Patent Publication Number: US-7915971-B2

Title: Nonreciprocal circuit device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a nonreciprocal circuit device, and particularly, to a nonreciprocal circuit device, such as an isolator or a circulator, used in a microwave band, and also to a manufacturing method of the nonreciprocal circuit device. 
     2. Description of the Related Art 
     Nonreciprocal circuit devices, such as an isolator and a circulator, have characteristics to transmit signals only in a specific direction but not in the direction opposite thereto. By using these characteristics, for example, isolators are used in transmission circuit portions of mobile communication apparatuses, such as an automobile phone and a mobile phone. 
     In International Publication WO 2007/046229, a nonreciprocal circuit device is disclosed in which a first central electrode and a second central electrode are wound around a substantially rectangular parallelepiped ferrite in an electrically insulated manner so as to intersect each other, a pair of permanent magnets is disposed on two primary surfaces of the ferrite to define a ferrite-magnet assembly so as to apply a direct current magnetic field to the ferrite, and side portions of the ferrite-magnet assembly mounted on a circuit board are surrounded by a yoke. 
     However, in the nonreciprocal circuit device disclosed in International Publication WO 2007/046229, although the periphery of the ferrite-magnet assembly is surrounded by the yoke, since a cavity is provided around the periphery, the device described above is unfavorably influenced by humidity. In addition, since the side portions of the ferrite-magnetic assembly are surrounded by the yoke, the number of components is increased, and a manufacturing process is complicated. 
     SUMMARY OF THE INVENTION 
     To overcome the problems described above, preferred embodiments of the present invention provide a nonreciprocal circuit device which eliminates the adverse influence of humidity and which can be efficiently manufactured and, a manufacturing method for the nonreciprocal circuit device. 
     According to a preferred embodiment of the present invention, a nonreciprocal circuit device includes a ferrite-magnet element which includes ferrite having two primary surfaces on which central electrodes are arranged to intersect each other in an electrically insulated manner and a pair of permanent magnets arranged on the two primary surfaces of the ferrite so as to apply a direct current magnetic field to the ferrite, a substrate having a surface to which the ferrite-magnet element is bonded so that the two primary surfaces of the ferrite are perpendicular or substantially perpendicular to the surface of the substrate, a flat plate yoke arranged to cover a top surface of the ferrite-magnet element, a first resin layer which is disposed at least at a bonding portion of the ferrite-magnet element bonded to the substrate and which is a cured liquid resin, and a second resin layer which is adhered to a rear surface of the flat plate yoke and which is a cured soft sheet-shaped resin. 
     According to another preferred embodiment of the present invention, a manufacturing method for a nonreciprocal circuit device includes the steps of bonding a ferrite-magnet element, which includes ferrite having two primary surfaces on which central electrodes are arranged to intersect each other in an electrically insulated manner and a pair of permanent magnets arranged on the two primary surfaces of the ferrite so as to apply a direct current magnetic field to the ferrite, to a surface of a substrate so that the two primary surfaces of the ferrite are arranged perpendicular or substantially perpendicular to the surface of the substrate, disposing a liquid resin at a bonding portion of the ferrite-magnet element bonded to the substrate, followed by curing to form a first resin layer, and disposing a flat plate yoke provided with a soft sheet-shaped resin adhered to a rear surface thereof on a top surface of the ferrite-magnet element, and after the soft sheet-shaped resin is softened, curing the soft sheet-shaped resin to form a second resin layer. 
     According to preferred embodiments of the present invention, since the periphery of the ferrite-magnet element is sealed with the first and second resin layers, the influence of humidity is eliminated. Since the permanent magnets are provided on the respective primary surfaces of the ferrite which is provided with the central electrodes, a yoke surrounding the side portions of the ferrite is not always required. In addition, the first and second resin layers can be easily formed, respectively, by automatically applying a liquid resin and by pressing and softening a sheet-shaped resin adhered to the flat plate yoke. Furthermore, when the substrates and the flat plate yokes are manufactured in the form of a mother substrate, manufacturing can be efficiently performed using a multiple-elements forming method. 
     Other features, elements, steps, processes, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view showing a nonreciprocal circuit device (e.g., two-port isolator) according to a first preferred embodiment of the present invention. 
         FIG. 2  is a perspective view showing a ferrite provided with central electrodes. 
         FIG. 3  is a perspective view showing a base body of the ferrite. 
         FIG. 4  is an exploded perspective view showing a ferrite-magnet element. 
         FIG. 5  is an equivalent circuit diagram showing one circuit example of a two-port isolator. 
