Abstract:
A push button switch includes a case consisting of an upper case member and a lower case member, a stem vertically movably provided in the case, and a switch element for effecting on-and-off operation of the switch by vertical movement of the stem. A holding structure for the switch element has a first projection formed at an upper end of a frame of the switch element, a second projection formed around a terminal of the switch element, a projection insert hole formed through the upper case member and engaged with the first projection, and a terminal insert hole formed through the lower case member and engaged with the second projection.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a keyboard switch employable for various input devices of a personal computer and a word processor, etc., and more particularly to an improvement in a structure of a push button switch. 
     A conventional push button switch is disclosed in Japanese Utility Model Laid-Open Publication No. 58-193428, for example, as shown in FIG. 6. Referring to FIG. 6, a case 1 is formed with a switch element mount hole 1a for mounting therein a switch element 2 having a pair of terminals 2a and 2b and an actuator 2c, and with a stem insert hole 1b for vertically movably receiving a stem 3. The stem 3 is inserted over a coil spring 4 into the stem insert hole 1b. A pusher plate 5 has a pair of engagement pawls 5a and 5b to be engaged with a pair of engagement portions 1c (only one is shown). Thus, the pusher plate 5 is fixed to the upper surface of the case 1. Further, a key top 6 is formed at its lower portion with a projection (not shown) to be engaged with an engagement hole 3a of the stem 3. 
     However, in the conventional push button switch as mentioned above, the terminals 2a and 2b of the switch element 2 project from recesses 1d and 1e of the case 1. Therefore, soldering flux, which is applied to a printed board for the purpose of soldering the terminals 2a and 2b to the printed board, is elevated along the terminals 2a and 2b to penetrate from the receses 1d and 1e into a contact portion of the switch element 2, causing imperfect contact of the contact portion. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a push button switch which may prevent penetraton of the flux into a contact portion upon soldering of terminals of the push button switch to the printed board. 
     It is another object of the present invention to provide a push button switch which may effect a stable contact operation. 
     According to the present invention, in a push button switch including a case consisting of an upper case member and a lower case member, a stem vertically movably provided in the case, and a switch element for effecting on-and-off operation of the switch by vertical movement of the stem; the improvement comprises a first projection formed at an upper end of a frame of the switch element, a second projecton formed around a terminal of the switch element, a projection insert hole formed through the upper case member and engaged with the first projection, and a terminal insert hole formed through the lower case member and engaged with the second projection. 
     With this arrangement, there is no possibility of the flux penetrating between the second projecton and the terminal of the switch element or between the second projection and the terminal insert hole of the lower case member. 
    
    
     Other objects and features of the invention will be more fully understood from the following detailed description and appended claims when taken with the accompaning drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of the push button switch of a preferred embodiment according to the present invention; 
     FIG. 2 is a perspective view of the switch element according to the present invention; 
     FIG. 3 is a bottom plan view of the push button switch; 
     FIG. 4 is a side view of the push button switch as mounted on the printed board; 
     FIG. 5a is a bottom plan view of the upper case; 
     FIG. 5b is a top plan view of the lower case; and 
     FIG. 6 is an exploded perspective view of the push button switch in the prior art. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 to 5b, reference numeral 11 designated an upper case formed of resin or the like. The upper case 11 is formed at its central portion with a stem receiving hole 11a. A stem 13 is received in the stem receiving hole 11a in such a manner as to be vertically movable by means of a coil spring 12. The stem 13 is formed on its one side surface with a projection 13a. The projection 13a is vertically slidable in a vertically elongated guide groove 11c formed between the stem receiving hole 11a and a contact receiving hole 11b. The contact receiving hole 11b is formed between the stem receiving hole 11a and one side wall of the upper case 11, so as to receive a switch element 14. The switch element 14 includes a substantially U-shaped frame 15. The frame 15 holds therein L-shaped fixed and movable contact members 16 and 17 by insert molding. The fixed and movable contact members are provided with contacts S1 and S2, respectively, which are arranged in opposed relation to each other. Terminals T1 and T2 of the contact members 16 and 17 extend from the lower end connected to the frame 15, and are formed with respective ribs A in the vicinity of the lower ends thereof. The frame 15 is further formed on its side surface with a pair of projections 15a engaged with holes 18a of an actuator 18 fixed by caulking. The actuator 18 includes a pusher member 18b adapted to push a projection 17a of the movable contact member 17 when the pusher member 18b is pushed by the projection 13a of the stem 13 in its initial state. That is, the pusher member 18b (rear side in the FIG. 2) initially bears against the movable contact 17 to hold the contacts apart so that the switch is normally open. When the stem 13 is depressed, the projection 13a is moved downward in the groove 11c, and the pusher member 18b is released, so that the contacts S1 and S2 of the fixed and movable contact members 16 and 17 are in contact with each other. The frame 15 is formed at its upper both ends with a pair of circular projections 15b to be engaged with a pair of projection insert holes 11d of the upper case 11. The terminals T1 and T2 are formed at their respective bases with a pair of circular projections 15c to be engaged with a pair of terminal insert holes 19a of a lower case 19. LED 20 has a pair of terminals 20a to be inserted into a pair of terminal insert holes 19b of the lower case 19, and a body of the LED 20 is fixedly mounted in a LED mount portion 11e of the upper case 11. A conductive member 21 is provided to connect patterns on a printed board 22 with each other. The conductive member 21 has a pair of terminals 21a to be inserted into a pair of conductive member insert holes 19c of the lower case 19. 
