Patent Publication Number: US-2019180930-A1

Title: Dc-dc converter module

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Japanese Patent Application No. 2016-184206 filed on Sep. 21, 2016 and is a Continuation Application of PCT Application No. PCT/JP2017/030485 filed on Aug. 25, 2017. The entire contents of each application are hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a DC-DC converter module including a substrate and a shield cover. 
     2. Description of the Related Art 
     A DC-DC converter module having a configuration in which an IC including a switching element (hereinafter referred to as a switching-element-incorporating IC), a coil, and a capacitor (an input capacitor or an output capacitor), etc. are disposed at a substrate is known. 
     For example, Japanese Unexamined Patent Application Publication No. 2011-193724 discloses a DC-DC converter module in which the above-described switching-element-incorporating IC, the coil, etc. are covered with a shield cover. In this DC-DC converter module, the shield cover functions as a shield to shield noise emitted from, for example, the switching-element-incorporating IC. Noise emitted from the DC-DC converter module is able to therefore be reduced. 
     Such a shield cover is typically connected to the ground to increase a noise removal effect. 
     However, in a case in which a shield cover is connected to the ground of a capacitor, noise induced by the shield cover may flow to the input-side or output-side of a DC-DC converter module via the ground and the capacitor. Accordingly, even if the shield cover is connected to the ground, the noise removal effect of the shield cover may not be sufficiently obtained and the influence of noise on the input-side or output side of the DC-DC converter module may increase. 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the present invention provide DC-DC converter modules in each of which a shield cover connected to the ground is provided and the flow of noise to the input side or output side thereof is reduced or prevented. 
     A DC-DC converter module according to a preferred embodiment of the present invention includes a substrate, a first ground electrode, and a second ground electrode which are provided at the substrate, a switching-element-incorporating IC including an input end, an output end, and a first ground end, a coil element connected to the input end or the output end, a capacitor element including a first end connected to the input end or the output end and a second end connected to the first ground electrode, and a shield cover that is connected to the second ground electrode and covers at least one of the switching-element-incorporating IC, the coil element, and the capacitor element which is disposed on a surface of the substrate. 
     In this configuration, the shield cover and the capacitor element, which are connected to the ground, are separated from each other. Accordingly, the flow of noise induced by the shield cover to the input side or output side of the DC-DC converter module via the capacitor element is reduced or prevented. The DC-DC converter module in which the flow of noise to the input side or the output side thereof is reduced or prevented is therefore able to be achieved. 
     A DC-DC converter module according to a preferred embodiment of the present invention includes a substrate, a ground electrode provided at the substrate, a switching-element-incorporating IC including an input end, an output end, and a first ground end, a coil element connected to the input end or the output end, a capacitor element including a first end connected to the input end or the output end and a second end connected to the ground electrode, and a shield cover that is connected to the ground electrode and covers at least one of the switching-element-incorporating IC, the coil element, and the capacitor element which is disposed on a surface of the substrate. The second end and the shield cover are physically connected and are electrically disconnected at a frequency higher than or equal to a predetermined frequency. 
     With this configuration, even if the second end of the capacitor element and the shield cover are physically connected, the shield cover is connected to the second ground electrode that is electrically different from the first ground electrode to which the capacitor element is connected at the predetermined frequency. Accordingly, the flow of noise induced by the shield cover to the input side or output side of the DC-DC converter module is reduced or prevented. The DC-DC converter module in which the flow of noise to the input or output side thereof is reduced or prevented is therefore able to be achieved. 
     In a DC-DC converter module according to a preferred embodiment of the present invention, an inductor that includes a predetermined inductance component at the predetermined frequency may be connected between the second end and the shield cover. 
     In a DC-DC converter module according to a preferred embodiment of the present invention, the inductor preferably a conductive pattern provided at the substrate. Since the inductor is provided using a conductive pattern provided at the substrate in this configuration, there is no need to separately provide an element. This facilitates manufacturing and reduces cost. 
     In a DC-DC converter module according to a preferred embodiment of the present invention, the inductor preferably includes an interlayer connection conductor provided at the substrate. Since the inductor is provided using an interlayer connection conductor provided at the substrate in this configuration, there is no need to separately provide an element. This leads to the ease of manufacturing and the reduction in cost. 
     In a DC-DC converter module according to a preferred embodiment of the present invention, the first ground end and the shield cover may be electrically connected. 
     In a DC-DC converter module according to a preferred embodiment of the present invention, the DC-DC converter module further includes a protection member that is provided on a surface of the substrate and covers at least one of the switching-element-incorporating IC, the coil element, and the capacitor element which is disposed on the surface of the substrate. The shield cover is preferably defined by a conductor provided on a surface of the protection member. With this configuration, the coil element and the capacitor element are protected by the protection member. Accordingly, the DC-DC converter module is rugged, and the mechanical strength of the DC-DC converter module and the resistance of the DC-DC converter module to, for example, external forces are increased. With this configuration, as compared with a case in which, for example, the coil element is connected at the substrate by only soldering, the strength of connection of the coil element at the substrate is able to be improved and the reliability of electric connection between the coil element and the substrate is improved. 
     In a DC-DC converter module according to a preferred embodiment of the present invention, the substrate is preferably a resin substrate and the switching-element-incorporating IC is preferably buried in the substrate. With this configuration, the switching-element-incorporating IC is protected by the substrate. Accordingly, the mechanical strength of the switching-element-incorporating IC and the resistance of the switching-element-incorporating IC to, for example, external forces are increased. 
     In a DC-DC converter module according to a preferred embodiment of the present invention, the substrate may be a ferrite substrate and the coil element may be defined by a conductor provided at the substrate. 
