paste containing metal nanoparticles to the thermoelectric conversion element using a mechanical dispensing machine, bringing it into contact with a second conductive member. That is, the overall bonding method is as follows: while the paste containing metal nanoparticles is in contact with both sides of the thermoelectric conversion element, heating is performed, thereby bonding the first conductive member, the thermoelectric conversion element, and the second conductive member in a single step.

[0064] The paste containing metal nanoparticles may simply contain the metal nanoparticles of the bonding member and an organic solvent such as water, glycol-based solvent, or glycol ether-based solvent as the main solvent. By including these components, excessive aggregation of the bonding member composed of metal nanoparticles can be prevented, and the dispersion of the bonding member can be maintained. If the dispersion of the metal nanoparticles is maintained, stable coating can be performed using a mechanical dispensing machine described later.

[0065] Furthermore, the paste containing metal nanoparticles preferably includes a dispersant and a thickener to maintain dispersion during sedimentation tests. Firstly, a dispersant refers to an agent that adheres to the surface of the metal nanoparticles and functions by hindering van der Waals forces that interact between the particles. Examples of substances that function as dispersants in organic solvents include: glycol ethers or esters, ester ethers, phenyl ethers, alkyl glucosides, acid amides, amines, alkanolamides, and other nonionic surfactants. Systems containing polyoxyalkylene groups in their molecular chains are particularly effective due to the presence of both hydrophilic and hydrophobic groups; diethylene glycol monobutyl ether or diethylene glycol monobutyl ether acetate, dipropylene glycol methyl ether, etc., are preferred.

[0066] Next, the term "thickener" refers to a substance that increases the viscosity of a paste, thus slowing down the settling speed of particles. Thickeners include solutions with high viscosity and substances that act as binders. A binder is a substance that increases viscosity by restricting interactions between particles and solutions or between particles themselves using organic molecular chains with polar groups. Representative binders include polyoxyalkylene oxides or polyvinyl alcohols, which, in pastes using metal nanoparticles, ideally volatilize at temperatures below 300°C, which is lower than the sintering temperature. Polydiols with an average molecular weight of 400 or less and which are liquid at room temperature are particularly desirable. The dispersant and thickener can be arbitrarily determined based on factors such as the viscosity of the paste. For example, relative to the volume of solvent only (excluding metal nanoparticles), the thickener ratio is preferably greater than 0 vol% and less than 100 vol%, more preferably 5 vol% or more and 95 vol% or less, and particularly preferably 30 vol% or more and 90 vol% or less.

[0067] The sedimentation test is explained below. In the sedimentation test, a certain amount of suspension of metal nanoparticles is placed in a graduated cylinder and allowed to stand. The ratio of the clear region to the turbid region is observed at regular intervals for evaluation. Here, the suspension refers to only the solvent, excluding the metal nanoparticles. The clear region is defined as the region with the same transparency as a liquid prepared in another graduated cylinder containing no metal nanoparticles and using organic solvents such as water, glycol-based solvents, or glycol ether-based solvents as the main solvent. An example is shown below. Figure 12 . Figure 12 From left to right, the images are side-view photographs of graduated cylinders containing suspensions with thickener ratios of 0 vol%, 20 vol%, 40 vol%, 60 vol%, 80 vol%, and 100 vol% after 6 days. The dashed line represents the baseline (10%) of the clarified region relative to the total mass. Samples with less clarified region in the evaluated metal nanoparticle suspension maintain better dispersibility and are less prone to sedimentation. In this invention, dispersion is considered maintained when the clarified region becomes less than 10% of the total mass after 6 days.

[0068] When applying a paste containing metal nanoparticles to a thermoelectric conversion element, a mechanical dispensing machine controls the amount of paste applied by adjusting the screw rotation. Compared to air pulse dispensing machines or printing methods, this method allows for the application of the paste containing metal nanoparticles in a controlled amount, which is preferable. The screw rotation speed can be appropriately set according to the coating conditions, etc. For example, a screw rotation speed of less than 20 rpm is preferred to maintain the dispersion state of the metal nanoparticles in the main solvent of the applied paste. On the other hand, considering an appropriate cycle time based on the paste application time, a speed of 5 rpm or more is preferable. From the viewpoint of the dispersion state of the metal nanoparticles and the cycle time, 5 rpm to 15 rpm is more preferable.

