JP2009194200A - Solid electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor which is jacketed with mold resin that is excellent in barrier property against gas and steam and whose reliability during repeated reflow when mounted on a circuit board is assured, being excellent in mass productivity. <P>SOLUTION: In a solid electrolytic capacitor element, an anodic oxidation coating 2 is formed on a porous valve action metal, and a solid electrolytic layer 4, a graphite layer 5, and a conductive paste layer 6 are sequentially stacked on the anodic oxidation coating 2 to provide a cathode part, with an anode part of conductive member provided at the place other than the cathode part. The anode part and the cathode part are respectively electrically connected using an external anode terminal 8 and an external cathode terminal 10, being armored with an insulating mold resin 13. A buffer layer 12 whose main component is metal is formed on the conductive paste layer 6 at such portion as covered with the mold resin 13 of the cathode part, and then the solid electrolytic capacitor element is armored with the mold resin 13. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a solid electrolytic capacitor using a valve action metal, and more particularly to a solid electrolytic capacitor using a conductive polymer as an electrolyte, which is resistant to stress due to reflow during circuit board mounting.

  In recent years, digital devices have become smaller and more advanced, and solid electrolytic capacitors are also used around CPUs, directly under CPUs or in semiconductor packages for the purpose of noise reduction and power supply voltage stabilization. The role of is becoming important.

  As an example of a conventional solid electrolytic capacitor using a conductive polymer as a solid electrolyte, a method for forming an aluminum solid electrolytic capacitor having a flat element structure related to the present invention will be described. First, a dielectric film, which is an insulating film, is formed on the surface of an aluminum substrate made of a porous plate-like aluminum metal, which is a valve action metal, by anodic oxidation. Next, an insulator is formed with epoxy resin or the like at a predetermined position of the dielectric film to divide the aluminum substrate into two regions, and a solid electrolyte layer made of a conductive polymer is formed only in one of the regions. . Further, a graphite layer is formed on the solid electrolyte by screen printing or the like, and a conductive paste layer is formed on the graphite layer to form a cathode portion. On the other hand, in another region separated by the insulator, the aluminum substrate is exposed by peeling the dielectric film or the like, and the metal lead frame is welded to form an anode portion. The anode part and the cathode part of the solid electrolytic capacitor element are electrically connected to the external anode terminal and the external cathode terminal of the electrode substrate, respectively, to form a mounting terminal for the solid electrolytic capacitor. Next, a solid electrolytic capacitor is formed by molding an exposed portion of the capacitor element not connected to the electrode substrate with an epoxy resin. In this way, a solid electrolytic capacitor covered with a mold resin excellent in gas and vapor barrier properties can be obtained.

  However, in the case of a solid electrolytic capacitor, a conductive paste containing a resin in the paste is often used when forming the cathode portion, and therefore, the epoxy resin of the mold and the resin in the conductive paste layer are in close contact when the mold is packaged. When the mold expands and contracts due to heat during reflow, the conductive paste layer follows the mold side, causing peeling from the underlying graphite layer, which increases ESR and increases the impedance in the high frequency region. There has been a problem of relatively increasing.

  As a solution, firstly, a method of forming a capacitor with an exterior material other than a mold may be considered. However, for example, when the exposed portion of the capacitor element is covered with a resin case, it is necessary to process the resin case with high accuracy and to insert the element therein, which causes a disadvantage that the cost is likely to increase.

  As a method for realizing a capacitor that is resistant to the stress of the mold due to the above reflow, a second method is to provide an organic buffer layer at the interface between the mold and the conductive paste layer, and this buffer layer can relieve the stress from the mold. . In general, a liquid mold release agent is used, and a method of increasing the mold release property between the mold and the conductive paste layer is used. However, when a low viscosity mold release agent is used, in addition to the conductive paste layer, an electrode substrate is used. In many cases, a release agent is applied, peeling occurs between the mold and the electrode substrate, and the resin of the conductive paste layer is dissolved and swollen by the solvent of the release agent, which may cause deterioration of characteristics. is there. In addition, when a release agent having a high viscosity is used, the unevenness tends to increase due to the application shape of the release agent, making it difficult to reduce the size of the product.