     According to preferred embodiments of the present invention, DC-DC converter modules are able to be realized in each of which a shield cover connected to the ground is provided and the flow of noise to the input side or output side thereof is suppressed. 
     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 cross-sectional view of a main portion of a DC-DC converter module  101  according to a first preferred embodiment of the present invention. 
         FIG. 2  is a circuit diagram of the DC-DC converter module  101 . 
         FIG. 3  is a cross-sectional view of a main portion of an electronic apparatus  301  according to the first preferred embodiment of the present invention. 
         FIG. 4A  is a cross-sectional view of a main portion of a DC-DC converter module  102  according to a second preferred embodiment of the present invention, and  FIG. 4B  is a cross-sectional view taken along the line A-A in  FIG. 4A . 
         FIG. 5  is a circuit diagram of the DC-DC converter module  102 . 
         FIG. 6A  is a cross-sectional view of a main portion of a DC-DC converter module  103  according to a third preferred embodiment of the present invention, and  FIG. 6B  is a cross-sectional view taken along the line B-B in  FIG. 6A . 
         FIG. 7  is a cross-sectional view of a main portion of a DC-DC converter module  104 A according to the fourth preferred embodiment of the present invention. 
         FIG. 8A  is a cross-sectional view taken along the line C-C in  FIG. 7 , and  FIG. 8B  is a cross-sectional view taken along the line D-D in  FIG. 7 . 
         FIG. 9A  is a cross-sectional view of a main portion of a DC-DC converter module  104 B according to a fourth preferred embodiment of the present invention, and  FIG. 9B  is a cross-sectional view taken along the line E-E in  FIG. 9A . 
         FIG. 10  is a cross-sectional view of a main portion of a DC-DC converter module  105 A according to a fifth preferred embodiment of the present invention. 
         FIG. 11  is a cross-sectional view of a main portion of another DC-DC converter module  105 B according to the fifth preferred embodiment of the present invention. 
         FIG. 12  is a cross-sectional view of a main portion of a DC-DC converter module  106  according to a sixth preferred embodiment of the present invention. 
         FIG. 13A  is a circuit diagram of a DC-DC converter module  107 A according to a seventh preferred embodiment,  FIG. 13B  is a circuit diagram of another DC-DC converter module  107 B according to the seventh preferred embodiment, and  FIG. 13C  is a circuit diagram of another DC-DC converter module  107 C according to the seventh preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described below with reference to the drawings. The same or similar elements and components are denoted by the same reference symbols in the drawings. While the preferred embodiments are described separately for the sake of convenience in consideration of ease of explanation and understanding of key points, configurations described in the different preferred embodiments may be partially replaced or combined. In the second and subsequent preferred embodiments, descriptions of structural elements or portions common to those in the first preferred embodiment will be omitted and only different structure will be described. In particular, descriptions of similar advantageous effects obtained with similar configurations will not be repeated in each of the preferred embodiments. 
     First Preferred Embodiment 
       FIG. 1  is a cross-sectional view of a main portion of a DC-DC converter module  101  according to a first preferred embodiment of the present invention. 
     The DC-DC converter module  101  includes, for example, a substrate  1 , first ground electrodes G 11 , G 12 , and G 13 , a second ground electrode G 2 , a coil element  3 , capacitor elements  21  and  22 , a switching-element-incorporating IC  4 , and a shield cover  2 . 
     The substrate  1  is preferably a rectangular or substantially rectangular parallelepiped insulating plate including a first main surface S 1  and a second main surface S 2 . The substrate  1  is preferably a thermoplastic resin substrate (sheet) made of, for example, polyimide (PI) or liquid-crystal polymer (LCP). 
     The first ground electrodes G 11 , G 12 , and G 13  and the second ground electrode G 2  are conductors provided on the first main surface S 1  of the substrate  1 . On the second main surface S 2  of the substrate  1 , conductors  11 ,  12 ,  13 ,  14 ,  15  and  16  are provided. The conductor  13  is connected to the first ground electrode G 11  via an interlayer connection conductor V 1  provided in the substrate  1 . The conductor  16  is connected to the first ground electrode G 12  via an interlayer connection conductor V 2  provided in the substrate  1 . The first ground electrodes G 11 , G 12 , and G 13 , the second ground electrode G 2 , and the conductors  11 ,  12 ,  13 ,  14 ,  15 , and  16  are preferably conductive patterns made of, for example, Cu foil. 
     The switching-element-incorporating IC  4  is buried in the substrate  1 . As will be described later, the switching-element-incorporating IC  4  includes an input end, an output end, and a first ground end and incorporates a switching element to switch a current flowing through the coil element  3 . The first ground end of the switching-element-incorporating IC  4  is connected to the first ground electrode G 13  via an interlayer connection conductor V 3  provided in the substrate  1 . The switching-element-incorporating IC is preferably, for example, a microprocessor chip or an IC chip. The switching-element-incorporating IC  4  is buried in the substrate  1  such that a cavity is provided in a multilayer body including a plurality of insulating substrate layers preferably made of, for example, a thermoplastic resin and the multilayer body including the switching-element-incorporating IC  4  in the cavity is heated and pressurized. 
     The coil element  3  and the capacitor elements  21  and  22  are disposed on the second main surface S 2  of the substrate  1 . The coil element  3  and the capacitor elements  21  and  22  are disposed on the second main surface S 2  via a conductive joining material, such as solder, for example. More specifically, the coil element  3  is joined (connected) between the conductors  11  and  12 , the capacitor element  21  is joined (connected) between the conductors  13  and  14 , and the capacitor element  22  is joined (connected) between the conductors  15  and  16 . The coil element  3  is preferably, for example, a chip inductor. The capacitor element  21  is an input capacitor and the capacitor element  22  is an output capacitor. The capacitor elements  21  and  22  are preferably, for example, chip capacitors. 
