Abstract:
A button battery is installed in a electronic device such as a signal transmitter and electrically connected by a terminal contacting a flat electrode terminal of the button battery. The terminal has a circular spring-contact member surrounding a terminal base, and the spring-contact member is connected to the terminal base by a pair of connecting portions. The terminal base is fixed to a substrate by soldering. Since the spring-contact member is formed in a circular shape, its length can be made sufficiently long to make its spring modulus low and to reduce spring-load imposed thereon, thereby avoiding plastic deformation of the spring-contact member. The terminal base soldered to the substrate is prevented from being peeled off by eliminating twisting force applied to the spring-contact member.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims benefit of priority of Japanese Patent Application No. 2002-53540 filed on Feb. 28, 2002, the content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a terminal for electrically connecting a button battery in a signal transmitter or the like. 
     2. Description of Related Art 
     A conventional terminal for electrically connecting a button battery is shown in  FIGS. 7A and 7B . The terminal  400  is made of a flat conductive plate and composed of a terminal base  410  and a pair of spring-contacts  420 . The terminal base  410  is mounted on a substrate  20  by soldering. As shown in  FIG. 7B , a button battery  30  having a minus-electrode flat terminal  31  and a plus-electrode terminal  32  is contained in a signal transmitter or the like. The pair of spring contacts  420  resiliently contacts the flat terminal  31 . 
     A contact pressure between the spring-contacts  420  and the flat terminal  31  has to be set to a level that attains a good electrical connection. If the contact pressure is lower than a minimum pressure for attaining a good electrical contact (referred to as a required minimum contact pressure), a battery power is consumed in a contact resistance at the contacting point. A width W and a thickness t of the spring-contacts  420  are set to attain the required minimum contact pressure. A spring modulus of the spring contact is determined by the width W, the thickness t and a length L 2  of the spring-contact  420 . Because an amount of deflection of the spring-contact  420  also depends on its dimensional dispersion and other factors, the width W and the thickness t are set to secure the required minimum contact pressure even if the amount of deflection becomes low. 
     On the other hand, when the deflection amount of the spring-contact  420  becomes too large due to the dimensional dispersion or other factors, there is a possibility that the spring-contact  420  plastically deforms due to an internal stress exceeding a yield stress. The possibility of such plastic deformation increases as the spring modulus becomes high. Accordingly, it is preferable to set the spring modulus to a sufficiently low level by making the length L 2  long. However, the length L 2  cannot be made sufficiently long in the conventional structure of the spring contact  420  because it extends straight from the terminal base  410 . It would be possible to make the spring modulus low by reducing the thickness t and narrowing the width W. In this case, however, the possibility of plastic deformation cannot be avoided because the internal bending stress in the spring-contact  420  becomes too large. 
     To cope with the afore-mentioned problem, a terminal  401  shown in  FIG. 8  has been proposed. The terminal  401  is composed of a terminal base  411  and three curved spring-contacts  421  connected to the terminal base  411 . It is possible to make a length L 3  of the spring-contact  421  long and to make the spring modulus low by forming the spring contact  421  in a curved shape. However, another problem is involved in this structure. When the spring-contact  421  is bent by pushing the flat terminal  31  of the button battery  30  against the spring-contact  421 , the spring-contact  421  deflects in a twisted manner. That is, a portion along line X-Y moves as a lever having a fulcrum at point Y. In other words, a large force is applied to point X due to deflection of the spring-contact  421 . Accordingly, the terminal base  411  connected to the substrate by soldering will be peeled off from the substrate during a long time usage. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an improved terminal for a button battery, in which a possibility of plastic deformation and peeling off of a soldered portion is avoided. 
     A button battery is installed in an electronic device such as a keyless entry transmitter or a transmitter for sending signals for wirelessly operating a starter motor mounted an automotive vehicle. The button battery installed in the transmitter is electrically connected by a terminal. The terminal is composed of a terminal base, a spring-contact member and connecting portions connecting the spring-contact member to the terminal base. The terminal is formed by stamping a flat plate made of a resilient and conductive material. 
     The spring-contact member is formed in a circular shape surrounding the terminal base and includes contacting portions resiliently contacting a flat electrode terminal of the button battery. The base terminal connected to the spring-contact member by the connecting portions is fixed to a substrate by soldering or the like. Preferably, a pair of contacting portions is formed on the spring-contact member at symmetrical positions with respect to the terminal base. Preferably, the spring-contact member is connected to the base terminal by a pair of connecting portions positioned symmetrically with respect to the terminal base. 
     The spring-contact member may be formed in a polygonal shape such as an octagonal shape to minimize a material loss in a stamping process. The terminal base may be formed in a polygonal shape such as a rectangular shape to prevent rotation of the terminal base relative to the substrate in a reflow soldering process. 
