JP2018067589A - Method for manufacturing thermoelectric conversion module - Google Patents

Abstract

A method of manufacturing a thermoelectric conversion module that can prevent the occurrence of cracks due to a difference in thermal expansion of a thermoelectric conversion element and has stable thermoelectric conversion performance is provided. A method of manufacturing a thermoelectric conversion module includes: one electrode surface of a P-type thermoelectric conversion element (high-strength thermoelectric conversion element) 3 and an N-type thermoelectric conversion element (low strength) on an electrode portion 11 of one wiring board 2A. The first bonding step for bonding one electrode surface of the thermoelectric conversion element 4), and after the first bonding step, the electrode portion 12 of the other wiring board 2B is connected to the other electrode surface of the P-type thermoelectric conversion element 3 and N A second joining step of joining the other electrode surface of the thermoelectric conversion element 4 at a joining temperature lower than the joining temperature of the first joining step. [Selection] Figure 1

Description

  The present invention relates to a method for manufacturing a thermoelectric conversion module in which a plurality of P-type thermoelectric conversion elements and N-type thermoelectric conversion elements are arranged in combination.

  In the thermoelectric conversion module, a pair of P-type thermoelectric conversion elements and N-type thermoelectric conversion elements are combined in a connected state with electrodes between wiring boards (insulating boards). P-type, N-type, P-type, N-type It is configured to be electrically connected in series so as to be alternately arranged in the order of the mold, and both ends are connected to a DC power source, and heat is transferred in each thermoelectric conversion element by the Peltier effect (in P type, current and current are transferred). In the same direction, N type is moved in the direction opposite to the current), or a temperature difference is given between both wiring boards to generate electromotive force in each thermoelectric conversion element by Seebeck effect. Can be used.

  The thermoelectric conversion performance of each of the P-type and N-type thermoelectric conversion elements is represented by a dimensionless figure of merit called ZT, which is a guideline for element selection, but using the same base material and the same operating temperature environment, The P-type thermoelectric conversion element and the N-type thermoelectric conversion element often do not always have the same thermoelectric conversion performance, and need to be adjusted.

  For example, in Patent Document 1, an element that is normally formed in a prismatic shape having a square cross section is formed in a rectangular shape in cross section, and in different shapes depending on the carrier concentration of each of P type and N type. It is described to form.

  Patent Document 2 describes that when a thermoelectric conversion element is soldered to a warped substrate, the thickness of the solder layer is varied according to the distance between the substrate and the element.

  In order to obtain closer thermoelectric conversion performance (ZT) in the same operating temperature environment, it is conceivable to select P-type and N-type thermoelectric conversion elements with different base materials. Further, since the thermal expansion coefficient and the like are also greatly different, damage to a low-strength element is increased (cracking is preferentially generated).

  Therefore, Patent Document 3 proposes a thermoelectric conversion module in which a stress relaxation layer made of a Cr—Cu alloy is formed between a thermoelectric conversion element and an electrode.

JP 2013-12571 A JP 2013-157348 A International Publication No. 2013/145843

  However, even if a stress relaxation layer made of a Cr—Cu alloy is used as in the thermoelectric conversion module described in Patent Document 3, there is a concern that the stress relaxation capability is insufficient, and cracking of the thermoelectric conversion element is prevented. Is insufficient. And when a crack or the like occurs in the thermoelectric conversion element, even if the operation of the thermoelectric conversion module becomes impossible or does not lead to inoperability, a gap is generated between the wiring board and the thermoelectric conversion element. There is concern that the amount of power generation (power generation efficiency) will drop significantly.

  The present invention has been made in view of such circumstances, and can provide a method for manufacturing a thermoelectric conversion module that can prevent the occurrence of cracks due to a difference in thermal expansion of thermoelectric conversion elements and has stable thermoelectric conversion performance. With the goal.

  The method for manufacturing a thermoelectric conversion module of the present invention includes a low-strength side thermoelectric conversion element having a small strength and a large thermal expansion coefficient between a pair of opposingly arranged wiring boards, and a strength higher than that of the low-strength side thermoelectric conversion element. A high-strength side thermoelectric conversion element having a large thermal expansion coefficient is a method for manufacturing a thermoelectric conversion module provided via the wiring board, and is provided on an electrode portion of one of the wiring boards. A first joining step for joining one electrode surface of the high-strength side thermoelectric conversion element and one electrode surface of the low-strength side thermoelectric conversion element; and after the first joining step, the other of the wiring boards The other electrode surface of the high-strength thermoelectric conversion element and the other electrode surface of the low-strength thermoelectric conversion element are bonded to the electrode portion of the wiring board at a bonding temperature lower than the bonding temperature in the first bonding step. A second joining step.

