Patent Publication Number: US-2022239260-A1

Title: Amplification device and matching circuit board

Description:
TECHNICAL FIELD 
     The present disclosure relates to an amplification device and a matching circuit board. 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2020-060465, filed on Mar. 30, 2020, the entire contents of which are incorporated herein by reference. 
     BACKGROUND ART 
     As a radio frequency amplification device, for example, Patent Literature 1 discloses a technology relating to an internal matching type high-output field-effect transistor. The internal matching type high-output field-effect transistor includes a package, an amplification element which amplifies a radio frequency (RF) signal on the package, an input-side matching circuit which is connected between an input end of the amplification element and an input terminal of the package and performs impedance conversion, and an output-side matching circuit which is connected between an output end of the amplification element and an output terminal of the package and performs impedance conversion. 
     CITATION LIST 
     Patent Literature 
     [Patent Literature 1] Japanese Unexamined Patent Publication No. S63-86904 
     SUMMARY OF INVENTION 
     One aspect of the present disclosure relates to an amplification device. This amplification device includes a base substrate, an amplification element, and a matching circuit board. The amplification element is mounted on the base substrate. The matching circuit board is mounted on the base substrate and includes a circuit pattern which is electrically connected to the amplification element. The matching circuit board includes a first side surface and a second side surface each extending in a longitudinal direction of the matching circuit board. A first recess is provided in the first side surface. A second recess facing the first recess is provided in the second side surface. 
     Another aspect of the present disclosure relates to a matching circuit board. This matching circuit board can be mounted on the base substrate and includes a circuit pattern to perform impedance conversion. The matching circuit board includes a first side surface and a second side surface each extending in a longitudinal direction of the matching circuit board. A first recess is provided in the first side surface. A second recess facing the first recess is provided in the second side surface. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a plan view showing an internal configuration of a radio frequency amplification device according to an embodiment. 
         FIG. 2  is a cross-sectional view of the radio frequency amplification device along line II-II of  FIG. 1 . 
         FIG. 3A  is a plan view showing a matching circuit on the input side shown in  FIG. 1 . 
         FIG. 3B  is a plan view showing a matching circuit on the output side shown in  FIG. 1 . 
         FIG. 4  is a perspective view showing a part of a radio frequency amplification device according to a comparative example. 
         FIG. 5A  is a cross-sectional view of the radio frequency amplification device along line VA-VA of  FIG. 4 . 
         FIG. 5B  is a diagram for explaining a state in which a matching circuit of  FIG. 5A  is affected by a temperature change. 
         FIG. 6  is a diagram showing a stress distribution state of a dielectric substrate according to the comparative example. 
         FIG. 7  is a diagram showing a stress distribution state of a dielectric substrate according to the present embodiment. 
         FIG. 8  is a plan view showing a matching circuit according to the modified example. 
         FIG. 9  is a diagram showing a stress distribution state of a dielectric substrate according to the modified example. 
         FIG. 10A  is a diagram showing a recess according to the modified example. 
         FIG. 10B  is a diagram showing a recess according to the modified example. 
         FIG. 10C  is a diagram showing a recess according to the modified example. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Problems to be Solved by the Present Disclosure 
     A matching circuit board for forming the input-side matching circuit or the output-side matching circuit described in Patent Literature 1 is mainly used for forming a capacitive circuit in the impedance conversion. Thus, a thickness of the matching circuit board may be defined from the viewpoint of obtaining a desired capacitance. Further, the thickness of the matching circuit board may be restricted by dimensions of other electronic components mounted in a package shared by the matching circuit board (a thickness of a board different from the matching circuit board, a height of a cavity, or the like). In these cases, it is conceivable that a member having a thickness in a relatively thin range (for example, 0.1 mm to 0.5 mm) be used for the matching circuit board. 
     It is conceivable that the radio frequency amplification devices on the market will be used in a wide range of temperature conditions (for example, −65° C. to 150° C.). When a temperature change occurs in this temperature range, and a coefficient of linear expansion of a material which constitutes the package on which the matching circuit board is mounted is different from a coefficient of linear expansion of a material which constitutes the matching circuit board, the matching circuit board may be affected by tensile stress, compressive stress, and the like. As described above, since the matching circuit board includes a relatively thin thickness, it is conceivable that cracks and the like will occur in an unspecified manner on the matching circuit board due to the influence of these stresses. In such a case, a circuit function of the matching circuit board may be impaired according to a location at which cracks occur. 
     However, when countermeasures are taken by adopting a configuration (for example, the thickness of the matching circuit board, an outer size of the matching circuit board, a mounting position of the matching circuit board on the package, a type of a base material of the package, and the like) which avoids the occurrence of cracks in the matching circuit board, countermeasures such as a test are required every time the configuration is changed, and this takes a lot of work. 
     Effects of the Present Disclosure 
     According to the present disclosure, a degree of loss of the circuit function of the matching circuit board can be reduced. 
     Explanation of Embodiments of the Present Disclosure 
     First, the details of embodiments of the present disclosure will be listed and described. An amplification device according to one embodiment includes a base substrate, an amplification element, and a matching circuit board. The amplification element is mounted on the base substrate. The matching circuit board is mounted on the base substrate and includes a circuit pattern which is electrically connected to the amplification element. The matching circuit board includes a first side surface and a second side surface each extending in a longitudinal direction of the matching circuit board. A first recess is provided in the first side surface. A second recess facing the first recess is provided in the second side surface. 
     In this amplification device, the first recess and the second recess facing each other are provided in the first side surface and the second side surface of the matching circuit board, respectively. When stress which can cause cracks occurs in such a matching circuit board, the first recess or the second recess preferentially becomes a starting point of a crack. Further, cracks are likely to occur along a line which connects the first recess and the second recess. Thus, it is possible to control a location at which cracks occur in the matching circuit board by the first recess and the second recess. Therefore, even when cracks occur in the matching circuit board, the degree of loss of the circuit function of the matching circuit board can be reduced by providing the first recess and the second recess so that the line which connects the first recess and the second recess is located at a position at which the degree of loss of the circuit function can be reduced (for example, a position at which the matching circuit does not become electrically disconnected). According to such a configuration, even when the coefficient of linear expansion of the material which constitutes the base substrate and the coefficient of linear expansion of the material of the matching circuit board are different from each other, it is possible to reduce the degree of loss of the circuit function of the matching circuit board by a temperature change. 