     The shield cover  2  is a metal cover that covers the coil element  3  and the capacitor elements  21  and  22  which are disposed on the second main surface S 2  of the substrate  1 . As illustrated in  FIG. 1 , the shield cover  2  is connected to the second ground electrode G 2  provided on the first main surface S 1  of the substrate  1 . 
       FIG. 2  is a circuit diagram of the DC-DC converter module  101 . In  FIG. 2 , the coil element  3  is represented by a coil L, the capacitor element  21  is represented by an input capacitor C 1 , and the capacitor element  22  is represented by an output capacitor C 2 . The illustration of a voltage input portion Vin and a voltage output portion Vout in  FIG. 2  is omitted in  FIG. 1 . 
     The switching-element-incorporating IC 4  and the coil L are connected between the voltage input portion Vin that receives a DC voltage and the voltage output portion Vout. The switching-element-incorporating IC 4  incorporates an element to switch a current flowing through the coil L. The switching-element-incorporating IC 4  is connected to each of the voltage input portion Vin, the coil L, and the first ground electrode G 13 . The coil L is connected between the switching-element-incorporating IC 4  and the voltage output portion Vout. The input capacitor C 1  is connected between the voltage input portion Vin and the first ground electrode G 11 . The output capacitor C 2  is connected between the voltage output portion Vout and the first ground electrode G 12 . The shield cover  2  is connected to the second ground electrode G 2 . 
     Specifically, an input end IP of the switching-element-incorporating IC 4  is connected to the voltage input portion Vin. A first ground end GP of the switching-element-incorporating IC 4  is connected to the first ground electrode G 13 . An output end OP of the switching-element-incorporating IC 4  is connected to a first end of the coil L. A second end of the coil L is connected to the voltage output portion Vout. A first end E 1   a  of the input capacitor C 1  is connected to the voltage input portion Vin, and a second end E 2   a  of the input capacitor C 1  is connected to the first ground electrode G 11 . A first end E 1   b  of the output capacitor C 2  is connected to the voltage output portion Vout, and a second end E 2   b  of the output capacitor C 2  is connected to the first ground electrode G 12 . The shield cover  2  is connected to the second ground electrode G 2 . 
     Thus, the DC-DC converter module  101  is a step-down DC-DC converter module. 
     Next, a state in which the DC-DC converter module  101  is disposed on a mounting board using a conductive joining material will be described with reference to a drawing.  FIG. 3  is a cross-sectional view of a main portion of an electronic apparatus  301  according to the first preferred embodiment. 
     The electronic apparatus  301  includes, for example, a DC-DC converter module and a mounting board and is preferably, for example, a cellular phone terminal, a so-called smartphone, a tablet terminal, a notebook PC, a PDA, a wearable terminal (for example, a so-called smart watch or so-called smart glasses), a camera, a game machine, or a toy. 
     The electronic apparatus  301  includes, for example, the DC-DC converter module  101 , a mounting board  201 , and a surface-mount component  6 . The mounting board  201  is preferably, for example, a printed-circuit board. 
     On the main surface of the mounting board  201 , the DC-DC converter module  101  and the surface-mount component  6  are disposed. The surface-mount component  6  is preferably, for example, a chip inductor. 
     On the main surface of the mounting board  201 , conductors  61 ,  62 ,  63 ,  64 ,  65 , and  66  are provided. In the mounting board  201 , a conductor  67  is provided. The first ground electrode G 11  is connected to the conductor  61  via a conductive joining material  5 . The first ground electrode G 12  is connected to the conductor via the conductive joining material  5 . The first ground electrode G 13  is connected to the conductor  63  via the conductive joining material  5 . The second ground electrode G 2  is connected to the conductor  64  via the conductive joining material  5 . A voltage input portion (not illustrated) and a voltage output portion (not illustrated) of the DC-DC converter module are connected to a conductor (not illustrated) provided at the mounting board  201 . The conductive joining material  5  is preferably, for example, solder. The conductors  61 ,  62 ,  63 , and  64  are connected to different grounds of the mounting board  201 . The conductors  65  and  66  are connected to respective circuits provided at the mounting board  201 . 
     Using the DC-DC converter module  101  according to the present preferred embodiment, the following advantageous effects are obtained. 
     The DC-DC converter module  101  has a configuration in which the coil element  3  and the capacitor elements  21  and  22  disposed on the second main surface S 2  of the substrate  1  are covered with the shield cover  2 . With this configuration, noise that is caused by switching and is emitted from, for example, the coil element  3  or the switching-element-incorporating IC is shielded by the shield cover  2 . Accordingly, noise emitted from the DC-DC converter module is reduced or prevented. 
     In the present preferred embodiment, the shield cover  2  is connected to the second ground electrode G 2  that is different from the first ground electrodes G 11  and G 12  to which the capacitor elements  21  and  22  are connected, respectively. In this configuration, the shield cover  2  and each of the capacitor elements  21  and  22 , which are connected to the respective grounds, are separated from one another. Accordingly, the flow of noise induced by the shield cover  2  (switching noise that is emitted from, for example, the coil element  3  or the switching-element-incorporating IC  4  and is shielded by the shield cover  2 ) to the input side or output side of the DC-DC converter module via the capacitor elements  21  and  22  is reduced or prevented. A DC-DC converter module in which the flow of noise to the input side or the output side thereof is reduced or prevented is provided. 
     In the present preferred embodiment, the switching-element-incorporating IC  4  is buried in the substrate  1 . With this configuration, the switching-element-incorporating IC  4  is protected by the substrate  1 . Accordingly, the mechanical strength of the switching-element-incorporating IC  4  and the resistance of the switching-element-incorporating IC  4  to, for example, external forces are increased. 
