Patent Publication Number: US-8124902-B2

Title: Push button switch

Description:
CROSS-REFERENCE TO THE RELATED APPLICATION 
     The application is based on and claims the priority benefit of Japanese Patent Application No. 2008-31654, filed on Feb. 13, 2008, the entire description of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a push button switch, especially to a lateral-push button switch used in small electronic equipment and devices such as mobile phones, portable game devices, digital cameras, mobile personal computers, and so on. 
     2. Description of the Related Art 
     A conventional general lateral-push button switch includes a circuit board provided with a fixed contact and a resilient snap dome as a base part, a cover covering the base part of the push button switch and having at a peripheral side surface of the push button switch an opening, and an operating controller inserted in the opening to be disposed slidably in a lateral horizontal direction and configured to press the snap dome toward the fixed contact downwardly (for reference, see Japanese Patent Application Publication Nos. 2006-244977 and 2005-209565). 
     The base part includes a molded article in which a flat plate-like circuit board or lead frame is formed by insert molding, and the circuit board includes a plurality of solder pads which are provided on a lower surface of the circuit board and electrically connected to the fixed contact and the snap dome. The cover member includes a slope extending inward from an upper part of the cover member, and the slope is inclined to press the operating controller from obliquely above when the operating controller is laterally slid into the push button switch. 
     When the operating controller is pressed and laterally slid into the push button switch, a leading end portion or inner end portion of the operating controller is downwardly guided and pressed from obliquely above by the slope, and the snap dome comes into contact with the fixed contact. 
     In this way, by sliding the operating controller in a lateral direction, the snap dome with the fixed contact is configured to execute switch-on and -off operations. 
     In the push button switch having the aforementioned structure, the cover member is fixed to the base part to cover the snap dome and the fixed contact. The push button switch used in an electronic device is mounted on a motherboard of an electronic device by bonding the base part onto the motherboard directly through soldering. 
     Because thinning is required in small electronic devices in each of which a push button switch is surface-mounted on a motherboard of the electronic devices, the push button switch is also required to be thin. When the push button switch is surface-mounted on an electronic device, the fixation and the electric connection of the push button switch to the motherboard of the small electronic equipment are simultaneously executed by a reflow process. 
     However, in the lateral-push button switch having the aforementioned structure, because a user&#39;s pushing force on the operating controller that is pressed against the slope of the covering member accompanies performance of the switch-on and -off operations of the snap dome and the fixed contact, it is necessary to increase the strength of the cover member to a certain extent relative to the base part provided with the snap dome and the fixed contact or a motherboard on which the push button switch is finally mounted in an electronic device. In addition, the lateral-push button switch is often installed in small electronic devices such as mobile phones, portable game devices, digital cameras, mobile personal computers and so on as a lateral-push button switch provided at a side surface of the electronic device. However, because a user carries around a mobile phone and other small electronic devices as portable devices, it often happens that the small electronic devices are accidentally dropped or hit on an object, and strong impacts and large stresses often cause problems in the switch function of the push button switch or physical destruction. 
     In most cases the destruction begins first from a side surface of a cover member, the side surface facing a sliding direction of the operating controller, and thereafter reaches the base part provided with the snap dome and the fixed contact. Therefore, it is necessary to particularly increase strength of a portion of the push button switch close to a switch operation part exposed on a side surface of the mobile phone and other electronic devices. 
     Furthermore, because the push button switch is finally surface-mounted on the motherboard of an electronic device, it is often bonded by solder in a reflow process. In the reflow process, joint strength tends to increase in proportion to a size of solder-joining area. Therefore, a process of securing a large solder-joining area of the base part of the push button switch to the motherboard has conventionally been executed. However, if the solder-joining area of the circuit board becomes larger, for example, the circuit board and the push button switch become larger which goes against the demand for thinner and smaller push button switches to be mounted in small electronic devices such as mobile phones and other portable electronic devices. Also, if the base part is formed by inserting a lead frame, it is not easy to ensure a large solder-joining area, because a size of electrodes is previously determined. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a push button switch reducing a mounting space of a motherboard on which the push button switch is mounted, and a push button switch that is impact resistant, prevented from being destroyed and becoming detached from the motherboard even if a large impact due to dropping or hitting is applied to an electronic device in which the push button switch is disposed. 
