JP4013895B2 - Thermoelectric module - Google Patents

Description

  The present invention relates to a thermoelectric module using the Peltier effect, and more particularly to a thermoelectric module in which a plurality of thermoelectric elements are connected.

  FIG. 5 is a cross-sectional view schematically showing a conventional general thermoelectric module. In FIG. 5, a connecting member portion such as solder is omitted in order to make the structure easy to see. In a conventional thermoelectric module, a lower substrate 1 on which a lower electrode 3 is formed and an upper substrate 2 on which an upper electrode 4 is formed are arranged in parallel so that the lower electrode 3 and the upper electrode 4 face each other. A plurality of thermoelectric elements are disposed between the two. A pair of p-type thermoelectric elements 5 a and n-type thermoelectric elements 5 b are joined to the lower electrode 3. Among the thermoelectric elements joined on the adjacent pair of lower electrodes 3, the adjacent p-type thermoelectric elements 5 a and 5 n are joined. By joining the upper parts of the thermoelectric element 5a and the n-type thermoelectric element 5b to one upper electrode 4, the p-type thermoelectric element and the n-type thermoelectric element are alternately connected in series. An Sn-plated Cu lead wire 7 (for example, a diameter of 0.3 mm) is connected to the lower electrode 3 to which the thermoelectric elements at both ends of the series connection body are joined by a method such as soldering. However, when the Sn-plated Cu lead wire 7 is connected by soldering or the like, the strength of the connecting portion is low. For this reason, in the conventional thermoelectric module, disconnection and peeling due to deterioration or fatigue of the connecting portion has been a problem. . Further, the wiring work of the Sn-plated Cu lead wire 7 is difficult to automate, there is a problem in workability, and the cost is increased.

  Conventionally, in order to improve solderability, an Au plating layer is provided on the surface of the electrode to improve the wettability with respect to the solder, but a similar method is used between the substrate and the thermoelectric element in the thermoelectric module. Methods for improving solder wettability have been proposed (for example, Patent Documents 1 and 2). In recent years, a method of using an Au wire as a lead by a wire bonding method instead of soldering has started to be applied (see, for example, Patent Documents 3 to 5).

JP 2001-156342 A (page 2-6, FIG. 6) JP 2002-43637 A (page 2-6, FIG. 1-2) Japanese Patent Laid-Open No. 11-54806 (2nd page, FIG. 1) Japanese Patent No. 3082170 (page 1-3, FIG. 1-3) JP 2000-164945 A (Page 8, FIG. 8)

  However, the conventional techniques described above have the following problems. First, the method of providing an Au plating layer on the electrode surface described in Patent Documents 1 and 2 is for the purpose of connecting a thermoelectric element and a substrate. When the law is applied, there is a problem that sufficient characteristics cannot be obtained because no consideration is given to this. In addition, in the thermoelectric module of Patent Document 3 to which the wire bonding method is applied, the external connection terminal is also heated to a high temperature during soldering in the module assembly process, but since the countermeasure is not taken, it is difficult to bond the Au wire. There is a problem of becoming. Further, since the thermoelectric module of Patent Document 5 to which the wire bonding method is applied uses a post electrode formed by another member, it is difficult to join the post electrode to the substrate. Since the joining cost is high, there is a problem that the cost becomes high.

  This invention is made | formed in view of this problem, Comprising: It aims at providing the thermoelectric module which is excellent in wire-bonding property and durability, and can be manufactured at low cost.

A thermoelectric module according to the present invention includes a plurality of thermoelectric elements, a substrate having a plurality of electrodes for electrically connecting the thermoelectric elements and a pair of external connection terminals formed on one surface. In the thermoelectric module provided, the external connection terminals and the electrodes connected to the external connection terminals are formed as one pattern, and an Au layer is formed on the outermost surface of the one pattern by electrolytic plating, This one pattern is divided into two regions, a thick Au layer and a thin Au layer. An external connection bonding wire is connected to the thick Au layer, and the thermoelectric element is connected to the thin Au layer. It is characterized by being.

