JP2005236070A - Flat surface magnetic element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flat surface magnetic element achieved in size reduction, the lowering of a back, and resistance reduction. <P>SOLUTION: The flat surface magnetic element comprises a coil terminal of a planar coil, and a connector for connecting electrically external electrodes. The connecting face of the connector by the side of the external electrodes is provided with the same face as the external electrode surface. It is preferable that the connecting area may be formed in a hollow shape. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a structure of a planar magnetic element.

  In recent years, as the use of portable devices has become active, electronic components used inside are becoming smaller, lower in profile (thinner), and lower in power consumption. In particular, for planar magnetic elements such as transformers and inductors used for power supplies and the like, it has become an important issue to reduce the size and height of the planar magnetic elements. Further, from the viewpoint of reducing power consumption, the resistance of planar magnetic elements has been reduced.

  By the way, conventionally, a method of forming an external electrode electrically connected to a planar coil of a planar magnetic element with a low-temperature curing type conductive paste such as an Ag paste has been performed (see Patent Document 1).

  Hereinafter, based on FIG. 3, the manufacturing process and structure of the conventional planar magnetic element are demonstrated easily.

  In a conventional planar magnetic element, a planar coil 1 having a coil terminal 3 is first formed on a magnetic substrate 2. Next, the upper magnetic layer 6 is formed so as to embed the planar coil 1 on the entire surface except on the coil terminal 3 (see FIG. 3A).

  Then, the external electrode 5 is formed using a low-temperature curable conductive paste such as an Ag paste (see FIG. 3B).

As described above, in the conventional method of forming the external electrode with the low temperature curing type conductive paste, the conductive paste is dropped on the coil terminal 3 to be electrically connected, and the coil terminal 3 and the external electrode 5 are electrically connected. Is required.
JP 2001-244124 A

  However, since the space on the coil terminal 3 is a closed space surrounded by the upper magnetic layer 6, even if the conductive paste is dropped, air in the space does not escape well and remains as a gap 9. There is a problem that the conductive paste cannot be uniformly connected on the coil terminals.

  For this reason, useless connection resistance is generated between the conductive paste serving as the external electrode 5 and the coil terminal 3, which increases the resistance of the planar magnetic element.

  The present invention solves the problem of unnecessary connection resistance between the external electrode and the coil terminal generated as described above, and realizes further reduction in resistance of the planar magnetic element.

  When forming the external electrode using the low-temperature curing type conductive paste, the present inventors, when the coil terminal as the connection destination is at the bottom of the space surrounded by the upper magnetic layer and recessed and closed, Focusing on the fact that the conductive paste is obstructed by the air in the space and is not uniformly connected onto the coil terminal, it is conceived that the coil terminal should be prevented from being in such a recessed bottom. Thus, the present invention has been completed.

  In other words, if the connection part that is electrically connected from the coil terminal is formed in advance and the surface of the connection part is set to the same position as the surface of the external electrode, the coil terminal can be eliminated from the recessed bottom. , I am not disturbed by the air.

  Moreover, when the present inventors investigated and examined the connection resistance between the connection portion and the external electrode in more detail, it was found that the connection resistance can be reduced by making the conductive paste as thick as possible.

  However, if the thickness of the conductive paste is simply increased, the thickness of the planar magnetic element is increased, and the low profile shape characteristic of the planar magnetic element is impaired. Therefore, as a result of earnest and examination, as a result of making the connection portion hollow and dropping the conductive paste into it, the thickness of the conductive paste is increased without increasing the external electrode thickness, As a result, the inventors have conceived that the connection resistance can be further reduced.

  That is, the present invention has a connection portion for electrically connecting the coil terminal of the planar coil and the external electrode, and the connection surface on the external electrode side of the connection portion is connected as the same surface as the external electrode surface. The above problems have been solved by the planar magnetic element.

  In the present invention, it is preferable that the connecting portion is hollow.

  In the present invention, since the connection surface on the external electrode side of the connection portion electrically connected from the coil terminal of the planar magnetic element can be made the same surface as the external electrode surface, the connection resistance between the two is greatly reduced. I was able to do it.

  Furthermore, by making the connecting portion hollow, the thickness of the conductive paste connected to the connecting portion can be substantially increased without increasing the electrode thickness of the external electrode (FIG. 2 (d)). The connection resistance can be further reduced.

  From the above, the planar magnetic element can be further reduced in resistance.

  The manufacturing process and structure of the planar magnetic element of the present invention will be briefly described based on the schematic cross-sectional views shown in FIGS. In addition, the example of a specific manufacturing process is further explained in full detail in the below-mentioned Example.

  1 and 2, reference numeral 1 is a planar coil, 2 is a magnetic substrate, 3 is a coil terminal, 4 is a connection portion, 5 is an external electrode, and 6 is an upper magnetic layer.

  In the present invention, first, as shown in FIGS. 1 (a) and 2 (a), a through hole 10 for forming a connection portion is formed at a position of a coil terminal portion of the magnetic substrate 2 by a method such as shot blasting. .

  Next, the planar coil 1 and the coil terminal 3 of the planar coil 1 are formed on the magnetic substrate 2 by a Cu electroplating method or the like. Here, Cu is also embedded in the through hole 10, but when the diameter is small, as shown in FIG. 1B, the through hole 10 is completely filled with Cu to form the connection portion 4. Become. On the other hand, when the diameter of the through hole 10 is not less than a certain level, a hollow space 11 can be left in the connecting portion 4 as shown in FIG.

  Next, as shown in FIGS. 1C and 2C, the upper magnetic layer 6 is formed on the entire surface of the planar coil 1 other than the coil terminal 3.