     Second Preferred Embodiment 
     In a second preferred embodiment of the present invention, an exemplary case in which the first ground end of a switching-element-incorporating IC is electrically connected to a shield cover will be described. 
       FIG. 4A  is a cross-sectional view of a main portion of a DC-DC converter module  102  according to the second preferred embodiment, and  FIG. 4B  is a cross-sectional view taken along the line A-A in  FIG. 4A .  FIG. 5  is a circuit diagram of the DC-DC converter module  102 . 
     The DC-DC converter module  102  includes, for example, the substrate  1 , the first ground electrodes G 11  and G 12 , the second ground electrode G 2 , the coil element  3 , the capacitor elements  21  and  22 , the switching-element-incorporating IC  4 , and the shield cover  2 . 
     The DC-DC converter module  102  differs from the DC-DC converter module  101  according to the first preferred embodiment in that a ground conductor  31  is provided in the substrate  1 . The remaining configuration is the same or substantially the same as that of the DC-DC converter module  101 . A configuration different from a configuration according to the first preferred embodiment will be described below. 
     The ground conductor  31  is preferably a rectangular or substantially rectangular conductive pattern provided in the substrate  1  as illustrated in  FIG. 4B . The ground conductor  31  is preferably made of, for example, Cu foil. 
     A portion of the ground conductor  31  (the top side and bottom side of the ground conductor  31  in  FIG. 4B ) is exposed at the end surfaces of the substrate  1  and is connected to the shield cover  2 . As illustrated in  FIG. 4A , the ground conductor  31  is connected to the first ground end of the switching-element-incorporating IC  4  via the interlayer connection conductor V 3 A provided in the substrate  1 . The ground conductor  31  is connected to the second ground electrode G 2  via the interlayer connection conductor V 3 B provided in the substrate  1 . 
     That is, as illustrated in  FIG. 5 , the first ground end GP of the switching-element-incorporating IC  4  and the shield cover are connected to the second ground electrode G 2  and are electrically connected to each other. 
     With this configuration, the flow of noise induced by the shield cover  2  (switching noise that is emitted from, for example, the coil element  3  or the switching-element-incorporating IC  4  and is shielded by the shield cover  2 ) to the input side or output side of the DC-DC converter module via the capacitor elements  21  and  22  rarely occurs as compared with a case in which the shield cover  2  is electrically connected to the second ends of the capacitor elements  21  and  22 . Accordingly, the first ground end GP of the switching-element-incorporating IC  4  and the shield cover  2  may be electrically connected to each other as in the present preferred embodiment. 
     Third Preferred Embodiment 
     In a third preferred embodiment of the present invention, an exemplary case in which a capacitor element and a shield cover are physically connected will be described. 
       FIG. 6A  is a cross-sectional view of a main portion of a DC-DC converter module  103  according to the third preferred embodiment, and  FIG. 6B  is a cross-sectional view taken along the line B-B in  FIG. 6A .  FIG. 7  is a cross-sectional view of a main portion of a DC-DC converter module  104 A according to the fourth preferred embodiment. 
     The DC-DC converter module  103  differs from the DC-DC converter module  102  according to the second preferred embodiment in that a ground conductor  32  is provided in the substrate  1 . The remaining configuration is the same or substantially the same as that of the DC-DC converter module  102 . A configuration different from a configuration according to the second preferred embodiment will be described below. 
     The ground conductor  32  is a conductive pattern provided in the substrate  1 . A portion of the ground conductor  32  (portions of the top side and bottom side of the ground conductor  32  in  FIG. 6B ) is exposed at the end surfaces of the substrate  1  and is connected to the shield cover  2 . As illustrated in  FIG. 6A , the ground conductor  32  is connected to the first ground end of the switching-element-incorporating IC  4  and the second ends of the capacitor elements  21  and  22  via the interlayer connection conductors V 1 A, V 2 A, and V 3 A provided in the substrate  1 . The ground conductor  32  is connected to the first ground electrodes G 11  and G 12  and the second ground electrode G 2  via the interlayer connection conductors V 1 B, V 2 B, and V 3 B provided in the substrate  1 , respectively. 
     That is, the first ground end of the switching-element-incorporating IC  4 , the second ends of the capacitor elements  21  and  22 , and the shield cover  2  are physically connected. 
     The ground conductor  32  includes narrow-width portions GL 1   a , GL 1   b , GL 2   a  and GL 2   b  as illustrated in  FIG. 6B . The narrow-width portion GL 1   a  has a narrow conductor width (a conductor width Y 1 ) that is provided at an electric path between the second ground electrode G 2  and the first ground electrode G 11 . The narrow-width portion GL 1   b  has a narrow conductor width (the conductor width Y 1 ) that is provided at an electric path between the second ground electrode G 2  and the first ground electrode G 12 . The narrow-width portion GL 2   a  has a narrow conductor width (a conductor width X 1 ) that is provided at an electric path between the first ground electrode G 11  and the shield cover  2 . The narrow-width portion GL 2   b  has a narrow conductor width (the conductor width X 1 ) that is provided at an electric path between the first ground electrode G 12  and the shield cover  2 . The conductor widths of the narrow-width portions GL 1   a , GL 1   b , GL 2   a , and GL 2   b  are relatively narrower than a conductor width X 0  of the other portion (X 0 &gt;X 1 , X 0 &gt;Y 1 ). 
     The narrow-width portions GL 1   a , GL 1   b , GL 2   a , and GL 2   b  are electrically disconnected at a frequency higher than or equal to a predetermined frequency. Specifically, the conductor widths and conductor lengths of the narrow-width portions GL 1   a , GL 1   b , GL 2   a , and GL 2   b  are set such that a predetermined inductance component is provided at a predetermined frequency. Accordingly, between each of the second ends of the capacitor elements  21  and  22  and the shield cover  2 , an inductor (the narrow-width portions GL 1   a , GL 1   b , GL 2   a , and GL 2   b ) that has a predetermined inductance component at a predetermined frequency is connected. 
