Patent Publication Number: US-2013248340-A1

Title: Electric SMD Type Switching Element

Description:
TECHNICAL FIELD 
     The present invention concerns an SMD type electric switching element in accordance with the preamble of Claim  1 , in particular, an electrically illuminating push button of the SMD type. 
     PRIOR ART 
     The SMD manufacturing process, whereby the abbreviation stands for Surface Mounted Device, is a technique for populating printed circuit boards that presents multiple advantages. If a computerized populating method is used, the electric elements to be inserted can be soldered directly on the surface of a printed circuit board. Since no parts of the electric components pierce through the printed circuit board, it is advantageous that both sides of the printed circuit board can be populated with circuits. 
     An optical contact switch is known from DE 10 2006 040 803, which is arranged as an SMD component on a support featuring SMS contacts, which can then be electrically connected with the conductor path of a printed circuit board. 
     Thereby, the insertion effort for attaching a switch onto a printed circuit board can be reduced. The four lateral SMD contacts allow contact between the plate-type optical switching element and a printed circuit board. The switch is protected against direct contact by a cover panel and functions as an optical contact switch. 
     DESCRIPTION OF THE INVENTION 
     Based on this prior art, the object of the invention is to describe an electric SMD type switching element of the type mentioned at the beginning, which is designed as a pressure switch. A further objective of the invention is to describe an illuminated SMD push button. 
     Another object of the present invention is to enhance the operational reliability of this type of switch. 
     This object has been achieved with the characteristics of Claim  1  according to the invention. 
     An electric SMD type switching element has a body incorporating the switching element, at least two contact surfaces arranged on the underside of the body for attaching the SMD, and an actuating element arranged on the opposite side from the underside, which is movably connected to the body as a moving portion in keeping with the longitudinal axis of the switching element. Thereby, an electrically conducting connection is now established between the contacts via a switching contact, which can be closed by the relative movement of the actuating element, in particular, a movement along the longitudinal axis of the switching element that is the central axis vertical to the printed circuit board, relative to the switching contact. The body now has a lower section, which features the two contact surfaces and the switching contact, and an upper section, which comprises the actuating element. At the same time, the lower section and the upper section should be connected via complimentary catch mechanisms. Thereby, the lower section can be manufactured from a plastic capable of withstanding the heat of soldering an SMD, while the upper section can be manufactured using conventional materials. This is only placed on the lower section after soldering, and the switch or push button is completed. 
     The second object is achieved with the characteristics of Claim  7 . This type of switching element has an actuating element with an actuating lug, with which the contacts can be closed by the said movement of the actuating element relative to the switching contact. Advantageously, the switching contact is a flexible blade, which is permanently connected to a contact (soldered, for example), and has a section projecting into the movement range of the actuating lug, which can therefore be pushed away. Here, the switching contact is an elongated spring, which is divided into at least two parallel flexible blades by at least one slot running lengthwise. Here, with two or more longitudinal slots, these at least partially differ in length, whereby all slots pierce at least the contact area between the blade and the counter contact, whereby at least one projects into the end range of the flexible blades. 
     Further embodiments are indicated in the dependent Claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the invention are described in the following by reference to the drawings, which only serve the purposes of explanation and should not be interpreted as limiting. The drawings depict: 
         FIG. 1  a partially cutaway cross-section view of two push buttons in accordance with one example of the realization of the invention arranged next to each other on a printed circuit board, 
         FIG. 2  a perspective view of a pressure switch from  FIG. 1 , 
         FIG. 3  an exploded view of the switch in accordance with  FIG. 2 , 
         FIG. 4  a partially cutaway perspective view of the lower section of the push button in accordance with  FIG. 2 , featuring redundant contact, 
         FIG. 5  a partially cutaway plan view of the lower section in accordance with  FIG. 4 , and 
         FIG. 6  a partially cutaway cross-section view of the push button mounted on a printed circuit board. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows a partially cutaway cross-section view of two push buttons  1  arranged next to each other on a printed circuit board, which are connected to a printed circuit board  2 , whereby the actuation caps  3  of the push button  1  project through a front panel  4 . The electric SMD type switching element in accordance with the invention is an electrically illuminated push button or pressure switch. The depiction of the printed circuit board  2  is schematic. On a control panel, a printed circuit board  2  is usually fitted with an appropriate circuit, which can be switched via various actuating elements, in particular the push button  1 . Here, the printed circuit board  2  is arranged in a frame underneath the front panel  4  of an operating console, whereby the actuation caps  3  of the control elements project as far as the front panel  4 . On the left-hand side of  FIG. 1 , the push button  1  has not been activated, that is, the contact has not been closed, while for the pressed push button  1  on the right-hand side of the depiction, the contact has been closed. 
     The structure of the push button  1  will now be described in more detail in association with the perspective depiction in  FIG. 2  and the exploded view in  FIG. 3 . 
     In place of a push button  1 , which clicks into place on the detachable snap-in lugs  15  and  16  and consequently defines an ON and an OFF position, it can also be a simple rocker switch, which returns to its initial position after contact, whereby the illumination would have to be designed differently due to the greater distance from the optical fiber  13  to the diffuser  5 . 
