Patent Publication Number: US-2015070816-A1

Title: Capacitor fabrication using nano materials

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 61/874,409, filed Sep. 6, 2013, the entire disclosure of which is hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD OF INVENTION 
     This disclosure generally relates to a multi-layer capacitor, and more particularly relates to a capacitor with endcaps formed of conductive nano material. 
     BACKGROUND OF INVENTION 
     Metallized film capacitors typically form electrical and mechanical connections between layers of conductors separated by dielectric films using an arc spray process. Arc spray uses DC power to energize two conductive wires of Babbitt metal by applying a voltage to one wire relative to the other. This energized wire is then fed through a feeder into a gun head. It is at the gun head that the wires meet and arc against each other, thereby creating molten material. Then dry compressed air is introduced to the arc zone, the molten material is atomized into tiny droplets that are propelled toward a prepared part or target. As the droplets hit the target, they flatten out and make molten dots. The molten dots interlock one on top another and form a mechanical and electrical bond. 
     This arc spray process is generally considered to be a messy, time consuming process, involving preparing the target surface, cleaning, wrapping other surfaces to protect other surfaces from over spray, spraying, removing wrapping, cleaning of the overspray surfaces and inspection depending on the application lead attachment, welding or soldering is then performed. The electrical interconnection formed by the arc spray process is sometimes considered to be a weak link in a capacitor&#39;s design. Furthermore, the arc spray process can cause intrusion of the Babbitt material into the inner layers of the capacitor, which can lead to shorts and reduced capacitance. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment, a multi-layer capacitor is provided. The capacitor includes an anode, a cathode, a dielectric material, a first endcap, and a second endcap. The anode is formed of one or more layers of conductive material. The cathode is formed of one or more layers of conductive material interlaced with the layers of the anode. The dielectric material is interposed between each of the layers of the anode and the cathode. The first endcap is configured to interconnect each of the layers of the anode. The second endcap is configured to interconnect each of the layers of the cathode. The first endcap and the second endcap are formed of conductive nano material. 
     In another embodiment, a method of forming an endcap of a capacitor configured to interconnect one or more layers of conductive material is provided. The method includes the step of applying conductive nano material to exposed conductive surfaces of at least one of an anode and a cathode of the one or more layers of conductive material. The method also includes the step of exposing the nano material to a source of energy effective to initiate self-sintering of the nano material. 
     Further features and advantages will appear more clearly on a reading of the following detailed description of the preferred embodiment, which is given by way of non-limiting example only and with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention will now be described, by way of example with reference to the accompanying drawings, in which: 
         FIG. 1  is a sectional side view of a capacitor with endcaps formed of nano material in accordance with one embodiment; 
         FIGS. 2A-2E  are a sequence of illustrations showing fabrication steps of the capacitor of  FIG. 1  in accordance with one embodiment; and 
         FIG. 3  is flowchart of a method of forming an endcap of the capacitor of  FIG. 1  in accordance with one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Described herein is a means to form electrical connections between conductive layers or plates of a capacitor using nano metal materials or nano materials that are self-sintered after exposure to a source of energy effective to initiate sintering of the nano material. Optionally, nano materials may also be used to attach an electrically conductive lead or wire to the capacitor. 
       FIG. 1  illustrates a non-limiting example of a multi-layer capacitor, hereafter referred to as the capacitor  10 . While the illustration shows a configuration that is sometimes referred to as a stacked capacitor, it is contemplated that the teachings presented herein are also applicable to other capacitor configurations such as wound capacitors, see  FIG. 2 . In general, the capacitor  10  includes or defines an anode  12  that includes or is formed of one or more layers  14 A of conductive material, and a cathode  16  that includes or is formed of one or more layers  14 B of conductive material interlaced (i.e. alternating layers) with the layers  14 A of the anode  12 . Wound capacitors typically have a single conductive layer for the anode, and a single conductive layer for the cathode. The layers  14 A and  14 B may be formed of aluminum or other conductive metals as will be recognized by those in the capacitor arts. The layers  14 A and  14 B may include edge metallization  18 A and  18 B formed of, for example, a 400 {acute over (Å)} thick layer of zinc. It is contemplated that the capacitor  10  can be either polarized or non-polarized. That is, the use of the modifiers ‘anode’ and ‘cathode’ are only for the purpose of distinguishing the two electrical connections, and not meant to suggest in any way that the capacitor described herein is necessarily a polarized capacitor. 
     The capacitor  10  also includes an arrangement of a dielectric material  20  interposed between each of the layers  14 A and  14 B of the anode  12  and the cathode  16 , respectively. The dielectric material  20  may be, for example, a 2.5 um thick layer of polypropylene (PP) film. The width, length, thickness of dielectric, and number of layers used to form the capacitor  10  may be varied to achieve a desired capacitance value of the capacitor  10 , as will be recognized by those in the capacitor arts. 
     The capacitor  10  may also include a first endcap  22 A configured to electrically and mechanically interconnect each of the layers  14 A of the anode  12 , and a second endcap  22 B configured to mechanically and electrically interconnect each of the layers  14 B of the cathode  16 . Preferably, the first endcap  22 A and the second endcap  22 B are formed of conductive nano material. Nano material may include various mixtures of Al, Ag, Cu, Zn, or other suitable conductive metals and is available from nanoComposix of San Diego, Calif. or NovaCentrix of Austin, Tex. The nano material can be dispersed in a binder material to provide a thick-film ink type material, or in the form of a tape, tube or other disposable material to hold the nano material in place. Once dispersed, the nano material is briefly exposed to an energy source to cause the nano materials to self-sinter. Some non-limiting examples of energy sources include a spark, matches (fire), a camera flash, and a beam from a laser. The amount of nano material needed is preferably enough (and may require multiple passes of apply nano-material and sintering) to form a low-resistance electrical connection to the edge metallization  18 A and  18 B, for example a resistance less than 2 Ω/□. 