[0069] The following explains in detail why mechanical coating is particularly preferred in the application of a dispensing machine. The ratio of the main solvent to the metal nanoparticles in the paste also affects the sedimentation rate, dispersibility, or thixotropy of the metal nanoparticles themselves. Thixotropy is a characteristic fluid property, representing the change in paste viscosity relative to shear rate (the rate of deformation when force is applied to the paste) or its change over time. It is particularly evident when the influence of interactions between metal nanoparticles is greater than the interaction between metal nanoparticles and the solvent. To confirm whether thixotropy exists, for example, if... Figure 14 The correlation between viscosity and shear rate can be confirmed as shown in the figure. Figure 14 The diagram illustrates three examples of thixotropy. The mixed-ratio metal nanoparticles exhibit stronger interparticle interactions than typical powders due to their increased specific surface area, leading to easier particle aggregation. In regions with higher shear rates, the interactions between metal nanoparticles in the main solvent are disrupted, resulting in a sharp decrease in viscosity. This corresponds to a smaller slope on the side of higher shear rate compared to the side of lower shear rate in the previously described viscosity-shear rate correlation. In other words, high thixotropy becomes a characteristic feature. Figure 14 In the three examples exhibiting thixotropy, all showed regions where the viscosity decreased sharply. In the case of a mechanical dispensing machine, unlike the air-pulsation method, the dispensing volume is mechanically controlled by the rotation of a servo motor, thus suppressing the effects of air pressure inhomogeneity common in air-pulsation methods. That is, compared to air-pulsation methods, it is less likely to cause changes in the agglomeration or dispersion structure of metal nanoparticles before and after needle passage due to pressure variations. A mechanical dispensing machine is defined as one that applies a force other than an extrusion force, such as a rotational shear force, to the paste. Specifically, a structure in which the piston rotates while extruding the paste is conceived. Using a force other than an extrusion force, even if the interaction between metal nanoparticles is strong and they agglomerate, it is easier to cause the agglomerates to break down, and therefore this is preferable.

[0070] In thermoelectric conversion modules, a paste containing metal nanoparticles is applied to both the top and bottom of the thermoelectric conversion element. However, when the paste is applied to at least the thermoelectric conversion element, a mechanical dispensing machine is used. For example, when the paste is applied to the thermoelectric conversion element by printing, the screen mask or metal mask comes into contact with the thermoelectric conversion element during printing, causing a short circuit that leads to positional displacement of the thermoelectric conversion element, resulting in a decrease in the power generation performance of the thermoelectric conversion module. In contrast, with a mechanical dispensing machine, the paste can be applied to the thermoelectric conversion element in a non-contact manner, suppressing positional displacement of the thermoelectric conversion element. Here, "above" and "below" are used for ease of explanation, but as mentioned above, they can also be replaced with "first and second," or one of them and the other, etc. That is, the important point in this invention is that a mechanical dispensing machine is used to apply a controlled amount of the paste containing metal nanoparticles to the thermoelectric conversion element that has already been coated with the paste containing metal nanoparticles.

[0071] Figure 4 This graph illustrates the relationship between screw speed and coating amount when the screw speed is set to 10 rpm for applying a paste containing metal nanoparticles. It shows that the coating amount increases steadily and linearly with increasing screw speed. That is, the amount of paste containing metal nanoparticles can be applied in a controlled manner by adjusting the screw speed. Within the specified screw speed range, this can achieve… Figure 4 The coating shown is stable. The viscosity of the paste containing metal nanoparticles is preferably 100 Pa·s to 1600 Pa·s at 1 rpm, 50 Pa·s to 900 Pa·s at 3 rpm, 50 Pa·s to 450 Pa·s at 5 rpm, 50 Pa·s to 150 Pa·s at 10 rpm, and below 50 Pa·s at 15 rpm. If the viscosity of the paste containing metal nanoparticles is within the aforementioned range, the coating amount is easily controlled and applied appropriately, and short circuits are less likely to occur, thus easily suppressing the reduction in power generation of the thermoelectric conversion module, which is therefore preferred.

