Abstract:
A polymeric cradle molded about the periphery of an anode pellet in an electrolytic capacitor is described. The polymeric cradle contacts between a welding strap surrounding the butt seam between mating “clam shell” casing portions and the anode pellet sidewall. This prevents the anode pellet from moving along both an x- and y-axes. Having the cathode active material contacting the opposed major casing sidewalls being in a closely spaced relationship with the anode pellet through an intermediate separator prevents movement along the z-axis. The resulting capacitor is particularly well suited for use in high shock and vibration conditions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application claims priority based upon provisional application Ser. Nos. 60/548,954, filed Mar. 1, 2004 and 60/563,328, filed Apr. 19, 2004. 

   BACKGROUND OF THE INVENTION 
   The present invention generally relates to a capacitor and, more particularly, to a capacitor capable of being subjected to high shock and vibration forces without failing. 
   SUMMARY OF THE INVENTION 
   Capacitors are used frequently in applications where high shock and vibration levels are experienced. A notable example is in the oil and gas industry where “measurement while drilling” applications can cause severe stress forces to a capacitor. Under high shock and vibration conditions, capacitors without adequate stabilization are capable of failing due to movement of the electrodes within the case, for example the anode pellet in an electrolytic capacitor. This movement can result in mechanical failure of the anode pellet lead rendering the capacitor inoperative. In that respect, mechanical stabilization of the anode pellet inside the casing is important to improving the reliability and safety of capacitors subjected to high shock and vibration conditions. 
   The capacitor of the present invention provides such mechanical stabilization through a surrounding polymeric cradle that contacts between the casing sidewall and the anode pellet sidewall to lock the anode in place. Alternatively, the polymeric cradle contacts between a welding strap surrounding the butt seam between mating “clam shell” casing portions and the anode pellet sidewall. This structure prevents the anode pellet from moving along both an x- and y-axes. Having the cathode active material contacting the opposed major casing sidewalls being in a closely spaced relationship with the anode pellet through an intermediate separator prevents movement along the z-axis. 
   These and other aspects of the present invention will become more apparent to those skilled in the art by reference to the following description and to the appended drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a capacitor  10  according to the present invention. 
       FIG. 2  is a side elevational view of an anode  12  having an embedded anode wire  34  extending from a notch  32  thereof. 
       FIG. 3  is a cross-sectional view of a glass-to-metal seal  38  for an anode lead  36 . 
       FIG. 4  is a side elevational view of the anode lead  36  including the glass-to-metal seal  38  connected to the embedded wire  34  of anode  12 . 
       FIG. 5  is a plan view of the anode  12  including the glass-to-metal seal  38  positioned in a mold portion  48  with a plurality of spacers  54 A to  54 J positioned about its periphery and interior of a welding strap  50 . 
       FIG. 6  is a plan view showing polymeric material being injected into the mold shown in  FIG. 5 . 
       FIG. 7  is a side elevational view showing the anode  12  being held in position inside the weld strap  50  by the polymeric web  58  and integral protrusions  58 A to  58 J after being removed from the mold shown in  FIG. 6 . 
       FIG. 8  is a side elevational view of a casing portion  20  supporting a cathode active material  14  on a face wall  28  thereof. 
       FIG. 9  is a side elevational view showing the assembly of  FIG. 7  comprising the anode  12 , polymeric material  58  and welding strap  50  after being nested in the casing portion  20  of  FIG. 8 . 
       FIG. 10  is a cross-sectional view along line  10 — 10  of  FIG. 9 . 
       FIGS. 10A and 10B  are alternate embodiments similar to the view shown in  FIG. 10 , but with the capacitor housed in different casings. 
       FIG. 11  is a plan view of the anode  12  including the glass-to-metal seal  38  positioned in a mold portion  48  with a plurality of spacer pegs  102 A to  102 L positioned about its periphery and interior of the welding strap  50 . 
