Patent Publication Number: US-2013235535-A1

Title: Composite substrate, module, and composite-substrate production method

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a composite substrate including a ceramic substrate including a circuit wire on which electronic components are to be mounted, a module including the composite substrate, and a composite-substrate production method. 
     2. Description of the Related Art 
     Japanese Unexamined Patent Application Publication No. 2007-311596 discloses a composite substrate including a ceramic substrate (circuit board) having, on one surface, a circuit wire on which electronic components are to be mounted, and a plurality of external connection terminals (projection electrodes) provided in a peripheral edge portion of the other surface of the ceramic substrate and vertically extending from the other surface. Further, in the composite substrate, a resin layer is provided on the other surface of the ceramic substrate such that at least end surfaces of the plurality of external connection terminals are exposed therefrom. The resin layer is formed by covering the other surface of the ceramic substrate with resin after forming plated layers on the exposed end surfaces of the plurality of external connection terminals. For example, the ceramic substrate is formed of low temperature co-fired ceramic material. 
     In the composite substrate disclosed in Japanese Unexamined Patent Application Publication No. 2007-311596, since the external connection terminals are columnar or prismatic, the cross-sectional area thereof is constant, and there is a limit on an increase in the cross-sectional area of connecting portions between the external connection terminals and the ceramic substrate. If the cross-sectional area of the connecting portions between the external connection terminals and the ceramic substrate cannot be sufficiently large, stress applied to the external connection terminals, for example, due to a fall cannot be distributed, and sufficient connection strength cannot be ensured between the ceramic substrate and the external connection terminals. This may cause trouble, for example, the external connection terminals may come off the ceramic substrate. 
     In a composite-substrate production method disclosed in Japanese Unexamined Patent Application Publication No. 2007-311596, after a plurality of external connection terminals are formed in a peripheral edge portion of the other surface of a ceramic substrate, plated layers are formed on exposed end surfaces of the plurality of external connection terminals. For this reason, when the plated layers are formed on the exposed end surfaces of the plurality of external connection terminals, the connection strength between the ceramic substrate and the external connection terminals may be reduced, for example, by entry of plating solution into boundary portions between the ceramic substrate and the external connection terminals. 
     Further, since the external connection terminals are provided in the peripheral edge portion of the other surface of the ceramic substrate in the composite substrate disclosed in Japanese Unexamined Patent Application Publication No. 2007-311596, the number of external connection terminals that can be formed on the other surface of the ceramic substrate is limited. To ensure a necessary number of external connection terminals, it is necessary to increase the size of the composite substrate itself, and the size of the composite substrate cannot be reduced. Still further, since the external connection terminals are provided in the peripheral edge portion of the other surface of the ceramic substrate, stress applied to the external connection terminals, for example, due to a fall cannot be distributed, and breakage is likely to be caused by concentration of the stress at one or some of the external connection terminals. 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the present invention provide a composite substrate in which stress applied to external connection terminals, for example, due to a fall is distributed and sufficient connection strength is ensured between a ceramic substrate and the external connection terminals, a module including the composite substrate, and a composite-substrate production method. 
     A composite substrate according to a preferred embodiment of the present invention includes a ceramic substrate including, on at least one surface, a circuit wire on which an electronic component is to be mounted, a plurality of external connection terminals provided on one surface of the ceramic substrate, and a resin layer provided on the one surface of the ceramic substrate. The external connection terminals have a shape whose cross-sectional area decreases with increasing distance from the one surface of the ceramic substrate, and end surfaces of the external connection terminals opposite to end surfaces connected to the ceramic substrate are partially or entirely exposed from the resin layer. 
     In the above structure, the external connection terminals preferably have a shape whose cross-sectional area decreases with increasing distance from the one surface of the ceramic substrate, and the end surfaces of the external connection terminals opposite to the end surfaces connected to the ceramic substrate are partially or entirely exposed from the resin layer. Therefore, the cross-sectional area of connecting portions between the external connection terminals and the ceramic substrate can be made larger than in columnar or prismatic external connection terminals having a constant cross-sectional area. Hence, stress applied to the external connection terminals, for example, due to a fall is distributed, and sufficient connection strength is ensured between the ceramic substrate and the external connection terminals. While the ceramic substrate is used as the substrate on which the electronic component is mounted, since the resin layer is provided, even when stress is applied to the composite substrate, for example, due to a fall, deformation of the composite substrate can be prevented. Since sufficient strength is ensured even when the thickness is reduced, the thickness of the composite substrate can be reduced. 
     In the composite substrate according to preferred embodiments of the present invention, a height of the external connection terminals from the one surface of the ceramic substrate is preferably less than a thickness of the resin layer. 
     In the above structure, since the height of the external connection terminals from the one surface of the ceramic substrate is less than the thickness of the resin layer, when plated layers are formed on the exposed end surfaces of the external connection terminals, the plated layers can be arranged so as not to protrude from the resin layer, and one surface of the composite substrate where the external connection terminals are provided can be made flat or substantially flat. 
     In the composite substrate according to a preferred embodiment of the present invention, outer peripheral edges of the end surfaces of the external connection terminals opposite to the end surfaces connected to the ceramic substrate are preferably covered with the resin layer. 
     In the above structure, since the outer peripheral edges of the end surfaces of the external connection terminals opposite to the end surfaces connected to the ceramic substrate are covered with the resin layer, when plated layers are provided after the resin layer is provided, the connection strength between the ceramic substrate and the external connection terminals is unlikely to be reduced, for example, by entry of plating solution into boundary portions between the ceramic substrate and the external connection terminals. 
     In the composite substrate according to a preferred embodiment of the present invention, plated layers are preferably provided on the end surfaces of the external connection terminals exposed from the resin layer. 
     In the above structure, since the plated layers are provided on the end surfaces of the external connection terminals exposed from the resin layer, the exposed end surfaces of the external connection terminals can be protected. Moreover, when the external connection terminals and a mount substrate are connected by solder, connection reliability can be enhanced. 
     In the composite substrate according to a preferred embodiment of the present invention, the plated layers are preferably arranged so as not to protrude from the resin layer. 
