BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a non-reciprocal circuit element and, more particularly, to a non-reciprocal circuit element of a surface mount type having a structure in which a magnetic rotator is mounted on a substrate.

Description of Related Art

A non-reciprocal circuit element such as an isolator or a circulator which is a kind of a magnetic device has a structure in which a necessary component such as a magnetic rotator is incorporated in a magnetic metal case functioning as a yoke. The magnetic metal case functions also as a grounding member and can thus be used as an external terminal for grounding. However, in this case, a signal input/output terminal needs to be formed separately, and a structure allowing an electrical signal to be drawn outside the magnetic metal case is required. That is, the signal input/output terminal needs to be led outside by penetrating the magnetic metal case constituting the bottom part of a product.

As a method of forming the external terminal, JP 2002-141709A states that a conductive magnetic body is insertion-molded in an insulating resin, in the course of which an external terminal is formed so as to stride over the bottom surface of the magnetic metal case in the thickness direction thereof. However, the conventional non-reciprocal circuit element described in JP 2002-141709A, in which a resin case including the external terminal is formed by insertion molding, has thus a complicated structure.

On the other hand, the non-reciprocal circuit element described in JP 2015-50689A has a structure in which a substrate mounting thereon a magnetic rotator is sandwiched by an upper yoke and a lower yoke, and a part of the lower surface of the substrate, at which a terminal electrode is formed, is exposed from the lower yoke. This makes it possible to achieve a configuration allowing the terminal electrode to be easily led outside the magnetic metal case without using the resin case or the like.

However, since the non-reciprocal circuit element described in JP 2015-50689A has a structure in which the lower yoke goes around to the lower surface of the substrate from the side surface thereof, so that it is necessary to reduce the thickness of a part of the substrate that is covered with the lower yoke and, conversely, to increase the thickness of a part of the substrate that is exposed from the lower yoke. This involves advanced machining technology for machining the substrate, making it difficult to reduce manufacturing cost.

SUMMARY

It is therefore an object of the present invention is to reduce manufacturing cost of a non-reciprocal circuit element of a surface mount type having a structure in which a magnetic rotator is mounted on a substrate by simplifying the shape of the substrate.

A non-reciprocal circuit element according to the present invention includes a substrate, a magnetic metal layer provided on the lower surface of the substrate, a magnetic rotator provided on the upper surface of the substrate, and a permanent magnet for applying a magnetic field to the magnetic rotator. The magnetic metal layer has a lower yoke provided at a position overlapping the magnetic rotator in a plan view and a plurality of terminal electrodes connected to the magnetic rotator.

According to the present invention, the magnetic metal layer provided on the lower surface of the substrate functions as the lower yoke and terminal electrodes, thus eliminating the need for the lower yoke to go around to the lower surface of the substrate from the side surface thereof. This in turn eliminates such a machining process as locally thinning the thickness of the substrate, thereby allowing reduction in manufacturing cost. In addition, the lower yoke and the terminal electrodes constitute the same plane, so that when the non-reciprocal circuit element is mounted on a motherboard, no interference occurs between the lower yoke147and the motherboard.

In the present invention, the magnetic metal layer may be made of a magnetic metal material having iron as a main component. Thus, the magnetism and conductivity of the magnetic metal material can be utilized by the lower yoke, and terminal electrodes, respectively.

In the present invention, the substrate may have a through hole formed at a position overlapping the lower yoke, the magnetic rotator may include a ferrite core, and the ferrite core may be inserted into the through hole so as to overlap the lower yoke. With this configuration, the substrate is not interposed between the magnetic rotator and the lower yoke, allowing higher magnetic characteristics to be obtained. In addition, the ferrite core is inserted into the through hole, allowing the height of the non-reciprocal circuit element to be reduced.

In this case, the magnetic rotator may further include a laminated structure body having a plurality of center conductors and a plurality of insulating layers which are laminated alternately and having, on one surface thereof, a plurality of connection patterns connected to the plurality of center conductors, a plurality of wiring patterns may be formed on the upper surface of the substrate, and the laminated structure body may be mounted on the upper surface of the substrate such that it covers the through hole and that the plurality of connection patterns and the plurality of wiring patterns are mutually connected. With this configuration, the laminated structure body including the center conductor can be surface-mounted on the substrate, thus allowing reduction in manufacturing cost.

Further, in this case, the laminated structure body may include a first insulating layer, a first center conductor formed on one surface of the first insulating layer, a second center conductor formed on the other surface of the first insulating layer, a second insulating layer laminated on the first insulating layer so as to cover the second center conductor, a third center conductor formed on the surface of the second insulating layer, and first, second, and third connection patterns formed on the one surface of the first insulating layer and connected respectively to one ends of the first, second, and third center conductors, the plurality of wiring patterns may include first, second, and third wiring patterns connected respectively to the first, second, and third connection patterns, and the plurality of terminal electrodes may include first, second, and third terminal electrodes connected respectively to the first, second, and third wiring patterns. This eliminates the need for a process of folding the center conductor and thus allows a further reduction in manufacturing cost. In addition, the three center conductors are each formed on the surface of the insulating layer, enhancing pattern accuracy and allowing a plurality of the laminated structure bodies to be collectively produced at a time using an aggregate substrate.

Further, in this case, the laminated structure body may further include fourth, fifth, and sixth connection patterns formed on the one surface of the first insulating layer and connected respectively to the other ends of the first, second, and third center conductors, the plurality of wiring patterns may include fourth, fifth, and sixth wiring patterns connected respectively to the fourth, fifth, and sixth connection patterns, and the lower yoke may be connected to the fourth, fifth, and sixth wiring patterns. With this configuration, the lower yoke can be used as a ground terminal.

Further, in this case, the non-reciprocal circuit element may further include first, second, and third capacitors mounted on the upper surface of the substrate, and the lower yoke may be connected to the first, second, and third wiring patterns respectively through the first, second, and third capacitors. With this configuration, a predetermined capacitance can be given to the first, second, and third terminal electrodes.

The non-reciprocal circuit element according to the present invention may further include an upper yoke that covers the upper surface of the substrate so as to house therein the magnetic rotator and the permanent magnet, and the upper yoke may be fixed to the lower yoke. With this configuration, the magnetic rotator and the permanent magnet can be housed in a space formed between the substrate having the lower yoke thereon and the upper yoke.

In this case, the upper yoke may include a top plate part that covers the magnetic rotator and the permanent magnet from the upper side and first and second side plate parts that face each other and cover the magnetic rotator and the permanent magnet from the side, the end portion of the first side plate part may be fixed to one end of the lower yoke, and the end portion of the second side plate part may be connected to the other end of the lower yoke. With this configuration, a magnetic circuit can be constituted by the upper and lower yokes.

Further, in this case, the upper yoke may further include third and fourth side plate parts that face each other and cover the magnetic rotator and the permanent magnet from the side, and the third and fourth side plate parts may have first and second plate spring parts that sandwich the permanent magnet and bias it. With this configuration, the permanent magnetic before magnetization can be held inside the upper yoke, thus eliminating the need for a tentative magnetization process which is performed for preventing coming-off of the non-magnetized permanent magnet.

As described above, according to the present invention, in the non-reciprocal circuit element of a surface mount type having a structure in which the magnetic rotator is mounted on the substrate, the shape of the substrate is simplified, thus allowing reduction in manufacturing cost.

