Abstract:
A thermoelectric module and method of manufacture thereof, capable of preventing short-circuits between electrodes due to solder without causing increases in size or cost. A thermoelectric module is configured with lower electrodes formed on the inside surface of a lower substrate, placed in opposition to an upper substrate, on the inside surface of which are formed upper electrodes; the end faces of thermoelectric elements are soldered to the lower electrodes and upper electrodes. Each of the electrodes is configured from three layers, which are a copper layer, a nickel layer formed on one face of the copper layer, and a gold layer formed on one face of the nickel layer; a visor portion, protruding outward, is formed in the nickel layer, so that when positioning the thermoelectric elements above the electrodes and soldering the electrodes to the thermoelectric elements, the flowing of solder  18   a  from the side portions of electrodes to the insulating substrate is prevented.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to a thermoelectric module which performs thermoelectric conversion, and to a manufacturing method for same.  
         [0003]     Priority is claimed on Japanese Patent Application No. 2005-37767, filed Feb. 15, 2005, the content of which is incorporated herein by reference.  
         [0004]     2. Description of Related Art  
         [0005]     Thermoelectric modules, which utilize the Peltier effect and the Seebeck effect in thermoelectric power conversion, have conventionally been used in heating and cooling equipment and other applications. Such thermoelectric modules are configured by forming multiple electrodes at prescribed locations on the opposing inside surfaces of a pair of insulating substrates, and by soldering the upper and lower ends of thermoelectric elements to the opposing electrodes, to fix in place multiple thermoelectric elements between the pair of insulating substrates.  
         [0006]     Among such thermoelectric modules, there are devices having a structure which prevents the occurrence of short-circuits across electrodes due to the flow of solder in the molten state on the insulating substrates when soldering the thermoelectric elements to the electrodes. Among these devices, there are thermoelectric modules in which electrodes are configured from three layers, which are a copper layer, a nickel layer formed over the entire surface of the copper layer, and a metal plated layer of gold or similar formed on the upper surface (the upper surface when forming the electrodes) of the nickel layer, and in which the nickel layer which has less solderability is exposed on the side surfaces of the electrodes (see for example, Japanese Unexamined Patent Application, First Publication No. 2004-140250).  
         [0007]     There are also devices in which grooves are provided between the electrodes on the insulating substrates, to prevent the flow of solder in the molten state onto other electrodes (see for example, Japanese Unexamined Patent Application, First Publication No. 2003-100983).  
         [0008]     However, of the above-described thermoelectric modules, the former entails the difficulty of processing to cause the nickel layer to be exposed on the side faces of the electrodes, as a result of which there are the problems that the number of processes is increased, production yields are lowered and manufacturing times lengthened, and in addition costs are increased. In methods to manufacture such thermoelectric modules, prior to removal by-etching of the unwanted portions of the metal plated layer (the side-face portions of the electrodes), resist is formed on the upper surface of the metal plated layer; and there is the problem that during this processing, a shift in the electrodes and mask causes resist to touch the side faces of electrodes, giving rise to short-circuits.  
         [0009]     Further, in the case of the latter thermoelectric modules of the prior art, grooves are formed between the electrodes on the insulating substrates respectively, so that the distances between electrodes are increased, and there is the problem that the thermoelectric modules are increased in size (with reduced densities). Moreover, because grooves are formed, the number of processes is increased, production yields are lowered and manufacturing time is prolonged as well as increased costs.  
         [0010]     The present invention was devised in order to address the above-described problems, and has as an object the provision of a thermoelectric module and manufacturing method for a thermoelectric module capable of preventing short-circuits between electrodes due to solder, without resulting in increases in size or cost.  
       SUMMARY OF THE INVENTION  
       [0011]     In order to attain this object, a thermoelectric module of this invention is configured by forming electrodes at prescribed locations on the opposing inside surfaces of a pair of insulating substrates, arranged in opposition, and by soldering the end faces of a plurality of thermoelectric elements to the respective opposing electrodes, to fix the thermoelectric elements between the pair of insulating substrates, and is characterized in that a visor portion, protruding outward, is formed on the edge portion of the thermoelectric element-side portion of the electrodes, and when thermoelectric elements are positioned on the upper sides of electrodes and electrodes soldered to thermoelectric elements, the solder is prevented from flowing from the side portions of the electrodes to the insulating substrates.  