  Since the thermal expansion coefficient of the high strength side thermoelectric conversion element is smaller than the thermal expansion coefficient of the low strength side thermoelectric conversion element, the length of the high strength side thermoelectric conversion element and the length of the low strength side thermoelectric conversion element at 25 ° C. are the same. Even so, at a high temperature, the length of the low-strength side thermoelectric conversion element becomes longer (larger) than the length of the high-strength side thermoelectric conversion element. For this reason, when each wiring board and each thermoelectric conversion element are joined at the same heating temperature, the low-strength side thermoelectric conversion element heat-shrinks much more than the high-strength side thermoelectric conversion element during cooling. Tensile stress is generated in the low-strength thermoelectric conversion element. In particular, brittle materials (ceramics, semiconductor materials, etc.) used for thermoelectric conversion elements are less resistant to tensile stress than compressive stress. For this reason, a crack etc. may arise in the low intensity | strength side thermoelectric conversion element.

  In this invention, after joining one wiring board and each thermoelectric conversion element (high intensity | strength side thermoelectric conversion element, low intensity | strength side thermoelectric conversion element) in a 1st joining process, in a 2nd joining process, a 1st joining process The other wiring board and each thermoelectric conversion element are bonded at a bonding temperature lower than the bonding temperature. In use, one wiring board is arranged on the high temperature side, and the other wiring board is arranged on the low temperature side. At this time, the temperature of one wiring board disposed on the high temperature side is higher than the temperature of the second bonding step. Therefore, when each thermoelectric conversion element thermally expands in the environment where the thermoelectric conversion module is used, tensile stress can be generated in the high-strength side thermoelectric conversion element, and compressive stress can be generated in the low-strength side thermoelectric conversion element. Therefore, the occurrence of cracks due to the difference in thermal expansion of each thermoelectric conversion element can be prevented, and the electrical conductivity between each wiring board and each thermoelectric conversion element can be maintained, ensuring stable thermoelectric conversion performance of the thermoelectric conversion module. it can.

  Moreover, in the manufacturing method of the thermoelectric conversion module of this invention, joining of said 1st joining process can be made into brazing, and joining of said 2nd joining process can be made into joining using solder or silver (Ag) paste. .

  ADVANTAGE OF THE INVENTION According to this invention, generation | occurrence | production of the crack etc. by the thermal expansion difference of a thermoelectric conversion element can be prevented, and the thermoelectric conversion module which has the stable thermoelectric conversion performance can be manufactured.

It is a figure explaining the manufacturing method of the thermoelectric conversion module of embodiment of this invention. It is a longitudinal cross-sectional view of the thermoelectric conversion module manufactured by the manufacturing method of the thermoelectric conversion module of embodiment of this invention. FIG. 3 is a cross-sectional plan view taken along the line AA in FIG. FIG. 3 is a cross-sectional plan view in the direction of the arrows along line BB in FIG. 2. It is a plane sectional view similar to FIG. 3 which shows the thermoelectric conversion module manufactured by the manufacturing method of the thermoelectric conversion module of other embodiment of this invention. FIG. 6 is a plan sectional view similar to FIG. 4 showing the thermoelectric conversion module of FIG. 5.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
As shown in FIGS. 2 to 4, the thermoelectric conversion module 1 manufactured by the manufacturing method of the thermoelectric conversion module of the present embodiment includes a P-type thermoelectric conversion element between a pair of facing wiring boards 2 </ b> A and 2 </ b> B. 3 and N-type thermoelectric conversion elements 4 are arranged in a linear (one-dimensional) form. For simplicity, FIGS. 2 to 4 show an example in which the P-type thermoelectric conversion element 3 and the N-type thermoelectric conversion element 4 are arranged in two pairs, and a total of four thermoelectric conversion elements 3 and 4 are included. It is provided in a line. In the figure, the P-type thermoelectric conversion element 3 is expressed as “P”, and the N-type thermoelectric conversion element 4 is expressed as “N”.