     In the amplification device according to one embodiment, a tip end of the first recess and a tip end of the second recess may be located on the same straight line which extends in a direction orthogonal to the longitudinal direction. In this case, the positional relationship between the first recess and the second recess has the shortest distance. 
     In the amplification device according to one embodiment, the first recess and the second recess may be provided substantially at a center of the matching circuit board in the longitudinal direction. 
     In the amplification device according to one embodiment, the line which connects the first recess and the second recess may be separate from a circuit pattern. In this case, even when cracks occur in the matching circuit board, the circuit pattern is prevented from becoming cracked. Therefore, it is possible to reduce the degree of loss of the circuit function in the circuit pattern, and the circuit function can be maintained. 
     In the amplification device according to one embodiment, the matching circuit board may further include a resistance pattern. The line which connects the first recess and the second recess may be separate from the resistance pattern. In this case, even when cracks occur in the matching circuit board, the resistance pattern is prevented from becoming cracked. Therefore, it is possible to reduce a degree of loss of a function obtained by the resistance pattern, and the function obtained by the resistance pattern can be maintained. 
     In the amplification device according to one embodiment, the matching circuit board may include a dielectric substrate on which a circuit pattern is provided. The first recess and the second recess may be provided on the dielectric substrate. The material constituting the base substrate may include a copper alloy. The dielectric substrate may contain barium titanate. Since a dielectric substrate including barium titanate (BaTiO 3 ) is a plastic material, it is considered that cracks are likely to occur in such a dielectric substrate when a tensile stress is generated in the dielectric substrate. A coefficient of linear expansion of copper (Cu) is about 16.7×10 −6 /K, and a coefficient of linear expansion of barium titanate is about 9.6×10 −6 /K. In this case, since the coefficient of linear expansion of the material constituting the base substrate is larger than the coefficient of linear expansion of the material constituting the dielectric substrate, when the temperature rises (for example, when temperature changes from 25° C. to 150° C.), an amount of thermal expansion of the base substrate becomes larger than an amount of thermal expansion of the dielectric substrate. Thus, tensile stress is generated on the dielectric substrate, and cracks are likely to occur. On the other hand, according to such an amplification device, since the location at which cracks occur in the dielectric substrate can be controlled by the first recess and the second recess, even when cracks occur, it is possible to prevent loss of the circuit function of the matching circuit board. Therefore, the amplification device according to the present disclosure is advantageous in such a configuration in which cracks are likely to occur in the dielectric substrate. 
     In the amplification device according to one embodiment, a thickness of the base substrate may be 1 mm or more and 3 mm or less, and a thickness of the dielectric substrate may be 0.1 mm or more and 0.5 mm or less. In this case, since the thickness of the dielectric substrate is relatively thin, cracks are likely to occur in the dielectric substrate due to the matching circuit board being affected by the temperature change. On the other hand, according to the radio frequency amplification device, since the location at which cracks occur in the dielectric substrate can be controlled by the first recess and the second recess, even when cracks occur, it is possible to prevent loss of the circuit function of the matching circuit board. Therefore, the amplification device according to the present disclosure is advantageous in such a configuration in which cracks are likely to occur in the dielectric substrate. 
     The matching circuit board according to one embodiment can be mounted on the base substrate and be provided with a circuit pattern to perform impedance conversion. The matching circuit board may include a pair of side surfaces each extending in the longitudinal direction of the matching circuit board. In each of the side surfaces, the first recess and the second recess are provided at positions at which they face each other. According to the matching circuit board, similarly to the above, the first recess or the second recess preferentially becomes the starting point of a crack, and a crack is likely to occur along the line which connects the first recess and the second recess. Thus, it is possible to control the location at which cracks occur in the matching circuit board by the first recess and the second recess and to reduce the degree of loss of circuit function. 
     In the matching circuit board according to one embodiment, a tip end of the first recess and a tip end of the second recess may be located on the same straight line which extends in a direction orthogonal to the longitudinal direction. In this case, the positional relationship between the first recess and the second recess has the shortest distance. 
     In the matching circuit board according to one embodiment, the first recess and the second recess may be provided substantially at a center of the matching circuit board in the longitudinal direction. 
     In the matching circuit board according to one embodiment, the line which connects the first recess and the second recess may be separated from the circuit pattern. 
     In the matching circuit board according to one embodiment, the matching circuit board may further include a resistance pattern. The line which connects the first recess and the second recess may be separated from the resistance pattern. 
     In the matching circuit board according to one embodiment, the matching circuit board may further include a dielectric substrate on which a circuit pattern is provided. The first recess and the second recess may be provided on the dielectric substrate. The dielectric substrate may include barium titanate. 
     In the matching circuit board according to one embodiment, a thickness of the dielectric substrate may be 0.1 mm or more and 0.5 mm or less. 
     Details of Embodiments of the Present Disclosure 
     Specific examples of the radio frequency amplification device according to one embodiment of the present disclosure will be described below with reference to the drawings. The present disclosure is not limited to this example, but is indicated by the scope of claims and is intended to include all modifications within the meaning and scope of the claims. In the following description, the same elements or elements having the same function will be designated by the same reference numerals, and duplicate description will be omitted. In the description, an XYZ Cartesian coordinate system shown in the drawings may be referred to. 
       FIG. 1  is a plan view showing an internal configuration of a radio frequency amplification device  1  according to one embodiment of the present disclosure.  FIG. 2  is a cross-sectional view of the radio frequency amplification device  1  along line II-II of  FIG. 1 . As shown in  FIG. 1 , the radio frequency amplification device  1  includes an input terminal  2 , an output terminal  3 , an amplification element part  10 , a branch circuit board  20 , a synthesis circuit board  30 , a matching circuit  40 , and a matching circuit  50 . In the present embodiment, the radio frequency amplification device  1  includes two matching circuits  40  and two matching circuits  50  as an example. Further, the amplification element part  10  includes two amplification elements  11 . An output per amplification element  11  may be, for example,  30  W, and the output of the entire amplification element part  10  is, for example, 60 W. The radio frequency amplification device  1  includes a package  4  which accommodates the amplification element part  10 , the branch circuit board  20 , the synthesis circuit board  30 , and the matching circuits  40  and  50 , and a housing  5  which accommodates the package  4 . 
