JPH1145809A - Laminated inductance element and manufacture therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated inductance element, in which ceramic sheets having damping action are interposed between an upper and a lower through- hole connection part to eliminate cracks produced when laminated and pressed, and a manufacturing method therefor. SOLUTION: A mixture of a PVA water solution and ferrite raw material power are stirred by a ball mill to manufacture two kinds of ferrite green sheets A, B by a doctor blade method. A PVA having a polymerization degree of 800 is used for the sheet A, and a PVA having a polymerization degree of 1000 is used for the sheet B. A through-hole 2 is made in the manufactured sheet and a coil pattern 3 is printed on the sheet as an inner electrode to make a laminated inductance. The laminated inductance has double spiral structure, and the sheet B is used as one of a double printed inner electrode (cushioning sheet 1a), and the remaining part including a dummy layer is made of the sheet A (ordinary sheet 1).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a multilayer inductance element and a method for manufacturing the same.

[0002]

2. Description of the Related Art Multilayer chip inductors are required to be smaller and have higher performance, and the thickness of a ceramic layer constituting the multilayer chip inductor is as thin as approximately the thickness of a conductor layer formed on the ceramic layer. It has become to. In addition, there is a demand for an improvement in the allowable current value of the current flowing through the coil and an improvement in the Q value. As a countermeasure, means for forming a double coil conductor to reduce the DC resistance of the coil conductor and also improve the Q value Has been proposed. For example, Japanese Utility Model Application Hei 5-57817
As shown in FIG. 2, as shown in FIG. 2, a through-hole 2 is provided at a necessary portion of a ferrite sheet piece 1, and a coil pattern 3 is printed with a conductive paste to form a sheet 2 on which the same coil pattern is formed. By laminating and laminating one by one, a part of the coil conductor is branched into two lines, so-called double coil conductors are formed, and connection with through-hole conductors is repeated to form one coil.
As another example, there has been proposed an example in which two sheets on which the same coil pattern is formed are stacked and laminated, and connected by coil conductor terminals, thereby improving the allowable current value and the Q value. It is going to be.

[0003]

However, when a large number of conventional inductors having a double coil conductor are manufactured,
There is a problem that the yield and the reliability are reduced due to the inclusion of a component having a low inductance value or a component having a crack. The inventors investigated the cause, and found that the through-hole connection portion broke the ceramic layers located above and below it during lamination and crimping, and when the ceramic layer was broken, the adjacent coil conductors came into contact. Conduction, apparently the number of turns of the coil is reduced, so that the inductance value is drastically reduced as is called so-called turn omission, even if it does not break until conduction, cracks occur near it, withstand voltage, It has been found that the reliability of moisture resistance is reduced. The object of the present invention is to laminate and stack a ceramic green sheet having a buffering action above and below a through-hole connection part.
It is an object of the present invention to provide a multilayer inductance element and a method for manufacturing the same, which solve the above-mentioned problems that occur during crimping.

[0004]

To solve the above-mentioned problems, the present inventor has conducted trial and error. As a result, by making the ceramic layer in contact with the through-hole conductor terminal more porous, a high-yield and highly reliable laminated ceramic is obtained. The present inventors have found a method of manufacturing an inductor, and have been able to provide a multilayer ceramic inductor of the present invention and a method of manufacturing the same. That is,
The first aspect of the present invention is that the coil conductor provided in the laminate is connected to the through-hole conductor to be partially branched into a plurality of portions, and the branched coil conductor terminals are connected again to the through-hole conductor to join. In a multilayer ceramic inductor in which one coil is repeatedly formed as a whole,
A ceramic layer (hereinafter referred to as a buffer sheet) at least in contact with a through-hole conductor terminal is more porous than a ceramic layer (hereinafter referred to as a normal sheet) constituting another layer; Then, a coil conductor pattern is formed from a conductive paste on a ceramic green sheet having a through hole formed therein, and the green sheets having the same coil conductor pattern are laminated and pressed so that at least two layers overlap with each other, and then fired to form a laminate. The internally provided coil conductors are connected by through-hole conductors to be partially branched into a plurality of portions, and the branched coil conductor terminals are connected again by the through-hole conductors to join together to form one coil as a whole. In the method for manufacturing a laminated inductance element, the formation of the buffer sheet and the A method for producing a laminated inductance element, characterized in that binders having different degrees of polymerization are always used for forming a sheet. Thirdly, the binder used for forming the buffer sheet is polyvinyl alcohol (PVA) having a degree of polymerization of 1300 or more and 3000 or less. ) Or polyvinyl butyral (PVB). Fourth, the degree of polymerization of PVA or PVB as a binder used for forming the buffer sheet is generally lower than that for forming a sheet. The method for producing a multilayer inductance element as described above, wherein the degree of polymerization is higher than that of PVA or PVB as a binder by 500 or more.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A through-hole connecting conductor portion according to the present invention is formed by, for example, superposing two sheets on which the same coil pattern is formed, connecting the terminals thereof with the through-hole conductor, and forming a part of the coil conductor. Is divided into two lines, that is, a so-called double coil conductor is formed, so that the through-hole forming portion is overlapped by three holes, and the through-hole connecting conductor portion is thicker than the conventional one. Therefore, when the ceramic green sheets are overlapped and pressed together, the stress due to the pressure is concentrated on the end of the through-hole conductor, and the stress is applied above and below the through-hole connecting conductor.