As shown in FIG. 2, the thermoelectric conversion module 1 is entirely housed in a case 5 so as to be interposed between a high temperature side channel 6 through which high temperature gas flows and a low temperature side channel 7 through which cooling water flows. The thermoelectric conversion apparatus 81 is comprised by being attached to. Note that the case 5 is not necessarily required, and the case 5 may not be provided.
As shown in FIG. 2, one wiring board 2 </ b> A arranged on the upper side of the thermoelectric conversion module 1 is arranged adjacent to the high temperature side flow path 6 and the other wiring board 2 </ b> B arranged on the lower side of the thermoelectric conversion module 1. Is disposed adjacent to the low temperature side flow path 7, and when the thermoelectric converter 81 is used, one wiring board 2A is heated to a high temperature and the other wiring board 2B is cooled to a low temperature. In the thermoelectric conversion device 81, each thermoelectric conversion element 3, 4 generates an electromotive force according to the temperature difference between the two wiring boards 2 </ b> A, 2 </ b> B, so that each of the external wiring portions 14 </ b> A, 14 </ b> B at both ends of the array A total potential difference of electromotive forces generated in the thermoelectric conversion elements 3 and 4 is obtained. A heat sink 8 having rod-like heat absorbing fins 8a is provided in the high temperature side flow path 6, and an elastic member 9 such as a spring for pressing the heat absorbing fins 8a toward the one wiring substrate 2A is provided. .

The wiring substrates 2A and 2B are aluminum nitride (AlN), alumina (Al ₂ O ₃ ), silicon nitride (Si ₃ N ₄ ), silicon carbide (SiC), carbon plate, diamond thin film substrate formed on a graphite plate, etc. The electrode parts 11, 12 and the like described later are formed on an insulating ceramic substrate 30 having a high thermal conductivity.

  Two wiring boards 2A on the upper side in FIG. 2 have two rectangular shapes in plan view that are connected to each pair of adjacent P-type thermoelectric conversion elements 3 and N-type thermoelectric conversion elements 4, as shown in FIG. 2 is formed, and the other wiring substrate 2B on the lower side of FIG. 2 has four square shapes in plan view connected to each of the thermoelectric conversion elements 3 and 4, as shown in FIG. Of each pair of thermoelectric conversion elements 3 and 4 that are connected by the electrode section 12 and the electrode section 11 of one wiring board 2A, one pair of N-type thermoelectric conversion elements 4 and the other pair of P-type thermoelectric elements. External wiring portions 14A and 14B for connecting the internal wiring portion 13 for connecting the conversion element 3 to the outside, one pair of P-type thermoelectric conversion elements 3 and the other pair of N-type thermoelectric conversion elements 4 respectively. And are formed.

  These electrode portions 11 and 12 are formed by bonding copper or a copper alloy, aluminum or an aluminum alloy, or a laminate of these to the surface of the ceramic substrate 30. The sizes of the electrode portions 11 and 12 are appropriately set according to the size of the thermoelectric conversion elements 3 and 4. For example, with respect to the thermoelectric conversion elements 3 and 4 having a 4 mm square cross section, the electrode portion 11 is formed in a 5 mm × 10 mm rectangle, and the electrode portion 12 is formed in a 4.5 mm square shape. The thickness of the electrode parts 11 and 12 can be made into the range of 0.05 mm-2.0 mm, and the thickness of 0.3 mm is suitable. The ceramic substrate 30 of the wiring boards 2A and 2B is formed in a planar shape that can secure a space of 2 mm or more in width between and around the electrode portions 11 and 12, and the thickness is, for example, aluminum nitride, When it consists of alumina, it can be in the range of 0.1 mm to 1.5 mm, and when it consists of silicon nitride, it can be in the range of 0.05 mm to 1.5 mm. As a preferred example, a ceramic plate made of aluminum nitride is used as the ceramic substrate 30 and the size is 30 mm × 12.5 mm and the thickness is 0.6 mm.

  Further, the wiring portions 13, 14 </ b> A, 14 </ b> B are formed of, for example, a wire made of copper or aluminum, and are joined to the surface of the ceramic substrate 30 like the electrode portions 11, 12. The width is in the range of 0.3 mm to 2.0 mm, and the thickness is in the range of 0.05 mm to 4.0 mm.