       FIG. 12  is a plan view showing polymeric material being injected into the mold shown in  FIG. 11 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the drawings,  FIG. 1  is a perspective view showing a capacitor  10  according to the present invention. The capacitor  10  comprises an anode  12  ( FIG. 2 ) of an anode active material and a cathode of a cathode active material  14  ( FIG. 8 ) housed inside a hermetically sealed casing  16 . The capacitor electrodes are operatively associated with each other by a working electrolyte (not shown) contained inside the casing, as will be described in detail hereinafter. The capacitor  10  is of an electrolyte type with the cathode comprising a conductive substrate having capacitive properties. 
   As particularly shown in  FIGS. 1 and 8  to  10 , the casing  16  is of a metal material comprising first and second casing portions  18  and  20 . Casing portion  18  comprises a surrounding sidewall  22  extending to a face wall  24 . Similarly, casing portion  20  comprises a surrounding sidewall  26  extending to a face wall  28 . Sidewall  26  is sized so that sidewall  22  is in an overlapping relationship therewith. Then, the casing portions  18 ,  20  are hermetically sealed together by welding the overlapping sidewalls  22 ,  26  where they contact. The weld  30  is provided by any conventional means; however, a preferred method is by laser welding. 
   The mating casing portions  18 ,  20  are preferably selected from the group consisting of tantalum, titanium, nickel, molybdenum, niobium, cobalt, stainless steel, tungsten, platinum, palladium, gold, silver, copper, chromium, vanadium, aluminum, zirconium, hafnium, zinc, iron, and mixtures and alloys thereof. Preferably, the face and sidewalls of the casing portions have a thickness of about 0.005 to about 0.015 inches. 
   The active material of the anode  12  is typically of a metal selected from the group consisting of tantalum, aluminum, titanium, niobium, zirconium, hafnium, tungsten, molybdenum, vanadium, silicon, germanium, and mixtures thereof in the form of a pellet. As is well known by those skilled in the art, the anode metal in powdered form, for example tantalum powder, is compressed into a pellet having a notch  32  from which an embedded anode wire  34  ( FIGS. 2 ,  4  to  7  and  9 ) extends. The anode wire  34  preferably comprises the same material as the anode active material. The anode pellet is sintered under a vacuum at high temperatures and then anodized in a suitable electrolyte. The anodizing electrolyte fills the pores of the pressed powder body and a continuous dielectric oxide is formed thereon. In that manner, the anode  12  and extending wire  34  are provided with a dielectric oxide layer formed to a desired working voltage. The anode can also be of an etched aluminum, niobium, or titanium foil. 
   After the anode  12  and extending wire  34  are anodized to the desired formation voltage, the dielectric oxide is removed from the wire and there connected to an anode lead  36  supported in an insulative glass-to-metal seal  38  (GTMS). The weld and lead are then re-anodized. The glass-to-metal seal  38  comprises a ferrule  40  defining an internal cylindrical through bore or passage  42  of constant inside diameter. An insulative glass  44  provides a hermetic seal between the bore  42  and the anode lead  36  passing there through. The anode lead  36  has a J-shaped proximal portion  36 A that is subsequently connected to a crook in the anode wire  34  such as by laser welding to secure them together. The glass  44  is, for example, ELAN® type  88  or MANSOL™ type  88 . As shown in  FIGS. 1 and 9 , in the final capacitor assembly the GTMS  38  electrically insulates the anode lead  36  connected to the anode wire  34  from the metal casing  18 . 
   A separator  46  of electrically insulative material in the shape of a bag completely surrounds and envelops the anode  12  except the extending wire  34 . The separator  46  prevents an internal electrical short circuit between the anode  12  and cathode active materials  14  in the assembled capacitor and has a degree of porosity sufficient to allow flow there through of the working electrolyte during the electrochemical reaction of the capacitor  10 . Illustrative separator materials include woven and non-woven fabrics of polyolefinic fibers including polypropylene and polyethylene or fluoropolymeric fibers including polyvinylidene fluoride, polyethylenetetrafluoroethylene, and polyethylenechlorotrifluoroethylene laminated or superposed with a polyolefinic or fluoropolymeric microporous film, non-woven glass, glass fiber materials and ceramic materials. Suitable microporous films include a polyethylene membrane commercially available under the designation SOLUPOR® (DMS Solutech), a polytetrafluoroethylene membrane commercially available under the designation ZITEX® (Chemplast Inc.), a polypropylene membrane commercially available under the designation CELGARD® (Celanese Plastic Company, Inc.), and a membrane commercially available under the designation DEXIGLAS® (C. H. Dexter, Div., Dexter Corp.). Cellulose based separators also typically used in capacitors are contemplated by the scope of the present invention. Depending on the electrolyte used, the separator can be treated to improve its wettability, as is well known by those skilled in the art. 
