Patent Publication Number: US-2021166896-A1

Title: Switch unit and method for producing switch substrate

Description:
TECHNICAL FIELD 
     The present application relates to a switch unit having noiselessness and a method for producing a switch substrate. 
     BACKGROUND ART 
     Conventionally, a push-type switch device includes: a switch substrate; a contact member formed on the switch substrate; and a pressing member made up of elements such as a conductive flat spring that is brought into contact with the contact member to make a conduction. In this push-type switch device, a switching operation is performed by elastically deforming the pressing member toward the contact member.  FIG. 34  illustrates one example of a switch unit  201 , which constitutes a conventional switch device. The switch unit  201  includes a switch substrate  202 , a first contact point  13 , a second contact point  14 , and a conduction spring member  15 , which is a pressing member. 
     The switch unit  201  is mounted on a mount substrate  23 , such as a mother board. Generally, the switch substrate  202  is made of a hard material such as a glass epoxy substrate (FR-4). The first contact point  13  is provided at a center portion on the switch substrate  202 . The second contact point  14  is provided around the first contact point  13 . The conduction spring member  15  is provided over the first contact point  13  and the second contact point  14 , which are contact members, and is elastically deformable to contact the first contact point  13 , thereby making a conduction between the first contact point  13  and the second contact point  14 . 
     While the pressing member is being pressed, there is a conduction between the pressing member and the contact members. Upon release from the pressing state, the conduction between the pressing member and the contact members is broken. In this press manipulation, contact sound is generated at the time when the pressing member contacts the contact members. This contact sound serves as a way of confirming that a switching is performed reliably. If, however, the contact sound generated is higher than necessary, the contact sound is equivalent to impact sound. 
     In order to reduce such contact sound generated at the time of a switching operation, some switch devices have been proposed that incorporate a material such as a shock-absorbing material and a sound-absorbing material between the switch substrate and the pressing member. Patent document 1 discloses a switch device that includes a cover member, a click sheet, a buffer conductive sheet, and a switch substrate having a fixed contact formed on a surface of the switch substrate. In this cover member, a base and a key top are connected to each other at a skirt. The key top has a plunger that is formed on the lower surface of the key top and that protrudes downward. Patent document 2 and patent document 3 disclose switch devices each including: a switch substrate having a pair of contact members provided on a surface of the switch substrate; a pressing member made of a dome-shaped metal plate having a property of a deformable spring; and a shock-absorbing material provided between the switch substrate and the pressing member. 
     Patent document 4 discloses a touch panel device that includes: a touch panel substrate; a transmitter that transmits an elastic surface wave to the touch panel substrate; a receiver that receives the elastic surface wave that has been transmitted through the touch panel substrate; and a sheet material serving as a pressing member. The sheet material has an input surface and is provided at a distance from the touch panel substrate such that the surface opposite to the input surface faces the touch panel substrate. The sheet material is flexible and includes: a soft layer made of a soft material; and a pair of hard layers made of a hard material harder than the soft material. By pressing the input surface, the pressed portion is partially bent into contact with the touch panel substrate. 
     RELATED ART DOCUMENTS 
     Patent Documents 
     Patent document 1: JP 2001-43772A 
     Patent document 2: JP 2012-243609A 
     Patent document 3: JP 2017-79133A 
     Patent document 4: JP 2009-3672A 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the switch device recited in patent document 1, the buffer conductive sheet is provided on the switch substrate. In this switch device, the buffer conductive sheet is provided with a predetermined degree of hardness to improve click sensitivity. This switch device, however, has no structure that decreases contact sound generated by clicking. In the switch devices recited in patent document 2 and patent document 3, a shock-absorbing material is provided between the switch substrate and the pressing member in order to decrease contact sound generated at the time when the pressing member is pressed into contact with the switch substrate. This shock-absorbing material, however, is made up of an upper sheet and a lower sheet attached to each other via a spacer sheet having a removal hole at a position corresponding to a fixed contact portion. This leaves a gap between the upper sheet and the lower sheet, and the gap may undermine the click sensitivity of the shock-absorbing material. 
     In the touch panel device recited in patent document  4 , the sheet material facing the touch panel substrate is made up of: a hard layer that maintains the shape of the sheet material; and a soft layer covering the hard layer. This configuration decreases the contact sound generated at the time when the sheet material is pressed toward the touch panel substrate. However, the soft layer may absorb the repulsive force generated when the sheet material is pressed toward the touch panel substrate, undermining the click sensitivity of the sheet material. Also, it is not easy to produce a sheet material made up of a soft layer and a hard layer while securing a predetermined distance from the touch panel substrate, and there may be stroke variations occurring when the sheet material is pressed toward the touch panel substrate. 
     In light of the considerations above, it is an object of the present application to provide a switch unit including a switch substrate that decreases contact sound generated at the time of switching without undermining switching operability. 
     Solution to Problem 
     A switch unit according to a first embodiment of the present application includes: a substrate including a hard layer and a soft layer; a first contact point provided on an upper surface of the substrate and above the soft layer; a second contact point provided on the upper surface of the substrate and around the first contact point; a conduction spring member provided in a non-contact state with the first contact point above the first contact point and in contact state with the second contact point, the conduction spring member being elastically deformable into contact with the first contact point to make a conduction between the first contact point and the second contact point; a first external electrode provided at an end portion of the substrate; a first through-hole electrode provided at an inside portion of the substrate and electrically connected to the first contact point; and a first wiring pattern provided on a lower surface of the substrate and electrically connected to the first external electrode and the first through-hole electrode. 
     A switch unit according to a second embodiment of the present application includes: a substrate including a hard layer and a soft layer; a first contact point provided on an upper surface of the substrate and above the soft layer; a second contact point provided on the upper surface of the substrate and around the first contact point; a conduction spring member provided in a non-contact state with the first contact point above the first contact point and in contact state with the second contact point, the conduction spring member being elastically deformable into contact with the first contact point to make a conduction between the first contact point and the second contact point; a first external electrode and a second external electrode provided at end portions of the substrate; a first connection electrode provided at an inside portion of the substrate and electrically connecting the first contact point and the first external electrode to each other; and a second connection electrode provided at an inside portion of the substrate and electrically connecting the second contact point and the second external electrode to each other. 
     A switch unit according to a third embodiment of the present application includes a substrate, a first contact point, a second contact point, and a conduction spring member. The substrate includes: a cavity formed in the substrate; an opening formed on an upper surface of the substrate; and a connection hole connecting the opening and the cavity to each other. The first contact point is provided on the upper surface of the substrate. The second contact point is provided around the first contact point. The conduction spring member is provided in a non-contact state with the first contact point above the first contact point and in contact state with the second contact point, the conduction spring member being elastically deformable into contact with the first contact point to make a conduction between the first contact point and the second contact point. A maximum value of a sectional area of the connection hole parallel to the upper surface of the substrate is smaller than a maximum value of a sectional area of the cavity parallel to the upper surface of the substrate. 
