JPH04333206A - Laminated ceramic capacitor - Google Patents

Abstract

PURPOSE:To prevent creeping discharge at low cost and to easily mount the title capacitor on a circuit substrate without generation of cracks in the internal part and also without requiring many man-hours. CONSTITUTION:A band 15, consisting of an organic insulator, is provided on the surface of the bare chip located between terminal electrodes of the laminated ceramic capacitor 10 on which a plurality of inner electrodes 14 are opposingly provided in the bare chip 11 and also a pair of terminal electrodes 12a and 12b, which are electrically connected to an internal electrode 14, are provided on both terminal parts 11a and 11b of the bare chip. Even when high AC voltage is applied to the capacitor 10, a current is hardly allowed to flow from the terminal electrode on one side to the other terminal electrode along the surface of the bare chip by the presence of the band 15.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-mounted multilayer ceramic capacitor for medium and high voltages. More specifically, the present invention relates to an outer surface structure for preventing creeping discharge of a multilayer ceramic capacitor.

0002

[Prior Art] Multilayer ceramic capacitors form a bare chip in which a plurality of internal electrodes face each other by alternately laminating internal electrodes and ceramic dielectrics, and the internal electrodes are extracted from the ends of this bare chip. It is made by covering the end of the bare chip, including the extracted portion, to form terminal electrodes for external connection. On the other hand, the technological development of multilayer ceramic capacitors has progressed in recent years, and multilayer ceramic capacitors are beginning to be used in fields where tantalum capacitors and electrolytic capacitors have traditionally been used. Examples include smoothing capacitors for switching power supplies. In such applications, capacitors are required to have large capacity and high voltage resistance, and voltage resistance characteristics under alternating current are important.

In particular, this type of multilayer ceramic capacitor is susceptible to a phenomenon called creeping discharge when a high voltage is applied in the air. This is a phenomenon in which corona discharge occurs between terminal electrodes and current flows along the bare chip surface. This phenomenon occurs particularly markedly with alternating current, and occurs at about 500 Vrms, and therefore becomes a big problem in power supply applications. When a voltage higher than the corona generation voltage is applied, the corona becomes larger and eventually violently discharges between a pair of terminal electrodes.
There was a risk of insulation failure or dielectric breakdown of the dielectric layer. Conventionally, in order to prevent this creeping discharge, after the capacitor has been mounted on a circuit board and soldered, insulation treatment has been performed, such as applying insulating oil to the capacitor surface or sealing the entire circuit with resin. Ta. Another method for preventing creeping discharge is to solder lead wires to the terminal electrodes at both ends of the capacitor, coat each lead wire with epoxy resin to form a radial lead product, and then solder it to the circuit board. Ta.

0004

[Problem to be Solved by the Invention] However, in the former method of preventing creeping discharge, it is necessary to apply oil or seal with resin to each mounted circuit board, which requires a large amount of man-hours. There was a problem in that the manufacturing cost was high. Further, in the latter method, when the epoxy resin coating the lead wires is cured, it shrinks and curing cracks are likely to occur inside the capacitor, and the manufacturing cost is also increased. An object of the present invention is to provide a multilayer ceramic capacitor that prevents creeping discharge at low cost without requiring a large number of man-hours, without causing internal cracks, and which can be easily mounted on a circuit board. be.

[0005]

[Means for Solving the Problems] The present inventors have discovered that creeping discharge can be prevented by providing an obstacle for corona discharge that occurs along the bare chip surface between terminal electrodes on the bare chip surface, and the present invention has been made based on the present invention. Reached. That is, in the present invention, as shown in FIG. 1, a plurality of internal electrodes 14 are provided inside a bare chip 11 facing each other, and a pair of internal electrodes 14 are electrically connected to both ends 11a and 11b of the bare chip. This is an improvement of a multilayer ceramic capacitor 10 provided with terminal electrodes 12a and 12b. Its characteristic structure lies in that a band 15 made of an organic insulator is wrapped around the surface of the bare chip 11 between the terminal electrodes 12a and 12b.