     In the above structure, since the plated layers are arranged so as not to protrude from the resin layer, one surface of the composite substrate where the external connection terminals are provided can be made flat or substantially flat. 
     In the composite substrate according to a preferred embodiment of the present invention, the plurality of external connection terminals are preferably arranged in a lattice configuration on the one surface of the ceramic substrate. 
     In the above structure, since the plurality of external connection terminals are arranged in a lattice configuration on the one surface of the ceramic substrate, as compared with the case in which the external connection terminals are provided in a peripheral edge portion of the one surface of the ceramic substrate, the number of external connection terminals that can be provided on one surface of the ceramic substrate can be increased, and the size of the composite substrate can be reduced while ensuring a necessary number of external connection terminals. Further, since the plurality of external connection terminals are arranged in a lattice configuration without being arranged only in the peripheral edge portion of the one surface of the ceramic substrate, stress applied to the external connection terminals, for example, due to a fall can be distributed, and breakage can be prevented from being caused by concentration of stress at one or some of the external connection terminals. 
     Next, to achieve the above benefits, a module according to a preferred embodiment of the present invention includes the composite substrate including the above-described structure, and an electronic component mounted on both surfaces of the ceramic substrate or a surface opposite to the surface on which the external connection terminals are provided. 
     In the above structure, there are provided the composite substrate including the above-described structure, and the electronic component mounted on both surfaces of the ceramic substrate or the surface opposite to the surface on which the external connection terminals are provided. Hence, the cross-sectional area of connecting portions between the ceramic substrate and the external connection terminals can be made larger than in a module including columnar or prismatic external connection terminals having a constant cross-sectional area. Therefore, stress applied to the external connection terminals, for example, due to a fall, can be distributed, and sufficient connection strength can be ensured between the ceramic substrate and the external connection terminals. 
     Preferably, the module according to a preferred embodiment of the present invention further includes a sealing layer in which the electronic component mounted on the surface opposite to the surface on which the external connection terminals are provided is sealed with resin. 
     In the above structure, since there is provided the sealing layer in which the electronic component mounted on the surface opposite to the surface on which the external connection terminals are provided is sealed with resin, it is possible to protect the electronic component mounted on the surface opposite to the surface on which the external connection terminals are provided and to significantly reduce or prevent warping of the module. 
     Next, to achieve the above benefits, a composite-substrate production method according to a preferred embodiment of the present invention includes a first step of forming, in a resin sheet, a plurality of holes whose aperture area is smaller on one side than on the other side and filling the plurality of holes with a conductive material, a second step of stacking a plurality of the resin sheets on one surface of an unfired ceramic substrate including, on at least one surface, a circuit wire on which an electronic component is to be mounted so that the aperture area of the plurality of holes successively decreases, and firing the resin sheets to form a plurality of external connection terminals having a shape whose cross-sectional area decreases with increasing distance from the one surface of the fired ceramic substrate, and a third step of forming a resin layer on the one surface of the ceramic substrate so that end surfaces of the external connection terminals opposite to end surfaces connected to the ceramic substrate are exposed partially or entirely. 
     In the above structure, a plurality of holes whose aperture area is smaller on one side than on the other side are arranged in the resin sheet, and the plurality of holes are filled with the conductive material. On one surface of the unfired ceramic substrate including, on at least one surface, the circuit wire on which the electronic component is to be mounted, a plurality of the resin sheets are stacked so that the aperture area of the plurality of holes successively decreases, and are fired to define a plurality of external connection terminals having a shape whose cross-sectional area decreases with increasing distance from the one surface of the fired ceramic substrate. The resin layer is arranged on the one surface of the ceramic substrate so that the end surfaces of the external connection terminals opposite to the end surfaces connected to the ceramic substrate are exposed partially or entirely. Hence, the cross-sectional area of connecting portions to the ceramic substrate can be made larger than in a module including columnar or prismatic external connection terminals having a constant cross-sectional area. Therefore, stress applied to the external connection terminals, for example, due to a fall can be distributed, and it is possible to produce a composite substrate in which sufficient connection strength is ensured between a ceramic substrate and external connection terminals. 
     Next, to achieve the above benefits, a composite-substrate production method according to a preferred embodiment of the present invention includes a first step of screen-printing a conductive material a plurality of times on one surface of an unfired ceramic substrate including, on at least one surface, a circuit wire on which an electronic component is to be mounted so as to form a plurality of unfired external connection terminals having a shape whose cross-sectional area decreases with increasing distance from the one surface of the ceramic substrate, a second step of firing the ceramic substrate on which the plurality of unfired external connection terminals are arranged, and a third step of forming a resin layer on the one surface of the ceramic substrate so that end surfaces of the external connection terminals opposite to end surfaces connected to the ceramic substrate are exposed partially or entirely. 
     In the above structure, the conductive material is screen-printed a plurality of times on one surface of the unfired ceramic substrate including, on at least one surface, the circuit wire on which the electronic component is to be mounted so as to define a plurality of unfired external connection terminals having a shape whose cross-sectional area decreases with increasing distance from the one surface of the ceramic substrate. The ceramic substrate on which the plurality of unfired external connection terminals are arranged is fired, and the resin layer is formed on the one surface of the ceramic substrate so that the end surfaces of the external connection terminals opposite to the end surfaces connected to the ceramic substrate are exposed partially or entirely. Thus, the cross-sectional area of connecting portions to the ceramic substrate can be made larger than in columnar or prismatic external connection terminals having a constant cross-sectional area. Hence, stress applied to the external connection terminals, for example, due to a fall can be distributed, and it is possible to produce a composite substrate in which sufficient connection strength is ensured between a ceramic substrate and external connection terminals. 
     Next, to achieve the above benefits, a composite-substrate production method includes a first step of forming, in an unfired ceramic sheet, a plurality of holes whose aperture area is smaller on one side than on the other side and filling the plurality of holes with a conductive material, a second step of stacking a plurality of the ceramic sheets on one surface of an unfired ceramic substrate having a sintering temperature lower than that of the ceramic sheets and including, on at least one surface, a circuit wire on which an electronic component is to be mounted so that the aperture area of the holes successively unsintered ceramic sheets to form a plurality of external connection terminals having a shape whose cross-sectional area decreases with increasing distance from the one surface of the ceramic substrate, and a third step of forming a resin layer on the one surface of the ceramic substrate so that end surfaces of the external connection terminals opposite to end surfaces connected to the ceramic substrate are exposed partially or entirely. 
