JPH0447448B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a multilayer capacitor element and a method for manufacturing the same, and particularly relates to a multilayer capacitor element with high bonding strength between an external electrode and the element and good solderability. BACKGROUND ART In recent years, multilayer ceramic capacitors have been rapidly becoming popular due to the demand for smaller ceramic capacitor elements and larger capacitance. Furthermore, as circuits become more frequent, it is becoming necessary to use multilayer ceramic capacitor elements in areas where electrolytic capacitors were conventionally used. Multilayer ceramic capacitors are usually manufactured by a process in which internal electrodes and ceramic are fired together. Barium titanate-based materials have traditionally been used for high-permittivity ceramic capacitor materials, but because the firing temperature is as high as 1300°C, expensive metals such as Pt and Pd are used as internal electrode materials. The need arose. In response, the inventors have proposed a lead composite perovskite material that can be fired in a low oxygen partial pressure atmosphere and has high resistivity, and a multilayer capacitor element using this dielectric and using copper as an electrode. Generally, in a multilayer capacitor element, the outer electrode contains glass frit in order to increase the adhesive strength between the outer electrode and the element. However, if the external electrode containing glass frit is fired together with the element, the glass frit and the element will react and the dielectric properties will be impaired, so the external electrode is formed after the element is fired, and the external electrode is baked at a temperature lower than the firing temperature of the element. This required multiple steps, which led to complicated manufacturing methods and increased costs. On the other hand, a multilayer capacitor element in which the outer electrode contains powder of the same quality as the dielectric layer and the outer electrode and the element can be integrally fired, and a method for manufacturing the same have been disclosed (Japanese Patent Application Laid-Open No. 107818/1983). Problems to be Solved by the Invention In a multilayer capacitor element that uses a lead composite perovskite dielectric and uses copper or a copper-based alloy for the internal and external electrodes, the external electrode contains lead that is the same or similar to the dielectric. When a composite perovskite-based inorganic oxide is contained, the adhesive strength of the external electrode to the element increases, but there is a problem in that the solderability to the external electrode decreases. SUMMARY OF THE INVENTION In view of these problems, it is an object of the present invention to provide a multilayer capacitor element having external electrodes with high adhesive strength to the element and good solderability, and a method for manufacturing the same. Means to Solve the Problems In a multilayer capacitor element in which a dielectric layer is made of ceramic mainly composed of a composite perovskite oxide containing lead, and copper or a copper-based alloy is used for the internal and external electrodes. , at least a portion of the external electrode layer contains the following composition, i.e.
Group A consisting of Pb, Ca, Sr and Ba and Mg, Ni,
The element surface contains an inorganic oxide containing a component selected from Group B consisting of Ti, Zn, Nb, and W, and further includes an external electrode layer containing the above-mentioned inorganic oxide at 5% by volume or more and 50% by volume or less. The structure consists of at least two layers: a contacting layer and an externally exposed surface layer containing the above-mentioned inorganic oxide at 5% by volume or less. In addition, in the manufacturing method, metal copper or a copper compound and inorganic oxide are applied to both end surfaces of an unfired multilayer capacitor element where internal electrodes are exposed so that the volume percent of the above-mentioned inorganic oxide is 5% or more and 50% or less after firing. A step of applying and drying a first electrode paste containing a mixture of the above-mentioned metal copper or a copper compound and an inorganic oxide so that the volume percent of the above-mentioned inorganic oxide is 5% or less after firing. The method includes a step of applying and drying a first electrode paste, then applying and drying the paste, and a step of simultaneously firing the unfired multilayer capacitor element and the external electrode formed as described above. Effect In the multilayer capacitor element of the present invention, a large adhesive strength between the external electrode layer and the element can be obtained due to the presence of the layer in contact with the element surface containing 5% by volume or more and 50% by volume or less of inorganic oxide, and the inorganic oxide Good solderability can be obtained by an externally exposed surface layer having a content of 5% by volume or less. Furthermore, as mentioned above, by taking the step of simultaneously firing the unfired multilayer capacitor element and the external electrode, it is possible to obtain a multilayer capacitor element in which the adhesive strength between the external electrode and the element is high, and the adhesive strength between the layers inside the external electrode is high. . Embodiment FIG. 1 is a cross-sectional view of the external electrode portion of the multilayer capacitor element of the present invention, in which 11 is a dielectric layer;
2 is an internal electrode layer made of copper or an alloy containing copper as a main component; 13 is an external electrode layer in contact with the element surface;
4 is an external electrode layer exposed to the outside. The reason why the content of the inorganic oxide is limited in the present invention is as follows. In other words, if the content of inorganic oxide in the external electrode layer in contact with the element surface exceeds 50% by volume, the electrical connection between the internal and external electrodes will deteriorate and the electrical resistance of the external electrode layer will also increase, resulting in a decrease in capacitance. and a decrease in dielectric loss occurs.