In the method of the present invention, as shown in FIG. 1, ceramic green sheets formed using a binder having a high degree of polymerization are used as buffer sheets 1a on ceramic green sheets located above and below the through-hole connecting conductor. I do. Since this buffer sheet 1a using a binder having a high degree of polymerization is highly flexible, by arranging this in the ceramic layer which receives the stress, the stress is absorbed by this layer and the ceramic green sheet is prevented from being damaged. You can do it. Further, when the ceramic green sheets are laminated and subjected to the binder removal treatment, the binder removal rate of the green sheets using the binders having different polymerization degrees differs depending on the polymerization degree of the binders. That is, a binder having a low degree of polymerization decomposes and burns at a low temperature, and a binder having a high degree of polymerization decomposes and burns at a high temperature. Therefore, when the binder is gradually removed from the low temperature stage and the binder having a high degree of polymerization decomposes and burns, sufficient voids are already formed around the binder, so that rapid decomposition and combustion hardly occur. That is, a gentle binder removal treatment is performed, so that cracks and the like do not occur. Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

[0007]

Example 1 1.5 kg of a 20% aqueous solution of PVA (polyvinyl alcohol) was added to 3 kg of a Ni-Zn ferrite raw material powder, mixed and stirred by a ball mill for 20 hours, and a ferrite green sheet was prepared by a doctor blade method. . The prepared sheets are two types of A and B, and the sheet A has a sheet thickness of 30 using PVA having a polymerization degree of 800.
μm ferrite green sheet (corresponding to the normal sheet 1 shown in FIGS. 1 and 2), and sheet B has a degree of polymerization of 170.
Ferrite green sheet using PVA of 0 and a sheet thickness of 30 μm (corresponding to the buffer sheet 1a shown in FIG. 1)
It is. A through hole was formed in the produced sheet, and the internal electrode paste was printed to produce a laminated inductor. The chip I was manufactured using only the sheet A and had a double spiral structure. Chip II also has a double spiral structure, but sheet B was used for one of the double internal electrode printing (buffer sheet 1a in FIG. 1). The remaining portion is the sheet A including the dummy layer. That is, the chip I is a conventional inductor having a double spiral structure (FIG. 2), and the chip II is a product of the present invention (FIG. 1).

For 300 finished products, L value, Q value, R
_{The DC} value, the number of cracks after firing, and the number of missing turns were evaluated. Table 1 shows the results.

[0009]

[Table 1]

[0010] In the chip II (product of the present invention), no cracks or missing turns are observed, and the L value is improved. Based on the results, the following experiment was conducted to check the appropriate range of the degree of polymerization of the binder for the buffer sheet.

[0011]