     The push button  1  consists of multiple operating elements, which are prefabricated as a unit and incorporate the pressure cap  3  as a protruding element. Advantageously, the pressure cap  3  already consists of multiple parts and consists of a transparent pressure cap  3  as such, under which an also transparent diffuser cap  5  is arranged. This advantageous double arrangement allows labeling foils to be inserted between the pressure cap  3  and the diffuser  5  or, for example, direct laser labeling of the surface of the diffuser  5 , which is then protected from abrasion due to the use of the pressure cap  3 . In principle, a one-piece embodiment is also possible here. The pressure cap  3  clips onto a guide frame  6 . This embodiment of the connection of the pressure cap  3  and the diffuser  5  is known in principle and could also be produced by means of bonding or welding. The guide frame  6  has multiple slide sections moving down from the pressure cap  3 , of which one is designated by Reference Symbol  7 . A corresponding profile groove  8  of the guide frame  6  has been labeled as Reference Symbol  8 . 
     Furthermore, the guide profiles  7  forming a closed frame, as depicted in the cutaway plan view in  FIG. 5 , incorporate an actuation panel  9 , with which the contact blade  10  of the push button  1  can be switched. This operating part of the switch  1 , in particular, moves along its main axis  43  towards the upper section  11  of the switch and the lower section  12  of the switch. These actuating elements  3 ,  6 ,  9  clip advantageously into the upper section  11  of the switch, such that the said longitudinal movement between the upper section  11  and the operating elements  3  and  6  of the push button is possible, but these elements, both prior to assembly as well as following assembly, do not fall apart on being operated. The optical fiber  13  is integrated in this frame that is connected in particular to the upper section  11 . The optical fiber  13  is set centrally in the upper section  11  and in the guide frame  6 . Here, the guide frame  6  can be clasped by the lug  16  located in a recess, in and under the corresponding lugs  15  in the upper section  11 . 
     The optical fiber  13  meshes into corresponding connection lugs in the upper section  11  with lateral notches  14 . Corresponding recesses  28  are provided in the guide frame  6  for this purpose, such that the guide frame  6  can be moved longitudinally over the optical fiber  13  and between its connection with the upper section  11 , that is, along the main axis  43  of the button. 
     Hence, after operating the switch, the guide frame  6  returns to its initial position, shown on the left in  FIG. 1 , with the pressure cap  3 . Two springs  17  are provided, which are supported on a base plate provided in the upper section  11  and have their counter bearing opposite, on a lower edge of the guide frame  6  in the upper section  11 . 
     The lower section  12  of the push button  1  has four snap-in lugs  18 . The snap-in lugs  18  are arranged on the lateral surfaces of the lower section  12 , on opposite sides respectively. Here, in each case, two are arranged near the corners. The snap-in lugs  18  extend upwards in the direction from which the upper section  11  can be positioned and they can be positioned in corresponding lug seatings  19  in the upper section  11  and can then be snapped into place. Hence, the lower section  12  and the upper section  11  can be connected to the installed, separately snapped-in operating part  3 ,  6 ,  13 , as one functional unit. 
     The lower section  12  has a contact support  20  extending into the upper section  11 , which, for example, can be formed as one piece with and from the same material as this. The contact  23  ends on the contact support  20  in a contact strip running along the upper edge, on which a free end of the contact blade  10  is fixed, in particular, soldered on. The other end of the contact blade  10  with the Reference Symbol  40  extends to the side of the contact support  20  turned towards the outer side of the housing. This is arranged with a lateral clearance from a counter contact  22  which essentially runs in the contact support  20  in its principal plane and hence is arranged with its broad surface opposite the contact blade  10  and a section of spring  35 . The counter contact  22 , then, has a surface on the external surface of the lower section  12 , which is designed for contact with the printed circuit board  2 . In  FIG. 3  it can also be seen that the contact  23  can be connected to the printed circuit board  2  via a connection on the inside of the housing via the contact plate  24 . The contact plate is set down behind a shoulder and, along with the corresponding contact plate  22 , is located on the underside  42  of the lower section  12 , for example in a corresponding recess. In particular, these contact surfaces line up precisely with the underside  42  of the lower section  12 . 
     The run of the contact sequence as depicted is advantageous for the depicted example of the realization of the invention. Initially, however, only the incorporation of the SMD-capable contacts  22  and  24  on the lower section  12  is essential, whereby one part of the contact chain  24 - 23 - 20 - 35 - 22 , namely the contact  35 , can be actuated by the actuating lug  39  of the upper section  11 . 
     Positioning guides  25  are also depicted in  FIGS. 2 and 4 , two of which can be provided in particular on diametrically opposite corners of the underside  42  of the lower section  12 . These, then, protrude, as shown in  FIG. 6 , preferably from the component side of the push button  1  into blind holes  26  provided in the printed circuit board  2 . This positioning aid makes sense, particularly when mounting the lower sections  12  on the printed circuit board  2  manually, while these positioning guides  25  are not necessary and therefore can be omitted where SMD mounting is automated. Hence, they enhance the versatility of the push button  1  in multiple embodiments for various customer requirements. 
     For an illuminated SMD button  1  in accordance with the invention, it is advantageous that due to the frame design of the lower section  12  there is an internal cavity or aperture  29 , in which one, two or three LEDs  30 , in particular LED SMDs, can be mounted on the printed circuit board  2 . Here, the optical fiber  13  is positioned in respect of the upper section  11 , and hence, via the direct connection with the lower section  12 , also fixed in position in respect of the printed circuit board  2 , such that the underside  31  of the optical fiber  13 , which preferably forms a smooth rectangular surface  31 , is arranged with as little clearance as possible, of 2 to 3 mm above the upper edge of the SMD-connected LEDs  30 . Hence, with the advantageously curved, here plano-convex, upper shape  32 , which combines with the plano-concave design of the diffuser cap  5 , a good luminous efficiency can also be guaranteed. 
     The segmentation of the housing of the push button  1  into a lower section  12  able to be inserted as an SMD and an upper section  11  incorporating the operating part  5 ,  6 ,  8  and the optical fiber  13  is important in terms of manufacturing. 