  In the present invention, since the lead electrode or the post electrode made of another member is not used, the connection process can be simplified. Further, by forming the Au layer of the external connection terminal thicker than the Au layer of the thermoelectric element connection electrode, even if the external connection terminal is heated in the assembly process of the thermoelectric module, the Ni layer is not oxidized. Stable wire bonding properties can be obtained without adversely affecting the Au layer provided on the substrate. Further, since the thermoelectric module of the present invention has a thick Au layer only for the external connection terminals, the amount of Au used is smaller than that of the thick Au layer of all the electrodes, and the manufacturing cost increases compared to the conventional product. That can be suppressed.

  According to the present invention, the Au layer is provided on the outermost surfaces of the electrode and the external connection terminal, and the external connection terminal Au layer is thicker than the Au layer of the electrode, so that the Ni layer is oxidized even when heated in the module assembly process. Therefore, stable wire bonding can be obtained, and since the Au layer of the electrode is thin, the amount of Au contained in the solder joining the thermoelectric element and the substrate is reduced, and durability is improved.

  Hereinafter, a thermoelectric module according to an embodiment of the present invention will be specifically described with reference to the accompanying drawings. In the thermoelectric module of the present embodiment, a lower connection terminal is provided on the lower substrate. FIG. 1 is a sectional view showing a thermoelectric module of the present embodiment, and FIG. 2 is a plan view showing a lower substrate thereof. As shown in FIG. 1, in the thermoelectric module of this embodiment, a lower electrode 3 and an upper substrate 4 are formed on an insulating lower substrate 1 and an upper substrate 2 such as ceramics by plating or the like, respectively. 2 is arranged in parallel so that the lower electrode 3 and the upper electrode 4 face each other, and a plurality of thermoelectric elements are arranged therebetween. A pair of p-type thermoelectric elements 5a and n-type thermoelectric elements 5b are joined to the lower electrode 3, and among the thermoelectric elements joined on the adjacent pair of lower electrodes 3, the adjacent p-type thermoelectric elements 5a. P-type thermoelectric elements and n-type thermoelectric elements are alternately connected in series by joining the top of n-type thermoelectric element 5b to one upper electrode 4. In addition, as shown in FIG. 2, external connection terminals 6 are formed on the lower substrate 1 in contact with the lower electrodes 3 to which the thermoelectric elements at both ends of the series connection body are joined. Each has an Au wire bonded thereto.

  Next, the operation of the thermoelectric module of the present embodiment configured as described above will be described. In the thermoelectric module of the present embodiment, when current is supplied through the Au wire 8, current flows from the lower electrode 3 to the n-type thermoelectric element 5 b via the external connection terminal 6, and further passes through the upper electrode 3. Flow into the p-type thermoelectric element 5a. At this time, since energy moves in the direction opposite to the current, the energy is insufficient on the upper electrode side and the temperature decreases (heat absorption), and the energy is released on the lower electrode side and the temperature increases (heat dissipation).

  FIG. 3 is a cross-sectional view showing the configuration of the lower electrode 3 and the external connection terminal 6 of the thermoelectric module of the present invention. As shown in FIG. 3, the lower electrode 3 and the external connection terminal 6 of the thermoelectric module of the present embodiment have a Cu layer 9 formed on the lower substrate 1, a Ni layer 10 formed thereon, and an outermost surface. It has a three-layer structure in which the Au layer 11 is formed.

  The thickness of the Au layer of the lower electrode 3 in the thermoelectric module of this embodiment is preferably 0.05 to 0.80 μm. Note that 0.05 μm, which is the lower limit of the thickness of the Au layer, is a region generally called flash gold plating. When the thickness of the Au layer is less than 0.05 μm, the wettability of the solder is remarkably lowered. If the Au layer is thicker than 0.80 μm, Sn-Pb eutectic solder, Sn-Sb solder, Sn-Zn solder, Sn-Cu solder, Sn-Ag solder, Sn-Ag-Cu solder, etc. are used. When the thermoelectric element 5 is bonded, the amount of Au—Sn compound generated increases, resulting in poor connection durability. Furthermore, even when using Au—Sn eutectic solder, if the Au layer is thicker than 0.80 μm, the Au content in the composition of the eutectic solder increases, so the wettability of the solder is significantly reduced, Good frets are not generated, resulting in poor connection durability.