If it is less than 5% by volume, the adhesive strength between the element and the external electrode will decrease. Furthermore, if the content of inorganic oxide in the surface layer of the external electrode exposed to the outside exceeds 5% by volume, the adhesive strength between the external electrode and the solder decreases. These problems are solved within the content range of the invention. Next, by making the external electrode layer have a two-layer structure, we can eliminate the phenomenon that when the element is immersed in a solder bath, the external electrode dissolves and diffuses into the solder bath and the external electrode layer disappears. Disappearance of the external electrode due to the eating phenomenon is prevented, and the adhesive strength between the solder, the external electrode, and the element becomes strong. Further, according to the method for manufacturing a multilayer capacitor element of the invention, a first external electrode paste is applied to an unfired multilayer capacitor element and dried, and then a second external electrode paste is applied thereon and dried, and these are integrally fired. As a result, the adhesion between the external electrode and the element and the two layers inside the external electrode becomes stronger compared to when these are constructed and fired one after another. In addition, in this case, the binder and solvent contained in the first external electrode paste and the second external electrode paste must be the same, and the solvent must be compatible with the binder of the unfired dielectric layer. When the external electrode paste is applied, the surface of the dielectric layer is formed between the first external electrode paste and the dried surface of the first external electrode paste, which partially dissolves into the second external electrode paste after firing. The adhesion becomes stronger. Examples will be described in detail below. A material represented by the following compositional formula was used as the dielectric. (Pb _1.00 Ca _0.025 ) (Mg _1/3 Nb _2/3 ) _0.70 Ti _0.25 (Ni _1/2
W _1/2 ) _0.05 O _3.025 dielectric powder was manufactured according to a conventional ceramic manufacturing method. The calcination conditions were 800°C for 2 hours. The pulverized calcined powder was mixed in a ball mill with 5wt% polyvinyl butyral resin and 50wt% solvent based on the calcined powder, and then milled using a doctor blade to a thickness of 35 μm.
It was made into a sheet. Internal electrode is 20wt% Cu ₂ O
These powders were blended into the composition ratio including the dielectric described above, and then kneaded with 0.5wt% ethyl cellulose and 25wt% solvent using a triple roll to form an electrode paste, and an internal electrode pattern was printed on the sheet using a screen printing method. . This was laminated so that the electrodes were drawn out alternately on the left and right sides, and then cut. The external electrode is made by mixing Cu ₂ O powder and inorganic oxide powder so that the volume fraction after firing becomes a predetermined ratio.
1.0 wt% ethyl cellulose, 25 wt% ethyl carbitol, and 10 wt% butyl acetate were added and kneaded using a triple roll to form an external electrode paste. The end faces from which the electrodes were alternately drawn out were first immersed in a first electrode paste in which the volume percent of the metal oxide after firing was 5% or more and 50% or less, then pulled up and dried. Next, the end face coated with the first electrode paste was immersed again in a second electrode paste in which the volume percent of metal oxide after firing was 5% or less, and then the end face was pulled up and dried. The laminate created in this way is placed on a porcelain boat with coarse-grained zirconia laid out on top of it and placed in the air.
The binder was burnt out at 450°C. As shown in Fig. 2, a porcelain boat 22 carrying a burnt-out laminate 21 is placed inside a reactor core tube 23 with an inner diameter of 50 mm, and nitrogen gas bubbled with 3wt% ammonia water 24 at 20°C is heated every minute. 1 liter was poured into the solution and held at 500° C. for 8 hours to reduce Cu ₂ O in the internal and external electrodes to form metallic copper. FIG. 3 shows a cross section of a magnesia porcelain container in which a laminate is placed during firing, and FIG. 4 shows a cross section of a firing furnace core tube. Inside the magnesia porcelain container 31, the above-mentioned calcined powder 32 was spread about 1/3 of its volume, and about 1 mm of 200 mesh ZrO ₂ powder 33 was spread, and on top of that was placed the laminate 35 that had undergone burnout and electrode reduction. .