[0072] Ideally, the assembly method for the thermoelectric conversion module involves applying a paste containing metal nanoparticles to the thermoelectric conversion element using a mechanical dispensing machine, and then using a mounting machine to place the thermoelectric conversion element and conductive components. More preferably, the paste containing metal nanoparticles is compressed and unfolded during the placement of the thermoelectric conversion element or conductive components. The mounting machine can use a suction nozzle to pick up the components and mount them in a designated position, resulting in high assembly accuracy. Furthermore, the mounting height can be adjusted when mounting the components in the designated position, or the mounting load can be adjusted by using a spring-loaded nozzle. That is, the metal nanoparticle paste applied by the mechanical dispensing machine can be unfolded using a designated load during component mounting. In the following explanation, the load required to unfold the metal nanoparticle paste will be defined as the paste load. Figure 5The figure shows the relationship between the pressing load and the contact area ratio of the paste containing metal nanoparticles. The paste contact area ratio (%) represents the ratio of the area of ​​the paste containing metal nanoparticles applied to and spread on the conductive component relative to the area of ​​the mating surface (4mm × 4mm) of the thermoelectric conversion element. Furthermore, Figure 5 The coating conditions 1 and 2 shown illustrate variations in the coating amount. The paste contact area ratio refers to the macroscopic bonding area, excluding voids (pores) within the bonding area as seen microscopically. Loading loads of 1.6N, 4N, 8N, 16N, and 32N are presented. As shown here, the paste contact area ratio increases sharply from the initial coating load (0N) using a mechanical dispensing machine up to 1.6N. However, even with increased load, the increase is not linear. If a certain load is exceeded, the paste containing metal nanoparticles becomes difficult to spread.

[0073] For the bonding surface of a thermoelectric conversion element or conductive component, there are one or more independent patterns coated using a mechanical dispensing machine, thus applying surface pressure (Pa) to each pattern group with a small coating area. Therefore, even under low load, the local surface pressure becomes high, allowing the contact area to expand rapidly. On the other hand, at 4N and above, the increase rate of the paste contact area ratio relative to the increase in load is small. Depending on the coating conditions, above 32N (equivalent to 2MPa for a 4mm × 4mm element area), the contact area ratio is large but does not exceed 100%. Above 1.6N, the separately existing independent coating patterns fuse due to pressure, thus dispersing the surface pressure. Therefore, even with increased load, the paste contact area does not increase to a necessary extent. That is, when compression is applied using a second conductive component, it is mainly the paste containing metal nanoparticles on the thermoelectric conversion element that expands, while the expansion area of ​​the paste containing metal nanoparticles on the first conductive component remains almost unchanged. Therefore, short circuits caused by paste exudation are less likely to occur. Therefore, according to Figure 5 The relationship between load and paste contact area ratio shown can suppress excessive spread of the paste on the previously compressed first conductive member during the process of compressing the paste after coating the upper surface of the thermoelectric conversion element with a paste containing metal nanoparticles. Furthermore, even under excessive pressure due to the influence of clamps, excessive spread of the paste can be suppressed. Therefore, short circuits in the thermoelectric conversion module can be suppressed, which is preferable. Furthermore, by coating the bonding surface of the thermoelectric conversion element at multiple locations or at positions where the spread shape is envisioned, the shape of the bonding member can be easily controlled, which is also preferable. For example, if the bonding surface of the thermoelectric conversion element 20 has a shape with four corners (rectangular or square), it is preferable to coat it at positions extending from the center to each corner, thereby spreading it to the four corners.

[0074] Figure 2In step (f), a paste containing metal nanoparticles disposed between the thermoelectric conversion element and the conductive component is sintered. The sinterability of the metal nanoparticles is improved due to the reduction reaction, therefore bonding is more preferably performed in a gaseous environment exhibiting a reduction reaction, such as hydrogen or a nitrogen + hydrogen mixture. The bonding temperature is in the range of 300–400°C, and the pressure applied vertically to the upper and lower surfaces of the thermoelectric conversion element is preferably greater than 0 MPa and less than 2 MPa, more preferably 0.1 MPa to 0.5 MPa. By applying pressure during sintering, close contact is achieved between the metal nanoparticles serving as bonding components and with the bonded material (the anti-diffusion layer or conductive component formed on the surface of the thermoelectric conversion element), thus facilitating sintering and improving bonding strength. The pressure range is... Figure 3 Within the range shown, even under pressure during sintering, excessive exudation of the paste containing metal nanoparticles is unlikely to occur. The bonding area of ​​the metal nanoparticles can be controlled during mounting using a mounting machine, thus preventing a decrease in bonding strength due to insufficient bonding area.

[0075] The preferred embodiments relating to the joining members will be described below.

