Abstract:
Embodiments of the present invention provide a circuit structure that allows the use of a single sided Printed Circuit Board (PCB) with a mechanical key structure that has a light emitting element in the middle of the key structure. An LED with pins for protruding through a printed circuit board allows a layout only on the bottom side of the PCB. In one embodiment, the PCB includes at least one low ohm resister forming a bridge for a switch matrix conductor over a perpendicular switch matrix conductor.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a nonprovisional of and claims the benefit of priority of U.S. Provisional Application No. 62/051,551, entitled, “Keyboard Illuminated Switch,” filed on Sep. 17, 2014, which is herein incorporated by reference in its entirety for all purposes 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to illuminated keys in mechanical keyboards. 
     There are many different types of keyboards. Some well-known keyboards are capacitive (non-mechanical) and mechanical. Mechanical keyboards include membrane (rubber dome) and metal contact (with a spring) keyboards. Membrane keyboards are used for lower profile keyboards, and have a rubber dome that is depressed to actuate a switch. Other mechanical keyboards use a spring mechanism. The spring sometimes takes the form of a scissors mechanism. Mechanical keyboards are often used for gaming, for example. 
       FIG. 1  is a diagram of a prior art Cherry™mechanical key switch for a mechanical keyboard. A spring  102  is mounted in the center below a plunger/actuator mechanism  104 . Off to the side are vertically arranged wire contacts  106  and  108  which are opened and closed by a member  110  as the plunger moves up and down. Not shown is a keycap mounted on top of plunger  104 . 
     Illuminated keyboards can illuminate the keys, in particular the letters, numbers or other indicia on the keys. This has been done with light guides, or with LEDs in the keys themselves. An example of a light guide approach is in Shipman U.S. Pat. No. 7,283,066, Muurinen U.S. Pat. No. 5,408,060 and Chiang (Darfon) U.S. Pat. No. 6,860,612. 
       FIG. 2  is a diagram of a prior art illuminated key from US Published Application No. 20140168936. An LED  202  is mounted on the side of a scissors structure  204  supporting the keycap  206 . 
     BRIEF SUMMARY OF THE INVENTION 
     Embodiments of the present invention provide a circuit structure that allows the use of a single sided Printed Circuit Board (PCB) with a mechanical key structure that has a light emitting element in the middle of the key structure. 
     In one embodiment, an LED with pins for protruding through a printed circuit board is used. This allows a layout on the bottom side of the PCB, simplifying the manufacturing process. With the higher LED structure compared to a surface mount LED, no light guide is needed since the light emitting surface of the LED will be sufficiently close to the key cap. 
     In one embodiment, the PCB includes at least one low ohm resister forming a bridge for a switch matrix conductor over a perpendicular switch matrix conductor. In another embodiment, a third pin is included in the switch, with one of the electrical connections to the two switch pins being made internal to the switch, eliminating the need for a cross-over on the PCB. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of a prior art plunger and switching key mechanism. 
         FIG. 2  is a diagram of a prior art illuminated key with a light emitter on one side. 
         FIG. 3  is an exploded view of the elements of a key structure according to an embodiment of the invention. 
         FIG. 4  is a diagram of the bottom surface of the base of the key structure of  FIG. 3 . 
         FIG. 5  is a diagram of the top portion of the base of  FIG. 4 . 
         FIG. 6  is a diagram of a partially assembled key structure according to an embodiment showing the spring and light guides mounted. 
         FIG. 7  is another diagram of a partially assembled key structure according to an embodiment including a plunger. 
         FIG. 8  is a diagram of a completed key structure according to an embodiment. 
         FIG. 9  is a diagram showing a plated through hole (PTH) LED and a surface mount device (SMD) LED as used in embodiments of the present invention. 
         FIG. 10  is a diagram of a first circuit layout for a key switch PCB according to an embodiment of the invention. 
         FIG. 11  is a diagram of a second circuit layout for a key switch PCB according to an embodiment of the invention. 
         FIG. 12  is a diagram of a third circuit layout for a key switch PCB showing adjacent switch structures according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Example Key Structure with Center LED Mount to Support the Invention 
       FIG. 3  is an exploded view of the elements of a center LED mount key structure. The key structure includes a base  302 , a light guide  304 , a spring  306 , a plunger/actuator  308 , a plunger holder  310  and a key cap  311 . Base  302  includes a central hole  312  for an LED. 
     Contact wires  316  and  318  are arranged horizontally around the central hole  312 . By extending each wire around a corner of the switch base, a spring force is provided. The corresponding separation points near a second corner provide maximum leverage for the spring. The sidewalls  307  and  309  of the plunger  308  are able to separate the spring biased contact portions near the corners. 
     Light guide  304  will be mounted over the LED. A Plated Through Hole (PTH) LED is used without light guide  304 . PTH LED will be taller than a SMD LED, thus eliminating the need for the light guide. In one embodiment, it is a 3 mm LED. 
     The top of light guide  304  can have a diffusion pattern  314  for diffusing the light to key cap  311 . Key cap  311  is mounted over plunger  308 . The letters “ALT” appears on the key cap in translucent manner, with the rest of the key cap being black or other opaque material. Other key caps have different letters or numerals for backlighting. Alternately, the whole or a portion of the key can be at least partially translucent to allow the key to glow when backlit. 
     Plunger holder  310  includes a pair of tabs  320  and  322  which interlock with portions  324  and  326  of base  302 . 