   As shown in  FIG. 5 , the anode  12  connected to the anode lead  36  supported in the GTMS  38  is then positioned inside a mold portion  48 . A metal welding strap  50  is also positioned in the mold portion  48  in a generally enclosing, but spaced relationship with the anode  12  and GTMS  38 . The welding strap  50  is discontinuous at  52  to provide a space for the GTMS  38 . As will be described in detail hereinafter, the metal strap  50  serves as a backing to protect the anode  12  and separator  46  from the laser welding light when the casing portions  18  and  20  are welded to each other during final capacitor assembly. 
   Once the anode  12  and GTMS  38  enclosed by the welding strap  50  are properly positioned in the mold portion  48 , a plurality of spacers  54 A to  54 J are positioned about the periphery of the anode. The spacers are shaped to conform to the peripheral contour of the anode sidewall portion that they contact. However, the spacers  54 A to  54 J are spaced from each other as well as from the welding strap  50 . 
   After the mold is closed, a nozzle  56  is hooked up to the mold. The nozzle  56  is used to inject a polymer material into the void between the welding strap  50  and the spacers  54 A to  54 J and the uncovered peripheral portions of the anode side wall. If desired, there can be more than one nozzle positioned at spaced locations about the periphery of the mold. The polymeric material is preferably of a fast curing type including a polyolefin, a fluoropolymer, a hot melt adhesive, or a UV curable adhesive. A relatively slow curing silastic material is also useful. This forms a polymeric cradle around the sidewall perimeter of the anode  12 . Specifically, the cradle comprises a surrounding web  58  of the polymeric material supporting integral protrusions  58 A to  58 I formed between the spacers  54 A to  54 J. The surrounding web  58  contacts the welding strap  50  while the protrusions  58 A to  58 I contact the separator  46  along the anode sidewall. A rather large protrusion  58 J is formed between spacers  54 A and  54 J to completely encase the GTMS  38  including the insulated anode lead  36  connected to the anode wire  34 . The anode  12  held in position inside the weld strap  50  by the polymeric cradle comprising the web  58  and integral protrusions  58 A to  58 J is then removed from the mold  48  as an assembly ( FIG. 7 ). 
   The cathode active material  14  preferably coats the face walls  24 ,  28 , spaced from the respective sidewalls  22 ,  26 . The pad printing process described in U.S. patent application Ser. No. 10/920,942, filed Aug. 18, 2004, is preferred for making such a coating. Ultrasonically generated aerosol as described in U.S. Pat. Nos. 5,894,403; 5,920,455; 6,224,985; and 6,468,605, all to Shah et al., are also suitable deposition methods. These patents and patent application are assigned to the assignee of the present invention and incorporated herein by reference. 
   As shown in  FIG. 8 , casing portion  20  is provided with the cathode active material  14  coated on its face wall  28  in a pattern that generally mirrors the shape of the anode  12 . The cathode active material  14  has a thickness of about a few hundred Angstroms to about 0.1 millimeters and is either directly coated on the inner surface of the face wall  28  or it is coated on a conductive substrate (not shown) in electrical contact with the inner surface of the face wall. The other casing portion  18  has the cathode active material  14  similarly coated on its face wall  24  or on a conductive substrate secured to the inner surface of the face wall in electrical contact therewith. In that respect, the face walls  24 ,  28  may be of an anodized-etched conductive material, have a sintered active material with or without oxide contacted thereto, be contacted with a double layer capacitive material, for example a finely divided carbonaceous material such as graphite or carbon or platinum black, a redox, pseudocapacitive or an under potential material, or be an electroactive conducting polymer such as polyaniline, polypyrole, polythiophene, polyacetylene, and mixtures thereof. 