         [0012]     In a thermoelectric module of this invention configured in this way, an outward-protruding visor portion is formed on the upper-end edge portions (the portions on the upper side when performing solder treatment) of electrodes to be fixed to thermoelectric elements with solder; hence when using solder to fix the lower-end portions of thermoelectric elements to the upper faces of electrodes positioned on the upper surface of an insulating substrate, molten-state solder which has overflowed from bonded portions accumulates on the upper faces and side faces of the visor portions.  
         [0013]     As a result, events in which the solder flows as far as the insulating substrate surface, making contact with solder which has flowed from other electrodes and causing short-circuits between electrodes, can be prevented. Further, when fixing the other end portions of thermoelectric elements to electrodes formed on the other insulating substrate also, with the insulating substrate positioned below, by fixing the lower end portions of the thermoelectric elements to the upper faces of electrodes positioned on the upper surface of the insulating substrate, flowing of solder to the insulating substrate can be prevented.  
         [0014]     Other configuration characteristics of a thermoelectric module of this invention are the formation of electrodes from a plurality of layers consisting of metal layers of different types, and the formation in the visor portion of a metal layer with less solderability with respect to the solder, among the metal layers making up the plurality of layers.  
         [0015]     Here, the less solderability with respect to solder generally indicates a property of strongly repelling solder. In this invention, “less solderability” is taken to mean that, in tests in conformance with JIS C 0053 (1996), the time interval A-t0 (known in the industry as the zero-cross time) stipulated is 3 seconds or longer. This test is performed by plotting, against time, the change in force when a specimen-is immersed in molten solder; the zero-cross time is the time from the start of immersion of the specimen in the solder vat, until the state in which the force with which the specimen is pushed upward from the solder vat is in equilibrium with the force pulling the specimen into the solder vat (force due to solderability).  
         [0016]     By forming a visor portion in this metal layer with less solderability, flowing of solder in the molten state past the visor portion from the side faces of electrodes to the side of the insulating substrate can be prevented more reliably. Further, in this case the layer in which the visor portion is formed is not limited to the uppermost layer among the plurality of layers, but can be any metal layer in a position in which a visor portion can be formed in a state maintaining a prescribed interval from the insulating substrate. Metals having less solderability with respect to solder include nickel and magnesium. Conversely, metals having good solderability with respect to solder include gold, tin, tin alloys (tin-antimony, tin-bismuth, tin-copper, tin-copper-silver) and similar.  
         [0017]     Still another configuration characteristics of a thermoelectric module of this invention is the configuration of electrodes from three layers, which are a copper layer formed on one face of the insulating substrate, a nickel layer formed on one face of the copper layer, and a gold layer formed on one face of the nickel layer, and with the visor portion formed in the nickel layer.  
         [0018]     Because of its superior conductivity, copper is widely used in electrodes, and because of its superior solderability with respect to solder, gold is appropriate as the surface layer of electrodes when an electrode is to be fixed to a thermoelectric element by means of solder. And by forming a layer of nickel, with less solderability with respect to solder, between the copper layer and the gold layer, causing the edge portion of the nickel layer to protrude so as to form a visor portion, flowing of molten-state solder to the side of the insulating substrate can be reliably-prevented. In this case, the peripheral portion of the gold layer may be formed to protrude toward the outside together with the nickel layer visor portion; however, the side portion of the visor portion must be exposed without being covered.  
         [0019]     Still another configuration characteristics of a thermoelectric module of this invention is the configuration of electrodes from a single layer consisting of a metal layer of one type. In this case the metal used in the metal layer is required to have superior conductivity and also to have less solderability with respect to solder, and so it is appropriate that nickel or magnesium be used. By this means, although the strength of adhesion of electrodes and thermoelectric elements due to the solder is somewhat weaker, the reliability with which short-circuits between electrodes due to solder can be prevented is increased. Further, because the number of processes for forming electrodes is reduced, thermoelectric modules can be easily manufactured, and costs can be reduced. Still another configuration characteristics of a thermoelectric module of this invention is the setting of both the thickness of the base end and protrusion length of the visor portion to 1 μm or greater. Here, the base end of the visor portion is the border portion between the main portion of the electrode and the visor portion. By this means, when soldering electrodes and thermoelectric elements, the visor portion can be ensured to be sufficiently strong and long enough to prevent the flow of molten solder.  