     The above-mentioned push button switch is assembled in the following manner. First, the stem 13 is inserted into the stem receiving hole 11a of the upper case 11, and then the projections 15b of the switch element 14 are engaged with the projection insert holes 11d to mount the switch element 14 in the contact receiving hole 11b. Then, the coil spring 12 is brought into abutment against the lower surface of the stem 13. On the other hand, the terminals 20a of the LED 20 and the terminals 21a of the conductive member 21 are engaged with the terminal insert holes 19b and the conductive member insert holes 19c of the lower case 19, respectively. Then, the lower end of the coil spring 12 is engaged with a projection 19d of the lower case 19. Further, the projections 15c of the switch element 14 are firmly engaged with the terminal insert holes 19a of the lower case 19. Simultaneously, a pair of snap members 19e of the lower case 19 are engaged ina snap-in fashion with two pairs of projections 11f of the upper case 11. Thus, the push button switch is constructed. Thereafter, the terminals 21a of the conductive member 21 are bent into a V-shaped configuration. Then, the terminals 21a of the conductive member 21, the terminals T1 and T2 of the switch element 14 and the terminals 20a of the LED 20 are all inserted into the printed board 22, and are soldered thereto, thus completing the assembling of the push button switch. In this embodiment, since the terminals 21a of the conductive member 21 are in a V-shaped configuration, and the terminals T1 and T2 of the switch element 14 are formed with the ribs A, the push button switch is firmly fixed to the printed board 22. 
     In operation, when the stem 13 is depressed against a spring pressure of the coil spring 12, the projection 13a that normally pushes the pusher member 18b of the actuator 18 in the initial condition is lowered. As a result, the contact S2 of the movable contact member 17 of the switch element 14 is brought into contact with the contact S1 of the fixed contact member 16 to thereby turn on the switch. At the same time, the LED 20 is operated to emit a light. When the depression force applied to the stem 13 is removed, the stem 13 is returned to its initial condition by the spring pressure of the coil spring 12. 
     In the construction of the push button switch as mentioned above, each pair of projections 15b and projections 15c are formed at the upper and lower ends of the frame 15 of the switch element 14, wherein the projections 15b are engaged with the projection insert holes 11d of the upper case 11, while the projections 15c are firmly engaged with the terminal insert holes 19a of the lower case 19. Accordingly, when soldering the push button switch to the printed board, there is no possibility of the flux penetrating from between the terminals T1 and T2 and the projections 15c or between the projections 15c and the terminal insert holes 19a. Furthermore, since the terminals 21a of the conductive member 21 for connecting the patterns on the printed board 22 with each other are formed in a V-shaped configuration, and the terminals T1 and T2 of the switch element 14 are formed with the projecting ribs A, the push button switch may be easily mounted on the printed board 22. In addition, since the push button switch is firmly fixed to the printed board 22 by soldering, and the switch element 14 is sandwiched by the upper case 11 and the lower case 19, a stable contact operation of the push button switch may be achieved without any slippage of position. 
     Further, as the conductive member 21 for connecting the patterns on the printed board 22 is located at the lower portion of the case to provide an increased distance from the key top to the terminals 21a of the conductive member 21, static elasticity accumulated in a human body would not adversely affect a circuit of the printed board in the operation of the push button switch. 
     While the invention has been described with reference to specific embodiments, the description is illustrative and is not to be construed as limiting the scope of the invention. Various modifications and changes may occur to those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.