     The package  4  is made of a metal material and is connected to a reference potential. An example of the metal material constituting the package  4  is a copper (Cu) alloy. A coefficient of linear expansion of the Cu alloy is, for example, about 16.7×10 −6 /K. A planar shape of the package  4  is substantially rectangular. The package  4  includes end walls  4   a  and  4   b  which face each other in a first direction, and side walls  4   c  and  4   d  which face each other in a second direction. The first direction and the second direction intersect each other, and in one example, they are orthogonal to each other. In the present embodiment, the first direction is a Y-axis direction and the second direction is an X-axis direction. 
     The package  4  includes a rectangular flat bottom plate  4   e  (a base substrate). The bottom plate  4   e  extends along a plane defined by the Y-axis direction and the X-axis direction. A thickness D 1  of the bottom plate  4   e  (here, a length in a Z-axis direction) is, for example, 1 mm or more and 3 mm or less. The end walls  4   a  and  4   b  stand upright along a pair of sides (sides extending in the X-axis direction) of the bottom plate  4   e,  and the side walls  4   c  and  4   d  stand upright along another pair of sides (sides extending in the Y-axis direction) of the bottom plate  4   e.  The package  4  further includes a lid part (not shown). The lid part seals an upper opening defined by the end walls  4   a  and  4   b  and the side walls  4   c  and  4   d.    
     The housing  5  is made of a metal material. A coefficient of linear expansion of the metal material constituting the housing  5  is larger than, for example, the coefficient of linear expansion of the metal material constituting the package  4 . An example of the metal material constituting the housing  5  is aluminum (Al). The coefficient of linear expansion of Al is, for example, about 23.7×10 −6 /K. A planar shape of the housing  5  is substantially rectangular. The housing  5  includes a rectangular flat bottom plate  5   a.  The package  4  is disposed on the bottom plate  5   a.  The bottom plate  5   a  extends along a plane defined by the Y-axis direction and the X-axis direction. A thickness D 2  of the bottom plate  5   a  (here, a length in the Z-axis direction) is larger than, for example, the thickness D 1 . The thickness D 2  is, for example, 5 mm or more and 20 mm or less. The housing  5  may further include side walls (not shown) which extend along respective sides of the bottom plate and a lid part (not shown). 
     The input terminal  2  is a metal wiring pattern, and inputs a radio frequency signal from the outside of the radio frequency amplification device  1 . The radio frequency signal is a signal based on a multi-carrier transmission method, and is formed by superimposing a plurality of signals having different carrier signal frequencies. A frequency band of the carrier signal is, for example, 500 MHz or less. The input terminal  2  is provided at a center portion of the end wall  4   a  in the X-axis direction, and extends from the outside to the inside of the package  4 . 
     The amplification element part  10  is disposed at a substantially center portion of the package  4  in the Y-axis direction which is on the bottom plate  4   e  of the package  4 . Each of the amplification elements  11  of the amplification element part  10  includes a built-in transistor. The transistor is, for example, a field effect transistor (FET), and is a high electron mobility transistor (HEMT) in one example. Each of the amplification elements  11  includes a plurality of gate fingers, a plurality of source fingers, and a plurality of drain fingers. In the Y-axis direction, the source fingers and the drain fingers are alternately arranged, and the gate fingers are disposed between the source fingers and the drain fingers. Gate pads (signal input ends) and source pads are alternately arranged on an end side of each of the amplification elements  11  near the input terminal  2 , and drain pads (signal output ends) are arranged on an end side of each of the amplification elements  11  near the output terminal  3 . Each of the source pads is electrically connected to the bottom plate  4   e  of the package  4  via a via hole passing through the amplification element  11  in a thickness direction (here, the Z-axis direction), and is set as a reference potential. Each of the amplification elements  11  amplifies a radio frequency signal input to each of the gate pads, and outputs an amplified radio frequency signal from each of the drain pads. 
     The branch circuit board  20  is disposed on the bottom plate  4   e  of the package  4 . The branch circuit board  20  is disposed together with the input terminal  2  and the amplification element part  10  in the Y-axis direction, and is located between the input terminal  2  and the amplification element part  10 . The branch circuit board  20  includes a ceramic substrate  21  and a branch circuit  22  provided on a main surface of the substrate  21 . A planar shape of the substrate  21  is, for example, a rectangle, with one long side  21   a  facing the input terminal  2 , and the other long side  21   b  facing the amplification element part  10  via the matching circuit  40 . A back surface of the substrate  21  faces the bottom plate  4   e  of the package  4 . One short side  21   c  of the substrate  21  is located near the side wall  4   c  of the package  4 , and the other short side  21   d  of the substrate  21  is located near the side wall  4   d  of the package  4 . That is, the substrate  21  extends from the vicinity of one end of the package  4  to the vicinity of the other end thereof in the X-axis direction. 
     The branch circuit  22  includes a wiring pattern  23  provided on the main surface of the substrate  21 . The wiring pattern  23  is electrically connected to the input terminal  2  via a bonding wire  9   a.  The radio frequency signal is input to the wiring pattern  23  from the center portion of the substrate  21  in the X-axis direction. The wiring pattern  23  has a shape which is line-symmetrical with respect to a center line of the substrate  21  in the Y-axis direction. The wiring pattern  23  repeats bifurcation starting from a connection point with the bonding wire  9   a,  and finally reaches eight metal pads  23   a.  The eight metal pads  23   a  are arranged along the long side  21   b.  The metal pads  23   a  adjacent to each other are connected to each other via a film resistor to constitute a Wilkinson type coupler. Thus, while isolation between the plurality of gate pads of the amplification element part  10  is ensured, matching of an input impedance of the amplification element part  10  as seen from the input terminal  2  is promoted. In the drawing, only one film resistor  23   b  is shown as a representative. The eight metal pads  23   a  are electrically connected to the matching circuit  40  via the bonding wires  9   b.    