     A “predetermined frequency” is determined in accordance with the switching frequency of the switching-element-incorporating IC  4 . A “predetermined inductance component” varies in accordance with the above-described “predetermined frequency”. For example, the “predetermined inductance component” preferably has an inductance value less than or equal to about 5 μH when the “predetermined frequency” is greater than or equal to about 1 MHz and is less than about 100 MHz, has an inductance value less than or equal to about 5 nH when the “predetermined frequency” is greater than or equal to about 100 MHz and is less than about 1 GHz, and has an inductance value less than or equal to about 0.5 nH when the “predetermined frequency” is greater than or equal to 1 GHz and is less than or equal to about 2 GHz. 
     With the DC-DC converter module  103  according to the present preferred embodiment, the following advantageous effects are obtained. 
     In the present preferred embodiment, each of the second ends of the capacitor elements  21  and  22  and the shield cover  2  are electrically disconnected at a frequency higher than or equal to the predetermined frequency. Even if each of the capacitor elements  21  and  22  and the shield cover  2  are physically connected, the shield cover  2  is connected at a frequency higher than or equal to the predetermined frequency to the second ground electrode G 2  that is electrically different from the first ground electrodes G 11  and G 12  to which the capacitor elements  21  and  22  are connected, respectively. Accordingly, as in the first preferred embodiment, the flow of noise induced by the shield cover to the input side or output side of the DC-DC converter module is reduced or prevented. The DC-DC converter module in which the flow of noise to the input side or output side thereof is reduced or prevented is therefore achieved. 
     In the present preferred embodiment, the first ground end of the switching-element-incorporating IC  4  and each of the second ends of the capacitor elements  21  and  22  are physically connected via, for example, the ground conductor  32 . With this configuration, a direct-current electric path between the first ground end of the switching-element-incorporating IC  4  and each of the second ends of the capacitor elements  21  and  22  is short. Accordingly, as compared with a case in which the first ground end of the switching-element-incorporating IC 4  and the second ends of the capacitor elements  21  and  22  are connected to different grounds, the power conversion efficiency of the DC-DC converter module is improved. 
     In the present preferred embodiment, since an inductor is structured using the ground conductor  32  (conductive pattern) provided at the substrate  1 , there is no need to separately provide an element. This facilitates manufacturing and reduces cost. 
     Fourth Preferred Embodiment 
     In a fourth preferred embodiment of the present invention, an exemplary configuration in which a capacitor element and a shield cover are physically connected and which is different from a configuration according to the third preferred embodiment will be described. 
       FIG. 7  is a cross-sectional view of a main portion of a DC-DC converter module  104 A according to the fourth preferred embodiment.  FIG. 8A  is a cross-sectional view taken along the line C-C in  FIG. 7 , and  FIG. 8B  is a cross-sectional view taken along the line D-D in  FIG. 7 . 
     The DC-DC converter module  104 A differs from the DC-DC converter module  102  according to the second preferred embodiment in that ground conductors  33 A and  33 B are provided in the substrate  1 . The remaining configuration is the same or substantially the same as that of the DC-DC converter module  102 . A configuration different from a configuration according to the second preferred embodiment will be described below. 
     The ground conductors  33 A and  33 B are preferably rectangular or substantially rectangular conductive patterns and provided in the substrate  1 . A portion of the ground conductor  33 A (the top side and bottom side of the ground conductor  33 A in  FIG. 8A ) is exposed at the end surfaces of the substrate  1  and is connected to the shield cover  2 . The ground conductor  33 A is connected to the second end of the capacitor element  21  and the first ground electrode G 11  via the interlayer connection conductors V 1 A and V 1 B provided in the substrate  1 , respectively as illustrated in  FIG. 7 . A portion of the ground conductor  33 B (the top side and bottom side of the ground conductor  33 B in  FIG. 8A ) is exposed at the end surfaces of the substrate  1  and is connected to the shield cover  2 . The ground conductor  33 B is connected to the second end of the capacitor element  22  and the first ground electrode G 12  via the interlayer connection conductors V 2 A and V 2 B provided in the substrate  1 , respectively. 
     That is, each of the second ends of the capacitor elements  21  and  22  and the shield cover  2  are physically connected. 
     As illustrated in  FIG. 8A , in the ground conductor  33 A, the conductor width X 1  of an electric path between the first ground electrode G 11  and the shield cover  2  is relatively narrower than the conductor width of an electric path between the second ground electrode G 2  and the shield cover  2  (the conductor width X 0  of the ground conductor  31 ) (X 0 &gt;X 1 ). In the ground conductor  33 B, the conductor width X 1  of an electric path between the first ground electrode G 12  and the shield cover  2  is relatively narrower than the conductor width of an electric path between the second ground electrode G 2  and the shield cover  2  (the conductor width X 0  of the ground conductor  31 ) (X 0 &gt;X 1 ). 
     Accordingly, an inductor that has a predetermined inductance component at a predetermined frequency is connected between each of the second ends of the capacitor elements  21  and  22  and the shield cover  2 . 
     Next, another DC-DC converter module according to the present preferred embodiment will be described.  FIG. 9A  is a cross-sectional view of a main portion of another DC-DC converter module  104 B according to the fourth preferred embodiment, and  FIG. 9B  is a cross-sectional view taken along the line E-E in  FIG. 9A . 
     The DC-DC converter module  104 B differs from the DC-DC converter module  102  according to the second preferred embodiment in that ground conductors  34 A and  34 B and interlayer connection conductors V 4  and V 5  are provided in the substrate  1 . The remaining configuration is the same or substantially the same as that of the DC-DC converter module  102 . A configuration different from a configuration according to the second preferred embodiment will be described below. 
