Patent Publication Number: US-2010108117-A1

Title: Thermoelectric module package and manufacturing method therefor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to packages holding semiconductor devices such as semiconductor lasers, and in particular to thermoelectric module packages including metal bases and metal frames joining peripheries of metal bases, in which insulating resin layers bond metal frames to thermoelectric modules for heating or cooling semiconductor devices. The present invention also relates to manufacturing methods of thermoelectric module packages. 
     The present application claims priority on Japanese Patent Application No. 2008-279388, the content of which is incorporated herein by reference. 
     2. Description of the Related Art 
     Various types of thermoelectric module packages and optical module packages have been developed and disclosed in various documents such as Patent Documents 1-3.
         Patent Document 1: Japanese Unexamined Patent Application Publication No. H07-128550   Patent Document 2: Japanese Patent No. 3426717   Patent Document 3: Japanese Patent No. 4101181       

       FIGS. 8A and 8B  show a package  20  including a thermoelectric module  20   a  and a metal base  21  composed of a copper-tungsten (CuW) material having a good thermal conductivity with a high thermal expansion coefficient approximating to that of an iron-nickel-cobalt alloy (namely, “Kovar”, a registered trademark). A silver brazing alloy  29  (melting point: 770° C.) bonds the metal base  21  to a metal frame  22  composed of an iron-nickel-cobalt alloy (i.e. Kovar) at a high temperature. This technology is disclosed in Patent Documents 1 and 2. 
     Patent Document 1 discloses that the thermoelectric module  20   a  joins to the metal base  21  of the package  20  via a solder  23   a  (melting point: 118-280° C.) composed of lead (Pb), tin (Sb), indium (In), and bismuth (Bi). Patent Document 3 discloses various joining materials such as a Sn—Ag solder (melting point: 221° C.) and a Sn—Zn solder (melting point: 199° C.). 
     Since numerous thermoelectric elements  28  linearly join together in the thermoelectric module  20   a  shown in  FIG. 8B , pairs of lower electrodes  24  and upper electrodes  26  join to the lower and upper ends of thermoelectric elements  28 . The lower electrodes  24  are formed on a ceramic substrate  23 , while the upper electrodes  26  are formed on a ceramic substrate  25 . The package  20  holding the thermoelectric module  20   a  dissipates heat from the thermoelectric elements  28  via the ceramic substrate  23  and the metal base  21  composed of a copper-tungsten (CuW) material having a thermal conductivity of 160-200 W/mK; hence, it suffers from insufficient heat dissipation. 
       FIGS. 9A and 9B  show a package  30  holding a thermoelectric module  30   a , which is bonded to a metal base  31  (composed of copper) having a good thermal conductivity of 400 W/mK substituting for the metal base  21  composed of the CuW material via a solder  33   a . A silver brazing alloy  39  (melting point: 770° C.) bonds the metal base  31  to a metal frame  32  composed of an iron-nickel-cobalt alloy (i.e. “Kovar”) at a high temperature. The thermoelectric module  30  includes numerous thermoelectric elements  38  with lower and upper ends joining to lower electrodes  34  and upper electrodes  36 , which are paired and formed on ceramic substrates  33  and  35 . 
     When the silver brazing alloy  39  bonds the metal base  31  to the metal frame  32 , the metal base  31  greatly bends due to a large difference between the copper&#39;s thermal expansion coefficient (or linear expansion coefficient α) of 1.68×10 −6 /K and the iron-nickel-cobalt&#39;s thermal expansion coefficient (or linear expansion coefficient α) ranging from 5.7×10 −6 /K to 6.5×10 −6 /K. The metal base  31  bends like the bottom of a ship with a deflection of 100 μm, for example. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a thermoelectric module package including a metal base and a metal frame for holding a thermoelectric module, in which the metal base composed of good conductive materials such as copper, aluminum, and silver does not bend when joining to the metal frame. 
     The present invention is directed to a package adapted to a thermoelectric module including a plurality of thermoelectric elements sandwiched between an upper electrode and a lower electrode. The package includes a metal base constituted of a metal plate composed of copper, aluminum, silver, or alloy, a metal frame attached to the periphery of the metal base, and an insulating resin layer having good thermal conductivity, via which the thermoelectric module is attached onto the metal base and circumscribed by the metal frame. The metal frame is attached to the metal base via a solder having a melting point lower than that of a solder used for bonding the thermoelectric elements with the upper electrode and the lower electrode in the thermoelectric module. 
     In the above, since the package has a small thermal resistance, the metal base easily dissipates (or exhausts) heat generated by the thermoelectric elements. Since the low melting point solder is used to bond the metal base and the metal frame together, the other solder used for forming the thermoelectric elements does not melt when soldering the metal frame to the metal base. 
     It is possible to further incorporate a secondary metal plate composed of copper, aluminum, silver, or alloy, which is attached onto the upper electrode of the thermoelectric module via a secondary insulating resin layer having good thermal conductivity. This makes it easy to connect other components disposed on the thermoelectric module. 
     It is possible to form a trench or a recess in the metal plate to engage with the lower portion of the metal frame. This makes it easy to establish the positioning between the metal base and the metal frame, and this improves the joining strength between the metal base and the metal frame. 
     It is possible to coat the surface of the metal base is coated with metal coating layer having good corrosion resistance and good soldering wettability, preferably, a nickel plating layer or a gold plating layer deposited on the nickel plating layer. This improves the corrosion resistance of the metal base, and this makes it easy to additionally attach heat-dissipation fins onto the metal base. 
     Preferably, the metal frame is composed of an iron-nickel-cobalt alloy or a stainless steel alloy. Herein, it is preferable to perform the surface processing of nickel on the metal frame. 
     When the insulating resin layer is formed using an insulating resin sheet including fillers having good thermal conductivity, it is possible to improve the thermal conductivity of the insulating resin layer, thus making it further easy to dissipate heat from the thermoelectric elements via the metal plate. Examples of fillers include, but not limited to, alumina powder, aluminum nitride powder, magnesium oxide powder, and silicon carbide powder. Examples of insulating resin sheets include, but not limited to, polyimide resin and epoxy resin. 
     The present invention is also directed to a manufacturing method of the aforementioned package. Specifically, the lower electrode of the thermoelectric module is bonded onto the metal base, which is a metal plate composed of copper, aluminum, silver, or alloy, via the insulating resin layer having a good thermal conductivity; a plurality of thermoelectric elements is aligned on the lower electrode and below the upper electrode joining to a heat-resistant resin film so that the thermoelectric elements are bonded with the lower electrode and the upper electrode via a first solder; the heat-resistant resin film is extracted from the upper electrode; then, the metal frame is positioned above and bonded onto the periphery of the metal base via a second solder whose melting point is lower than a melting point of the first solder. 
