JPH0752696B2 - Multilayer ceramic capacitor and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a multilayer ceramic capacitor having internal electrodes made of nickel.

(Prior Art) For manufacturing a multilayer ceramic capacitor, a method in which a capacitor element body was previously sintered, a conductive paste was applied, and the external electrode was formed by sintering again in a reducing atmosphere was used. Was taken.

However, if the insulator inside the capacitor is exposed to a high temperature reducing atmosphere twice as described above, the insulation resistance of the ceramic is lowered and the electrical characteristics of the capacitor are deteriorated. Moreover, there are many disadvantages such as a facility for creating a reducing atmosphere for firing the external electrodes, which increases the manufacturing cost of the multilayer ceramic capacitor.

Therefore, in the conventional technique, a technique of performing the ceramic sintering and the external electrode firing in one step without such a disadvantage has been adopted. The detailed procedure is as follows.

First, a conductive paste containing conductive particles such as nickel is printed on one main surface of a plurality of long unsintered derivative ceramic sheets to form a plurality of conductive layers for internal electrodes. Every other time, shift in the longitudinal direction and stack them, then crimp,
The conductive layers of the shifted sheet and the conductive layer of the non-shifted sheet are cut at positions where they are exposed on the cut surfaces, respectively, to form a large number of capacitor bodies. Then, a conductive paste made of nickel powder, ethyl cellulose and butyl carbitol is applied to both end faces where the conductive layer of the capacitor body is exposed and the peripheral edge portions continuing to the exposed end face to form a conductive layer to be an external electrode. After the formation, the internal nickel electrode, the ceramic and the external electrode are simultaneously sintered and fired in a reducing atmosphere at a temperature of 1150 to 1250 ° C.

According to the above-described manufacturing method, the monolithic ceramic capacitor can be manufactured by placing the ceramic in the reducing atmosphere at a high temperature only once, so that the insulation resistance of the ceramic does not decrease.

(Problems to be Solved by the Invention) However, as in the above-mentioned prior art, when an attempt is made to apply a conductive paste to the unsintered ceramic sheet laminate to sinter and fire the ceramic and the conductor at the same time, firing The volume of the ceramic sheet changes greatly before and after binding.
On the other hand, the volume of the external electrode also changes before and after firing, but the difference in volume change that occurs between the ceramic sheet and the external electrode is because the conductive paste was applied to the already sintered ceramic sheet to fire the external electrode. The one obtained by applying and firing the conductive paste on the unsintered ceramic sheet is larger than the one, and therefore the internal strain in the ceramic also becomes large. Therefore, the connection portion between the external electrode and the internal nickel electrode of the multilayer ceramic capacitor manufactured by the conventional technique,
In addition, a large distortion is generated in the ceramic portion at the peripheral edge of the external electrode formed at the peripheral edge portion of the capacitor body, and remains after the product is manufactured.

When a thermal shock is applied to a monolithic ceramic capacitor having such a large strain, cracks are likely to occur in the strained part of the ceramic. When thermal shock is applied, defective products with insulation resistance of 10 ³ MΩ or less occur.
There was a problem.

In addition, such a material causes a crack in the connection portion between the internal nickel electrode and the external electrode and peeling between the electrodes at the same time, which hinders the electrical connection, resulting in a large dielectric loss tangent and deterioration in the electrical characteristics. 5 to 8 of the total number are those that result in defective products and the value of the dielectric loss tangent varies.
There was a problem that about%.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a multilayer ceramic capacitor and a method for manufacturing the same that solves the above problems.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the first invention of the present application is such that conductive layers for internal electrodes containing nickel as a main component and ceramic layers are alternately laminated and sintered. The capacitor element body, and both end faces of the capacitor element body and the peripheral edge portion continuous with this,
In a multilayer ceramic capacitor having a conductive layer for external electrodes, which is formed by coating and firing a conductive paste composed of conductive powder and a binder, the conductive powder is 1 to 50% by weight.
Of silver and 50-99% by weight of zinc, the second
The invention is to laminate a plurality of unsintered ceramic sheets on which a conductive layer for internal electrodes having nickel as a main component is laminated and press-bonded to sinter the unsintered capacitor element body. In a method for producing a multilayer ceramic capacitor, in which a conductive paste composed of a conductive powder and a binder is applied to the surface and the peripheral edge portion continuous with the surface and then fired, the conductive powder is 1 to 50% by weight of silver and 50 to 99%. Of zinc, and the firing is performed in the atmosphere.