Cover the magnesia porcelain lid 34, insert it into the furnace core tube 36 of the tubular electric furnace, and after degassing the inside of the furnace core tube with a rotary pump, replace it with a N ₂ - H ₂ mixed gas, and add N ₂ to a predetermined oxygen partial pressure. A mixed gas was flowed while adjusting the mixing ratio of H 2 gas and H ₂ gas, and the temperature was raised to 980°C at a rate of 400°C/hr, held for 2 hours, and then lowered at a rate of 400°C/hr. Po ₂ in the reactor core tube was determined by the following equation from the voltage E (V) between the electrodes drawn from the platinum electrodes configured on the atmospheric side of the inserted stabilized zirconia oxygen sensor 37 and on the inner side of the reactor. Po ₂ = 0.2・exp (4FE/RT) where F is Faraday constant 96489 clone, R
is the gas constant 8.3144J/deg・mol, and T is the absolute temperature. The outer dimensions of the multilayer capacitor element are 2.8x1.4x0.9mm, and the effective electrode area is 1.3125mm ² (1.75x0.75mm) per layer.
mm), the thickness of the electrode layer is 2.0 μm, the dielectric layer is 25.0 μm per layer, there are 30 effective layers, and 2 invalid layers above and below.
Layer by layer. The thickness of the external electrode at the center of the element end face is 80 μm, and a boundary between the two layers exists around the thickness of 40 μm. Furthermore, the length of the external electrode overlapping the side surface of the element is 0.4 mm. The capacitance and tanδ of the multilayer capacitor element were measured at a frequency of 1kHz by applying an AC voltage of 1V. Further, the resistivity was determined from the value 1 minute after applying a voltage of 50V. In addition, the multilayer capacitor element 51 after firing is sandwiched between Ni plating wires 52 (diameter 0.45 mm) shown in FIG.
After immersing it in a solder bath at 260°C, it was pulled out, the Ni-plated wire 52 was cut at points A and B in Fig. 5, and it was pulled from side to side to determine the adhesive strength of the external electrode to the element, and the solder 53 of the external electrode. The adhesion strength and failure status were observed. Table 1 shows the composition, capacity, and composition of the surface layer of the layer in contact with the element surface of the external electrode in the scope of the present invention and comparative examples.
The tanδ, resistivity, adhesion strength of the external electrode, and failure status are shown. Sample No. 14 of Comparative Example is an example in which the dielectric binder is not compatible with the solvent of the external electrode, and Sample No. 15 is an example in which the dielectric binder is not compatible with the solvent of the external electrode. This is an example in which an external electrode is applied and baked after reduction and baking. Table 2 shows details of the composition of the external electrode layer shown in Table 1.

【table】

[Table] Effects of the Invention The multilayer capacitor element and the manufacturing method thereof of the present invention have high adhesion strength of the external electrode to the element, excellent solderability to the external electrode, and eliminates the phenomenon of loss of the external electrode due to solder erosion. The present invention provides an excellent multilayer capacitor element.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a multilayer capacitor element according to the present invention, FIG. 2 is a sectional view of a firing furnace during electrode reduction treatment,
Figure 3 is a cross-sectional view of the magnesia container during firing, Figure 4
The figure is a sectional view of the firing furnace core tube, and FIG. 5 is a plan view showing the element and Ni plating line when measuring the adhesive strength of the external electrode. 11... Dielectric layer, 12... Internal electrode layer, 1
3, 14...external electrode layer.

Claims (1)

[Scope of Claims] 1. A multilayer capacitor element in which a ceramic mainly composed of a composite perovskite oxide containing lead is used for the dielectric layer, and copper or an alloy mainly composed of copper is used for the internal and external electrodes, At least a portion of the external electrode layer contains the following composition, i.e.
It contains an inorganic oxide containing both a component selected from Group A consisting of Pb, Ca, Sr and Ba and a component selected from Group B consisting of Mg, Ni, Ti, Zn, Nb and W, and The electrode layer has a content of 5% by volume or more50
A multilayer capacitor element comprising at least two layers: a layer in contact with the element surface containing the above-mentioned inorganic oxide in an amount of 5% by volume or less, and an externally exposed surface layer containing the above-mentioned inorganic oxide in an amount of 5% by volume or less. . 2 A component selected from Group A consisting of Pb, Ca, Sr, and Ba and Mg, Ni, Ti, Zn, and Nb are applied to both end surfaces of the unfired multilayer capacitor element where the internal electrodes are exposed.
and metallic copper or a copper compound, the inorganic oxide containing both components selected from group B consisting of
a step of applying and drying a first electrode paste blended to have a concentration of 50% or less; and a step of mixing the metal copper or copper compound and the inorganic oxide so that the volume percent of the inorganic oxide after firing is 5% or less. Applying the blended second electrode paste to the first electrode paste,
A method for manufacturing a multilayer capacitor element, comprising the steps of drying, coating, and drying, and simultaneously firing the unfired multilayer capacitor element and the external electrode formed as described above. 3. The binder and solvent contained in the first electrode paste and the second electrode paste are the same, and the solvent is compatible with the binder of the unfired dielectric ceramic layer. A method for manufacturing a multilayer capacitor element according to claim 2.