Example 2 P having a polymerization degree of 600 to 5000
As shown in Table 2, nine types of VA were prepared in stages, and a 20 wt% aqueous solution of each PVA was prepared as a binder solution. 1.5 kg of the binder solution was added to 3 kg of the Ni-Zn ferrite raw material powder, and the mixture was stirred with a ball mill for 20 hours to prepare respective slurries using the nine kinds of binders. A 30 μm ferrite green sheet was formed. For the ferrite green sheet, the degree of polymerization of the binder used was directly described as a green sheet name. Through-holes were formed in these ferrite green sheets, and coil conductors were printed. When these preparations were completed, a laminated inductor was formed by combining a green sheet having a binder polymerization degree of 800 with other green sheets. That is, the column of the degree of polymerization of the buffer sheet binder of 800 in Table 2 corresponds to the conventional example, and shows that the laminated inductor was configured using sheets using the binder of the degree of polymerization of 800 for all sheets. In the column of the binder polymerization degree of 1300, if a sheet using a binder having a polymerization degree of 1300 is used as a green sheet in contact with the through-hole terminal to form a coil as shown in FIG. A green sheet using a binder having a degree of polymerization of 800 in consideration of arranging the sheets, that is, a normal sheet 1 and a green sheet having a degree of polymerization of 1
The green sheets using the 300 binders, that is, the buffer sheets 1a alternately overlap with each other, indicating that a laminated inductor was formed.

With respect to the present laminated inductance element, 300 pieces selected at random are selected and the inductance (L) is selected.
The value, Q value, and DC resistance (R _DC ) of the coil were measured, and the average value was shown in Table 2. In the measurement of the L value, the number of those which showed a large change in the L value, which is considered to be a change in the number of coil turns, is shown in Table 2 as missing turns.

[0013]

[Table 2]

Separately, 300 laminated inductance elements were randomly selected, polished and observed for cracks, and the number of cracked products was shown as cracks in the corresponding column of Table 2.

From this table, it is not preferable that a laminated inductor using a green sheet having a binder polymerization degree of 600 has a low L value, and has many cracks and missing turns. Also, if a green sheet having a binder polymerization degree of 4000 or more is used, the green sheet becomes hard and the adhesiveness is reduced. It is crimped.
In such a case, the cross-sectional area (core area) surrounding the coil conductor becomes small, and the L value decreases, which is not preferable.
Therefore, the degree of polymerization of the binder of the buffer sheet is 1300 to
It is desirable to be within the range of 3000. When the same test was repeated using PVB instead of PVA as a binder in each of the above examples, similar results were obtained.

[0016]

According to the method of the present invention, breakage of the ceramic green sheet during lamination and pressure bonding can be avoided by the flexible buffer sheet, and so-called turn-off can be prevented. Further, since the degree of polymerization of the binder used in the normal sheet and the binder used in the buffer sheet are different, the binder removal gradually proceeds during the binder removal treatment, and chips with less delamination and cracks can be obtained. Therefore, a highly reliable multilayer ceramic inductor can be manufactured with a high yield by the method of the present invention.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing a stacking order of green sheets in an embodiment of the present invention.

FIG. 2 is an exploded perspective view showing a stacking order of green sheets according to a conventional method.

[Explanation of symbols]

1: Normal ferrite green sheet piece (normal sheet) 1a: Buffer ferrite green sheet piece (buffer sheet) 2: Through hole 3: Coil pattern

Claims (4)

[Claims] 1. A method in which a coil conductor provided in a laminated body is connected by a through-hole conductor and partially branched into a plurality of parts, and the branched coil conductor terminals are connected again by a through-hole conductor and merge to repeat. 1. A multilayer inductance element comprising a multilayer ceramic inductor having a single coil as a whole, wherein at least a ceramic layer in contact with a terminal of a through-hole conductor is more porous than a ceramic layer forming another layer. 2. A method of forming a coil conductor pattern with a conductive paste on a ceramic green sheet having a through hole formed therein, laminating and pressing at least two green sheets having the same coil conductor pattern, followed by firing. The coil conductor provided in the laminated body is connected by the through-hole conductor and partially branched into plural parts, and the branched coil conductor terminals are connected again by the through-hole conductor and merge to repeat one coil as a whole. Wherein a binder having a different degree of polymerization is used for forming at least a ceramic layer in contact with a through-hole conductor terminal and forming a ceramic layer constituting another layer. Of manufacturing a laminated inductance element. 3. A binder used for forming a ceramic layer in contact with a through-hole conductor terminal has a degree of polymerization of 1300 or more.
The method for producing a multilayer inductance element according to claim 2, wherein the multilayer inductance element is polyvinyl alcohol (PVA) or polyvinyl butyral (PVB) of 000 or less. 4. A PV as a binder used for forming a ceramic layer in contact with a conductor terminal of a through-hole conductor connection
PVA or PV as a binder used for forming a ceramic layer in which the degree of polymerization of A or PVB constitutes another layer
4. The method according to claim 2, wherein the degree of polymerization of B is higher than that of B by 500 or more.