     The ground conductors  34 A and  34 B are preferably rectangular or substantially rectangular conductive patterns provided in the substrate  1 . A portion of the ground conductor  34 A (the left side of the ground conductor  34 A in  FIG. 9B ) is exposed at the end surface of the substrate  1  and is connected to the shield cover  2 . The ground conductor  34 A is connected to the first ground electrode G 11  via the interlayer connection conductor V 4  provided in the substrate  1  as illustrated in  FIG. 9A . A portion of the ground conductor  34 B (the right side of the ground conductor  34 B in  FIG. 9B ) is exposed at the end surface of the substrate  1  and is connected to the shield cover  2 . The ground conductor  34 B is connected to the first ground electrode G 12  via the interlayer connection conductor V 5  provided in the substrate  1 . 
     That is, each of the second ends of the capacitor elements  21  and  22  and the shield cover  2  are physically connected. 
     In the present preferred embodiment, the conductor diameters and conductor lengths of the interlayer connection conductors V 4  and V 5  are set such that a predetermined inductance component is provided at a predetermined frequency. Accordingly, between each of the second ends of the capacitor elements  21  and  22  and the shield cover  2 , an inductor that has a predetermined inductance component at a predetermined frequency is connected. 
     Fifth Preferred Embodiment 
     In a fifth preferred embodiment of the present invention, an example of a DC-DC converter module in which a switching-element-incorporating IC is disposed on the surface of a substrate will be described. 
       FIG. 10  is a cross-sectional view of a main portion of a DC-DC converter module  105 A according to the fifth preferred embodiment. 
     The DC-DC converter module  105 A includes, for example, a substrate  1 A, mounting electrodes P 1  and P 2 , a first ground electrode G 1 , the second ground electrode G 2 , a coil  3 A, the capacitor elements  21  and  22 , the switching-element-incorporating IC  4 , and the shield cover  2 . 
     The DC-DC converter module  105 A differs from the DC-DC converter module  101  according to the first preferred embodiment in that it includes the substrate  1 A. In addition, the DC-DC converter module  105 A differs from the DC-DC converter module  101  in that the switching-element-incorporating IC  4  is disposed on the second main surface S 2  of the substrate  1 A. A configuration different from a configuration according to the first preferred embodiment will be described. 
     The substrate  1 A is a multilayer body including a magnetic substance layer  51  and non-magnetic substance layers  52  and  53 , and is preferably a rectangular or substantially rectangular parallelepiped insulating plate including the first main surface S 1  and the second main surface S 2 . In the substrate  1 A, the magnetic substance layer  51  is sandwiched between the non-magnetic substance layers  52  and  53 . The substrate  1 A is preferably, for example, a ferrite substrate. The magnetic substance layer  51  is preferably, for example, a magnetic substance ferrite sheet. The non-magnetic substance layers  52  and  53  are non-magnetic substance ferrite sheets. 
     The mounting electrodes P 1  and P 2 , the first ground electrode G 1 , and the second ground electrode G 2  are conductors provided on the first main surface S 1  of the substrate  1 A. On the second main surface S 2  of the substrate  1 A, the conductors  11 ,  12 ,  13 ,  14 ,  15 , and  16  are provided. Each of the conductors  11 ,  13 , and  15  are connected to a ground conductor  35  provided at the non-magnetic substance layer  53  via an interlayer connection conductor. The ground conductor  35  is connected to one end of an end-surface conductor  41  provided at the end surface of the magnetic substance layer  51 . The other end of the end-surface conductor  41  is connected to a ground conductor  36  provided at the non-magnetic substance layer  52 . The ground conductor  36  is connected to the first ground electrode G 1  via an interlayer connection conductor. 
     The switching-element-incorporating IC  4  and the capacitor elements  21  and  22  are disposed on the second main surface S 2  of the substrate  1 A. The switching-element-incorporating IC  4 , and the capacitor elements  21  and  22  are disposed on the second main surface S 2  via the conductive joining material  5 , such as solder, for example. More specifically, the switching-element-incorporating IC  4  is joined (connected) between the conductors  11  and  12 , the capacitor element  21  is joined (connected) between the conductors  13  and  14 , and the capacitor element  22  is joined (connected) between the conductors  15  and  16 . Accordingly, the first ground end of the switching-element-incorporating IC 4  and the second ends of the capacitor elements  21  and  22  are connected to the first ground electrode G 1 . 
     The coil  3 A is preferably a helical coil including coil conductors  71 ,  72 , and  73  provided in the magnetic substance layer  51 . The coil conductors  71 ,  72 , and  73  are preferably loop or spiral conductive patterns. 
     The shield cover  2  is a metal cover that covers, for example, the switching-element-incorporating IC  4  and the capacitor elements  21  and  22  disposed on the second main surface S 2  of the substrate  1 A. The shield cover  2  is connected to the second ground electrode G 2  via a ground conductor  37  and an interlayer connection conductor which are provided in the substrate  1 A. 
     As described in the present preferred embodiment, the switching-element-incorporating IC  4  may be disposed on the surface of the substrate  1 A. As described in the present preferred embodiment, a coil may be defined by conductors provided in the substrate  1 A. As described in the present preferred embodiment, a DC-DC converter module may include a mounting electrode other than a ground electrode. 
     Next, another example of a DC-DC converter module according to the present preferred embodiment will be described.  FIG. 11  is a cross-sectional view of a main portion of another DC-DC converter module  105 B according to the fifth preferred embodiment. 
     The DC-DC converter module  105 B includes, for example, a substrate  1 B, a mounting electrode P 1 , the first ground electrodes G 11  and G 12 , the second ground electrode G 2 , the coil element  3 , the capacitor elements  21  and  22 , the switching-element-incorporating IC  4 , and the shield cover  2 . 