(Working) The conductive powder of the conductive paste for forming the external electrodes is
Since silver and zinc are contained in the ranges of 1 to 50% by weight and 50 to 99% by weight, respectively, it is not necessary to fire the external electrode in a reducing atmosphere, and the external electrode can be fired in the atmosphere. .

That is, since silver absorbs oxygen when heated and releases oxygen when cooled, when silver and zinc are made to coexist and heated in the atmosphere, silver absorbs oxygen during firing of the external electrode and oxygen It shuts off the supply, prevents zinc from becoming zinc oxide in the insulator, and releases oxygen when cooled to improve the electrical conductivity between the external electrode and the internal nickel electrode.

Therefore, even if the conductive paste is not applied during the sintering of the ceramic and the external electrode is baked by applying the conductive paste after the ceramic is sintered, it is possible to perform the baking in the atmosphere, which is a special case. No equipment needed.

Further, since the volume change of the ceramic is small, the difference in volume change between the external electrode and the ceramic is also small, so that the strain remaining between the two is small, and even if a thermal shock is applied, the difference between the external electrode and the internal nickel electrode is small. The connection will not break.
Further, unlike the conventional capacitor, distortion does not occur in the ceramic at the peripheral edge of the external electrode, and after the capacitor according to the present invention is soldered to the printed board, thermal shock is applied to the board. Since the ceramic does not crack, the insulation resistance does not fall below 10 ³ MΩ.

Further, since nickel of the internal electrode and zinc of the external electrode surely form a solid solution, and zinc and silver surely form a solid solution to form a nickel-zinc solid solution and a silver-zinc solid solution, respectively. Are securely connected by the solid solution.

It should be noted that the case where the amount of silver in the conductive powder of the conductive paste is less than 1% by weight (the amount of zinc exceeds 99% by weight) is excluded because the amount of silver is below that value during firing. This is because the adsorption of oxygen by silver becomes insufficient, which hinders the connection between the internal electrode and the external electrode, and the insulation resistance after thermal shock deteriorates.

In addition, the silver content exceeding 50% by weight (zinc content less than 50% by weight) was excluded except that when the amount of zinc was small, the nickel-zinc solid solution was not sufficiently formed and This is because some of the internal electrodes are not electrically connected to the external electrodes, and as a result, the capacitance of the multilayer ceramic capacitor decreases and the dielectric loss tangent increases.

(Embodiment) An embodiment of the present invention will be described below with reference to the drawings.

Example 1 75 g of zinc powder (purity 99.9%, average particle size 2.5 μm), 25 g of silver powder (purity 99.9%, average particle size 1.5 μm), 20 g of ethyl cellulose, 150 g of butyl carbitol, and PbO-B ₂ O ₃ −
After mixing 2 g of SiO-based glass powder with a crusher for 24 hours, the mixture was kneaded with a three-roll mill for 3 hours to prepare an external electrode paste.

Separately from this, there are formed 50 μm ceramic layers with a thickness of 17 μm, and external electrodes having a length of 3.1 mm, a width of 1.5 mm, and a height of 0.9 mm in which internal electrodes made of nickel conductors are interposed between the ceramic layers are not formed. A capacitor body was prepared. The capacitor body was manufactured under the same conditions and methods as those of the conventional one described above.