     Since the spring-contact member is formed in a circular or polygonal shape surrounding the base terminal, its length can be made longer compared with a spring-contact extending straight from the terminal base. Accordingly, a spring modulus of the spring-contact member can be made sufficiently low, thereby reducing a spring-load imposed on the spring-contact member upon its deflection. Therefore, plastic deformation of the spring-contact member is effectively suppressed or avoided. Further, since no twisting force is applied to the spring-contact member upon its deflection, the base plate soldered to the substrate is prevented from being peeled off. 
     Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view showing a keyless entry transmitter; 
         FIG. 2  is a plan view showing a terminal for electrically connecting a button battery in the keyless entry transmitter, viewed in direction A shown in  FIG. 1 ; 
         FIG. 3  is a side view showing the terminal, viewed in direction B shown in  FIG. 2 ; 
         FIG. 4  is another side view showing the terminal, viewed in direction C shown in  FIG. 3 ; 
         FIG. 5  is a graph showing a relation between an amount of deflection of a spring-contact and a spring-load imposed on the spring-contact; 
         FIG. 6  is a plan view showing a modified form of the terminal shown in  FIG. 1 ; 
         FIG. 7A  is a plan view showing a conventional terminal for electrically connecting a button battery; 
         FIG. 7B  is a side view showing the conventional terminal, viewed in direction D shown in  FIG. 7A ; and 
         FIG. 8  is a plan view showing another conventional terminal. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of the present invention will be described with reference to  FIGS. 1-6 . First, referring to  FIG. 1 , a keyless entry transmitter, in which a terminal for electrically connecting a button battery is used, will be described. The keyless entry transmitter is a transmitter for sending signals for wirelessly operating a door lock system installed in an automotive vehicle. 
     A printed circuit board substrate  20 , on which electronic components, including an integrated circuit  60 , a quartz oscillator  61  and a tact switch  62  are mounted, and a button battery  30  for supplying power to the electronic components are contained in a casing composed of an upper resin case  10  and a lower resin case  11 . A terminal  40  contacting a minus-electrode flat terminal  31  of the button battery  30  is mounted on a rear surface of the substrate  20 . Another terminal  50  contacting a plus-electrode terminal  32  of the button battery  30  is also connected to the rear surface of the substrate  20 . 
     A waterproof packing  70  is disposed in the casing as shown in  FIG. 1 , and its lips  71  are sandwiched between the upper resin case  10  and the lower resin case  11  to prevent water from entering the casing. A push button  80  is disposed at an outside portion of the waterproof packing  70 . The tact switch  62  is operated by pushing the push button  80 , and electric power is supplied to electronic components from the button battery  30 . The quartz oscillator  61  generates signals for locking or unlocking the door lock in response to pushing operation of the push button  80 . The signals generated by the quartz oscillator  61  are wirelessly sent to the door lock system installed in an automobile. 
     Now, referring to  FIGS. 2-4 , the terminal  40  contacting the flat terminal  31  of the button battery  30  will be described.  FIG. 2  shows a plan view of the terminal  40 ,  FIG. 3  shows its side view, viewed in direction B shown in  FIG. 2 , and  FIG. 4  shows a side view of its contacting portion, viewed in direction C shown in FIG.  3 . As shown in  FIG. 2 , the terminal  40  includes a terminal base  41 , a circular spring-contact member  42 , and a pair of connecting portions  43  connecting the spring-contact member  42  to the terminal base  41 . The terminal  40  is formed by stamping a flat plate made of a copper alloy, such as phosphor bronze or beryllium copper, covered by nickel and plated with gold. The flat plate may be made of other materials such as silver-plated stainless steel having spring action. In this particular embodiment, a flat plate that is made of phosphor bronze covered with nickel and further plated with gold on nickel is used. It is preferable to use the flat plate having a thickness of 0.1-0.3 mm. In this particular embodiment, the flat plate having a 0.15 mm thickness is used. 
     The terminal base  41  is formed in a rectangular shape in this embodiment, but it may be formed in other polygonal shapes. The terminal base  41  is connected to the rear surface of the substrate  20  by soldering. The spring-contact member  42  is formed in a circular ring surrounding the terminal base  41  and is connected to the terminal base  41  by a pair of connecting portions  43 . The pair of connecting portions  43  are positioned in line with each other and symmetrically with respect to the terminal base  41 . 
     As shown in  FIG. 3 , the spring-contact member  42  is bent toward the button battery  30  at bent portions  42   a,  as shown in  FIG. 3. A  bending angle α is about 30° in this embodiment. The spring-contact member  42  resiliently deflects to a position shown with a chained line in  FIG. 3  when it contacts the flat terminal  31  of the button battery  30 . A pair of contacting portions  42   b  that contacts the flat terminal  31  of the button battery  30  is formed on the spring-contact member  42 . The pair of contacting portions  42   b  is positioned symmetrically with respect to the terminal base  41 , as shown in FIG.  2 . Each contacting portion  42   b  is curved toward the button battery  30 , as shown in FIG.  4 . 