     A method for producing the switch substrate according to the first embodiment of the present application includes a forming step of obtaining an aggregate switch substrate by forming a soft layer on a lower surface of an aggregate switch substrate member. The aggregate switch substrate member includes: an aggregate substrate including a hard layer; a plurality of first contact points provided on an upper surface of the aggregate substrate; a plurality of second contact points provided on the upper surface of the aggregate substrate and around the respective first contact points; a plurality of first through-hole electrodes provided at an inside portion of the aggregate substrate and electrically connected to the respective first contact points; a plurality of second through-hole electrodes electrically connected to the respective second contact points; a plurality of through holes extending between the upper surface and a lower surface of the aggregate substrate, each through hole of the through holes including a conduction layer as a side surface of the each through hole; a plurality of first wiring patterns provided on a lower surface of the aggregate substrate, each first wiring pattern of the first wiring patterns being electrically connected to the conduction layer and each first through-hole electrode of the first through-hole electrodes; and a plurality of second wiring patterns each electrically connected to the conduction layer and each second through-hole electrode of the second through-hole electrodes. The soft layer covers at least portions immediately under the plurality of first contact points, and does not cover the plurality of through holes. The method also includes a cutting step of obtaining individual switch substrates by cutting the aggregate switch substrate through at least the plurality of through holes. 
     A method for producing the switch substrate according to the second embodiment of the present application includes a joining step of obtaining an aggregate switch substrate by joining a first aggregate substrate and a second aggregate substrate to each other. The first aggregate substrate includes: a plurality of first contact points formed on an upper surface of the first aggregate substrate; a plurality of second contact points provided around the respective first contact points and formed on the upper surface of the first aggregate substrate; and a plurality of through holes. The second aggregate substrate includes a plurality of cavities open on an upper surface of the second aggregate substrate. A maximum value of a sectional area of each of the cavities parallel to the upper surface of the first aggregate substrate is larger than a maximum value of a sectional area of each of the through holes parallel to the upper surface of the first aggregate substrate. The plurality of through holes overlap the plurality of respective cavities in a vertical direction. The method also includes a cutting step of obtaining individual switch substrates by cutting the aggregate switch substrate. 
     Advantageous Effects of Invention 
     In the switch unit according to the first embodiment of the present application, the substrate includes a hard layer and a soft layer, and a first contact point is provided above the soft layer. This configuration ensures that the pressing force of pressing the conduction spring member is supported by the hard layer, and that the soft layer absorbs: the contact sound generated at the time when the conduction spring member contacts the first contact point; and the sound that is caused when a vibration involved in the collision of the conduction spring member with the first contact point is amplified and caused to propagate from the substrate. Thus, the switch unit according to the first embodiment decreases, without undermining switching operability: the contact sound generated at the time when the conduction spring member and the first contact point contact each other; and the sound that is caused when a vibration involved in the collision of the conduction spring member with the first contact point is amplified and caused to propagate from the substrate. 
     In the switch unit according to the third embodiment of the present application, sound generated near the first contact point is absorbed in, through the connection hole, the cavity extending between the opening formed on the upper surface of the substrate and the inside of the substrate. With this configuration, the switch unit according to the third embodiment decreases: the contact sound generated at the time when the conduction spring member and the first contact point contact each other; and the sound that is caused when a vibration involved in the collision of the conduction spring member with the first contact point is amplified and caused to propagate from the substrate. 
     In the method for producing the switch substrate according to the present application, an aggregate switch substrate is cut to obtain a switch substrate used in a switch unit having noiselessness. This ensures that a switch substrate used in a switch unit having noiselessness is efficiently produced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a sectional view of a switch unit according to the first embodiment. 
         FIG. 2  is a sectional view of a switch device including the switch unit according to the first embodiment. 
         FIG. 3  is an exploded perspective view of the switch device including the switch unit according to the first embodiment. 
         FIG. 4  is a sectional view of a switch unit according to the second embodiment. 
         FIG. 5  is a sectional view of a switch unit according to the third embodiment. 
         FIG. 6  is a bottom view of the switch unit according to the third embodiment. 
         FIG. 7  is a sectional view of a switch unit according to the fourth embodiment. 
         FIG. 8  is a sectional view of a switch unit according to the fifth embodiment. 
         FIG. 9  is a sectional view of a switch unit according to the sixth embodiment. 
         FIG. 10  is a sectional view of a switch unit according to the seventh embodiment. 
         FIG. 11  is a sectional view of a switch unit according to the eighth embodiment. 
         FIG. 12  is a sectional view of a switch unit according to the ninth embodiment. 
         FIG. 13  is a plan view of an aggregate switch substrate member used as a material of a switch substrate of the switch unit according to the third embodiment. 
         FIG. 14  is a sectional view of the aggregate switch substrate member used as the material of the switch substrate of the switch unit according to the third embodiment. 
         FIG. 15  is a bottom view of the aggregate switch substrate member used as the material of the switch substrate of the switch unit according to the third embodiment. 
         FIG. 16  is a sectional view of the aggregate switch substrate member used as the material of the switch substrate of the switch unit according to the third embodiment. 
         FIG. 17  is a bottom view of the aggregate switch substrate member used as the material of the switch substrate of the switch unit according to the third embodiment. 
         FIG. 18  is a sectional view of a switch unit according to the tenth embodiment. 
         FIG. 19  is a sectional view of a switch device including the switch unit according to the tenth embodiment. 
         FIG. 20  is an exploded perspective view of the switch device including the switch unit according to the tenth embodiment. 
         FIG. 21( a )  is a partial sectional view of the switch unit according to the tenth embodiment.  FIG. 21( b )  is a partial sectional view of a switch unit according to a modification of the tenth embodiment. 
         FIG. 22( a )  is an exploded partial perspective view of a first substrate member and a second substrate member of the switch unit according to the tenth embodiment.  FIG. 22( b )  is a partial perspective view of a substrate of the switch unit according to the tenth embodiment. 
         FIG. 23  is a partial plan view of the substrate of the switch unit according to the tenth embodiment. 
         FIG. 24( a )  is a partial plan view of a substrate of a switch unit according to the eleventh embodiment.  FIG. 24( b )  is a partial sectional view of the substrate of the switch unit according to the eleventh embodiment. 
         FIG. 25  is a partial plan view of a substrate of a switch unit according to the twelfth embodiment. 
         FIG. 26( a )  is a partial plan view of a substrate of a switch unit according to the thirteenth embodiment.  FIG. 26( b )  is a partial plan view of a substrate of a switch unit according to the fourteenth embodiment. 
         FIG. 27( a )  is a partial plan view of a substrate of a switch unit according to the fifteenth embodiment.  FIG. 27( b )  is a partial sectional view of the substrate of the switch unit according to the fifteenth embodiment. 
         FIG. 28( a )  is a partial plan view of a substrate of a switch unit according to the sixteenth embodiment.  FIG. 28( b )  is a partial sectional view of the substrate of the switch unit according to the sixteenth embodiment. 
         FIG. 29  is a sectional view of a three-layer structure substrate of a switch unit according to another embodiment. 
         FIG. 30( a )  is a partial perspective view of an aggregate first substrate having a plurality of connection holes and an aggregate second substrate having a plurality of cavities.  FIG. 30( b )  is a partial perspective view of an aggregate substrate in which the aggregate first substrate and the aggregate second substrate are joined to each other. 
         FIG. 31  is a plan view of an aggregate switch substrate member used as a material of a switch substrate of the switch unit according to the tenth embodiment. 
         FIG. 32  is a sectional view of the aggregate switch substrate member used as the material of the switch substrate of the switch unit according to the tenth embodiment. 
         FIG. 33  is a bottom view of the aggregate switch substrate member used as the material of the switch substrate of the switch unit according to the tenth embodiment. 
         FIG. 34  is a sectional view of a switch unit using a conventional switch substrate. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     By referring to embodiments and drawings, detailed description will be made below with regard to a switch unit according to the present application and a method according to the present application for producing a switch substrate. It is to be noted that the drawings are schematic representations of a switch unit, a switch substrate, constituent elements of the switch unit and the switch substrate, and peripheral elements of the switch unit and the switch substrate. It is also to be noted that the dimensions and dimension ratios on the drawings may not necessarily be actual dimensions and dimension ratios. It is also to be noted that descriptions deemed redundant will not be repeated, as the case may be, and identical reference numerals will be assigned to identical elements. In the present application, by way of description, vertical directions and lateral directions are defined based on the directions indicated in the drawings, such as  FIGS. 1, 11, and 18 , unless noted otherwise. 
