JP2007287775A - Solid electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce failure resulting from thermal stress incident to reflow, or the like. <P>SOLUTION: A dielectric oxide film 2, a solid electrolytic layer 4, a carbon layer 5, and a silver paste layer 6 are provided sequentially on the surface of a valve action metal 1 to obtain a capacitor element 7 which is then coated with coating resin 12 to produce a solid electrolytic capacitor wherein the solid electrolytic layer 4 is composed of at least conductive polymer which is incompressible at temperatures of its glass transition point or above. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solid electrolytic capacitor used in various electronic devices.

  In recent years, electronic components have been rapidly becoming chips with the progress of light and thin electronic devices and surface mounting technology. Solid electrolytic capacitors, which are one of the chip components, are used in various electronic devices such as personal computers and digital televisions, and are characterized by a larger capacity per unit volume than other capacitors such as ceramic capacitors. It is a surface mount component.

  Electronic components are generally used by being soldered to a printed circuit board, so that they are subjected to thermal stress during soldering. For example, when soldering is performed by reflow, the electronic component is exposed to a temperature at which the solder melts for several tens of seconds.

  In particular, in recent years, the replacement of tin-lead eutectic solder with a low melting point with lead-free solder having a high melting point with a low environmental load has progressed, so the reflow temperature has increased from 230 ° C to 260 ° C, It is exposed to a more severe environment for electronic components.

  In the case of a solid electrolytic capacitor, the dielectric oxide film may be damaged by thermal stress due to reflow or the like. As a result, the leakage current increases, and sometimes a short circuit may occur. Therefore, product design that can withstand various conditions (heat stress) during soldering is essential. For this reason, in order to alleviate the stress at the time of soldering, methods such as adjusting the moisture absorption of the solid electrolytic capacitor or screening for defective products by heat treatment before soldering are performed. ing.

For example, for heat treatment before soldering, a solid electrolytic capacitor after resin molding is vacuum-dried at 100 ° C. or higher, then a thermal load of 240 to 260 ° C. is applied, and then the characteristics are measured to remove the deteriorated capacitor. (For example, refer to Patent Document 1) and the like have been proposed.
JP 2004-304061 A

  However, the above method is only a screening, and has no effect in reducing the defect rate. Therefore, an object of the present invention is to reduce the defect rate due to thermal stress.

  To achieve this object, the present invention provides a solid electrolytic capacitor in which a capacitor element in which a dielectric oxide film, a solid electrolyte layer, and a current collector layer are sequentially provided on the surface of a valve metal is covered with an exterior resin. The solid electrolyte layer is composed of at least a conductive polymer, and the conductive polymer is non-shrinkable at a temperature equal to or higher than its glass transition point.

  The solid electrolytic capacitor of the present invention can reduce damage to the dielectric oxide film because the conductive polymer is non-shrinkable at a temperature equal to or higher than the glass transition point even when subjected to thermal stress. It is possible to reduce product defects due to.

  That is, various materials constituting the solid electrolytic capacitor are expanded by applying heat due to reflow or the like to the solid electrolytic capacitor. In particular, the difference in expansion coefficient between the dielectric oxide film and the conductive polymer is The inventors have found that this greatly affects the damage. Therefore, paying attention to the linear expansion coefficient of the conductive polymer, the use of the conductive polymer that is non-shrinkable at the temperature above the glass transition point reduces the stress on the dielectric oxide film and suppresses the damage. It is possible to reduce product defects due to thermal stress.

  Hereinafter, an embodiment of the solid electrolytic capacitor of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view of a solid electrolytic capacitor according to the present embodiment. An aluminum etched foil which is valve action metal 1 is used as an anode, and a dielectric oxide film 2 is provided on the surface of the aluminum etched foil leaving an anode portion. Further, a manganese oxide layer is formed on the surface of the dielectric oxide film 2. 3. A conductive polymer layer 4, a carbon layer 5, and a silver paste layer 6 are sequentially provided as a solid electrolyte layer to form a cathode portion to constitute a capacitor element 7.

  Two capacitor elements 7 configured as described above are laminated via the silver paste layer 6 of the cathode part, and the anode part of each capacitor element is electrically connected to the anode terminal 11, while the cathode part is The cathode terminal 9 and each capacitor element 7 are electrically connected by a silver paste 8 so that the two stacked capacitor elements sandwich the cathode terminal 9 from above and below. And the capacitor | condenser element 7 is coat | covered using the exterior resin 12 so that each edge part of the anode terminal 11 and the cathode terminal 9 may be exposed, and the solid electrolytic capacitor is comprised.

  Next, the manufacturing method of the solid electrolytic capacitor of this invention is demonstrated.

