JP3132053B2 - Solid electrolytic capacitors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolytic capacitor for use in electronic equipment, and particularly to a solid electrolytic capacitor exhibiting excellent characteristics when mounted on a surface.

[0002]

2. Description of the Related Art In recent years, with the progress of electronic equipment, electronic components have been formed into chips, and it has become mainstream that electronic circuits are assembled by surface mounting. For this reason, not only the solderability of the lead terminals of the chip component is required, but also the heat resistance that can withstand the high temperature during soldering for a long time has been required. Conventionally, in the field of electrolytic capacitors, which are said to have poor heat resistance, due to advances in materials and technology,
Chip components that can be surface mounted are becoming mainstream. For example, as shown in FIGS. 7A and 7B, there is known a solid electrolytic capacitor in which a capacitor element is molded with a resin together with a lead frame serving also as an anode terminal 1 and a cathode terminal 2, and a resin exterior 3 is provided. .

[0003]

However, in a solid electrolytic capacitor provided with such a resin sheath 3, the hermeticity of the resin sheath 3 is reduced due to exposure to a high temperature during soldering during surface mounting. As a result, oxygen and water vapor in the air enter the inside from the outside, so that the internal capacitor element is often damaged and the characteristics are often deteriorated. The possible reasons are as follows.

(1) A solder alloy or tin metal layer is provided on the entire surface of the lead frame in order to improve the solderability at the time of surface mounting of chip components. The melting point metal is melted, and a gap is formed between the exterior resin and the surface of the lead frame, so that the airtightness is reduced.

(2) Since the base metal used for the lead frame and the exterior resin have different coefficients of thermal expansion, a gap is formed between the exterior resin and the lead frame due to expansion and contraction, resulting in reduced airtightness.

In order to solve these problems, the present inventors have proposed to form a copper metal layer on the surface of a lead frame and to roughen the surface. In this case, the above two problems could be completely solved by roughening the copper metal layer on the surface of the lead frame. However, a new problem concerning solderability, which is considered to be due to the following reasons, was found. occured.

(1) Since the oxidation of the roughened copper metal surface proceeds rapidly, the wettability of the solder deteriorates. As a result, the solderability of the lead frame serving as the lead-out terminal is reduced by the solder alloy layer or tin. This is considerably lower than that having a metal layer.

(2) When the exterior is formed by the transfer molding method, solder is used to cover the surface of the lead frame which becomes a lead terminal by firmly adhering as thin burrs on the lead frame on which the burrs of the exterior resin are roughened. Causes a marked decline in gender.

SUMMARY OF THE INVENTION An object of the present invention is to provide a highly reliable solid electrolytic capacitor that can withstand thermal shock during surface mounting and that has excellent solderability.

[0010]

In order to achieve the above object, a solid electrolytic capacitor according to the present invention is characterized in that an anode oxide film formed on a valve metal is used as a dielectric, and a predetermined portion of this dielectric is A capacitor element is formed by sequentially forming a conductive polymer layer and a conductor layer, and a lead frame serving as a lead terminal is connected to the valve metal part and the conductor layer part of the capacitor element. In a solid electrolytic capacitor in which a part of a frame is covered with a mold resin, a solder alloy layer or a tin metal layer based on a copper metal layer is formed on a surface of the lead frame other than a portion in contact with the mold resin, and the mold resin Only the copper metal layer is formed on the lead frame portion in contact with the substrate, and the surface of the copper metal layer is roughened.

[0011]

According to the above construction, a copper metal layer is formed on the surface of the lead frame, which is a lead terminal connected to the valve metal portion and the conductor layer portion of the capacitor element, except for the portion where the mold resin and the lead frame are in contact. A portion having a solder alloy layer or a tin metal layer as an underlayer, and a portion where the mold resin and the lead frame are in contact with each other has only the copper metal layer without the solder alloy layer or the tin metal layer, and the portion thereof Only the surface of the lead frame is roughened, so when the lead frame is surface-mounted on a printed circuit board by soldering, the lead frame surface has a low melting point solder alloy layer or tin metal layer, which makes soldering easier. Is excellent, and the adhesion to the exterior resin is much better than other configurations due to the roughened surface of the copper metal layer. Also able to withstand thermal shock expansion and contraction at the time of mounting, and because also excellent exterior tightness is obtained, in which it is possible to obtain a highly reliable solid electrolytic capacitor.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

(Embodiment 1) First, as shown in FIG. 1, an aluminum conversion foil, which is a valve metal having a thickness of 100 μm and roughened by etching, is used as an electrode body 11, and this electrode body 11 is attached to the electrode body 11 as shown in FIG. 2), a strip-shaped heat-resistant insulating film 13 to which an adhesive 12 was applied was attached, and a cathode portion 14 and an anode portion 15 were separated. Then, as shown in FIGS. 2 (a) and 2 (b), a thin-film manganese oxide layer which is a conductive material layer 17 is formed on the chemical conversion film 16 of the cathode portion 14, and then an alkylnaphthalene sulfonate is supported. Electropolymerization was performed in an emulsion containing pyrrole as an electrolyte to form a conductive polymer layer 18 of polypyrrole on the conductive material layer 17. Further, a conductor layer composed of a graphite layer 19 and a silver paint layer 20 was sequentially formed thereon by a known method to obtain a capacitor element 21 shown in FIGS. 2A and 2B.