   According to one preferred aspect of the present invention, the redox or cathode active material  14  includes an oxide of a first metal, the nitride of the first metal, the carbon nitride of the first metal, and/or the carbide of the first metal, the oxide, nitride, carbon nitride and carbide having pseudocapacitive properties. The first metal is preferably selected from the group consisting of ruthenium, cobalt, manganese, molybdenum, tungsten, tantalum, iron, niobium, iridium, titanium, zirconium, hafnium, rhodium, vanadium, osmium, palladium, platinum, nickel, and lead. 
   The cathode active material  14  may also include a second or more metals. The second metal is in the form of an oxide, a nitride, a carbon nitride or carbide, and is not essential to the intended use of the conductive face walls  24 ,  28  as a capacitor electrode. The second metal is different than the first metal and is selected from one or more of the group consisting of tantalum, titanium, nickel, iridium, platinum, palladium, gold, silver, cobalt, molybdenum, ruthenium, manganese, tungsten, iron, zirconium, hafnium, rhodium, vanadium, osmium, and niobium. In a preferred embodiment of the invention, the cathode active material  14  includes an oxide of ruthenium or oxides of ruthenium and tantalum. 
   As shown in  FIG. 9 , the anode  12  surrounded by the polymeric cradle and the welding strap  50  as an assembly is then nested in the casing portion  20  with the GTMS  38  received in an opening  60  ( FIG. 8 ) in the casing sidewall  26 . The ferrule  40  of the GTMS has a distal step  40 A ( FIG. 3 ) that fits into the casing opening  60  in a tight fitting relationship. The welding strap  50  is likewise sized to fit inside the perimeter of the casing sidewall  26  in a closely spaced relationship. The ferrule  40  is then secured to the casing sidewall  26  such as by laser welding. This provides the anode  12  secured inside the casing portion  20  held in position by the polymeric cradle comprising the web  58  and integral protrusions  58 A to  58 J and the welding strap  50 . In this position, the anode major face wall  12  ( FIG. 10 ) is resting on the casing sidewall  26 . However, the intermediate separator  46  prevents direct contact between the anode  12  and the cathode active material  14 . 
   The other casing portion  18  is then mated to the casing portion  20  with their respective sidewalls  22  and  26  overlapping each other. The continuous weldment  30  provided about the perimeter of the casing sidewalls  22  and  26 , such as by laser welding, secures the casing portions  18  and  20  to each other. The welding strap  50 , however, prevents the laser light from penetrating into the interior of the capacitor to damage the anode  12  and separator  46  among other heat sensitive components. 
   A working electrolyte (not shown) is then provided in the capacitor through an opening in one of the casing portions  18 ,  20 . A suitable working electrolyte for the capacitor  10  is described in U.S. Pat. No. 6,219,222 to Shah et al., which includes a mixed solvent of water and ethylene glycol having an ammonium salt dissolved therein. U.S. Pub. Nos. 2003/0090857 and 2003/0142464 describe other working electrolytes for the present capacitors. The working electrolyte of the former publication comprises water, a water-soluble inorganic and/or organic acid and/or salt, and a water-soluble nitro-aromatic compound while the latter relates to an electrolyte having de-ionized water, an organic solvent, isobutyric acid and a concentrated ammonium salt. These publications and patent are assigned to the assignee of the present invention and incorporated herein by reference. The electrolyte fill opening is then closed by a hermetic closure (not shown), as is well known by those skilled in the art. 
   The spaces formed between the protrusions  58 A to  58 J of the polymeric cradle provide for the electrolyte to thoroughly wet the anode  12  including the enveloping separator  46  and the cathode active materials  14  to provide the capacitor  10  in a functional state. The welding strap  50  encloses and contacts the polymeric web  58  including protrusions  58 A to  58 J that, in turn, contact the separator  46  at the anode sidewall and encase the GTMS  38 . This prevents any movement of these components should the capacitor be subject to high shock and vibration conditions. 