     In this type of illuminated push button  1 , the well-aligned arrangement of the optical fiber  13  fixed opposite the upper part of the housing  11  and the guidance of the pressure cap  3  opposite this upper part of the housing  11  is crucial. This increased precision in the manufacture of components is temperature-sensitive and the upper housing part  11  should therefore not be exposed to increased temperatures, as it would normally be during SMD soldering. Therefore, this component  11  of the push button  1  is separated from the component  12 , which, together with the contact  20 ,  22 ,  23  and  24  preferably integrated into this, can be soldered on the printed circuit board  2  in SMD architecture. For this reason, the lower section  12  consists of a high-temperature resistant plastic, possibly quite contrary to the upper section  11 , for which conventional plastics can be utilized, such that, in terms of its dimensions, the lower section  12  will not warp due to the impact of heat during the SMD mounting process. Hence, after this mounting step, the upper section  11  can then be clipped on in order to assemble the finished push button  1 . 
     A high-temperature resistant plastic, which withstands the temperatures occurring during the soldering and remains dimensionally stable when the SMD is soldered, is suitable for the lower section  12 . In the process, depending on the method and soldering furnace used, temperatures, in particular, from 180 to 280 degrees Celsius, can occur over a period of 1 to 2 minutes. Thermostable means that the lower section does not change or only changes negligibly with respect to its original shape prior to soldering, that is it physically and materially exhibits the same external shape and it also, advantageously, exhibits no chemically altered characteristics. 
       FIG. 5  is a good depiction of some of the elements of the drawings described above in a partial cutaway plan view, in particular, the positioning of the springs  17  on the corresponding cylinders  33  and the three guide profiles, the laterally overhanging profiles  7  and the profile groove  8 , into which a lug  34  of the upper section  12  projects. A complementary recess  41  in the side panel of the upper section  11  faces the profile  7 , which reduces the panel thickness. Here, it should be noted that, if the upper section  11  facing the guide frame  6  becomes hot, that is, exhibits a substantial difference in temperature, this would damage the guidance characteristics between the sliding surfaces  7 - 41  and  8 - 34 . After assembly, three-point guidance with respect to the interior panel of the upper part of the housing  11  is provided by the elements  7  and  8 , with a noise-reduced surface feel. 
     Furthermore, it should be realized that the base of the optical fiber  13  occupies a substantial part of the internal space of the upper section  11  and thus, in contrast to the lower surface  31 , also covers the entire cavity  29  of the lower section  12  with its tapered shape and hence, in terms of the light circuit, is not susceptible in relation to the exact positioning of one, two or three LEDs  30  between the SMD fastening points for the push button  1 . In place of the cylinders  33  with a counterface in the region of the underside  27  appearing, for example, in the form of a collar between the guide frame  6  and the diffuser  5 , as a counterpressure surface for compression springs  17 , tensions springs can also be utilized, which are then mounted on corresponding stop collars on the upper section  12  and the frame  6 . 
     In particular, this type of switch can be used, for example, for a video desk and the back of the printed circuit board  2  can then be equipped with further components, without limitation. 
     Thus, more functions can be accommodated in the same space. The lower section  12  of the push button  1 , for example, is mounted on the printed circuit board  2  by means of a re-flow soldering process. Advantageously, the lamps  30  are SMD LEDs  30 , which are mounted centrally between the contacts  22 ,  24  of the push button  1 . 
     The lower section or contact support  12  is positioned on the printed circuit board  2  by hand (if the lugs  25  have been provided) or in an automated process and are then soldered with the printed circuit board  2  by means of a re-heating furnace soldering process. After cooling, the upper part of the button  11  can then be plugged into the lower part of the button or contact support  12  and can be clicked into the recesses  19  using the lugs  18 . 
     A further object of the present invention is to guarantee the functionality of the switching system over a very large number of several hundred thousand switching operations. The push button described is not a completely encapsulated system, allowing contaminants to get into the housing over time via the upper section  11  and the lower section  12  and allowing the functionality of the switching system to be compromised. 
     In principle, the contact blade  10  is switched in the traditional manner by the actuation panel  9  of the frame  6  and there, in particular, by the contact lug  39  depicted in  FIG. 3  against the counter contact  22 . This contact blade  10  features an overhanging spring area  35  in the direction of the counter contact  22  for this purpose, while an opposing projection  36  is provided for the contact with the contact lug  39 . The slotted contact blade  10  is now positioned across the elements  35  and  36  in the embodiment depicted. In the example of the realization depicted, there are three slots  37  running longitudinally over the spring  35  and recesses  36 , which divide the contact blade  10  into four blades  38 . If a contaminant now finds its way onto or under the contact blade  10 , then it is very probable that, due to the size of the elements penetrated, these will only span a part of the area of the width of the blade and hence one or more blades will still be able to be actuated by the actuating lug  39 . 
     It can also be seen in  FIG. 4  that the lengths of the slots  37  are varied. In one advantageous embodiment with at least three blades  38  and hence two or more slots  37 , it became apparent in experiments that it is very advantageous when the slots  37  are of varying lengths, such that only one slot  37  ends in the end range  40  of the contact blade  10  and the other slots  37  are set back and hence form a larger area of solid material of the flexible contact blade  10  on the apex of the contact blade  40 . As a result, the number of cycles of operation can be increased by a factor of 5 to 10 in comparison with when all blade slots  37  are of the same length before material fatigue occurs. In particular, the blade slots  37  pass over the section forming the spring lug  35  across from the contact  22 , however, not all pass over the opposing elevation  36  actuated by the lug  39 . 
     