  In order to avoid the above problem, there is an example disclosed in Patent Document 1 as a solid electrolytic capacitor in which molding is performed after temporarily covering with a heat-shrinkable tube or film.

JP-A-5-251285

  If the respective technologies relating to the solid electrolytic capacitor disclosed in Patent Document 1 above can be used, it is considered that the stress on the mold due to reflow can be alleviated to some extent. However, this technique uses a method of covering the solid electrolytic capacitor element with a film as a method of forming the buffer layer, and is unsuitable as a mass production method.

  Accordingly, the object of the present invention is to provide a solid electrolytic that is externally molded with a mold resin having excellent barrier properties against gases and vapors, that ensures reliability during repeated reflow during circuit board mounting, and that is excellent in mass productivity. The purpose is to produce a capacitor.

  In the solid electrolytic capacitor of the present invention, an anodized film is formed on a porous valve action metal, and a solid electrolyte layer, a graphite layer, and a conductive paste layer are sequentially formed on the anodized film, and a cathode portion is formed. The anode part and the cathode part in a solid electrolytic capacitor element provided with an anode part made of a conductive member at a place other than the cathode part are electrically connected by an external anode terminal and an external cathode terminal, respectively. In the solid electrolytic capacitor packaged with an insulating mold resin, after forming a buffer layer mainly composed of metal on the conductive paste layer at the portion covered with the cathode portion and the mold resin, the solid electrolytic capacitor A solid electrolytic capacitor is formed by covering the element with the mold resin. As the means for forming the buffer layer, it is possible to use a nano metal particle paste, plating or the like, and one or more of gold, silver, copper, platinum, nickel, palladium as the metal component in the buffer layer A metal is selected, and the resin component in the buffer layer is less than 1% by weight.

  By forming a buffer layer with a small amount of a resin component mainly composed of a metal between the conductive paste layer and the mold resin as in the above-mentioned means, the mold resin has poor adhesion to the metal component. Even with respect to stress, the buffer layer peels off from the mold resin, and the conductive paste layer hardly receives stress. In addition, as a forming method, a method such as paste printing or plating can be used, which is excellent in mass productivity. As a result, it is possible to realize a solid electrolytic capacitor that is externally molded with a mold resin excellent in gas and vapor barrier properties, is reliable during repeated reflow during circuit board mounting, and is excellent in mass productivity. .

  FIG. 1 shows the configuration of a solid electrolytic capacitor according to an embodiment of the present invention. FIG. 1A is a perspective view thereof, and FIG. 1B is a cross-sectional view taken along the plane A-A ′ of FIG.

  In FIG. 1, an aluminum substrate 1 is made of a rectangular aluminum foil, and both surfaces thereof are made porous by etching. Anodized film 2 is formed on both surfaces of this aluminum substrate 1 by anodic oxidation. Next, an insulator 3 is formed at a predetermined position of the anodized film 2 with an epoxy resin or the like to divide the aluminum substrate 1 into two regions, and a solid electrolyte layer made of a conductive polymer is formed only in one of the regions. 4, a graphite layer 5 and a conductive paste layer 6 are formed to constitute a cathode portion. A rectangular metal lead frame 7 is provided by welding only on one surface of the anodic oxide film 2 at a position separated by the insulator 3 and where the cathode portion is not formed, thereby forming the anode portion. The metal lead frame 7 is made of a metal member such as copper foil, and has a role of electrically connecting the anode between the external anode terminal 8 provided on the mounting surface of the solid electrolytic capacitor and the aluminum substrate 1. The anodized film 2 is peeled off at the connection portion between the aluminum base 1 and the metal lead frame 7, and both can be connected by ultrasonic welding. The solid electrolytic capacitor element thus produced has a rectangular plate shape and a cross-sectional shape shown in FIG. Next, the metal lead frame 7 of the solid electrolytic capacitor element and the external anode terminal 8 in the electrode substrate 9, and the conductive paste layer 6 and the external cathode terminal 10 are electrically connected with the conductive adhesive 11, respectively. The mounting surface in the electronic circuit of the electrolytic capacitor was formed.