       FIGS. 2A-2E  illustrates a non-limiting example of a sequence of steps that can be used to electrically attach a first lead  24  to a body portion  26  the capacitor  10 .  FIG. 2A  in this example illustrates the capacitor  10  as a wound type capacitor where the body portion  26  includes the layers  14 A and  14 B, and the dielectric material  20  wound around an axis  28 . Accordingly, the edge metallization  18 A may be exposed on the end of the body portion  26 . It should be recognized that the orientation of the layers  14 A and  14 B for  FIGS. 2A-2E  are oriented perpendicular to that shown in  FIG. 1 . 
       FIG. 2B  illustrates the body portion  26  with nano material  34  applied to the end of the body portion  26 . As suggested above, the nano material  34  may be a preformed part, or may be in the form of a paste or powder that is applied to the body portion  26  using any of a variety of known techniques. 
       FIG. 2C  illustrates the first endcap  22 A attached to the body portion  26  after energy  30  is applied to the un-sintered nano material  34  to form the first endcap  22 A by self-sintering of the nano material  34 . 
       FIG. 2D  illustrates the first lead  24  placed onto the first endcap  22 A with an additional layer of un-sintered nano material  34  applied over and/or around the first lead  24 . The first lead  24  may be a wire or ribbon of electrically conductive material such as zinc coated copper. 
       FIG. 2E  illustrates how the first lead  24  is electrically attached to the first endcap  22 A when the additional un-sintered nano material  34  is sintered following an exposure to energy  32  whereby nano material is used to electrically attach the first lead  24  to the first endcap  22 A. 
     Alternatively, the steps of forming the first endcap  22 A and electrically attaching the first lead  24  may be combined. For example, the nano material could be dispersed in a in a manner similar to that described above after placing a wire or other electrical interconnect in contact with the previously applied but un-sintered nano material, and then all of the un-sintered nano material self-sintered at one time as describe above. Or as previously described, the combined lead attach process mentioned above can be a two-step process where electrical interconnection of the edge metallization nano material is done first, the first lead  24  is electrically attached by a second application of nano materials. A capacitor to capacitor interconnect can be formed in a similar way where the electrical interconnect is replaced with another capacitor. This creates either a series or parallel connection of multiple capacitors. 
     Similarly, the capacitor  10  may include a second lead (not shown) electrically attached to the second endcap  22 B. The second lead may be attached using any of the techniques described above, and may be attached at the same time as the first lead  24  is attached, or as part of a separate process. 
     As described above, a wire or bus bar (e.g. the first lead  24 ) may be electrically and mechanically attached to an endcap (e.g. the first endcap  22 A or the second endcap  22 B) in the same way the endcap was formed. Alternatively, the first lead  24  may be soldered to the first endcap  22 A. 
       FIG. 3  illustrates a non-limiting example of a method  300  of forming an endcap (e.g. the first endcap  22 A or the second endcap  22 B) of the capacitor  10  configured to interconnect one or more layers (e.g. the layers  14 A and  14 B) of conductive material. 
     Step  310 , APPLY NANO MATERIAL, may include applying conductive nano material (e.g. the nano material  34 ) to exposed conductive surfaces (e.g.—the edge metallization  18 A and  18 B) either or both the anode  12  and the cathode  16 . 
     Step  320 , SINTER NANO MATERIAL, may include exposing the nano material  34  to a source of energy effective to initiate self-sintering of the nano material  34  such as a spark, matches (fire), a camera flash, or a beam from a laser. 
     Step  330 , PLACE LEAD IN CONTACT NANO MATERIAL, may include placing a lead (e.g. the first lead  24 ) in contact with the nano material  34 . Step  330  may be followed by the application of additional nano material and another self-sintering process to electrically attach the lead to the previously formed endcap. It is contemplated that steps  320  and  330  could be reversed relative to the order shown in  FIG. 3  so the lead could be attached by one or more applications of un-sintered nano material followed by a single sintering step. Alternatively, the lead could be attached to a sintered endcap by other methods such as soldering. 
     Accordingly, a way to form electrical connections between conductor layers of a capacitor is provided. This process could also be used to interconnect capacitor to capacitor in either a series or parallel connection. This process is generally faster and yields a higher quality electrical connection as the connection is a solid layer of dense metal as opposed to an interconnection of molten metal dots provided by Babbitt metal. Unlike the known arc spray process, the process described herein has no overspray which eliminates the masking, unmasking and cleaning steps found in the arc spray process. The process can readily form electrical connections with different thickness layers without intrusion of metals to the inner layers of the capacitor, and lowers the overall temperatures necessary to form electrical connections when compared to the arc spray process. It is recognized that an end cap may require one or more layers of nano metals where each one sintered by an energy source to achieve the desired electrical resistance. Multiple layers may be advantageous as self-sintering one thick layer of nano metal may generate enough heat to melt materials underlying the nano metal. As such, it may be advantageous to build up a thick layer by a progression of lower energy sintering steps. 
     While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.