       FIG. 1  illustrates a basic configuration of a switch unit  11  according to the first embodiment of the present application. The switch unit  11  is provided on a mount substrate  23 , such as a mother board. The switch unit  11  includes a substrate  12 , a first contact point  13 , a second contact point  14 , and a conduction spring member  15 . The substrate  12  includes a hard layer  12   a  and a soft layer  12   b.  The first contact point  13  is provided at the center of the upper surface of the substrate  12 . The second contact point  14  is provided on the upper surface of the substrate  12  and around the first contact point  13 . 
     The conduction spring member  15  is out of contact with the first contact point  13  above the first contact point  13 _and is in contact with the second contact point  14 . Specifically, the conduction spring member  15  is mounted on the upper surface of the second contact point  14  at an outer circumference portion of the conduction spring member  15 , and faces the first contact point  13  at a center portion of the conduction spring member  15 . The conduction spring member  15  is elastically deformable into contact with the first contact point  13  to make a conduction between the first contact point  13  and the second contact point  14 . That is, the conduction spring member  15  serves as a pressing member of the switch unit  11 . 
       FIG. 2  illustrates a sectional structure of a switch device  10 , which includes the switch unit  11 .  FIG. 3  illustrates an exploded structure of the switch device  10 . As illustrated in  FIGS. 2 and 3 , a frame sheet  18  is provided on the substrate  12 . The frame sheet  18  has, at its center, an opening  18   a,  which has a large quadrangular shape. The opening  18   a  contains the conduction spring member  15 . The conduction spring member  15  has a size corresponding to the opening  18   a  and has a dome shape. The switch device  10  includes a pressing aid member  21  over the switch unit  11 . The pressing aid member  21  includes: a flexible cover sheet  17 , which covers the upper surface of the switch unit  11 ; and a pressing protrusion  26 , which is provided over the cover sheet  17 . 
     The cover sheet  17  is made up of a thin resin sheet of polyimide or phthalamide. On the inner surface of the cover sheet  17 , a pressing element  16  is provided in advance. The pressing element  16  is in contact with an apex portion  15   a  of the conduction spring member  15 . The pressing element  16  is provided for the purpose of reinforcing the pressing point of the apex portion  15   a.  The shape of the pressing element  16  may be other than the cylindrical shape illustrated in  FIG. 3  and may be a protrusion shape such as a dome shape. The cover sheet  17  covers the conduction spring member  15  via the pressing element  16 . 
     That is, as illustrated in  FIGS. 2 and 3 , the conduction spring member  15  is covered by the cover sheet  17 , which includes the pressing element  16 , which contacts the apex portion  15   a.  The circumference of the cover sheet  17  is bonded to the upper surface of the frame sheet  18 . The cover sheet  17  may be mounted on the conduction spring member  15  in such a manner that the cover sheet  17  and the conduction spring member  15  are hot pressed to each other with the pressing element  16  housed in the cover sheet  17 , whereby the cover sheet  17  and the conduction spring member  15  are integral to each other. 
     The substrate  12  includes: the upper hard layer  12   a,  on which the first contact point  13  and the second contact point  14  are provided; and the lower soft layer  12   b.  That is, as illustrated in  FIG. 1 , the substrate  12  according to the first embodiment has a two-layer structure made up of the upper hard layer  12   a  and the lower soft layer  12   b.  It is to be noted that the soft layer  12   b  is lower in hardness than the hard layer  12   a.  The hard layer  12   a  and the soft layer  12   b  have approximately the same shapes. The hard layer  12   a  and the soft layer  12   b  may be joined to each other by: radiating ultrasonic or laser to their joint surfaces; or via a bonding layer such as a binder or a bonding sheet (neither of which is illustrated) of epoxy resin or acrylic resin. 
     The first contact point  13  and the second contact point  14  may be prepared by patterning such as etching of an electrode film, such as copper foil, formed on the upper surface of the hard layer  12   a.  At both end portions of the substrate  12 , a first external electrode  20   a  and a second external electrode  20   b  are provided respectively. At an inside portion of the substrate  12 , a first through-hole electrode  22   a  and a second through-hole electrode  22   b  are provided. The first through-hole electrode  22   a  is electrically connected to the first contact point  13 , and the second through-hole electrode  22   b  is electrically connected to the second contact point  14 . That is, the first through-hole electrode  22   a  and the second through-hole electrode  22   b  of the switch unit  11  penetrate the substrate  12 . 
     Also, on the lower surface of the substrate  12 , that is, on the lower surface of the soft layer  12   b,  a first wiring pattern  19   b  and a second wiring pattern  19   b  are provided. The first wiring pattern  19   b  is electrically connected to the first external electrode  20   a  and the first through-hole electrode  22   a,  and the second wiring pattern  19   b  is electrically connected to the second external electrode  20   b  and the second through-hole electrode  22   b.  The first wiring pattern  19   b  and the second wiring pattern  19   b  may be prepared by patterning such as etching of an electrode film, such as copper foil, formed on the lower surface of the soft layer  12   b.  Also, the first external electrode  20   a  and the second external electrode  20   b  may be prepared by patterning such as etching of an electrode film, such as copper foil, formed on the side surfaces of the hard layer  12   a  and the soft layer  12   b.    
     The conduction spring member  15  is made up of elements such as a metal takt spring having a dome shape. The conduction spring member  15 , at its center portion, is out of contact with the first contact point  13  while no external force is being added to the conduction spring member  15 . As illustrated in  FIG. 1 , a switching operation is performed by pressing and elastically deforming the apex portion  15   a  of the conduction spring member  15  in the direction indicated by arrow line P, thereby bringing the reverse apex portion  15   a  into contact with the first contact point  13 . 
     Since the upper part of the substrate  12  is the hard layer  12   a,  the first contact point  13  is able to reliably receive the pressing force from the conduction spring member  15 . This ensures a stable switching stroke of the switch unit  11 , resulting in a reliable switching operation. Also, the soft layer  12   b  is provided at a lower portion of the hard layer  12   a  and under the first contact point  13 ; in the first embodiment, the soft layer  12   b  is provided immediately under the first contact point  13 . This configuration enables the soft layer  12   b  to absorb: the contact sound generated at the time when the conduction spring member  15  contacts the first contact point  13  (the contact sound generated at the time when the conduction spring member contacts the first contact point will be hereinafter occasionally referred to simply as “contact sound”); and the sound that is caused when a vibration involved in the collision of the conduction spring member  15  with the first contact point  13  amplified and caused to propagate from the substrate  12  (the sound that is caused when a vibration involved in the collision of the conduction spring member with the first contact point is amplified and caused to propagate from the substrate will be hereinafter occasionally referred to as “amplification sound”). 
     Thus, the switch unit  11  has reliable switchability and noiselessness. It is to be noted that there is no particular limitation to the layer thicknesses of the hard layer  12   a  and the soft layer  12   b.  It is preferable, however, that the hard layer  12   a  has a substantial degree of thickness, since the strength of the substrate as a whole and switching stability depend on the hard layer  12   a.  In contrast, the soft layer  12   b  may be thinner than the hard layer  12   a,  since it is sufficient for the soft layer  12   b  to be thick enough to absorb the contact sound and the amplification sound generated at the time when the conduction spring member  15  contacts the first contact point. 
     The hard layer  12   a  may be made of, for example, glass epoxy resin such as FR- 4 . The soft layer  12   b  may be made of, for example, polyimide resin. The soft layer  12   b  is preferably made of polyimide resin having a Rockwell hardness of from 30 to 130 HRM. It is to be noted that there is no limitation to the materials of the hard layer  12   a  and the soft layer  12   b  insofar as the materials have an insulating property and have a hardness approximately equivalent to the hardnesses of glass epoxy resin and polyimide resin. 
       FIG. 4  illustrates a switch unit  31  according to the second embodiment of the present application. In the switch unit  31 , a substrate  32  includes: a pair of an upper hard layer  12   a  and a lower hard layer  12   c;  and a soft layer  12   b,  which is held between the pair of hard layers  12   a  and  12   c.  That is, as illustrated in  FIG. 4 , in the second embodiment, the substrate  32  has a three-layer structure made up of the hard layers  12   a  and  12   c  and the soft layer  12   b.  The hard layers  12   a  and  12   c  and the soft layer  12   b  have approximately same shapes. 