  Next, the nano metal particle paste is applied by screen printing on the conductive paste layer 6 on the cathode portion opposite to the surface connected to the electrode substrate of the solid electrolytic capacitor element, and dried at a temperature of about 125 ° C. The buffer layer 12 having a residual resin component of less than 1% by weight is formed by volatilizing the solvent in the paste and further short-time heat treatment in a furnace at about 150 to 300 ° C. to cure the nano metal particle paste. To do. As the metal paste used here, a paste composed of nano-sized metal fine particles, a mixed paste of an organic metal and a metal oxide, etc. are used. These pastes are associated with surface activity depending on the particle size, desorption of organic substances and oxygen. The metal particles cause fusion due to the activity of the metal particles, and the buffer layer 12 mainly composed of metal is formed. In addition to using a metal paste as a method for forming the buffer layer 12, the buffer layer 12 can be formed by electrolytic plating and electroless plating on the conductive paste layer 6. Further, as the metal component used in the buffer layer, one or more metals selected from gold, silver, copper, platinum, nickel, and palladium may be used, and the buffer layer 12 mainly composed of this metal may be used. By the way, when the amount of the resin component contained in the buffer layer 12 is 1% by weight or more, the adhesive strength with the mold resin 13 becomes strong, and the increase in ESR after reflow exceeds the practical allowable value. The amount is preferably less than 1% by weight.

  Next, the solid electrolytic capacitor of the present embodiment is formed by covering the exposed portion of the solid electrolytic capacitor element other than the mounting surface with the mold resin 13 and performing the exterior.

  Next, examples of the present invention will be further described.

(Example 1)
A solid electrolytic capacitor of Example 1 of the present invention was produced by the following method, and its electrical characteristics were measured.

Example 1 shows a method for producing a solid electrolytic capacitor in which the buffer layer of the cathode portion of the solid electrolytic capacitor element is formed of a nano metal particle paste. Referring to FIG. 1, a foil-like aluminum substrate 1 was first made porous, and an anodized film 2 was formed on the surface thereof. Here, the foil-like aluminum substrate 1 is made of a material that is commercially available for an aluminum electrolytic capacitor, and has a nominal formation voltage of 4 V per unit area (cm ² ) for forming the anodized film 2 on the surface. The capacitance is 260 μF and the thickness is 105 μm. Here, the thickness of the porous portion having the anodized film 2 on the aluminum substrate 1 is 50 μm on one side. This foil-like aluminum substrate 1 is cut into a rectangular shape having a width of 3.0 mm and a length of 7.0 mm, and is cut from one end in the length direction to a rectangular region of 3.0 mm in the width direction and 4.5 mm in the length direction. The cathode part is formed, and the anode part is formed in a rectangular area of 3.0 mm in the width direction and 1.0 mm in the length direction from the end in the length direction on the side where the cathode part is not formed. . Next, in order to electrically insulate between the anode part and the cathode part, an epoxy resin is screened so that the width of the insulator 3 layer is 0.5 mm and the thickness is 15 μm between the anode part and the cathode part. Formed by printing. Next, the molar ratio of 3,4-ethylenedioxythiophene as a monomer, ammonium peroxodisulfate as an oxidant, and paratoluenesulfonic acid as a dopant on the surface of the anodized film 2 on the cathode portion on both sides of the aluminum substrate 1 is as follows. A solid electrolyte layer 4 made of a conductive polymer is formed by reaction at a ratio of 6: 1: 2, and further a graphite layer 5 is formed on the surface to have a thickness of 15 μm by screen printing. A conductive paste layer 6 having a melamine resin of not less than wt% and a silver content of not less than 80 wt% was formed to a thickness of 30 μm.

  Next, a metal lead frame 7 made of a copper foil having nickel and silver plated on both sides in advance is fixed on the anode portion, and the metal lead frame 7 and the aluminum base 1 of the anode portion are electrically connected by ultrasonic welding. Connected to enable conduction of the anode part of the capacitor element.

  Next, the external anode terminal 8 and the external cathode terminal 10 of the electrode substrate 9 for circuit board mounting are electrically connected to the metal lead frame 7 and the conductive paste layer 6 constituting the anode part and the cathode part by the conductive adhesive 11, respectively. Joined.