     In the above structure, a plurality of holes whose aperture area is smaller on one side than on the other side are arranged in the unfired ceramic sheet, and the plurality of holes are filled with the conductive material. A plurality of the ceramic sheets are stacked on one surface of the unfired ceramic substrate having a sintering temperature lower than that of the plurality of ceramic sheets and including, on at least one surface, the circuit wire on which the electronic component is to be mounted so that the aperture area of the plurality of holes successively decreases, and are fired, and the unsintered ceramic sheets are removed to form a plurality of external connection terminals having a shape whose cross-sectional area decreases with increasing distance from the one surface of the ceramic substrate. Since the resin layer is arranged on the one surface of the ceramic substrate so that the end surfaces of the external connection terminals opposite to the end surfaces connected to the ceramic substrate are partially or entirely exposed, the cross-sectional area of connecting portions to the ceramic substrate can be made larger than in columnar or prismatic external connection terminals having a constant cross-sectional area. Hence, stress applied to the external connection terminals, for example, due to a fall can be distributed, and it is possible to produce a composite substrate in which sufficient connection strength is ensured between a ceramic substrate and external connection terminals. Further, since the unfired ceramic sheets significantly reduce or prevent shrinkage of the ceramic substrate during firing, a composite substrate with high dimensional accuracy can be produced. 
     In the composite-substrate production method according to a preferred embodiment of the present invention, preferably, the ceramic substrate preferably is a ceramic multilayer substrate formed by stacking a plurality of ceramic layers. 
     In the above structure, since the ceramic substrate is a ceramic multilayer substrate defined by stacking a plurality of ceramic layers, it is possible to produce a composite substrate including a ceramic substrate including a complicated circuit wire. 
     In the composite-substrate production method according to a preferred embodiment of the present invention, preferably, in the third step, the end surfaces of the external connection terminals opposite to the end surfaces connected to the ceramic substrate are partially or entirely exposed by grinding a surface of the formed resin layer. 
     In the above structure, since the end surfaces of the external connection terminals opposite to the end surfaces connected to the ceramic substrate are partially or entirely exposed by grinding the surface of the resin layer, the height of the external connection terminals from the one surface of the ceramic substrate can be easily adjusted by grinding the external connection terminals together with the resin layer. This allows one surface of the composite substrate where the external connection terminals are provided to be made flat or substantially flat. 
     In the composite-substrate production method according to a preferred embodiment of the present invention, preferably, in the third step, the resin layer is formed so that a thickness of the resin layer is more than a height of the external connection terminals from the one surface of the ceramic substrate. 
     In the above structure, since the resin layer is provided so that the thickness thereof is more than the height of the external connection terminals from the one surface of the ceramic substrate, when plated layers are provided on the exposed end surfaces of the external connection terminals, the plated layers can be arranged so as not to protrude from the resin layer. 
     In the composite-substrate production method according to a preferred embodiment of the present invention, preferably, in the third step, the resin layer is formed to cover outer peripheral edges of the end surfaces of the external connection terminals opposite to the end surfaces connected to the ceramic substrate. 
     In the above structure, since the resin layer is arranged to cover the outer peripheral edges of the end surfaces of the external connection terminals opposite to the end surfaces connected to the ceramic substrate, when the plated layers are provided on the exposed end surfaces of the external connection terminals after the resin layer is formed, the connection strength between the ceramic substrate and the external connection terminals is unlikely to be reduced, for example, by entry of plating solution into boundary portions between the ceramic substrate and the external connection terminals. 
     In the composite-substrate production method according to a preferred embodiment of the present invention, preferably, in the third step, plated layers are arranged on the end surfaces of the external connection terminals exposed from the resin layer so as not to protrude from the resin layer. 
     In the above structure, since the plated layers are arranged on the end surfaces of the external connection terminals exposed from the resin layer so as not to protrude from the resin layer, the exposed end surfaces of the external connection terminals can be protected. Moreover, when the external connection terminals are connected to a mount substrate by solder, connection reliability can be enhanced. Further, since the plated layers are provided after the resin layer is provided, solder wettability is not reduced by seepage of a resin component from the resin layer onto the end surfaces of the external connection terminals on which the plated layers are arranged, and this can enhance connection reliability. Still further, one surface of the composite substrate where the external connection terminals are provided can be made flat or substantially flat. 
     According to the above structure, the external connection terminals have a shape whose cross-sectional area decreases with increasing distance from one surface of the ceramic substrate, and the end surfaces of the external connection terminals opposite to the end surfaces connected to the ceramic substrate are partially or entirely exposed from the resin layer. Hence, the cross-sectional area of the connecting portions between the external connection terminals and the ceramic substrate can be made larger than in columnar or prismatic external connection terminals having a constant cross-sectional area. Therefore, stress applied to the external connection terminals, for example, due to a fall can be distributed, and sufficient connection strength can be ensured between the ceramic substrate and the external connection terminals. Further, while the ceramic substrate is used as the substrate on which the electronic component is mounted, since the resin layer is provided, deformation of the composite substrate can be prevented even when stress is applied to the composite substrate, for example, by a fall, and sufficient strength can be ensured even when the thickness is reduced. Therefore, the thickness of the composite substrate can be reduced. 
     Since the composite substrate including the above structure and the electronic component mounted on both surfaces of the ceramic substrate or the surface opposite to the surface where the external connection terminals are provided are provided, the cross-sectional area of connecting portions between the ceramic substrate and the external connection terminals can be made larger than in a module including a composite substrate in which columnar or prismatic external connection terminals having a constant cross-sectional area are provided. Hence, stress applied to the external connection terminals, for example, due to a fall can be distributed, and sufficient connection strength can be ensured between the ceramic substrate and the external connection terminals. 
