Abstract:
In an embodiment of the invention, a package for high frequency waves mounted by a high frequency electronic circuit comprises an hermetic box-shaped high frequency package containing a high frequency electronic circuit in the inside and shielded by a conductor, an input terminal and an output terminal partly led out to the outside of the high frequency package, an input side feed-through section having one of its opposite ends connected to the input terminal and the other end connected to the high frequency electronic circuit and having a predetermined characteristic impedance; and an output side feed-through section having one of its opposite ends connected to the output terminal and the other end connected to the high frequency electronic circuit and having a characteristic impedance lower than the characteristic impedance of the input side feed-through section as viewed from the output terminal side.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This invention contains subject matter related to Japanese Patent Application JP 2005-266938 filed on Sep. 14, 2005, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     (1) Field the Related Art 
     The present invention relates to a package for high frequency waves and, more particularly, it relates to a high performance package for high frequency waves that enables outputting a large electric current. 
     (2) Description of the Related Art 
     Devices and instruments are generally designed as 50Ω type in the field of microwaves. 
     Similarly, as for packages for high frequency waves that contain elements for high frequency waves and matching circuits, characteristic impedances are generally designed as 50Ω type as viewed from the input terminal and the output terminal. Additionally, the input terminal and the output terminal are normally made to show a same profile and a same size regardless of the level of the flowing electric current. However, signals are more often than not amplified depending on the element circuits for high frequency waves contained in a high frequency package, a large electric current flows to the output terminal if compared with the input terminal. 
     For example, if the characteristic impedance of a feed-through section sandwiched between 0.6 mm-thick ceramic pieces is 50Ω, the line width is 0.6 mm and the limit for metal thickness is about 0.1 μm for achieving hermetic condition when sandwiched between ceramic pieces. Then, a large ohm loss is produced when an electric current is flowed to a line showing such a relatively high resistance. For this reason, there arises a problem that the applied voltage is not effectively conveyed to a semiconductor chip and the line can be fused by Joule heat generated when an electric current flows through the resistance components at the output terminal side to make it impossible to obtain a sufficient current capacity. 
     GaAs FET packages where the input side gate terminal is made to show a small width to raise the impedance so as to be used as part of a noise factor matching circuit are known and disclosed in Jpn. Pat. Appln. Laid-Open Publication No. 7-94649. However, such a package also has high resistance components at the output side to make it impossible to obtain a sufficient current capacity and hence can give rise to the above described problem. Additionally, such a package is also accompanied by a drawback that the high frequency characteristics are damaged when the line width of the input terminal or the output terminal is changed abruptly. 
     In view of the above identified problems, it is therefore the object of the present invention to provide a high performance package for high frequency waves containing a high frequency electronic circuit that can secure a sufficient current capacity at the output section and shows good frequency characteristics. 
     In an aspect of the present invention, the above object is achieved by providing a package for high frequency waves comprising: an hermetic box-shaped high frequency package containing a high frequency electronic circuit in the inside and shielded by a conductor; an input terminal and an output terminal partly led out to the outside of the high frequency package; an input side feed-through section having one of its opposite ends connected to the input terminal and the other end connected to the high frequency electronic circuit and having a predetermined characteristic impedance; and an output side feed-through section having one of its opposite ends connected to the output terminal and the other end connected to the high frequency electronic circuit and having a characteristic impedance lower than the characteristic impedance of the input side feed-through section as viewed from the output terminal side. 
     Thus, according to the present invention, it is possible to raise the current capacity at the output side of a package for high frequency waves by having line width wider, that is having the characteristic impedance of the output side feed-through section lower than the characteristic impedance of the input side feed-through section within a range that allows matching the internal high frequency circuit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic bird&#39;s-eye view of an embodiment of package for high frequency waves according to the present invention; 
         FIG. 2A  is a schematic cross sectional view of the output side feed-through section of the embodiment of  FIG. 1 , illustrating the structure thereof, and  FIG. 2B  is a schematic perspective view of the output side feed-through section of the embodiment of  FIG. 1 , illustrating the structure thereof. 
