JPH0416927B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to the structure of a multilayer inductor.

In recent years, due to the demand for smaller and thinner electronic devices and devices, electronic components to be mounted have become smaller and thinner.
There is a rapid demand for thinner devices, and as part of this, research is being conducted on chip parts, Melf-type parts, and even composite parts that combine these elements rather than single-part elements, and these are being put into practical use.

Regarding resistors and capacitors, products with standardized shapes such as chip resistors, Melf-type resistors, chip capacitors, and Melf-type ceramic capacitors are produced, and composite parts are also available in resistor arrays and CR parts. They have started to be seen in electronic devices and devices that require smaller size and thinner thickness.

On the other hand, due to the demand for smaller and thinner devices, such as coils and transformers,
There is a rapid movement towards chips.

There are two types of chip coils: one uses a ferrite core as a magnetic core, winds a thin copper wire around this core, forms electrodes at both ends, and molds it into a chip. There is a multilayer inductor in which a pattern of conductive material is printed on a sheet of magnetic material and then laminated.

FIG. 1 shows a recently commercialized multilayer chip inductor, which has the features of being small and thin, and has an inductance value of 0.1 to 47 μH.

It is known that the inductance of such a coil is expressed as L=4π・μe・N ² /Σl/A×10 ^-3 (μH) when a closed magnetic circuit is formed using the magnetic core material, and the cross-sectional area A is It can be seen that the shorter the magnetic path length l, the greater the inductance. For this reason, it becomes necessary to increase the diameter of the loop forming the coil and to increase the cross-sectional area within the loop forming the magnetic circuit.

However, since the shape of chip parts is required to be as small as possible, Figure 1
In a pattern shape like this, when the loop diameter is increased, the cross-sectional area of the magnetic circuit outside the loop becomes smaller, and the inductance becomes smaller. For this reason, it is not possible to obtain efficient inductance with the inductor having the above-mentioned loop structure. Furthermore, since the multilayer chip inductor having such a structure has conductor patterns 11 stacked on top of each other, it has a large line capacitance.

Such line capacitance Co is expressed as Co=8.855・εs・A/t (pF). Therefore, in order to reduce the line capacitance, the width of the conductor pattern should be made small so that when stacked, there is no overlap. It is necessary to reduce the area A of the portion where , and further increase the thickness t between the lines.

However, if the pattern width is made smaller, conductor resistance increases, which limits usable circuits. Furthermore, in order to increase the thickness between the lines, it is necessary to increase the thickness of the sheet forming the pattern, or to use a type in which a dummy insulating sheet is inserted. For this reason, the chip shape becomes thick in the thickness direction.

The object of the present invention is to eliminate these drawbacks,
Taking advantage of its small size and low line capacitance,
The objective is to provide a structure that can obtain large inductance.

A multilayer inductor consisting of a laminate of a magnetic material and a conductive material, in which one conductive material orbits around two predetermined points within the magnetic material, and a magnetic material is formed at a position midway between the two points. The conductors are arranged so as to cross each other through the body, and both ends of the conductors are connected to lead-out terminals formed at positions exposed on the surface of the laminate through through-holes and lead-out electrode patterns. The multilayer inductor is characterized in that an external electrode connected to the lead terminal is formed on the surface of the multilayer body.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

The magnetic material used in the examples of the present invention is
Fe ₂ O ₃ 50 parts by weight, NiO 20 parts by weight, ZnO 24 parts by weight,
A composition in which 0.5 parts by weight of Co ₂ O ₃ was added to a mixture of 6 parts by weight of CuO was used as a raw material, which was mixed in a ball mill and then preheated at 800°C. This magnetic material, polyvinyl butyral as an organic binder, ethyl cellosolve and butyl carbitol as organic solvents, and ethylene glycol monobutyl ether as a plasticizer are stirred and mixed using a homomixer to form a slurry. Next, the slurry was applied to an organic film with a thickness of 50 μm using a slip casting method using a doctor blade.
Form a film with a thickness of ~200 μm. A magnetic green sheet formed on an organic film is peeled from the film and then punched into a shape of 100 x 70 mm to form a magnetic green sheet used for the chip L.

FIG. 2 is a diagram of a coil pattern showing an embodiment of the present invention, in which a sheet 21 forming a magnetic material is formed with a loop forming a coil having two centers 22 and 23, and sheet 2
The pattern is such that they intersect at the center 24 of 1.

This intersecting pattern is divided into two sheets forming the magnetic material, and includes a pattern 25 shown by a broken line and a pattern 2 shown by a solid line in the figure.
6 are formed in separate sheets. A through hole 27 is provided so that these two patterns are connected in series.

FIG. 3 shows the lamination relationship showing an example of a multilayer structure.

