JPH06204039A - Layered transformer - Google Patents

Abstract

PURPOSE:To realize high efficiency of power conversion efficiency of a transformer by realizing decreased height, improved thermal reliability and low loss. CONSTITUTION:The device has a multilayer substrate which is formed by laminating a plurality of insulating sheets, and a pattern coil 8 is formed of conductor paste in a main surface of a plurality of green sheets. Green sheets 2a to 2d contain ceramic material and glass frit. A main element of the conductive paste is a conductive metallic material of at least one or more kinds of Ag, Cu, Au, and glass frit which is different from the glass frit of the green sheets 2a to 2d is added by 10wt.% or less so that a sheet resistance value of the pattern coil 8 is 3.0mOMEGA/square or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated transformer,
In particular, the present invention relates to a laminated transformer using a multilayer circuit technology, which is used in electronic devices and electronic devices.

[0002]

2. Description of the Related Art In recent years, there have been strong demands for miniaturization, high performance, and low price of electronic parts used in electronic equipment and electronic devices. In particular, a transformer used in a circuit unit such as a switching power supply of an electronic device is a relatively large component among the components used, and in order to achieve downsizing and thinning of the power source unit, Miniaturization and surface mounting are required.

Conventional transformers used in electronic equipment are
Generally, a copper winding is wound around a bobbin and an E-type ferrite core is inserted into the bobbin. In such a conventional transformer, in order to enable surface mounting, the coil body is joined to a substrate having a terminal electrode formed on the bottom surface, and it is extremely difficult to reduce the size and the density. Therefore, Japanese Utility Model Publication No. 1-100471 and Japanese Utility Model Publication Sho 61-1
Japanese Patent No. 17269 discloses that a pattern coil is formed on each of the multilayer printed wiring boards. In a laminated transformer using these multilayer printed wiring boards,
A thinner transformer can be realized.

[0004]

In the conventional device, the laminated transformer is formed by using the multilayer printed wiring board.
The multilayer printed wiring board is generally made of an organic material such as epoxy resin or phenol resin. Such an organic material has insufficient thermal reliability and is not particularly desirable for use as a transformer which causes a temperature rise.

Further, in the conventional laminated transformer, a noble metal conductor paste such as Ag-Pd or a base metal conductor paste such as Ni is used as the conductor paste for forming the pattern coil. In these conductor pastes, in the case of Ag-Pd, the sheet resistance value is about 25 mΩ / □, and
For Ni or the like, it is about 55 mΩ / □, and the Joule heat generated in this portion becomes large. As a result, the transformer has a large power loss, which leads to a reduction in power conversion efficiency, and adversely affects peripheral circuit elements. Therefore, it is conceivable to use an Ag-based or Cu-based conductor paste, but these sheet resistance values are usually 10 to 3 mΩ /
It is about □, and power loss cannot be suppressed sufficiently.

An object of the present invention is to achieve a low profile, high thermal reliability, and low loss.

[0007]

A laminated transformer according to the present invention has an insulating substrate formed by laminating a plurality of insulating sheets, and a pattern coil is formed on a main surface of the plurality of insulating sheets with a conductor paste. Has been done. The insulating sheet includes a ceramic material and a glass frit, and the conductive paste is at least one of Ag, Cu and Au.
A glass frit containing, as a main component, one or more kinds of conductive metal materials and having a yield point lower than the glass frit sintering start temperature of the insulating sheet so that the sheet resistance value of the pattern coil is 3.0 mΩ / □ or less. Is added in an amount of 10% by weight or less.

[0008]

In the laminated transformer according to the present invention, the sheet forming the insulating substrate is made of a ceramic material, and therefore, the heat dissipation is excellent and the thermal reliability is improved. Also,
It is desirable to add glass frit to the conductor paste in consideration of thermal deformation between the conductor paste and the insulating sheet.
By limiting the content to 0% by weight or less, Ag, Cu, Au
The sheet resistance value of the conductive paste containing at least one conductive metal material as a main component is 3.0 mΩ / □ or less. Therefore, generation of Joule heat and power loss can be suppressed.

[0009]

1 is an external perspective view of a laminated transformer as an embodiment of the present invention, and FIG. 2 is an enlarged sectional view of FIG. In these figures, the laminated transformer 1 is composed of an insulating multilayer substrate 2 and a magnetic member 3.

The multi-layer substrate 2 is obtained by laminating four glass frit green sheets 2a, 2b, 2c and 2d and integrally firing them, and has a through hole 4 in the center. On the surface of the first sheet 2a, the surface terminal electrodes 5a,
5b is formed. Further, the primary pattern coil 6a is formed on the surface of the second sheet 2b by 3 turns (three turns), and the outermost peripheral portion is connected to the surface terminal electrode 5a via the via-hole conductor 7a. Further, the primary pattern coil 6b is formed on the surface of the third sheet 2c for three turns. The innermost peripheral portion of the primary pattern coil 6b is connected to the innermost peripheral portion of the primary pattern coil 6a in the upper layer via the via hole conductor 7b, and the outermost peripheral portion thereof is connected to the surface terminal electrode 5b via the via hole conductor 7c. It is connected to the. Further, the secondary pattern coil 8 is formed in three turns on the front surface of the fourth sheet 2d, and the surface terminal electrodes 5c and 5d are formed on the back surface. The outermost peripheral portion of the secondary pattern coil 8 is connected to the surface terminal electrode 5c via the via-hole conductor 7d, and the innermost peripheral portion thereof is connected to the surface terminal electrode 5d via the via-hole conductor 7e.