         FIG. 3A  is a schematic plan view of the input side feed-through section of the embodiment of  FIG. 1 ,  FIG. 3B  is a schematic plan view of the embodiment of package for high frequency waves of  FIG. 1 ,  FIG. 3C  is a schematic plan view of the output side feed-through section of the embodiment of  FIG. 1 , and  FIG. 3D  is a schematic cross sectional view of the embodiment of package for high frequency wave of  FIG. 1  taken along X-X′ line in  FIG. 3C , showing the high frequency package thereof. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Now, the present invention will be described in greater detail by referring to the accompanying drawings that illustrate a preferred embodiment of the invention. 
       FIG. 1  is a schematic bird&#39;s-eye view of an embodiment of package for high frequency waves according to the present invention. The lower grounded metal plate  13  of the embodiment of package for high frequency waves needs to be made of a metal showing good grounded characteristics and, at the same time, a good thermal conductivity. Examples of metals that can be used for the grounded metal plate include Cu, CuW (copper tungsten) and CuMo (copper molybdenum). A ceramic plate having a thickness of about 0.6 mm is used as terminal forming substrate, which will make a lower dielectric  17   b  as will be described hereinafter. 
     A metal frame  12  that is typically about 0.7 mm width and about 5 to 8 mm high and made of Cu or an alloy of Fe, Ni and Co is bonded onto the surface of the grounded metal plate  13 . 
     The metal frame  12  has notches where an input terminal  10  and an output terminal  15  are formed by way of a feed-through section  14 . A metal-made cover  11  is bonded onto the surface of the frame. Metals of the grounded metal plate  13 , the metal frame  12  and the cover  11  need to have respective thermal expansion coefficients that are substantially equal to each other. Additionally, they have to be selected from the viewpoint of easy machining. 
       FIG. 2A  is a schematic cross sectional view of the output side feed-through section  14   b  in the vicinity of the output terminal  15  of the embodiment of package for high frequency waves and  FIG. 2B  is a schematic perspective view of the output side feed-through section  14   b  of the embodiment, illustrating the structure thereof. The output side feed-through section  14   b  is-formed by sandwiched a signal line  18  that operates as through conductor between an upper dielectric  17   a  and a lower dielectric  17   b . The upper dielectric  17   a  and the lower dielectric  17   b  are typically made of ceramic. 
     The lower dielectric  17   b  is made longer than the upper dielectric  17   a  and each of the lower dielectric  17   b  and the upper dielectric  17   a  is made connectable to the output terminal and a bonding such as a wire at the opposite sides thereof. The output terminal  15  is soldered and bonded onto the signal line  18  at the outside of the feed-through section  14 . Since a meniscus profile  16  is produced at this time to show a contour that appears like of a attenuation curve by the surface tension of the solder so that the signal line  18  and the output terminal  15  are bonded highly reliably. 
     A feed-through section is formed both at the input side and at the output side. As seen in  FIG. 3 , the input side feed-through section is denoted by  14   a  and the output side feed-through section is denoted by  14   b . The feed-through sections  14   a  and  14   b  have similar respective structures except their dimensions. 
     Thus, the package for high frequency waves comprises a grounded metal plate  13 , a metal frame  12 , a cover  11 , an input side feed-through section  14   a  and an output side feed-through section  14   b  and the inside thereof is made hermetic typically by sealing it with nitrogen. 
       FIGS. 3A ,  3 B,  3 C and  3 D schematically illustrate the structure of this embodiment of package for high frequency waves. 
