This application claims the benefit of Taiwan application Serial No. 099146678, filed Dec. 29, 2010, the subject matter of which is incorporated herein by reference.
1. Field of the Disclosure
The disclosure relates in general to a thermoelectric module and method of manufacturing the same, and more particularly to a thermoelectric module operable stably at over temperature and method of manufacturing the same.
2. Description of the Related Art
The thermoelectric module, able to operate as a heat pump, has been widely employed in precise temperature control unit. Besides, the thermoelectric module is also used to be a power generator through converting the temperature difference ΔT of hot end temperature (Th) and cold end temperature (Tc) of the module into electricity. The converting efficiency η is predominantly decided by the product (ZT) of thermoelectric figure of merit (Z) of the thermoelectric elements and temperature (T), and also decided by the temperature difference ΔT across the module. The temperature difference ΔT sets the upper limit of efficiency through the Carnot efficiency, ηc=ΔT/Th. The ZT of the thermoelectric elements influences how close the converting efficiency η to approach the upper limit of carnot cycle, μc, through the thermoelectric figure of merit, Z, defined by α2·σ/κ, where α is the seebeck coefficient of the thermoelectric elements, σ is the electric conductivity of the thermoelectric elements, κ is the thermal conductivity of the thermoelectric elements, which all vary with temperature.
Since the ZT values of almost thermoelectric materials are below 2 so far and all vary with temperature, it is impossible to achieve high convert efficiency of a module by using homogeneous thermoelectric elements under large temperature differences. Therefore, processes of segmenting a homogeneous thermoelectric material with high ZT at specific temperature and another homogeneous thermoelectric material with high ZT at higher temperature, and even two-stage thermoelectric devices have been proposed to be developed, in order to increase the converting efficiency above. In order to increase the converting efficiency or the generation output of the thermoelectric module, high temperature difference ΔT is the necessarily operation condition, no matter for the traditional one-stage thermoelectric module or the two-stage thermoelectric module, even the thermoelectric module comprising the segmented thermoelectric elements. However, large temperature difference operation may lead to higher degree thermal expansion mismatch inside the thermoelectric device or cause the melting of bonding layers between the thermoelectric elements and the metal electrodes occasionally. Although some high-temperature welding alloys such as SnTe, Sn—Te—Bi, Cu—In, or Cu—Sb and corresponding welding processes could be chosen to overcome the latter problem, the thermoelectric figure of merit of thermoelectric elements could be deteriorated because of the high-temperature bonding processes usually. The most common and easily applied for industrial bonding process on thermoelectric module is solder reflowing, but the industrial solders hardly withstand service temperature over 300° C. It is very likely either the thermoelectric elements falls down in case of liquid-phase solder squeezing out, thus destroying the thermoelectric device, or the liquid-phase of solder melt overflows to adjacent metal electrodes, thereby decreasing the converting efficiency of the thermoelectric module.
A thermoelectric generator is built to withstand and operate with condition of high temperature difference or momentary over-temperature fluctuations ideally, but the welded structure composed of thermoelectric elements and metal electrodes definitely experiences a thermal stress caused by the influence of thermal expansion mismatches, this may cause a de-bonding of welded structure or splitting failure of the thermoelectric elements. In practice, the thicker the solder layers bonding the thermoelectric elements and the corresponding solder layers are and the softer the solder layers are, the easier the solder layers deform, so as to accommodate the thermal stress described above. Although it is easier to adjust the thermal stress of a thermoelectric device by partially melting and thus softening the thick solder layers under over-temperature condition, the melted solder liquid could be extruded out, thereby causing the short circuit due to overflow of the melted solder liquid. This would lead to the dramatic drop of the converting efficiency of the thermoelectric generator.