     Further, according to the above structure, a plurality of holes whose aperture area is smaller on one side than on the other side are provided in the resin sheet, and the plurality of holes are filled with the conductive material. A plurality of resin sheets are stacked on one surface of the unfired ceramic substrate including, on at least one surface, the circuit wire on which the electronic component is to be mounted so that the aperture area of the holes successively decreases, and are fired to define the plurality of external connection terminals having a shape whose cross-sectional area decreases with increasing distance from the one surface of the fired ceramic substrate. The resin layer is arranged on the one surface of the ceramic substrate so that the end surfaces of the external connection terminals opposite to the end surfaces connected to the ceramic substrate are exposed partially or entirely. Thus, the cross-sectional area of the connecting portions to the ceramic substrate can be made larger than in columnar or prismatic external connection terminals having a constant cross-sectional area. Therefore, stress applied to the external connection terminals, for example, due to a fall can be distributed, and it is possible to produce a composite substrate in which sufficient connection strength is ensured between a ceramic substrate and external connection terminals. 
     According to the above structure, the conductive material is screen-printed a plurality of times on one surface of the unfired ceramic substrate including, on at least one surface, the circuit wire on which the electronic component is to be mounted so as to define a plurality of unfired external connection terminals having a shape whose cross-sectional area decreases with increasing distance from the one surface of the ceramic substrate. The ceramic substrate on which the plurality of unfired external connection terminals are provided is fired, and the resin layer is arranged on the one surface of the ceramic substrate so that the end surfaces of the external connection terminals opposite to the end surfaces connected to the ceramic substrate are exposed partially or entirely. Since the cross-sectional area of connecting portions connected to the ceramic substrate can be made larger than in columnar or prismatic external connection terminals having a constant cross-sectional area, stress applied to the external connection terminals, for example, due to a fall can be distributed. Thus, it is possible to produce a composite substrate in which sufficient connection strength is ensured between a ceramic substrate and external connection terminals. 
     Further, according to the above structure, a plurality of holes whose aperture area is smaller on one side than on the other side are provided in the unfired ceramic sheet, and the plurality of holes are filled with the conductive material. A plurality of ceramic sheets are stacked on one surface of the unfired ceramic substrate having a sintering temperature lower than that of the ceramic sheets and having, on at least one surface, the circuit wire on which the electronic component is to be mounted so that the aperture area of the plurality of holes successively decreases, and are fired, and the unsintered ceramic sheets are removed to define a plurality of external connection terminals having a shape whose cross-sectional area decreases with increasing distance from the one surface of the ceramic substrate. Since the resin layer is arranged on the one surface of the ceramic substrate so that the end surfaces of the external connection terminals opposite to the end surfaces connected to the ceramic substrate are exposed partially or entirely, the cross-sectional area of the connecting portions to the ceramic substrate can be made larger than in columnar or prismatic external connection terminals having a constant cross-sectional area. Hence, stress applied to the external connection terminals, for example, due to a fall can be distributed, and it is possible to produce a composite substrate in which sufficient connection strength is ensured between a ceramic substrate and external connection terminals. Further, since the unfired ceramic sheets significantly reduce or prevent shrinkage of the ceramic substrate during firing, a composite substrate with high dimensional accuracy can be produced. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view illustrating a structure of a module according to a first preferred embodiment of the present invention. 
         FIG. 2  is a plan view illustrating a structure of a side of the module of the first preferred embodiment of the present invention on which external connection terminals are provided. 
         FIGS. 3A to 3F  include schematic views illustrating a composite-substrate production procedure according to the first preferred embodiment of the present invention. 
         FIGS. 4A to 4E  include schematic views illustrating another composite-substrate production procedure according to the first preferred embodiment of the present invention. 
         FIGS. 5A to 5C  include schematic views illustrating a further composite-substrate production procedure according to the first preferred embodiment of the present invention. 
         FIGS. 6A and 6B  include schematic views illustrating a structure of a module according to a second preferred embodiment of the present invention. 
         FIG. 7  is a plan view illustrating structures of one external connection terminal and its surroundings in the module according to the second preferred embodiment of the present invention. 
         FIG. 8  is a schematic view illustrating a module in which an electronic component is mounted on a portion of one surface of a ceramic substrate where external connection terminals are not provided. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described in detail below with reference to the drawings. 
     First Preferred Embodiment 
       FIG. 1  is a schematic view illustrating a structure of a module according to a first preferred embodiment of the present invention. As illustrated in  FIG. 1 , a module  10  preferably includes a ceramic substrate  1 , a plurality of external connection terminals  3  provided on one surface of the ceramic substrate  1 , a plurality of electronic components  2  mounted on a surface of the ceramic substrate  1  opposite to the surface with the external connection terminals  3 , a sealing layer  4  in which the electronic components  2  mounted on the surface of the ceramic substrate  1  opposite to the surface with the external connection terminals  3  are sealed with resin, and a resin layer  5  that covers the one surface of the ceramic substrate  1  with the plurality of external connection terminals  3 . The ceramic substrate  1 , the external connection terminals  3 , and the resin layer  5  define a composite substrate  20 . 
     As the ceramic substrate  1 , for example, an LTCC (Low Temperature Co-fired Ceramic) substrate is preferably used. The ceramic substrate  1  may be a ceramic single-layer substrate defined by one ceramic layer, or a ceramic multilayer substrate defined by a plurality of stacked ceramic layers. On at least one surface of the ceramic substrate  1 , a circuit wire (not illustrated) on which the electronic components  2  are mounted is preferably provided. The electronic components  2  are surface mount electronic components (surface mount devices) that can be surface-mounted on the ceramic substrate  1 . While the ceramic substrate  1  is used as the substrate on which the electronic components  2  are mounted, since the resin layer  5  is provided, even when stress is applied to the composite substrate  20 , for example, due to a fall, deformation of the composite substrate  20  is prevented. Since sufficient strength is ensured even when the thickness is reduced, the thickness of the composite substrate  20  can be reduced. 