     In another aspect of the manufacturing method, the lower electrode of the thermoelectric module is bonded onto the metal base, which is a metal plate composed of copper, aluminum, silver, or alloy, via a first insulating resin layer having good thermal conductivity; a secondary metal plate composed of copper, aluminum, silver, or alloy is bonded onto the upper electrode of the thermoelectric module via a second insulating resin layer having good thermal conductivity; a plurality of thermoelectric elements is aligned on the lower electrode and below the upper electrode joining to the second insulating resin layer so that the thermoelectric elements are bonded with the lower electrode and the upper electrode via a first solder; then, the metal frame is bonded onto the periphery of the metal base via a second solder whose melting point is lower than a melting point of the first solder. 
     In a further aspect of the manufacturing method, the lower electrode of the thermoelectric module joins to a lower heat-resistant resin film while the upper electrode of the thermoelectric module joins to an upper heat-resistant resin film; a plurality of thermoelectric elements is aligned on the lower electrode and below the upper electrode so that the thermoelectric elements are bonded with the lower electrode and the upper electrode via a first solder; the upper heat-resistant resin and the lower heat-resistant resin film are respectively extracted from the upper electrode and the lower electrode so as to complete the production of the thermoelectric module; the thermoelectric module is bonded onto the metal base, which is a metal plate composed of copper, aluminum, silver, or alloy, via the insulating resin layer; then, the metal frame is positioned above and bonded onto the periphery of the metal base via a second solder whose melting point is lower than a melting point of the first solder. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects, aspects, and embodiments of the present invention will be described in more detail with reference to the following drawings. 
         FIG. 1A  is a plan view of a thermoelectric module package including a metal base and a metal frame according to a preferred embodiment of the present invention. 
         FIG. 1B  is a cross-sectional view taken along line A-A in  FIG. 1A . 
         FIG. 2A  is a plan view showing a first example of the metal base. 
         FIG. 2B  is a cross-sectional view taken along line B-B in  FIG. 2A . 
         FIG. 3A  is a plan view showing a second example of the metal base. 
         FIG. 3B  is a cross-sectional view taken along line C-C in  FIG. 3A . 
         FIG. 4  is a graph showing heat dissipation characteristics of thermoelectric module packages according to the preferred embodiment and the first comparative example. 
         FIGS. 5A to 5G  are cross-sectional views showing a first manufacturing method of the thermoelectric module package. 
         FIGS. 6A to 6G  are cross-sectional views showing a second manufacturing method of the thermoelectric module package. 
         FIGS. 7A to 7G  are cross-sectional views showing a third manufacturing method of the thermoelectric module package. 
         FIG. 8A  is a plan view showing a first comparative example of a thermoelectric module package including a metal frame and a metal base. 
         FIG. 8B  is a cross-sectional view taken along line D-D in  FIG. 8A . 
         FIG. 9A  is a plan view showing a second comparative example of a thermoelectric module package including a metal frame and a copper base. 
         FIG. 9B  is a cross-sectional view taken along line E-E in  FIG. 9A . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will be described in further detail by way of examples with reference to the accompanying drawings. 
     A thermoelectric module package according to a preferred embodiment of the present invention will be described with reference to  FIGS. 1A and 1B ,  FIGS. 2A and 2B , and  FIGS. 3A and 3B . 
       FIG. 1A  is a plan view of the thermoelectric module package including a metal base and a metal frame, and  FIG. 1B  is a cross-sectional view taken along line A-A in  FIG. 1A .  FIG. 2A  is a plan view showing a first example of the metal base, and  FIG. 2B  is a cross-sectional view taken along line B-B in  FIG. 2A .  FIG. 3A  is a plan view showing a second example of the metal base, and  FIG. 3B  is a cross-sectional view taken along line C-C in  FIG. 3A .  FIG. 4  is a graph showing heat dissipation characteristics (i.e. the amount of heat absorption relative to the power consumption) of thermoelectric module packages according to the present embodiment and the first comparative example.  FIGS. 5A to 5G  are cross-sectional views showing a first manufacturing method of the thermoelectric module package;  FIGS. 6A to 6G  are cross-sectional views showing a second manufacturing method of the thermoelectric module package; and  FIGS. 7A to 7G  are cross-sectional views showing a third manufacturing method of the thermoelectric module package. 
     1. Preferred Embodiment 
     As shown in  FIGS. 1A and 1B , a package  10  is constituted of a metal base  11  and a metal frame  12  which is bonded to the periphery of the metal base  11  via a solder  18 . A thermoelectric module  10   a  joins to the prescribed position of the metal base  11  via an insulating resin layer  13 . The thermoelectric module  10   a  includes a plurality of thermoelectric elements  17  which join together with pairs of lower electrodes (serving as heat-dissipation electrodes)  14  and upper electrodes (serving as heat-absorption electrodes)  15  via solders  16   a  and  16   b.    
     The “adhesive” insulating resin layer  13  bonds the lower electrodes  14  to the prescribed position of the metal base  11 , thus unifying the thermoelectric module  10   a  with the package  10 . A plurality of leads joins with the upper portion of the metal frame  12  (while partially penetrating through the metal frame  12 ) and is connected to terminals of the thermoelectric module  10   a  and other terminals (not shown). 
     The metal base  11  is composed of a copper plate of a 400 W/mK thermal conductivity and is 1-3 mm in thickness so that the overall area thereof is 30 mm×30 mm, for example. Instead of the copper plate, it is possible to use an inexpensive copper alloy of good thermal conductivity such as bronze and brass, aluminum, and silver as well as their alloys. It is preferable that the surface of the metal base  11  be coated or plated with a metal layer having good corrosion resistance and good soldering wettability, such as a nickel plating layer and a gold plating layer (formed on the nickel plating layer). 
       FIGS. 2A and 2B  show the first example of the metal base  11  in which a peripheral trench  11   a  is formed in the periphery with a depth of 0.2 mm, for example. The width of the peripheral trench  11   a  is approximately equal to the width of the metal frame  12  and is thus engaged with the lower portion of the metal frame  12 . This improves the joining strength between the metal base  11  and the metal frame  12  and makes it easy to establish the precise positioning therebetween. Alternatively,  FIGS. 3A and 3B  show the second example of the metal base  11  in which a hollow portion  11   b  is formed with a depth of 0.2 mm except for the periphery. This also improves the joining strength between the metal base  11  and the metal frame  12  and makes it easy to establish the precise positioning therebetween. 
     The metal frame  12  is formed by molding an iron-nickel-cobalt alloy (preferably, the Kovar with a thermal expansion coefficient or linear expansion coefficient α ranging from 5.7×10 −6 /K to 6.5×10 −6 /K) into a rectangular frame shape. 
