JP2003257746A - Planar magnetic element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a planar magnetic element wherein a planar coil is so provided on the surface of a lower ferrite magnetic layer as to provide an upper ferrite magnetic layer on the planar coil inclusive of its clearance present between its coil wires. <P>SOLUTION: Each external electrode connected with each of the coil terminals present in both the end portions of the planar coil is so formed as to reach the respective three side surfaces of the planar magnetic element. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar magnetic element, and more particularly to a planar magnetic element suitable for surface mounting for soldering a wiring board or the like.

[0002]

2. Description of the Related Art In recent years, battery-powered small portable devices such as mobile phones and notebook computers have become popular. Further miniaturization and weight reduction are always required for these small portable devices. Further, there is also a demand for higher functionality such as realization of a function of processing a large amount of information represented by image data at high speed.

In order to meet such demands for performance improvement, various devices such as a CPU, an LCD and a functional module have been newly mounted. While these devices are driven at various voltage levels, the battery mounted in the device remains at a single voltage, so a small power supply element (DC-) that performs conversion to the corresponding voltage level. The demand for DC converters) is increasing.

A magnetic element such as a transformer or an inductor is indispensable for this power supply element. To reduce the size, weight and thickness of the power supply element, the magnetic element should also be made smaller, lighter and thinner. Must be realized. Further, in order to realize miniaturization, weight reduction, and thinning, surface mounting technology is particularly useful, and it is preferable that the magnetic element is also a small planar magnetic element.

As an example of a small-sized planar magnetic element, the technique disclosed in Japanese Patent Laid-Open No. 2001-244124 (“planar magnetic element and switching power supply”) is already known, and a planar coil suitable for thinning is known. A planar magnetic element sandwiched between magnetic layers is disclosed. That is, the planar magnetic element is a two-layered structure in which a planar coil is formed on the surface of the lower ferrite magnetic layer, and then the upper ferrite magnetic layer is formed so as to fill the entire space including the gap between the coil wires of the planar coil. The structure is such that external electrodes connected to the coil terminals at both ends of the planar coil are provided on the surface thereof.

An example of a conventional planar magnetic element is shown in FIG.
It will be described based on. FIG. 5A is a plan view in which the upper layer of the magnetic layer 12 of the planar magnetic element 11 is peeled off to expose the planar coil 14 inside. The planar coil 14 is formed by spirally winding the coil, and the coil terminals 13 are provided on the outermost and innermost ends of the coil. Then, as shown in FIG. 5B, the coil terminals 13 are formed on the outer surface of the planar magnetic element 11.
An external electrode 15 connected to is attached.

By the way, since the planar coil 14 has no polarity, which external electrode 15 is connected to the wiring board (here,
It may be connected to a wiring terminal (not shown). However, since the arrangement itself of the external electrodes 15 is asymmetric, it is essential to match the directions when mounting the planar magnetic element. For example, if you rotate it by 90 degrees and attach it,
The positions of the external electrodes of the planar magnetic element and the wiring terminals of the wiring board do not match, resulting in poor connection.

Therefore, as shown in FIG. 5 (c), a positioning mark 20 is provided on the surface opposite to the surface on which the external electrode 15 is arranged, which is used for positioning during mounting. Next, an example of mounting the conventional planar magnetic element 11 on the wiring board 21 will be described with reference to FIG. When mounting, first, the wiring board 21
Solder is placed at a predetermined position in (1), the direction of the planar magnetic element 11 is determined with the positioning mark 20 as a reference, and the planar magnetic element 11 is placed and a reflow process is performed (FIG. 6A).

If the soldering is performed normally, the planar magnetic element
Whether or not 11 is mounted on the wiring board 21 can usually be confirmed by forming a solder fillet 17. When soldering is normally performed, the solder is in a wet state and closely adheres to the terminal surface, and solidifies into a swelled shape due to surface tension. Such a rising shape of the solder is called a fillet. That is, it is possible to confirm the quality of the soldering state based on the fillet formation state.

That is, as shown in FIGS. 6B and 6C, if the formation state of the fillet 17 can be confirmed from the side surface direction, the external electrode 15 of the planar magnetic element 11 and the wiring board 21 can be confirmed.
It is possible to confirm the solder connection state between the upper wiring terminals 22.

[0011]

However, in practice, the area of the external electrode 15 of the planar magnetic element 11 is small, and since it is hidden on the back surface of the planar magnetic element 11, it is necessary to check the fillet as it is. I can't. Also,
The magnetic layer of the planar magnetic element 11 even if the amount of solder is increased.
Since 12 and solder have poor wettability, it is not possible to confirm fillet formation due to solder flow.