U.S. Pat. No. 7,278,199 provides a method of manufacturing thermoelectric module to overcome the thermal stress problem of the thermoelectric module. The junction surface between the electrodes on direct bond copper substrate and the cold side of multi-pair electrically series connection P-type and N-type thermoelectric elements is welded by solder layers, but the junction between the hot side of the thermoelectric elements and the electrodes use sliding contact mode. Although using the sliding contact mode has function of adjusting thermal stress, the contact resistance of the hot side interface raises and thus series circuit resistance increases. Besides, US patent publication No. US2010/0101620 provides a thermoelectric module structure having micron-sized protrusions grown on electrode surfaces. The fine conical protrusions are applied to disperse the heat passing through the thermoelectric elements and thus to lower the temperature difference between the substrate and the thermoelectric elements. However, the height of the protrusions is only a few microns and is much smaller than the solder layers thickness of general thermoelectric generators. Therefore, the thermoelectric module comprising the above protrusions must operate at hot side temperature below the melting point of solder layers inside, or else the electrode surfaces modified with the micron-sized protrusions can hardly stop the overflow of massive melt solder.
Additionally, when manufacturing the thermoelectric module 100 in
To sum up, the high temperature difference operation condition is a necessity to increase the converting efficiency or generation output of the thermoelectric device. Thus, it is desired to provide a thermoelectric module which not only the thickness thereof is easily controlled in the manufacturing process, but also has the capability of stabilizing the minimum thickness of the solder layers even the solder layers are partially melting during momentary over-temperature operation.
The disclosure is directed to a thermoelectric module having a plurality of spacers joined with the solder layers and method of manufacturing the same. The spacers are mainly disposed between the metal electrodes and the thermoelectric elements of the thermoelectric module. The melting point of the spacers is higher than the liquidus temperature of the solder layers, thus the thickness stability of solder layers between the metal electrode and the thermoelectric element could be maintained, thereby not only improving yield of manufacturing the thermoelectric module but also improving the operation reliability of the thermoelectric module.
According to a first aspect of the present disclosure, a thermoelectric module is provided. The thermoelectric module comprises a first substrate, a second substrate, a plurality of P-type and N-type thermoelectric elements, a plurality of first metal electrodes, a plurality of first solder layers, a plurality of second metal electrodes, a plurality of second solder layers and a plurality of spacers.
The first substrate and the second substrate are disposed opposite to each other.
The thermoelectric elements comprise P-type and N-type thermoelectric elements. Each of the thermoelectric elements has an upper end surface and a lower end surface and is disposed between the first substrate and the second substrate. The P-type and the N-type thermoelectric elements are disposed alternately.
The first metal electrodes are disposed between the first substrate and the lower end surfaces of the P-type and the N-type thermoelectric elements for electrically connecting to each of the thermoelectric elements respectively or electrically connecting to the adjacent P-type thermoelectric element and the N-type thermoelectric element.
The first solder layers are for joining the first metal electrodes and the lower end surfaces of the P-type and the N-type thermoelectric elements respectively.
The second metal electrodes are disposed between the second substrate and the upper end surfaces of the P-type and the N-type thermoelectric elements for electrically connecting to each of the thermoelectric elements or electrically connecting to the adjacent P-type thermoelectric element and the N-type thermoelectric elements respectively.
The second solder layers are for joining the second metal electrodes and the upper end surfaces of the P-type and the N-type thermoelectric elements respectively.
The spacer is at least disposed at and contacting one of the first solder layers and the second solder layers. The melting point of the spacer is higher than the liquidus temperature of at least one of the first solder layers and the second solder layers contacting the spacer.
According to a second aspect of the present disclosure, a method of manufacturing a thermoelectric module is provided. First, a first substrate, a second substrate, a plurality of P-type thermoelectric elements and a plurality of N-type thermoelectric elements are provided. Each of the thermoelectric elements has an upper end surface and a lower end surface.
A plurality of first and second metal electrodes are provided. There is at least one spacer at a surface of one of the end surfaces of at least one of the first and the second metal electrodes. The one of the end surfaces points to the thermoelectric elements.
The first and the second metal electrodes are disposed between the first substrate and the second substrate. The P-type and N-type thermoelectric elements are disposed alternately and between the first and the second metal electrodes. The lower faces of the thermoelectric elements are connected to the first metal electrodes while the upper faces of the thermoelectric elements are connected to the second metal electrodes.
A plurality of first solder plates are provided on the surfaces of the first metal electrodes and a plurality of the second solder plates are provided on the surfaces of the second metal electrodes. The spacer is contacted at least one solder plate of the first and the second solder plates wherein the melting point of the spacer is higher than the liquidus temperature of the first and the second solder layers.