     The external connection terminals  3  preferably have a shape whose cross-sectional area decreases with increasing distance from one surface of the ceramic substrate  1 , for example, a substantially truncated conical shape or a substantially truncated pyramidal shape. Since the cross-sectional area of connecting portions to the ceramic substrate  1  can be made larger in the external connection terminals  3  than in columnar or prismatic external connection terminals having a constant cross-sectional area, stress applied to the external connection terminals  3 , for example, due to a fall can be distributed, and sufficient connection strength is ensured between the ceramic substrate  1  and the external connection terminals  3 . The cross sections of the external connection terminals  3  may have a circular shape, a rectangular shape, other polygonal shapes, etc. End surfaces of the external connection terminals  3  opposite to end surfaces connected to the ceramic substrate  1  are preferably partially or entirely exposed from the resin layer  5 . The exposed end surfaces  3   a  of the external connection terminals  3  are provided with plated layers  6 . The external connection terminals  3  provided with the plated layers  6  are connected to a mount substrate (for example, a motherboard) by solder. For example, the plated layers  6  are preferably defined by a film deposition of Ni/Sn or Ni/Au formed using wet plating. 
       FIG. 2  is a plan view illustrating a structure of a side of the module  10  of the first preferred embodiment of the present invention where the external connection terminals  3  are provided. As illustrated in  FIG. 2 , the plurality of external connection terminals  3  are preferably not provided in a peripheral edge portion of one surface of the ceramic substrate  1 , but are arranged in a lattice configuration on the one surface of the ceramic substrate  1 . In this preferred embodiment, the external connection terminals  3  have a substantially truncated pyramidal shape. Hence, the end surfaces  3   a  exposed from the resin layer  5  are rectangular, and the plated layers  6  are provided on the exposed end surfaces  3   a.    
     Since the plurality of external connection terminals  3  are arranged in a lattice configuration on one surface of the ceramic substrate  1 , compared with a case in which the external connection terminals are provided in a peripheral edge portion of one surface of the ceramic substrate  1 , the number of external connection terminals  3  that can be formed on the one surface of the ceramic substrate  1  can be increased, and the size of the module  10  (composite substrate  20 ) can be reduced while ensuring a necessary number of external connection terminals  3 . Further, since the plurality of external connection terminals  3  are preferably arranged in a lattice configuration without being provided only in the peripheral edge portion of one surface of the ceramic substrate  1 , stress applied to the external connection terminals  3 , for example, due to a fall can be distributed, and breakage can be prevented from being caused by concentration of the stress at one or some of the external connection terminals  3 . Still further, since a large number of external connection terminals  3  can be provided on one surface of the ceramic substrate  1 , it is possible to efficiently exhaust heat generated by the electronic components  2  that are mounted on the surface of the ceramic substrate  1  opposite to the surface where the external connection terminals  3  are provided. 
       FIGS. 3A to 3F  include schematic views illustrating a production procedure for the composite substrate  20  according to the first preferred embodiment of the present invention. First, as illustrated in  FIG. 3A , a resin sheet  31  made of a material that is burnt down in a firing step, such as, for example, polypropylene or acrylic, is prepared. When the use of only the resin sheet  31  makes the shape unstable, a base material  32  made of a material harder than the resin sheet  31  is preferably stuck on the resin sheet  31 . 
     As illustrated in  FIG. 3B , a plurality of holes  33  are formed in a lattice configuration in the resin sheet  31  by using, for example, laser light, a die, etc. The holes  33  are preferably tapered to narrow from the resin sheet  31  toward the base material  32 . The holes  33  are shaped like a substantially truncated cone such that the area of apertures  33   b  of the holes  33  (aperture area on one side) is smaller than the area of apertures  33   a  on a side of the resin sheet  31  opposite to the base material  32  (aperture area on the other side). Since the base material  32  is stuck on the resin sheet  31 , it has substantially truncated conical holes continuing from the holes  33 . 
     As illustrated in  FIG. 3C , the holes  33  provided in the resin sheet  31  are preferably filled with a conductive material  34  containing, for example, Ag, Cu, Pd, and a compound including at least one of these. Since the base material  32  is stuck on the resin sheet  31 , the substantially truncated conical holes continuing from the holes  33  are also filled with the conductive material  34 . 
     As illustrated in  FIG. 3D , the resin sheet  31  with the holes  33  filled with the conductive material  34  and a plurality of ceramic green sheets  35   a  to  35   d  including circuit wires (not illustrated) are prepared. The resin sheet  31  is provided in a state separated from the base material  32  and is turned upside down. The plurality of ceramic green sheets  35   a  to  35   d  are preferably produced by a conventional method. For example, a ceramic green sheet having a thickness of about 10 μm to about 200 μm is preferably produced by coating a PET film with ceramic slurry and then drying the ceramic slurry. 
     As illustrated in  FIG. 3E , the resin sheet  31  and the plurality of ceramic green sheets  35   a  to  35   d  are stacked. When the resin sheet  31  is stacked on the ceramic green sheet  35   a , it is preferably stacked such that a surface thereof having the apertures  33   a  of the holes  33  having a larger aperture area comes into contact with the ceramic green sheet  35   a . For example, the resin sheet  31  and the plurality of ceramic green sheets  35   a  to  35   d  thus stacked are pressure-bonded with a pressure of about 100 kg/cm 2  to about 1500 kg/cm 2  and at a temperature of about 40° C. to about 100° C. Here, the stacked ceramic green sheets  35   a  to  35   d  define an unfired ceramic substrate. The ceramic green sheets  35   a  to  35   d  are not limited to a plurality of stacked sheets, and may alternatively be replaced with one sheet if so desired. 
     As illustrated in  FIG. 3F , the resin sheet  31  and the plurality of ceramic green sheets  35   a  to  35   d  are fired in a stacked state. By firing the resin sheet  31  and the plurality of ceramic green sheets  35   a  to  35   d  in the stacked state, a ceramic substrate  1  is formed. By firing, the resin sheet  31  is burnt down, and a plurality of substantially truncated conical external connection terminals  3 , whose cross-sectional area decreases with increasing distance from one surface of the ceramic substrate  1 , are formed on the one surface of the ceramic substrate  1 . Firing is performed at about 850° C. in air when the conductive material  34  is composed mostly of Ag, and at about 950° C. in a reductive atmosphere when the conductive material  34  is composed mostly of Cu, for example. 