         FIG. 6  is a cross-sectional view of the nonreciprocal circuit device taken along the line A-A shown in  FIG. 1 . 
         FIGS. 7A to 7D  are cross-sectional views showing a manufacturing process for the nonreciprocal circuit device taken along the line B-B shown in  FIG. 1 . 
         FIG. 8  is an exploded perspective view showing a nonreciprocal circuit device (e.g., two-port isolator) according to a second preferred embodiment of the present invention. 
         FIG. 9  is a cross-sectional view of the nonreciprocal circuit device taken along the line A-A shown in  FIG. 8 . 
         FIGS. 10A to 10D  are cross-sectional views each showing a manufacturing process for the nonreciprocal circuit device taken along the line B-B shown in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of a nonreciprocal circuit device and a manufacturing method thereof according to the present invention will be described with reference to the accompanying drawings. 
     First Preferred Embodiment 
       FIG. 1  is an exploded perspective view showing a two-port isolator  1  according to the first preferred embodiment of a nonreciprocal circuit device of the present invention. This two-port isolator  1  preferably is a lumped constant isolator and includes a flat plate yoke  10 , a substrate  20 , a ferrite-magnet element  30  composed of ferrite  32  and a pair of permanent magnets  41 , a first resin layer  50 , and a second resin layer  60 . 
     As shown in  FIG. 2 , a first central electrode  35  and a second central electrode  36 , which are electrically insulated from each other, are arranged on a front first primary surface  32   a  and a rear second primary surface  32   b  of the ferrite  32 . In this preferred embodiment, the ferrite  32  is a substantially rectangular parallelepiped having the first primary surface  32   a  and the second primary surface  32   b , which are parallel or substantially parallel to each other. 
     In addition, the permanent magnets  41  are adhered to the primary surfaces  32   a  and  32   b  of the ferrite  32  with epoxy adhesives  42  provided therebetween so as to apply a direct current magnetic field to the primary surfaces  32   a  and  32   b  in a direction perpendicular or substantially perpendicular thereto (see  FIG. 4 ), so that the ferrite-magnet component  30  is provided. Primary surfaces  41   a  of the permanent magnets  41  each have the same or substantially the same dimension as that of each of the primarily surfaces  32   a  and  32   b  of the ferrite  32  and are arranged to face the respective primary surfaces  32   a  and  32   b  so that their peripheries coincide or substantially coincide with each other. 
     The first central electrode  35  is made of a conductive film. That is, as shown in  FIG. 2 , the first central electrode  35  is arranged from a right bottom side of the first primary surface  32   a  of the ferrite  32 , is extended while being divided into two portions to a left top side at a relatively low inclined angle with respect to a long side of the first primary surface  32   a , is then extended to the second primary surface  32   b  through an interconnection electrode  35   a  provided on a top surface  32   c , and is arranged on the second primary surface  32   b  while being divided into two portions so as to be overlapped with the central electrode  35  on the first primary surface  32   a  through the ferrite  32 , and one end of the first central electrode  35  is then connected to a connection electrode  35   b  provided on a bottom surface  32   d . In addition, the other end of the first central electrode  35  is connected to a connection electrode  35   c  provided on the bottom surface  32   d . As described above, the first central electrode  35  is wound one turn around the ferrite  32 . In addition, the first central electrode  35  and the second central electrode  36  which will be described below intersect each other so as to be insulated from each other with an insulating film provided therebetween. The intersection angle between the central electrodes  35  and  36  is determined in accordance with requirements, so that input impedance and insertion loss are adjusted. 
     The second central electrode  36  is preferably made of a conductive film. The second central electrode  36  includes a first half turn portion  36   a  arranged obliquely on the first primary surface  32   a  from the right bottom side to the left top side at a relatively large angle with respect to the long side of the first primary surface  32   a  so as to intersect the first central electrode  35  and is extended to the second primary surface  32   b  through an interconnection electrode  36   b  provided on the top surface  32   c , and a first turn portion  36   c  extended from the first half turn portion  36   a  is provided on the second primary surface  32   b  so as to perpendicularly or substantially perpendicularly intersect the first central electrode  35 . A lower end portion of the first turn portion  36   c  is extended to the first primary surface  32   a  through an interconnection electrode  36   d  provided on the bottom surface  32   d , and a first-and-half turn portion  36   e  extended from the first turn portion  36   c  is provided on the first primary surface  32   a  parallel or substantially parallel to the first half turn portion  36   a  so as to intersect the first central electrode  35  and is extended to the second primary surface  32   b  through an interconnection electrode  36   f  provided on the top surface  32   c . Subsequently, in the same manner as described above, a second turn portion  36   g , an interconnection electrode  36   h , a second-and-half turn portion  36   i , an interconnection electrode  36   j , a third turn portion  36   k , an interconnection electrode  36   l , a third-and-half turn portion  36   m , an interconnection electrode  36   n , and a fourth turn portion  36   o  are provided on the surfaces of the ferrite  32 . In addition, the two ends of the second central electrode  36  are connected to the connection electrode  35   c  and a connection electrode  36   p  provided on the bottom surface  32   d  of the ferrite  32 . As described above, the connection electrode  35   c  is used as the connection electrodes at the end portions of the first and the second central electrodes  35  and  36 . 
