Abstract:
A capacitor and a method for assembling a capacitor. A capacitor is assembled from a case, which contains an anode that is electrically insulated from the case by isolators. A washer is placed above the anode. This washer transfers force from a capacitor cap to the isolators and anode, securing the anode in place. A cap is placed on the case. The cap may be shaped as a toroid with an outer and an inner annular wall. The annular walls may meet at the top and have an opening at the bottom creating a cap cavity in order to store electrolyte or other materials in the cap. The cap also supports a glass seal that insulates the lead tube and lead wire coming from the anode. Once assembled, the capacitor is filled with electrolyte. A weld extends around the cap to secure the cap to the case. The weld may be administered from the top of the capacitor.

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field 
   This invention generally relates to a tantalum capacitor case that increases the electrolyte volume of the standard size case, and to a method for assembling the tantalum capacitor. 
   2. Background Art 
   There are at least two common conventional tantalum electrolytic capacitor configurations. The first configuration is illustrated by FIG.  1 . The capacitor assembly is contained in a case  13  having a height greater than its diameter. The case  13  contains an isolator  12 , which is formed from an electrically insulative material and is shaped so that it may receive a tantalum anode  8 . The isolator  12 , as shown in  FIG. 1 , is a flat disk of insulative material that sits under the anode  8  and prevents the anode  8  from coming into contact with the case  13 . The isolator  12  also comprises a ring of insulative material that fits down around the sides of the anode  8 . The isolator  12  may also be arranged so that legs on the isolator  12  extend upward and allow the anode  8  to be placed inside them. 
   With the anode  8  in place, the case  13  is filled with electrolyte. A plug  6 , which is typically formed from Teflon due to its resilience and resistance to electrolyte, has an ‘O’ ring  11  placed around it. The plug  6  and the ‘O’ ring  11  are then placed on top of the anode  8 . The case  13  is then crimped around the plug  6  and the ‘O’ ring  11  with an annular crimp  10 . This crimp  10  around the ‘O’ ring  11  forms a seal and prevents the electrolyte from leaking beyond the plug  6 . A cap  2  is then placed on top of the case  13 . The cap  2  must be aligned with the top of the case  13  in order to create a second seal over the end of the case  13 . The cap  2  is then welded into place with a weld around the edge of the cap  2  from the side. The cap  2 , which was constructed prior to attachment, contains a glass insulative seal  14 . The seal  14  contains a lead tube  15 , which allows a lead  16  from the anode  8  to extend through the cap  2 . The lead tube is sealed off by a weld. An extension lead  18  formed from a metal alloy such as tin-coated copper or tin-coated nickel is then welded to the sealed lead tube  15 . A second lead (not shown) is conventionally welded to the bottom of the case  13  and acts as the cathode lead. 
   The second conventional tantalum capacitor configuration is illustrated in FIG.  2 . The capacitor is contained in a case  13  having a height less than its diameter. An isolator  50  is placed in the bottom of the case  13 . This isolator  50  is simply a disk of insulative material that the anode  8  rests on. Another isolator  51  is placed around the anode  8 . The bottom and side isolators  50  and  51  are conventionally formed of an electrically insulative material such as Teflon. A tantalum anode  8  is placed on the isolator  50  and the side isolator  51 . The isolators  50  and  51  function to hold the anode  8  in place and prevent the anode  8  from contacting the wall of the case  13 . A third isolator  52  is placed on top of the anode  8 . The lid  2  is secured to the case  13  and then the case  13  is filled with electrolyte  54 . The lid  2  fits down inside the case  13 , pressing firmly against the second isolator. The broad support provided by the cap  2  against the top isolator  52  provides substantially even support on the anode  8 . A weld is then run along the edge of the case  13  and the cap  2 . The cap  2  also contains an insulative glass seal  14 . This seal  14  contains a lead tube  15 , which allows a lead  16  to be passed from the anode  8  to the inside of the tube  15 . 
   In the tantalum capacitor field there are several known conventional methods of filling capacitors of the type shown in  FIG. 2  with electrolyte. One method is to utilize a vacuum to draw the electrolyte into the capacitor after the cap  2  is in place. After the capacitor is sealed with the cap  2 , it is placed in a tub of electrolyte under vacuum. The vacuum forces the air out of the capacitor. When the vacuum is removed, the electrolyte flows into the case  13  through the lead tube  16 , which is the only opening in to the capacitor. The lead tube  16  is then sealed with a weld. The capacitor may also be filled with electrolyte through an additional orifice designed to receive electrolyte. The orifice is then welded shut. 