One of the P-type thermoelectric conversion element 3 and the N-type thermoelectric conversion element 4 is a low-strength side thermoelectric conversion element having a small strength (compressive strength) and a high thermal expansion coefficient, and the other is a high-strength thermal expansion element. A high-strength side thermoelectric conversion element having a small coefficient is used, and a combination of thermoelectric conversion elements having different strengths and thermal expansion coefficients is used.
As a material of the P-type thermoelectric conversion element 3 and the N-type thermoelectric conversion element 4, a silicide-based material, an oxide-based material, a skutterudite (intermetallic compound of transition metal and pnictogen), a half-Whistler, and the like can be used. For example, the combinations shown in Table 1 are used.

  A P-type thermoelectric conversion element composed of manganese silicide and an N-type thermoelectric conversion element composed of magnesium silicide are each pulverized after a mother alloy is pulverized by a ball mill to produce a pulverized powder having a particle size of 75 μm or less, for example. The powder is sintered by plasma discharge sintering, hot pressing, hot isostatic pressing, and a bulk material having, for example, a disk shape or a square plate shape is prepared, and this is cut into, for example, a prismatic shape or a cylindrical shape. Is formed.

  A P-type thermoelectric conversion element composed of silicon germanium (Si-Ge) is composed of Si powder (79.7 at%), Ge powder (20.1 at%), and B powder (0.2 at%). Using the mixed mixture, a fine spherical powder of Si (Ge) doped with B (boron) is produced by a gas atomization method, and then the granular powder is sintered by an electric heating sintering method (1250 ° C, held for 1 minute). In conclusion, for example, a disk-shaped or square-plate-shaped bulk material is prepared, and is formed by cutting the material into, for example, a prismatic shape or a cylindrical shape.

  A metallized layer (not shown) including any one of nickel, silver, and gold is formed on both end faces of each thermoelectric conversion element formed in this manner by plating or sputtering. When the metallized layer is made of silver or gold, a barrier layer (not shown) made of a single layer made of either nickel or titanium or a laminated structure thereof is formed on both end faces of the thermoelectric conversion element, A metallized layer may be formed through this barrier layer.

Of the thermoelectric conversion elements configured as described above, No. 1 shown in Table 1 is used. In the combination of 1, the P-type thermoelectric conversion element composed of manganese silicide has a compressive strength of, for example, 2300 MPa at room temperature (25 ° C.) (1200 MPa at 500 ° C.) and a thermal expansion coefficient of 10.8 × 10 ⁻⁶ / K. In contrast, an N-type thermoelectric conversion element made of magnesium silicide has a compressive strength of, for example, 1000 MPa (260 MPa at 500 ° C.) at room temperature (25 ° C.) and a thermal expansion coefficient of 17.0 × 10 ⁻⁶ / K. It is. In the combination of the P-type thermoelectric conversion element of manganese silicide and the N-type thermoelectric conversion element of magnesium silicide, the compression strength of the P-type thermoelectric conversion element is larger than the compression strength of the N-type thermoelectric conversion element. The thermal expansion coefficient is smaller than the thermal expansion coefficient of the N-type conversion element.

No. 1 shown in Table 1 In the combination of thermoelectric conversion elements 2, a P-type thermoelectric conversion element composed of silicon germanium has a compressive strength of, for example, 1600 MPa at room temperature (25 ° C.) (460 MPa at 500 ° C.) and a thermal expansion coefficient of 4.6 × 10 ^{− 6} / K, the N-type thermoelectric conversion element composed of magnesium silicide has a compressive strength of, for example, 1000 MPa at room temperature (25 ° C.) (260 MPa at 500 ° C.) and a thermal expansion coefficient as described above. 17.0 × 10 ⁻⁶ / K. Even in the combination of the silicon germanium P-type thermoelectric conversion element and the magnesium silicide N-type thermoelectric conversion element, the compression strength of the P-type thermoelectric conversion element is larger than that of the N-type thermoelectric conversion element. The thermal expansion coefficient of is smaller than that of the N-type conversion element.