         [0020]     A method of manufacture of thermoelectric modules of this invention, in which electrodes are formed in prescribed locations on the opposing inside surfaces of a pair of insulating substrates, arranged in opposition, and the end faces of a plurality of thermoelectric elements are soldered to the respective opposing electrodes, to fix in place the thermoelectric elements between the pair of insulating substrates, is characterized in having a resist layer formation process of forming a resist layer on one surface of the insulating substrates; an exposure process of exposing the surface of the resist layer, in a state of masking prescribed portions of the surface of the resist layer formed in the resist layer formation process; a development process of removing the masked portions in the resist layer through development of the resist layer exposed in the exposure process; an electrode formation process of forming electrodes, consisting of a plurality of metal layers, between the resist layer of prescribed shape formed in the development process; a resist layer removal process of removing the resist layer of prescribed shape; and, an visor formation process of removing a portion of the side portion of a metal layer on the insulating substrate side, among the plurality of metal layers of the electrodes, to form a visor portion on the edge portion of the electrodes.  
         [0021]     By this means, a simple method can be used to obtain a thermoelectric module in which the flowing of solder to the insulating substrates is prevented, and short-circuits between electrodes due to solder do not occur. The resist layer formed in the resist layer formation process is not limited to direct formation on one surface of the insulating substrates, but may be formed via a prescribed seed layer. When forming a seed layer, this seed layer is removed by ion beam etching after removal of the resist layer.  
         [0022]     In this case, the visor portion can be formed in the metal layer with less solderability with respect to solder among the plurality of metal layers making up the electrodes formed in the electrode formation process. Further, the electrodes formed in the electrode formation process can consist of three metal layers, which are a copper layer formed on one surface of the insulating substrates, a nickel layer formed on one surface of the copper layer, and a gold layer formed on one surface of the nickel layer, and the visor portion can be formed in the nickel layer.  
         [0023]     Another method of manufacture of thermoelectric modules of this invention, in which electrodes are formed in prescribed locations on the opposing inside surfaces of a pair of insulating substrates, arranged in opposition, and the end faces of a plurality of thermoelectric elements are soldered to the respective opposing electrodes, to fix in place the thermoelectric elements between the pair of insulating substrates, is characterized in having a resist layer formation process of forming a resist layer on the upper surfaces of the insulating substrates; an exposure process of exposing the surface of the resist layers, in a state of masking prescribed portions of the surface of the resist layers formed in the resist layer formation process; a development process of removing the masked portions in the resist layers through development of the resist layers exposed in the exposure process; an electrode formation process of forming electrodes, in which the top-end edge portion is formed into a visor portion, between the resist layer formed into a prescribed shape in the development process and in a portion of the surface of the resist layer; and, a resist layer removal process of removing the resist layer of prescribed shape.  