     To accomplish the above object, a push button switch according to one embodiment of the present invention includes a base part, a fixed contact provided on the base part, a snap dome provided on the base part to cover the fixed contact, a cover member disposed to cover at least one portion of the base part, an operating controller disposed in the base under the cover member and configured to perform switch-on and -off operations of electrical connection between the snap dome and the fixed contact, and the cover member including at least a pair of side extended portions extending downwardly along sides of the base part, and extensions extending laterally along a same level of a lower surface of the base part. The base part includes at a lower surface thereof solder pad portions, and at least two of the solder pad portions are electrically connected to the snap dome and the fixed contact. 
     Further, each of the extensions of the cover member includes a lower surface extending in a same plane as a lower surface of each of the solder pad portions. A solder pad portion of the circuit board is disposed adjacent to each of the extensions. The solder pad portions adjacent to the extensions are provided on the lower surface of the base part, positioned at both sides of the opening in which the operating controller is inserted. 
     In an electronic device including a push button switch according to the present invention, the extensions and the adjacent solder pad portions are fixed together to a motherboard of the electronic device. Other solder pad portions provided on the lower surface of the circuit board of the push button switch may be used for electrical connection and also used to fix the push button switch to the motherboard. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing an upper side or cover-member side of a push button switch according to one embodiment of the present invention, as viewed from above. 
         FIG. 2  is a perspective view showing a lower side or circuit board side of the push button switch, as viewed from above. 
         FIG. 3  is a sectional view of the push button switch taken along line III-III line in  FIG. 1 . 
         FIG. 4  is an exploded perspective view of the push button switch. 
         FIG. 5  is a plan view showing an upper side or cover-member side of the push button switch disposed on a motherboard of an electronic device, as viewed from above. 
         FIG. 6  is a plan view showing a lower side or circuit board side of the push button switch, showing solder-joining portions to the motherboard. 
         FIG. 7  is an operative view showing a state of a usual switch-on operation in a push button switch. 
         FIG. 8  is an operative view showing a state in which a large external lateral force is applied to a push button switch. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1 to 3  illustrate a push button switch  21  according to one embodiment of the present invention. 
       FIG. 3  shows a push button switch  21  mounted on a motherboard of an electronic device. The push button switch  21  has a predetermined mounting area, for example, square mounting portions M (see  FIG. 5 ), each of which includes an electrode or a solder pad portion provided on a lower surface of the circuit board, and two of the solder pad portions adjacently disposed to lower surfaces of extensions of a cover member, respectively. The two soldering portions each include a solder pad portion and an extension extended from the cover member. The push button switch  21  includes, as a base part  22 , a circuit board  26 , a fixed contact  23   a  disposed on an upper surface of the circuit board  26 , a snap dome with elasticity disposed on the upper surface of the circuit board over the fixed contact  23   a , and a cover member  24  disposed to cover the base part  22  and the push button switch having an opening at a side surface thereof between the cover member and the base part  22 , and an operating controller  25  that is inserted in the opening and slidably disposed above the base part  22  under the cover member  24 , in other words, the operating controller slidably disposed inside the push button switch and configured to press at an inner end of the operating controller the snap dome  23   b  from above, resulting in an electrical connection between the fixed contact  23   a  and the snap dome  23   b  (see  FIG. 3 ). 
     The operating controller  25  includes a push-button part  32  that receives a lateral pressing force to move the operating controller  25  laterally in the push button switch to make an electrical connection of the switch unit  23 . When the push button switch  21  is used in an electronic device such as a mobile phone, the circuit board  26  of the push button switch  21  is electrically mounted on a motherboard  20  of the electronic device, and the push-button part  32  of the push button switch  21  is disposed on an outside surface of a housing of the electronic equipment, so that a user can push the push-button part  32 . The push-button part  32  may be disposed to appear at a side surface of a housing of an electronic device when the push button switch is mounted in the electronic device. The snap dome  23   b  and the fixed contact  23   a  are electrically connected or disconnected in accordance with movements of the operating controller  25  (see  FIG. 3 ). When the operating controller  25  presses the snap dome  23   b  from above, the snap dome  23   b  is pressed to be in contact with the fixed contact  23   a , and when the push-button part  32  of the operating controller  25  is released, the snap dome  23   b  is released and resiliently returns to an original position that is electrically disconnected from the fixed contact  23   a.    
       FIG. 4  illustrates an exploded perspective view of a push button switch  21  according to an embodiment of the present invention. The base part  22  includes a circuit board  26  which has, for example, a substantially square shape and is provided with a fixed contact  23   a  having, for example, a circular shape, a base sheet  27 , which has a substantially annular shape, disposed on a peripheral portion of the upper surface of the circuit board  26 , with the fixed contact  23   a  being disposed in a center of the annular shape, the resilient snap dome  23   b  having a generally dome-like shape and being disposed on the upper surface of the circuit board  26  over the fixed contact  23   a  and the snap dome  23   b  at a center thereof disposed vertically away from the fixed contact  23   a  as an initial position (see  FIG. 3 ), a water-proof protection sheet  28  covering the snap dome  23   b , and a mold frame  30  including a hole that vertically passes through the frame  30  and a concave portion to receive the operating controller  25  from a lateral direction. 