  Thus, the thermoelectric conversion module 1 has a compressive strength higher than that of the N-type thermoelectric conversion element 4 (low-strength side thermoelectric conversion element) having a small compressive strength (strength) and a large thermal expansion coefficient, and the N-type thermoelectric conversion element 3. Thermoelectric conversion elements 3 and 4 in combination with a high-strength side thermoelectric conversion element (P-type thermoelectric conversion element 3) having a large (strength) and a small thermal expansion coefficient are used.

  These thermoelectric conversion elements 3 and 4 are formed in, for example, a prismatic shape with a square cross section (for example, one side is 1 mm to 8 mm) or a circular column with a circular cross section (for example, a diameter is 1 mm to 8 mm). The length (the length along the facing direction of the wiring boards 2A and 2B) is 2 mm to 10 mm. Of these thermoelectric conversion elements 3 and 4, the length of the P-type thermoelectric conversion element 3 having a relatively large strength and a small thermal expansion coefficient is an N-type thermoelectric conversion element having a small strength and a large thermal expansion coefficient. 4 is set to be equivalent (approximately the same length) at 25 ° C.

A method for manufacturing the thermoelectric conversion module 1 configured as described above will be described.
In the present embodiment, a combination of manganese silicide (MnSi _1.73 ) and magnesium silicide (Mg ₂ Si) thermoelectric conversion elements 3 and 4 made of a silicide-based material that has little influence on the environment and abundant resource reserves. The method for manufacturing the thermoelectric conversion module will be described. The thermoelectric conversion module 1 is manufactured through two joining steps, a first joining step and a second joining step.

(First joining process)
First, one electrode surface of the P-type thermoelectric conversion element 3 and one electrode surface of the N-type thermoelectric conversion element 4 are joined to the electrode portion 11 of one wiring board 2A. In addition, joining of the electrode part 11 of one wiring board 2A and each thermoelectric conversion element 3 and 4 is performed at the junction temperature more than the use temperature of one wiring board 2A. Specifically, as shown in FIG. 1 (a), one of the thermoelectric conversion elements 3 and 4 is placed on the electrode part 11 of one wiring board 2A via a brazing material (silver (Ag) brazing) 21. The electrode surfaces are arranged so as to overlap each other, and in a state where pressure is applied in the stacking direction (pressing load): 0.05 MPa to 1.5 MPa, bonding temperature: 605 ° C. to 780 ° C., bonding time: 1 minute to By heating in 10 minutes, the electrode part 11 of one wiring board 2A and the one electrode surface of the thermoelectric conversion elements 3 and 4 are joined, and as shown in FIG. 1B, these one wiring board 2A. And the thermoelectric conversion elements 3 and 4 are formed. In addition to silver brazing, Al-based, Cu-based, Au-based, Ni-based, Ti-based, and the like can be used for the brazing material 21 depending on the heat resistance of the thermoelectric element material and the maximum operating temperature of the thermoelectric conversion module. .
Thus, in the first joining step, the electrode part 11 and the thermoelectric conversion elements 3 and 4 are brazed by the brazing material 21, and the brazing part 41 is interposed between the electrode part 11 and the thermoelectric conversion elements 3 and 4. Is formed.

(Second joining process)
After the first bonding step, the other electrode surface of the P-type thermoelectric conversion element 3 and the other electrode surface of the N-type thermoelectric conversion element 4 are bonded to the electrode portion 12 of the other wiring board 2B, 2B, the thermoelectric conversion module 1 in which the P-type thermoelectric conversion element 3 and the N-type thermoelectric conversion element 4 are electrically connected in series is manufactured.

  At this time, the bonding body 1 of the one wiring board 2A formed in the first bonding step and the thermoelectric conversion elements 3 and 4 is previously bonded to a solder material at a bonding temperature (139 ° C. to 315 ° C.) or normal temperature (for example, 25 ° C.). Allow to cool down. And joining of the other wiring board 2B and each thermoelectric conversion element 3 and 4 is performed at a joining temperature lower than the joining temperature of one wiring board 2A and each thermoelectric conversion element 3 and 4 in a 1st joining process. The bonding of the other wiring board 2B and the thermoelectric conversion elements 3 and 4 is performed at a bonding temperature lower than the use temperature of one wiring board 2A and higher than the use temperature of the other wiring board 2B. Specifically, as shown in FIG. 1B, the other of the thermoelectric conversion elements 3 and 4 is placed on the electrode portion 12 of the other wiring board 2B via the solder material (Sn-58Bi) 22. It arrange | positions so that an electrode surface may be piled up, and it is a pressurizing force (pressing load): 0.01MPa-1MPa in the lamination direction, joining temperature: 139 degreeC-150 degreeC, joining time: 1 minute-10 minutes After being heated at the temperature, it is cooled to room temperature (25 ° C.), thereby joining the electrode portion 12 of the other wiring board 2B and the other electrode surface of the thermoelectric conversion elements 3 and 4 as shown in FIG. Then, the thermoelectric conversion module 1 is manufactured.