     Similarly to the substrate  12  according to the first embodiment, the soft layer  12   b  is provided under the first contact point  13 ; in the second embodiment, the soft layer  12   b  is provided immediately under the first contact point  13 . This configuration enables the soft layer  12   b  to absorb the contact sound and the amplification sound, keeping the switch unit  31  noiseless. Further, in the switch unit  31 , the pair of upper and lower hard layers  12   a  and  12   c  receive the press of the conduction spring member  15  to provide excellent click sensitivity. 
     Also, a hard layer,  12   c,  is also provided on the lower surface of the soft layer  12   b.  This improves the workability with which the switch unit  31  is mounted on the mount substrate  23 , such as a mother board. Further, at least one of the hard layer  12   a  and the hard layer  12   c  may be thinner. Similarly to the first embodiment, the pair of hard layers  12   a  and  12   c  and the soft layer  12   b  may be joined to each other by: radiating ultrasonic or laser to their joint surfaces; or via bonding layers such as binders or bonding sheets (neither of which is illustrated) of epoxy resin or acrylic resin. 
       FIGS. 5 and 6  illustrate a switch unit  41  according to the third embodiment of the present application. In the switch unit  41 , a substrate  42  includes an upper hard layer  12   a  and a lower soft layer  12   d.  That is, as illustrated in  FIG. 5 , the substrate  42  according to the third embodiment has a two-layer structure made up of the hard layer  12   a  and the soft layer  12   d.  On the lower surface of the hard layer  12   a,  a first wiring pattern  19   b  is provided. The first wiring pattern  19   b  is electrically connected to the first contact point  13  via the first through-hole electrode  22   a,  which penetrates the hard layer  12   a.  Also, on the lower surface of the hard layer  12   a,  a second wiring pattern  19   b  is provided. The second wiring pattern  19   b  is electrically connected to the second contact point  14  via the second through-hole electrode  22   b,  which penetrates the hard layer  12   a.    
     As illustrated in  FIG. 6 , the first wiring pattern  19   b  connects the first through-hole electrode  22   a  of the first contact point  13  to the first external electrode  20   a,  which is provided at one end portion of the substrate  42 . Also, the second wiring pattern  19   b  connects the second through-hole electrode  22   b  of the second contact point  14  to the second external electrode  20   b,  which is provided at another end portion of the substrate  42 . In the third embodiment, the first wiring pattern  19   b  and the second wiring pattern  19   b  are thin and linear conduction patterns. With this configuration, the area of the first wiring pattern  19   b  and the second wiring pattern  19   b  combined is quite smaller than the area of the soft layer  12   d.  It is to be noted that the wiring patterns in the first embodiment and the second embodiment may be thin and linear conduction patterns, similarly to the third embodiment. 
     In the third embodiment, in a plan view, the outer circumference of the first contact point  13  is located at a position inner than the right and left outer circumferences  12   d ′ of the soft layer  12   d.  Also, the right and left outer circumferences  12   d ′ of the soft layer  12   d  are located at positions inner than the right and left outer circumferences  12   a ′ of the hard layer  12   a.  More specifically, the right and left outer circumferences  12   d ′ of the soft layer  12   d  are located at positions close to and inner than the first external electrode  20   a  and the second external electrode  20   b,  which are provided at both end portions of the hard layer  12   a.  Alternatively, the right and left outer circumferences  12   d ′ of the soft layer  12   d  may be located at positions further inner than the first external electrode  20   a  and the second external electrode  20   b;  for example, inner than the second contact point  14 . The soft layer  12   d  is joined to the lower surface of the hard layer  12   a  via a bonding layer  12   e,  which is a bonding material or a bonding sheet such as epoxy resin and acrylic resin. 
     The switch unit  41  according to the third embodiment is similar to the switch unit  11  and the switch unit  31  in that the soft layer  12   d  provided immediately under the first contact point  13  absorbs the contact sound and the amplification sound, ensuring noiselessness of the switch unit  41 . Also, the hard layer  12   a  receives the press of the conduction spring member  15  to enable the switch unit  41  to provide excellent click sensitivity. Also as illustrated in  FIG. 5 , the soft layer  12   d  covers a lower portion of the hard layer  12   a  including the first wiring pattern  19   b  and the second wiring pattern  19   b.  With this configuration, the switch unit  41  ensures that the soft layer  12   d  effectively absorbs the contact sound and the amplification sound without undermining the click sensitivity intended to be felt when the conduction spring member  15  is pressed. 
     Further, in the third embodiment, the first wiring pattern  19   b  and the second wiring pattern  19   b  are linear patterns which are narrow in width. The wiring pattern area of the first wiring pattern  19   b  and the second wiring pattern  19   b  combined is quite smaller than the area of the soft layer  12   d.  This eliminates or minimizes a situation in which contact sound and amplification sound are generated by the first wiring pattern  19   b  and the second wiring pattern  19   b,  which are hard patterns made of copper foil. 
     In the third embodiment, the first wiring pattern  19   b  and the second wiring pattern  19   b  are narrow in width linear patterns so that a shortest connection distance is realized between the first through-hole electrode  22   a  and the first external electrode  20   a  and between the second through-hole electrode  22   b  and the second external electrode  20   b.  It is possible, however, to set the wiring patterns in any other desired manner in terms of thickness, shape, and area. From the viewpoint of the switch unit  41 &#39;s noiselessness, however, the wiring pattern area of the first wiring pattern  19   b  and the second wiring pattern  19   b  combined is preferably smaller than the area of the soft layer  12   d.    
       FIG. 7  illustrates a switch unit  51  according to the fourth embodiment of the present application. The switch unit  51  has a configuration approximately the same as the configuration of the switch unit  41  according to the third embodiment except that a through hole  53  is formed at the center of a soft layer  12   f  In the fourth embodiment, the soft layer  12   f  has the through hole  53 . The area of the through hole  53  is larger than the area of the first contact point  13 . However, there is no particular limitation to how large the area of the through hole  53  is. For example, the area of the through hole  53  may be smaller than the area of the first contact point  13 . 
     The through hole  53  is preferably positioned immediately under the first contact point  13 . The shape of the through hole  53  may be a circular shape or a polygonal shape such as a rectangle. In the fourth embodiment, the substrate  52  has a two-layer structure made up of the hard layer  12   a  and the soft layer  12   f,  and the through hole  53  of the soft layer  12   f  is provided immediately under the first contact point  13 . This configuration enables the soft layer  12   f  to absorb the contact sound and the amplification sound. Further, the contact sound and the amplification sound can be externally released through the through hole  53 . This increases the reliability with which noiselessness of the switch unit  51  is ensured. It is to be noted that the soft layer  12   f  is joined to the lower surface of the hard layer  12   a  via the bonding layer  12   e.    
       FIG. 8  illustrates a switch unit  61  according to the fifth embodiment of the present application. In the switch unit  61 , a substrate  62  includes: a hard layer  12   a,  which is provided at an upper portion of the substrate  62 ; and a soft layer  12   g,  which is provided at a lower portion of the substrate  62 . That is, as illustrated in  FIG. 8 , the substrate  62  according to the fifth embodiment has a two-layer structure made up of the hard layer  12   a  and the soft layer  12   g.  The switch unit  61  has a configuration approximately the same as the configuration of the switch unit  41  according to the third embodiment except that in a plan view, the outer circumference of the soft layer  12   g  is located at a position inner than the outer circumference of the first contact point  13 . 
     As illustrated in  FIG. 8 , even though the soft layer  12   g  is smaller than the first contact point  13 , by providing the soft layer  12   g  immediately under the first contact point  13 , the soft layer  12   g  is able to reliably absorb the contact sound and the amplification sound. The shape of the soft layer  12   g  may be a circular shape or a polygonal shape such as a rectangle. Thus, the substrate  62  has a two-layer structure made up of the hard layer  12   a  and the soft layer  12   g,  and the soft layer  12   g  is provided immediately under the first contact point  13 . This configuration enables the soft layer  12   g  to absorb the contact sound and the amplification sound, ensuring noiselessness of the switch unit  61 . The soft layer  12   g  is joined to the lower surface of the hard layer  12   a  via the bonding layer  12   e.  It is to be noted that in a plan view, a size of the outer circumference of the soft layer  12   g  may be identical to a size of the outer circumference of the first contact point  13 . 