[0076] First, considering the thermal conductivity of the bonding member, the contact area ratio of the paste in the bonding member is preferably formed to be 50% or more and 100% or less. If it is 50% or more, the heat conducted from the conductive member can be sufficiently conducted to the thermoelectric conversion element, which is therefore preferred. If it is 100% or less, short circuits caused by excessive exudation from the bonding member can be prevented, which is also preferred. Furthermore, 85% or more is preferred, and more preferably 95% or more is preferred.

[0077] The bonding member that unfolds within the area of ​​the thermoelectric conversion module, viewed from above the first or second conductive member, does not short-circuit with adjacent conductive members, and is therefore preferred. This can be achieved by ensuring that the paste containing metal nanoparticles is unfolded at least within the area of ​​the first or second conductive member before sintering, and maintains this state after sintering. As an example, in Embodiment 4 described later, a thermoelectric conversion element is disposed on a paste containing metal nanoparticles coated on the first conductive member. After the process of compressing and unfolding the paste containing the metal nanoparticles, a photograph of the first conductive member viewed from the thermoelectric conversion element side is shown. Figure 6 . Figure 6 The microscope's observation direction is 70°. Figure 15For observation purposes, it can be seen that at this time, the paste that has seeped from the area of ​​the thermoelectric conversion element and the bonding member is contained within the area of ​​the first conductive member. Furthermore, it is preferable to coat it within the area of ​​the thermoelectric conversion element, thereby more reliably preventing short circuits. The seepage of paste containing metal nanoparticles from the first conductive member leads to a short circuit. If a short circuit occurs, it becomes a parallel circuit, thus resulting in a decrease in output density. Therefore, in the embodiments described later, a case where the paste containing metal nanoparticles does not seep from the first conductive member is recorded as good, and a case where it does seep is recorded as bad.

[0078] and, Figure 6 The structure is such that the paste containing metal nanoparticles does not contact the corner 73 of the thermoelectric conversion element (the back side is an anti-diffusion layer). Therefore, when a temperature difference is generated in the thermoelectric conversion module, stress concentration at the corner of the thermoelectric conversion element can be reduced, which is preferable. When the thermoelectric conversion module is under bonding stress during operation, stress locally concentrates at the shape change portion. To suppress stress concentration, it is important to make the shape change slow. After the thermoelectric conversion material is sintered, a prismatic thermoelectric conversion element is made using a multi-wire saw or the like. Therefore, stress easily concentrates at the corner of the thermoelectric conversion element. When the paste containing metal nanoparticles does not contact the corner of the thermoelectric conversion element, the bonding portion undergoes a slow shape change, thus reducing the thermal stress on the thermoelectric conversion element or the anti-diffusion layer compared to coating the entire bonding surface. That is, damage to the anti-diffusion layer or the thermoelectric conversion element is less likely to occur, and a thermoelectric conversion module structure with high output density can be manufactured. In this thermoelectric conversion module, a first conductive member, a thermoelectric conversion element, and a second conductive member are joined by a joining member of a predetermined and controlled amount. The thermoelectric conversion element has corners in its cross-sectional shape, and the joining member extends to the extent of the thermoelectric conversion element, excluding at least a portion of the corners. In particular... Figure 6 The middle part is preferred because it includes the area excluding all four corners.

[0079] Hereinafter, as a preferred embodiment related to the joining member, the case in which the grease contact area ratio of the joining member is formed to be 70% or more and 100% or less will be described.

[0080] Regarding the thickness of the bonding member, it is defined as the thickness of the bonding layer formed between the thermoelectric conversion element and the conductive member. Preferably, the thickness is 5 μm or more and 80 μm or less. More preferably, the thickness of the bonding member is 5 μm or more and 30 μm or less. If it is 5 μm or more, the amount discharged to the outside of the thermoelectric conversion element is reduced, thus further preventing a short circuit. If it is 80 μm or less, the pressure applied during bonding is appropriate, thereby reducing the likelihood of unbonded portions forming at the bonding interface and facilitating heat conduction from the first and second conductive members to the thermoelectric conversion element, which is therefore preferred. When the thickness is 30 μm or less, the unbonded portions at the bonding interface are further reduced, thus also leading to improved bonding strength, which is even more preferable. Figure 7 Image (a) is a partial cross-sectional view of the joint in Example 4 described later, with a joint thickness of 80 μm. Although an unjoined portion 71 is locally generated at the joint interface, a joined portion 72 is also present. Therefore, the output density is 1.6 W / cm³. 2 Therefore, heat conduction or transfer can be considered to be without problems. On the other hand, due to the low density of the joint, the deformation capacity of the joint itself is improved, and a stress relief effect can be expected. Figure 7 (b) is a partial cross-sectional view of the joint of Example 7 described later, with a joint thickness of 30 μm. Figure 7 (c) is another cross-sectional view of the same joint in Example 7, with a joint thickness of 20 μm, and almost no unjoined parts were generated at the joint interface.