The external electrode paste is applied to both end surfaces of the capacitor element body and the peripheral edge portions continuous with the same, dried at 125 ° C. for 10 minutes, and subsequently sintered in air at 700 ° C. for 10 minutes to form a laminated ceramic capacitor. Obtained.

The external electrodes were plated with nickel.

After soldering a plurality of the capacitors to copper electrodes on a glass epoxy wiring board, a commercially available LCR meter (YHP 4274A)
And the capacitance and dielectric loss tangent (tan δ) of the capacitor are 100
It measured about the piece.

Then, the insulation resistance value (at 50 V) of the capacitor was measured for 100 pieces with an insulation resistance measuring device (Toa Denpa SW-9E). The measured insulation resistance values were all 10 ³ MΩ or more. After that, place the wiring board with the capacitor on -55
Leave in a constant temperature bath maintained at a temperature of ℃, after 30 minutes,
Immediately move to a constant temperature bath maintained at a temperature of 125 ° C, and
After leaving for 1 minute as one cycle, this was subjected to a 100-cycle thermal shock test, and then the capacitance, the dielectric loss tangent, and the insulation resistance were measured again by the above measuring instrument. None of them changed at all. The measurement results are shown in Table 1.
Examples 2-6 In Example 2, 65 g of zinc powder and 35 g of silver powder were used.
Is 85 g of zinc powder and 15 g of silver powder.
50 g, silver powder 50 g, Example 5 was zinc 92 g, silver 8 g,
In Example 6, 99 g of zinc powder and 1 g of silver powder were used. In all other examples, the same method and conditions as in Example 1 were used. The measurement results are shown in Table 1.

Comparative Examples 1 and 2 In Comparative Example 1, 100 g of zinc powder and zero silver powder were used, and Comparative Example 2
Was carried out in the same manner as in Example 1 except that 40 g of zinc and 60 g of silver were used. The measurement results are shown in Table 1.

A product having an insulation resistance value of 10 ³ MΩ or less was regarded as a defective product.

Comparative Example 3 Comparative Example 3 was manufactured by the above-described conventional method under the same conditions as the capacitor element body of Example 1. The measurement results are shown in Table 1.

(Effects of the Invention) As described above, according to the present invention, since firing can be performed in the atmosphere, an inexpensive multilayer ceramic capacitor can be obtained without requiring special equipment for creating a reducing atmosphere. You can

In addition, when the ceramic is sintered, the conductive paste is not applied, but the conductive paste is applied after the ceramic is sintered to fire the external electrodes. No distortion of the ceramic occurs at the peripheral edge of the ceramic, and even if the multilayer ceramic capacitor manufactured by the method of the present invention is soldered to a printed circuit board and then subjected to thermal shock, the ceramic does not crack. In addition, the electrical connection between the external electrode and the internal nickel electrode does not occur.

Claims (2)

[Claims] 1. A capacitor element body in which conductive layers for internal electrodes containing nickel as a main component and ceramic layers are alternately laminated and sintered, and both end faces of the capacitor element body and peripheral edge portions continuous with the both end surfaces. In a multilayer ceramic capacitor provided with a conductive layer for external electrodes, which is formed by applying and firing a conductive paste composed of a conductive powder and a binder, the conductive powder is 1 to 50% by weight of silver and 50 to 99% by weight. A multilayer ceramic capacitor characterized by containing zinc. 2. A plurality of unsintered ceramic sheets having a conductive layer for internal electrodes, which is mainly composed of nickel, is laminated,
A multilayer ceramic capacitor in which a non-sintered capacitor element body obtained by pressure bonding is sintered, and then a conductive paste made of a conductive powder and a binder is applied to both end faces of the element body and peripheral edge portions continuous with the element body and then fired. 2. The method for producing a multilayer ceramic capacitor according to claim 1, wherein the conductive powder contains 1 to 50% by weight of silver and 50 to 99% of zinc, and the firing is performed in the atmosphere.