The solder material 22 includes Sn-Pb, Sn-Ag-Cu, Sn-Sb, Sn-Zn, Sn-Bi, Sn-In-Ag-Bi, In-Sn, Sn -Pb-Bi system, Sn-Cu system, etc. can also be used.
Although illustration is omitted, silver (Ag) paste can be used in place of the solder material 22 in the second joining step. The silver paste contains silver powder having a particle size of 0.05 μm to 100 μm, a resin, and a solvent. The composition of the silver paste is such that the silver powder content is 60% by mass or more and 92% by mass or less of the entire silver paste, the resin content is 1% by mass or more and 10% by mass or less of the entire silver paste, and the balance is the solvent. Good. This silver paste is applied to the electrode portion 12 of the wiring board 2B or the other electrode surface of the thermoelectric conversion elements 3 and 4 by screen printing or the like, dried at 100 ° C. to 150 ° C., and then applied with pressure (pressing load) in the stacking direction. ): Pressurized at 0.01 MPa to 5 MPa, bonding (sintering) temperature: 150 ° C. to 300 ° C., so that the electrode portion 12 of the wiring board 2B and the other electrode surface of the thermoelectric conversion elements 3 and 4 Can be bonded via a silver bonding layer.
As described above, in the second joining step, the electrode portion 12 and the thermoelectric conversion elements 3 and 4 are joined by the solder material 22 or the silver paste, and the solder is interposed between the electrode portion 12 and the thermoelectric conversion elements 3 and 4. The attaching portion 42 or a silver bonding layer (not shown) is formed.

  Since the thermoelectric conversion elements 3 and 4 are also heated up to the melting temperature of the solder material 22 when the other wiring board 2B and the thermoelectric conversion elements 3 and 4 are bonded in the second bonding step, the P-type thermoelectric conversion is performed. There is a difference between the length of the element 3 and the length of the N-type thermoelectric conversion element 4. That is, the length of the N-type thermoelectric conversion element 4 having a large thermal expansion coefficient is longer (larger) than the length of the P-type thermoelectric conversion element 3 having a small thermal expansion coefficient, but the bonding temperature of the solder material 22 is 139. Since the bonding can be performed at a relatively low temperature, the difference in thermal expansion between the P-type thermoelectric conversion element 3 and the N-type thermoelectric conversion element 4 at the time of bonding can be reduced. For this reason, when the thermoelectric conversion module 1 is cooled to room temperature, the N-type thermoelectric conversion element 4 having a larger coefficient of thermal expansion than the P-type thermoelectric conversion element 3 having a smaller coefficient of thermal expansion tends to contract more greatly. Tensile stress is generated in the N-type thermoelectric conversion element 4 having a compressive strength lower than that of the type thermoelectric conversion element 3. However, since the difference in thermal expansion between the P-type thermoelectric conversion element 3 and the N-type thermoelectric conversion element 4 at the time of bonding in the second bonding step is reduced, the magnitude of the tensile stress acting on the N-type thermoelectric conversion element 4 is also small. it can. Therefore, it is possible to prevent cracks and the like from occurring in the N-type thermoelectric conversion element 4 having a low compressive strength.

  In the thermoelectric conversion module 1 manufactured as described above, a heat source (high temperature side channel 6) is arranged on one wiring board 2A, and a cooling channel or the like (low temperature side channel 7) is arranged on the other wiring board 2B. Is generated in each of the thermoelectric conversion elements 3 and 4 according to the temperature difference between the two wiring boards 2A and 2B, and the thermoelectric conversion elements are arranged between the external wiring portions 14A and 14B at both ends of the array. The potential difference of the sum of the electromotive forces generated in 3 and 4 is obtained.