The first substrate, the first metal electrodes, the P-type thermoelectric elements, the N-type thermoelectric elements, the second metal electrodes and the second substrate are assembled by reflow process to make the first solder plates form the first solder layers and join the first metal electrodes and a plurality of lower end surfaces of the P-type and the N-type thermoelectric elements, and to make the second solder plates form the second solder layers and join the second metal electrodes and a plurality of upper end surfaces of the P-type and the N-type thermoelectric elements.
According to a third aspect of the present disclosure, another method of manufacturing a thermoelectric module is further provided. First, a first substrate, a second substrate, a plurality of P-type thermoelectric elements and a plurality of N-type thermoelectric elements, a plurality of first and second metal electrodes, a paste solder and a plurality of granulated spacers are provided. Each of the thermoelectric elements has an upper end surface and a lower end surface. The melting point of the granulated spacers is higher than the liquidus temperature of the metallized solder after reflowing.
The granulated spacers are mixed with the paste solder.
The paste solder mixed with the granulated spacers is coated on the surface of at least one of the first and/or the second metal electrodes for forming the first solder layers and the second solder layers after subsequent reflow assembly.
The first and the second metal electrodes are disposed between the first substrate and the second substrate. The P-type and N-type thermoelectric elements are disposed alternately and between the first and the second metal electrodes. The lower faces of the thermoelectric elements are connected to the first metal electrodes while the upper faces of the thermoelectric elements are connected to the second metal electrodes.
The first substrate, the first metal electrodes, the P-type thermoelectric elements, the N-type thermoelectric elements, the second metal electrodes and the second substrate are assembled by reflow process to make the first solder layers spread the granulated spacers therein join the first metal electrodes and the lower end surfaces of the P-type and the N-type thermoelectric elements, and/or to make the second solder layers spread the granulated spacers therein join the second metal electrodes and the upper end surfaces of the P-type and the N-type thermoelectric elements.
The above and other aspects of the disclosure will become better understood with regard to the following detailed description of the preferred but non-limiting embodiment(s). The following description is made with reference to the accompanying drawings.
The thermoelectric module disclosed according to the embodiment mainly includes a plurality of spacer disposed in the solder layer between the metal electrodes and the thermoelectric elements. The melting point of the spacer is higher than the liquidus temperature of the solder layer. Even the solder layer be melted because of high temperature in the thermoelectric module in operation, at least the minimum thickness of the solder layer could be maintained and prevent large amounts of melted solder from being squeezed out of the junction interface in the supporting effects of the spacers within the solder layer, so as to improve the operation reliability of the thermoelectric module. The shape of the spacers is not limited, and may be a single shape or a combination of different shapes. Examples of the spacers include strip-shaped spacers, granulated spacers, and other shaped spacers.
The first and second embodiments are provided as following to describe the disclosure, but not to limit the disclosure. In the first embodiment, the spacers are strip-shaped spacers as example. In the second embodiment, the spacers are granulated spacers as example.
Several pairs of the thermoelectric elements 240 are disposed between the first substrate 211 and the second substrate 212. Each pair of the thermoelectric elements 240 includes a P-type thermoelectric element 242 and a N-type thermoelectric element 244 which are electrically connected to each other. The N-type thermoelectric elements 244 of each pair of the thermoelectric elements are electrically connected to adjacent P-type thermoelectric elements 242 of each pair of the thermoelectric elements. The several first metal electrodes 214 are disposed between the first substrate 211 and the lower end surfaces of the P-type thermoelectric elements 242 and the N-type thermoelectric elements 244 to electrically connect to the P-type thermoelectric elements 242 and the N-type thermoelectric elements 244 of each part of the thermoelectric element respectively. Several second metal electrodes 216 are disposed between the second substrate 212 and the upper end surfaces of the P-type thermoelectric elements 242 and the N-type thermoelectric elements 244 to electrically connect to P-type thermoelectric elements 242 and N-type thermoelectric elements 244 of adjacent two pairs of the thermoelectric elements, a P-type thermoelectric element 242 and a N-type thermoelectric element 244 of adjacent one pair of thermoelectric element 240, and a N-type thermoelectric element 244 and a P-type thermoelectric element 242 of adjacent one pair of thermoelectric element 240 to make the P-type thermoelectric elements 242 and the N-type thermoelectric elements 244 electrically series connect to each other.
