Abstract:
A tantalum capacitor including: a capacitor body containing a tantalum powder and having a mounting surface; a cathode lead frame having the capacitor body mounted thereon; a tantalum wire having an insertion portion located inside the capacitor body and a non-insertion portion located outside the capacitor body; an anode lead frame connected to the non-insertion portion of the tantalum wire; and a resin mold surrounding the capacitor body and the tantalum wire, wherein the insertion portion of the tantalum wire has at least one bending.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of Korean Patent Application No. 2006-94960 filed on Sep. 28, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a tantalum capacitor, more particularly, in which a capacitor body has a greater usable area and a tantalum wire is disposed to achieve miniaturization of the tantalum capacitor. 
         [0004]    2. Description of the Related Art 
         [0005]    Tantalum Ta carries mechanical and physical properties such as high melting point, and superior ductility and corrosion resistance, thus widely utilized across the industry, including electrics and electronics, mechanics, chemistry, medicine, space and military field. Notably, of all metals, tantalum allows formation of a most stable anode oxidized film, thus broadly used as a material for an anode in a small capacitor. Moreover, tantalum has been drastically increased in use by 10% annually due to rapid development of IT industry such as electronics and telecommunication. 
         [0006]    Generally, a capacitor is an electrical device that can store energy temporarily. In the capacitor, two conductive plate electrodes are closely spaced with each other, separated by a dielectric, and electric charges build up on each plate electrode. That is, the capacitor is used to obtain capacitance by storing electrical charges between the two conductors. 
         [0007]    A tantalum capacitor utilizes pores generated when a tantalum powder is sintered and cured. For this tantalum capacitor, an oxidized tantalum Ta 2 O 5  is formed by anode oxidization on a surface of tantalum which acts as an electrode metal. Then, a manganese dioxide MnO 2  layer is formed as an electrolyte on the oxidized tantalum which serves as a dielectric. Also, a graphite layer is formed on the manganese dioxide MnO 2  layer, and a metal layer is formed on the graphite layer to derive a cathode electrode. 
         [0008]      FIGS. 1A and 1B  are a front view and a plan view illustrating an internal structure of a conventional tantalum capacitor, respectively. 
         [0009]    Referring to  FIGS. 1A and 1B , the conventional tantalum capacitor includes a rectangular parallelepiped capacitor body  11  containing tantalum powder, a tantalum wire  13  partially inserted into the capacitor body, a cathode lead frame  12 , a cathode lead frame  12  connected to the capacitor body  11  and an anode lead frame  14  connected to the tantalum wire  13 . 
         [0010]    The tantalum wire  13  is bent twice perpendicularly at a portion not inserted into the capacitor body  11 . Such bending allows the tantalum wire  13  to be directly connected to the anode lead frame  14 . 
         [0011]    Carbon and silver are applied on the capacitor body  11  and the cathode lead frame  14  is connected to the capacitor body  11  by a silver adhesive  12   a . The tantalum wire  13  may be bonded to the anode lead frame  14  by one of spot welding, a conductive paste and laser welding. 
         [0012]    In this tantalum capacitor structured as above, a larger volume of the capacitor body enhances a usable area of the capacitor but increases a physical volume thereof, thereby hampering miniaturization of the capacitor. 
       SUMMARY OF THE INVENTION 
       [0013]    An aspect of the present invention provides a tantalum capacitor capable of enhancing a usable area without increase in an overall volume and increasing bonding strength between a capacitor body and a tantalum wire. 
         [0014]    According to an aspect of the present invention, there is provided a tantalum capacitor including: a capacitor body containing a tantalum powder and having a mounting surface; a cathode lead frame having the capacitor body mounted thereon; a tantalum wire having an insertion portion located inside the capacitor body and a non-insertion portion located outside the capacitor body; an anode lead frame connected to the non-insertion portion of the tantalum wire; and a resin mold surrounding the capacitor body and the tantalum wire, wherein the insertion portion of the tantalum wire has at least one bending. 
         [0015]    The insertion portion of the tantalum wire may have at least one of both surfaces pressurized. 
         [0016]    The non-insertion portion of the tantalum wire may have one side disposed coplanar with a bottom of the capacitor body. 