     In addition, the connection electrodes  35   b ,  35   c , and  36   p  and the interconnection electrodes  35   a ,  36   b ,  36   d ,  36   f ,  36   h ,  36   j ,  36   l , and  36   n  are formed by applying or filling an electrode conductor, such as silver, a silver alloy, copper, or a copper alloy, in concave portions  37  (see  FIG. 3 ) provided in the top and the bottom surfaces  32   c  and  32   d  of the ferrite  32 . Furthermore, dummy concave portions  38  are also provided in the top and the bottom surfaces  32   c  and  32   d  parallel or substantially parallel to the concave portions  37 , and dummy electrodes  39   a ,  39   b , and  39   c  are provided therein. This type of electrode is formed such that, after a through-hole is formed in advance in a mother ferrite substrate, the through-hole is filled with a conductive conductor, and the substrate is then cut so as to divide the through-hole. In addition, the connection and interconnection electrodes may preferably be made of conductive films provided in the concave portions  37  and  38 . 
     As the ferrite  32 , YIG ferrite or other suitable ferrite may preferably be used, for example. The first and second central electrodes  35  and  36  and the other electrodes may preferably be formed of a thick film or a thin film of silver or a silver alloy, for example, by a printing, a transfer, or a photolithographic method. As the insulating film provided between the central electrodes  35  and  36 , a dielectric thick film formed, for example, from glass or alumina or a resin film formed from polyimide may preferably be used, for example. These films described above may also preferably be formed, for example, by a printing, a transfer, or a photolithographic method. 
     In addition, the ferrite  32  may preferably be simultaneously fired together with the insulating film and the electrodes. In this case, the various electrodes are preferably made using Pd, Ag, or Pd/Ag, each of which can withstand high-temperature firing, for example. 
     As the permanent magnet  41 , a strontium-based, a barium-based, or a lantern-cobalt-based ferrite magnet is preferably used, for example. As the adhesive  42  which adheres the permanent magnet  41  to the ferrite  32 , a one-component type thermosetting epoxy adhesive is most preferably used, for example. 
     The substrate  20  is preferably made of the same type of material that is commonly used for a printed circuit board, for example, and the terminal electrodes  21   a  to  21   d  for soldering the connection electrodes  35   b ,  35   c , and  36   p  of the ferrite-magnet element  30  and chip type matching circuit elements CS 1  and R (see  FIG. 5 ), input and output electrodes (not shown), and a ground electrode (not shown) are provided on the surface of the substrate  20 . In addition, inside the substrate  20 , matching circuit elements C 1 , C 2 , and CS 2  (see  FIG. 5 ) are preferably defined by internal electrodes. 
     The ferrite-magnet element  30  is disposed on the substrate  20 , the connection electrodes  35   b ,  35   c , and  36 P provided on the bottom surface  32   d  of the ferrite  32  are integrally connected to the terminal electrodes  21   a ,  21   b , and  21   c  on the substrate  20  by reflow soldering, and the bottom surfaces of the permanent magnets  41  are integrally adhered to the substrate  20  with an adhesive, for example. In addition, the matching elements CS 1  and R are reflow-soldered to the terminal electrodes  21   b ,  21   c , and  21   d.    
     The flat plate yoke  10  functions as an electromagnetic shield and is adhered to the top surface of the ferrite-magnet element  30  with the second resin layer  60  provided therebetween, which will be described below. 
     One circuit example of the isolator  1  is shown by an equivalent circuit in  FIG. 5 . An input port P 1  is connected to the matching capacitor C 1  and the terminal resistance R through the matching capacitor CS 1 , and the matching capacitor CS 1  is connected to one end of the first central electrode  35 . The other end of the first central electrode  35  and one end of the second central electrode  36  are connected to the terminal resistance R and the capacitors C 1  and C 2  and are further connected to an output port P 2  through the capacitor CS 2 . The other end of the second central electrode  36  and the capacitor C 2  are connected to a ground port P 3 . 
