JP2602801B2 - Multilayer chip inductor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer chip inductor having a coiled conductor formed inside a magnetic laminate, and more particularly to a multilayer chip inductor having a high withstand voltage.

[0002]

2. Description of the Related Art In the production of multilayer chip inductors,
There are two processes for obtaining a laminate, a printing method and a sheet method. The former printing method is a method in which a magnetic material layer and a conductive paste are sequentially applied by screen printing or the like to form a magnetic material layer and a circling conductor. In the latter sheet method, magnetic sheets on which conductors are printed in advance by screen printing or the like are laminated, and the conductors on each magnetic sheet are connected by through holes.

[0003] In the laminate obtained by any of the above methods,
Finally, it is baked, and furthermore, a conductive paste is baked on both exposed end surfaces of the conductor to form external electrodes. Thereby, a multilayer chip inductor is obtained. Inside the magnetic laminate thus obtained, there is provided a coil-shaped conductor that is superposed and circulates in the laminating direction.

In such a multilayer chip inductor, in order to obtain a reliable electric conduction state at a connection portion between the coil-shaped conductor formed inside the multilayer body and the external electrode,
At a portion where the conductor is connected to the outer conductor, an inner conductor lead portion which is sufficiently wider than other conductors is formed. The conductor having the internal conductor lead-out portion is formed to have substantially the same film thickness by using a screen having the same emulsion thickness as the other conductors. As a result, the printed film thickness of the internal conductor lead portion and the conductor and the conductor thickness after firing become substantially the same.

FIG. 2 shows a sectional view of such a conventional multilayer chip inductor. In the figure, reference numeral 21 denotes a laminate formed by laminating magnetic layers. Reference numerals 23, 25, and 26 denote circular conductors formed inside the laminate 21 and sequentially connected through through holes (not shown) to be continuous in a coil shape. Of these, the upper and lower conductors 23, 25
The internal conductor lead-out portion 2 leading to the end face of the laminate 21
7, 28, each of which is wider than the other portions of the conductors 23, 25. Reference numerals 22 and 24 denote external electrodes formed on the end surfaces of the laminate 21. These external electrodes are in contact with the internal conductor lead-out portions 27 and 28 and are conductive.

However, the internal conductor lead-out portion 27,
28 is thin, the external electrodes 22, 2
There is a problem in that the contact with No. 4 is weakened and poor conduction easily occurs. In order to solve this problem, it has been proposed to increase the thickness of the internal conductor lead portions 27 and 28 so as to ensure reliable contact with the external electrodes 22 and 24 . According to this method, since the contact between the internal conductor lead-out portion and the external electrode is ensured, conduction failure can be reduced.

[0007]

However, when a pulse breakdown test is performed on the above-described conventional laminated inductor, it has been confirmed that the conductor breaks at the base from the internal electrode lead-out portion to the conductor. Was. It was examined for this reason, the base of the portion extending to the conductor from the inner conductor drawer section, the inner conductor lead-out portion and the conductor
In addition to the sudden narrowing of the conductor width at the border,
When the pulse voltage is applied to the inductor, the difference in the amount of charge per unit cross-sectional area between the internal conductor lead-out portion and the conductor causes the internal conductor lead-out portion to reach the conductor because the thickness is also rapidly reduced. It was found that the charge was concentrated at the base and this part was destroyed.

In the above-mentioned conventional multilayer chip inductor in which the conductor thickness of the internal conductor lead portion is increased, it is effective in improving the contact with the external electrode. The voltage is not different from the previous one, and there is a problem that much deterioration is caused by the pulse voltage and the reliability is still low. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems of the conventional multilayer chip inductor and to provide a highly reliable multilayer chip inductor having high withstand voltage.

[0009]

That is, in the present invention,
In order to achieve the above object, a circular conductor is provided between layers of the magnetic laminate, and the conductor is connected to each other between adjacent magnetic layers to form a coil, and a part of the conductor is formed in the laminate. of having a sufficiently wide internal conductor lead-out portion which reaches the end surface, the multilayer chip inductor internal conductor lead-out portion is connected to the external electrodes formed on the end face of the laminate, a conductor having the inner conductor lead-out portion Boundary portion between the above-described internal conductor lead portion and a narrow portion connected thereto
Of the conductor formed between the layers of other magnetic material
A multilayer chip inductor characterized by being formed thicker than a conductor .

[0010]

In the multilayer chip inductor according to the present invention ,
The width of the inner conductor drawer and the conductor connected to it is narrow
The thickness of the conductor film at the boundary between the
Thicker than the conductor thickness of the conductor formed
Therefore, the amount of charge per unit cross-sectional area at the boundary portion of the conductor pattern is reduced, and the concentration of charges at the boundary portion between the internal conductor lead-out portion and the conductor is reduced. Thereby, the durability in the pulse destruction test is improved.