  In such a use environment of the thermoelectric conversion module 1, both the thermoelectric conversion elements 3 and 4 are heated from the high temperature side flow path 6 through the one wiring substrate 2 </ b> A to be thermally expanded, and the P-type thermoelectric conversion element 3 and A difference in thermal expansion (difference in length) occurs between the N-type thermoelectric conversion element 4. That is, the N-type thermoelectric conversion element 4 having a larger thermal expansion coefficient than the P-type thermoelectric conversion element 3 having a smaller thermal expansion coefficient tends to expand greatly.

  However, in this thermoelectric conversion module 1, the other wiring board 2B and the thermoelectric conversion elements 3 and 4 are joined at a temperature lower than the usage environment of the one wiring board 2A. Is higher than the temperature during the second bonding step (bonding temperature). For this reason, the difference in thermal expansion between the two thermoelectric conversion elements 3 and 4 accumulated in the second joining step is canceled, or the difference in thermal expansion between the two thermoelectric conversion elements 3 and 4 that occurs in the environment where the thermoelectric conversion module 1 is used. Becomes larger. Then, the N-type thermoelectric conversion element 4 having a larger thermal expansion coefficient than the P-type thermoelectric conversion element 3 having a smaller thermal expansion coefficient tends to expand greatly, so that the N-type having a smaller compressive strength than the P-type thermoelectric conversion element 3. A compressive stress is generated in the thermoelectric conversion element 4. Here, the generated compressive stress is reduced because it cancels out the tensile stress in the second joining step.

  Thus, in the thermoelectric conversion module 1, when each thermoelectric conversion element 3 and 4 thermally expands in a use environment, a tensile stress is generated in the P-type thermoelectric conversion element 3 having a high compressive strength, and an N-type having a low compressive strength. A compressive stress can be generated in the thermoelectric conversion element 4. Therefore, the occurrence of cracks due to the difference in thermal expansion between the thermoelectric conversion elements 3 and 4 can be prevented, and the electrical conductivity between the wiring boards 2A and 2B and the thermoelectric conversion elements 3 and 4 can be maintained. The stable thermoelectric exchange performance of the module 1 can be ensured.

  A prismatic P-type thermoelectric conversion element (high-strength side thermoelectric conversion element) made of manganese silicide and a prismatic N-type thermoelectric conversion element (low-strength side thermoelectric conversion element) made of magnesium silicide were produced. The bottom surface of each thermoelectric conversion element at 25 ° C. was 4 mm × 4 mm, and the length of each thermoelectric conversion element was 7 mm.

These P-type thermoelectric conversion elements and N-type thermoelectric conversion elements are combined in 8 pieces (8 pairs) as shown in FIGS. 5 and 6 and arranged in a plane (2D) of 4 columns × 4 rows. A conversion module was produced. In this example, the drawing corresponding to FIG. 2 of the first embodiment is omitted, but the longitudinal sectional structure is substantially the same as FIG. 2, and FIG. 5 is a drawing corresponding to FIG. 3 of the first embodiment, FIG. This corresponds to FIG. 4 of the first embodiment. Then, as shown in FIGS. 5 and 6, by connecting the thermoelectric conversion elements 3 and 4 between the wiring boards 2A and 2B, the thermoelectric conversion elements 3 and 4 are connected in series between the external wiring portions 14A and 14B. Connected.
As the ceramic substrate of the wiring board of each example, aluminum nitride having a thickness of 0.6 mm was used, and copper having a thickness of 0.05 mm was used as the electrode portion.

Then, the bonding (first bonding step) between one wiring board and each thermoelectric conversion element is performed on one electrode of each thermoelectric conversion element on the electrode portion of one wiring board via the high temperature side bonding material described in Table 2. The electrode surface was arranged, and the heating was performed at the bonding temperature shown in Table 2 in the state of applying pressure (pressing load): 0.1 MPa in the stacking direction (first bonding step).
In addition, after joining the other wiring board and each thermoelectric conversion element (second joining process), after cooling to 25 ° C. after the first joining process, on the electrode part of the other wiring board, as described in Table 2 The other electrode surface of each thermoelectric conversion element is disposed via the low-temperature side bonding material, and heated at the bonding temperature described in Table 2 in a state where the pressure (pressing load) is 0.1 MPa in the stacking direction. (Second joining step).
When the low-temperature side bonding material was a silver (Ag) paste, a silver paste made of silver (Ag) powder having a particle size of 5 μm, ethyl cellulose, and α-terpineol was used. And it dried at 120 degreeC after application | coating of a silver paste.
In Experimental Examples 42 to 47, the first joining step and the second joining step were performed simultaneously.