The glass frit forming each of the green sheets 2a to 2d contains, for example, MgO-Al2 O3-SiO2 as a main component and a ceramic material. As the ceramic material, for example, an inorganic filler such as alumina, mullite or cordierite is used. This ceramic material may be added alone or as a mixture of two or more kinds. The ceramic material is usually added to the glass frit at about 10 to 45% by weight.
The glass frit green sheet was obtained by kneading the above-mentioned glass frit, a ceramic material, an organic binder (eg acrylic resin), an organic solvent (eg toluene), and a plasticizer (eg dibutyl phthalate). It is obtained by forming the paste into a sheet by, for example, a doctor blade method.

The pattern coils 6a, 6b and 8 are
It is formed on the green sheets 2b to 2d by a screen printing method using a conductor paste. The conductor paste forming the pattern coil is composed of a conductive metal material, a glass frit, and an organic vehicle. As the conductive metal material, for example, Ag, Au, Cu or the like is used. Further, the glass frit is composed of the green sheets 2a-2.
different from the glass frit which constitutes d, for example, B2O3-S
The main component is iO2-CaO-Al2O3. That is, B2O3-SiO2-CaO-Al2O
By using a glass frit of an alkaline earth metal borosilicate such as 3 or the like, viscous flow easily occurs in the sintering process, and the yield point is set to 700 ° C to 850 ° C. The organic vehicle can be obtained, for example, by mixing ethyl cellulose and 2,2,4-trimethyl-1,3 pentanediol monoisobutyrate.

Here, in order to reduce the loss of the coil and the transformer, it is necessary to reduce the conductor resistance value of the pattern coil, and the conductive metal material used for the conductor paste is Ag having a small specific resistance value. Is preferred. In addition to the conductive metal material as the main component, it is necessary to add an appropriate amount of glass frit to the conductor paste for the purpose of matching the sintering shrinkage behavior with the green sheet. By adding the glass frit, it is possible to suppress the warp of the substrate after firing and further stabilize the variation in the shrinkage of the substrate. However, the addition of glass frit has an adverse effect on reducing the conductor resistance value of the pattern coil.

Therefore, the glass frit added to the conductor paste is 10% by weight or less of the conductive metal material. 1
If it is 0% by weight or more, the original good conductivity of Ag is impaired, the conductor resistance value of the pattern coil becomes high, the sheet resistance value of 3.0 mΩ / □ cannot be achieved, and the Q value of the coil is lowered. In addition, in a transformer that utilizes the mutual induction phenomenon of coils, Joule heat is largely generated due to the flow of current, which increases power loss, causing a decrease in conversion efficiency and a rise in substrate temperature, which causes heat to the peripheral circuit elements. Have a negative impact. However, in consideration of the warp of the substrate and the variation in the shrinkage of the substrate, the glass frit is practically 5
An addition amount of at least wt% is required, and this glass frit must have a sag point in consideration of the sintering behavior of the conductive metal material powder, and the sag point is the glass of the green sheets 2a to 2d. It must be lower than the frit's onset temperature. For example, in the case of Ag powder, a glass frit having a yield point of 700 ° C to 850 ° C is used. When the yield point is 700 ° C. or lower, the glass flow becomes fast, the conductive metal powders are attracted to each other, and the sintering is promoted. As a result, the conductive metal material becomes over-sintered, and the warpage of the substrate and the variation in shrinkage occur. generate. On the other hand, when the yield point is 850 ° C. or higher, the softening fluidity of the glass frit deteriorates, and the conductive metal material does not have a uniform sintering behavior, so that the substrate warps and the substrate shrinkage varies.

The average particle size of the above-mentioned conductive metal material powder and glass frit is preferably 10 μm or less. If the average particle size exceeds 10 μm, the screen may be clogged when screen printing a pattern coil, for example. is there. Further, the average particle size of glass frit is 1
If it exceeds 0 μm, the state of dispersion with the conductive metal material powder is deteriorated, uniform sintering behavior is not exhibited, and warpage of the substrate and unevenness of substrate shrinkage occur.

The conductor paste used for the via-hole conductors 7a to 7e has a low thermal expansion coefficient different from that of the glass frit added to the conductor paste forming the pattern coil in order to bring it close to the coefficient of thermal expansion at the time of firing the green sheet as the insulating substrate. Glass frit is added. The via-hole conductor paste is filled in a through-hole having a diameter of 0.1 to 0.3 mm formed by punching a green sheet by using, for example, a printing method.