     The DC-DC converter module  105 B differs from the DC-DC converter module  101  according to the first preferred embodiment in that it includes the substrate  1 B. The DC-DC converter module  105 B differs from the DC-DC converter module  101  in that the switching-element-incorporating IC  4  is disposed on the second main surface S 2  of the substrate  1 B. A configuration different from a configuration according to the first preferred embodiment will be described below. 
     The substrate  1 B is preferably a rectangular or substantially rectangular parallelepiped insulating plate including the first main surface S 1  and the second main surface S 2 . The substrate  1 B is preferably, for example, a printed-circuit board. 
     The mounting electrode P 1 , the first ground electrodes G 11  and G 12 , and the second ground electrode G 2  are conductors provided on the first main surface S 1  of the substrate  1 B. On the second main surface S 2  of the substrate  1 A, the conductors  11 ,  12 ,  13 ,  14 ,  15 ,  16  and  17  are provided. The conductor  14  is connected to the first ground electrode G 11  via another conductor and an interlayer connection conductor. The conductor  15  is connected to the first ground electrode G 12  via another conductor and an interlayer connection conductor. A conductor  17  is connected to the second ground electrode G 2  via another conductor and an interlayer connection conductor. 
     The switching-element-incorporating IC  4 , the coil element  3 , and the capacitor elements  21  and  22  are disposed on the second main surface S 2  of the substrate  1 B. The switching-element-incorporating IC  4 , the coil element  3 , and the capacitor elements  21  and  22  are disposed on the second main surface S 2  via the conductive joining material  5 , such as solder, for example. More specifically, the coil element  3  is joined (connected) between the conductors  11  and  12 , the switching-element-incorporating IC is joined (connected) between the conductors  12  and  17 , the capacitor element  21  is joined (connected) between the conductors  13  and  14 , and the capacitor element  22  is joined (connected) between the conductors  15  and  16 . Accordingly, the second end of the capacitor element  21  is connected to the first ground electrode G 11 , and the second end of the capacitor element  22  is connected to the first ground electrode G 12 . The first ground end of the switching-element-incorporating IC 4  is connected to the second ground electrode G 2 . 
     The shield cover  2  is a metal cover that is disposed on the second main surface S 2  of the substrate  1 B and covers, for example, the switching-element-incorporating IC  4 , the coil element  3 , and the capacitor elements  21  and  22 . The outer edge of the shield cover  2  is joined via, for example, a conductive joining material to be electrically connected to the conductor  17  formed on the second main surface S 2  of the substrate  1 B. The shield cover  2  is therefore connected to the second ground electrode G 2 . The first ground end of the switching-element-incorporating IC 4  and the shield cover  2  are electrically connected. 
     Sixth Preferred Embodiment 
     In a sixth preferred embodiment of the present invention, an exemplary case in which the configuration of a shield cover differs from that of shield covers in the other configurations will be described. 
       FIG. 12  is a cross-sectional view of a main portion of a DC-DC converter module  106  according to the sixth preferred embodiment. 
     The DC-DC converter module  106  includes, for example, the substrate  1 , the mounting electrode P 1 , the first ground electrodes G 11  and G 12 , the second ground electrode G 2 , the coil element  3 , the capacitor elements  21  and  22 , the switching-element-incorporating IC  4 , a protection member  7 , and a shield cover  2 A. 
     The DC-DC converter module  106  differs from the DC-DC converter module  102  according to the second preferred embodiment in that it includes the protection member  7 . The DC-DC converter module  106  is different in the configuration of the shield cover  2 A from the DC-DC converter module  102 . A configuration different from a configuration according to the second preferred embodiment will be described below. 
     The mounting electrode P 1 , the first ground electrodes G 11  and G 12 , and the second ground electrode G 2  are conductors provided on the first main surface S 1  of the substrate  1 . On the second main surface S 2  of the substrate  1 , the conductors  11 ,  12 ,  13 ,  14 ,  15 , and  16  are provided. Each of the conductors  14  and  15  is connected to the ground conductor  31  provided in the substrate  1  via an interlayer connection conductor. The ground conductor  31  is connected to the first ground electrodes G 11  and G 12  via interlayer connection conductors. 
     The switching-element-incorporating IC  4  is buried in the substrate  1 . The first ground end of the switching-element-incorporating IC 4  is connected to the ground conductor  31  via an interlayer connection conductor. 
     The coil element  3  and the capacitor elements  21  and  22  are disposed on the second main surface S 2  of the substrate  1 . The coil element  3  and the capacitor elements  21  and  22  are disposed on the second main surface S 2  via a conductive joining material, such as solder, for example. More specifically, the coil element  3  is joined (connected) between the conductors  11  and  12 , the capacitor element  21  is joined (connected) between the conductors  13  and  14 , and the capacitor element  22  is joined (connected) between the conductors  15  and  16 . Accordingly, the first ground end of the switching-element-incorporating IC 4  and the second ends of the capacitor elements  21  and  22  are connected to the first ground electrodes G 11  and G 12 . 
     The protection member  7  is a block that is provided on the second main surface S 2  of the substrate  1  and covers the coil element  3  and the capacitor elements  21  and  22  disposed (mounted) on the second main surface S 2 . That is, the coil element  3  and the capacitor elements  21  and  22  are buried in the protection member  7  provided on the second main surface S 2  of the substrate  1 . The protection member  7  is preferably, for example, a thermosetting resin such as an epoxy resin. 