  Finally, as shown in FIGS. 1D and 2D, the surface of the connection portion 4 electrically connected from the coil terminal 3 on the side of the external electrode 5 is a magnetic substrate on which the external electrode 5 is formed. The external electrode 5 is formed so as to be on the same plane as 2.

  By doing so, uniform connection is possible when the external electrode 5 is formed, and a planar magnetic element realizing low resistance can be completed.

  In addition, since the closed space is eliminated, the problem of air in the space can be solved, and a uniform connection between the external electrode 5 and the coil terminal 3 can be established via the connection portion 4.

  The same surface as used herein means that the surface on the external electrode 5 side of the connecting portion 4 and the surface on the connecting portion 4 side of the external electrode 5 are overlapped and coincide with each other, or within 50 μm as shown in FIG. Say that you are located in.

  When the present inventors examined in detail the unevenness of the connection portion 4 with respect to the surface of the magnetic substrate 2, the case where the connection portion 4 is convex from the surface of the magnetic substrate 2 is positive, and the case where the connection portion 4 is concave is negative. It could be clarified that −50 μm or more is a suitable range. That is, if the connection part 4 is recessed 50 μm or more, the conductive paste cannot be connected well as in the conventional example, and the connection resistance increases (see FIG. 4).

  On the other hand, in the case of convexity, the external electrode becomes thicker by the convexity. Therefore, from the viewpoint of reducing the height, it is disadvantageous to make the convexity large, and it is preferable to overlap and match.

  In the case of FIG. 2 (d), the conductive paste enters the hollow space 11, and an external electrode penetration portion 12 made of a conductive paste portion thicker than the thickness of the external electrode is formed there. Thereby, the connection resistance can be further reduced.

  As a result of examining the hollow space 11 in detail, it was found that the inner diameter (hereinafter referred to as “hollow diameter”) is preferably 50 μm or more. That is, when the hollow diameter is smaller than 50 μm, the conductive paste is difficult to enter the hollow portion.

  Next, the present invention will be described more specifically with reference to examples.

Fe ₂ O ₃ / ZnO / CuO / NiO = 49/23/12/16 (mol%) composition ferrite substrate 100, 150, 180, and 210 μm for forming the connecting portion at the coil terminal position by shot blasting A through hole having a diameter was formed. Next, a Cu film having a thickness of 0.5 μm was formed by sputtering as a seed film for electroplating. Next, after applying a photoresist on the seed film, a spiral coil resist frame having a thickness of 90 μm and 7 turns was formed by photolithography. After depositing Cu in the resist frame by electroplating, the resist frame was peeled off, and the plating base between the coils was removed by wet etching to complete a planar coil.

  At that time, when the through-hole diameter was 100 μm, the through-hole was closed with plated Cu, resulting in a closed connection portion.

  In addition, in order to change the positional relationship between the surface of the connection portion on the side of the external electrode and the surface of the external electrode, electroplating was also performed by arbitrarily placing wax in the through hole. In this way, the distance from the external electrode surface of the connection surface on the external electrode side of the connection portion was adjusted.

  On the other hand, when the through-hole diameters were 150, 180, and 210 μm, it was possible to form a connecting portion having a hollow space with a hollow diameter of 20, 50, and 80 μm without being blocked by the plated Cu.

Thereafter, a resin ferrite paste in which magnetic powder having a composition of Fe ₂ O ₃ / ZnO / CuO / NiO = 49/23/12/16 (mol%) is mixed with a resin is screen-printed on a planar coil other than the coil terminal portion. An upper magnetic layer having a thickness of 150 μm was formed by heat curing at 150 ° C.

  Next, a low-temperature curing type conductive paste mainly composed of Ag is used on the ferrite substrate side, screen printed to form an external electrode, and thermally cured at 150 ° C. to form a 30 μm thick external electrode. A planar magnetic element was completed.

  In addition, for comparison, a conventional planar magnetic element in which the final process was performed from the upper magnetic layer side was made as a comparative example, without performing through-hole formation by shot blasting, and the intermediate process was the same as described above. .

  100 planar magnetic elements prepared as described above were prepared, and their resistances were measured and compared with average values. Table 1 shows the resistance evaluation results of the obtained planar magnetic element.

  From Table 1, it can be seen that in the planar magnetic element of the present invention provided with a connection portion electrically connected from the coil terminal, the resistance can be greatly reduced as compared with the comparative example having no connection portion.

  Furthermore, when the distance from the external electrode surface of the connection surface on the external electrode side of the connection portion is seen, it is found that the case of a recess within 50 μm is preferable.

  Moreover, it turns out that resistance is reducing further in the connection part which has a hollow space compared with the obstruct | occluded connection part. In particular, when attention is paid to the hollow diameter, the thickness is preferably 50 μm or more.

It is a cross-sectional schematic diagram explaining the manufacturing process of the planar magnetic element of this invention. It is a cross-sectional schematic diagram explaining the manufacturing process of the planar magnetic element of another aspect of this invention. It is a cross-sectional schematic diagram explaining the manufacturing process of the conventional planar magnetic element. In the planar magnetic element of this invention, it is a partial cross section schematic diagram explaining the tolerance | permissible_range of the clearance gap between a connection part and an external electrode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Planar coil 2 Magnetic substrate 3 Coil terminal 4 Connection part 5 External electrode 6 Upper magnetic layer 7 Thickness of conductive paste 8 Hollow diameter 9 Void part
10 Through hole
11 Hollow space
12 External electrode penetration

Claims (2)

  A planar magnetic element comprising a connecting portion for electrically connecting a coil terminal of a planar coil and an external electrode, wherein a connecting surface on the external electrode side of the connecting portion is connected as the same surface as the external electrode surface .   The planar magnetic element according to claim 1, wherein the connection portion is hollow.

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