     The matching circuit  40  (the matching circuit board) is disposed on the bottom plate  4   e  of the package  4  and is disposed between the branch circuit board  20  and the amplification element part  10  in the Y-axis direction. Two matching circuits  40  are arranged in the X-axis direction between the branch circuit board  20  and the amplification element part  10 .  FIG. 3A  is a plan view showing the matching circuit  40  of  FIG. 1 . The matching circuit  40  is, for example, a die capacitor. As shown in  FIG. 3A , the matching circuit  40  includes a dielectric substrate  41  and a plurality of metal pads  42 . 
     The dielectric substrate  41  is, for example, a plastic body. A coefficient of linear expansion of the dielectric material constituting the dielectric substrate  41  is smaller than, for example, the coefficient of linear expansion of the metal material constituting the package  4 . Examples of the dielectric material constituting the dielectric substrate  41  include those containing barium (Ba) and titanium (Ti). As an example, the dielectric material constituting the dielectric substrate  41  is barium titanate (BaTiO 3 ). A coefficient of linear expansion of barium titanate is, for example, about 9.6×10 −6 /K. A planar shape of the dielectric substrate  41  is substantially rectangular. The dielectric substrate  41  extends along a plane defined by the Y-axis direction and the X-axis direction. A thickness D 3  (here, a length in the Z-axis direction) of the dielectric substrate  41  is, for example, 0.1 mm or more and 0.5 mm or less. The dielectric substrate  41  includes a main surface  41   a  (a first main surface) fixed to the bottom plate  4   e,  a main surface  41   b  (a second main surface) opposite to the main surface  41   a,  side surfaces  41   c  and  41   d  connected to the main surfaces  41   a  and  41   b,  and end surfaces  41   e  and  41   f  (also refer to  FIG. 2 ). The main surface  41   a  faces the bottom plate  4   e.  The side surface  41   c  (a first side surface) and the side surface  41   d  (a second side surface) extend in a direction along each other (here, the X-axis direction). The end surface  41   e  and the end surface  41   f  extend in a direction along each other (here, the Y-axis direction). The side surfaces  41   c  and  41   d  are long sides of the dielectric substrate  41 , and the end surfaces  41   e  and  41   f  are short sides of the dielectric substrate  41 . In this example, a longitudinal direction of the dielectric substrate  41  and the matching circuit  40  (the matching circuit board) is the X-axis direction. A transverse direction of the dielectric substrate  41  and the matching circuit  40  (the matching circuit board) is the Y-axis direction. 
     A recess  41   g  (a first recess) recessed toward the side surface  41   d  is provided in the side surface  41   c,  and a recess  41   h  (a second recess) recessed toward the side surface  41   c  is provided in the side surface  41   d.  The recesses  41   g  and  41   h  are provided at positions at which they face each other. In other words, the recesses  41   g  and  41   h  facing each other are provided in the pair of long sides of the dielectric substrate  41 , respectively. Specifically, the recesses  41   g  and  41   h  face each other in a direction in which cracks are desired to occur in the dielectric substrate  41 . In the present embodiment, as an example, the recesses  41   g  and  41   h  face each other in a direction (here, the Y-axis direction) orthogonal to an extension direction of the side surfaces  41   c  and  41   d.  The recesses  41   g  and  41   h  may face each other in a direction inclined with respect to the extension direction of the side surfaces  41   c  and  41   d.  As an example, the positions at which the recesses  41   g  and  41   h  are provided are substantially center portions of the dielectric substrate  41  and the matching circuit  40  (the matching circuit substrate) in the X-axis direction. The substantially center portion refers to, for example, a position within ±5% of a length in the X-axis direction from a center of the length in the X-axis direction. A planar shape of each of the recesses  41   g  and  41   h  is, for example, a semicircular shape. In this example, a tip end of the recess  41   g  and a tip end of the recess  41   h  are located on the same straight line which extends in the Y-axis direction orthogonal to the X-axis direction. 
     The metal pad  42  is an example of the circuit pattern in the present embodiment. The metal pads  42  are, for example, gold (Au) plated. Each of the metal pads  42  is provided on the main surface  41   b  of the dielectric substrate  41 . On the main surface  41   b,  a line N 1  which connects the above-described recesses  41   g  and  41   h  is separated from the metal pads  42 . That is, the line N 1  does not intersect the metal pads  42 . In this example, the line N 1  extends in the Y-axis direction. The number of metal pads  42  is, for example, the same as the number of metal pads  23   a  ( 8  in this case) in the two matching circuits  40 , and is evenly distributed in each of the matching circuits  40 . The plurality of metal pads  42  are arranged in a row in the X-axis direction. Each of the metal pads  42  is electrically connected to the corresponding metal pad  23   a  via the bonding wires  9   b  and is electrically connected to the corresponding gate pad(s) of the amplification element part  10  via a bonding wires  9   c.    
     In the matching circuit  40 , a T-type filter circuit (a matching circuit) is configured of inductance components of the bonding wires  9   b  and  9   c  and capacitance of the metal pad  42  connected between a node between the inductance components and a reference potential (the bottom plate  4   e ). The matching circuit  40  achieves impedance matching with respect to the amplification element part  10  by performing impedance conversion with the T-type filter circuit. Normally, the impedance with which the inside of the transistor is able to be estimated from the gate pad in the amplification element part  10  is different from the characteristic impedance of a transmission line (for example, 50Ω). The matching circuit  40  converts this impedance to 50Ω in which the inside of the package  4  is estimated from the input terminal  2  by the T-type filter circuit. 
     The matching circuit  50  (the matching circuit board) is disposed on the bottom plate  4   e  of the package  4  and is disposed between the amplification element part  10  and the synthesis circuit board  30  in the Y-axis direction. Two matching circuits  50  are arranged in the X-axis direction between the amplification element part  10  and the synthesis circuit board  30 .  FIG. 3B  is a plan view showing the matching circuit  50  of  FIG. 1 . The matching circuit  50  is, for example, a parallel plate type capacitor (the die capacitor) like the matching circuit  40 . As shown in  FIG. 3B , the matching circuit  50  includes a dielectric substrate  51  and a plurality of metal pads  52 . 