The present invention will be explained in detail below. As shown in FIGS. 1 and 2, the multilayer ceramic capacitor 10 is a surface-mounted chip capacitor. The capacitor 10 has a pair of terminal electrodes 12 at both ends 11a and 11b of the bare chip 11.
a, 12b. The bare chip 11 is formed by laminating a plurality of ceramic dielectric layers each having internal electrodes 14 printed on their surfaces so that the internal electrodes face each other. The internal electrodes 14 are located at both ends 11a, 11 of the bare chip.
b and is electrically connected to terminal electrodes 12a and 12b. The ceramic dielectric layer constituting the bare chip 11 is made of barium titanate, lead perovskite, or other dielectric, and the internal electrodes 14 are made of Pt, Ag/Pd.
The terminal electrodes are formed by printing a paste of noble metals such as Ni, Fe, Co, Cu, etc. or base metals such as Ni, Fe, Co, Cu, etc. on the surface of the dielectric layer. It is formed by applying a paste containing it to the end surface of a bare chip and baking it.

Bare chip 1 between terminal electrodes 12a and 12b
A band 15 made of an organic insulator is wrapped around the surface of the substrate 1 . The band 15 is preferably located on the central surface of the bare chip 11. There are no particular restrictions on the organic insulator as long as it is heat resistant, has good adhesion to the bare chip, and can be easily formed into a band by printing or coating.
Commercially available products can be used. Examples include adhesives such as cyanoacrylate, polyurethane, epoxy resin, phenol resin, and isocyanate, and solder resists made by mixing ester resin and phenol resin. Preferably, the width of band 15 is at least 10% of the length of capacitor 10. If the width of the band is narrower than this, the effect of preventing creeping discharge will be insufficient. After forming the terminal electrodes 12a and 12b on the bare chip 11, the band 15 is
It is formed by applying an organic insulator to the bare chip surface by printing or brushing and drying it.

[0008]

[Operation] Even if a high AC voltage is applied to the multilayer ceramic capacitor 10, since the band 15 made of an organic insulator is wrapped around the surface of the bare chip 11, the presence of this band 15 allows one terminal to be connected along the surface of the bare chip. It becomes difficult for current to flow from one electrode to the other terminal electrode.

[0009]

[Effects of the Invention] As described above, in the past, capacitors were coated with oil or sealed with resin for each circuit board mounted, or capacitors were formed into radial lead products, which required a large amount of man-hours. However, according to the present invention, creeping discharge can be prevented at low cost and with little effort by simply wrapping an organic insulating band around the surface of a bare chip. In particular, in the multilayer ceramic capacitor of the present invention, there is no risk of curing cracks occurring as in radial lead products.

0010

EXAMPLES Next, examples of the present invention will be explained together with comparative examples. <Example 1> As a multilayer ceramic capacitor, a multilayer ceramic chip capacitor (product number C70R2H222K) with a length of 4.5 mm, a width of 3.2 mm, and a thickness of 1.0 mm has the characteristics of a capacitance of 220 μF at a rated DC voltage of 500 V.
, manufactured by Mitsubishi Materials Co., Ltd.) was used. The above multilayer ceramic chip capacitor has internal electrodes of Ag/Pd (Ag70/Pd30) in a lead perovskite ceramic dielectric, and an A
It has a baked electrode layer of g paste. In this example, an odorless solder resist (product number: S-30, manufactured by Taiyo Ink Manufacturing Co., Ltd.) containing epoxy acrylate as a main component was used as the organic insulator. Apply this resist to the center of the surface of the bare chip and dry it at 150°C for 20 minutes to make a width of 1 mm.
A band of organic insulator with a thickness of 0.3 mm was wrapped around it.