     The circuit board  26  is made of a resin such as glass epoxy or the like and provided with wiring patterns disposed on the upper surface of the circuit board  26  and electrically connected to the snap dome  23   b  and the fixed contact  23   a . The circuit board  26  also includes at least two through-hole electrodes  40  electrically connected to the wiring patterns, the through-hole electrodes  40  being disposed at a peripheral side surface of the circuit board  26  and extending from the upper surface to the lower surface of the circuit board (see  FIG. 6 ). In the illustrated embodiment, four through-hole electrodes  40  are provided adjacent to four corners of the circuit board  26 . Four through-hole electrodes  40  are extended to four solder pad portions  41  on the lower surface of the circuit board  26 , and the four solder pad portions  41  may be fixed to a motherboard  20  of an electronic device. The switch unit  23  is electrically connected to a motherboard through at least two solder pad portions  41  and other solder pad portions  41  may be dummy electrodes that can be used to fix the push button switch to the motherboard (see  FIGS. 1 ,  3  and  5 ). The solder pad portions  41  are formed, for example, by applying metallic plating on the lower surface of the circuit board  26  and some of the solder pad portions  41  are disposed adjacent to at least two lower surfaces of extensions  38  of the covering member  24  that are extended to a same level of the lower surface of the circuit board  26  or the solder pad portions  41 . The two solder pad portions  41  and adjacent disposed two lower surfaces of the extensions  38  of the covering member  24  are two solder-pad-portion-extension-connecting mounting portions M that are fixed to a motherboard of an electronic device. In addition, other two solder pad portions  41  can be fixed to the motherboard and may be used for electrical connection to the motherboard. 
     The snap dome  23   b  is, for example, an electrically conductive plate-like spring or a dome-like spring and is formed by a thin resilient plate of a metallic material such as stainless steel (SUS), brass, and so on. The snap dome  23   b  has a central portion which comes into contact with the fixed contact  23   a , when being pressed by the operating controller from above. The operating controller  25  is laterally slid into the inside of the push button switch and an inner end of the operating controller  25  is pressed from above by a part of the cover member  24 , when the push-button part  32  of the controller  25  is pressed. In a usual state, the snap dome  23   b  is disposed in an upwardly slightly inflated dome-like shape so as not to be in contact with the fixed contact  23   a  and positioned at a central portion of the circuit board  26  by the base sheet  27  (see  FIG. 3 ). 
     The operating controller  25  includes a plunger  31  and a press stick  33  that laterally extend from an inner surface of the push-button part and are disposed in the concave portion of the mold frame  30  of the base part  22 . Even if the plunger  31  and the press stick  33  are contained in the mold frame  30 , the push-button part  32  is disposed outside the mold frame  30 . The press stick  33  laterally extends from a central part of the inner surface of the push-button part  32 , and an inner end of the press stick  33  is formed into a free end portion. The free end portion of the press stick  33  is provided with a pressing portion, for example, a protrusion  34  which is positioned above a top of the snap dome  23   b  at a generally central portion of the base part  22  of the push button switch (see  FIG. 3 ). 
     The cover member  24  is configured to cover the plunger  31 , the press stick  33 , and the mold frame  30  and the cover member  24  has at least two portions around side surfaces of the base part  22  downwardly extended to a level of the lower surface of the circuit board  26 . The side downwardly extended portions of the cover member  24  at downward ends thereof may have extensions  38  laterally extended along the level of the lower surface of the circuit board  26 . The cover member  24  includes an opening  42  into which the plunger  31  is inserted, a top panel portion  35  covering the plunger  31 , side extended portions  36  configured to extend downwardly from opposite sides of the top panel portion  35  to the circuit board  26  across the operating controller  25 , a plurality of engaging portions  37  that extend downwardly and engage with the mold frame  30 , and extensions  38  which extend approximately horizontally from lower ends of the side extended portions  36 , outwardly from the circuit board  26  (see  FIG. 4 ). 