  And with respect to the obtained thermoelectric conversion module, one wiring board repeats temperature rising / falling in a 30 minute cycle between 450 degreeC and 300 degreeC with an electric heater, and the other wiring board is 60 with a chiller (cooler). A 48-hour cycle test was carried out while maintaining the temperature at ℃, and the peeling between the element and the electrode was investigated.

  The peeling of the element and the electrode causes peeling (including partial peeling) of the element and the electrode on the high temperature side and the low temperature side using an ultrasonic image measuring instrument (INSIGHT-300 manufactured by Insight Co., Ltd.) after the cycle test. Evaluation was based on the ratio of the devices. In each experimental example, since 16 thermoelectric conversion elements are used, 32 bonding surfaces between the element and the electrode are formed, but the peeling rate is 10% or more at each of the 32 bonding surfaces. The number of bonded surfaces with peeling was counted.

  These results are shown in Table 2.

  As can be seen from Table 2, after joining one wiring board arranged on the high temperature side and both thermoelectric conversion elements, at the temperature (low temperature side joining temperature) lower than the joining temperature (high temperature side joining temperature), the other By joining the wiring board and both thermoelectric conversion elements (Experimental Examples 1-41), compared with the case where the high-temperature side joining temperature and the low-temperature side joining temperature are joined at the same temperature (Experimental Examples 42-47), It was found that the number of joint surfaces with peeling can be reduced.

  Note that the present invention is not limited to the above-described embodiment, and various modifications other than those described above can be added without departing from the spirit of the present invention.

  For example, in the above embodiment, the cross-sectional shape of each thermoelectric conversion element is also a square, but may be formed in a rectangle, a circle, or the like. Further, when both thermoelectric conversion elements are arranged in a planar shape, both the thermoelectric conversion elements may be arranged in a rectangular shape, a circular shape, or the like in a plan view as well as an arrangement in a square shape in plan view. In that case, it is only necessary to arrange thermoelectric conversion elements having high strength at a plurality of locations at appropriate intervals in the circumferential direction in the peripheral portion, and it is preferable to arrange them uniformly.

  Moreover, although both the wiring boards are brought into contact with the high-temperature side flow path or the low-temperature side flow path, the circuit board is not necessarily limited to the one having the flow path configuration, and may be anything that contacts the heat source and the cooling medium.

1 Thermoelectric conversion module 2A, 2B Wiring board 3 P-type thermoelectric conversion element (high-strength side thermoelectric conversion element)
4 N-type thermoelectric conversion element (low-strength thermoelectric conversion element)
5 Case 6 High-temperature side flow path 7 Low-temperature side flow path 8 Heat sink 8a Heat-absorbing fin 9 Elastic member 10 Joint body 11, 12 Electrode section 13 Internal wiring section 14A, 14B External wiring section 21 Brazing material 22 Solder material 30 Ceramic substrate 41 Brazing Part 42 soldering part 81 thermoelectric conversion device

Claims (2)

A low-strength thermoelectric conversion element having a low strength and a high thermal expansion coefficient between a pair of opposingly arranged wiring boards, and a high-strength side having a higher strength and a lower thermal expansion coefficient than the low-strength side thermoelectric conversion element The thermoelectric conversion element is a manufacturing method of a thermoelectric conversion module provided via the wiring board,
A first bonding step of bonding one electrode surface of the high-strength side thermoelectric conversion element and one electrode surface of the low-strength side thermoelectric conversion element to the electrode portion of one of the wiring substrates;
After the first bonding step, the other electrode surface of the high-strength thermoelectric conversion element and the other electrode surface of the low-strength thermoelectric conversion element are formed on the electrode portion of the other wiring substrate of the wiring substrates. And a second joining step of joining at a joining temperature lower than the joining temperature of the first joining step.   2. The thermoelectric conversion module according to claim 1, wherein the joining in the first joining step is brazing, and the joining in the second joining step is soldering or joining using silver paste. Method.

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