       FIG. 9  illustrates a switch unit  71  according to the sixth embodiment of the present application. As illustrated in  FIG. 9 , in the switch unit  71 , a substrate  72  includes: a soft layer  12   h,  which is in contact with the lower surface of the first contact point  13 ; and a hard layer  12   a,  which is in contact with the lower surface of the second contact point  14  and provided around the soft layer  12   h.  In the switch unit  71 , since the soft layer  12   h  is provided immediately under the first contact point  13 , the soft layer  12   h  reliably absorbs the contact sound and the amplification sound. 
       FIG. 10  illustrates a switch unit  81  according to the seventh embodiment of the present application. As illustrated in  FIG. 10 , in the switch unit  81 , a substrate  82  includes: a soft layer  12   j,  which is in contact with the lower surface of the first contact point  13 ; and a hard layer  12   a,  which is in contact with the lower surface of the second contact point  14  and provided around the soft layer  12   j.  The soft layer  12   j  is thinner than the hard layer  12   a.  In the switch unit  81 , since the soft layer  12   j  is provided immediately under the first contact point  13 , the soft layer  12   j  reliably absorbs the contact sound and the amplification sound. 
     The switch units  11 ,  31 ,  41 ,  51 ,  61 ,  71 , and  81  are also applicable to switch devices using lead frames.  FIG. 11  illustrates a switch unit  91  according to the eighth embodiment of the present application. The switch unit  91  includes a lead frame. The switch unit  91  includes a substrate  92 , a first contact point  13 , a second contact point  14 , a conduction spring member  15 , a first external electrode  27   a,  a second external electrode  27   b,  a first connection electrode  28   a,  and a second connection electrode  28   b.  The substrate  92  includes a hard layer  12   a  and a soft layer  12   k,  which is provided on the lower surface of the hard layer  12   a.    
     The first contact point  13  is provided on the upper surface of the substrate  92  and above the soft layer  12   k.  The first contact point  14  is provided on the upper surface of the substrate  92  and around the first contact point  14 . The conduction spring member  15  is provided above the first contact point  13  in a non-contact state with the first contact point  13 , and in a contact state with the second contact point  14 . And the conduction spring member  15  is elastically deformable into contact with the first contact point  13  to make a conduction between the first contact point  13  and the second contact point  14 . The first external electrode  27   a  and the second external electrode  27   b  are provided at end portions of the substrate  92 . 
     The first connection electrode  28   a  is provided at an inside portion of the substrate  92 , and electrically connects the first contact point  13  and the first external electrode  27   a  to each other. The second connection electrode  28   b  is provided at an inside portion of the substrate  92 , and electrically connects the second contact point  14  and the second external electrode  27   b  to each other. The switch unit  91  is mounted on the mount substrate  23 , such as a mother board, via the soft layer  12   k.  In the switch unit  91 , since the soft layer  12   k  is provided under the first contact point  13 , the soft layer  12   k  reliably absorbs the contact sound and the amplification sound. 
       FIG. 12  illustrates a switch unit  101  according to the ninth embodiment of the present application. The switch unit  101  includes a lead frame. The switch unit  101  has a configuration approximately the same as the configuration of the switch unit  91  according to the eighth embodiment except that the hard layer  12   a  also exists around a soft layer  12   m.  The substrate  102  includes the hard layer  12   a  and the soft layer  12   m,  which is provided on the lower surface of the hard layer  12   a.  In the switch unit  101 , since the soft layer  12   m  is provided under the first contact point  13 , the soft layer  12   m  reliably absorbs the contact sound and the amplification sound. 
     By referring to  FIGS. 13 to 17 , description will be made with regard to a method for producing a switch substrate  43  using an aggregation method.  FIG. 13  illustrates the upper surface of an aggregate switch substrate member  44 , which is a material of the switch substrate  43 , which constitutes the switch unit  41  according to the third embodiment.  FIG. 14  is a sectional view of the aggregate switch substrate member  44 .  FIG. 15  illustrates the lower surface of the aggregate switch substrate member  44 . The aggregate switch substrate member  44  includes an aggregate substrate  45 , a plurality of first contact points  13 , a plurality of second contact points  14 , a plurality of first through-hole electrodes  22   a,  a plurality of second through-hole electrodes  22   b,  a plurality of through holes  46 , a plurality of first wiring patterns  19   a,  and a plurality of second wiring patterns  19   b.    
     The aggregate substrate  45  is made up of a hard layer  12   a.  The plurality of first contact points  13  are provided on the upper surface of the aggregate substrate  45 . The plurality of second contact points  14  are provided on the upper surface of the aggregate substrate  45  and provided around the respective first contact points  13 . The plurality of first through-hole electrodes  22   a  are provided at an inside portion of the aggregate substrate  45  and electrically connected to the respective first contact points  13 . The plurality of second through-hole electrodes  22   b  are electrically connected to the respective second contact points  14 . 
     The plurality of through holes  46  extend between the upper surface and the lower surface of the aggregate substrate  45 , and conduction layers  47  are provided on the side surfaces of the through holes  46 . The plurality of first wiring patterns  19   a  are provided on the lower surface of the aggregate substrate  45  and electrically connected to the respective conduction layers  47  and the respective first through-hole electrodes  22   a.  The plurality of second wiring patterns  19   b  are electrically connected to the respective conduction layers  47  and the respective second through-hole electrodes  22   b.  The method for producing the switch substrate  43  includes a forming step and a cutting step. 
     In the forming step, an aggregate switch substrate  49  is obtained by forming a soft layer  48  on the lower surface of the aggregate switch substrate member  44  in such a manner that the soft layer  48  covers a portion located at least immediately under the plurality of first contact points  13  and does not cover the plurality of through holes  46 .  FIG. 16  is a sectional view of the aggregate switch substrate  49  as of the time after the forming step.  FIG. 16  is a sectional view of the aggregate switch substrate  49  as of the time after the forming step.  FIG. 17  illustrates the lower surface of the aggregate switch substrate  49  as of the time after the forming step. In the cutting step, individual switch substrates  43  are obtained by cutting the aggregate switch substrate  49  along the lattice-shaped broken lines illustrated in  FIG. 17  and through at least the plurality of through holes  46 . By the cutting step, the through hole  46  is divided into the first external electrode  20   a  and the second external electrode  20   b.    
     The switch substrate  43  thus obtained includes: a substrate  45 ′, which includes the hard layer  12   a  and the soft layer  48 ; the first contact point  13 ; the second contact point  14 ; the first through-hole electrode  22   a;  the second through-hole electrode  22   b;  the first external electrode  20   a;  the second external electrode  20   b;  the first wiring pattern  19   a;  and the second wiring pattern  19   b.  The forming step may include a step of bonding, to the lower surface of the aggregate switch substrate member  44 , a plurality of soft plates  48 ′ in a stripe arrangement. The soft plates  48 ′ are made up of the soft layer  48 . By this step, the soft layer  48  is efficiently formed on the lower surface of the aggregate substrate  45 , which is made up of the hard layer  12   a.    
       FIG. 18  illustrates a switch unit  111  according to the tenth embodiment of the present application. The switch unit  111  includes a substrate  112 , a first contact point  13 , a second contact point  14 , and a conduction spring member  15 ′. The substrate  112  is mounted on the mount substrate  23 , such as a mother board. The substrate  112  includes a first substrate member  112   a  and a second substrate member  112   b.  On the back surface of the second substrate member  112   b,  a pair of external electrodes  19  and  20  are formed. 
     The substrate  112  includes: a cavity  132 , which is formed inside the substrate  112 ; an opening  134 , which is formed on the upper surface of the substrate  112 , and a connection hole  133   a,  which connects the opening  134  and the cavity  132  to each other. The first contact point  13  is provided on the upper surface of the substrate  112 . The second contact point  14  is provided around the first contact point  13 . The conduction spring member  15 ′ is provided above the first contact point  13  in a non-contact state with the first contact point  13  and in a contact state with the second contact point  14 . And the conduction spring member  15 ′ is elastically deformable into contact with the first contact point  13  to make a conduction between the first contact point  13  and the second contact point  14 . The second contact point  14  is electrically connected to the external electrode  19  via a through hole  22 , which penetrates the substrate  112 . 