  Next, an organic silver / silver oxide mixed paste made of organic silver, silver oxide, a diluting solvent, etc. is screen-printed on the conductive paste layer 6 of the cathode portion opposite to the surface connected to the electrode substrate 9 of the solid electrolytic capacitor element. The coating film is dried at 125 ° C., only the diluting solvent in the components is volatilized, and further heat-treated in a furnace at 250 ° C. for 30 seconds to obtain an organic silver / silver oxide mixed paste. By curing, the organic matter in the organic silver and the oxygen in the silver oxide are separated, and the silver particles are activated to promote fusion, so that the resin component in the component has a buffer of 0.1% by weight or less. Layer 12 was formed.

  Next, the entire exposed portion of the solid electrolytic capacitor element not connected to the electrode substrate 9 was covered with a mold resin 13 made of an epoxy resin, and the resin was cured by heat treatment at 200 ° C. to produce a solid electrolytic capacitor. The number of solid electrolytic capacitors produced by this method was 30.

  Electrical characteristics were measured for the 30 solid electrolytic capacitors produced. The measurement items were three items of capacitance, ESR, and leakage current, and electrical characteristics were measured before reflow, after first reflow, and after second reflow, respectively. The reflow conditions were heat treatment in an atmosphere of 260 ° C. for 30 seconds, repeated twice, and the electrical characteristics were measured each time. Capacitance and ESR are both measured by the AC impedance bridge method. Among these, the measurement conditions of the capacitance were that the frequency of the applied reference signal was 120 Hz, the voltage was 1 Vrms, and the DC bias was 0V. On the other hand, in the ESR, the frequency of the applied reference signal is 100 kHz, the voltage is 1 Vrms, and the DC bias is 0V. As for the leakage current, a signal voltage of 2.5 V, which is the rated voltage of the solid electrolytic capacitor, was applied, and the value after 1 minute was measured. The average value of each characteristic of the produced 30 solid electrolytic capacitors is shown in the column of Example 1 in Table 1, Table 2, and Table 3 for each stage of reflow.

(Example 2)
Example 2 shows a method for producing a solid electrolytic capacitor in which the buffer layer 12 of the cathode portion of the solid electrolytic capacitor element is formed by plating.

  A solid electrolytic capacitor element was produced in the same manner as in Example 1, and the anode part and the cathode part of the solid electrolytic capacitor element were connected to the external anode terminal 8 and the external cathode terminal 10 of the electrode substrate 9, respectively. Unlike Example 1, a power supply terminal is connected to a part of the conductive paste layer 6 in the cathode portion of the solid electrolytic capacitor element, and a bath containing copper ions is filled in a bathtub connected to the power supply terminal, The cathode side of the electrolytic capacitor element is immersed so as not to immerse the power supply terminals, and the power supply terminals are electrically connected to each other, and a copper plating layer having an average of 5 μm is formed as the buffer layer 12. The exposed portion of the element was covered with a mold resin 13 to form a solid electrolytic capacitor. The number of solid electrolytic capacitors produced by this method was 30. The evaluation by reflow and the measurement of electric characteristics are the same as in Example 1. The average values of the characteristics of the 30 solid electrolytic capacitors produced are shown in the column of Example 2 in Tables 1, 2 and 3.

(Comparative Example 1)
As a comparative example, a method for producing a conventional solid electrolytic capacitor in which the buffer layer 12 in the cathode portion of the solid electrolytic capacitor element is not provided will be described. FIG. 2 shows a solid electrolytic capacitor of this comparative example, FIG. 2 (a) is a perspective view thereof, and FIG. 2 (b) is a sectional view taken along the plane BB ′ of FIG. 2 (a).

  A solid electrolytic capacitor element was produced in the same manner as in the example, and the anode part and the cathode part of the capacitor element were connected to the external anode terminal 8 and the external cathode terminal 10 of the electrode substrate 9, respectively. Unlike Examples 1 and 2, the buffer layer 12 was not provided on the conductive paste layer 6, and the exposed portion of the solid electrolytic capacitor element including the conductive paste layer 6 was covered with the mold resin 13 to form a solid electrolytic capacitor. . The number of solid electrolytic capacitors produced by this method was 30. The evaluation by reflow and the measurement of electric characteristics are the same as in the example, and the average values of the characteristics of the 30 solid electrolytic capacitors thus prepared are shown in the column of Comparative Example 1 in Tables 1, 2 and 3.