Note that charge concentration also occurs at the connection between the above conductor having a large conductor thickness and another conductor having a small conductor thickness. However, the difference in the amount of charge per unit cross-sectional area at the connection between the conductors is smaller than the difference in the amount of charge per unit cross-sectional area between the inner conductor lead-out portion and the conductor. Concentration is not remarkable, and conductor breakdown by the pulse breakdown test is unlikely to occur. By the way, as a method of alleviating the concentration of charges, there is a method of increasing the width of a conductor.
However, according to this method, the area of the magnetic body inside the coil cannot be increased, and a desired inductance cannot be obtained, which is not practical.

[0012]

Next, an embodiment of the present invention will be specifically described with reference to the drawings. FIG. 3 is a conceptual diagram showing a method of laminating magnetic sheets when the multilayer chip inductor according to the present invention is manufactured by a so-called sheet method. Using a magnetic slurry in which a magnetic powder such as a ferrite powder is dispersed in a binder, thin magnetic sheets 31, 31... Are formed by means such as a doctor blade method. The through-holes 3 are previously provided at predetermined positions of these magnetic sheets 31, 31.
After punching 2, 32 ..., the conductors 3a, 3b,
3c, 3d, 3e, and 3f are printed, and through-hole conductors are printed in the through-holes 32.

Depending on the required number of coil turns, the conductor 3
A proper number of sets of magnetic sheets having a, 3b, 3c, and 3d are prepared, and these are sequentially laminated. .. On both sides of these magnetic sheets 31, 31.
Conductors 3e, 3 having internal conductor lead-out portions 35, 26, respectively.
f, the printed magnetic sheets 33 and 34 are laminated,
Further, a magnetic sheet 3 having no conductor printed on both sides thereof
7 and 38 are laminated as protective layers.

Then, the laminated body is pressed and baked to obtain a baked magnetic laminated body 11 as shown in FIG. In the figure, reference numerals 13, 15, and 16 denote circulating conductors which are formed inside the laminated body 11 and are sequentially connected through through holes (not shown) to be continuous in a coil shape. Things. Of these, the upper and lower conductors 13 and 15 have internal conductor lead-out portions 17 and 18 extending to the end surfaces of the laminated body 11, respectively, and this portion is wider than the other portions of the conductors 13 and 15. A conductive paste is applied to both end surfaces of the laminate 11 and is baked to form external electrodes 12 and 14. The external electrodes 12 and 14 are provided on the end face of the laminate 11
The inner conductors 17 and 18 are in contact with each other and are electrically connected.

As is apparent from FIG.
The conductors 13 and 15 having the internal conductor lead portions 17 and 18 in contact with the conductors 2 and 14 are thicker than the other conductors 16 and 16. In order to form such thick conductors 13 and 15, unfired conductors 3e and 3 as shown in FIG.
When forming f, the conductor paste is applied to other conductors 3a, 3b,
Print thicker than 3c and 3d. Conductors 3a, 3b, 3
As a method of printing thicker c and 3d, the emulsion thickness of the printing screen is made thicker so that the conductive paste is printed thicker on the magnetic sheets 33 and 34, or the conductor 3e,
It is common to print 3f multiple times using the same screen.

Although FIG. 3 shows the magnetic sheets 31, 33, 34, 37, and 38 laminated on one laminated chip inductor, in practice, the conductors are arranged vertically and horizontally on a wide magnetic sheet. Is manufactured by laminating a plurality of printed sheets, cutting the laminated chips into individual laminated chips, and then firing. Next, more specific examples of the present invention will be described.

(Example 1) A ferrite powder, which is an elementary material, is formed into a sheet using a binder containing polyvinyl butyral as a main component. In addition, Ag powder as an internal conductor material, using ethyl cellulose as a binder,
α-terpineol and butyl carbitol acetate are mixed as a solvent to form a conductive paste.

Next, as shown in FIG. 3, the conductive paste is printed on magnetic sheets 31, 31...
b, 3c and 3d are formed. In this case, a printing screen in which an emulsion having a thickness of about 15 μm was applied to a 250-mesh screen mesh was used. The conductors 3e and 3f having the internal conductor lead-out portions 35 and 36 have an emulsion thickness about twice as large as that used when printing the other conductors 3a, 3b, 3c and 3d, that is, about 30 μm. Print using a thick printing screen. This allows
The printed film thickness of the conductors 3e, 3f is changed to the other conductors 3a, 3b, 3
c, about 2 times as large as 3d.