     After that, a composite substrate  20  illustrated in  FIG. 1  can be produced by arranging a resin layer  5  on the one surface of the ceramic substrate  1  on which the plurality of external connection terminals  3  are provided. As an exemplary method of forming the resin layer  5 , resin is applied to cover the one surface of the ceramic substrate  1  having the plurality of external connection terminals  3 , and is set under a predetermined condition to form a resin layer  5 . Further, a surface of the formed resin layer  5  is ground to partially or entirely expose end surfaces of the external connection terminals  3  opposite to end surfaces connected to the ceramic substrate  1 . Alternatively, for example, in a state in which the end surfaces of the external connection terminals  3  opposite to the end surfaces connected to the ceramic substrate  1  are partially or entirely exposed, resin is filled between the plurality of external connection terminals  3  by screen printing and is set to provide a resin layer  5 . The resin material used for the resin layer  5  is preferably a thermosetting resin such as, for example, epoxy resin. 
     Further, since plated layers  6  are arranged on the exposed end surfaces  3   a  of the external connection terminals  3  after the resin layer  5  is provided on the one surface of the ceramic substrate  1  in the composite substrate  20 , when the plated layers  6  are arranged, boundary portions between the ceramic substrate  1  and the external connection terminals  3  are covered with the resin layer  5 . Thus, for example, plating solution is unlikely to enter the boundary portions, and this reduces the influence of plating. For this reason, in the composite substrate  20 , the connection strength between the ceramic substrate  1  and the external connection terminals  3  is unlikely to decrease. 
     The method for producing the composite substrate  20  is not limited to the method illustrated in  FIG. 3A to 3F . For example,  FIGS. 4A to 4E  include schematic views illustrating another production procedure for the composite substrate  20  of the first preferred embodiment of the present invention. First, as illustrated in  FIG. 4A , a conductive material  42  is preferably screen-printed in a lattice configuration on one surface of a ceramic green sheet  41   a  after firing. When the use of only the ceramic green sheet  41   a  makes the shape unstable, a base material  43  harder than the ceramic green sheet  41   a  is stuck onto the ceramic green sheet  41   a . The conductive material  42  preferably contains, for example, Ag, Cu, Pd, and a compound including at least one of these. 
     Next, as illustrated in  FIG. 4B , the conductive material  42  is preferably screen-printed on the one surface of the ceramic green sheet  41   a  a plurality of times such that a plurality of unfired external connection terminals having a substantially truncated conical shape, whose cross-sectional area decreases with increasing distance from the one surface of the ceramic green sheet  41   a , are formed on the one surface of the ceramic green sheet  41   a . By using a plurality of screen printing plates that are different in size of an aperture portion, the external connection terminals  3  having the above-described shape can be provided. 
     Then, as illustrated in  FIG. 4C , the ceramic green sheet  41   a  including the one surface on which the plurality of unfired truncated conical external connection terminals are provided, and a plurality of ceramic green sheets  41   b  to  41   e  having circuit wires (not illustrated) are prepared. The ceramic green sheet  41   a  is separated from the base material  43 . 
     Further, as illustrated in  FIG. 4D , the plurality of ceramic green sheets  41   a  to  41   e  are stacked. When the ceramic green sheet  41   a  is stacked on the ceramic green sheet  41   b , the ceramic green sheet  41   a  including the unfired external connection terminals is stacked on the ceramic green sheet  41   b . For example, the plurality of stacked ceramic green sheets  41   a  to  41   e  are preferably pressure-bonded with a pressure of about 100 kg/cm 2  to about 1500 kg/cm 2  and at a temperature of about 40° C. to about 100° C. Here, the plurality of stacked ceramic green sheets  41   a  to  41   e  define an unfired ceramic substrate. Further, the ceramic green sheets  41   a  to  41   e  are not limited to a plurality of stacked sheets, and may alternatively be replaced with one sheet if so desired. 
     Then, as illustrated in  FIG. 4E , the plurality of ceramic green sheets  41   a  to  41   e  are fired in a stacked state. By firing the plurality of ceramic green sheets  41   a  to  41   e  in the stacked state, a ceramic substrate  1  is formed. By firing, a plurality of substantially truncated conical external connection terminals  3 , whose cross-sectional area decreases with increasing distance from one surface of the ceramic substrate  1 , are defined on the one surface of the ceramic substrate  1 . After that, a resin layer  5  is arranged on the one surface of the ceramic substrate  1  with the plurality of external connection terminals  3  so that end surfaces of the external connection terminals  3  opposite to end surfaces connected to the ceramic substrate  1  are partially or entirely exposed, whereby a composite substrate  20  illustrated in  FIG. 1  can be produced. 
       FIGS. 5A to 5C  include schematic views illustrating a further production procedure for the composite substrate  20  of the first preferred embodiment of the present invention. First, as illustrated in  FIG. 5A , a plurality of shrinkage-suppressing ceramic green sheets (ceramic sheets)  50   a  to  50   c  containing a sintering-resistant ceramic material, which is not sintered at a firing temperature of a low temperature co-fired ceramic material, as a main component are prepared. As powder containing the sintering-resistant ceramic material as a main component, alumina powder is preferably used as an example. By dispersing the alumina powder in an organic vehicle to prepare slurry and shaping the prepared slurry into a sheet by casting, shrinkage-suppressing ceramic green sheets  50   a  to  50   c  are produced. The sintering temperature of the shrinkage-suppressing ceramic green sheets  50   a  to  50   c  is preferably about 1500° C. to about 1600° C., which is much higher than the sintering temperature of a ceramic green sheet made of a low-temperature co-fired ceramic material (for example, about 900° C.) Hence, the shrinkage-suppressing ceramic green sheets  50   a  to  50   c  are substantially not sintered at the firing temperature of the ceramic green sheet made of a low-temperature co-fired ceramic material. As the powder containing a sintering-resistant ceramic material as a main component, besides alumina, for example, powder of zirconia or magnesia can be used. 
     A plurality of holes  51  are preferably formed in a lattice configuration in the shrinkage-suppressing ceramic green sheets  50   a  to  50   c  by using laser light, a die, etc. Since the plurality of shrinkage-suppressing ceramic green sheets  50   a  to  50   c  are used in a stacked state, the holes  51  whose aperture area successively increases from the shrinkage-suppressing ceramic green sheet  50   a  to the shrinkage-suppressing ceramic green sheet  50   c , take a continuous and substantially truncated conical shape when the shrinkage-suppressing ceramic green sheets  50   a  to  50   c  are stacked. The holes  51  defined in the shrinkage-suppressing ceramic green sheets  50   a  to  50   c , whose aperture area successively increases, are filled with a conductive material  52  preferably containing, for example, Ag, Cu, Pd, and a compound including at least one of these. 