(Comparative Example 2)
As a comparative example, a method for producing a solid electrolytic capacitor containing 1% by weight of a resin component in the buffer layer 12 in the cathode portion of the solid electrolytic capacitor element is shown.

  A solid electrolytic capacitor element was produced in the same manner as in the example, and the anode part and the cathode part of the capacitor element were connected to the external anode terminal 8 and the external cathode terminal 10 of the electrode substrate 9, respectively. Unlike Examples 1 and 2, the buffer layer 12 of the capacitor element is formed using a silver paste layer containing 1% by weight of an epoxy resin, and then the exposed portion of the solid electrolytic capacitor element is molded resin 13 as in the example. Covered to form a solid electrolytic capacitor. The number of solid electrolytic capacitors produced by this method was 30. The evaluation by reflow and the measurement of electrical characteristics are the same as in the example, and the average values of the characteristics of the 30 solid electrolytic capacitors thus prepared are shown in the columns of Comparative Example 2 in Tables 1, 2 and 3.

  From Table 1, ESR before reflow is almost the same in both Examples and Comparative Examples, whereas ESR after the first reflow is significantly increased in Comparative Example 1 compared to Examples 1 and 2. Example 2 also increased slightly. Similarly, ESR after the second reflow increased significantly in Comparative Example 1 compared to Examples 1 and 2, and Comparative Example 2 also increased slightly.

  As a result, compared to Comparative Example 1 in which the buffer layer 12 is not provided and Comparative Example 2 in which the buffer layer 12 includes 1% by weight of the resin component, Example 1 and Example 2 according to the present invention are based on reflow and repeated reflow. It can be seen that the conductive paste layer 6 of the solid electrolytic capacitor element is prevented from being peeled off against the expansion and contraction of the mold resin 13 and the electrical characteristics of the solid electrolytic capacitor are prevented from deteriorating.

  As described above, according to the solid electrolytic capacitor of the present invention, by forming the buffer layer 12 having a metal as a main component between the conductive paste layer 6 and the mold resin 13, the mold resin 13 has a metal component. Since the adhesive strength is poor, the buffer layer 12 peels off from the mold resin 13 against stress due to reflow, and the conductive paste layer 6 hardly receives stress. As a result, a solid electrolytic capacitor is realized with a mold resin 13 having an excellent barrier property against gas and vapor, ensuring reliability during repeated reflow during circuit board mounting, and excellent in mass productivity. it can.

The figure which shows an example of the solid electrolytic capacitor which concerns on this invention. FIG. 1A is a perspective view thereof, and FIG. 1B is a cross-sectional view taken along the plane A-A ′ of FIG. The figure which shows the solid electrolytic capacitor of the comparative example 1. 2A is a perspective view thereof, and FIG. 2B is a cross-sectional view taken along the plane B-B ′ of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Aluminum base body 2 Anodized film 3 Insulator 4 Solid electrolyte layer 5 Graphite layer 6 Conductive paste layer 7 Metal lead frame 8 External anode terminal 9 Electrode substrate 10 External cathode terminal 11 Conductive adhesive 12 Buffer layer 13 Mold resin

Claims (3)

  An anodized film is formed on the porous valve action metal, and a cathode part in which a solid electrolyte layer, a graphite layer, and a conductive paste layer are sequentially laminated on the anodized film is provided. Solid electrolytic capacitor in which the anode part and the cathode part in a solid electrolytic capacitor element provided with an anode part made of a conductive member are electrically connected to an external anode terminal and an external cathode terminal, respectively, and are covered with an insulating mold resin And forming a buffer layer mainly composed of metal on the conductive paste layer of the portion to be coated with the mold resin at the cathode portion, and then covering the solid electrolytic capacitor element with the mold resin. Solid electrolytic capacitor characterized by   2. The solid electrolytic capacitor according to claim 1, wherein at least one metal selected from gold, silver, copper, platinum, nickel, and palladium is selected as the metal component in the buffer layer.   The solid electrolytic capacitor according to claim 1, wherein the resin component in the buffer layer is less than 1% by weight.

Images