     The dielectric substrate  51  is, for example, a plastic body. A coefficient of linear expansion of a dielectric material constituting the dielectric substrate  51  is, for example, the same as the coefficient of linear expansion of the dielectric material constituting the dielectric substrate  41 , and is smaller than the coefficient of linear expansion of the metal material constituting the package  4 . The dielectric material constituting the dielectric substrate  51  is, for example, the same as the dielectric material constituting the dielectric substrate  41 . A planar shape of the dielectric substrate  51  is substantially rectangular. The dielectric substrate  51  extends along a plane defined by the Y-axis direction and the X-axis direction. A thickness D 4  (here, a length in the Z-axis direction) of the dielectric substrate  51  is, for example, 0.1 mm or more and 0.5 mm or less. The dielectric substrate  51  includes a main surface  51   a  (a first main surface) fixed to the bottom plate  4   e,  a main surface  51   b  opposite to the main surface  51   a,  side surfaces  51   c  and  51   d  connected to the main surfaces  51   a  and  51   b,  and end surfaces  51   e  and  51   f  (also refer to  FIG. 2 ). The main surface  51   a  faces the bottom plate  4   e.  The side surface  51   c  (a first side surface) and the side surface  51   d  (a second side surface) extend in a direction along each other (here, the X-axis direction). The end surface  51   e  and the end surface  51   f  extend in a direction along each other (here, the Y-axis direction). The side surfaces  51   c  and  51   d  are long sides of the dielectric substrate  51 , and the end surfaces  51   e  and  51   f  are short sides of the dielectric substrate  51 . In this example, a longitudinal direction of the dielectric substrate  51  and the matching circuit  50  (the matching circuit board) is the X-axis direction. A transverse direction of the dielectric substrate  51  and the matching circuit  50  (the matching circuit board) is the Y-axis direction. 
     A recess  51   g  (a first recess) recessed toward the side surface  51   d  is provided in the side surface  51   c,  and a recess  51   h  (a second recess) recessed toward the side surface  51   c  is provided in the side surface  51   d.  The recesses  51   g  and  51   h  are provided at positions at which they face each other. In other words, the recesses  51   g  and  51   h  facing each other are provided on the pair of long sides of the dielectric substrate  51 , respectively. Specifically, the recesses  51   g  and  51   h  face each other in a direction in which cracks are desired to occur in the dielectric substrate  51 . In the present embodiment, as an example, the recesses  51   g  and  51   h  face each other in a direction (here, the Y-axis direction) orthogonal to an extension direction of the side surfaces  51   c  and  51   d.  The recesses  51   g  and  51   h  may face each other in a direction inclined with respect to the extension direction of the side surfaces  51   c  and  51   d.  As an example, the positions at which the recesses  51   g  and  51   h  are provided are substantially center portions of the dielectric substrate  51  and the matching circuit  50  (the matching circuit board) in the X-axis direction. The substantially center portion refers to, for example, a position within ±5% of a length in the X-axis direction from a center of the length in the X-axis direction. A planar shape of the recesses  51   g  and  51   h  is, for example, a semicircular shape. The dielectric substrate  51  may be configured in the same manner as the dielectric substrate  41 . In this example, a tip end of the recess  51   g  and a tip end of the recess  51   h  are located on the same straight line which extends in the Y-axis direction orthogonal to the X-axis direction. 
     The metal pad  52  is an example of the circuit pattern in the present embodiment. Each of metal pads  52  is provided on the main surface  51   b  of the dielectric substrate  51 . On the main surface  51   b,  a line N 2  which connects the above-described recesses  51   g  and  51   h  is separated from the metal pads  52 . That is, the line N 2  is not in contact with the metal pads  52 . In this example, the line N 2  extends in the Y-axis direction. The number of metal pads  52  is, for example, the same as the number of metal pads  23   a  ( 8  in this case) in the two matching circuits  50 , and is evenly distributed in each of the matching circuits  50 . The plurality of metal pads  52  are arranged in a row in the X-axis direction. Each of the metal pads  52  is electrically connected to the corresponding drain pad of the amplification element part  10  via bonding wires  9   d,  and is electrically connected to a corresponding metal pad  33   a  (described later) of the synthesis circuit board  30  via a bonding wire  9   e.    
     Also in the matching circuit  50 , a T-type filter circuit (a matching circuit) is configured of inductance components of the bonding wires  9   d  and  9   e  and capacitance of the metal pad  52  connected between a node between the inductance components and a reference potential (the bottom plate  4   e ). The matching circuit  50  achieves impedance matching with respect to the amplification element part  10  by performing impedance conversion with the T-type filter circuit. Normally, the impedance with which the inside of the transistor is able to be estimated from the drain pad in the amplification element part  10  is different from the characteristic impedance of the transmission line (for example, 50Ω), and is generally smaller than 50Ω. The matching circuit  50  matches this impedance with 50Ω in which the inside of the package  4  is estimated from the output terminal  3  by the T-type filter circuit. 
     The synthesis circuit board  30  is disposed on the bottom plate  4   e  of the package  4 . The synthesis circuit board  30  is disposed together with the amplification element part  10  and the output terminal  3  in the Y-axis direction, and is located between the amplification element part  10  and the output terminal  3 . The synthesis circuit board  30  includes a ceramic substrate  31  and a synthesis circuit  32  provided on the main surface of the substrate  31 . A planar shape of the substrate  31  is, for example, rectangular, one long side  31   a  faces the amplification element part  10  via the matching circuit  50 , and the other long side  31   b  faces the output terminal  3 . A back surface of the substrate  31  faces the bottom plate  4   e  of the package  4 . One short side  31   c  of the substrate  31  is located near the side wall  4   c  of the package  4 , and the other short side  31   d  of the substrate  31  is located near the side wall  4   d  of the package  4 . That is, the substrate  31  extends from the vicinity of one end to the vicinity of the other end of the package  4  in the X-axis direction. 