       FIG. 3A  is an enlarged schematic plan view of the input side feed-through section  14   a  of the package for high frequency waves.  FIG. 3B  is a schematic plan view of the package for high frequency waves, showing the inside thereof.  FIG. 3C  is an enlarged schematic plan view of the output side feed-through section  14   b .  FIG. 3D  is a schematic cross sectional view of the package for high frequency wave taken along X-X′ line in  FIG. 3C . 
     Referring to  FIG. 3B , the input terminal  10  is connected to an input matching circuit  33  at a bonding  35  by way of the input side feed-through section  14   a . The expression of a bonding as used herein refers to a spot where electric connection is established typically by means of wire bonding, ribbon boding. 
     The input matching circuit  33  is connected to a field effect transistor (FET) or a monolithic microwave integrated circuit (MMIC) that constitutes an electronic circuit  34  at a bonding  35 , while the electronic circuit  34  that is mounted internally is connected to an output side matching circuit  36  at a bonding  35 , which output matching circuit  36  is connected to the output terminal  15  by way of a bonding  35  and the output side feed-through section  14   b.    
     As shown in  FIGS. 2A and 2B , the output side feed-through section  14   b  is formed by a through conductor that operates as the signal line  18 , the upper dielectric  17   a  and the lower dielectric  17   b , the upper dielectric  17   a  and the lower dielectric  17   b  being typically made of ceramic. Output side micro-strip lines  37 ,  39  are formed on the lower dielectric  17   b . The characteristic impedances of each of them as viewed from the input side or the output side are determined by the electrostatic capacity it produces with the grounded metal plate  13  and the inductance component of its own. 
     The input side feed-through section  14   a  has a configuration substantially same as the output side feed-through section  14   b . More specifically, the signal line  18  is sandwiched between the upper dielectric  17   a  and the lower dielectric  17   b  that are typically made of ceramic and surrounded by the conductors of the metal frame  12  and the grounded metal plate  13 . The width Wif of the input side feed-through line  31  is reduced if compared with the width Wim of the micro-strip lines  30 ,  31  at the part thereof that is surrounded by the metal frame  12  in order to make that part show an impedance substantially same as the preceding and succeeding parts thereof (see  FIG. 2B )  FIG. 3A  shows the input side feed-through section  14   a  when the characteristic impedance is 50Ω. Taking the thickness of the lower dielectric  17   b , the line width Wif of the input side feed-through line  31  is about 0.4 mm and the line width Wim of the micro-strip lines  30 ,  32  is about 0.6 mm. The input terminal  10  is soldered and bonded onto the micro-strip line  30 . 
     In order to bond the input terminal and the signal line well, it is preferable to produce a meniscus structure as described above by referring to  FIG. 2A . A meniscus region requires at least 0.1 mm for this embodiment. Therefore, the width of the input terminal  10  needs to be made smaller by 0.2 mm than the width of the micro-strip line  30  for the purpose of forming a meniscus region. Thus, it is possible to bond the input terminal  10  and the micro-strip line  30  well by reducing the width of the input terminal  10  to about 0.4 mm. 
     On the other hand,  FIG. 3C  shows the dimensions of the output side feed-through section  14   b  when the characteristic impedance is assumed to be about 30Ω. The line width Wom of the micro-strip line  37  can be increased to 0.9 mm while the line width Wof of the feed-through line  38  can be increased to 0.7 mm by lowering the characteristic impedance, taking the thickness of the lower dielectric  17   b  into consideration. 
     If 0.1 mm is spared for forming each meniscus region as described above by referring to  FIGS. 2A and 2B , it is possible to secure about 0.7 mm for the line width Wc in thesolder bonding region of the output terminal  15 . Then, it is possible to make the line width greater than the input terminal  10 , which is 0.4 mm when the characteristic impedance is 50Ω. The line width of the micro-strip line  39  is made to be substantially equal to that of the micro-strip line (1 to 2 mm) of an external substrate (not shown) on which a package according to the present invention is mounted in order to make them match each other well. In other words, the line width of the micro-strip line  39  is made greater than the line width Wom of the micro-strip line  37 . 