     If a contact pressure between the contacting portion  42   b  and the flat terminal  31  of the button battery  30  is lower than a required minimum pressure Fmin, a power loss occurs due to a contact resistance. The required minimum pressure Fmin defined as a contact pressure between each contacting portion  42   b  and the flat terminal  31  is 50 grams when a nickel-gold type button battery is used. In this embodiment, the nickel-gold type button battery  30  is used. 
       FIG. 5  shows a spring characteristic, a relation between an amount of deflection S of a spring-contact member and a spring-load F applied thereto. A spring modulus of a spring-contact member is defined as an inclination angle of a line showing a spring-characteristic. Line K 1  shows a spring characteristic of the spring-contact member  42  having a spring modulus K 1  used in the present embodiment, and line K 2  shows a spring characteristic of a spring-contact member having a spring modulus K 2  which is larger than K 1 . 
     When the spring-contact member  42  is pressed against the flat terminal  31  of the button battery  30 , it deflects by the amount of deflection S as shown in FIG.  3 . The amount of deflection S is not always exactly constant, but it varies due to dimensional dispersion of the spring-contact member  42  or other factors. When the spring-contact member  42  is designed to deflect by an amount of S 2  (a target amount of deflection), an actual amount of deflection varies in a range ΔS between S 1  and S 3 . It is necessary to set the spring modulus K 1  so that the required minimum pressure Fmin is attained even when the deflection amount is the smallest level, i.e., S 1 . Since a pair of contacting portions  42   b  is provided in this embodiment, the spring modulus K 1  has to be set to attain a minimum spring-load F 1  equal to (2×Fmin). Because the required minimum pressure Fmin is 50 grams in this embodiment as mentioned above, the minimum spring-load F 1  is 100 grams. 
     When the spring modulus is set to K 1  to attain the spring-load F 1  at the smallest deflection S 1 , the spring-load becomes F 2  at the target deflection S 2 , and F 3  at the largest deflection S 3 . The length L 1  of the spring-contact member  42  is longer than the spring length L 2  of the conventional spring-contact  420  shown in  FIG. 7A , because the spring-contact member  42  is formed in a circular shape. Assuming that both of the spring-contact member  42  and the conventional spring-contact  420  are made of a same material having a same thickness, the spring modulus K 2  of the conventional spring-contact  420  becomes higher than K 1  because L 2  is shorter than L 1 . The same level of the required minimum pressure Fmin is required also in the conventional spring-contact  420  at its smallest deflection S 10 . In the conventional spring-contact  420  attaining F 1  at deflection S 10  its spring-load becomes F 20  at a target deflection S 20  and F 30  at a largest deflection S 30 . 
     Assuming the spring deflection S varies in the same range of ΔS in both of the conventional spring-contact and that of the present invention, a spring-load variation ΔF 1  of the spring-contact member  42  of the present invention is smaller than ΔF 2  of the conventional spring-contact  420 . Therefore, the maximum spring-load F 3  applied to the spring-contact member  42  of the present invention can be made much smaller than the maximum spring-load F 30  applied to the conventional spring-contact  420 . Accordingly, a possibility of the plastic deformation of the spring-contact member  42  is considerably reduced, compared with that of the conventional spring-contact  420 . 
     Further, the problem of twisted deflection occurred in the spring-contact  421  shown in  FIG. 8  is also avoided in the spring-contact member  42  of the present invention. Therefore, terminal base  41  that is soldered to the substrate  20  is not peeled off in a course of repeated deflection of the spring-contact member  42 . Since the terminal base  41  is connected to the rear surface of the substrate  20  by soldering, the terminal  40  is easily and automatically mounted. Since the terminal base  41  is formed in a rectangular or polygonal shape, the terminal  40  does not rotate relative to the substrate  20  when it is soldered by reflow soldering. 
     The present invention is not limited to the embodiment described above, but it may be variously modified. For example, the spring-contact member  42  may be formed in an octagonal shape as shown in FIG.  6 . By forming the spring-contact member  42  in the octagonal shape, plural terminals  40  can be formed from a single mother plate, while minimizing a stamping loss in the mother plate. Though a pair of connecting portion  43  is formed in the embodiment described above, it is possible to form three or more connecting portions. Though a pair of contacting portions  42   b  is formed in the embodiment described above, three or more contacting portions may be made. Alternatively, a single contacting portion may be made at one position on the spring-contact member  42 . Though the contacting portion  42   b  is formed in a curved projection, it may be made in a shape of a round projection to further reduce a contact resistance. Further, the terminal base  41  may be made in a circular shape. Though the terminal base  41  is connected to the substrate  20  by soldering, it may be mechanically connected to the substrate. 
     Though the terminal  40  is described as a terminal for electrically connecting a button battery in a keyless entry transmitter, the terminal  40  according to the present invention may be used in other devices such as a transmitter for wirelessly sending signals for operating a starter motor mounted on an automobile. 
     While the present invention has been shown and described with reference to the foregoing preferred embodiment, it will be apparent to those skilled in the art that changes in form and detail may be made therein without departing from the scope of the invention as defined in the appended claims.