     The synthesis circuit  32  synthesizes signals output from the plurality of drain pads of the amplification element part  10  into one output signal. The synthesis circuit  32  includes a wiring pattern  33  provided on the main surface of the substrate  31 . The wiring pattern  33  has a shape which is line-symmetrical with respect to a center line of the substrate  31  in the Y-axis direction. The wiring pattern  33  includes four metal pads  33   a.  The four metal pads  33   a  are arranged along the long side  31   a.  The metal pads  33   a  adjacent to each other are connected to each other via a film resistor to form a Wilkinson type coupler. Thus, while isolation between the plurality of drain pads of the amplification element part  10  is ensured, matching of output impedance of the amplification element part  10  as seen from the output terminal  3  is promoted. In the drawing, only one film resistor  33   b  is shown as a representative. Each of the metal pads  33   a  is electrically connected to two corresponding metal pads  52  of the matching circuit  50  via the bonding wires  9   e.  The wiring pattern  33  finally reaches a connection point with the bonding wire  9   f  while coupling from the four metal pads  33   a  is repeated. The wiring pattern  33  is electrically connected to the output terminal  3  via the bonding wires  9   f.  An amplified radio frequency signal is output to the output terminal  3  from the center portion of the substrate  31  in the X-axis direction. 
     The output terminal  3  is a metal wiring pattern, and outputs the amplified radio frequency signal to the outside of the radio frequency amplification device  1 . The output terminal  3  is provided at a center portion of the end wall  4   b  in the X-axis direction, and extends from the inside to the outside of the package  4 . 
     Effects of the above-described radio frequency amplification device  1  will be described. First, a comparative example will be described.  FIG. 4  is a perspective view showing a part of a radio frequency amplification device  1 X according to the comparative example.  FIG. 5A  is a cross-sectional view of the radio frequency amplification device  1 X along VA-VA line of  FIG. 4 . The radio frequency amplification device  1 X is different from the radio frequency amplification device  1  in that a matching circuit  40 X is provided in place of the matching circuit  40  and a matching circuit  50 X is provided in place of the matching circuit  50 . Other configurations of the radio frequency amplification device  1 X are the same as those of the radio frequency amplification device  1 , and are shown schematically in the drawing. 
     The matching circuit  40 X is different from the matching circuit  40  in that a dielectric substrate  41 X is provided in place of the dielectric substrate  41 , and is similar to the matching circuit  40  in other configurations. The dielectric substrate  41 X is different from the dielectric substrate  41  in that the recesses  41   g  and  41   h  are not provided. Other configurations of the dielectric substrate  41 X are the same as those of the dielectric substrate  41 . 
     The radio frequency amplification device  1 X having such a configuration may be used in a wide range of temperature conditions (for example, −65° C. or higher and 150° C. or lower). When a temperature change occurs in this temperature range, since the coefficient of linear expansion of the material constituting the package  4  and the coefficient of linear expansion of the material constituting the dielectric substrate  41 X of the matching circuit  40 X are different each other, the dielectric substrate  41 X is subject to stress such as tensile stress or compressive stress.  FIG. 5B  is a diagram for explaining a state in which the matching circuit  40  of  FIG. 5A  is affected by the temperature change.  FIG. 5B  shows a case in which the radio frequency amplification device  1 X which was in the state shown in  FIG. 5A  under a temperature environment of room temperature (for example, 25° C.) is placed in a temperature environment of a higher temperature (for example, 150° C.). 
     In the radio frequency amplification device  1 X, similarly to the radio frequency amplification device  1 , the material constituting the package  4  contains a Cu alloy, and the dielectric substrate  41 X contains Ba and Ti. For example, the dielectric material constituting the dielectric substrate  41 X is barium titanate (BaTiO 3 ). Since the dielectric substrate  41 X containing barium titanate is a plastic body, it is considered that cracks are likely to occur in the dielectric substrate  41 X when a tensile stress is generated in the dielectric substrate  41 X. Further, since the coefficient of linear expansion of the material constituting the package  4  is larger than the coefficient of linear expansion of the material constituting the dielectric substrate  41 X, when the temperature rises (that is, a case shown in  FIG. 5B ), an amount of thermal expansion of the package  4  becomes larger than an amount of thermal expansion of the dielectric substrate  41 X. Therefore, expansion of the dielectric substrate  41 X cannot follow thermal expansion of the package  4 , and tensile stress is generated over almost the entire dielectric substrate  41 X. Specifically, as shown in  FIG. 5B , stress is generated so that the dielectric substrate  41 X warps toward the package  4 . 
       FIG. 6  is a diagram showing a stress distribution state of the dielectric substrate  41 X according to the comparative example.  FIG. 7  is a diagram showing a stress distribution state of the dielectric substrate  41  according to the present embodiment.  FIGS. 6 and 7  show the stress distribution states (simulation results) of the dielectric substrates  41  and  41 X when they are affected by the temperature change from 25° C. to 125° C. In  FIGS. 6 and 7 , illustration of other members is omitted. In  FIGS. 6 and 7 , the stress is shown by contour lines, and as the color becomes darker, the stress increases. From  FIG. 6 , it can be seen that a stress of 70 MPa or more and 80 MPa or less is generated in the dielectric substrate  41 X. Further, from  FIG. 6 , it can be seen that in the dielectric substrate  41 X, the stress distribution in a long side direction is gentle, and a large or steep change in the stress does not occur at a specific location. It can be said that cracks C (refer to  FIG. 4 ) are likely to occur at unspecified positions on the dielectric substrate  41 X due to a variation in a mounting position of the dielectric substrate  41 X on the bottom plate  4   e  of the package  4 . 