     The lower portion of the metal frame  12  is bonded to the periphery of the metal base  11  via the solder  18  such as the In solder (melting point: 156° C.), BiSn solder (melting point: is 138° C.), and SnInAg solder (melting point: 187° C.). 
     The solder  18  used for bonding the metal base  11  and the metal frame  12  together is low in melting point, which is lower than the melting point of the solders  16   a  and  16   b  used for forming the thermoelectric module  10   a , such as the SnSb solder (melting point: 235° C.), the SnAu solder (melting point: 280° C.), and the SnAgCu solder (melting point: 220° C.). This prevents the solders  16   a  and  16   b  (used for forming the thermoelectric module  10   a ) from unexpectedly melting when the metal frame  12  joins to the metal base  11  via the solder  18  after the thermoelectric module  10   a  joins to the prescribed position of the metal base  11 . 
     The adhesive insulating resin layer  13  is composed of an electrically insulating synthetic resin such as the polyimide resin and epoxy resin and is formed as a resin sheet with a thickness of 100 μm, for example. It is preferable to add fillers composed of alumina powder, aluminum nitride powder, magnesium oxide power, and silicon carbide power to the polyimide resin and epoxy resin, thus improving their thermal conductivity. The insulating resin layer  13  is not necessarily limited to the resin sheet but is applied to the adhesive composed of the electrically insulating synthetic resin such as the polyimide resin and epoxy resin. In this case, it is preferable to add fillers of alumina powder, aluminum nitride powder, magnesium oxide powder, and silicon carbon powder to the polyimide resin and epoxy resin, thus improving their thermal conductivity. 
     The lower electrode  14  and the upper electrode  15  are each composed of a copper plate with a 0.1-0.2 mm thickness and formed in prescribed electrode patterns. Herein, copper plates serving as the lower electrode  14  and the upper electrode  15  are adhered to resin sheets or heat-resistant resin films, which are then subjected to pattern etching with prescribed electrode patterns. It is possible to additionally form nickel plating layers on the lower electrodes  14  and/or the upper electrodes  15 . 
     The thermoelectric elements  17  are composed of P-type semiconductor compounds and N-type semiconductor compounds and are each formed in prescribed dimensions (i.e. length×width×height) of 2 mm×2 mm×2 mm. Preferably, the thermoelectric elements  17  adopt thermoelectric sintered materials such as bismuth-tellurium (Bi—Te) demonstrating high performance at room temperature; P-type semiconductor compounds adopt ternary compounds of Bi—Sb—Te; and N-type semiconductor compounds adopt quartary compounds of Bi—Sb—Te—Se. Specifically, P-type semiconductor compounds have the composition of Bi 0.5 Sb 1.5 Te 3 , and N-type semiconductor compounds have the composition of Bi 1.9 Sb 0.1 Te 2.6 Se 0.4 , wherein both compounds are formed by way of a hot-press sintering method. 
     It is preferable to form nickel plating layers (used for soldering) on the lower ends of the thermoelectric elements  17  (joining to the lower electrodes  14 ) and the upper ends of the thermoelectric elements  17  (joining to the upper electrodes  15 ). The thermoelectric elements  17  are electrically connected in series in the alternating order of P, N, P, N, . . . so that the lower ends and upper ends thereof are bonded to the lower electrodes  14  and the upper electrodes  15  via the solders  16   a  and  16   b  composed of the SnSb solder (melting point: 235° C.), SnAu solder (melting point: 280° C.), and SnAgCu solder (melting point: 220° C.). 
     As shown in  FIG. 6G , it is possible to additionally arrange a metal plate  15   a  with a 0.1-0.2 mm thickness on the upper electrodes  15  via an insulating resin layer  13   a . The metal plate  15   a  makes it easy to dispose various components bonded onto the thermoelectric module  10   a.    
     2. First Comparative Example 
       FIGS. 8A and 8B  show the package  20  of the first comparative example, which is constituted of the metal base  21  composed of the CuW material, the metal frame  22  composed of the iron-nickel-cobalt alloy (Kovar) which joins to the periphery of the metal base  21  via the silver brazing alloy  29  (melting point: 770° C.), and the thermoelectric module  20   a  which joins to the prescribed position of the metal base  21 . The thermoelectric module  20   a  includes a plurality of thermoelectric elements  28  that join together between the lower electrodes  24  (i.e. the heat-dissipation electrodes formed on the ceramic lower substrate  23 ) and the upper electrodes  26  (i.e. the heat-absorption electrodes formed on the ceramic upper substrate  25 ) via the solders  27   a  and  27   b  such as the SnSb solder. The first comparative example is characterized in that the thermoelectric module  20   a  joins to the prescribed position of the metal base  21  after the metal frame  22  joins to the metal frame  21 . 
     Then, the solder  23   a  bonds the lower substrate  23  having the lower electrodes  24  to the prescribed position of the metal base  21 , thus unifying the metal base  21  and the thermoelectric module  20   a . The solder  23   a  is a low melting point solder, such as the InAg solder, SnInAg solder, and InSn solder, which is lower than the solders  27   a  and  27   b  (e.g. the SnSb solder used for bonding the thermoelectric elements  28  together) in melting point. A plurality of leads  22   a  running through the upper portion of the metal frame  22  are connected to terminals of the thermoelectric module  20   a  and other terminals (not shown). 
     3. Second Comparative Example 
       FIGS. 9A and 9B  show the package  30  of the second comparative example, which is constituted of the metal base  31  (composed of a copper plate of a 400 W/mK thermal conductivity with a 1-3 mm thickness), the metal frame  32  composed of the iron-nickel-cobalt alloy (Kovar) which joins to the periphery of the metal base  31  via the silver brazing alloy (melting point: 770° C.)  39 , and the thermoelectric module  30   a  which joins to the prescribed position of the metal base  31 . The thermoelectric module  30   a  includes a plurality of thermoelectric elements  38  which join together between the lower electrodes  34  (i.e. the heat-dissipation electrodes formed on the ceramic lower substrate  33 ) and the upper electrodes  36  (i.e. the heat-absorption electrodes formed on the ceramic upper substrate  35 ) via the solders  37   a  and  37   b  (e.g. the SnSb solder). The second comparative example is characterized in that the thermoelectric module  30   a  joins to the prescribed position of the metal base  31  after the metal frame  32  joins to the metal base  31 . 
     Then, the solder  33   a  bonds the lower substrate  33  having the lower electrodes  34  to the prescribed position of the metal base  31 , thus unifying the thermoelectric module  30   a  to the metal base  31 . The solder  33   a  is a low melting point solder, such as the InAg solder, SnInAg solder, and InSn solder, which is lower than the solders  37   a  and  37   b  (e.g. the SnSb solder used for bonding the thermoelectric elements  38  together) in melting point. A plurality of leads  32   a  running through the upper portion of the metal frame  32  are connected to terminals of the thermoelectric module  30   a  and other terminals (not shown). 
     4. Evaluation Testing 
     The present inventors conducted evaluation testing on the packages  10 ,  20 , and  30  so as to measure bends (or deflections) of the metal bases  11 ,  21 , and  31 , the result of which is shown in Table 1. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Metal 
                 Metal 
                 Ceramic 
                   