     Referring to  FIG. 3C , the width Wos of the output terminal  15  is about 1 to 2 mm but turned to a smaller width Wc at a part of the output terminal  15  where it is bonded to the micro-strip line  39  to produce a structure that satisfactorily secure meniscus when the output terminal  15  is soldered to the micro-strip line  39  and hence good bonding characteristics. 
     More specifically, the output terminal  15  is tapered toward the part thereof where it is soldered to the micro-strip line  39  to reduce its width from Wos. Differently stated, the output terminal  15  gradually increases its width as it moves away from the corresponding end of the micro-strip line  39 . 
     This tapered profile is devised to prevent the output signal from being reflected because a reflected wave, if produced, degrades the performance of the external terminal if the width of the external terminal is changed abruptly. 
     As described above, the line width of the micro-strip line in the feed-through section and also that of the feed-through section are increased at the output terminal side to lower the characteristic impedance to below 50Ω. Thus, it is possible to establish matching with the external circuit at the output side by designing the matching circuit in the inside of the package, reducing the impedance to about 30Ω and its electric length to less than ¼ of the wavelength, taking the impedance of the terminal into consideration. 
     With this arrangement, the signal line is no longer fused by Joule heat at the output terminal side when a circuit that requires a large electric current is mounted. 
     Thus, it is possible to establish matching at the input side by reducing the line width of the input terminal that does not require any current capacity and holding the characteristic impedance to 50Ω in this embodiment of package for high frequency waves having the above described configuration. 
     In other words, it is possible to design the feed-through section so as to make it show a wide line width by lowering the characteristic impedance within a range that allows a good matching with the internal circuit only for the output terminal that requires a current capacity for the package for high frequency waves. Then, the matching with the line width of the micro-strip line of the external circuit substrate is improved the high frequency characteristics by gradually and continuously broadening the external output terminal. Thus, it is possible to provide a high performance semiconductor package with high output and good frequency characteristics. 
     Particularly, from the viewpoint of the above-described embodiment, the number of bonding wires to be connected can be increased by increasing the line width of the micro-strip line  37  in order to prevent the bonding wires from being fused by a large electric current. It is highly desirable to raise the width of the feed-through line  38  of the output side feed-through section from the viewpoint of preventing fusion by a large electric current. Thus, it is possible to prevent fusion from taking place at the output side by a large electric current by increasing the line width of the feed-through line  38  and those of the micro-strip lines  37 ,  38  at the output terminal side within an allowable range from the viewpoint of matching with the high frequency electronic circuit. 
     Additionally, it is desirable to make the line width of the micro-strip line  39  greater than that of the micro-strip line  37  from the viewpoint of raising the width of the output terminal  15  and forming a meniscus structure sufficient for achieving a good bonding characteristic at the soldered connecting section of the output terminal  15  and the micro-strip line  39 . 
     The present invention is by no means limited to the above-described embodiment and can be embodied in various different ways without departing from the spirit and scope of the present invention. 
     The line width of the micro-strip lines,  37 ,  38  at the output side feed-through section and the line width of the feed-through line of the above described embodiment are not limited to the above described ones and can be increased to lower the characteristic impedance within an allowable range from the viewpoint of matching with the high frequency electronic circuit contained in the high frequency package as viewed from the external terminal. The width of the external terminal can also be increased for the same reason. 
     While only the output terminal requires a current capacity for a package for high frequency waves according to the present invention in the above description, a similar arrangement can be provided at the input terminal side if a current capacity is required at the input terminal side. 
     While a FET or a MMIC is arranged in the high frequency package as high frequency electronic circuit in the above description, the above-described idea is equally applicable to a bipolar transistor. Finally, while an input matching circuit  33  and an output matching circuit  36  are arranged in the above described embodiment, either or both of them are not required if the mounted high frequency electronic circuit comprises either or both of them, whichever appropriate.