         [0024]     By this means, a simple method can be used to obtain a thermoelectric module in which the flowing of solder to the insulating substrates is prevented, and short-circuits between electrodes due to solder do not occur. In this case, electrodes formed in the electrode formation process may be configured from single layers consisting of a single type of metal layer, or may be configured from a multilayer film consisting of a plurality of metal layers. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  is an oblique perspective figure showing the thermoelectric module of one embodiment of the invention;  
         [0026]      FIG. 2  is a front view of the thermoelectric module shown in  FIG. 1 ;  
         [0027]      FIG. 3  is a cross section showing the state of an insulating substrate fixed to a thermoelectric element via an electrode;  
         [0028]      FIG. 4  is a cross section showing an electrode formed on-an insulating substrate;  
         [0029]      FIG. 5A -D shows processes for formation of electrodes, in which  FIG. 5A  is a cross section of resist,  FIG. 5B  is a cross section showing the state in which a copper layer, nickel layer, and gold layer are formed within the resist;  FIG. 5C  is a front view showing the state in which resist has been removed; and,  FIG. 5D  is a front view showing the state of formation of an electrode;  
         [0030]      FIG. 6  is a cross section showing the state of an electrode fixed to a thermoelectric element by solder;  
         [0031]      FIG. 7  is a cross section showing thermoelectric elements fixed to the upper faces of electrodes formed on an insulating substrate;  
         [0032]      FIG. 8  is a cross section showing an electrode with a thermoelectric element in another embodiment;  
         [0033]      FIG. 9A -C shows processes for formation of the electrode shown in  FIG. 8 , where  FIG. 9A  is a cross-sectional view of resist,  FIG. 9B  is a cross-sectional view showing the state of formation of electrodes consisting of a copper layer in resist, and  FIG. 9C  is a front view showing the state of formation of an electrode with the resist moved; and,  
         [0034]      FIG. 10  is a cross-sectional view showing an electrode with a thermoelectric module in still another embodiment. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]     Hereinafter, embodiments of the present invention are explained referring to the drawings.  FIG. 1  and  FIG. 2  show a thermoelectric module  10  of one embodiment. This thermoelectric module  10  has a pair of insulating substrates, which are a lower substrate  11   a  and an upper substrate  11   b ; lower electrodes  12   a  are formed in prescribed positions of the upper surface of the lower substrate  11   a , and upper electrodes  12   b  are formed in prescribed positions of the lower surface of the upper substrate  11   b . The lower-end faces of multiple thermoelectric elements  13 , consisting of chips, are fixed in place to the lower electrodes  12   a  by solder; and, the upper-end faces are fixed with solder to the upper electrodes  12   b  respectively, to integrally link the lower substrate  11   a  and the upper substrate  11   b.    
         [0036]     The lower electrodes  12   a  and upper electrodes  12   b  are installed at positions shifted distances equal to substantially the width of one of the thermoelectric elements  13 . Upper electrodes  12   b  are bonded to the upper-end faces of two thermoelectric elements respectively while there are two types of lower electrodes  12   a , one is bonded to the lower-end face of only one thermoelectric element  13 , and another is bonded to the lower-end faces of two thermoelectric elements  13 . Lower electrodes  12   a  to which the lower-end face of only one thermoelectric element  13  is bonded are provided in two corner portions on one side (the rear-end portion in  FIG. 2 ) of the lower substrate  11   a ; lead wires  14   a ,  14   b  are connected to the rear-side portions of these lower electrodes  12   a , enabling connection to external equipment.  
         [0037]     The lower substrate  11   a  and upper substrate  11   b  consist of sheets of alumina; the thermoelectric elements  13  consist of alloy derived from bismuth-tellurium and are formed in a rectangular parallelepiped shape. Each of the thermoelectric elements  13  is electrically connected to the substrates via the lower electrodes  12   a  and upper electrodes  12   b . The lower-end faces of the thermoelectric elements  13  and lower electrodes  12   a , the upper-end faces of the thermoelectric elements  13  and the upper electrodes  12   b , and the rear-side portions of the lower electrodes  12   a  formed in edge side of the lower substrate  11   a  and the lead wires  14   a ,  14   b , are respectively fixed in place using solder.  
         [0038]     The lower electrodes  12   a  and upper electrodes  12   b  are formed into substantially the same shape, configured as shown in  FIG. 3 . In the following explanations, the lower electrodes  12   a  and upper electrodes  12   b  are both described as electrodes  12 , and the lower substrate  11   a  and upper substrate  11   b  are both described as insulating substrates  11 . The electrodes  12  are configured as three metal layers, which are a copper layer  15  formed on the upper surface of the insulating substrate  11 , a nickel layer  16  formed on the upper surface of the copper layer  15 , and a gold layer  17  formed on the upper surface of the nickel layer  16 .  
         [0039]     On the periphery of the nickel layer is formed a visor portion  16   a , protruding outward from the outer-circumference face of the copper layer  15 , so that a step is formed between the nickel layer  16  and the copper layer  15 . The gold layer  17  is formed on the upper surface of the nickel layer  16 , in a state which causes the portion in proximity to the side face at the side-face portion and upper face of the nickel layer  16  to be exposed slightly. By using solder  18  to bond the upper face of the electrode  12  to the lower-end portion of the thermoelectric element  13 , the electrode  12  and thermoelectric element  13  are fixed in place.  