                 Bends 
               
               
                 Package 
                 Base 
                 Frame 
                 Substrate 
                 Joining Material 
                 (μm) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 10 
                 Copper 
                 Kovar 
                 None 
                 Solder 
                 25 
               
               
                 20 
                 CuW 
                 Kovar 
                 Equipped 
                 Silver brazing alloy 
                 20 
               
               
                 30 
                 Copper 
                 Kovar 
                 Equipped 
                 Silver brazing alloy 
                 100 
               
               
                   
               
            
           
         
       
     
     Table 1 clearly shows that the package  30  (in which the silver brazing alloy  39  bonds the metal frame  32  composed of copper to the metal base  31  composed of Kovar) causes a 100 μm bend of the metal base  31 , which exceeds the practical upper limit of bending of a metal base (which is empirically deduced), i.e. 50 μm; hence, the package  30  does not conform with the practical use. This is due to a large difference of thermal expansion coefficients between the copper (where α=16.8×10 −6 ) of the metal base  31  and the Kovar (where α=5.7×10 −6  through α=6.5×10 −6  at 30-5000° C.) of the metal frame  32  at a certain soldering temperature. 
     In contrast, the package  10  (in which the solder  18  bonds the metal frame  12  composed of Kovar to the metal base  11  composed of copper) causes a 25 μm bend of the metal base  11 , which is larger than a 20 μm bend occurring in the package  20  (in which the silver brazing alloy  29  bonds the metal frame  22  composed of Kovar to the metal base  21  composed of CuW (where α=6.5×10 −6 ) by 5 μm; however, the package  10  is still suitable for the practical use. According to this result, it is preferable to solder the metal frame composed of Kovar to the metal base composed of copper. 
     Next, electric resistances are measured on the packages  10  and  30  in which the metal bases  11  and  31  are both composed of copper. That is, the packages  10  and  30  are repeatedly subjected to heat/cool testing by 100 cycles, wherein they are alternately subjected to a low-temperature atmosphere of −40° C. for thirty minutes and a high-temperature atmosphere of 85° C. for thirty minutes in each cycle. After heat/cool testing, electrical resistances are measured on the packages  10  and  30 , and the result is shown in Table 2. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Pack- 
                 Metal 
                 Metal 
                 Ceramic 
                 Joining 
                 Electric Resistance (Ω) 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 age 
                 Base 
                 Frame 
                 Substrate 
                 Material 
                 Before Test 
                 After Test 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 10 
                 Copper 
                 Kovar 
                 None 
                 Solder 
                 2 
                 2.008 
               
               
                 30 
                 Copper 
                 Kovar 
                 Equipped 
                 Silver 
                 2 
                 10.125 
               
               
                   
                   
                   
                   
                 brazing 
               
               
                   
                   
                   
                   
                 alloy 
               
               
                   
               
            
           
         
       
     
