Patent Publication Number: US-2007114264-A1

Title: Mesotube electode attachment

Description:
FIELD OF THE INVENTION  
      The present invention relates to mesotube construction. More particularly, the invention relates to construction of mesotubes in which the electrodes that support mesotube grids in a precisely aligned configuration.  
     BACKGROUND OF THE INVENTION  
      In many electronic devices such as mesotubes and the like, it is necessary to place grids or other plates in precise relationship to other similar grids or plates. In a mesotube, the grids must be essentially parallel to each other and must be spaced by a precise distance to operate efficiently. The grids or plates are supported on electrodes that permit the device to function.  
      For example, a tungsten lower grid in a typical mesotube is to be supported on three header pins or electrodes that are perpendicular to the plane of the grid and the upper grid is to be supported on three other header pins or electrodes that also are perpendicular to that grid. The two grids are to be spaced by a precise distance, in one design by 15 to 20 mils with a tolerance of no more than about ±1 mil. The preferred method of attaching the grids to the electrodes, as is done in many present day electronic devices using grids, is to spot weld the grid to the electrode.  
      In prior attempts to accomplish precise placement and orientation of grids on the ends of header pins or electrodes, direct spot welding on the heard pins has failed. The pins are often made from a nickel plated Kovar, which is a Westinghouse trade name for an alloy of iron, nickel and cobalt, that has the same thermal expansion as glass and for that reason is often used for glass-to-metal or ceramic-to-metal seals. The problem with spot welding is that the pins or electrodes are held in place by insulators and these insulators do not survive the heat of the welding process. Production failure renders the use of the device much more expensive than necessary.  
      It would be an advantage in the art if a way could be devised that would permit spot welding of pins and electrodes to plates and grids without damage to adjacent components such as insulators.  
      Yet another advantage would be if a device could be provided that would not only protect adjacent components but would assist in the precise alignment of the pins and electrodes with respect to the grids or plates to insure proper alignment and optimum functional results.  
      Other advantages will appear hereinafter.  
     SUMMARY OF THE INVENTION  
      It has now been discovered that the above and other advantages of the present invention may be obtained in the following manner. Specifically, the present invention provides a device for gripping the pin or electrode and directing the weld heat away from other components.  
      The device includes a support or insulating fixture for mounting the device that has a shaft extending up and parallel to the electrode or pin being attached to a plate or grid. The fixture is referenced to the header floor in which the pins are precisely located and connected. The insulating fixture prevents any conductive paths from the clamp electrode to the header base through the insulators and locates the header pins precisely with respect to the top weld electrode. This top weld electrode pushes the plate or grid against the pin being welded to it. The clamp is preferably a spring loaded, split ring, conducting clamp.  
      In operation, the fixture is put in place proximate the specific pin being welded, the clamp grips the pin and is maintained in contact with its spring loading. The grid or plate is place in the desired position in contact with the pin, a welding electrode is placed on the other side of the grid, and welding takes place. The heat passes through the welding electrode, through the grid, into the pin and is then diverted from the pin to the clamp, thus insulating the remaining portion of the pin and the equipment associated with it.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      For a more complete understanding of the invention, reference is hereby made to the drawings, in which:  
       FIG. 1  is a schematic view of a mesotube being assembled; and  
       FIG. 2  is a top view of the clamp of this invention. 
    
    
      In the figures, like reference characters designate identical or corresponding components and units throughout the several views.  
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      The present invention is admirably suited for attaching grids, plates and other flat objects to pins, posts, electrodes and other components that are conductive and perpendicular to the first object.  FIG. 1  illustrates a typical application of the present invention, in which mesotube grids are attached to a plurality of pins. As can be appreciated, the mesotube shown in  FIG. 1  only shown the internal components of grids, pins and insulators, and the whole device is not illustrated.  
      Header  11  is provided for mounting the various components of the mesotube, and includes insulators  13  that mount and support pins  15 . A top view would show header  11  as a circular plate on which the insulators  13  and pins  15  are positioned so that three pins  15   a,    15   b  and  15   c  are positioned to contact and support tungsten grid  17  and three more pins  15   d,    15   e  and  15   f  are positioned to contact and support upper grid  19 . Tungsten grid  17  is about 4 mil thick in this example. This is conventional construction, though the manner in which the grids are attached to the pins is not.  
      As shown on the right side of  FIG. 1 , an insulating fixture  21  is mounted to header  11 . Fixture  21  supports shaft  23 , which in turn positions clamp  25  in the appropriate alignment to allow clamp  25  to engage a pin, in this case pin  15   a  using spring  27  as seen in  FIG. 2 . Wafer  17  is then spot welded to pin  15   a  by applying electrode  29  to the other side of wafer  17  and welding using, for example, a 400 volt welding potential. Current passes through the electrode  29  into wafer  17  and pin  15   a.  Current is prevented from reaching other parts of the mesotube such as insulator  13   a  as the current is directed into the body of clamp  25  and shaft  23 , but is stopped by insulation fixture  21 . Each pin  15   a,    15   b,  and  15   c  is welded to wafer  17  individually by moving fixture  21  and thus clamp  25  to the position where clamp  25  engages the specific pin. Similarly, grid  19  is attached sequentially to pins  15   d,    15   e,  and  15   f  in the same manner.  
      Prior art efforts to spot weld wafers to similar devices have failed because damage was done to the components of the mesotube. In  FIG. 1 , a prior art attempt to directly weld wafer  17  to pin  15   c  is shown on the left hand side where electrode  29   c  contacts one side of wafer  17  and welding current passes through wafer  17  into pin  15   c  down to insulator  13   c,  which is damaged and renders the device inoperative.  
      The present invention has been shown for use with mesotubes that employ wafers and pins to support them in precise alignment. The invention is also admirably suited for use with any similar device, electronic or not, which requires precise positioning of a flat surface on a pin or pole or other round or otherwise shaped element, perpendicularly aligned or at an angle, where spot welding is used. Accordingly, the terms wafer and pin are to be broadly interpreted to represent any such flat surface and shaped element.  
      While particular embodiments of the present invention have been illustrated and described, it is not intended to limit the invention, except as defined by the following claims.