Further, in surface mounting, there is almost no gap between the planar magnetic element 11 and the wiring substrate 21 due to the demand for thinning, and the solder in the depth of the gap causes a fillet even when viewed from the side. It is difficult to confirm whether it is forming. By the way, in Japanese Unexamined Patent Publication No. 2001-244123 (“Surface-Mounted Planar Magnetic Element and Method for Manufacturing the Same”), as compared with the planar magnetic element 11 shown in FIG.
It is disclosed that the metal cap type external electrode 18 is formed as shown in FIG. If such external electrodes are soldered, it is possible to confirm the formation state of the fillet protruding outside from above the planar magnetic element 11.

However, in order to obtain the planar magnetic element of FIG. 7B, it is necessary to add a step of forming a cap on a small member called the planar magnetic element. Another problem is that the cost is high. It is an object of the present invention to provide a small planar magnetic element for planar mounting, which can easily confirm the formation state of a fillet without the problem of additional steps and cost increase.

The present invention also provides a small planar magnetic element for planar mounting, which does not require a positioning mark on the surface of the planar magnetic element and allows the mounting direction on the wiring board to be easily identified.

[0015]

Means for Solving the Problems The inventors of the present invention have made earnest studies so that a fillet hidden behind the back surface of the planar magnetic element can be confirmed at the end face of the planar magnetic element during surface mounting. It was noted that the fillet is formed so as to bulge on the side surface of the external electrode placed on the solder. Then, by configuring the side surface of the external electrode so as to coincide with the side surface of the planar magnetic element, the fillet is formed so as to bulge on the side surface of the planar magnetic element, and the appearance inspection of the fillet shape can be easily performed. .

Further, in order to confirm the formation of the fillet more surely, the fillet is formed on the three side surfaces of the planar magnetic element. That is, the present invention is a planar magnetic element having a plane coil on the surface of a lower ferrite magnetic layer, and including an upper ferrite magnetic layer on the plane coil including a gap between coil wires of the plane coil. The above problem is solved by a planar magnetic element characterized in that the external electrodes connected to the coil terminals at both ends of the planar coil are formed so as to reach three side surfaces of the planar magnetic element, respectively.

Further, the positioning mark for identifying the mounting direction is not required, and instead of the positioning mark, the positioning direction can be easily discriminated from the shape of the planar magnetic element. That is, the above problem is solved by the planar magnetic element described above, which is characterized in that the planar shape thereof is a rectangle.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION A preferred embodiment of a planar magnetic element 1 of the present invention will be described as an example with reference to FIG. The planar magnetic element 1 of the present invention includes an external electrode 5 connected to the coil terminals 3 at both ends of the planar coil 4 via connection terminals 6.
Are formed so as to reach the three side surfaces of the planar magnetic element, respectively. Here, schematic views of the side surface of the planar magnetic element 1 viewed from the A direction and the B direction are shown in (b) and (c) of FIG. 1, respectively. In addition, a C-C cross section is shown in FIG.

By the way, in order to improve the wettability of the solder to the external electrode reaching the side surface of the planar magnetic element and to make the fillet formation more reliable, as shown in FIG. You may make it form even to the side surface of the layer 2. Further, the external electrode 5 may be connected to the coil terminals 3 at both ends of the planar coil 4 through the connection terminals 6 and reach the three side surfaces of the planar magnetic element,
Instead of forming as shown in FIG. 1A, for example, it may be as shown in FIG.

In the present invention, since the external electrodes are constructed as described above, as shown in FIG. 4, the fillet 7 formed on the planar magnetic element 1 mounted on the wiring board 10 is a side surface of the planar magnetic element 1. Therefore, it is possible to easily and surely inspect the presence or absence of fillet formation. Further, since the planar magnetic element has a rectangular shape, its mounting direction can be easily identified, and troubles such as mistaking the mounting direction due to a mark reading error can be eliminated.

By the way, since the coil width of the planar coil is determined by the length of the short side of the planar magnetic element, when the planar magnetic element has a rectangular shape, a dead space in which no coil is arranged in the longitudinal direction is generated with the same coil width. become. Thus, the fact that there is a dead space on both sides in the longitudinal direction means that there is a margin to increase the coil wire width of the plane coil parallel to the short side of the plane magnetic element.

Therefore, when the width of the coil wire parallel to the short side of the plane coil in the plane magnetic element is increased, it was found that the coil DC resistance can be significantly reduced as compared with the conventional case. Based on the above findings, it is preferable to configure the planar coil embedded in the planar magnetic element of the present invention as follows. (1) The width of the coil wire of the plane coil parallel to the short side of the planar magnetic element is made wider than the width of the coil wire parallel to the long side.

The planar coil may be wound in a rectangular shape as shown in FIG. 8 (a), or may be wound in an elliptical spiral shape as shown in FIG. 8 (b). (2) In (1) above, the long side length of the planar magnetic element is a, the long side length of the middle window is f, the width of the coil wire parallel to the long side is d, the coil wire interval is s, and When the number of turns is n, the width e of the coil wire parallel to the short side satisfies the following expression d <e ≦ (af−s) / 2n (see FIG. 9).