     In the two-port isolator  1  having the above-described equivalent circuit, one end of the first central electrode  35  is connected to the input port P 1 , the other end is connected to the output port P 2 , one end of the second central electrode  36  is connected to the output port P 2 , and the other end is connected to the ground port P 3 . Thus, a two-port lumped constant isolator having a low insertion loss is provided. In addition, during operation, a large high-frequency current flows through the second central electrode  36 , and a high-frequency current does not significantly flow through the first central electrode  35 . 
     In addition, since the ferrite  32  and a pair of the permanent magnets  41  are integrated with the adhesives  42  to define the ferrite-magnet element  30 , the mechanical properties thereof are stabilized, and thus, a robust isolator that is not deformed or damaged by vibration and/or impact is obtained. 
     Next, the first and second resin layers  50  and  60  will be described. As shown in  FIGS. 6 and 7B , the first resin layer  50  is a liquid thermosetting resin (such as a fine-grain epoxy resin) at room temperature disposed at bonding portions of the ferrite-magnet element  30  bonded to the substrate  20 , and after being applied to the bonding portions, the liquid thermosetting resin is cured by heating. In  FIGS. 6 and 7A  to  7 D, reference numeral  55  indicates bonding solder for the matching elements CS 1  and R, and reference numeral  56  indicates bonding solder for the connection electrodes  35   b ,  35   c , and  36   p  of the ferrite-magnet element  30 . 
     As shown in  FIG. 7C , the second resin layer  60  is formed from a soft sheet-shaped thermosetting resin  60 ′ (such as an epoxy resin) adhered to a rear surface of a mother yoke  10 ′, which is a base material for the flat plate yokes  10 , and is obtained such that the thermosetting resin  60 ′ is disposed on the surface of the substrate  20  while pressure is applied, is then softened, and is finally cured. 
     Next, a manufacturing process for the isolator  1  according to the first preferred embodiment including the steps of forming the first and the second resin layers  50  and  60  will be described. 
     First, a plurality of the ferrite-magnet elements  30  is bonded to a surface of a mother substrate  20 ′ in a matrix so that the primary surfaces  32   a  and  32   b  of each ferrite  32  are disposed perpendicular or substantially perpendicular to the surface of the mother substrate  20 ′, and the matching elements CS 1  and R are also bonded to the surface thereof (see  FIG. 7A ). Next, a liquid resin is applied to the bonding portions of the ferrite-magnet elements  30  and the matching elements CS 1  and R which are bonded to the mother substrate  20 ′ and is then cured, so that the first resin layer  50  is formed (see  FIG. 7B ). The liquid resin is a liquid at room temperature and is cured, for example, by heating at approximately 165° C. for approximately 90 minutes. The first resin layer  50  is filled in gaps formed on the surface of the substrate  20 ′ between the solder bonding portions of the ferrite-magnet elements  30  and the matching circuit elements CS 1  and R. 
     Next, as shown in  FIG. 7C , after the mother yoke  10 ′ provided with the soft sheet-shaped resin  60 ′ which is adhered on the rear surface thereof is disposed on the upper surfaces of the ferrite-magnet elements  30 , the soft sheet-shaped resin  60 ′ is softened and is then cured, so that the second resin layer  60  is formed. The soft sheet-shaped resin  60 ′ is softened and is then cured by heating at approximately 150° C. for approximately 180 minutes while pressure is applied. When being softened, the soft sheet-shaped resin  60 ′ enters gaps formed between the ferrite-magnet elements  30  and the matching circuit elements CS 1  and R and seals these elements from the outside (see  FIG. 7D ). 
     In particular, the step of forming the second resin layer  60  is performed such that an oven in which an inside pressure can be set at a high level is used, and the inside pressure of the oven is increased, for example, to approximately 4 to 5 atmospheric pressure. 
     Subsequently, the mother substrate  20 ′ and the mother yoke  10 ′ are cut together along the dotted lines Y shown in  FIG. 7D , and each unit obtained by cutting is used as the isolator  1 . In this step, cutting is also performed for each unit in a direction perpendicular or substantially perpendicular to the dotted lines Y. 