Furthermore, the first solder layer (such as solder layer) 221 is melted and joined to the first metal electrodes 214 and the lower end surfaces of the P-type thermoelectric elements 242 and N-type thermoelectric elements 244. The second solder layer (such as solder layer) 222 is melted and joined to the second metal electrodes 216 and the upper end surfaces of the P-type thermoelectric elements 242 and N-type thermoelectric elements 244.
In the embodiment, the strip-shaped spacers 284 are disposed in and contacted with the second solder layer 222. The melting point of the strip-shaped spacer 284 is higher than the liquidus temperature of the material of second solder layer 222 contacting the spacers 248. In a manufacturing procedure, the strip-shaped spacers 284 could be disposed on the surface 216a of the second metal electrodes 216 and contact with the second solder layer 222. In an embodiment, the height of the strip-shaped spacer 284 is in a range of about 50% to 100% of the thickness of the second solder layer 222, while the height of the strip-shaped spacers is in a range of about 15 μm to about 500 μm. Thus, the strip-shaped spacers 284 would contact with the upper end surfaces of the P-type thermoelectric elements 242 and the N-type thermoelectric element 244, and the contacting part could be, for example, exposed outside the second solder layer 222.
Although only the second solder layer 222 contains the strip-shaped spacers 284 as illustrated in
The first substrate 211 and the second substrate 212, for example, are a ceramic plate and an insulative sheet material with high thermal conductivity, respectively. The ceramic plate and the first metal electrode 214 directly attached on the surface of the ceramic plate (i.e. the first substrate 211) are generally called direct covered metal ceramic plate. The insulative sheet material (i.e. the second substrate 212) only contacts with the second metal electrode 216 without joining to each other.
The first metal electrode 214 and the second metal electrode 216 are the metal plates made of, for example, copper, aluminum, iron, nickel, cobalt or alloy thereof, or the coated metal plates such as the copper plates coated by nickel, the aluminum plates coated by nickel or the iron plates coated by tin. The strip-shaped spacers 284 are metal wires, for example, steel alloy wires, nickel-chromium alloy wires, nickel wires, nickel-plated aluminum wires or nickel-plated copper wires and so on. In an embodiment, the material of the strip-shaped spacers 284, for example, is selected from the group consisting of iron, cobalt, nickel, chromium, copper, manganese, zirconium, titanium and a combination thereof so as to form reactive intermetallic compounds with liquid tin during reflowing process. The surfaces of the strip-shaped spacers 284 also may be selectively coated by the nickel, silver or tin as the solder top of the spacers.
Moreover, in an embodiment, the strip-shaped spacer 284 may be partially or completely fixed at the second metal electrode 216 by welding, electroplating or coating. The strip-shaped spacers 284 also may be fixed to each other by winding wires. The strip-shaped spacers 284 may be fixed at the second metal electrode 216 by a combination of welding, electroplating, coating and wire-winding.
According to the thermoelectric module 200 provided by the embodiment, the original thickness T of the second solder layer 222 could be adjusted easily by the height t (i.g. the diameter of the wire) of the strip-shaped spacers 284, since the strip-shaped spacer 284 are fixed on the surfaces 216a of the second metal electrode 216. A soft solder layer is easy to be deformed by self-plasticity (functioning like a soft pad). The thicker the thickness T of the second solder layer 222 is, the easier the thermal stress of the thermoelectric module 200 can be adjusted in operation to prevent relatively brittle thermoelectric element from being broken. Besides, with the supporting effects of the strip-shaped spacer 284 in the second solder layer 222, even the solder layer (i.g. the second solder layer 222) on the upper end of the P-type and N-type thermoelectric elements occur fusion during operation, the thickness of the solder layer could still be maintained at a stable thickness, so as to prevent large amounts of fusion solder liquid be squeezed out of the welding surface, thereby improving the operation reliability of the thermoelectric module 200. In other words, when the thermoelectric module 200 is operated, a possible minimum distance between the second solder layer 222 and P-type and N-type thermoelectric elements is determined according to the height t of the strip-shaped spacers 284.