By making the width of the coil wire parallel to the short side as wide as space allows, the resistance of the entire coil can be reduced accordingly. However, if the width of the coil wire becomes too wide, in other words, the distance between the coil wires becomes too narrow, the magnetic flux across the upper and lower ferrite magnetic layers will cross the coil, resulting in an increase in eddy current loss.

Therefore, by defining an appropriate range of the coil wire width parallel to the short side, a particularly good relationship can be obtained.

[0026]

EXAMPLES Examples of the planar magnetic element of the present invention will be specifically described below. _{Fe 2 O 3 / ZnO / CuO} / NiO =
Polyimide was spin-coated on a ferrite substrate having a composition of 49/23/12/16 (mol%), flattened, and thermally cured. Next, a Cu film having a thickness of 0.5 μm was formed on the polyimide film by an electroless plating method to form a base plating layer. Then, a photoresist was applied to the Cu film and the coil pattern was photoetched to form a spiral coil resist frame having a line width of 50 μm, a line interval of 30 μm, a thickness of 110 μm, and 20 turns. Next, electroplating was performed to deposit Cu in the resist frame, the resist frame was peeled off, and the flat coil was completed by removing the plating base between the coils by wet etching. An epoxy resin paste containing ferrite magnetic powder was screen-printed so as to fill the space between the coils of the plane coil and further cover the upper part, and heat cured at 150 ° C. Here, the coil terminal portion is provided with a contact hole for connection with an external electrode. The composition of the ferrite magnetic powder mixed in the epoxy resin paste is Fe ₂ O ₃ / ZnO / CuO / NiO.
= 49/23/12/16 (mol%).

The magnetic element portion is formed by the above steps. Then, using a pre-patterned screen, a conductive paste containing Ag is printed on the surface of the magnetic element portion and heat-cured at 150 ° C. to form an external electrode. Here, in the present invention, the two external electrodes are formed so as to reach the three side surfaces of the planar magnetic element, respectively.

Next, the mounting of the completed planar magnetic element on the wiring board will be described. In advance, cream solder is printed on the wiring terminals, which are the connecting portions on the wiring board. Next, the planar magnetic element is placed on the wiring board. Here, the mounting direction of the planar magnetic element can be easily determined from the rectangular shape. Then, reflow processing is performed and soldering is performed, and mounting is completed. Whether or not the mounted planar magnetic element is soldered can be easily determined by observing the fillets formed in each of the three directions on the end surface of the planar magnetic element.

[0029]

By applying the planar magnetic element of the present invention, the appearance of the fillet can be easily inspected. Then, it becomes possible to easily and surely determine whether the soldering is acceptable or not. Also, it is not necessary to mark the surface of the planar magnetic element.

According to the present invention, the manufacturing process of the planar magnetic element can be reduced and the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic view showing a preferred embodiment of a planar magnetic element of the present invention.

FIG. 2 is a schematic view showing another embodiment of the planar magnetic element of the present invention.

FIG. 3 is a schematic view showing an example of external wiring of the planar magnetic element of the present invention.

FIG. 4 is a schematic view showing a state of a fillet when the planar magnetic element of the present invention is mounted on a wiring board.

FIG. 5 is a schematic diagram showing an example of a conventional planar magnetic element.

FIG. 6 is a schematic view showing a state of a fillet when a conventional planar magnetic element is mounted on a wiring board.

FIG. 7 is a schematic diagram showing a cap-type external electrode mounted on a conventional planar magnetic element.

FIG. 8 is a schematic view showing another example of the coil shape inside the planar magnetic element of the present invention.

FIG. 9 is an explanatory diagram defining each dimension inside the planar magnetic element of the present invention.

[Explanation of symbols]

1 Planar magnetic element (of the invention) 2,12 magnetic layer 2a, 12a Lower ferrite magnetic layer (magnetic substrate) 2b, 12b Upper ferrite magnetic layer (magnetic film) 3, 13 coil terminals 4,14 plane coil 5, 15 External electrode 6 connection terminals 7, 17 (solder) fillet 10, 21 wiring board 11 (Conventional) planar magnetic element 18 (Cap type) External electrode 20 Positioning mark 22 Wiring terminal

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hideaki Kohioki             1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Made in Kawasaki             Technical Research Institute of Iron Co., Ltd. F-term (reference) 5E043 EB01

Claims (2)

[Claims] 1. A planar magnetic element having a plane coil on the surface of a lower ferrite magnetic layer, and including an upper ferrite magnetic layer on the plane coil including a gap between coil wires of the plane coil. A planar magnetic element, wherein external electrodes connected to coil terminals at both ends of the planar coil are formed so as to reach three side surfaces of the planar magnetic element. 2. The planar magnetic element according to claim 1, wherein the planar shape is a rectangle.