     On the other hand, in the radio frequency amplification device  1 , recesses  41   g  and recesses  41   h  facing each other are provided in the side surface  41   c  and the side surface  41   d  of the dielectric substrate  41  of the matching circuit  40 . When a stress which may cause cracks occurs in such a dielectric substrate  41 , as shown in  FIG. 7 , it can be seen that a particularly large stress (a stress of 120 MPa or more and 130 MPa or less in the example of  FIG. 7 ) is generated in the recess  41   g  and the recess  41   h.  As described above, since the large stress locally occurs, the recess  41   g  or the recess  41   h  preferentially serves as a starting point of the crack. Further, cracks are likely to occur in a direction perpendicular to a stress direction, and are likely to occur along a line N 1  which connects the recess  41   g  and the recess  41   h.  Therefore, a location which cracks occur in the dielectric substrate  41  can be controlled by the recess  41   g  and the recess  41   h.  Therefore, even when cracks occur in the dielectric substrate  41 , the degree of loss of the circuit function of the matching circuit  40  can be reduced by providing the recess  41   g  and the recess  41   h  so that the line N 1  which connects the recess  41   g  and the recess  41   h  is located at a position at which the matching circuit  40  is not electrically disconnected. According to such a configuration, even when the coefficient of linear expansion of the material constituting the package  4  and the coefficient of linear expansion of the material constituting the dielectric substrate  41  of the matching circuit  40  are different from each other, it is possible to reduce the degree of loss of the circuit function of the matching circuit  40  by the temperature change. The same applies to the matching circuit  50 . 
     In the radio frequency amplification device  1 , the line N 1  which connects the recess  41   g  and the recess  41   h  is separated from the metal pad  42 . With such a configuration, even when cracks occur in the dielectric substrate  41  of the matching circuit  40 , cracks are prevented from reaching the metal pad  42 . Therefore, it is possible to reduce the degree of loss of the circuit function in the metal pad  42 , and the circuit function can be maintained. The same applies to the matching circuit  50 . 
     In the radio frequency amplification device  1 , the material constituting the package  4  contains a copper alloy, and the dielectric substrate  41  contains barium titanate. Thus, as described above, cracks are likely to occur when tensile stress is applied to the dielectric substrate  41 . On the other hand, according to the radio frequency amplification device  1 , since the location at which cracks occur in the dielectric substrate  41  can be controlled by the recess  41   g  and the recess  41   h,  even when cracks occur, it is possible to reduce the degree of loss of the circuit function of the matching circuit  40 . Therefore, the radio frequency amplification device  1  is advantageous in such a configuration in which cracks are likely to occur in the dielectric substrate  41 . The same applies to the matching circuit  50 . 
     In the radio frequency amplification device  1 , the thickness D 1  of the bottom plate  4   e  of the package  4  is 1 mm or more and 2 mm or less, and the thickness D 3  of the dielectric substrate  41  is 0.1 mm or more and 0.5 mm or less. Since the thickness D 3  of the dielectric substrate  41  is relatively thin, cracks are likely to occur in the dielectric substrate  41  due to the influence of the temperature change on the dielectric substrate  41 . On the other hand, according to the radio frequency amplification device  1 , since the location at which cracks occur in the dielectric substrate  41  can be controlled by the recess  41   g  and the recess  41   h,  even when cracks occur, it is possible to reduce the degree of loss of the circuit function of the matching circuit  40 . Therefore, the radio frequency amplification device  1  is advantageous in such a configuration in which cracks are likely to occur in the dielectric substrate  41 . The same applies to the matching circuit  50 . 
     The above-described embodiment describes one embodiment of the radio frequency amplification device according to the present disclosure. The radio frequency amplification device according to the present disclosure may be an arbitrary modification of each of the above-described embodiment. 
     For example, the radio frequency amplification device  1  according to the above-described embodiment includes two matching circuits  40  and two matching circuits  50 , and the amplification element part  10  includes two amplification elements  11 , but the present disclosure is not limited to such a configuration. The radio frequency amplification device  1  may include one matching circuit  40  and one matching circuit  50 , or may include three or more matching circuits  40  and three or more matching circuits  50 . The amplification element part  10  may include a single amplification element  11 , or may include three or more amplification elements  11 . 
     Further, the radio frequency amplification device  1  may include a matching circuit  60  shown in  FIG. 8  instead of the matching circuit  40 .  FIG. 8  is a plan view showing the matching circuit  60  according to a modified example. The matching circuit  60  is different from the matching circuit  40  in that a dielectric substrate  61  is provided in place of the dielectric substrate  41 , a metal pad  62  is provided in place of the metal pad  42 , and a resistance film  63  (a resistance pattern) is further provided. Other configurations of the matching circuit  60  are the same as those of the matching circuit  40 . The dielectric substrate  61  is different from the dielectric substrate  41  in that it includes side surfaces  61   c  and  61   d  instead of the side surfaces  41   c  and  41   d,  and is similar to the dielectric substrate  41  in other respects. The side surfaces  61   c  and  61   d  are long sides of the dielectric substrate  61  like the side surfaces  41   c  and  41   d.  The side surface  61   c  (a first side surface) and the side surface  61   d  (a second side surface) extend in a direction along each other (here, the X-axis direction). In this example, a longitudinal direction of the dielectric substrate  61  and the matching circuit  60  (the matching circuit board) is the X-axis direction. A transverse direction of the dielectric substrate  61  and the matching circuit  60  (the matching circuit board) is the Y-axis direction. 
     Two recesses  61   g  (first recesses) recessed toward the side surface  61   d  are provided in the side surface  61   c,  and two recesses  61   h  (second recesses) recessed toward the side surface  61   c  are provided in the side surface  61   d.  The recesses  61   g  and  61   h  are provided at positions at which they face each other. In other words, the recesses  61   g  and  61   h  facing each other are provided on the pair of long sides of the dielectric substrate  61 , respectively. The positions at which the recesses  61   g  and  61   h  are provided are both end portions of the dielectric substrate  41  in the X-axis direction. A planar shape of the recesses  61   g  and  61   h  is, for example, a semicircular shape. In this example, a tip end of the recess  61   g  and a tip end of the recess  61   h  are located on the same straight line which extends in the Y-axis direction orthogonal to the X-axis direction. The metal pad  62  is different from the metal pad  42  in that it has a thickness (a length in the Z-axis direction) larger than the thickness of the metal pad  42  (the length in the Z-axis direction), and is similar to the metal pad  42  in other configurations. The resistance film  63  is disposed between two metal pads  62  adjacent to each other in the X-axis direction, and is electrically connected to the two metal pads  62 . A line N 3  which connects the above-described recesses  61   g  and  61   h  is separated from the resistance film  63 . That is, the line N 3  does not intersect the resistance film  63 . In this example, the line N 1  extends in the Y-axis direction. 