     FIG. 10A  shows an alternate embodiment of a casing for the present capacitor. The casing comprises portion  20 A having a surrounding sidewall  26 A extending to a face wall  28 A supporting the cathode active material  14 . The sidewall  26 A has a step at its upper end that received a plate  24 A serving as a second face wall for supporting the cathode active material  14 . The plate  24 A is nested therein. A weld  30  secures the plate  24 A to the sidewall  26 A at the step with the upper surface of the plate being coplanar with the upper end of the sidewall  26 A. The remaining structure for this capacitor is as previously described. 
     FIG. 10B  shows another embodiment of a casing for the present capacitor. The casing comprises portion  20 B having a surrounding sidewall  26 B extending to a face wall  28 B supporting the cathode active material  14 . A plate  24 A rests on the upper edge of the sidewall  26 B and serves as a second face wall for supporting the cathode active material  14 . Plate  24 A extends a short distance out beyond the sidewall  26 B. A weld  30  then secures the plate  24 A to the sidewall  26 B where the plate overhangs or extends past the sidewall. Also, in this embodiment, the weld strap has been eliminated from the mold shown in  FIG. 5  and the height of the polymeric web is shortened from that shown in the other embodiments. Elimination of the welding strap is possible with the laser beam being aimed at the corner where the plate  24 A extends past the sidewall  26 B. The remaining structure for this capacitor is as previously described. 
     FIGS. 11 and 12  show an alternate embodiment for providing a polymeric cradle according to the present invention. The anode  12  connected to the anode lead  36  supported in the GTMS  38  is first positioned inside a mold portion  100 . The metal welding strap  50  is also positioned in the mold portion  100  in a generally enclosing, but spaced relationship with the anode  12  and GTMS  38 . Once the anode  12  and GTMS  38  enclosed by the welding strap  50  are properly positioned in the mold portion  100 , a plurality of spacer pegs  102 A to  102 M are positioned about the periphery of the anode. The pegs  102 A to  102 L are cylindrically shaped with a diameter to contact both the welding strap  50  and the perimeter of the anode sidewall. A relatively large cylindrically shaped peg  102 M is positioned in a corner of the welding strap  50 , but it is not in contact with the anode sidewall. This peg is for the purpose of maintaining the position of the welding strap. The pegs  102 A to  102 L are spaced from each other. 
   After the mold is closed, the nozzle  56  is hooked up to it. As before, the nozzle  56  is used to inject a polymer material into the spaces or gaps between the pegs  102 A to  102 L and the uncontacted peripheral portions of the anode sidewall. The polymeric material is similar to that used in the previous embodiment and forms a polymeric cradle  104  around the sidewall perimeter of the anode  12 . In this case, the cradle  104  comprises the surrounding polymeric material contacting between the welding strap  50  and the anode sidewall. The anode  12  held in position inside the weld strap  50  by the polymeric cradle  104  is then removed from the mold  48  as an assembly for further processing into a functional capacitor as previously described with respect to the first embodiment of the present invention continuing with  FIG. 9 . 
   The casing  16 , including the portions  18 ,  20 , being of a conductive metal serves as the negative terminal for making electrical connection between the capacitor  10  and its load. A pin (not shown) is welded to one of the casing portions  18 ,  20  to provide this. The anode lead  36  extending outside the capacitor  10  is hermetically sealed from the interior of the capacitor and insulated from the mating casing portions  18 ,  20  by the GTMS  38  to serve as the positive terminal for the capacitor  10 . 
   While all of the embodiments described herein show the polymeric cradle used with a single anode pellet, that should not be construed as limiting. It is contemplate by the scope of the present invention that the polymeric cradle can be used with two or more side-by-side anodes provided in one of the previously described casings. Such a multiple anode design is shown in U.S. Pat. No. 6,850,405 to Mileham et al. This patent is assigned to the assignee of the present invention and incorporated herein by reference. 
   It is appreciated that various modifications to the inventive concepts described herein may be apparent to those of ordinary skill in the art without departing from the spirit and scope of the present invention as defined by the appended claims.