The printed sheets thus obtained are laminated as shown in FIG. 3, and a plurality of magnetic sheets 37 and 38 on which conductors are not printed on the upper and lower surfaces of the laminated sheets are stacked as protective layers. The laminate thus obtained is heated at 90 ° C. for 4 hours.
Thermocompression bonding is performed at 00 kg / cm ² . Next, the obtained laminate is cut into a predetermined size such that the internal conductor lead portions 35 and 36 of the conductors 3e and 3f are exposed at the end surfaces. The cut piece is fired at 900 ° C. for 1 hour in the air. As shown in FIG. 1, the thus obtained laminate 1
An Ag paste for an external electrode is applied to both end surfaces of the laminated chip inductor 1 and baked in the air at a temperature of 600 ° C. for 20 minutes to form external electrodes 12 and 14 that are electrically connected to the internal conductor lead portions 17 and 18. Get.

One hundred multilayer chip inductors thus obtained were randomly taken out and subjected to a pulse breakdown test. That is, the initial resistance value of each chip to be tested is measured in advance, and the average value is determined. The chips are placed one by one in a test apparatus, and after applying a certain pulse breaking energy, the resistance value after the test is measured. If the resistance value has increased by 0.5Ω or more from the average value, it is determined as a defective product, and the non-defective product ratio is examined.
After measuring the resistance value, the same samples except for the defective products are put into a test apparatus one by one, and a stronger pulse destruction energy is applied. Thereafter, the resistance value is measured again, and the non-defective product rate is checked.

In this test, the ratio of non-defective products to the applied breaking energy was examined for the product of the present invention and the conventional product, and the results are as shown in FIGS. 4 and 5. FIG. 4 shows the product of the present invention,
FIG. 5 shows a conventional product. This indicates that the product of the present invention has about twice the durability against breaking energy as compared with the conventional product.

Example 2 In Example 1, the conductors 3e and 3f and the conductors 3a, 3b, 3c and 3d of FIG. 3 were printed using a printing screen having the same emulsion thickness of 15 μm. However, for the conductors 3e and 3f, after printing once,
The conductor paste was dried, and the same pattern was again superimposed and printed thereon, to give a double printed film thickness. Other than that,
All of the laminated chip inductors were manufactured in the same manner as in Example 1, and the same pulse breakdown test was performed on them. As a result, in this example, the same result as in Example 1 was obtained in the pulse destruction test.

In the above-described embodiment, the width of the internal conductor lead-out portion is constant. However, the width of the internal conductor lead-out portion is gradually reduced toward the coil conductor side so that the connection portion has the same width as the coil conductor. With this configuration, the concentration of charges in the internal conductor lead-out portion is alleviated, so that destruction at the connection portion is reduced, and the same result as in the above-described embodiment is obtained.

[0024]

As described above, according to the present invention, poor conduction between the internal conductor and the external electrode of the multilayer chip inductor is reduced, and the deterioration of the conduction by the pulse breakdown test is reduced. The pulse voltage is improved.

[Brief description of the drawings]

FIG. 1 is a schematic vertical sectional side view of a multilayer chip inductor showing an embodiment of the present invention.

FIG. 2 is a schematic vertical sectional side view of a multilayer chip inductor showing a conventional example.

FIG. 3 is an exploded perspective view of a laminated sheet showing a production example of a laminated chip inductor according to the present invention.

FIG. 4 is a graph showing the relationship between the breaking energy and the yield rate showing the results of conducting a pulse breakdown test on the multilayer chip inductor according to the embodiment of the present invention.

FIG. 5 is a graph showing the results of conducting a pulse breakdown test on a multilayer chip inductor according to a conventional example, and showing the relationship between the breaking energy and the yield rate. Reference Signs List 11 laminated body 12 outer conductor 13 conductor 14 outer conductor 15 conductor 16 conductor 17 internal conductor lead-out part 18 internal conductor lead-out part

Continuation of the front page (72) Inventor Yoichi Yamamoto 6-16-20 Ueno, Taito-ku, Tokyo Taiyo Yuden Co., Ltd. (72) Inventor Kurata 6-16-20 Ueno, Taito-ku, Tokyo Taiyo Yuden Co., Ltd. (56) References JP-A-3-23603 (JP, A)

Claims (1)

(57) [Reference number] 0030128-01 [Claims] 1. A conductor having a circular shape between layers of a laminated body of magnetic materials, the conductors being connected to each other between adjacent magnetic layers to form a coil, and a part of the conductor is an end face of the laminated body. sufficiently have wide internal conductor lead-out portion to reach, in the multilayer chip inductor internal conductor lead-out portion is connected to the external electrodes formed on the end face of the laminated body, the conductor having the inner conductor lead-out portion above Internal conductor drawer
Thickness of the conductor at the boundary between the narrow portion connecting to it
But thicker than conductors formed between layers of other magnetic materials
Multilayer chip inductor, characterized in that it is.