         [0040]     When the electrode  12  is an upper electrode  12   b , the vertical-direction positional relationship of the insulating substrate  11 , electrode  12 , and thermoelectric element  13  are inverted from the vertical-direction state in  FIG. 3 . The thickness of the copper layer is set to 50 μm, the thickness of the nickel layer  16  is set to 4 μm, and the thickness of the gold layer  17  is set to 0.3 to 0.4 μm. The protrusion length a of the visor portion  16   a  shown in  FIG. 4  is set to from 1 to 5 μm. As the solder  18 , a solder of tin and antimony is used.  
         [0041]     Next, a method of manufacture of a thermoelectric module  10  configured as described above is explained. The thermoelectric module  10  is manufactured by a manufacturing method having the processes shown in  FIG. 5  and  FIG. 6 . In this case, a seed layer (not shown) consisting of a chromium layer and a copper layer is first formed on the upper surface of the insulating substrate  11  by sputtering (a method in which a high direct-current voltage is applied to an insulating substrate  11  and a target (of the material used to deposit the layer, in this case, chromium and copper) while introducing argon gas into an vacuum, so that ionized argon gas collides with the target and causes target material to be ejected and deposited on the insulating substrate  11 ).  
         [0042]     Dry film is applied to the upper surface of the seed layer, and using an exposure system (not shown) with prescribed areas masked, the surface is exposed for 120 seconds at an intensity of 150 mJ/cm2, after which development is performed for 2.5 minutes in a sodium carbonate solution at a temperature of 30 C. By this means, a pattern is formed in the resist  19  on the upper surface of the insulating substrate  11 , as shown in (a) of  FIG. 5 . This resist  19  is formed in portions in which, ultimately, electrodes  12  will not be formed on the upper surface of the insulating substrate  11 .  
         [0043]     A copper plating solution of 80 g/L of sulfuric acid, 190 g/L of copper sulfate, and 50 ppm of chlorine ions are used to perform plating at room temperature at a current density of 2 A/dm 2 , to form a copper layer  15   a  within the resist  19  (see  FIG. 5B ). The thickness of this copper layer  15   a  is set to approximately 40 to 100 μm. Then, a nickel plating solution of 240 g/L nickel sulfate, 45 g/L nickel chloride, and 6 g/L boric acid is used to perform plating at a temperature of 55 degrees Celsius at a current density of 2 A/dm 2  , to form a nickel layer  16  of thickness 4 μm on the upper surface of the copper layer  15   a  within the resist  19 .  
         [0044]     Then, the nickel layer  16  is immersed in a plating bath set to a temperature of 55 degrees Celsius, and by passing a current at current density 0.4 A/dm 2 , a gold layer of thickness approximately 0.3 to 0.4 μm is formed on the upper surface of the nickel layer  16 . By this means, as indicated in  FIG. 5B , three metal layers, which are a copper layer  15 , nickel layer  16 , and gold layer  17  are formed within the resist  19 . Next, a sodium hydroxide solution is used to remove the resist  19 , and ion beam etching (a method in which a specimen is treated by means of the sputtering reaction of an ion beam pulled from an ion source and accelerated) is used to remove the seed layer formed below the resist  19 , resulting in the state in  FIG. 5C .  
         [0045]     Then, a prescribed thickness is removed by immersing the side-face portion of the copper layer  15   a  in etching solution for  30  seconds, resulting in the state  FIG. 5D . By this means, an electrode  12  consisting of the copper layer  15 , the nickel layer  16  with a visor portion  16   a , and the gold layer  17  is formed on the prescribed portion of the surface of the insulating substrate  11 . Though not shown in the drawing, a seed layer consisting of a chromium layer and a copper layer is formed between the insulating substrate  11  and the copper layer  15 ; this seed layer is also contained in the electrode  12 . The electrodes  12  shown in  FIG. 4  and in  FIG. 5D  are, for convenience of explanation, shown with different shapes; but in substance they are the same.  