       FIG. 9  is a diagram showing a stress distribution state of the dielectric substrate  61  according to the modified example.  FIG. 9  shows the stress distribution state (simulation results) of the dielectric substrate  61  when it is affected by the temperature change from 25° C. to 125° C. In  FIG. 9 , illustration of other members is omitted. In  FIG. 9 , as in  FIGS. 6 and 7 , the stress is shown by contour lines, and as the color becomes darker, the stress increases. 
     When stress which may cause cracks occurs in the dielectric substrate  61 , as shown in  FIG. 9 , it can be seen that a particularly large stress (a stress of 120 MPa or more and 130 MPa or less in the example of  FIG. 9 ) occurs in the recess  61   g  and the recess  61   h.  As described above, since the large stress locally occurs, the recess  61   g  or the recess  61   h  preferentially serves as a starting point of the crack. Thus, also in the matching circuit  60 , it is possible to control the location at which a crack occurs in the dielectric substrate  61  by the recesses  61   g  and  61   h.  Even when cracks occur in the dielectric substrate  61 , cracks are prevented from reaching the resistance film  63 , and thus the degree of loss of the function obtained by the resistance film  63  can be reduced. As a result, the function obtained by the resistance pattern can be maintained. In the matching circuit  60 , when cracks occur in the dielectric substrate  61 , cracks may reach the metal pad  62 . On the other hand, since the metal pad  62  has a thickness larger than the thickness of the metal pad  42 , even when it is desired to avoid the occurrence of cracks in the metal pad  62 , it is possible to prevent the occurrence of cracks in the metal pad  62  by Au exerting viscosity. 
     The radio frequency amplification device  1  may include the matching circuit  60  instead of the matching circuit  50 . Alternatively, the matching circuit  60  may be provided instead of the matching circuits  40  and  50 . 
     Further, in the above-described embodiment and modified example, the planar shapes of the recesses  41   g,    41   h,    51   g,    51   h,    61   g,  and  61   h  are semicircular, but the planar shapes of the recesses (the first recess and the second recess) are not limited to such a configuration.  FIGS. 10A, 10B and 10C  are diagrams showing each of recesses  41   i,    41   j  and  41   k  according to the modified example. Hereinafter, they are described as modified examples of the recess  41   g,  and may be modified examples of any of the recess  41   g,    41   h,    51   g,    51   h,    61   g,  and  61   h.    
     As shown in  FIG. 10A , a recess  41   i  (a first recess) of which a planar shape is a shape obtained by dividing an ellipse into two in a major axis direction may be provided in the side surface  41   c.  As shown in  FIG. 10B , a recess  41   j  (a first recess) of which a plane shape is a shape obtained by dividing an ellipse into two in a minor axis direction may be provided in the side surface  41   c.  Alternatively, as shown in  FIG. 10C , a recess  41   k  (a first recess) of which a planar shape is triangular may be provided in the side surface  41   c.  At top portions of the recesses  41   g,    41   i,    41   j,  and  41   k  in a direction U in which cracks are desired to occur in the dielectric substrate  41  (for example, a direction orthogonal to a main direction V in which tensile stress occurs), as a curvature of an apex P having a shape symmetrical with respect to the direction U becomes larger, the stress which occurs at the apex increases. That is, the stress which may locally occur in the dielectric substrate  41  having the recesses is likely to increase. The curvature of the apex P of the recess  41   i  is smaller than the curvature of the apex P of the recess  41   g.  Further, the curvature of the apex P of the recess  41   j  is larger than the curvature of the apex P of the recess  41   g.  Further, the curvature of the apex P of the recess  41   k  is larger than the curvature of the apex P of the recess  41   j.  Therefore, the recesses  41   k,    41   j,    41   g,  and  41   i  are likely to be the starting points of cracks in this order. 
     Instead of the recesses  41   g,    41   h,    51   g,    51   h,    61   g,  and  61   h,  the recesses  41   i,    41   j,  and  41   k  may be arbitrarily adopted. 
     REFERENCE SIGNS LIST 
       1 ,  1 X Radio frequency amplification device 
       2  Input terminal 
       3  Output terminal 
       4  Package 
       4   a,    4   b  End wall 
       4   c,    4   d  Side wall 
       4   e  Bottom plate (base substrate) 
       5  Housing 
       5   a  Bottom plate 
       9   a  to  9   f  Bonding wire 
       10  Amplification element part 
       11  Amplification element 
       20  Branch circuit board 
       21  Substrate 
       21   a,    21   b  Long side 
       21   c,    21   d  Short side 
       22  Branch circuit 
       23  Wiring pattern 
       23   a  Metal pad 
       23   b  Film resistance 
       30  Synthesis circuit board 
       31  Substrate 
       31   a,    31   b  Long side 
       31   c,    31   d  Short side 
       32  Synthesis circuit 
       33  Wiring pattern 
       33   a  Metal pad 
       33   b  Film resistance 
       40 ,  40 X Matching circuit (matching circuit board) 
       41 ,  41 X Dielectric substrate 
       41   a  Main surface (first main surface) 
       41   b  Main surface (second main surface) 
       41   c  Side surface (first side surface) 
       41   d  Side surface (second side surface) 
       41   e  End surface 
       41   f  End surface 
       41   g,    41   i,    41   j,    41   k  Recess (first recess) 
       41   h  Recess (second recess) 
       42  Metal pad (circuit pattern) 
       50 ,  50 X Matching circuit (matching circuit board) 
       51  Dielectric substrate 
       51   a  Main surface (first main surface) 
       51   b  Main surface (second main surface) 
       51   c  Side surface (first side surface) 
       51   d  Side surface (second side surface) 
       51   e  End surface 
       51   f  End surface 
       51   g  Recess (first recess) 
       51   h  Recess (second recess) 
       52  Metal pad (circuit pattern) 
       60  Matching circuit 
       61  Dielectric substrate 
       61   c  Side surface (first side surface) 
       61   d  Side surface (second side surface) 
       61   g  Recess (first recess) 
       61   h  Recess (second recess) 
       62  Metal pad (circuit pattern) 
       63  Resistance film (resistance pattern) 
     C crack 
     D 1  to D 4  Thickness 
     P Apex 
     U Direction 
     V Main direction 
     N 1  to N 3  line