     As described above, according to this first preferred embodiment, since the periphery of the ferrite-magnet element  30  is sealed with the first and the second resin layers  50  and  60 , the influence of humidity is eliminated. Since the permanent magnets  41  are provided on the first and second primary surfaces  32   a  and  32   b  of the ferrite  32  which is provided with the central electrodes  35  and  36 , a yoke surrounding the side portions of the ferrite  32  is not always necessary. In addition, the first and the second resin layers  50  and  60  can be easily formed, respectively, by automatically applying a liquid resin and by applying a pressure to the sheet shaped resin  60 ′ adhered to the mother yoke  10 ′, followed by softening. Furthermore, since the substrates  20  and the flat plate yokes  10  are formed from the mother substrate  20 ′ and the mother yoke  10 ′, respectively, manufacturing can be efficiently performed by a multiple-elements forming method. 
     In particular, according to the first preferred embodiment, since the first resin layer  50  is formed at the bonding portions so as to have a relatively small thickness, the volume of a relatively expensive liquid resin can be decreased, and the mother substrate  20 ′ does not warp as the liquid resin is cured. 
     Second Preferred Embodiment 
       FIG. 8  is an exploded perspective view showing a two-port isolator  2  according to the second preferred embodiment of the nonreciprocal circuit device of the present invention. Since the two-port isolator  2  has substantially the same structure as that of the first preferred embodiment, the same elements and portion as those of the first preferred embodiment are designated by the same reference numerals, and a duplicated description will be omitted. The differences from the first preferred embodiment are that the first resin layer  50  has a relatively large thickness and the second resin layer  60  has a relatively small thickness. 
     That is, as shown in  FIG. 9 , the first resin layer  50  extends from the surface of the substrate  20  to the upper surface of the ferrite-magnet element  30  including the bonding portions of the ferrite-magnet element  30  and the matching circuit elements CS 1  and R which are bonded to the substrate  20 . The second resin layer  60  extends between the flat plate yoke  10  and the upper surface of the ferrite-magnet element  30 . 
     In a manufacturing process, first, a plurality of the ferrite-magnet elements  30  is bonded to the surface of the mother substrate  20 ′ in a matrix so that the two primary surfaces  32   a  and  32   b  of the ferrite  32  are arranged perpendicular or substantially perpendicular to the surface of the mother substrate  20 ′, and the matching circuit elements CS 1  and R are also bonded to the surface thereof (see  FIG. 10A ). Next, a liquid resin is applied from the surface of the mother substrate  20 ′ to the upper surfaces of the ferrite-magnet elements  30  and is then cured, so that the first resin layer  50  is formed (see  FIG. 10B ). The height of the ferrite-magnet element  30  is approximately 0.5 mm, and the liquid resin does not flow out of end portions of the mother substrate  20 ′ and enters gaps between the ferrite-magnet elements  30 . The heating temperature and the heating time for the liquid resin are approximately equivalent to those of the first preferred embodiment. 
     Subsequently, as shown in  FIG. 10C , after the mother yoke  10 ′ provided with the soft sheet-shaped resin  60 ′ which is adhered to the rear surface thereof is disposed on the upper surfaces of the ferrite-magnet elements  30 , the soft sheet-shaped resin  60 ′ is softened and is then cured, so that the second resin layer  60  is formed (see  FIG. 10D ). In the step of forming the second resin layer  60 , an oven in which an inside pressure can be set at a high level may also preferably be used in the second preferred embodiment. However, since the second resin layer  60  is provided between the flat plate yoke  10  and the upper surface of the ferrite-magnet element  30 , the applied pressure, the heating temperature, and the heating time similar to those of the first preferred embodiment are not always necessary. 
     Next, the mother substrate  20 ′ and the mother yoke  10 ′ are cut together along the dotted lines Y shown in  FIG. 10D , and each unit obtained by cutting is used as the isolator  2 . In this step, cutting is also performed for each unit in a direction perpendicular or substantially perpendicular to the dotted lines Y. 
     The function and the benefits of the isolator  2  according to the second preferred embodiment substantially the same as those of the first preferred embodiment. In particular, since the periphery of the ferrite-magnet element  30  is covered with the liquid resin, gaps are not formed at the above periphery, and since the second resin layer  60  is formed on a flat upper surface of the ferrite-magnet element  30  and the first resin layer  50 , the adhesion properties are greatly improved. 
     In addition, the nonreciprocal circuit device according to the present invention and the manufacturing method thereof are not limited to the preferred embodiments described above, and any changes and modifications may be made without departing from the spirit and the scope of the present invention. 
     In particular, the configuration of the matching circuit may be arbitrarily selected and all matching circuit elements may be provided on the substrate or may be embedded therein. In addition, in the ferrite-magnet element, the ferrite and the permanent magnets may be integrally fired. 
     While preferred embodiments of the invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the invention. The scope of the invention, therefore, is to be determined solely by the following claims.