[0081] The following explanation concerns the thermal stress applied to the joint components of the thermoelectric conversion module. Figure 9 The coating shape joins the thermoelectric conversion module, and the thermal stress loaded on the thermoelectric conversion element under a temperature change of 350°C to 25°C is calculated using finite element analysis. Relative to Figure 8 The coating shape has a thermal stress ratio of 0.52. In this invention, precise coating can be performed when preparing the paste containing metal nanoparticles, thus allowing control over the coating shape. Therefore, when manufacturing a thermoelectric conversion module with high output density, it is also possible to manufacture a thermoelectric conversion module with high thermal stress resistance. Furthermore, the paste contact area ratio is 90%. If the paste contact area ratio is 90% or less, a reduction in thermal stress is expected; if it is 70% or less, the thermal stress loaded on the thermoelectric conversion element or the anti-diffusion layer can be further reduced. The bonding area can be appropriately adjusted to correspond to the thermal stress loaded on the bonding member itself. It can be considered that by adjusting the bonding area, the thermal stress loaded on the thermoelectric conversion element or the anti-diffusion layer can be reduced, and the increase in stress loaded on the bonding member itself can be suppressed.

[0082] The following explanation concerns the thermal stress in the manufacturing method of the thermoelectric conversion module, specifically in the case of changing the shape of the joining member. Figure 10 The coating shape joins the thermoelectric conversion module, and the thermal stress loaded on the thermoelectric conversion element under a temperature change of 350°C to 25°C is calculated using finite element analysis. Relative to Figure 8 The coating shape achieves a thermal stress ratio of 0.65. That is, by spreading the metal nanoparticle paste to the area excluding the corners of the thermoelectric conversion element, a thermoelectric conversion module with high thermal stress resistance can also be manufactured. Furthermore, the paste contact area ratio at this point is 98%.

[0083] In this invention, with the preferred embodiment of the connecting member described above as the objective, it is believed that various effects can be obtained by appropriately adjusting conditions, etc.

[0084] Example

[0085] The first embodiment of the manufacturing method of the thermoelectric conversion module will be described below. The results of the first to ninth embodiments are summarized in Table 1. In the following embodiments, silicon nitride is used as the ceramic substrate in terms of strength and thermal conductivity. The first conductive member and the metal layer are formed by soldering a copper plate to the ceramic substrate and performing etching or other processes.

[0086] In this embodiment, an eight-pair thermoelectric conversion module is fabricated, using eight P-type and eight N-type thermoelectric conversion elements. The external dimensions are 20mm × 20mm × 5.8mm. To connect the eight thermoelectric conversion elements in series, a circuit pattern with a first conductive component is formed. After placing the ceramic substrate with the circuit pattern in a fixture for transfer to a placement machine, a paste containing metal nanoparticles is applied to the first conductive component using a mechanical dispensing machine within the placement machine. Copper is used as the metal nanoparticle; hereinafter, it is sometimes referred to as copper nanoparticle paste. Regarding the viscosity of the copper nanoparticle paste, a paste adjusted to the following viscosities is used: 400 Pa·s at 1 rpm, 100 Pa·s at 3 rpm, 91 Pa·s at 5 rpm, 63 Pa·s at 10 rpm, and 50 Pa·s at 15 rpm. The copper nanoparticle paste is applied in the following pattern: it is applied at equal intervals to a total of 9 points on the bonding surface of the thermoelectric conversion element. The screw speed during dispensing is set to 10 rpm.

[0087] Regarding the copper nanoparticle paste, copper nanoparticles for bonding purposes are used. The mass concentration of copper nanoparticles in the paste, relative to the total mass of the paste, is set at 87 mass%. Diethylene glycol monobutyl ether is used as the main solvent and dispersant. Polyethylene glycol with an average molecular weight of 400 is used as the thickener. In the copper nanoparticle paste, the dispersant is set at 60 vol% and the thickener at 40 vol% by volume ratio of solvent only (excluding copper nanoparticles), and the paste is prepared by mixing using a rotary mixer.