     The cover member  24  is formed by, for example, punching or folding one metallic plate. The top panel portion  35  includes a slope  39  that is a part of the top panel portion  35  and the slope  39  is inclined toward inside a central portion of the push button switch to be in contact with an upper surface of the protrusion  34  of the operating controller  25 . The slope  39  is configured to press the protrusion  34  of an inner open end of the press stick  33  of the plunger  31  toward the snap dome  23   b  which is disposed downwardly, when the plunger  31  is laterally pressed into the mold frame  30  by pressing the pressing section  32  to electrically connect the snap dome  23   b  and the fixed contact  23   a  (see  FIG. 7 ). In the embodiment, a surface of the protrusion  34  of the pressing section  32 , contacting with the slope  39  has an inclined surface along the slope  39  (see  FIG. 3 ). 
     In the aforementioned push button switch  21 , the base part  22  is placed on the motherboard  20  and the four solder pad portions  41  are downfacing and bonded on a predetermined mounting area of the motherboard  20  by soldering through a reflow process. 
     In a lateral-push button switch  21  having the aforementioned structure, the most important feature of the present invention is that the extensions  38  of the cover member  24  are disposed adjacent to some of the solder pad portions  41  formed at a lower surface of the circuit board  26 , and the extensions  38  are disposed adjacent to the solder pad portions  41 , and the side extended portions  36  and extensions  38  of the cover member  24  are positioned across a sliding direction of the operating controller  25 , as shown in  FIGS. 2 ,  5  and  6 . The extensions  38  may be disposed near the side where the push-button part  32  of the operating controller  25  is disposed. In addition, lower surfaces of the extensions  38  of the side extended portions of the cover member  24  are in a same plane as that of the circuit board  26  or that of each of the solder pad portions  41 . 
     In this way, by disposing the extensions  38  of the cover member  24  adjacent to some of the solder pad portions  41  of the base part  22 , the extensions  38  and the adjacent solder pad portions  41  can be firmly bonded together as mounting portions M to the motherboard  20  simultaneously, and thus the cover member  24  or the base part  22  can be prevented from failing or becoming detached from the motherboard  20  even if a large external force is applied to the push button switch  21 . 
     An operational effect of the push button switch  21  having the aforementioned structure in the case of a usual switch-on operation and where a large impact is applied is described hereinafter with reference to  FIGS. 3 ,  7  and  8 . Here,  FIG. 3  illustrates a state where the snap dome  23   b  and the fixed contact  23   a  are not electrically connected, and  FIG. 7  illustrates a state where the snap dome  23   b  and the fixed contact  23   a  are electrically connected.  FIGS. 3 and 7  illustrate states in a usual switch operation. On the other hand,  FIG. 8  illustrates in section a state where a large external force is applied to the push button switch  21  from an operation side, in other words, the side of the push button part of the operating controller, when the electronic device in which the push button switch  21  is mounted is dropped. 
     As shown in  FIG. 3 , in a state where the operating controller  25  is not pressed toward the snap dome  23   b  and the fixed contact  23   a , the leading end portion of the press stick  33  abuts with the slope  39  of the cover member  24 , but because the snap dome  23   b  is not pressed, an external force is not applied to either of the base part  22  or the cover member  24 . From this state, when the push-button part  32  of the operating controller  25  is pressed, as shown in  FIG. 7 , the protrusion  34  of the leading portion of the operating controller  25  descends along the slope  39  provided on the cover member  24  to press the resilient snap dome  23   b  down toward the fixed contact  23   a  against the resilience of the snap dome  23   b.    
     By this operation, a reaction force from the snap dome  23   b  is imparted to the cover member  24 , but because the cover member  24  is bonded at the extensions  38  of the cover member  24  onto the motherboard  20 , a usual switch-on operation of the snap dome  23   b  and the fixed contact  23   a  can be achieved stably. Even when the push-button part  32  of the operating controller  25  is released, the switch-off operation between the snap dome  23   b  and the fixed contact  23   a  can similarly be accomplished stably. 
     In a situation of accidentally dropping or hitting of an electronic device in which the push button switch  21  is mounted, if an excessively large external force which is more than a pressing force due to usual switch-on and -off operations is applied to the push-button part  32 , a part of an inner surface of the push-button part  32  collides with a side portion  22   a  of the base part  22  or an edge portion  24   a  of the cover member  24 , as shown in  FIG. 8 . In the bonding structure of the aforementioned conventional push button switches, if such a large laterally pressing force F (see  FIG. 8 ) is applied to the conventional push button switch, the base part, the cover member and the portions fixed to the motherboard receive a large stress, and consequently, the conventional push button switch tends to become detached from the motherboard. This is the reason that bonded positions of the base part and the cover member to the motherboard come loose, and therefore an impact force due to the external force F concentrates at either one of the base part or the cover member, in the conventional push button switch. 