Moreover, three strip-shaped spacers 284 distributed at the second metal electrode 216 on a P-type thermoelectric element 242 or a N-type thermoelectric element 244 are taken for illustration as shown in
In the thermoelectric module 200 of the embodiment, the strip-shaped spacers 284 could be metal wires or ceramic materials which are coated with metal layer, for example, nickel on the ceramic surface, while the metal electrode 216 could be a metal plate. Furthermore, the shapes of the metal electrodes 214 and 216 are not limit to flat, and other shapes are also applicable. Besides joining the metal electrodes with the strip-shaped spacers 284 in advance, the strip-shaped spacers 284 also could be connected with the solder layer and then joined with the metal electrodes simultaneously, followed by a reflow process to join each other.
In the following description, several types of the strip-shaped spacers in the thermoelectric module are taken for illustration, but the disclosure is not limit thereto. Some of the combination types of the metal electrodes 216 and spacers 284 in
In
In
In
In
In
In
In
Several pairs of the thermoelectric elements 340 are disposed between the first substrate 311 and the second substrate 312. Each pair of the thermoelectric elements 340 include a P-type segmented thermoelectric element 342 and a N-type segmented thermoelectric element 344 which are connected to each other electrically. The N-type segmented thermoelectric element 344 and the P-type segmented thermoelectric element 342 of each pair of the thermoelectric elements are connected to each other electrically. The several first metal electrodes 314 are disposed between the first substrate 311 and the lower end surfaces (such as exothermic end) of the P-type segmented thermoelectric element 342 and the N-type segmented thermoelectric element 344. The first metal electrodes 314 are connected to each pair of the P-type segmented thermoelectric element 342 and the N-type segmented thermoelectric element 344, respectively. The several second metal electrodes 316 are disposed between the second substrate 312 and the upper end surfaces (such as endothermic end) of the P-type segmented thermoelectric element 342 and the N-type segmented thermoelectric element 344. The second metal electrodes 316 are connected to the P-type segmented thermoelectric element 342 and the N-type segmented thermoelectric element 344 of adjacent two pairs of the thermoelectric element, a P-type segmented thermoelectric element 342 and a N-type segmented thermoelectric element 344 of a pair of thermoelectric element 340 which is adjacent to the P-type segmented thermoelectric element 342, and a N-type segmented thermoelectric element 344 and a P-type segmented thermoelectric element 342 of a pair of thermoelectric element 340 which is adjacent to the a N-type segmented thermoelectric element 344 to make the P-type segmented thermoelectric elements 342 and the N-type segmented thermoelectric elements 344 described above be connected to each other electrically.
Moreover, the first solder layers 321 are connected to the first metal electrodes 314 and the lower end surfaces of the P-type segmented thermoelectric elements 342 and the N-type segmented thermoelectric elements 344. The second solder layers 322 are connected to the second metal electrodes 316 and the upper end surfaces of the P-type segmented thermoelectric elements 342 and the N-type segmented thermoelectric elements 344.
In an embodiment, the granulated spacers 384 are distributed in the first solder layers 321 and the second solder layers 322. The melting point of the granulated spacers 384 are higher than the liquidus temperature of alloy material of the first and second solder layers 321 and 322. The shape of the granulated spacers 384 may be small particles with spherical, ellipsoid, cubic or other irregular shapes.
In an embodiment, an average diameter of the granulated spacers 384 is in a range of about 30% to about 100% of the thicknesses of the first and second solder layers 321 and 322. In another embodiment, an average diameter of the granulated spacers 384 is in a range of about 30% to about 60% of the thicknesses of the first and second solder layers 321 and 322. In an embodiment, an average diameter of the granulated spacers 384 is in a range of about 15 μm to about 300 μm. In another embodiment, an average diameter of the granulated spacers 384 is in a range of about 15 μm to about 100 μm. In an embodiment, the ratio of the length to the diameter of the granulated spacers 384 is about 1 to 10. Furthermore, the sizes the granulated spacers 384 of the embodiment may be substantially the same or different. Although the sizes of the granulated spacers 384 shown in
Moreover, although the granulated spacers 384 are disposed in the first and second solder layers 321 and 322 in
In the embodiment, the first and the second metal electrodes 314 and 316 are pure metal plates, or alloy plates. In an embodiment, the material of the granulated spacers 384 such as grains of pure metal or alloy is selected from the group consisting of iron, cobalt, nickel, chromium, copper, manganese, zirconium, titanium and a combination thereof so as to form intermetallic compounds with liquid tin. The surfaces of the granulated spacers 384 also may be coated with nickel, silver or tin selectively for facilitating the soldering effect. Examples of the first and the second solder layers 321 and 322 are tin alloy layers.