     A number of variations of this structure are possible. For example, four smaller springs could be used at the corners of the key module. Alternately, a wide scissors mechanism could be used, with enough space between the scissor blades for an LED, and a large scissors axle with a hole large enough to accommodate an LED or light guide. 
     The light guide is rectangular to provide optimum distribution of light to a rectangular key cap. Alternately, for a circular key cap, a cylindrical light guide could be used. For a larger key, a wider light guide could be used. Other shapes for keycaps can have correspondingly shaped light guides. Alternately, a wider key can have multiple key plunger structures, with the extra structures having an LED, but not the switching contacts. 
       FIG. 4  is a diagram of the bottom surface of the base  302  of the key structure of  FIG. 3 . The same hole  312  in base  302  can be seen. In the bottom view, contact pins  402  and  404  are shown which will engage with an underlying PCB. 
       FIG. 5  is a diagram of the top portion of the base  302  of  FIG. 4 . As described above in  FIG. 3 , and shown in a different view here, base  302  includes a central hole  312  for an LED. Contact wires  316  and  318  are arranged horizontally around the central hole  312 . This figure gives a better view of a circular depression  502  in base  302  for engaging spring  306 . Also shown again are light guide  304  and a portion of spring  306 . 
       FIG. 6  is a diagram of a partially assembled key structure according to an embodiment of the invention showing the spring and light guide mounted. As can be seen, base  302  has light guide  304  mounted over the central hole ( 312  of  FIG. 3 ). Spring  306  is mounted to engage a circular depression  502  in base  302 . Plunger  308  is shown from the bottom side, illustrating a circular indentation or depression  602  for engaging the other side of spring  306 . 
       FIG. 7  is another diagram of a partially assembled key structure according to an embodiment of the invention including a plunger. Plunger  308  is shown mounted on spring  306  over base  302 . Also, a view from the bottom of plunger holder  310  with locking tabs  320  and  322  is shown. 
       FIG. 8  is a diagram of a completed key structure according to an embodiment. This figure shows the assembled structure with plunger  308  extending through plunger holder  310  which is engaged with base  302 . This figure gives a better view of the pins  402  and  404  extending below the base for engaging with an underlying PCB. 
       FIG. 9  is a diagram showing a plated through hole (PTH) LED and a surface mount device (SMD) LED. A PTH LED  902  has a pair of pins  904  and  906  which extend through a PCB  908  to engage with a printed circuit on the bottom of the PCB by appropriate soldering or welding. A SMD LED has side contacts  912  and  914  for engaging with a circuit on the top of a PCB  916 . Alternately, contacts  912  and  914  can be underneath LED  910 . 
     Single Sided PCT Circuit According to Embodiments of the Invention 
       FIG. 10  is a diagram of a first circuit layout for a key switch PCB according to an embodiment of the invention.  FIG. 10  shows the underside of a PCB for a switch cell. Shown in phantom is where the switch  1002  will be on the top side of the PCB. Also shown in phantom is the outline of the LED  1004 . Conductive trace  1006  is the column line for the switch. Conductive trace  1008  is the row line for the switch. Conductive trace  1010  is the column line for the LED. Conductive trace  1012  is the row line for the LED. Contacts  1014  and  1016  connect with the pins of the switch. Contacts  1018  and  1020  connect with the pins of the LED. 
     A pair of low ohm resistors  1022  and  1024 , preferably 0 ohms, act as bridges for the cross-over of the column and row lines. This makes the layout on one side of the PCB practical. Zero-ohm resistors may be packaged like cylindrical resistors, or like surface-mount resistors. They can thus use the same automated equipment as for normal resistors to install them on the PCB. A SMD Schottky diode  1026  can be soldered below the switch on the bottom of the PCB. 
       FIG. 11  is a diagram of a second circuit layout for a switch PCB according to an embodiment of the invention. It is the same as  FIG. 10  except that one of the 0 ohm resistors, resistor  1022  of  FIG. 10 , has been eliminated. Instead, a third switch pin  1102  is added. Inside the switch, pin  1102  is connected to the pin at contact  1014 . Thus, the column line is completed inside the switch module. 
       FIG. 12  is a diagram of a third circuit layout for a switch PCB showing adjacent switch structures according to an embodiment of the invention. In this embodiment, all LEDs are connected in parallel, using a single control signal. Thus, the LED column line of  FIGS. 10 and 11  is eliminated. The cells for switches  1002  and  1202  use a single LED control trace  1204 . 
     Also shown is a dual diode  1206  connected between lines  1208  and  1210 , connected to switch pins of switches  1002  and  1202 . By rotating the switch by 90°, the soldering pads will be flipped (mirrored). This will make it possible to use a dual diode package (e.g., BAT54). A single bridge  1212 , over 3 lines, is used per switch. Since low current flows through this 0 ohm bridge, carbon tracks (Carbon Conductive Ink) can be used as a cross-over in another embodiment. 
     Alternate Embodiments 
     Although the invention has been described with respect to specific embodiments, it will be appreciated that the invention is intended to cover all modifications and equivalents within the scope of the following claims. For example, light emitters other than LEDs could be used. The LED can be a mono-color or multicolor LED. LEDs and switches with more pins could be used, with corresponding changes to the PCB layout traces. Accordingly, the foregoing described embodiments are intended to be illustrative, but not limiting, of the scope of the invention which is set forth in the following claims.