     Table 2 clearly shows that the package  30  (in which the thermoelectric module  30   a  having the lower substrate  33  joins to the metal base  31  composed of copper) suffers a very high resistance of 10.125Ω which markedly soars from the original resistance of 2Ω before testing. Visual observing the thermoelectric module  30   a  fixed to the package  30  indicates the occurrence of internal cracks in the thermoelectric elements  38 ; hence, the thermoelectric module  30   a  does not conform to the practical use. 
     In contrast, the package  10  (in which the thermoelectric module  10   a  having no lower substrate joins to the metal base  11  via the insulating resin layer  13  having good thermal conductivity) causes an electric resistance of 2.008Ω showing only 0.4% increase from the original resistance of 2Ω. Visually observing the thermoelectric module  10   a  does not indicate the occurrence of internal cracks in the thermoelectric elements  17 . According to this result, it is preferable to solder the thermoelectric module having no lower substrate (or ceramic substrate) to the metal base composed of copper via the insulating resin layer having a high thermal conductivity, thus producing the package at a high reliability. 
     Next, the present inventors examine heat-dissipation characteristics of packages including thermoelectric modules suited to the above testing results, wherein an electric voltage is applied to the thermoelectric modules  10   a  and  20   a  held in the packages  10  and  20  so as to measure the amount of heat absorption (W) relative to the power consumption (W), thus producing a graph of  FIG. 4  in which the horizontal axis represents the power consumption (W), and the vertical axis represents the heat absorption (W). Herein, each thermoelectric module is equipped with a heater (not shown) generating a prescribed amount of heat (or a prescribed amount of heat absorption) at the cooling terminal thereof, then, the thermoelectric module is electrified with an increasing current and is thus measured in the power consumption requiring the cooling terminal thereof to reach a prescribed temperature. 
       FIG. 4  clearly shows that the package  10  (in which the thermoelectric module  10   a  having no ceramic substrate joins to the metal base  11  composed of copper) requires a smaller power consumption in achieving the prescribed heat absorption in comparison with the package  20  (in which the thermoelectric module  20   a  having the ceramic substrate joins to the metal base  21  composed of CuW). In other words, it is preferable to bond the thermoelectric module having no ceramic substrate to the metal base composed of copper via the insulating resin layer having good thermal conductivity, thus efficiently dissipate heat from the thermoelectric elements via the metal base. 
     5. Manufacturing Methods 
     Next, various manufacturing methods will be described with respect to the package  10  holding the thermoelectric modules  10   a  by way of Examples 1 to 3. 
     (1) Example 1 
     First, there are provided the metal base  11 , the insulating resin layer  13 , and the lower electrode  14  serving as the heat-dissipation electrode. The metal base  11  is constituted of a copper plate having good thermal conductivity of 400 W/mK, which is 1-3 mm in thickness, and is formed in a rectangular shape with a size of 30 mm×30 mm. The insulating resin layer  13  is constituted of a synthetic resin sheet (composed of an electrically insulating and adhesive material such as a polyimide resin and an epoxy resin) which is 100 μm in thickness, for example. The lower electrode  14  is constituted of a copper plate with a thickness of 0.1-0.2 mm. 
     It is preferable that the surface of the metal base  11  be covered with a metal coating layer having good corrosion resistance and good soldering wettability such as a nickel plating layer. Preferably, the insulating resin layer  13  additionally include fillers such as alumina powder, aluminum nitride powder, magnesium oxide powder, or silicon carbide powder so as to improve in thermal conductivity. It is preferable that the thermal conductivity of the insulating resin layer  13  be set to 20 W/mK or more. 
     As shown in  FIG. 5A , the insulating resin layer  13  is laminated on the metal base  11 , which is then subjected to pressurization of 0.98 MPa at a temperature of 120-160° C. for ten minutes, thus temporarily crimping the insulating resin layer  13  with the metal base  11 . Next, the lower electrode  14  is laminated on the insulating resin layer  13  and is then subjected to pressurization of 2.94 MPa at a temperature of 170° C. for sixty minutes, thus bonding the metal base  11 , the insulating resin layer  13 , and the lower electrode  14  together to form a laminated structure. The laminated structure is subjected to masking, and the lower electrode  14  is pattern-etched to form a prescribed lower electrode pattern. This makes the lower electrode  14  have the prescribed lower electrode pattern as shown in  FIG. 5B . 
     In the meantime, there is provided an adhesive heat-resistant resin film  19  (e.g. a product No. 360UL manufactured by Nitto Denko Corporation, and a product No. 6462 manufactured by Teraoka Seisakusho Co., Ltd.) and the upper electrode  15  serving as the heat-absorption electrode. Similar to the lower electrode  14 , the upper electrode  15  is constituted of a copper plate with a thickness of 0.1-0.2 mm. As shown in  FIG. 5C , the upper electrode  15  is adhered onto the surface of the heat-resistant resin film  19 . The combination of the upper electrode  15  and the heat-resistant resin film  19  is subjected to masking so that the upper electrode  15  is subjected to pattern etching in a prescribed upper electrode pattern. This makes the upper electrode  15  have the prescribed upper electrode pattern as shown in  FIG. 5D . 