Next, an iron base material having a thickness of 0.1 mm is punched into a shape of a lead frame 22 shown in FIG. 3 by pressing, and a copper metal layer made of copper plating having a thickness of 3 μm is formed on the surface thereof. The lead frame 22 was formed by forming a solder alloy layer having a thickness of 1 to 10 μm by solder plating. Thereafter, as shown in FIG.
2 except for a predetermined portion 23 (a portion in contact with the resin of the resin mold exterior indicated by hatching in the figure) having a thickness of 1
Masked with a mask material made of butadiene rubber of mm, and other predetermined portions 23 are polished until the solder alloy layer is completely removed by dry sandblasting using an alumina abrasive to expose the copper metal layer, And this predetermined part 2
The surface of only 3 was roughened.

Then, a small amount of a conductive adhesive was applied to a position 24 corresponding to the cathode portion 14 on the partially roughened lead frame 22, and the capacitor element 21 was placed by lamination. Thereafter, the capacitor element 21 was fixed by bending a part of the lead frame 22 on the cathode section 14 side and the anode section 15 side of the capacitor element 21. Further, the two electrodes were connected to the lead frame 22 as shown in FIG. 4B by joining the anode part 15 by laser welding from above the anode pressing part 25.

As shown in FIG. 5, the lead frame 22 on which the capacitor elements 21 are installed is molded with an epoxy resin 26 as shown in FIG. 5, and then resin burrs at the time of molding are formed by sand blasting using resin beads as an abrasive. Then, the lead frame 22 was cut off to obtain a solid electrolytic capacitor.

The external airtightness of the thus obtained solid electrolytic capacitor was evaluated by performing a heat treatment in which the solid electrolytic capacitor was left in a thermostat at 250 ± 5 ° C. for 5 minutes and then taken out to room temperature three times. Autoradiography exterior tightness test. That is, after holding the test capacitor samples in an atmosphere of an inert gas pressurized to 7 MPa containing the radioactive isotope Kr85 for 30 minutes, the radiation dose held by each capacitor sample is measured, so that the inside of the exterior is measured. Quantify the amount of outside air taken in,
Then, the sample was exposed to light on a photographic film to detect an airtight breakage sample of the exterior.

The results are expressed as fractions as the number of defects with respect to the parameter, and are shown in Table 1. Further, in order to evaluate the solderability of the lead frame 22 of this capacitor, a solder wettability test was performed by the following method. That is, 230
The test lead frame 22 to which no flux was applied was immersed in a molten solder bath at a temperature of 2.0 mm per second to 5.0 mm at a speed of 2.0 mm per second, and the wetting state at that time was followed over time. The wet state is represented by a change in the contact angle between the solder and the metal to be soldered.
In the case of ゜ ≧ θ> 90 °, a positive acting force acts as a reaction from the solder bath, and the acting force becomes 0 when θ = 90 °. 90 °> θ where the solder gets wet with the metal to be soldered
In the range of ≧ 0 °, a negative acting force acts. This acting force was graphed as a function of time, and the wettability was evaluated by measuring the time from the start of immersion until θ = 90 °.
The test results and their graphs are shown in Table 1 and FIG.
(A).

(Embodiment 2) Lead frame 2 of Embodiment 1
2 In the plating above, instead of solder plating, thickness 1
A tin metal layer made of tin plating having a thickness of 10 to 10 μm was formed, and a capacitor manufactured in the same manner as in Example 1 was evaluated for exterior airtightness. The results are also shown in (Table 1).

The lead frame 2 of this capacitor
The results of a solder wettability test for evaluating solderability of No. 2 and a graph thereof are shown in (Table 1) and FIG. 6B, respectively.

(Comparative Example) Only a copper metal layer made of copper plating having a thickness of 3 μm was formed on the surface of an iron base material constituting a lead frame 22 having a thickness of 0.1 mm, and the entire surface was roughened. A capacitor was fabricated in the same manner as in Example 1 by using the lead frame 22 that was subjected to the above process and a lead frame in which only a predetermined portion was partially roughened as in Examples 1 and 2. The results of the evaluation of the exterior airtightness and the solder wettability test for the product and the graphs thereof are shown in (Table 1) and FIGS. 6 (c) and 6 (d), respectively.