  An aluminum foil that has been electrochemically etched using conventional techniques is subjected to an anodic oxidation treatment while leaving the anode portion, and a dielectric oxide film 2 is formed on the surface of the aluminum etched foil that is the valve action metal 1. Here, as a method of the surface expansion treatment, electrochemical etching treatment or aluminum vapor deposition treatment may be used. Moreover, you may perform the process which vapor-deposits an aluminum oxide after forming the dielectric oxide film 2. FIG.

  Next, the manganese oxide layer 3 is formed by applying a manganese nitrate aqueous solution to the surface of the dielectric oxide film 2 and thermally decomposing it. Subsequently, electrolysis using the electrode for electropolymerization immersed in at least the manganese oxide layer 3 in a polymerization solution composed of the monomer, dopant and solvent of the conductive polymer layer 4 and in contact with the manganese oxide layer 3 as an anode. A conductive polymer layer 4 is formed on the surface of the manganese oxide layer 3 by a polymerization method.

  Here, the reason for forming the manganese oxide layer 3 is that it is necessary to form a conductive layer on the surface of the dielectric oxide film 2 that is an insulator in order to form the conductive polymer layer 4 by the subsequent electrolytic polymerization method. Because there is. Therefore, the manganese oxide layer 3 is not limited as long as it has a function as a conductive layer. For example, a conductive polymer layer formed by a chemical polymerization method may be formed and used as the conductive layer. Alternatively, the conductive polymer layer 4 may be formed using only the chemical polymerization method without using the electrolytic polymerization method.

  As a material of the conductive polymer layer 4, pyrroles, thiophenes, furans, and derivatives thereof can be used. These materials can be used alone or in combination, that is, for example, a polythiophene layer can be formed on the surface of the polypyrrole layer.

  Here, the conductive polymer layer 4 is characterized by non-shrinkage at a temperature equal to or higher than the glass transition point. Thus, by not shrinking at a temperature higher than the glass transition point, it is possible to reduce damage to the dielectric oxide film 2 due to thermal stress such as reflow.

  Further, from the examples described later, the conductive polymer layer preferably has a linear expansion of 10 ppm or more at a temperature of the glass transition point or more, and more preferably 65 ppm or more.

  In order to impart such characteristics to the conductive polymer layer 4, for example, means such as heat treatment can be used. After forming the conductive polymer layer 4, for example, a heat treatment of 10 ° C./min up to 250 ° C. may be performed. In particular, the method of increasing the temperature over time is effective in terms of suppressing adverse effects due to a rapid environmental change. These conditions can be set according to the formed conductive polymer layer.

  For example, it can also be set by changing the concentration of a dopant, for example, sodium alkylnaphthalene sulfonate, in a solution containing a monomer, a dopant, etc. used in the step of forming the conductive polymer layer.

  Next, a carbon layer 5 and a silver paste layer 6 are sequentially formed as a current collector layer on the surface of the conductive polymer layer 4. The carbon layer 5 was formed by immersing a capacitor element in which the conductive polymer layer 4 was formed in a solution in which carbon was dispersed with alcohol or the like and then drying. The silver paste layer 6 was formed by applying a silver paste and then drying at 100 ° C., followed by heat treatment at 250 ° C.

  Two capacitor elements 7 produced as described above were laminated and dried via silver paste 8, and two sets of the laminated capacitor elements were produced.

  Then, the lead frame was sandwiched between two laminated capacitor elements so as to be sandwiched between silver pastes 8 and then dried to electrically connect the cathode part of each capacitor element 7 and the lead frame. On the other hand, the anode part of the capacitor element was similarly connected by resistance welding to the dielectric exposed part 10 of the anode part of the capacitor element laminated so as to sandwich the lead frame.

  The capacitor element 7 is molded with an exterior resin 12 so as to cover at least the anode part and the cathode part of the lead frame, and the lead frame part protruding from the exterior resin 12 is subjected to nickel plating and solder plating, and then the exterior resin. The anode terminal 11 and the cathode terminal 9 were formed by bending along the outer surface of 12, respectively.

  Thereafter, an aging treatment is performed as necessary to complete a solid electrolytic capacitor.

  Next, the solid electrolytic capacitor of the present invention will be described using examples.

(Example)
In this embodiment, an aluminum etched foil obtained by electrochemically etching an aluminum foil cut into a strip shape having a width of 3 mm in an aqueous solution containing hydrochloric acid as a main component is used, and an electrolyte such as ammonium adipate is applied to a predetermined portion. Anodization was performed in the aqueous solution containing 70 V for 1 hour to form a dielectric oxide film. A low-concentration aqueous solution of manganese nitrate was applied to a predetermined portion thereon, and pyrolyzed at 250 ° C. for 30 minutes to form a manganese oxide layer.

