Inductor devices – Coil or coil turn supports or spacers – Printed circuit-type coil
Reexamination Certificate
2001-02-23
2004-12-14
Mai, Anh (Department: 2832)
Inductor devices
Coil or coil turn supports or spacers
Printed circuit-type coil
C336S232000, C336S223000
Reexamination Certificate
active
06831543
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface mounting type planar magnetic device and production method thereof.
2. Description of the Related Art
In recent years, use of portable apparatuses driven by battery such as mobile phone and notebook-type personal computer has been accelerated. Since before, reduction of the weight and size of such portable apparatuses has been demanded and in addition to this demand, recently, higher functions such as communication function, display function and high-speed processing function for a large amount of information including image data have been also requested. Correspondingly, a demand for a power supply capable of transforming a single voltage from a battery to voltage levels necessary for various mounted devices such as CPU, LCD module, and communication power amplifier has been increased. Thus, to achieve the higher function as well as reduction of the size and weight, it has been an important theme to accelerate reductions of the size and thickness of such a magnetic device as transformer and inductor and the like to be mounted on the power supply.
Under this condition, a transformer or an inductor composed of sintered ferrite wound with coil is loaded on the conventional small portable apparatus. However, these components are difficult to thin thereby obstructing thinning of a power supply unit. A planar inductor composed of metal magnetic film layer, insulating layer, planar coil layer, insulating layer and metallic magnetic film layer on Si substrate in order to reduce the size and weight thereof has been described in Journal of the Magnetic Society of Japan 20(1996), pp. 922-924 and disclosed in Japanese Patent Application Laid-Open No. 4-363006. However, these conventional planar inductors have problems in terms of production cost and characteristic. That is, because metal magnetic film of 6 to 7 &mgr;m is formed by spattering method and an insulating layer needs to be formed between the metal magnetic film and the planar coil, production cost for the planar inductor is sure to rise with respect to the conventional magnetic device.
The problems in terms of the characteristic are as follows. Because the planar inductor is driven by high frequency in MHz band, power loss is increased by generation of eddy current inside metal magnetic film which is electrically conductive. As for another characteristic problem, because upper and lower metal magnetic layers oppose each other through a slight nonmagnetic space, vertical alternate magnetic flux intersects the planar coil, so that eddy current is generated thereby increasing power loss. For the former, it has been proposed to divide the eddy current to small parts by forming a high resistance region on the same plane as the metal magnetic film according to Japanese Patent Application Laid-Open No. 6-77055 and for the latter, it has been proposed to divide the planar coil conductor to small parts according to Japanese Patent Application Laid-Open No. 9-134820 in order to improve the characteristics. However, it cannot be said that the characteristics have been improved sufficiently.
To solve these problems, Japanese Patent Application Laid-Open No. 11-26239 has disclosed a planar magnetic device employing a ferrite magnetic film formed by printing method or sheet method instead of the metal magnetic film. According to this method, magnetic paste produced by mixing binder with ferrite powder is printed on Si substrate and baked so as to produce a high resistance ferrite magnetic film. After a coil pattern is formed on this film by the plating method, ferrite magnetic film is formed thereon so as to produce a magnetic device. However, this publication has not disclosed an external electrode which is a feature of the present invention, and further surface mount technology (SMT) cannot be applied.
SUMMARY OF THE INVENTION
According to the conventional technology, because wire bonding method is employed to connect wires to a wired substrate, surface mount technology (SMT) cannot be applied, thereby leading to increase of production cost. The present invention intends to eliminate defects of the conventional technology and provide a surface mounting type magnetic device which achieves excellent characteristics at low cost. Concrete subjects of the present invention are as follows.
(a) Planar magnetic device capable of being thinned and mounted on the surface of a printed board
(b) Planar magnetic device having small power loss and large inductance
(c) Excellent frequency characteristic, small disparity of the characteristic and excellent reliability
The inventors had considered means for solving the above described problems sincerely and finally, completed the present invention by employing the following means. The concrete means will be described in details separately. These means are effective even if they are used independently and further a more conspicuous effect can be obtained by combining two or more means.
According to a first embodiment of the present invention, there is provided a surface mounting type planar magnetic device comprised of upper ferrite magnetic film, lower ferrite magnetic film and a planar coil interposed therebetween, in which an opening is formed in the upper ferrite magnetic film above the planar coil terminal portion and an external electrode conductive with the coil terminal portion through the opening is formed on the upper ferrite magnetic film.
The conventional planar magnetic device has a substrate for supporting the magnetic film and coil, which occupy most thickness of the device. According to the present invention, by composing the structure of the planar magnetic device with lower ferrite magnetic film, planar coil, upper ferrite magnetic film and external electrode while removing the substrate, the planar magnetic device can be thinned further. Further, because an external electrode is provided, the surface mount technology can be applied. An example of production of a magnetic device free of the substrate (substrate free magnetic device) will be described. This is just an example and the present invention is not restricted to this example. Lower ferrite magnetic film containing Cu is formed on a Si substrate and consequently, a planar coil, upper ferrite magnetic film and external electrode are formed. After that, if this is left under constant temperature and humidity of 90° C., 95% RH (Relative Humidity) for more than 10 hours, for example, the ferrite magnetic film and substrate can be separated through an interface therebetween, so that the substrate free magnetic device can be obtained. If there occurs a trouble of handling upon actual use because it is too thin, this can be formed as a substrate provided magnetic device like conventionally and by adding an external electrode to this, the surface mounting type magnetic device may be produced.
According to a second embodiment of the present invention, there is provided a surface mounting type planar magnetic device wherein a lower ferrite magnetic film is formed on a substrate; a planar coil is formed on the lower ferrite magnetic film; an upper ferrite magnetic film having an opening above a terminal portion of the planar coil is formed; and an external electrode conductive with the planar coil terminal portion is formed. In this case, any substrate material can be used if it achieves a function as a supporting body. It is more preferable to use Si substrate or Al
2
O
3
(alumina) substrate which are used in semiconductor industry in terms of cost performance.
In the surface mounting type planar magnetic device of the present invention, preferably, the planar coil is a spiral coil or a combination of plural spiral coils connected in series. Further, the planar coil is preferred to be composed of Cu conductor. The reasons will be described below.
Although for example, spiral type, meander type and the like can be employed for the planar coil, the spiral type is preferable because it is capable of achieving a larger inductance. Further, by arra
Fukuda Yasutaka
Inoue Tetsuo
Mizoguchi Tetsuhiko
Tachi Yoshihito
Yatabe Shigeru
Kawatetsu Mining Co. Ltd.
Mai Anh
Oliff & Berridg,e PLC
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