   Electrolyte is consumed slowly over the life of a traditional electrolytic tantalum capacitor. Therefore, the more electrolyte that is available for use in the case, the longer the life of the capacitor will be. In the traditional capacitors, the cap or the combination of the cap and plug take up room inside the case, thereby reducing the amount of room available for electrolyte in the case. 
   DISCLOSURE OF THE INVENTION 
   The present invention may be readily adapted to a variety of capacitors, capacitor materials and methods of creating capacitors. Embodiments of the present invention may provide a longer lasting capacitor, a capacitor that is more resistant to shock and vibration, and a capacitor that is easier to manufacture, among other benefits. 
   The capacitor includes a case that contains an isolator. A tantalum anode may be placed on the isolator. A second isolator may then be placed on top of the anode. Both of the isolators may be formed from any material that does not conduct electricity and is resistant to electrolyte. The isolators may also be porous. The second isolator may also extend to the outer wall of the cap in order to support the cap. 
   Next, a washer may be placed on top of the second isolator. The washer transfers compressive force from the capacitor cap to the anode. This force holds the anode firmly in place. The washer may be formed from metal or an otherwise substantially rigid material. It may be porous in order to allow better electrolyte flow into the capacitor. The washer may be beveled or rippled in order to add strength. The washer may also be integral with the capacitor cap. The washer may also be angled in such a way that the force is directed to the center of the anode. 
   A cap may then be placed on top of the case. The cap may have a toroidal shape with an outer annular wall and an inner annular wall, the inner and outer annular walls may be connected continuously along their top ends so that a top side of the toroidal shape is enclosed. The bottom side of the toroidal shape may have an opening which creates a cavity between the inner and outer annular walls. The cap may also have walls angled inward in order to transmit force to the anode when the cap is attached. It is possible that the washer and the cap may be integral and therefore placed in one step. The cap is then welded to the case. 
   The toroid shaped cap may have an electrically insulative glass seal at its center. The seal supports a lead tube, which provides a way for a lead to travel from the anode to the outside of the capacitor. 
   Once the case is assembled, the capacitor is filled with electrolyte. This may be done by placing the case in a tub of electrolyte under vacuum. The vacuum forces the air out of the capacitor and when the vacuum is removed, electrolyte flows into the capacitor through the lead tube tending to fill the case and may fill the cap cavity. The lead tube is then sealed with a weld. 
   This capacitor design has many innovations that provide advantages over conventional wet tantalum capacitors. The cap shape allows extra electrolyte, cathode material or other material beneficial to the operation of the capacitor (for example a hydrogen absorbent material like Tantalum) to fill the empty spaces in the cap, and also allows for the cap to be attached so that the weld can run along the top of the case. Running the weld along the top of the case means that the assembly process for this capacitor is easily automated. Many conventional capacitors have a weld that runs around the side of the capacitor case. In order to create this weld, the case must either be turned on its side or the welding device must approach the case horizontally and then the case or the welding device must rotate and no more than one capacitor can be welded at a time. Embodiments of the present invention may include a weld that runs around the top and therefore the welding device approaches vertically and simply makes a circle around the top of the case. This allows an entire tray of capacitors to be welded while in the tray instead of welding each capacitor individually. The washer provides added strength to the capacitor to withstand external force and better supports the tantalum anode. The cap design also creates more room for electrolyte or other material in the case, prolonging the life of the capacitor. 
   The foregoing and other features and advantages of the invention will be apparent to those of ordinary skill in the art from the following more particular description of the invention and the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will hereinafter be described in conjunction with the appended drawings, where like designations denote like elements, and: 
       FIG. 1  is a first prior art diagram of an electrolytic capacitor; 
       FIG. 2  is a second prior art diagram of an electrolytic capacitor; 
       FIG. 3  is a diagram of an electrolytic capacitor configured according to an embodiment of the invention; 
       FIG. 4  is a diagram of the electrolytic capacitor of  FIG. 3  with the cap separated from the canister; 
       FIG. 5  is a diagram of the inside of an electrolytic capacitor showing the washer configured according to an embodiment of the invention; 
       FIG. 6  is a diagram of the inside of an electrolytic capacitor showing the isolator configured according to an embodiment of the invention; and 
       FIG. 7  is a flow diagram illustrating a method of constructing an electrolytic capacitor according to an embodiment of the invention. 