     As shown in  FIG. 5E , the solder  16   a  is applied to the lower electrode  14 , while the solder  16   b  is applied to the upper electrode  15 . Preferably, the solders  16   a  and  16   b  are composed of the SnSb solder (melting point: 235° C.), SnAu solder (melting point: 280° C.), and SnAgCu solder (melting point: 220° C.). In addition, there are provided multiple pairs of thermoelectric elements  17  composed of P-type semiconductor compounds and N-type semiconductor compounds. The thermoelectric elements  17  are each formed in a prescribed shape with prescribed dimensions (i.e. the length, width, and height) of 2 mm×2 mm×2 mm. It is preferable that nickel plating layers be formed on the lower electrode  14  (joining to the lower ends of the thermoelectric elements  17 ) and on the upper electrode  15  (joining to the upper ends of the thermoelectric elements  17 ) in order to facilitate soldering therebetween. 
     As shown in  FIG. 5F , the thermoelectric elements  17  are aligned on the lower electrode  14  in the alternating order of P, N, P, N, . . . electrically connected in series. Then, the upper electrode  15  is positioned above the thermoelectric elements  17  to join to the upper ends of the thermoelectric elements  17 . Then, the assembly is heated at a high temperature so as to melt the solders  16   a  and  16   b , so that the thermoelectric elements  17  are soldered together with and between the lower electrode  14  and the upper electrode  15 . Thereafter, the heat-resistant resin film  19  once adhered to the upper electrode  15  is peeled or extracted from the upper electrode  15  as shown in  FIG. 5G , thus completely forming the thermoelectric module  10   a  mounted on the metal base  11  via the insulating resin layer  13 . 
     Next, the solder  18  composed of the In solder (melting point: 156° C.), BiSn solder (melting point: 157° C.), and SnInAg solder (melting point: 180-190° C.) is applied to the periphery of the metal base  11 . Subsequently, the rectangular metal frame  12  composed of an iron-nickel-cobalt alloy (preferably, the Kovar (registered trademark) having the thermal expansion coefficient (or linear expansion coefficient α) of 5.7×10 −6 /K through 6.5×10 −6 /K) is disposed on the solder  18 . Then, the solder  18  is heated to melt and thereby bond the metal frame  12  onto the periphery of the metal base  11 , thus completing the production of the package  10  holding the thermoelectric module  10   a.    
     It is essential that the solder  18  used for bonding the metal base  11  and the metal frame  12  together has a low melting point solder such as the In solder (melting point: 156° C.), BiSn solder (melting point: 157° C.), and SnInAg solder (melting point: 180-190° C.), which is lower in melting point than the solders  16   a  and  16   b  used for forming the thermoelectric module  10   a  such as the SnSb solder (melting point: 235° C.), SnAu solder (melting point: 280° C.), and SnAgCu solder (melting point: 220° C.). 
     (2) Example 2 
     First, there are provided the metal base  11 , the “first” insulating resin layer  13 , and the lower electrode  14  serving as the heat-dissipation electrode. The metal base  11  is constituted of a copper plate having a good thermal conductivity of 400 W/mK with a thickness of 1-3 mm and is formed in a prescribed size of 30 mm×30 mm. The first insulating resin  13  is constituted of a synthetic resin sheet composed of an electrically insulating and adhesive material such as a polyimide resin and epoxy resin with a thickness of 100 μm, for example. The lower electrode  14  is constituted of a copper plate with a thickness of 0.1-0.2 mm. 
     It is preferable that the surface of the metal base  11  be covered with a metal coating layer having good corrosion resistance and good soldering wettability such as a nickel plating layer. Preferably, the first insulating resin layer  13  additionally includes fillers such as alumina powder, aluminum nitride powder, magnesium oxide powder, and silicon carbide powder so as to improve in thermal conductivity. Preferably, the thermal conductivity of the first insulating resin layer  13  is set to 20 W/mK or more. 
     As shown in  FIG. 6A , the first insulating resin layer  13  is laminated on the metal base  11 , which is then subjected to pressurization of 0.98 MPa at a high temperature of 120-160° C. for ten minutes, thus temporarily crimping the first insulating resin layer  13  with the metal base  11 . Next, the lower electrode  14  is laminated on the first insulating resin layer  13  and is then subjected to pressurization of 2.94 MPa at a high temperature of 170° C. for sixty minutes, thus forming the laminated structure including the metal base  11 , the first insulating resin layer  13 , and the lower electrode  14 . As shown in  FIG. 6B , the laminated structure is subjected to masking, and the lower electrode  14  is subjected to pattern etching and is formed in a prescribed lower electrode pattern. 
     In the meantime, there are provided an adhesive “second” insulating resin layer  13   a  and the upper electrode  15  serving as the heat-absorption electrode. Similar to the lower electrode  14 , the upper electrode  15  is constituted of a copper plate with a thickness of 0.1-0.2 mm. As shown in  FIG. 6C , a metal plate  15   a  (which is a copper plate with a thickness of 0.1-0.2 mm) is adhered onto the backside of the second insulating resin layer  13   a . The second insulating resin layer  13   a  and the metal plate  15   a  are temporarily crimped together by way of the pressurization of 0.98 MPa at a high temperature of 120-160° C. for ten minutes. The upper electrode  15  is adhered onto the surface of the second insulating resin layer  13   a . Then, second insulating resin layer  13   a , the metal plate  15   a , and the upper electrode  15  are crimped together by way of the pressurization of 2.94 MPa at a high temperature of 170° C. for sixty minutes. Thereafter, the crimped structure is subjected to masking so that the upper electrode  15  is pattern-etched to form a prescribed upper electrode pattern.  FIG. 6D  shows the prescribed upper electrode pattern formed in the upper electrode  15 . 