       FIG. 19  illustrates a sectional structure of a switch device  110 , which includes the switch unit  111 .  FIG. 20  illustrates an exploded structure of the switch device  110 .  FIG. 21( a )  is a partial sectional view of the substrate  112 , which includes the opening  134 , the connection hole  133   a,  and the cavity  132 .  FIG. 21( b )  is a partial sectional view of a substrate  112 ′, which is a modification of the substrate  112  and includes the opening  134 , a connection hole  133   b,  and the cavity  132 . The configuration of the switch device  110  from the pressing element  16  up is the same as the configuration of the switch device  10  from the pressing element  16  up. The switch device  10  includes the switch unit  11  according to the first embodiment. Therefore, the configuration of the switch device  110  from the pressing element  16  up will not be elaborated upon here. The shape of the conduction spring member  15 ′ is a circular dome shape. 
     As illustrated in  FIG. 19 , the substrate  112  includes the first substrate member  112   a  and the second substrate member  112   b,  which is provided under the first substrate member  112   a.  The first contact point  13  and the second contact point  14  are provided on the upper surface of the first substrate member  112   a.  The opening  134  and the connection hole  133   a  are formed in the first substrate member  112   a,  and the cavity  132  is formed in the second substrate member  112   b.  The cavity  132  has such a depth that the cavity  132  does not penetrate the second substrate member  112   b.  The connection hole  133   a  penetrates the first substrate member  112   a.    
       FIG. 22( a )  illustrates an exploded structure of part of the first substrate member  112   a  and the second substrate member  112   b.    FIG. 22( b )  illustrates part of the substrate  112 . As illustrated in  FIG. 22( b ) , the opening  134  is formed on the upper surface of the first substrate member  112   a  in such a manner that the opening  134  circumvents the first contact point  13  and the second contact point  14 . Then, as illustrated in  FIG. 22( a ) , the first substrate member  112   a  and the second substrate member  112   b  are joined to each other in such a manner that the opening  134  overlaps an opening  135  of the cavity  132 . 
       FIG. 23  illustrates the upper surface of part of the substrate  112 . As illustrated in  FIG. 23 , the maximum value of the sectional area of the connection hole  133   a  parallel to the upper surface of the substrate  112  is smaller than the maximum value of the sectional area of the cavity  132  parallel to the upper surface of the substrate  112 . That is, the sectional area in a plan view of the connection hole  133   a  is smaller than the sectional area in a plan view of the cavity  132 . The length of the connection hole  133   a  is determined by the thickness of the first substrate member  112   a.    
     The opening  134 , the connection hole  133   a,  and the cavity  132  constitute a silencer  131   a.  Also, the opening  134 , the connection hole  133   b,  and the cavity  132  constitute a silencer  131   b.  The silencer  131   a  is formed based on the principle of a Helmholtz resonator. An operation of the silencer  131   a  will be described below by referring to  FIG. 21( a ) . By a switching operation, the conduction spring member  15  is brought into contact with the first contact point  13 , generating a sound. This sound is accompanied by a puff of air, and the air is guided through the narrow opening  134  and the connection hole  133   a  and pressed into the cavity  132 . Pressed in the cavity  132 , the air has nowhere to go further and is pressed back toward the opening  134 . Pressed back out of the opening  134 , the air turns into negative pressure and is pressed again toward the cavity  132  through the opening  134 . By repeating this set of movements, an air friction is generated in the connection hole  133   a  and causes the contact sound to attenuate. 
     The connection hole  133   a  of the silencer  131   a  illustrated in  FIG. 22  penetrates the first substrate member  112   a  in a direction perpendicular to the upper surface of the first substrate member  112   a.  Alternatively, the connection hole  133   b  may be formed in a direction inclined relative to the upper surface of the first substrate member  112   a,  similarly to the silencer  131   b  illustrated in  FIG. 21( b ) . Thus, by forming the inclined connection hole  133   b,  the ventilation passage to the cavity  132  can be made longer. This ensures that a thin material can be employed as the first substrate member  112   a,  making the substrate  112  smaller in thickness as a whole. 
     The first substrate member  112   a  and the second substrate member  112   b  may be joined to each other by radiating ultrasonic and/or laser to their joint surfaces after positioning the cavity  132  and the connection hole  133   a.  Also, the first substrate member  112   a  and the second substrate member  112   b  may be joined to each other via a binder or a bonding sheet (neither of which is illustrated) of epoxy resin or acrylic resin. The first contact point  13  and the second contact point  14  are formed by patterning such as etching of an electrode film formed on the upper surface of the first substrate member  112   a.    
     Also, the first contact point  13  and the second contact point  14  are electrically connected to a first external electrode  119  and a second external electrode  20  through the through hole  122 , which penetrates the substrate  112 . The first external electrode  119  and the second external electrode  20  are formed on the lower surface of the second substrate member  112   b.  The first external electrode  119  and second external electrode  20  are formed by patterning such as etching of an electrode film formed on the lower surface of the second substrate member  112   b.    
     The connection hole  133   a  is formed by a quantity corresponding to the quantity of the cavity  132 , and each one cavity  132  is connected to a corresponding one connection hole  133   a.  In one example, a pair of silencers  131   a  are provided at positions where the silencers  131   a  face each other across the first contact point  13 , where contact sound is generated. Each silencer  131   a  is independently formed and made up of one cavity  132  and one connection hole  133   a.  The cavities  132  may be identical to each other in terms of capacity. The connection holes  133   a  may be identical to each other in terms of the length. The openings  134  may be identical to each other in terms of the diameter. While the tenth embodiment is an example in which a pair of silencers  131   a  are provided, at least one silencer  131   a  suffices to decrease the contact sound generated by the contact between the first contact point  13  and the conduction spring member  15 . Further, by providing three or more silencers  131   a  along the circumference of the first contact point  13 , the contact sound generated by the contact between the first contact point  13  and the conduction spring member  15  is further decreased. 
       FIG. 24( a )  illustrates the upper surface of part of the substrate of a switch unit according to the eleventh embodiment.  FIG. 24( b )  is an A-A line sectional view of the part of the substrate illustrated in  FIG. 24( a ) . In a silencer  131   c  according to the eleventh embodiment, the connection hole  133   a  is larger in quantity than the cavity  132   b,  and a plurality of connection holes  133   a  are connected to one cavity  132   b.  The silencer  131   c  illustrated in  FIGS. 24( a ) and 24( b )  is made up of: a large one cavity  132   b,  which is formed immediately under the first contact point  13 ; and two connection holes  133   a,  which are connected to the cavity  132   b.    
     The first substrate member  112   a  according to the eleventh embodiment is the same as the first substrate member  112   a  according to the tenth embodiment. By providing a larger depression at a center portion of the second substrate member  112   b,  the area of the circular cavity  132   b  is made larger than the area of the first contact point  13 . Thus, by increasing the capacity of the cavity  132   b,  a larger amount of inflowing air is pressed into the cavity  132   b  through the plurality of connection holes  133   a,  and the air pressed into the cavity  132   b  causes a larger level of vibration to be generated. This decreases the sound emitted externally from the cavity  132   b  through each connection hole  133   a.  It is to be noted that each connection hole  133   a  according to the eleventh embodiment may be formed in a direction perpendicular or inclined relative to the upper surface of the first substrate member  112   a,  similarly to the connection holes  133   a  and  133   b  according to the tenth embodiment. The connection holes according to the twelfth to fifteenth embodiments may also be formed in a direction perpendicular or inclined relative to the upper surface of the first substrate member. 
       FIG. 25  illustrates the upper surface of part of the substrate of a switch unit according to the twelfth embodiment. As illustrated in  FIG. 25 , a silencer  131   d  according to the twelfth embodiment includes one large circular cavity  132   b,  a plurality of (three or more) connection holes  133   a,  and a plurality of (three or more) openings  134 . It is to be noted that there is no particular limitation to the positions of the connection holes  133   a  and the openings  134 . In the twelfth embodiment, four openings  134  are provided at equal intervals in a circular arrangement over the cavity  132   b.  Thus, by providing a large quantity of connection holes  133   a  and openings  134  around the first contact point  13 , the contact sound emitted from the first contact point  13  and around thereof can be decreased over a wider range. 
