JPH04236412A - Electronic component of ceramic - Google Patents

Abstract

PURPOSE:To prevent the generation of cracks in an element occurring by temperature change at the time of soldering for board mounting, by constituting the outer electrode of an electronic ceramic component like a ceramic capacitor as a double-layered structure, and making the voids on the ceramic element main body side large as compared with the surface side. CONSTITUTION:A main body 1 is constituted by alternately laminating 20 layers of ceramic dielectric layers 2 and inner electrodes 3, and the end parts of the inner electrodes 3 are alternately exposed on facing side surfaces. Each side surface where the end parts are exposed, and the upper, the lower, the front and the rear surface parts in the vicinity of the side surfaces are coated with outer electrodes 9a, 9b whose voids are large. The outside thereof is coated with second outer electrodes 10a, 10b whose voids are small. By this packaging, a part of solder is wet and fixed on the surfaces of the second outer electrodes, and the solder is prevented from permeating into the first outer electrodes. As the result, the generation of cracks in the capacitor main body can be prevented, under rapid thermal change like a temperature cycle test.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to ceramic electronic components suitable for surface mounting, such as multilayer ceramic capacitors.

0002

2. Description of the Related Art A conventional multilayer ceramic capacitor having a structure shown in FIG. 2(A) is known. That is, 1 in the figure is an element body of a multilayer ceramic capacitor having a square chip shape, and this body 1 has ceramic dielectric layers 2 and internal electrode layers 3 alternately laminated, and the end portions of the internal electrodes 3. The structure is such that the panels are exposed alternately on opposite sides. External electrodes 4a and 4b cover each side surface of the main body 1 where the ends of the internal electrodes 3 are exposed, as well as the front and rear surfaces of the upper and lower surfaces near the side surfaces. These external electrodes 4a and 4b are formed by, for example, applying the main body 1 to an Ag-based or Ag/Pd-based conductive material paste containing 2 to 5 wt% of glass frit to improve adhesion to the ceramic dielectric layer 2. It is formed by dipping and baking the side surfaces and upper and lower surface portions in the vicinity thereof.

This multilayer ceramic capacitor is mounted on a circuit board by soldering, as shown in FIG. 2(B). That is, after temporarily fixing the capacitor having the above structure to the conductor layer 7 formed on the surface of the insulating base material 6 of the circuit board 5 so that the corner portion of the lower surface of the main body 1 is in contact with the conductor layer, the capacitor is then fixed by a flow or reflow method. Mounting is performed by joining the conductor layer 7 and external electrodes 4a, 4b located on the side surfaces of the main body 1 with a solder layer 8. In this case, the thickness of the external electrode is usually about 100 to 200 μm. In recent years, demand for large-capacity multilayer ceramic capacitors has increased, and for this reason, ceramic dielectrics with high dielectric constants mainly composed of lead perovskite compounds have come to be used. Therefore, its shape has also become larger, 5.6
Large multilayer ceramic capacitors such as 5.0 mm x 7.5 x 6.3 mm are also beginning to be manufactured using lead-based dielectric materials.

However, when such a mounted multilayer ceramic capacitor is subjected to sudden thermal changes such as a temperature cycle test or a thermal shock test, the ceramic dielectric layer, solder, conductor layer, and insulating base material each break down. There was a problem in that cracks occurred in the capacitor body 1 due to the difference in thermal expansion coefficients. This cracking is more likely to occur as the size of the multilayer ceramic capacitor body becomes larger, especially for 5.6 x 5.
There is a problem in that reliability decreases when a large chip multilayer ceramic capacitor with dimensions of 0 x 1.8 mm or more is mounted.

[0005]

[Problems to be Solved by the Invention] The present invention has been made to solve the above-mentioned problems. The aim is to provide a ceramic electronic component that is free from cracking even when exposed to heat. [Structure of the invention]

[0006]

Means for Solving the Invention and Effects of the Invention The present invention provides an external electrode applied to a ceramic element body, which is a ceramic element characterized in that an area close to the element body has a higher porosity than a surface area. It is an electronic component. Specifically, chip components such as ceramic capacitors can be mentioned.

[0007] Such ceramic electronic components are, for example,
In the step of applying and baking an electrode paste to form an external electrode, a first electrode paste consisting of 40 to 50 wt% conductive powder, 2 to 5 wt% inorganic binder, 20 to 30 wt% resin binder, and the remainder organic solvent is applied. After drying, conductive powder 40-50wt%, inorganic binder 0wt
%, a resin binder of 10 to 15 wt%, and the remainder of an organic solvent.A second electrode paste is applied and dried, and then the first electrode paste and the second electrode paste are baked at a high temperature to form an external electrode. can be manufactured.

In the present invention, the porosity ratio of the external electrodes can be easily compared by visual inspection, for example. Further, quantitatively, it can be defined by the area ratio of the pores in the cross section of the formed external electrode to the total cross section. Such a method is the same as the method described on page 60 of the EIA standard RS-198C as a map for pinhole or void analysis. Furthermore, the porosity ratio can be changed and controlled by controlling the content of the resin binder in the first and second external electrode pastes.

A multilayer ceramic capacitor as an example of the electronic component of the present invention has a structure as shown in FIG. 1(A). That is, 1 in the figure is a multilayer ceramic capacitor main body in the shape of a square chip, and this main body 1 has ceramic dielectric layers 2 and internal electrodes 3 stacked alternately, and the ends of the internal electrodes 3 face each other. It has a structure in which the sides are exposed alternately. The first external electrodes 9a, 9b are formed on each side surface of the main body 1 where the ends of the internal electrodes 3 are exposed, and on the upper, lower, front and rear surfaces in the vicinity of the side surfaces. Further, the second external electrodes 10a, 10b are similar to the first external electrodes 9a, 9.
formed on b.