   

   DESCRIPTION OF THE INVENTION 
   It will be understood by those of ordinary skill in the art that the invention is not limited to the specific components and assembly procedures disclosed herein. Many additional components and assembly procedures known in the art consistent with the intended capacitor and/or assembly procedures for a capacitor will become apparent for use with embodiments of the present invention from the disclosure herein. Accordingly, for example, although particular hardware is disclosed, such hardware and implementing components may comprise any shape, size, style, type, model, version, measurement, concentration, material, quantity, and/or the like as is known in the art for such hardware and implementing components, consistent with the intended operation of assembling a capacitor. It will also be understood by those of ordinary skill in the art that the invention is not limited to use of any specific components, provided that the components selected are consistent with the intended capacitor and/or method of assembling a capacitor. 
   In an embodiment of the present invention as illustrated in  FIGS. 3 and 5 , a porous tantalum anode  24  is contained in a case  20 . By convention, the case  20  may be cylindrical with one closed end and one open end. The case  20 , however, may also be any cross-sectional shape desired, so long as the shape does not interfere with the operation of the capacitor  18 . The case  20  may be formed from a metal, such as tantalum, silver or any other electrically conductive material for use as a cathode connection and container for the capacitor  18  that does not react with the electrolyte  38 , and can protect the components within the case  20 . 
   An isolator  22 , as shown in  FIGS. 3 ,  4  and  6 , may be placed in the case  20  (Step  60 , FIG.  7 ). One embodiment of the present invention utilizes an isolator  22  with a flat section surrounded by legs that are placed so that they may receive a tantalum anode  24  therebetween. The isolator  22  serves to insulate the anode  24  from the walls of the case  20 . The isolator  22  may be formed in any shape that serves to separate and support the anode  24 . For example, the isolator  22  may form a cup that surrounds the anode  24 , or even simply a flat member underneath the anode  24 . The isolator  22  may be formed from any material that is electrically insulative and resistant to the electrolyte  38  that is placed around it. Teflon is commonly used as isolator  22  material for tantalum capacitors because it not only does not react with the electrolyte  38 , it is also somewhat resilient, which tends to dampen forces applied to the capacitor  18  and reduces the likelihood of damage to the anode  24 . 
   The anode  24  is placed on the isolator  22  in the case  20  (Step  62 , FIG.  7 ). The anode  24  used in the embodiment of the invention shown in  FIG. 3  is a porous tantalum pellet. 
   Extra cathode material  39  may also be added to the case  20 . This cathode material  39  is formed in a ring that fits loosely around the anode  24 . The extra cathode material  39  is most often formed from pressed and centered tantalum like the anode  24 , which also acts as the cathode for the capacitor. The extra cathode material  39 , however, may be formed from any material that acts as a cathode for a tantalum capacitor. 
   A second isolator  26  may be placed on top of the anode  24  (Step  64 , FIG.  7 ). This isolator  24  may have the same shape as the first isolator  22  or it may be a different shape. This second isolator  26 , like the first isolator  22 , should be formed from a material that is electrically insulative and resistant to electrolyte  38 . Teflon works well. 
   A washer  28 , shown in  FIG. 4 , may be placed on top of the second isolator  26  (Step  66 , FIG.  7 ). The washer  28  is placed between the isolator  26  and a cap  30  that is later placed on the case  20 . The washer  28  transfers pressure from the cap  30  to the isolator  26 , holding the anode  24  firmly in place. The washer  28  may be much smaller than the Teflon plug in traditional capacitors and, therefore, it leaves much more room for an electrolyte  38  to fill in the case  20 , and even allows electrolyte  38  to enter the cap  30  region. In one particular embodiment, the washer  28  is a flat round disk with a hole in the center. In another particular embodiment shown in  FIG. 3 , the washer  28  angles downward as it approaches the center of the capacitor  18 . The downward angle directs the force transferred by the washer  28  from the cap  30  to the center of the anode  24 , which provides better support to the anode  24 . In another embodiment of the washer  28 , strength-enhancing ripples in the washer  28  or bevels increase the washer&#39;s  28  strength. These additional features provide added strength to the washer  28  with very little, if any, added material. This also allows the washer  28 , which takes up very little space in the case  20  to serve the supporting and force transferring functions of the Teflon plug. By taking up very little room, the washer  28  creates more space for the electrolyte  38 , or other materials, in the capacitor  18  case  20 . By allowing more room for electrolyte  38 , this embodiment of the invention may create a capacitor  18  with a longer life. It is also contemplated that the washer  28  may be combined with the cap  26 . This may be done by making the isolator  26  so that it extends to the outside wall of the cap  30  and so that it is integral with or rigidly coupled to the outside wall. The cap  30  may then be placed on the case  20 , pushing down on the isolator  26 . An isolator  26 , however, is conventionally made of a resilient material such as Teflon and therefore does not have the strength of metal. The advantage to having a resilient isolator  26  and a rigid washer  28  separate is that the properties of both are obtained. The washer  28  may be made out of many different materials. The only requirements for washer  28  materials is that the material be resistant to electrolyte  38  and sufficiently rigid so as to transfer the force from the cap  30  to the anode  24 . Tantalum, titanium, stainless steel and silver are all resistant to electrolyte  38  and may all be used as washer  28  material. Alternatively, the metallic washer  28  or a portion of the extended outer wall of the cap  30  may be coated with a Teflon layer to provide similar results. 