  Next, a stainless steel electrode provided in contact with the manganese oxide layer in an aqueous solution of pyrrole 0.5 mol / liter and alkyl naphthalene sulfonate sodium 0.1 mol / liter is used as an anode for electrolytic polymerization, and the manganese oxidation A polypyrrole conductive polymer layer, which becomes a solid electrolyte at a constant current of 2 mA, was formed on the entire material layer by electrolytic polymerization.

  Further, a carbon layer and a silver paste layer were sequentially formed for cathode extraction to obtain a capacitor element.

  Next, four capacitor elements formed as described above are laminated via silver paste, and then connected to the cathode terminal with silver paste, while the dielectric exposed portion is connected to the anode terminal by welding, Was covered with an exterior resin to produce a solid electrolytic capacitor.

(Comparative example)
In the step of forming the conductive polymer layer, a solid electrolytic capacitor was fabricated by the same production method as in the examples except that the polymerization was carried out in an aqueous solution of 0.5 mol / liter of pyrrole and 1.0 mol / liter of sodium alkylnaphthalene sulfonate. Produced.

  As described above, 1000 solid electrolytic capacitors of Examples and Comparative Examples were produced one by one and evaluated by the following methods.

  In order to make this solid electrolytic capacitor almost the same as the environment until it is used by the user, the solid electrolytic capacitor is allowed to absorb moisture by leaving it in a constant temperature and humidity of 30 ° C. and humidity 60 ° C. for 2 weeks. The preheating was performed at 150 ° C. to 180 ° C. for 120 seconds, the peak temperature was 260 ° C. for 10 seconds, and the main heating was 230 ° C. for 40 seconds.

  Next, an applied voltage of 16 V was applied to the reflowed solid electrolytic capacitor, and the leakage current value after 2 minutes was measured. If the leakage current exceeded 10 μA, the defective product was rated as 10 μA or less. Measured. The results are shown in (Table 1).

  On the other hand, the linear expansion of the conductive polymer was measured as follows.

  Since the conductive polymer is formed on the electrode for electrolytic polymerization used in the electrolytic polymerization of the solid electrolytic capacitor produced in this example, the conductive polymer is peeled off from the electrode for electrolytic polymerization, washed with water, and dried. Thereafter, linear expansion was measured by TMA. The result is shown in FIG.

  As apparent from (Table 1), the number of defects after reflow in the examples is 0, and it can be seen that the solid electrolytic capacitor of the present invention is resistant to thermal stress such as reflow.

  FIG. 2 is a diagram in which the linear expansion of the conductive polymer is measured. In the comparative example, the temperature of the conductive polymer indicated by the vertical axis is 230 ° C., which is a temperature higher than the glass transition point of the conductive polymer. It can be seen that the elongation is negative, that is, contracted.

  On the other hand, it can be seen that the conductive polymer of the example does not become negative and does not shrink even at a temperature equal to or higher than the glass transition point. Further, the numerical value of linear expansion is preferably 10 ppm or more, and particularly preferably 65 ppm or more.

  The present invention is characterized in that a conductive polymer that is non-shrinkable at a temperature equal to or higher than the glass transition point is used as an electrolyte, and is useful for an electrolytic capacitor that requires high resistance to thermal stress.

Sectional drawing of the solid electrolytic capacitor in one embodiment of this invention Measurement diagram of measuring the linear expansion of the conductive polymer in one embodiment of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Valve metal 2 Dielectric oxide film 3 Manganese oxide layer 4 Conductive polymer layer 5 Carbon layer 6 Silver paste layer 7 Capacitor element 8 Silver paste 9 Cathode terminal 10 Dielectric exposed part 11 Anode terminal 12 Exterior resin

Claims (4)

In a solid electrolytic capacitor in which a capacitor element in which a dielectric oxide film, a solid electrolyte layer, and a current collector layer are sequentially provided on the surface of a valve metal is coated with an exterior resin, the solid electrolyte layer is made of at least a conductive polymer. The conductive polymer is non-shrinkable at a temperature equal to or higher than its glass transition point. The solid electrolytic capacitor according to claim 1, wherein the conductive polymer has a linear expansion of 10 ppm or more at a temperature equal to or higher than a glass transition point thereof. The solid electrolytic capacitor according to claim 1, wherein the conductive polymer has a linear expansion of 65 ppm or more at a temperature equal to or higher than a glass transition point thereof. 4. The solid electrolytic capacitor according to claim 2, wherein the basic skeleton of the conductive polymer is at least one selected from the group consisting of pyrrole, thiophene, furan, and derivatives thereof.

Images