         [0046]     Next, on the upper face of the electrode  12  formed on the upper surface of the insulating substrate  11  through the processes shown in  FIG. 5 , a thermoelectric element  13  is positioned, and soldering is performed. Here, first a solder layer, of tin and antimony, is formed on the upper surface of the electrode  12 . Then, the end portion of two or of one thermoelectric element is placed on the upper faces of each of the electrodes  12 , and a weight or other member is used to maintain this state. In this state, the insulating substrate  11  is then inserted into a reflow furnace (not shown) and heated.  
         [0047]     By this means, the solder layer is melted and the state of the solder  18   a  becomes as shown in  FIG. 6 . Here, the gold layer  17  of the electrode  12  and the lower-end face of the thermoelectric element  13  are substantially in a state of contact, and the solder  18   a  is accumulated on the periphery of the bonded portion between the electrode  12  and the thermoelectric element  13 . Further, the solder  18   a  is prevented from dropping by the visor portion  16   a . Upon removal from the reflow furnace of the insulating substrate  11  and similar and cooling, the solder  18   a  shrinks and hardens, assuming the state of  FIG. 3 . By this means, each of the thermoelectric elements  13  is fixed to the insulating substrate  11  via electrodes  12 , resulting in the state of  FIG. 7 .  
         [0048]     When fixing another insulating substrate  11  on the other end portion of the thermoelectric elements  13 , electrodes  12  are formed in prescribed portions on the upper surface (after assembly, the lower surface) of the insulating substrate  11 , and two solder layers are formed, maintaining an interval between them respectively, on the upper faces of the electrodes  12 . The end portions of the thermoelectric elements are then placed on the upper faces of each of the solder layers, and the insulating substrate  11 , positioned above the thermoelectric elements  13 , is subjected to pressure by a weight or similar, placed into a reflow furnace and heated, followed by external cooling. By fixing in place the lead wires  14   a ,  14   b  to a prescribed electrode  12 , the thermoelectric module  10  shown in  FIG. 1  and  FIG. 2  is obtained.  
         [0049]     Thus in the thermoelectric module  10  of this aspect, an outward-protruding visor portion  16   a  is formed in the peripheral portion of the nickel layer  16  contained in the upper-end portions of electrodes  12 . Hence when using solder  18  to fix the lower-end portions of thermoelectric elements  13  to the upper faces of electrodes  12  formed on the upper surface of an insulating substrate  11 , molten-state solder  18   a  overflowing from the bonded portion accumulates on the upper face and side face of the visor portion  16   a , and dropping of the solder is prevented. By this means, it is possible to prevent the occurrence of short-circuits between electrodes  12  due to hardening of solder  18   a  which has flowed from different electrodes  12  onto the insulating substrate  11  and made mutual contact.  
         [0050]     Moreover, because electrodes are formed from three metal layers which are a copper layer  15 , nickel layer  16  and gold layer  17 , with a visor portion  16   a  formed in the nickel layer  16  having less solderability with respect to solder  18 , the molten-state solder  18   a  can be more reliably prevented from passing the visor portion  16   a  and flowing from the side face portion of the copper layer  15  to the side of the insulating substrate  11 . And, according to a method of manufacture of a thermoelectric module  10  of this embodiment, the visor portion  16   a  can be formed by a simple method. Hence a thermoelectric module  10  can be obtained in which solder  18   a  is prevented from flowing onto the insulating substrate  11 , and short-circuits between electrodes due to solder  18  do not occur.  
         [0051]      FIG. 8  shows a state in which an electrode  22  of a thermoelectric module of another embodiment of the invention is provided on the upper surface of an insulating substrate  21 . This electrode  22  consists of a single layer, which is a nickel layer; a visor portion  26   a , protruding outward, is formed in the peripheral portion of the upper end. The configuration of other portions of the thermoelectric module having such electrodes  22  is otherwise the same as in the above-described thermoelectric module  10 .  
         [0052]      FIG. 9  is used to explain a method of formation of the electrode  22  configured as described above. Here, as indicated in  FIG. 9A , processes up to the formation of a pattern in the resist  29  on the upper surface of the insulating substrate  21  are the same as in the above-described embodiment, therefore an explanation is omitted. After formation of this resist, the above-described method is used to form electrodes consisting of a nickel layer within the resist  29 . In this case, as indicated in  FIG. 5B , the upper-end edge of the electrode  22  is also formed on a portion of the upper face of the resist  29 .  