   The cap  30  ( FIG. 3 ) may be placed on the capacitor  18  case  20  (Step  68  FIG.  7 ). The cap  30  may be shaped like a toroid with an outer  41  and an inner  40  annulus wall. The annulus walls  41 ,  40  may be connected at the top  42  and have one or more openings  44  at the bottom. This configuration will create a cavity in the cap  30 . In other words, it may be an annular cap  30  with a ‘U’ shaped cross-section where the ‘U’ is facing downward. The center of the toroid may contain an insulative seal  32  of glass or other insulative material. This seal  32  provides electrical insulation and mechanical support for a lead tube  34 . The lead tube  34  helps create a way for a lead  36  attached to the anode  24  to have access to the outside. The cap  30  diameter may be larger or smaller than the case  20  as long as the cap  30  fits inside the case  20 . The cap  30  is fit into the case  20 . A small weld extends along the top edge of the case  20  creating a hermetic seal. The cap  30  fitting within the case  20  allows for a weld to be created from the top of the case  20  rather than around the side. Welding from the top of the capacitor  20  rather than the side simplifies the welding process and enables manufacturers to even, for example, weld an entire tray of capacitors at a time. 
   The walls of the cap  30  may end with a slight inward curve  46 . This curve  46  creates a small foot around the edge of the cap  30  that tends to put pressure on the washer  28  forcing the anode  24  into place. The cap  30  may be formed from many different materials. The materials should be resistant to the electrolyte  38  and have enough strength to provide protection to the capacitor  18 . Possible materials for use on a tantalum capacitor  18  cap  30  include tantalum, titanium and silver. 
   A seal  32 , which is normally created at the beginning of the cap  30  forming process, surrounds a lead tube  34  and is formed of an insulator such as glass. This hollow lead tube  34  creates an opening in the cap  30  of the capacitor  18  for a lead  36  wire attached to the anode  24  to pass outside of the case  20 . The insulating seal  32  is placed around the lead tube  34  to electrically isolate the lead  36  and help keep the lead  36 , which extends from the anode  24 , from coming into contact with the cap  30  material. 
   The final step in assembling a capacitor  18 , is to fill the case  20  with an electrolyte  38  (Step  70  FIG.  7 ). This may be done by placing the capacitor  18  assembly in a vat of electrolyte  38  which is all placed in a vacuum chamber. The vacuum forces the air out of the case  20 . When the vacuum is removed, the electrolyte  38  flows through the lead tube  34  into the case  20  to fill the void space in the case  20  and the cavity in the cap  30 . A small weld may be placed on the end of the lead tube  34 , which seals as well as electrically connects the lead  36  and the tube  34 . The weld seals the capacitor  18  against the electrolyte  38  spilling out. The electrolyte  38  may be any of a number of well-known electrolytes known in the art for use with tantalum capacitors. 
   The embodiments and examples set forth herein were presented in order to best explain the present invention and its practical applications and to thereby enable those of ordinary skill in the art to make and use the invention. However, those of ordinary skill in the art will recognize that the foregoing description and examples have been presented for the purposes of illustration and example only. The description as set forth is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the teachings above without departing from the spirit and scope of the forthcoming claims. Accordingly, any components of the present invention indicated in the drawings or herein are given as an example of possible components and not as a limitation. Similarly, any steps or sequence of steps of the method of the present invention indicated herein are given as examples of possible steps or sequence of steps and not limitations, since numerous processes and sequences of steps may be used to employ this method of assembling a capacitor.