       
         
           
               
             
               
                   
               
               
                 LIST OF REFERENCE SYMBOLS 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 1 
                 Push button 
               
               
                 2 
                 Printed circuit board 
               
               
                 3 
                 Pressure cap 
               
               
                 4 
                 Front panel 
               
               
                 5 
                 Diffuser 
               
               
                 6 
                 Guide frame 
               
               
                 7 
                 Profile 
               
               
                 8 
                 Profile groove 
               
               
                 9 
                 Actuation groove 
               
               
                 10 
                 Contact blade 
               
               
                 11 
                 Upper section 
               
               
                 12 
                 Lower section/Contact support 
               
               
                 13 
                 Optical fiber 
               
               
                 14 
                 Notch 
               
               
                 15 
                 Lug 
               
               
                 16 
                 Lug 
               
               
                 17 
                 Spring 
               
               
                 18 
                 Snap-in lug 
               
               
                 19 
                 Lug seating 
               
               
                 20 
                 Contact support 
               
               
                 21 
                 Contact surface 
               
               
                 22 
                 Counter contact 
               
               
                 23 
                 Contact 
               
               
                 24 
                 Contact 
               
               
                 25 
                 Positioning guide 
               
               
                 26 
                 Blind hole 
               
               
                 27 
                 Underside 
               
               
                 28 
                 Recess 
               
               
                 29 
                 Aperture 
               
               
                 30 
                 LED 
               
               
                 31 
                 Base 
               
               
                 32 
                 Convex lens shape 
               
               
                 33 
                 Cylinder 
               
               
                 34 
                 Lug 
               
               
                 35 
                 Spring 
               
               
                 36 
                 Recess 
               
               
                 37 
                 Slot 
               
               
                 38 
                 Blade 
               
               
                 39 
                 Contact lug 
               
               
                 40 
                 End range 
               
               
                 41 
                 Recess 
               
               
                 42 
                 Underside 
               
               
                 43 
                 Longitudinal axis