     Further, a plurality of ceramic green sheets  55   a  to  55   c  on which circuit wires  54  are provided and a plurality of shrinkage-suppressing ceramic green sheets  57   a  to  57   c  including no hole are prepared. Preferably, the shrinkage-suppressing ceramic green sheets  50   a  to  50   c  and  57   a  to  57   c  contain a component common to a ceramic component contained in the ceramic green sheets  55   a  to  55   c.    
     Next, as illustrated in  FIG. 5B , the plurality of shrinkage-suppressing ceramic green sheets  50   a  to  50   c , the plurality of ceramic green sheets  55   a  to  55   c , and the plurality of shrinkage-suppressing ceramic green sheets  57   a  to  57   c  are stacked. When the shrinkage-suppressing ceramic green sheets  50   a  to  50   c  are stacked on the ceramic green sheet  55   a , they are stacked so that the shrinkage-suppressing ceramic green sheet  50   c  with apertures  51   a  of the holes  51  having the largest aperture area comes into contact with the ceramic green sheet  55   a . For example, the plurality of shrinkage-suppressing ceramic green sheets  50   a  to  50   c , the plurality of ceramic green sheets  55   a  to  55   c , and the plurality of shrinkage-suppressing ceramic green sheets  57   a  to  57   c  thus stacked are pressure-bonded with a pressure of about 100 kg/cm 2  to about 1500 kg/cm 2  and at a temperature of 40° C. to 100° C. Here, the plurality of stacked ceramic green sheets  55   a  to  55   c  define an unfired ceramic substrate. Further, the shrinkage-suppressing ceramic green sheets  50   a  to  50   c , the ceramic green sheets  55   a  to  55   c , and the shrinkage-suppressing ceramic green sheets  57   a  to  57   c  are each not limited to a plurality of stacked sheets, and may alternatively be replaced with one sheet if so desired. 
     Then, as illustrated in  FIG. 5C , the plurality of shrinkage-suppressing ceramic green sheets  50   a  to  50   c , the plurality of ceramic green sheets  55   a  to  55   c , and the plurality of shrinkage-suppressing ceramic green sheets  57   a  to  57   c  are fired in a stacked state. By firing the plurality of stacked ceramic green sheets  55   a  to  55   c , a ceramic substrate  1  is provided. However, at the firing temperature of the ceramic green sheets  55   a  to  55   c  (for example, about 900° C.), the shrinkage-suppressing ceramic green sheets  50   a  to  50   c  and  57   a  to  57   c  having a sintering temperature of about 1500° C. to about 1600° C., which is much higher, are not sintered, and do not shrink in the planar direction, but shrink only in the height direction. Hence, a plurality of substantially truncated conical external connection terminals  3 , whose cross-sectional area decreases with increasing distance from one surface of the ceramic substrate  1 , are formed on the one surface of the ceramic substrate  1 . 
     When firing is performed at the temperature at which the shrinkage-suppressing ceramic green sheets  50   a  to  50   c  and  57   a  to  57   c  are not sintered, organic vehicles contained in the shrinkage-suppressing ceramic green sheets  50   a  to  50   c  and  57   a  to  57   c  are burnt into an aggregate of alumina powder. The aggregate of alumina powder can be easily removed, for example, by blasting. By removing the aggregate of alumina powder (unsintered shrinkage-suppressing ceramic green sheets  50   a  to  50   c  and  57   a  to  57   c ), a plurality of substantially truncated conical external connection terminals  3  are defined. By forming a resin layer  5  on the one surface of the ceramic substrate  1  on which the plurality of external connection terminals  3  are provided, a composite substrate  20  illustrated in  FIG. 1  can be produced. While the shrinkage-suppressing ceramic green sheets  57   a  to  57   c  are stacked on the surface of the ceramic substrate  1  on which the external connection terminals  3  are not formed in the production method of the first preferred embodiment, the ceramic substrate  1  may be formed without using these sheets. 
     As described above, in the composite substrate  20  of the first preferred embodiment, the external connection terminals  3  provided on one surface of the ceramic substrate have a shape whose cross-sectional area decreases with increasing distance from the one surface of the ceramic substrate  1  (a substantially truncated conical shape), and the end surfaces of the external connection terminals  3  opposite to the end surfaces connected to the ceramic substrate  1  are exposed partially or entirely. Hence, the cross-sectional area of the connecting portions between the external connection terminals  3  and the ceramic substrate  1  can be made larger than in columnar or prismatic external connection terminals having a constant cross-sectional area, and stress applied to the external connection terminals  3 , for example, due to a fall can be distributed. This ensures sufficient connection strength between the ceramic substrate  1  and the external connection terminals  3 . Further, while the ceramic substrate  1  is used as the substrate on which the electronic components  2  are mounted, since the resin layer  5  is provided, deformation of the composite substrate can be prevented even when stress is applied to the composite substrate  20 , for example, due to a fall, and sufficient strength can be ensured even when the thickness is reduced. Thus, the thickness of the composite substrate can be reduced. Further, the height of the external connection terminals  3  from the one surface of the ceramic substrate  1  (for example, about 10 μm) can be easily adjusted by grinding the external connection terminals  3  together with the surface of the resin layer  5 , and one surface of the composite substrate  20  on which the external connection terminals  3  are provided can be made flat or substantially flat. 
     Since the module  10  includes the composite substrate  20  and the electronic components  2  mounted on both surfaces of the ceramic substrate  1  or the surface of the ceramic substrate  1  opposite to the surface on which the external connection terminals  3  are provided, the cross-sectional area of the connecting portions between the ceramic substrate  1  and the external connection terminals  3  can be made larger than in the module including the composite substrate on which the columnar or prismatic external connection terminals having a constant cross-sectional area are provided. Thus, stress applied to the external connection terminals  3 , for example, due to a fall can be distributed, and sufficient connection strength is ensured between the ceramic substrate  1  and the external connection terminals  3 . Further, since the sealing layer  4  is provided, the electronic components  2  mounted on the surface of the ceramic substrate  1  opposite to the surface on which the external connection terminals  3  are provided are protected, and the module  10  is prevented from warping. 