       FIG. 26( a )  illustrates the upper surface of part of the substrate of a switch unit according to the thirteenth embodiment. In the thirteenth embodiment, a silencer  141   a  includes: a linearly extending opening  144 ; a connection hole  143 , which penetrates the first substrate member  112   a  and has a linear shape; and a cavity  142   a,  which has a planar shape surrounding the outer shape of the connection hole  143 . The silencer  141   a  is provided in the form of a pair each provided on one and the other sides of the first contact point  13 , where contact sound is generated. While  FIG. 26( a )  illustrates an example in which two silencers  141   a  are provided, at least one silencer  141   a  suffices to decrease the contact sound generated by the contact between the first contact point  13  and the conduction spring member  15 . By providing three or more silencers  141   a  along the circumference of the first contact point  13 , the contact sound generated by the contact between the first contact point  13  and the conduction spring member  15  is further decreased. 
       FIG. 26( b )  illustrates the upper surface of part of the substrate of a switch unit according to the fourteenth embodiment. In the fourteenth embodiment, a silencer  141   b  includes one larger quadrangular cavity  142   b  and two linear connection holes  143 , which are connected to the cavity  142   b.  The cavity  142   b  is formed by providing a larger quadrangular depression at a center portion of the second substrate member  112   b.  Thus, by increasing the capacity of the cavity  142   b,  the amount of air pressed into the cavity  142   b  through each connection hole  143  increases, and the air pressed into the cavity  142   b  causes a larger level of vibration to be generated. This decreases the sound emitted externally through each connection hole  143 . 
     In the fourteenth embodiment, it is possible to provide three or more connection holes  143  surrounding the first contact point  13 , with the planar space defined in the cavity  142   b  taken into consideration. Thus, by providing a plurality of connection holes  143 , the contact sound generated by the contact between the first contact point  13  and the conduction spring member  15  is further decreased. It is to be noted that the cavity  142   b  may have an area of space large enough to be connected to more than one connection hole  143 . Therefore, the shape of the cavity  142   b  will not be limited to a quadrangular shape but may be any other polygonal shape than a quadrangular shape or may be a circular shape. 
       FIG. 27( a )  illustrates the upper surface of part of the substrate of a switch unit according to the fifteenth embodiment.  FIG. 27( b )  is a B-B line sectional view of the part of the substrate illustrated in  FIG. 27( a ) . In the fifteenth embodiment, a silencer  151  includes: a ring-shaped cavity  152 , which is provided along the outer circumference of the first contact point  13  and has a predetermined circumferential width; and a connection hole  153 , which is connected to the cavity  152  approximately at the center of the opening width on the circumference of the cavity  152 . A ring-shaped opening  154  is connected to the connection hole  153  and formed on the upper surface of the first substrate member  112   a.  The silencer  151  is provided such that the silencer  151  surrounds the outer circumference of the first contact point  13 . This enables the silencer  151  to omni-directionally absorb the contact sound emitted from the first contact point  13 . As a result, the contact sound is efficiently decreased, without a leakage of the contact sound to outside the silencer  151 . 
       FIG. 28( a )  illustrates the upper surface of part of the substrate of a switch unit according to the sixteenth embodiment.  FIG. 28( b )  is a C-C line sectional view of the part of the substrate illustrated in  FIG. 28( a ) . In the sixteenth embodiment, the first contact point  13  has a ring shape provided with a circular hole at a center portion of the ring shape. On the upper surface of the first substrate member  112   a,  an opening  164  is formed. The opening  164  has a size corresponding to this circular hole. 
     A cavity  162  is a spacious circular cavity and formed immediately under the first contact point  13 . In the first substrate member  112   a,  a connection hole  163  is provided. The connection hole  163  connects the cavity  162  and the opening  164  to each other. In a silencer  161  according to the fifteenth embodiment, the ratio of the area of the cavity  162  to the area of the second substrate member  112   b  as a whole is large. With this configuration, the silencer  161  is more suitable for a small-size substrate in which the space between the first contact point  13  and the second contact point  14  is small. 
     In all the tenth to sixteenth embodiments, a two-layer substrate made up of the first substrate member  112   a  and the second substrate member  112   b  is used. Alternatively, it is possible to use a three-layer substrate formed by mounting a third substrate member  112   c  on a lower portion of the second substrate member  112   b.  In this case, a cavity  172  is formed in the second substrate member  112   b,  and the lower surface of the cavity  172  is defined by the upper surface of the third substrate member  112   c.  A through hole serving as the cavity  172  is defined by the second substrate member  112   b,  and the third plate  12   c  is provided under the cavity  172 . This configuration ensures that a silencer  171  is easily formed including an opening  174 , a connection hole  173 , and the bottomed cavity  172 . 
     It is preferable that the cavity  172  and the connection hole  173 , which constitute the silencer  171 , are sealed. In light of this, the materials of the first substrate member  112   a,  the second substrate member  112   b,  and the third substrate member  112   c  are preferably high-density hard materials such as glass epoxy substrate (FR-4). Using such hard members prevents the conduction spring member  15  from being kept in depressed state toward the first contact point  13 , and provides a moderate level of click sensitivity. This improves the switch unit&#39;s switching accuracy. 
     In conventional noiseless switch units, a shock-absorbing material is provided on the substrate or the substrate itself is made of a noiseless material, in order to alleviate the contact sound caused by switching. In a switch unit according to an embodiment of the present application, even though the switch unit is small and thin, a through hole or a depression having different opening widths are formed in the substrate having a multilayer structure such as a two-layer or three-layer structure. This ensures that the switch unit provides a silencing effect that is based on a Helmholtz resonator principle, which promotes positive absorption of sounds. The switch units according to the tenth to sixteenth embodiment and the switch units according to other embodiments including a three-layer substrate are also applicable to switch devices using lead frames. 
     It is possible to: form a large-size aggregate first substrate in which a plurality of first substrate members  112   a  can be formed; form a large-size aggregate second substrate in which a plurality of second substrate members  112   b  can be formed; stack the aggregate first substrate on the aggregate second substrate; and subject the substrate to dicing along a predetermined region. As a result, substrates  112  corresponding to respective switch units  111  according to the tenth embodiment can be formed collectively. The first substrate member  112   a  and the second substrate member  112   b  may be flexible substrates. An example is illustrated in  FIGS. 30( a ) and 30( b ) . 
     In this example, an aggregate first substrate  182   a  has a plurality of connection holes  133   a,  and an aggregate second substrate  182   b  has a plurality of cavities  132  and a lead portion  183 . The aggregate first substrate  182   a  is joined on the aggregate second substrate  182   b.  The aggregate first substrate  182   a  and the aggregate second substrate  182   b  that have been joined to each other are cut from the lead portion  183  and divided into regions of individual switch units  111 , which is not illustrated. It is to be noted that this aggregate substrate may also be used to form the substrate having the layer structure illustrated in  FIG. 29 . 
     By referring to  FIGS. 31 to 33 , description will be made with regard to a method for producing the switch unit  111  using an aggregation method.  FIG. 31  illustrates the upper surface of an aggregate switch substrate  149 , which is a material of the switch substrate  43 , which constitutes the switch unit  111  according to the tenth embodiment.  FIG. 32  is a sectional view of the aggregate switch substrate  149 .  FIG. 33  illustrates the lower surface of the aggregate switch substrate  149 . The method for producing a switch substrate  148  using the aggregation method includes a joining step and a cutting step. 
     In the joining step, the aggregate switch substrate  149  is obtained by joining a first aggregate substrate  191  and a second aggregate substrate  192  to each other. On the upper surface of the first aggregate substrate  191 , a plurality of first contact points  13  and a plurality of second contact points  14  are formed. The plurality of second contact points  14  are provided around the respective first contact points  13 . The first aggregate substrate  191  has a plurality of through holes  146 . The second aggregate substrate  192  has a plurality of cavities  132 . The maximum value of a sectional area of each cavity  132  parallel to the upper surface of the first aggregate substrate  191  is larger than the maximum value of a sectional area of each through hole  146  parallel to the upper surface of the first aggregate substrate  191 . Each of the cavities  132  is open only on the upper surface of the second aggregate substrate  192 . The plurality of through holes  146  overlap the plurality of respective cavities  132  in a vertical direction. In the cutting step, the aggregate switch substrate  149  is cut to obtain individual switch substrates  148 . Between the joining step and the cutting step, it is possible to perform a forming step of forming a plurality of resin layers in a stripe arrangement on the lower surface of the aggregate switch substrate  149 . 
     REFERENCE SIGNS LIST 
       