         [0017]    The insertion portion of the tantalum wire may be oriented toward a center of the capacitor body. 
         [0018]    The insertion portion of the tantalum wire may be bent twice perpendicular to a length direction thereof. 
         [0019]    According to another aspect of the present invention, there is provided a tantalum capacitor including: a capacitor body containing a tantalum powder and having a mounting surface; a cathode lead frame having the capacitor body mounted thereon; a tantalum wire having an insertion portion located inside the capacitor body and a non-insertion portion located outside the capacitor body; an anode lead frame connected to the non-insertion portion of the tantalum wire; and a resin mold surrounding the capacitor body and the tantalum wire, wherein the non-insertion portion of the tantalum wire has a thickness greater than a thickness of the insertion portion. 
         [0020]    The non-insertion portion of the tantalum wire may have one side disposed coplanar with a bottom of the capacitor body. The non-insertion portion of the tantalum wire may have one side disposed lower than a bottom of the capacitor body. 
         [0021]    The insertion portion of the tantalum wire may have at least one bending. 
         [0022]    The insertion portion of the tantalum wire may be bent toward a center of the capacitor body. 
         [0023]    The insertion portion of the tantalum wire may be bent twice perpendicular to a length direction thereof. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0025]      FIGS. 1A and 1B  are a front view and a plan view illustrating an internal structure of a conventional tantalum capacitor, respectively; 
           [0026]      FIGS. 2A through 2C  are a front view, a plan view and a side view illustrating an internal structure of a tantalum capacitor, respectively, according to an exemplary embodiment of the invention; and 
           [0027]      FIGS. 3A and 3B  are a front view and a side view illustrating an internal structure of a tantalum capacitor, respectively, according to another exemplary embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0028]    Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
         [0029]      FIGS. 2A to 2C  are a front view, a plan view and a side view illustrating an internal structure of a tantalum capacitor, respectively, according to an exemplary embodiment of the invention. 
         [0030]    Referring to  FIGS. 2A to 2C , the tantalum capacitor of the present embodiment includes a rectangular parallelepiped tantalum capacitor body  21 , a tantalum wire  23  partially inserted into the capacitor body, a cathode lead frame  22  connected to the capacitor body  21 , an anode lead frame  24  connected to the tantalum wire  23 , and a resin mold  25  surrounding the capacitor body  21  and the tantalum wire  23 . 
         [0031]    To manufacture the capacitor body  21 , a tantalum wire is inserted in tantalum powder mixed with a binder to form a tantalum structure of a desired size. Then, the tantalum structure is sintered for 30 minutes at a high vacuum atmosphere (10 −5  torr or less) of 1200 to 2000° C. to form a tantalum pellet and a conversion coating is formed on a surface of the tantalum pellet by anode oxidization and then sintered. Carbon and silver are applied on a surface of the capacitor body. 
         [0032]    Carbon is applied on the surface of the capacitor body to reduce contact resistance of a surface of MnO 2 . Also, silver is applied to derive a minus polarity. 
         [0033]    The capacitor body  21  is bonded to the linear cathode lead frame  22  by a silver adhesive  22   a.    
         [0034]    The tantalum wire  23  has an insertion portion inserted into the capacitor body  21  and a non-insertion portion formed outside the capacitor body  21 . 
         [0035]    The insertion portion of the tantalum wire  23  inserted into the capacitor body  21  has one bending. With this bending, the insertion portion of the tantalum wire, when inserted into the capacitor body, is solidly attached to the capacitor body. According to the present embodiment, the tantalum wire is bent once at an acute angle with respect to a bottom of the capacitor body and accordingly the bending may be inserted into the capacitor body to be located adjacent to the surface of the capacitor body. 
         [0036]    Furthermore, unlike the prior art, the bending of the tantalum wire is located inside the capacitor body to reduce a length of the non-insertion portion, thereby increasing a volume of the capacitor body. A larger volume of the capacitor body increases a usable area of the capacitor. 