  The thickness of the Au layer in the external connection terminal 6 is preferably 1 to 10 μm. If the thickness of the Au layer is less than 1 μm, the Ni layer under the Au layer is oxidized during soldering in the module assembly process, and the oxide protrudes to the surface of the Au layer. As a result, in the wire bonding process Defects occur. On the other hand, even if the thickness of the Au layer is made thicker than 10 μm, no further effect can be obtained. Therefore, it is desirable that the thickness of the Au layer be made 10 μm or less in view of manufacturing costs.

  As described above, in the thermoelectric module of the present embodiment, the Au layer of the external connection terminal 6 is formed thicker than the Au layer of the lower electrode 3. Thus, since only the Au layer of the external connection terminal 6 is thickened, the amount of Au used can be minimized, and an increase in manufacturing cost can be suppressed.

  As a method for forming the Au layer of the external connection terminal 6 in the thermoelectric module of the present embodiment, for example, a thick film is formed only on the external connection terminal portion by a wet method such as a plating method or a dry gas phase method such as a sputtering method. Or a method of forming an Au foil or the like by ultrasonic bonding, soldering or brazing so as to have a predetermined thickness after the same thickness as that of the lower electrode 3 is applied. Can do.

Hereinafter, the effect of the Example of this invention is demonstrated compared with the comparative example which remove | deviates from the scope of the present invention. First, as an example of the present invention, a thermoelectric module was manufactured by forming a lower electrode and an external connection terminal on a lower substrate by the following method. 4 (a) to 4 (g) are cross-sectional views showing the method of manufacturing the thermoelectric module of this embodiment in the order of the steps. First, as shown in FIG. 4A, a 0.05 μm thick Cu layer 9 a was formed on the Al ₂ O ₃ substrate 13. Next, as shown in FIG. 4B, a mask 12 was formed by applying a resist 12 on the Cu layer 9a and then exposing and removing unnecessary resist. Then, as shown in FIG. 4C, the Cu layer 9b was plated by 30 μm, the Ni layer 10 by 4.0 μm, and the Au layer 11a by 0.05 μm by electrolytic plating. Next, as shown in FIG. 4D, after removing the resist 12 between the electrodes, as shown in FIG. 4E, a mask 15 was formed in a portion other than the external connection terminals. Next, as shown in FIG. 4F, the Au layer 11b was plated by 3.95 μm by electrolytic plating, and as shown in FIG. 4G, the mask 15 and the Cu layer 9a between the electrodes were removed. The lower substrate was used and connected by wire bonding to produce the thermoelectric module of the example. The thickness of the Au layer of the lower electrode in the thermoelectric module of the present example produced by the above-described process was 0.05 μm, and the thickness of the Au layer of the external connection terminal was 4 μm.

Next, the lower electrode and the external connection terminal were formed on the lower substrate by the method shown below, and the thermoelectric module of Comparative Example 1 was produced. First, a Cu layer 9 a having a thickness of 0.05 μm was formed on the Al ₂ O ₃ substrate 13. Next, after applying a resist 12 on the Cu layer 9a, exposure was performed and an unnecessary resist was removed to form a mask pattern. Then, the Cu layer 9b was plated by 30 μm, the Ni layer 10 by 4.0 μm, and the Au layer 11a by 0.05 μm by electrolytic plating. Thereafter, the Cu layer 9a between the mask and the electrode was removed, and a lower substrate having a uniform thickness of the lower electrode and the external connection terminal was produced. The lower substrate was used and connected by wire bonding to produce a thermoelectric module of Comparative Example 1. The thickness of the thermoelectric element electrode of the thermoelectric module of this comparative example and the Au layer of the external connection terminal were both 0.05 μm.

Next, a lower electrode and an external connection terminal were formed on the lower substrate by the method described below to produce a thermoelectric module of Comparative Example 2. First, a Cu layer 9 a having a thickness of 0.05 μm was formed on the Al ₂ O ₃ substrate 13. Next, after applying a resist 12 on the Cu layer 9a, exposure was performed and an unnecessary resist was removed to form a mask pattern. Next, by electroplating, the Cu layer is plated by 30 μm, the Ni layer by 4.0 μm, and the Au layer by 4.0 μm, and then the Cu layer 9a between the mask and the electrodes is removed, and the lower substrate having a uniform electrode thickness Was made. The lower substrate was used and connected by wire bonding to produce a thermoelectric module of Comparative Example 2. The thickness of the Au layer of the lower electrode and the external connection terminal in the lower substrate of this comparative example was 4.0 μm.