[0088] Furthermore, during the preparation of the copper nanoparticle paste, as part of the elemental experiments, sedimentation tests were used to evaluate sedimentation separation performance in order to confirm the effect of adding a thickener to diethylene glycol monobutyl ether (DGE), which serves as both the main solvent and dispersant. The total volume of DGE and polyethylene glycol was set to 100 vol%, and the volume ratio of polyethylene glycol was set to 0 vol%, 20 vol%, 40 vol%, 60 vol%, and 80 vol% to disperse 0.1 mass% of copper nanoparticles. As shown in Table 2, in systems with a polyethylene glycol mixing ratio of 0 vol% and 20 vol%, particle sedimentation was confirmed within one day. However, in systems with a polyethylene glycol mixing ratio of 40 vol% or higher, complete particle sedimentation took more than 10 days. It can be considered that in systems with high particle concentrations, such as pastes, sedimentation is interfered with, and the sedimentation rate is slower compared to free sedimentation in experiments with dilute systems, thus making these systems difficult to separate over a long period. Regarding the difficulty in separation, this can be considered as a system with a long lifespan for the paste, allowing for more stable spraying. Based on the above, polyethylene glycol is ideally above 20 vol%, specifically above 40 vol%, with a selected thickener of 40 vol%.

[0089] Furthermore, the following describes the elemental experiments on the manufacturing method of the thermoelectric conversion module and the application of a paste containing metal nanoparticles. Copper nanoparticle paste was applied as a paste containing metal nanoparticles to a ceramic substrate with a circuit pattern formed but without module assembly. The copper nanoparticle paste used was the same as in Example 1. The screw speed during dispensing was set to 15 rpm. Continuous coating was performed on the circuit pattern at 320°, and four substrates were checked for any coating defects. Regarding the copper nanoparticle paste, copper nanoparticle paste that had just been poured into the dispensing cylinder, had been left to stand for 3 days, and had been left to stand for 18 days were prepared and applied separately. The results showed that no uncoated areas were observed. Based on these results, it can be concluded that even with variations in screw speed, a thermoelectric conversion module can be manufactured by applying copper nanoparticle paste.

[0090] For elemental comparison experiments, the following paste was used. This paste was made solely from diethylene glycol monobutyl ether (DEME) and copper nanoparticles without a thickener. Copper nanoparticle pastes were prepared after being poured into a dispensing cylinder and allowed to stand for 3 days and 18 days, respectively. Continuous coating was applied at 320 points on each of the four substrates to check for coating defects. The results showed that the 18-day-old sample exhibited uneven coating up to 320 points. At 321 points, the dispensing cylinder became clogged, preventing further coating.

[0091] Thermoelectric conversion elements were constructed using P-type (Fe-Sb skutterudite) and N-type (Co-Sb skutterudite) thermoelectric conversion elements, each with dimensions of 4mm × 4mm × 4mm. The P-type and N-type thermoelectric conversion elements were alternately mounted on copper nanoparticle paste using a mounting machine. The mounting load was adjusted to approximately 1.6N, and the copper nanoparticle paste was spread across the bonding surfaces of the P-type and N-type thermoelectric conversion elements using this load. Then, copper nanoparticle paste was applied to the upper surfaces of the P-type and N-type thermoelectric conversion elements using a mechanical dispensing machine. The application pattern was identical to that applied to the first conductive component. Finally, a second conductive component was mounted onto the nanoparticle paste with a 0.4mm gap using the mounting machine to fabricate the thermoelectric conversion module assembly. The second conductive component is a composite metal conductive component with copper and molybdenum as the main elements, taking into account the linear expansion coefficients of the P-type and N-type thermoelectric conversion elements. It measures 9.6mm × 4.6mm.

[0092] like Figure 3 As shown, an anti-diffusion layer is formed on the upper and lower surfaces of the P-type and N-type thermoelectric conversion elements. This anti-diffusion layer is essentially brought into contact with the copper nanoparticle paste to form a bonding layer for the bonding component. In this embodiment, the anti-diffusion layer, starting from the surface side of the thermoelectric conversion element, consists of two layers: a 200 μm thick layer containing aluminum-titanium and thermoelectric conversion element components, and a 100 μm thick nickel layer. The bonding temperature is set to 350°C, the bonding holding time is set to 15 minutes, the bonding gas environment is set to a hydrogen environment, and the bonding pressure is set to 0.5 MPa.