         [0037]    The non-insertion portion formed outside the capacitor body  21  is connected to the anode lead frame  24 . According to the present embodiment, the non-insertion portion formed outside the capacitor body  21  is disposed coplanar with the bottom of the capacitor body  21  to come in direct contact with the anode lead frame  24 . This allows the tantalum wire  23  and the anode lead frame  24  to be directly welded together. Here, the welding may be performed using, e.g., a silver adhesive and a conductive paste. 
         [0038]    According to Inventive Example, a capacitor package was manufactured, in which a capacitor body was shaped as a rectangular parallelepiped with a length, width and height of 0.73×0.50×0.38 mm, and accordingly a volume of 0.1387 mm 3 . The tantalum wire had a thickness of 0.15 mm. The capacitor package including a resin mold had a size of 1.15×0.65×0.55 mm, and a non-insertion portion formed outside the capacitor body had a length of 0.30 mm. The capacitor body of Inventive Example exhibited a usable area ratio of 33.75% and a maximum capacitance of 10 μF at 6V. 
         [0039]    Meanwhile, according to Comparative Example of  FIG. 1 , a capacitor package was manufactured, in which a tantalum wire inserted into a capacitor body formed inside a resin mold was bent outside the capacitor body. In this structure where the tantalum wire was bent outside the capacitor body while an overall package size was maintained, the capacitor body was formed in a less area, i.e., an area excluding a portion for bending. 
         [0040]    According to Comparative Example, the capacitor package including the resin mold had a size of 1.15×0.65×0.55 mm, and the capacitor body formed inside the resin mold had a size of 0.55×0.50×0.38 mm, and accordingly a volume of 0.1045 mm 3 . A non-insertion portion located outside the capacitor body had a length of 0.48 mm. The capacitor body demonstrated a usable area ratio of 25.43% and a maximum capacitance of 6.8 μF at 6V. 
         [0041]    Therefore, when Comparative Example and Inventive Example were compared together, the capacitor packages including the resin mold were found identically sized. However, the capacitor body in the capacitor package of Inventive Example was increased in volume and accordingly in a usable area ratio. 
         [0042]      FIGS. 3A and 3B  are a front view and a side view illustrating a tantalum capacitor according to another exemplary embodiment of the invention. 
         [0043]    Referring to  FIGS. 3A and 3B , an insertion portion of the tantalum wire  33  inserted into the capacitor body  31  is pressurized at both surfaces. 
         [0044]    Due to this pressurization, as shown in  FIG. 3A , the insertion portion of the tantalum wire inserted into the capacitor body  31  has a thickness smaller than a non-insertion portion of the tantalum wire located outside the capacitor body  31 . On the other hand, as shown in  FIG. 3B , the pressurized insertion portion of the tantalum wire has a width greater than the unpressurized non-insertion portion of the tantalum wire. 
         [0045]    The pressurization alters an external shape of the tantalum wire  33  however without changing an overall volume thereof. This as a result increases a usable area ratio of the capacitor as shown in a structure of  FIG. 2 . 
         [0046]    According to the present embodiment, the insertion portion inserted into the capacitor body, when pressurized, has a thickness difference from the non-insertion portion of the tantalum wire located outside the capacitor body. Therefore, with this thickness difference, the non-insertion portion of the tantalum wire located outside the capacitor body may easily have a side disposed coplanar with or lower than a bottom of the capacitor body. Also, when the tantalum wire is brought in contact with the anode lead frame  34 , the insertion portion of the tantalum wire inserted into the capacitor body is minimally affected by the contact. 
         [0047]    To achieve effects as described above, in place of pressurization of the insertion portion of the tantalum wire, the insertion portion and non-insertion portion of the tantalum wire may be formed to have a different thickness. 
         [0048]    Here, the non-insertion portion formed outside the tantalum wire may have a thickness greater than a thickness of the insertion portion. With this structure, the insertion portion inserted into the capacitor body may be spaced apart from the bottom of the capacitor body, without bending, and a side of the non-insertion portion may be brought into contact with the anode lead frame. 
         [0049]    As set forth above, according to exemplary embodiments of the invention, a capacitor body in a tantalum capacitor is increased in size while the tantalum capacitor is not altered in an external structure and size. This as a result produces the tantalum capacitor with a greater usable area ratio than a conventional capacitor. 
         [0050]    While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.