     The shield cover  2 A is a conductor provided on the surface of the protection member  7  and a portion of the substrate (end surfaces). The shield cover  2 A is a conductive pattern that covers, for example, the coil element  3  and the capacitor elements  21  and  22 . The shield cover  2 A is connected to the second ground electrode G 2  via a ground conductor  38  and an interlayer connection conductor which are provided in the substrate  1 . The shield cover  2 A is a metal film obtained by performing, for example, printing or sputtering using a conductive material upon the surface of the protection member  7 . 
     In the present preferred embodiment, the coil element  3  and the capacitor elements  21  and  22  disposed (mounted) on the second main surface S 2  of the substrate  1  are covered (sealed) with the protection member  7 . With this configuration, the coil element  3  and the capacitor elements  21  and  22  are protected by the protection member  7 . Accordingly, the DC-DC converter module is rugged, and the mechanical strength of the DC-DC converter module and the resistance of the DC-DC converter module to, for example, external forces are increased. With this configuration, as compared with a case in which, for example, the coil element  3  is disposed at the substrate  1  by only soldering, the strength of connection of the coil element at the substrate  1  is improved and the reliability of electric connection between the coil element and the substrate is improved. 
     Seventh Preferred Embodiment 
     In a seventh preferred embodiment of the present invention, an exemplary case in which a circuit configuration differs from that of the DC-DC converter module  101  according to the first preferred embodiment will be described. 
       FIG. 13A  is a circuit diagram of a DC-DC converter module  107 A according to the seventh preferred embodiment,  FIG. 13B  is a circuit diagram of another DC-DC converter module  107 B according to the seventh preferred embodiment, and  FIG. 13C  is a circuit diagram of another DC-DC converter module  107 C according to the seventh preferred embodiment. 
     The DC-DC converter module  107 A illustrated in  FIG. 13A  differs from the DC-DC converter module  101  according to the first preferred embodiment in that it does not include the first ground electrode G 11  and the input capacitor C 1 . The remaining configuration is the same or substantially the same as that of the DC-DC converter module  101  illustrated in  FIG. 2 . 
     As described in the present preferred embodiment, a DC-DC converter module may include only the output capacitor C 2 . Alternatively, a DC-DC converter module according to a preferred embodiment of the present invention may include only an input capacitor. 
     The DC-DC converter module  107 B illustrated in  FIG. 13B  is an example of a step-up DC-DC converter module. The basic configuration of the DC-DC converter module  107 B is the same or substantially the same as that of the DC-DC converter module  101  illustrated in  FIG. 2 . 
     The coil L is connected between the voltage input portion Vin and the switching-element-incorporating IC  4 . The switching-element-incorporating IC  4  is connected to the coil L, the voltage output portion Vout, and the first ground electrode G 13 . 
     Specifically, the first end of the coil L is connected to the voltage input portion Vin and the second end of the coil L is connected to the input end IP of the switching-element-incorporating IC  4 . The output end OP of the switching-element-incorporating IC  4  is connected to the voltage output portion Vout and the first ground end GP of the switching-element-incorporating IC 4  is connected to the first ground electrode G 13 . The first end E 1   a  of the input capacitor C 1  is connected to the voltage input portion Vin and the second end E 2   a  of the input capacitor C 1  is connected to the first ground electrode G 11 . The first end E 1   b  of the output capacitor C 2  is connected to the voltage output portion Vout and the second end E 2   b  of the output capacitor C 2  is connected to the first ground electrode G 12 . The shield cover  2  is connected to the second ground electrode G 2 . 
     The DC-DC converter module  107 C illustrated in  FIG. 13C  is an example of a step-up/down DC-DC converter module. The DC-DC converter module  107 C differs from the DC-DC converter module  101  according to the first preferred embodiment in that it includes the first ground electrode G 14 . The remaining configuration is the same or substantially the same as that of the DC-DC converter module  101  illustrated in  FIG. 2 . 
     The switching-element-incorporating IC  4  is connected between the voltage input portion Vin and the voltage output portion Vout. The coil L is connected to the output end OP of the switching-element-incorporating IC  4  and the first ground electrode G 14 . 
     Specifically, the input end IP of the switching-element-incorporating IC  4  is connected to the voltage input portion Vin, the output end OP of the switching-element-incorporating IC  4  is connected to the voltage output portion Vout, and the first ground end GP of the switching-element-incorporating IC 4  is connected to the first ground electrode G 13 . The first end of the coil L is connected to the output end OP of the switching-element-incorporating IC  4  and the second end of the coil L is connected to the first ground electrode G 14 . The first end E 1   a  of the input capacitor C 1  is connected to the voltage input portion Vin and the second end E 2   a  of the input capacitor C 1  is connected to the first ground electrode G 11 . The first end E 1   b  of the output capacitor C 2  is connected to the voltage output portion Vout and the second end E 2   b  of the output capacitor C 2  is connected to the first ground electrode G 12 . The shield cover  2  is connected to the second ground electrode G 2 . 
     The planar shape of the substrate  1  is rectangular or substantially rectangular in the above-described preferred embodiments, but does not necessarily have to be rectangular or substantially rectangular. The planar shape of the substrate  1  may be changed as appropriate within the range in which the advantageous effects of preferred embodiments of the present invention are achieved, and may be, for example, a circle, an ellipse, or a polygon. The shape of the DC-DC converter module is a rectangular or substantially rectangular parallelepiped in the above-described preferred embodiments, but may be changed as appropriate within the range in which the advantageous effects of the present invention are achieved. 
     In the above-described preferred embodiments, the DC-DC converter module includes the coil element  3 , the switching-element-incorporating IC  4 , and the capacitor elements  21  and  22 . However, electronic components included in the DC-DC converter module are not limited to those described above. The number of electronic components included in the DC-DC converter module, the types of the electronic components, and the arrangement of the electronic components may be changed as appropriate within the range in which the advantageous effects of the present invention are achieved. 
     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.