     However, in the push button switch  21  according to the present invention, as mentioned above, the extensions  38  of the cover member  24  are provided adjacent to some of the solder pad portions  41  of the base part  22  and further the extensions  38  are bonded to the mounting area of the motherboard  20  by soldering, together with the solder pad portions  41 . Thereby, if the excessive external force F is applied to the push button switch  21  from the direction as shown in  FIG. 8 , the external force can be received and supported by the entire mounting portions M. In particular, because in some of the mounting portions M, each have a combined planar space of a solder pad portion  41  and an extension  38 , it is possible to set the amount of solder applied to a large value and stably maintain a high mechanical bonding intensity. 
     As shown in  FIGS. 5 and 6 , by positioning the extensions  38  in the direction perpendicular to the sliding direction of the operating controller  25 , a stress at the time a large external force is applied to the push button switch  21  through the push-button part  32  can be supported by the extensions  38  extending in a direction across a sliding direction of the operating controller  25 , thus preventing a risk of breakage of the switch by excessive pressures on the cover member  24  and the base part  22  to be raised from the motherboard  20 . 
     Moreover, by bonding the extensions  38  extending from the side portions of the cover member  24  and some of the solder pad portions together as mounting portions M on a motherboard, the bonding positions of the cover member  24  and the base part  22  are aligned, and thus the cover member  24  and the base part  22  are bonded with higher intensity to the motherboard  20 . Consequently, it is possible for the push button switch  21  to maintain sufficient bonding intensity with connected and extended bonding areas, even if the extensions  38  themselves have small bonding portions. 
     Furthermore, it is possible to mount a push button switch according to the present invention in a limited area of a motherboard  20 , and therefore mobile phones and other small electronic devices can be miniaturized or thinned. 
     In the illustrated embodiment, to increase intensity of fixation from the side of the push-button part  32  which is the part of the push button switch  21  most easily affected by impact, the extensions  38  provided on the cover member  24  are configured to be disposed adjacent to the pair of solder pad portions  41  provided at a lower surface of the base part  22 . If such a push button switch  21  is structured to have an even greater intensity of fixation, the cover member  24  can be configured to provide additional extensions  38  which are disposed adjacent to a pair of solder pad portions  41  provided on a lower side of the base part  22 , in addition to the extensions  38  disposed adjacent to the solder pad portions  41  disposed on the lower surface of the base part  22 . 
     In the push button switch  21  according to the present invention, because the solder pad portions  41  provided on the lower surface of the base part  22  and extensions  38  of the cover member  24  covering the base part  22  are disposed adjacently, it is possible to bond one of the solder pad portions  41  and one of the extensions  38  by soldering together as connected mounting portions M when the push button switch is mounted on a motherboard. Consequently, stronger bonding of the solder pad portions  41  and the extensions  38  can be accomplished to prevent the base part  22  and the cover member  24  from easily being separated from the motherboard, even if a large external force such as dropping or the like is applied to the operating controller  25 . 
     In addition, because the extensions  38  and some of the solder pad portions  41  are bonded to a motherboard as connected mounting portions M respectively, the extensions  38  have sufficient bonding strength even if the extensions  38  each have a small area. Consequently, it is possible to keep a mounting space of the push button switch  21  small in an electronic device, while the push button switch becomes impact-resistant. 
     As mentioned above, because the lower surface of the extensions of the cover member  24  is bonded by soldering together with the adjacent solder pad portions  41 , it is possible to easily bond the extensions of the cover member  24  and the solder pad portions of the circuit board  26  of the base part  22  to a motherboard through a reflow process by previously applying solder plating to the lower surfaces of extensions of the cover member  24  and the solder pad portions of the circuit board. 
     Although the preferred embodiments of the present invention have been described, it should be understood that the present invention is not limited to these embodiments, and that various modifications and changes can be made to the embodiments. 
     For example, in the push button switch  21  in the aforementioned embodiment, the base part  22  is structured by a combination of the circuit board  26  made of epoxy resin and the mold frame  30  in which the snap dome  23   b , the fixed contact  23   a , and the operating controller  25  are contained, but the circuit board  26  may be replaced by a lead frame including external connecting terminals. 
     In this case, the push button switch  21  is structured by using a molded base part, which may be formed by inserting the lead frame. 
     A push button switch structured using the molded base part formed based on the lead frame has a bonding strength to the motherboard that is similar to that of push button switch  21 , by providing a cover body including extension portions disposed adjacent to portions corresponding to the exterior connecting terminals of the lead frame.