     Second Preferred Embodiment 
       FIGS. 6A and 6B  include schematic views illustrating a structure of a module according to a second preferred embodiment of the present invention. As illustrated in  FIG. 6A , a module  11  preferably includes a ceramic substrate  1 , a plurality of electronic components  2  mounted on both surfaces of the ceramic substrate  1  or a surface of the ceramic substrate  1  opposite to a surface on which external connection terminals  7  are provided, a plurality of substantially truncated pyramidal external connection terminals  7  provided on one surface of the ceramic substrate  1 , a sealing layer  4  in which the electronic components  2  mounted on the surface of the ceramic substrate  1  opposite to the surface on which the external connection terminals  7  are provided are sealed with resin, and a resin layer  8  that covers the one surface of the ceramic substrate  1  on which the plurality of external connection terminals  7  are provided. The ceramic substrate  1 , the external connection terminals  7 , and the resin layer  8  define a composite substrate  21 . The module  11  preferably has the same structure as that of the module  10  illustrated in  FIG. 1  except that the height of the resin layer  8  is different. Constituent elements other than the external connection terminals  7  and the resin layer  8  are denoted by the same reference numerals, and detailed descriptions thereof are skipped. 
       FIG. 6B  is an enlarged view of one external connection terminal  7  and its surroundings in an encircled portion of  FIG. 6A . As illustrated in  FIG. 6B , a height H of the external connection terminal  7  from one surface of the ceramic substrate  1  is preferably set to be less than a thickness B of the resin layer  8 . A recess is provided on a surface  8   a  of the resin layer  8  opposite to a ceramic-substrate  1  side surface, and an end surface of the external connection terminal  7  opposite to an end surface connected to the ceramic substrate  1  is preferably partially or entirely exposed from the recess. For this reason, when a plated layer  6  is provided on the exposed end surface  7   a  of the external connection terminal  7 , the plated layer  6  does not protrude from the surface  8   a  of the resin layer  8  opposite to the ceramic-substrate  1  side surface, and one surface of the composite substrate  21  where the external connection terminal  7  is provided can preferably be made flat or substantially flat. In particular, by arranging the plated layer  6  such that a surface  6   a  of the plated layer  6  provided on the exposed end surface  7   a  of the external connection terminal  7  is flush or substantially flush with the surface  8   a  of the resin layer  8  opposite to the ceramic-substrate  1  side surface, the one surface of the composite substrate  21  where the external connection terminal  7  is provided can be further flattened. 
       FIG. 7  is a plan view illustrating structures of one external connection terminal  7  and its surroundings in the module  11  according to the second preferred embodiment of the present invention. As illustrated in  FIG. 7 , the resin layer  8  is arranged to cover an outer peripheral edge of the exposed end surface  7   a  of the external connection terminal  7 , and the exposed end surface  7   a  of the external connection terminal  7  has an area  7   b  overlapping with the resin layer  8  all around the outer peripheral edge (four sides). The plated layer  6  is provided on the exposed end surface  7   a  of the external connection terminal  7  except for the area  7   b  overlapping with the resin layer  8 . Since the area  7   b  overlapping with the resin layer  8  is provided, even when the plated layer  6  is formed on the exposed end surface  7   a  of the external connection terminal  7  after the resin layer  8  is formed, the connection strength between the ceramic substrate  1  and the external connection terminal  7  is unlikely to be reduced, for example, by entry of plating solution into a boundary portion between the ceramic substrate  1  and the external connection terminal  7 . The exposed end surface  7   a  of the external connection terminal  7  does not always need to have the area  7   b  overlapping with the resin layer  8  all around the outer peripheral edge (four sides), and it is satisfactory as long as the end surface  7   a  has the area  7   b  overlapping with the resin layer  8  at least in part (for example, on one side). 
     As described above, in the module  11  (composite substrate  21 ) according to the second preferred embodiment of the present invention, the height (H) of the external connection terminals  7  from one surface of the ceramic substrate  1  is preferably set to be less than the thickness (B) of the resin layer  8 . Therefore, when the plated layers  6  are formed on the exposed end surfaces  7   a  of the external connection terminals  7 , the plated layers  6  preferably do not protrude from the surface  8   a  of the resin layer  8  opposite to the ceramic-substrate  1  side surface, and one surface of the composite substrate  21  where the external connection terminal  7  are provided can be made flat or substantially flat. Even if the plated layers  6  are thick and protrude from the surface  8   a  of the resin layer  8  opposite to the ceramic-substrate  1  side surface, the height of the portions protruding from the resin layer  8  can be reduced by adjusting the height of the external connection terminals  7 . 
     In the modules  10  and  11  (composite substrates  20  and  21 ) according to the first and second preferred embodiments of the present invention, a plurality of external connection terminals  3  and  7  preferably are arranged in a lattice configuration on one surface of the ceramic substrate  1 . However, the external connection terminals  3  and  7  do not always need to be arranged in a lattice configuration, and may be arranged in other manners if so desired. Further, electronic components may be mounted on a portion of the one surface of the ceramic substrate where the external connection terminals are not provided.  FIG. 8  is a schematic view illustrating a structure of a module in which electronic components are mounted on a portion of one surface of a ceramic substrate  1  where external connection terminals  3  are not provided. As illustrated in  FIG. 8 , a module  12  includes a plurality of external connection terminals  3  provided in a peripheral edge portion of one surface of a ceramic substrate  1 , a resin layer  5  provided on the one surface of the ceramic substrate  1 , an electronic component  9  mounted on a portion of the one surface of the ceramic substrate  1  where the external connection terminals  3  are not provided, electronic components  2  mounted on the other surface of the ceramic substrate  1  where the external connection terminals  3  are not provided, and a sealing layer  4  in which the other surface of the ceramic substrate  1  with the electronic components  2  mounted thereon is sealed with resin. That is, the module  12  may have a structure in which the electronic components  2  and  9  are mounted on both surfaces of the ceramic substrate  1 . 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.