         [0053]     Then, using a sodium hydroxide solution, the resist  29  is removed, and ion beam etching is used to remove the seed layer formed below the resist  29 , to obtain the state shown in  FIG. 9C . By this means, electrodes  22  consisting of a nickel layer having a visor portion  26   a  are formed in prescribed portions of the upper surface of the insulating substrate  21 . In this case also, a seed layer consisting of a chromium layer and a nickel layer is formed between the insulating substrate  21  and the nickel layer of the electrodes  22 . The method of fixing the electrodes  22  and thermoelectric elements  13  in place by soldering is the same as in the above-described embodiment, and so an explanation is omitted.  
         [0054]     Thus in a thermoelectric module of this embodiment the number of processes to form electrodes  22  is greatly reduced, so that thermoelectric modules can be easily manufactured, and in addition costs can be reduced. According to this method of manufacture of thermoelectric modules, the flowing of solder onto the insulating substrate  21  can be prevented by a still simpler method, and a thermoelectric module can be obtained in which short-circuits between electrodes  22  due to solder do not occur.  
         [0055]     Regarding another embodiment of the present invention,  FIG. 10  shows a state in which an electrode  32  of the thermoelectric module is provided on the upper surface of an insulating substrate  31 . This electrode  32  consists of two metal layers, which are a magnesium layer  36  formed on the upper face of a copper layer  35 ; a visor portion  36   a , protruding outward, is formed on the outer side of the periphery of the magnesium layer  36 . The configuration of other portions of the thermoelectric module having these electrodes  32  is otherwise the same as the above-described thermoelectric module  10 .  
         [0056]     Formation of this electrode  32  omits formation of the gold layer  17  in the formation method illustrated in  FIG. 5 , and in place of formation of the nickel layer  16 , a magnesium layer  36  is formed; otherwise the method is the same as the formation method shown in  FIG. 5 , and an explanation is omitted. When forming this electrode  32  also, the-number of processes to form the electrode  32  is reduced, so that the thermoelectric module can easily be manufactured, and costs can be reduced. Further, by means of this thermoelectric module manufacturing method, a simple method can be used to prevent the flowing of solder onto an insulating substrate  31  and to obtain a thermoelectric module in which short-circuits between electrodes  32  due to solder do not occur.  
         [0057]     Thermoelectric modules and manufacturing methods of this invention are not limited to the above-described embodiments, and various appropriate alterations are possible. For example, the electrode  12  of an above-described embodiment consists of three metal layers, with a visor portion  16   a  provided in the nickel layer  16  which is formed as the second layer; however, this visor portion can be formed in the uppermost metal layer. In this case, the thickness of the uppermost metal layer is set to 1 μm or greater.  
         [0058]     In the electrode  32 , a visor portion  36   a  is provided in the upper-portion magnesium layer  36 ; but the visor portion may instead be provided in the upper-end edge portion of the copper layer  35 , positioned below the magnesium layer  36 . Further, the magnesium layer  36  and the visor portion  36   a  in the electrode  32  may be formed integrally as the same layer with substantially the same thickness; or, the lateral cross-section of the lower-side portion of the magnesium layer  36  may be made the same as the lateral cross-section of the copper layer  35 , with the visor portion  36   a  formed at the edge of the upper end of the magnesium layer  36 .  
         [0059]     Further, electrodes may be formed from three or more layers, and in this case the metal materials used in the different layers may be selected and used as appropriate. For example, two layers may be formed on top of a copper layer, one layer consisting of nickel and magnesium, the other layer of gold, tin, a tin alloy, or similar, with the visor portion formed at the edge of this second layer. In this case, the copper layer portion may be formed as two layers, with the other layer formed from a metal other than copper. In addition, the layer in which the upper visor portion is formed may be a single layer, and the layer in the lower portion may consist of two or more layers.  
         [0060]     In the method of formation of electrodes  22  shown in  FIG. 9 , electrodes can also be formed from a plurality of layers. And, the material used as the solder  18  is not limited to tin and antimony, but can consist of tin and gold, tin and lead, and similar. The configurations of the other portions in each of the above-described embodiments can also be modified as appropriate, within the technical scope of this invention.