[0093] Performance was measured by clamping the upper and lower surfaces of the thermoelectric conversion module using a heating block and a cooling block, applying pressure while simultaneously supplying a temperature difference. The measured pressure was 1 MPa, and the temperatures of the upper and lower surfaces of the thermoelectric conversion module were set as shown in Table 1 (high-temperature and low-temperature sides, respectively). A result of 1.94 W / cm² was obtained. 2 The output can be used to manufacture thermoelectric conversion modules with high power generation output. The unfolding method of the copper nanoparticles in Example 1 is shown below. Figure 8Here, it is schematically shown through thermoelectric conversion elements, etc. At this time, the bonding area of ​​the copper nanoparticles is 100% relative to the bonding area of ​​the thermoelectric conversion element.

[0094] The following describes a second embodiment of the manufacturing method for the thermoelectric conversion module. The first embodiment is the same as the manufacturing method. This embodiment is based on the results obtained by evaluating the performance of the thermoelectric conversion module under a pressure of 2 MPa and other conditions as shown in Table 1. A result of 2.68 W / cm² was obtained. 2 The output can be used to manufacture thermoelectric conversion modules that have high power generation output even under high pressure environments.

[0095] The following describes a third embodiment of the manufacturing method for the thermoelectric conversion module. The manufacturing method is the same as that of the first embodiment. This embodiment is based on the performance evaluation results obtained by measuring the pressure at 3 MPa and other conditions as shown in Table 1. Even under a higher pressure environment than the second embodiment, an output density of 2.76 W / cm³ can be obtained. 2 It can manufacture thermoelectric conversion modules that have high power generation output even under higher pressure environments.

[0096] The following describes a fourth embodiment of the manufacturing method for a thermoelectric conversion module. In this embodiment, the module is manufactured... Figure 1 The thermoelectric conversion module shown uses 32 P-type thermoelectric conversion elements 201 and 32 N-type thermoelectric conversion elements 202, connected in series, forming a circuit pattern with a first conductive member 402. The copper nanoparticle paste 61 is patterned such that it is applied once at the center and four times at the four corners of the bonding surfaces of the thermoelectric conversion elements 20. The bonding temperature is set to 350°C, and the bonding pressure is set to 0.1 MPa. Other conditions are the same as in the first embodiment. An output density of 1.56 W / cm³ is achieved. 2 It is possible to manufacture thermoelectric conversion modules that have high power generation output even when the size of the thermoelectric conversion module increases.

[0097] The following describes a fifth embodiment of the manufacturing method for the thermoelectric conversion module. The bonding pressure is set to 0.5 MPa. In the performance evaluation of the thermoelectric conversion module, the high-temperature side temperature is set to 300°C and the low-temperature side temperature to 50°C. Other conditions are the same as in the fourth embodiment. An output density of 0.65 W / cm³ can be obtained. 2 It can manufacture thermoelectric conversion modules that can generate electricity even when the temperature difference between the high-temperature side and the low-temperature side is small.

[0098] The following describes a sixth embodiment of the manufacturing method for the thermoelectric conversion module. In the performance evaluation of the thermoelectric conversion module, the high-temperature side temperature is set to 400°C and the low-temperature side temperature to 50°C. Other conditions are the same as in the fourth embodiment. The output density is 1.29 W / cm³. 2It can manufacture thermoelectric conversion modules with higher output density if the temperature difference between the high-temperature side and the low-temperature side is greater.

[0099] The following describes the seventh embodiment of the manufacturing method for the thermoelectric conversion module. In the performance evaluation of the thermoelectric conversion module, the high-temperature side temperature is set to 500°C and the low-temperature side temperature to 50°C. Other conditions are the same as in the fourth embodiment. The output density is 2.21 W / cm³. 2 It can manufacture thermoelectric conversion modules with higher output density if the temperature difference between the high-temperature side and the low-temperature side is greater.

[0100] The following describes the eighth embodiment of the manufacturing method for the thermoelectric conversion module. In the performance evaluation of the thermoelectric conversion module, the high-temperature side temperature is set to 600°C and the low-temperature side temperature to 50°C. Other conditions are the same as in the fourth embodiment. The output density is 3.21 W / cm³. 2 It is possible to manufacture thermoelectric conversion modules with higher output density by further increasing the temperature difference between the high-temperature side and the low-temperature side.

[0101] The following describes the ninth embodiment of the manufacturing method for the thermoelectric conversion module. The screw speed during dispensing is set to 5 rpm. In the performance evaluation, the high-temperature side temperature is set to 500°C and the low-temperature side temperature to 50°C. Other conditions are the same as in the fourth embodiment. The output density is 2.00 W / cm³. 2 This allows for the development of thermoelectric conversion modules that achieve higher output density even when the screw speed is set to 5 rpm.