     As shown in  FIG. 6E , the solder  16   a  is applied to the lower electrode  14 , while the solder  16   b  is applied to the upper electrode  15 . The solders  16   a  and  16   b  are selected from the SnSb solder (melting point: 235° C.), SnAu solder (melting point: 280° C.), and SnAgCu solder (melting point: 220° C.), for example. In addition, there are provided multiple pairs of thermoelectric elements  17  serving as P-type semiconductor compounds and N-type semiconductor compounds. The thermoelectric elements  17  are each formed in a prescribed shape with prescribed dimensions (i.e. the length, width, and height) of 2 mm×2 mm×2 mm. Preferably, nickel plating layers are applied on the lower electrode  14  (joining to the lower ends of the thermoelectric elements  17 ) and on the upper electrode  15  (joining to the upper ends of the thermoelectric elements  17 ) so as to facilitate soldering therebetween. 
     As shown in  FIG. 6F , the thermoelectric elements  17  are aligned on the lower electrode  14  in the alternating order of P, N, P, N, . . . electrically connected in series. Subsequently, the upper electrode  15  is positioned above the thermoelectric elements  17 . Then, the solders  16   a  and  16   b  are heated to melt at a high temperature, so that the thermoelectric elements  17  join together between the lower electrode  14  and the upper electrode  15 , and the thermoelectric module  10   a  is mounted on the metal base  11  via the first insulating resin layer  13 . Example 2 is characterized in that the metal plate  15   a  (which is a copper plate with a thickness of 0.1-0.2 mm) is disposed on the upper electrode  15  via the second insulating resin layer  13   a . This makes other components join onto the thermoelectric module  10   a  with ease. 
     Next, the solder  18  composed of the In solder (melting point: 156° C.), BiSn solder (melting point: 157° C.), or SiInAg solder (melting point: 180-190° C.) is applied to the periphery of the metal base  11 . Subsequently, the metal frame  12  composed of an iron-nickel-cobalt alloy (preferably, the Kovar (registered trademark) having a thermal expansion coefficient (or linear expansion coefficient α) of 5.7×10 −6 /K through 6.5×10 −6 /K) is disposed on the solder  18 . Then, the solder  18  is heated to melt and thereby connect the metal base  11  and the metal frame  12  together, thus completing the production of the package  10  holding the thermoelectric module  10   a  in which the metal plate  15   a  is disposed on the upper electrode  15  via the second insulating resin layer  13   a.    
     It is preferable that the solder used for bonding the metal base  11  and the metal frame  12  together have a low melting point solder such as the In solder (melting point: 156° C.), BiSn solder (melting point: 157° C.), and SnInAg solder (melting point: 180-190° C.), which is lower in melting point than the solders  16   a  and  16   b  used for forming the thermoelectric module  10   a  such as the SnSb solder (melting point: 235° C.), SnAu solder (melting point: 280° C.), and SnAgCu solder (melting point: 220° C.). 
     (3) Example 3 
     First, there are provided an adhesive heat-resistant resin film  19   a  (e.g. the product No. 360UL manufactured by Nitto Denko Corporation, and the product No. 6462 manufactured by Teraoka Seisakusho Co., Ltd.) and the lower electrode  14  serving as the heat-dissipation electrode. The lower electrode  14  is constituted of a copper plate with a thickness of 0.1-0.2 mm. As shown in  FIG. 7A , the lower electrode  14  is adhered onto the surface of the heat-resistant resin film  19   a  and is then subjected to masking so that the lower electrode  14  is pattern-etched to form a prescribed lower electrode pattern.  FIG. 7B  shows the lower electrode  14  having the prescribed lower electrode pattern. Subsequently, the solder  16   a  is applied to the lower electrode  14  as shown in  FIG. 7C . The solder  16   a  is selected from among the SnSb solder (melting point: 235° C.), SnAu solder (melting point: 280° C.), and SnAgCu solder (melting point: 220° C.), for example. 
     In addition, there are provided an adhesive heat-resistant resin film  19   b  (e.g. the product No. 360UL manufactured by Nitto Denko Corporation, and the product No. 6462 manufactured by Teraoka Seisakusho Co., Ltd.) and the upper electrode  15  serving as the heat-absorption electrode. Similar to the lower electrode  14 , the upper electrode  15  is constituted of a copper plate with a thickness of 0.1-0.2 mm. As shown in  FIG. 7D , the upper electrode  15  is adhered onto the surface of the heat-resistant resin film  19   b  and is then subjected to masking so that the upper electrode  15  is pattern-etched to form a prescribed upper electrode pattern.  FIG. 7E  shows the upper electrode  15  having the prescribed upper electrode pattern. Subsequently, the solder  16   b  is applied to the upper electrode  15  as shown in  FIG. 7F . The solder  16   b  is selected from among the SnSb solder (melting point: 235° C.), SnAu solder (melting point: 280° C.), and SnAgCu solder (melting point: 220° C.), for example. 