<Example 2> The same multilayer ceramic capacitor as in Example 1 was used, and a heat-resistant masking adhesive tape (product number: No. 260, manufactured by Senju Metal Co., Ltd.) whose main component was silicone acrylic adhesive as an organic insulator was used. Co., Ltd.) was used. This adhesive tape was wrapped around the center of the surface of the bare chip and dried at 150°C for 90 minutes to a width of 2mm and a thickness of 0.5mm.
A 6 mm organic insulating band was wrapped around it. <Comparative Example 1> The same multilayer ceramic capacitor as in Example 1 was used, and a chloroprene rubber adhesive (product number: Quick-dry Bond G17, manufactured by Konishi Co., Ltd.) was used as the organic insulator. Apply this rubber adhesive to the center of the surface of the bare chip,
After drying at 50° C. for 20 minutes, a band of organic insulator with a width of 2 mm and a thickness of 0.8 mm was wrapped around it. <Comparative Example 2> The same ceramic capacitor as in Example 1 was used except that the organic insulating band was not formed.

<Test method> Examples 1 and 2 and comparative example 1,
Various characteristics of the ceramic capacitor No. 2 were measured using the following methods. The number n in parentheses is the number of samples tested. (a) Capacitance (nF) and dielectric loss tangent (%) (n=3
0) LCR meter (manufactured by Hewlett-Packard Company 42)
84 type) at 1 kHz and 1 Vrms. (b) Insulation resistance (Ω) (n=15) High resistance meter (Model 4329A manufactured by Hewlett-Packard)
After applying a DC voltage of 1000V for 5 seconds using
The resistance was measured after 25 seconds had elapsed. (c) Heat resistance of the strip (n=10) The sample was held with tweezers and immersed for 10 seconds in a solder bath where H63A eutectic solder melts at a temperature of 250°C. The heat resistance of the material was investigated. (d) DC dielectric breakdown test (n = 10) Cut off the DC voltage in air or silicone oil with a current of 10 mA.
The voltage was applied at a boost rate of 50 V/sec, and the voltage at which the sample started creeping discharge or breakdown was measured. The results of (a) to (c) above are shown in Table 1, and the results of (d) above are shown in Table 2.

[0013]

[Table 1]

[0014]

[Table 2]

<Test results and evaluation> From Table 1, Example 1,
2 and Comparative Examples 1 and 2 showed almost the same values in terms of capacitance and dielectric loss tangent. In Comparative Example 2, which did not have a band, creeping discharge occurred in the air, so its insulation resistance was measured in silicone oil. Since Examples 1 and 2 and Comparative Example 1 had bands, creeping discharge did not occur even in the air, and the insulation resistance value at that time was at the same level as the insulation resistance value of Comparative Example 2 in silicone oil. The band of Comparative Example 1 had poor heat resistance;
During the heat resistance test, six sample bands, or 60% of the total, melted. In contrast, not a single band was dissolved in the samples of Examples 1 and 2. In Table 2, breakdown mode A means dielectric breakdown, and breakdown mode B means creeping discharge. From Table 2, in Examples 1 and 2 and Comparative Example 1 having bands, it was possible to boost the voltage to the limit voltage at which the multilayer ceramic capacitor itself was destroyed. On the other hand, since Comparative Example 2 did not have a band, creeping discharge occurred at a voltage lower than the above-mentioned limit voltage. From the above, Examples 1 and 2 are Comparative Examples 1 and 2
It was found that this material has higher heat resistance than that of the conventional method, and also has extremely high creeping discharge prevention performance.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a multilayer ceramic capacitor of the present invention.

FIG. 2 is a perspective view thereof.

[Explanation of symbols]

10 Multilayer ceramic capacitor 11 Bare chip 11a, 11b End of bare chip 12a, 12b A pair of terminal electrodes 14 Internal electrode 15 Obi

Claims (2)

[Claims] 1. A plurality of internal electrodes (14) are provided inside a bare chip (11) facing each other, and the internal electrodes (14) are provided at both ends (11a, 11b) of the bare chip.
A pair of terminal electrodes (12a, 14) electrically connected to
A multilayer ceramic capacitor (10
), a band (15) made of an organic insulator is provided on the surface of the bare chip (11) between the terminal electrodes (12a, 12b).
A multilayer ceramic capacitor characterized by a circuit of . 2. A multilayer ceramic capacitor according to claim 1, wherein the band (15) has a width of at least 10% of the length of the capacitor (10).