[0022]

[Table 1]

As can be seen from Table 1, good results are obtained in the outer airtightness by any of the methods. However, in the solderability, the results of the solder wettability test of the capacitors of Example 1 and Example 2 were obtained. It is very good, and all the conditions are wetted within 0.5 seconds, while in the case of the comparative example, it can be seen that the solder wettability is reduced. In particular, when the entire lead frame 22 is roughened, the wettability thereof is significantly reduced, and the lead frame may hardly be wet.

As a result of surface analysis of the surface of the lead frame 22 in which the solder wettability was reduced and a solder non-wetting portion was formed in the comparative example, the presence of an oxide layer of several thousand angstroms of copper was confirmed. In observation with an electron microscope, lead frame 2
In the case where the entire surface of No. 2 was roughened, it was confirmed that resin burrs at the time of molding remained on the roughened surface, and these oxides and resin burrs reduced solder wettability. it is conceivable that.

In Examples 1 and 2, the presence of the above-mentioned oxide layer and resin burrs was not recognized, so that the solder alloy layer and the tin metal layer had better adhesion to the resin than the copper metal layer. It is considered that the burrs could be sufficiently removed by deburring the resin by the sand blast method.

[0026]

As described above, according to the solid electrolytic capacitor of the present invention, the mold resin and the lead frame in the lead frame serving as the lead terminal connected to the valve metal portion and the conductor layer portion of the capacitor element come into contact with each other. Except for the portion, the surface has a solder alloy layer or a tin metal layer with a copper metal layer as a base, and the portion where the mold resin and the lead frame are in contact does not have the solder alloy layer or the tin metal layer, Since it has only a metal layer and the surface of only that part is roughened, when the lead frame is surface-mounted on a printed circuit board by soldering, the surface of the lead frame must have a low melting point solder alloy layer or tin metal layer. By having this, excellent solderability can be obtained, and the adhesion to the exterior resin is compared to other configurations by roughening the surface of the copper metal layer. It is much more excellent and can withstand the thermal shock of expansion and shrinkage during surface mounting and also has excellent airtightness of the exterior, so it is possible to obtain a reliable solid electrolytic capacitor You can do it.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an electrode body using an aluminum conversion foil as a base material used in Example 1 of the present invention.

FIG. 2 (a) is a plan view of the capacitor element of Example 1; FIG. 2 (b) is a sectional view taken along line BB ′ in FIG.

FIG. 3 is a cross-sectional view showing the shape of the lead frame used in Example 1.

4A is a partially enlarged view showing an outline of the lead frame shown in FIG. 3; FIG. 4B is a partially enlarged view showing a state where a capacitor element is mounted on the lead frame shown in FIG. 3A;

FIG. 5 is a schematic view showing a shape in which a capacitor element is resin-molded together with a lead frame in Example 1.

6A is a graph showing the solder wettability of Example 1 of the present invention. FIG. 6B is a graph showing the solder wettability of Example 2 of the present invention. (D) A graph showing the solder wettability when the lead frame is partially roughened in the comparative example.

FIG. 7A is a top view showing a conventional solid electrolytic capacitor. FIG. 7B is a side view of the solid electrolytic capacitor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Electrode body 16 Chemical conversion film 17 Conductive material layer 18 Conductive polymer layer 19 Graphite layer 20 Silver paint layer 21 Capacitor element 22 Lead frame

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-267917 (JP, A) JP-A 64-37006 (JP, A) JP-A-2-132927 (JP, U) (58) Survey Field (Int.Cl. ⁷ , DB name) H01G 9/15 H01G 9/004

Claims (3)

(57) [Claims] An anodic oxide film formed on a valve metal is used as a dielectric, and a predetermined portion of the dielectric is provided with a conductive polymer layer and a conductive polymer layer.
A capacitor element is formed by sequentially forming a conductor layer, a lead frame serving as a lead terminal is connected to the valve metal part and the conductor layer part of the capacitor element, and a part of the capacitor element and a part of the lead frame are molded. In a solid electrolytic capacitor packaged with resin, a solder alloy layer or a tin metal layer based on a copper metal layer is formed on the surface of the lead frame other than the portion in contact with the mold resin, and the lead frame portion is in contact with the mold resin. A solid electrolytic capacitor characterized by forming only a copper metal layer and roughening the surface of the copper metal layer. 2. The valve metal according to claim 1, wherein the shape of the valve metal is a plate or a foil.
The solid electrolytic capacitor as described. 3. The solid electrolytic capacitor according to claim 1, wherein the surface of the lead frame is roughened by a sand blast method.