FIG. 3 shows the first and second external electrodes 9b.
and 10b are shown enlarged cross-sectional views. A first external electrode 12 is formed on the ceramic body 11 in the figure, a second external electrode 13 is formed thereon, and a solder layer 14 is further formed upon mounting. If the first external electrode has a higher porosity than the second external electrode, that is, it is porous, the strain due to the difference in thermal expansion that occurs during rapid temperature changes such as temperature cycle tests after being mounted on a circuit board etc. The first external electrode serves as a buffer member and has a softening effect. Although the thickness of the first external electrode varies depending on the shape and dimensions of the multilayer ceramic capacitor, the above-mentioned effects can be achieved if the thickness is at least 30 μm or more, preferably about 100 to 150 μm. On the other hand, the second external electrode needs to prevent solder from seeping in when mounting the circuit board.
It is necessary that the porosity be low. In addition, the thickness of the second external electrode is set to the necessary thickness, usually 3.5 mm, in order to prevent this solder from seeping in and to improve wettability during soldering.
It is necessary to have a thickness of 0 μm or more, but if it is too thick, the above-mentioned first problem will occur.
The thickness is preferably 100 μm or less because it hinders the buffering effect of the external electrode.

[0011] In the present invention, the case where the external electrode has two layers has been described as an example, but even in the case of three or more layers, the ceramic side of the external electrode has a high porosity and the surface side has a low porosity. It is sufficient if the following conditions are met. According to the present invention, it is possible to significantly enhance the effect of preventing cracks from occurring due to sudden thermal changes such as during a temperature cycle test after a large element is mounted on a circuit board.

0012

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1A is a sectional view of the multilayer ceramic capacitor of this example. 1 in the figure is, for example, the dimension 7
．． This is a multilayer ceramic capacitor body having a square chip shape of 5 x 6.3 x 2.0 mm, and this body 1 has 20 layers of ceramic dielectric layers 2 and internal electrodes stacked alternately.
Moreover, the structure is such that the ends of the internal electrodes 3 are exposed alternately on the opposing side surfaces. First external electrodes 9a, 9b having a high porosity are provided over each side surface of the main body 1 where the end portions of the internal electrodes 3 are exposed and the front and rear surfaces of the upper and lower surfaces near the side surfaces.
are each coated. These first external electrodes are made of, for example, 45 wt% Ag powder, 4 wt% glass frit,
After applying and drying a first electrode paste consisting of 25 wt% ethyl cellulose and the remainder 2-butyl carbitol,
It is formed by baking at around 700°C. Alternatively, baking may be performed simultaneously after applying and drying a second electrode paste to be described later.

Further, the outer sides of the external electrodes 9a and 9b are coated with second external electrodes 10a and 10b having a small porosity, respectively. These second external electrodes are made of, for example, 45 wt% Ag powder and 10 wt% ethyl cellulose.
, the remainder of butyl carbitol, and does not contain glass frit, is applied onto the first external electrode, dried, and then baked at around 700°C. In order to mount a multilayer ceramic capacitor having such a configuration on a circuit board, as shown in FIG. After temporarily fixing the corner portion of the lower surface of the main body 1 so that it is in contact with the conductor layer 7, the conductor layer 7 and the second external electrodes 10a and 10b located on the side surface of the main body 1 are soldered using a flow method or a reflow method. This is done by joining by 8.

By carrying out such mounting, the solder is partially wetted and fixed on the surface of the second external electrode, and the solder is prevented from seeping into the first external electrode.
As a result, even when subjected to sudden thermal changes such as during a temperature cycle test, the first external electrode effectively functions as a buffer layer, which prevents the capacitor body from cracking due to differences in the coefficient of thermal expansion of each member. A highly reliable multilayer ceramic capacitor can be obtained.

(Pb0.875 Ba0.125) (
Zn1/3 Nb2/3 )0.3 (Mg1/3 N
b2/3) A multilayer ceramic capacitor with a ceramic dielectric composition of 0.5 Ti0.2 O3 and dimensions of 7.5 x 6.3 x 2.0 mm was fabricated as described above, and the capacitor shown in Fig. 1(B) was prepared. Twenty samples mounted on circuit boards as described above were prepared, and a thermal cycle test was conducted at 125°C for 30 minutes and at -55°C for 30 minutes, and the number of failures over 50 cycles was measured. Note that a capacitor whose capacity decreased by more than 10% from the initial value was determined to be a failure. As a result, as many as 15 failures due to cracks were observed in the conventional samples, but in this example, all 20 were in good condition, with no failures occurring.

[0017]

Effects of the Invention As described in detail above, according to the present invention, a highly reliable product that prevents cracking even under sudden thermal changes such as temperature cycle tests after being mounted on a circuit board, etc. We can provide ceramic electronic components. It is also made of a perovskite compound containing lead, and has a shape of 5.6 x 5.0 x 1.8
It is particularly effective for multilayer ceramic capacitors with a diameter of mm or more.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the ceramic electronic component of the present invention.

[Fig. 2] Cross-sectional view of a conventional ceramic electronic component.

FIG. 3 is an enlarged cross-sectional view of the ceramic electronic component of the present invention.

Claims (1)

[Claims] 1. A ceramic electronic component characterized in that an external electrode applied to a ceramic element body has a higher porosity in a region closer to the element body than in a surface region.