Through holes 4 for inserting a ferrite core are formed in the thus obtained multilayer substrate 2 using, for example, a drill, and integrally fired at a peak temperature of 800 ° C. to 1050 ° C. to obtain an E type ferrite core. By inserting and mounting
A compact and low-profile laminated transformer can be obtained. Further, the surface terminal electrodes 5a to 5d are formed by printing a predetermined pattern on the surface of the sheet using a Ag-based or Cu-based conductor paste by a screen printing method and baking it.
Although this terminal electrode is used for surface mounting on a printed circuit board, in order to prevent corrosion by solder, the surface of the terminal electrode is plated with Ni, solder,
You may give Sn plating.

Experimental Example Here, the following tests were conducted in order to confirm the reduction of the coil loss and the high efficiency of power conversion as a transformer. The green sheet described in the above example (the sintering start temperature of the glass frit added to the green sheet is about 780).
C.), a conductor paste for forming a pattern coil is prepared by using Ag powder, glass frit, ethyl cellulose, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate and a three-roll mill. It was obtained by kneading. Glass frit is B2O3-SiO2-C
A material containing aO-Al2O3 as a main component and a yield point of 720 ° C. was used. The amount of glass frit added was set as shown in Table 1.

[0019]

[Table 1]

The obtained conductor paste is printed on the above-mentioned green sheet with a predetermined pattern coil, four green sheets are laminated so that two electrically independent pattern coils are formed, and a ferrite core is inserted. Through holes were formed using a drill, fired at a peak temperature of 900 ° C. for 30 minutes, and an E-type ferrite core was inserted and mounted to obtain a laminated transformer. The conductor resistance value of the pattern coil of the obtained laminated transformer was examined to determine the sheet resistance value. Further, the obtained laminated transformer was mounted on a DC-DC converter, and the power conversion efficiency was examined.

Sheet resistance value A conductor resistance value was measured by a four-terminal method (a resistance value measuring method using a Wheatstone bridge) to obtain a sheet resistance value. Power conversion efficiency It was mounted on a DC-DC converter, and the power conversion efficiency was calculated by the following formula.

Power conversion efficiency = (output power) × 100 /
(Input power)% According to the results of this experiment, as shown in Table 1, when the glass frit addition amount is set to 5 to 10% by weight, the sheet resistance value becomes 3.0 mΩ / □ or less. Further, as shown in FIG. 3, when the glass addition amount was 5 to 10% by weight, a power conversion efficiency of 70% or more was obtained. When the power conversion efficiency is 70% or less, it is difficult to contribute to the reduction of power consumption when used in a power supply circuit section of an electronic device, an electronic device or the like, for example. If the amount of glass frit added is less than 5% by weight, the warpage of the substrate,
Since the substrate shrinkage variation was outside the practically acceptable range, it was omitted from the test results this time.

The laminated transformer of this embodiment can be incorporated in a multilayer circuit board.

[0024]

As described above, according to the present invention, the conductive paste is mainly composed of at least one conductive metal material of Ag, Cu and Au, and the sheet resistance value of the pattern coil is 3. 10% by weight of glass frit different from the glass frit of the insulating sheet so as to be 0 mΩ / □ or less
Since it is added below, a coil with high thermal reliability and low loss can be realized, and the power conversion efficiency of the transformer can be improved.

[Brief description of drawings]

FIG. 1 is an external perspective view of a laminated transformer according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of FIG.

FIG. 3 is a diagram showing a relationship between a glass addition amount and power conversion efficiency in an experimental example based on the present embodiment.

[Explanation of symbols]

 1 Multilayer transformer 2 Multilayer substrate 2a-2d Green sheet 6a, 6b, 8 Pattern coil

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Suenaga 1-1 Yamashita-cho, Kokubun-shi, Kagoshima Prefecture Kyocera Stock Company, Kagoshima Kokubun Factory (72) Inventor Yasuyuki Tanaka 1-1 Yamashita-cho, Kokubun-shi, Kagoshima Kagoshima Inside the Kokubun Plant (72) Inventor Shinichi Yonezawa 1-1 Yamashita-cho, Kokubun-shi, Kagoshima Prefecture Kyocera Stock Company Inside the Kagoshima Kokubun Plant (72) Inventor Akira Imoto 1-1 Yamashita-cho, Kokubun-shi, Kagoshima Kagoshima Kokubun Co., Ltd. 72) Inventor Nobuyuki Yokote 10-13 Minamimachi, Hanno City, Saitama Prefecture Shindengen Industrial Co., Ltd. (72) Inventor Yoshiaki Hiruma 10-13 Minamimachi, Hanno City, Saitama Shindengen Industrial Co., Ltd.

Claims (1)

[Claims] 1. A laminated transformer having an insulating substrate formed by laminating a plurality of insulating sheets, wherein a pattern coil is formed on a main surface of the plurality of insulating sheets with a conductor paste. The conductive paste contains a ceramic material and a glass frit, and the conductive paste contains a conductive metal material of at least one kind of Ag, Cu, and Au as a main component, and a sheet resistance value of the pattern coil is 3.0 mΩ / □ or less. As described above, a laminated transformer in which 10% by weight or less of glass frit having a yield point lower than the glass frit sintering start temperature of the insulating sheet is added.