Furthermore, in an embodiment, the granulated spacers 384 may be connected with the first and the second metal electrodes 314 and 316 by welding or electroplating, then a stacked Sn/Ni/Sn layer (not shown) is coated on the joining (inner) surface of the metal electrodes to facilitate the connection between the inner surfaces of the metal electrodes and the first and the second solder layers 321 and 322.
In the embodiment, since the outer surfaces of the first and the second metal electrodes 314 and 316 are naked metal surfaces 314a and 316a. In order to protect electrical series circuit of the thermoelectric module 300, the first substrate 311 and the second substrate 312 may be, for example, a high conductivity and insulation sheeting material respectively are covered on the naked metal surfaces 314a and 316a described above. Besides use of the high conductivity and insulation sheeting material, in another embodiment, the metal naked surface 314a and 316a of the first and the second metal electrodes 314 and 316 could be respectively coated by an insulation layer.
In the embodiment, the first and the second solder layers 321 and 322 may be, for example, tin alloy layer. In another embodiment, the first and the second solder layers 321 and 322 also may be a multi-layer solder such as stacked tin sheets and stacked nickel sheets, or tin sheets and stacked silver sheets.
The thermoelectric module 300 provided in the embodiment as shown in
Besides welding or electroplating, the combination of the granulated spacers 384 and the first and the second metal electrodes 314 and 316 may also be processed by mixing the granulated spacers uniformly in a paste solder, then the paste solder with granulated spacers is coated on the metal electrode and metallized as being the solder layers by reflow process.
Similarly, the thermoelectric module 400 provided in
In
In
The positions, material and other related content of the other parts may be referred to the content described above and not described repeatedly.
In actual manufacturing, the granulated spacers 484, such as nickel particles or small pieces of nickel wire, may be mixed with the paste material of the solder in advance, then coated on the surfaces of the first metal electrodes 414 and the second metal electrodes 416. The interface of the first and the second metal electrodes 414 and 416, and interface of the P-type thermoelectric element 442 and the N-type thermoelectric element 444 are joined by reflow heating. Alternatively, the solder paste could be firstly coated on the surfaces of the first metal electrodes 414 and the second metal electrodes 416, and the small pieces of nickel wires or grains are then disposed on the solder paste described above. The reflow process is proceeded finally and the thermoelectric module 400 is assembled. In an embodiment, the granulated spacers 484 occupy in a range of about 5 volume percent to about 50 volume percent of the solder, for example, about 10 volume percent or other range of volume percent.
Several applications of the granulated spacers in the thermoelectric module of the second embodiment are described as below, but they do not intend to limit the disclosure.
Please refer to the
Please refer to the
In the first and second embodiments, the strip-shaped spacers and the granulated spacers are respectively taken for illustrating the supporting effect of the spacers of the disclosure. In practical applications, the spacers having different shapes such as a combination of the granulated and strip-shaped spacers also have the same supporting effects as the embodiments described above.
To sum up, the thermoelectric module having the solder layers with stable thickness is provided in the embodiments, wherein the spacers (such as the strip-shaped, the grain or a combination thereof) are disposed between the metal electrodes and electrical series of the P-type or N-type thermoelectric element. The melting point of the spacers is higher than the liquidus temperature of solder layer to maintain the minimum solder layer thickness between the metal electrodes and the thermoelectric elements to improve the operation reliability and extend the working life of the thermoelectric module.
While the disclosure has been described by way of example and in terms of the preferred embodiment(s), it is to be understood that the disclosure is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.
Number | Date | Country | Kind |
---|---|---|---|
99146678 | Dec 2010 | TW | national |