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 10, 100 Switch device 
               
               
                   
                 11, 31, 41, 51, 61, 71, 81, 91, 101, 111 Switch unit 
               
               
                   
                 12, 32, 42, 45′, 52, 62, 72, 82, 92, 102, 112, 112′ Substrate 
               
               
                   
                 12a, 12c Hard layer 
               
               
                   
                 12a′ Right and left outer circumference of hard layer 
               
               
                   
                 12b, 12d, 12e, 12f, 12g, 12h, 12j, 12k, 12m, 48 Soft layer 
               
               
                   
                 12d′ Right and left outer circumference of soft layer 
               
               
                   
                 13 First contact point 
               
               
                   
                 14 Second contact point 
               
               
                   
                 15, 15′ Conduction spring member 
               
               
                   
                 15a, 15a′ Apex of conduction spring member 
               
               
                   
                 16 Pressing element 
               
               
                   
                 17 Cover sheet 
               
               
                   
                 18 Frame sheet 
               
               
                   
                 18a Opening 
               
               
                   
                 19 External electrode 
               
               
                   
                 19a First wiring pattern 
               
               
                   
                 19b Second wiring pattern 
               
               
                   
                 20 External electrode 
               
               
                   
                 20a, 20c, 27a First external electrode 
               
               
                   
                 20b, 20d, 27b Second external electrode 
               
               
                   
                 21 Pressing aid member 
               
               
                   
                 22 Through hole 
               
               
                   
                 22a First through-hole electrode 
               
               
                   
                 22b Second through-hole electrode 
               
               
                   
                 23 Mount substrate 
               
               
                   
                 26 Pressing protrusion 
               
               
                   
                 26a Depression 
               
               
                   
                 28a First connection electrode 
               
               
                   
                 28b Second connection electrode 
               
               
                   
                 43, 148 Switch substrate 
               
               
                   
                 44 Aggregate switch substrate member 
               
               
                   
                 45 Aggregate substrate 
               
               
                   
                 46, 53, 146 Through hole 
               
               
                   
                 47 Conduction layer 
               
               
                   
                 48′ Soft plate 
               
               
                   
                 49, 149 Aggregate switch substrate 
               
               
                   
                 112a First substrate member 
               
               
                   
                 112b Second substrate member 
               
               
                   
                 112c Third substrate member 
               
               
                   
                 122 Through hole 
               
               
                   
                 131a, 131b, 131c, 131d, 141a, 141b, 151, 161, 171 Silencer 
               
               
                   
                 132, 132b, 142a, 142b, 152, 162, 172 Cavity 
               
               
                   
                 133a, 133b, 143, 153, 163, 173 Connection hole 
               
               
                   
                 134, 135, 144, 154, 164, 174 Opening 
               
               
                   
                 182a Aggregate first substrate 
               
               
                   
                 182b Aggregate second substrate 
               
               
                   
                 183 Lead portion 
               
               
                   
                 191 First aggregate substrate 
               
               
                   
                 192 Second aggregate substrate 
               
               
                   
                 193 Resin layer 
               
               
                   
                 201 Switch unit 
               
               
                   
                 202 Switch substrate