     Next, there are provided multiple pairs of thermoelectric elements  17  composed of P-type semiconductor compounds and N-type semiconductor compounds. The thermoelectric elements  17  are each formed in a prescribed shape with prescribed dimensions (i.e. the length, width, and height) of 2 mm×2 mm×2 mm. Preferably, nickel plating layers are applied on the lower electrode  14  (joining to the lower ends of the thermoelectric elements  17 ) and on the upper electrode  15  (joining to the upper ends of the thermoelectric elements  17 ) so as to facilitate soldering therebetween. As shown in  FIG. 7G , the thermoelectric elements  17  are aligned on the lower electrode  14  in the alternating order of P, N, P, N, . . . electrically connected in series. Then, the upper electrode  15  is positioned above the thermoelectric elements  17 . Then, as shown in  FIG. 7H , the solders  16   a  and  16   b  are heated to melt at a high temperature so as to bond the thermoelectric elements  17  together between the lower electrode  14  and the upper electrode  15 . Thereafter, the heat-resistant resin film  19   a  once adhered to the lower electrode  14  is peeled and extracted from the lower electrode  14 , and the heat-resistant resin film  19   b  once adhered to the upper electrode  15  is peeled and extracted from upper electrode  15 , thus completing the production of the thermoelectric module  10   a.    
     As shown in  FIG. 7I , there are provided the metal base  11  and the insulating resin layer  13 . The metal base  11  is constituted of a copper plate of a good thermal conductivity of 400 W/mK with a thickness of 1-3 mm and is formed in a prescribed size of 30 mm×30 mm. The insulating resin layer  13  is constituted of a synthetic resin sheet composed of an electrically insulating and adhesive material such as a polyimide resin and epoxy resin with a thickness of 100 μm, for example. 
     It is preferable that the surface of the metal base  11  be coated with a metal coating layer having good corrosion resistance and good soldering wettability such as a nickel plating layer. Preferably, the insulating resin layer  13  additionally includes fillers composed of alumina powder, aluminum nitride powder, magnesium oxide powder, and silicon carbide powder so as to improve in thermal conductivity. It is preferable that the thermal conductivity of the insulating resin layer  13  be set to 20 W/mK or more. 
     As shown in  FIG. 7J , the metal base  11  is laminated with the insulating resin layer  13  and is then subjected to a pressurization of 0.98 MPa at a high temperature of 120-160° C. for ten minutes, thus temporarily crimping the metal base  11  and the insulating resin layer  13 . Subsequently, the thermoelectric module  10   a  is laminated on the insulating resin layer  13  and is then subjected to a pressurization of 2.94 MPa at a high temperature of 170° C. for sixty minutes, thus bonding the thermoelectric module  10   a , the metal base  11 , and the insulating resin layer  13  together. As the insulating resin layer  13 , it is possible to use an adhesive synthetic resin having an electrically insulating property, such as a polyimide resin and epoxy resin, instead of the aforementioned synthetic resin sheet. Preferably, the polyimide resin or epoxy resin additionally includes fillers composed of alumina powder, aluminum nitride powder, magnesium oxide powder, and silicon carbide powder so as to improve in thermal conductivity. 
     Next, the solder  18  composed of the In solder (melting point: 156° C.), BiSn solder (melting point: 157° C.), or SnInAg solder (melting point: 180-190° C.) is applied to the periphery of the metal base  11 ; then, the rectangular metal frame  12  composed of an iron-nickel-cobalt alloy (e.g. the Kovar (registered trademark) with a thermal expansion coefficient (or a linear expansion coefficient α) of 5.7×10 −6 /K through 6.5×10 −6 /K) is disposed on the solder  18 . Subsequently, the solder  18  is heated to melt so as to bond the metal frame  12  to the metal base  11  via the solder  18 , thus completing the production of the package  10  including the thermoelectric module  10   a.    
     It is essential that the solder  18  used for bonding the metal base  11  and the metal frame  12  have a low melting point solder such as the In solder (melting point: 156° C.), BiSn solder (melting point: 157° C.), and SnInAg solder (melting point: 180-190° C.), which is lower than the solders  16   a  and  16   b  used for forming the thermoelectric module  10   a  such as the SnSb solder (melting point: 235° C.), SnAu solder (melting point: 280° C.), and SnAgCu solder (melting point: 220° C.). 
     The above description refers to the polyimide resin and epoxy resin as the synthetic resin material; but this is not a restriction. It is possible to use other materials (other than the polyimide resin and epoxy resin) such as the aramid resin and bismaleimide-triazine (BT) resin. 
     The above description also refers to the alumina powder, aluminum nitride powder, magnesium oxide powder, and silicon carbide powder as the filler material; but this is not a restriction. It is possible to use other high thermal conductivity materials such as the carbon powder and silicon nitride powder. The filler material is not necessarily limited to a single type of material; hence, it is possible to blend two or more types of filler materials. Furthermore, it is possible to adopt any shaping of fillers such as spherical shapes and acicular shapes or to blend different shapes of fillers. 
     Lastly, the present invention is not necessarily limited to the present embodiment and examples, which can be modified in various ways within the scope of the invention as defined by the appended claims.