  Table 1 below shows the specifications of the thermoelectric modules of Examples and Comparative Examples 1 and 2 manufactured by the method described above. In this embodiment, Au wire having a diameter of 20 μm was used for wire bonding.

  Next, bonding properties and durability tests were performed on the thermoelectric modules of Examples and Comparative Examples 1 and 2. In the bondability test, a hook was applied to the wire-bonded Au wire of the prototype thermoelectric module, and the wire was cut or pulled up until the joint surface peeled off. At that time, if the bonding interface has sufficient strength, the wire itself is cut. Further, if the bonding force of the bonding bonding surface is weak, the bonding surface peels off. Here, the case where the wire itself was cut was regarded as acceptable. In the durability test, the hot side of the thermoelectric module was kept constant at 85 ° C., I = 2A was turned ON / OFF every minute, and this was repeated 30,000 times to confirm the rate of change in electrical resistance before and after the test. The evaluation results are shown in Table 2 below.

  As shown in Table 2, since the thermoelectric module of Comparative Example 1 had a thin Au layer of the external connection terminal, the bonding strength of wire bonding was low, and peeling occurred at the interface between the Au wire and the external connection terminal surface. However, since the thickness of the Au layer of the lower electrode is also thin, the amount of Au contained in the solder between the thermoelectric element and the substrate is small, the generation of Au—Sn compound is suppressed, cracks do not occur, and the durability is It was good. In the thermoelectric module of Comparative Example 2, since the thickness of the Au layer of the external connection terminal was increased to 4.0 μm, the wire itself was cut without being peeled off at the bonding interface between the Au wire and the external connection terminal. As described above, by increasing the thickness of the Au layer of the external connection terminal, the bondability was improved and a strong bonding force was obtained. On the other hand, the electrical resistivity increased to 3.2%. High electrical resistivity indicates low durability, and further repetition of the test means disconnection at an early stage. Also, the increase in electrical resistivity is due to the fact that a large amount of Au—Sn compound was generated in the solder between the thermoelectric element and the substrate because the Au layer of the lower electrode was thick.

  On the other hand, the thermoelectric module of the example was superior to the thermoelectric modules of Comparative Examples 1 and 2 in both bonding properties and durability. Furthermore, the thermoelectric module of the example was able to produce a substrate at a cost about 5% lower than the thermoelectric module of Comparative Example 2.

It is sectional drawing which shows the thermoelectric module of this embodiment. It is a top view which shows the lower board | substrate of the thermoelectric module of this embodiment. It is sectional drawing which shows the structure of the electrode of the thermoelectric module of this embodiment, and an external connection terminal. (A) thru | or (g) is sectional drawing which shows the preparation methods of the thermoelectric module of a present Example in the order of the process. It is sectional drawing which shows the conventional thermoelectric module typically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1; Lower board | substrate 2; Upper board | substrate 3; Lower electrode 4; Upper electrode 5a; P-type thermoelectric element 5b; N-type thermoelectric element 6; External connection terminal 7; Lead wire 8; Au wire 9, 9a, 9b; ; Ni layer 11, 11a, 11b; Au layer 12; resist 13; _Al 2 _{O 3} substrate 14; solder 15; mask

Claims (1)

A plurality of thermoelectric elements, thermoelectric modules with a substrate on which the external connection terminals of the plurality of electrodes and a pair of patterned on one surface for electrically connecting the thermoelectric elements, each of said An external connection terminal and an electrode connected to the external connection terminal are formed as one pattern, and an Au layer is formed by electrolytic plating on the outermost surface of the one pattern. It is divided into two regions, a thick portion and a thin portion, wherein an external connection bonding wire is connected to a thick portion of the Au layer, and the thermoelectric element is connected to a thin portion of the Au layer. Thermoelectric module.

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