The sheets 31 of each layer in the figure are two sheets stacked as shown in FIG. 2, and
The stacked sheets have two patterns: a pattern 32 in which the winding direction is from the inside out and a pattern 33 in which the winding direction is from the outside to the inside. A sheet 35 having a take-out terminal 34 and a dummy sheet 36 for protecting the upper and lower surfaces are stacked and laminated and pressed at a temperature of 100 to 130° C. and a pressure of 200 to 300 kg/cm ² , followed by a cutting process and a binder removal process. A laminated inductor is obtained by firing at 950°C to 1050°C. In this way, in this laminated inductor, the conductor patterns 32, 33
is formed at a position exposed on the surface of the laminate through the through hole 38 and the lead-out electrode pattern, and is connected to the lead-out terminal.

FIG. 4 is an external perspective view of the multilayer inductor of the present invention obtained in FIG. 3, in which external electrodes 41 are formed at both ends of the chip for connection to lead terminals.

FIG. 5 is a cross-sectional view of the sintered body of the present invention taken through the two centers 22 and 23 in FIG. 2.

The coil pattern starts from one external electrode 50 and is connected in the order of subscripts 2 to 37 of each cross-sectional conductor, and the conductor with subscript 38 is connected to the other external electrode 51.

Therefore, the magnetic field in the loop on the left side of the center and the magnetic field in the loop on the right side are in opposite directions,
The magnetic field loop 52 provides a closed magnetic path only between the two loops.

As described above, since the multilayer inductor of the present invention has a closed magnetic path only within the two loops, the dimensions of the chip and the external dimensions of the coil can be made almost the same, and the cross-sectional area of the magnetic path can be increased. For this reason, the conventional disadvantage of reduced dimensional efficiency caused by the chip shape and the cross-sectional area of the magnetic path is eliminated, and the advantage of having a large inductance relative to the shape is obtained.

Furthermore, since multiple turns are formed on one sheet, a dummy sheet can be placed, compared to an inductor obtained with a conventional one-turn configuration, resulting in an inductor with smaller line capacitance.

In this example, the chip size is 4 mm x 8 mm.
Each sheet has 3 turns with a conductor pattern width of 100 μm and a line spacing of 100 μm, and the inner dimensions of the turns are 6.6 mm x 1.05 mm.A total of 10 pairs of two-layer sheets are stacked to form an effective configuration of 60 turns. There is.

With a chip inductor constructed in this way and fired at 1050°, it becomes μ250 (1KHz) and L
9μH, which is about 4 times the inductance of the conventional one.

On the other hand, since the capacitance between lines can be distributed as a plurality of turns on one sheet, its value can be reduced, and higher frequency characteristics can be obtained.

In the embodiment of the present invention, the coil pattern is obtained by through-hole connection near the central intersection.
This through hole can be positioned at any point on the sheet, and since the number of turns of the coil on the sheet is also limited by the dimensions of the sheet, the number of turns is also designed to obtain the desired inductance. It's obvious what you should do. Also, in this example, the sheet shape is rectangular, but
If two intersecting loops can exist on one sheet, the sheet shape is not limited, and by increasing the length in the intersecting direction, a pattern with a shorter magnetic path length can be obtained. It is clear that efficiency increases.

[Brief explanation of drawings]

Fig. 1 is a structural diagram of a conventional multilayer chip inductor, Fig. 2 is a coil pattern diagram of the present invention, Fig. 3 is a diagram showing an example of the structure of the multilayer inductor of the present invention when multilayered. FIG. 4 is an external view of a laminated and sintered multilayer inductor of the present invention, and FIG. 5 is a central sectional view of the multilayer inductor of the present invention. In the figure, 11... conductor pattern, 21...
Sheets forming magnetic material, 22 and 23... Center of coil pattern, 24... Center of sheet, 25
...First layer pattern, 26...Second layer pattern, 27...Through hole, 31...First layer and second layer
Sheet with combined layers, 32...pattern coming out from the inside, 33...pattern coming in from the outside, 3
4... Takeout terminal, 35... Sheet forming magnetic material, 36... Dummy sheet, 37... Takeout electrode pattern, 38... Through hole, 41...
...External electrode, 50...One external electrode, 51...
The other external electrode, 52...magnetic field loop.

Claims (1)

[Claims] 1. A laminated inductor consisting of a laminated body of a magnetic material and a conductive material, in which one conductive material circulates around two predetermined points within the magnetic material,
and are arranged so as to intersect with each other through a magnetic material at a position midway between the two points, and both ends of the conductive material are formed at positions exposed to the surface of the laminate through the through-hole and the lead-out electrode pattern. What is claimed is: 1. A multilayer inductor, which is connected to a lead-out terminal, and has an external electrode formed on the surface of the laminate to be connected to the lead-out terminal.