[0102] As a comparative example, in the process of coating copper nanoparticle paste onto the first conductive component and the thermoelectric conversion element, the copper nanoparticle paste was applied by printing instead of using a mechanical dispensing machine to fabricate the thermoelectric conversion module. Other conditions are as described in Table 1. The output density is 0.9 W / cm³. 2 If compared with the first, fourth, seventh, and ninth embodiments where the high-temperature and low-temperature temperatures and the measurement pressure are the same, the output density decreases. Figure 11 This is a magnified photograph of a portion of the assembled thermoelectric conversion module. Figure 11 The dotted line in the diagram represents the outline of the copper plate 402, which serves as the first conductive component. The copper nanoparticle paste 61, which bonds to the thermoelectric element 20, seeps out from the copper plate 402 and reaches the area of ​​the ceramic substrate 401. It can be considered that because the amount of copper nanoparticle paste applied is not controlled, the thermoelectric conversion module is prone to short circuits, resulting in a decrease in output density.

[0103] As Example 10, a reliability test was conducted on a thermoelectric conversion module with a ceramic substrate made of zirconia-reinforced alumina using the same manufacturing method as in Example 1. The conditions for the reliability test are described below.

[0104] In reliability testing, heating and cooling blocks are used to clamp the upper and lower surfaces of the thermoelectric conversion module. Pressure is applied while a temperature difference is simultaneously applied, subjecting the high-temperature side of the thermoelectric conversion module in contact with the heating block to a thermal cycling load. The cooling block maintains a certain cooling capacity, and changes in power generation performance are evaluated. The pressure is set to 1 MPa for the thermal cycle. One cycle is defined as a load of 400°C at high temperature on the heating block side, followed by a temperature change to 150°C. The cooling capacity is adjusted so that when the heating block side reaches 400°C, the cooling block side reaches 50°C; when the heating block side reaches 150°C, the cooling block side reaches 45°C. Figure 13 The value in the figure represents the output change during reliability evaluation. Measurements were taken up to 3650 cycles, and the output degradation compared to the maximum output was less than 2%, indicating minimal overall variation and confirming sufficient reliability.

[0105] The present invention has been described above using examples, but is not limited thereto. Various combinations of these examples can further enhance the effects of the present invention.

[0106] [Table 1]

[0107]

[0108] [Table 2]

[0109] 0 vol% 20 vol% 40 vol% 60 vol% 80 vol% Early stage dispersion dispersion dispersion dispersion dispersion 1 day later settlement settlement dispersion dispersion dispersion 6 days later settlement settlement dispersion dispersion dispersion 10 days later settlement settlement Local settlement Local settlement dispersion 30 days later settlement settlement Local settlement Local settlement dispersion

Claims

1. A method for manufacturing a thermoelectric conversion module, comprising manufacturing a thermoelectric conversion module formed by joining a first conductive component, a thermoelectric conversion element, and a second conductive component together via a joining component, characterized in that, include: After coating the first conductive component with a first paste containing copper nanoparticles, the cobaltite-type thermoelectric conversion element is disposed on the first paste, and the first paste is compressed and unfolded. After applying a second paste containing copper nanoparticles using a mechanical dispensing machine on the cobaltite-type thermoelectric conversion element by means of a controlled amount according to the screw rotation speed, the second conductive component is configured to compress and unfold the second paste. as well as The joining component is manufactured by simultaneously pressing and sintering the first and second pastes in a vertical direction. In the relationship between shear rate and viscosity, the slope of the side with higher shear rate is smaller than the slope of the side with lower shear rate.

2. The manufacturing method of the thermoelectric conversion module according to claim 1, characterized in that, The first and second pastes contain a dispersant and a thickener, and the ratio of the thickener is 30 vol% or more and 90 vol% or less relative to the volume of solvent only, excluding copper nanoparticles, to maintain dispersion in sedimentation tests.

3. The method for manufacturing the thermoelectric conversion module according to claim 1 or 2, characterized in that, The screw rotates at a speed of 5 rpm to 15 rpm to apply the first paste and the second paste in the controlled amount.

4. The method for manufacturing the thermoelectric conversion module according to claim 1 or 2, characterized in that, The first and second pastes extend to the mating surface of the thermoelectric conversion element, excluding at least a portion of the corners.

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