Patent Document

BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a high frequency module, and particularly, to a high frequency module that employs a semiconductor chip for processing high frequency signals, such as a power amplifier module.  
         DESCRIPTION OF THE PRIOR ART  
         [0002]    A module or package employing a high frequency semiconductor chip is described in, for example, Japanese Patent Application Laid Open No. 10-501102. According to this prior art, a semiconductor chip is mounted on a substrate constituting a package member by the wire bonding method or flip-chip mounting, and a metal cap is provided on the substrate to constitute the high frequency module.  
           [0003]    Another high frequency module is described in U.S. Pat. No. 5,831,836. According to this prior art, a semiconductor chip is mounted on a substrate by flip-chip mounting, and a back surface of the semiconductor chip is contacted with a roof portion of a metal cap to constitute the high frequency module.  
           [0004]    [0004]FIG. 1 is a schematic sectional diagram showing the high frequency module described in U.S. Pat. No. 5,831,836.  
           [0005]    As shown in FIG. 1, the high frequency module  1  employs a substrate  2 , a semiconductor chip  3 , and a metal cap  4 . The metal cap  4  is also used as a heat sink. The substrate  2  and the semiconductor chip  3  are electrically connected to each other via microbumps  5  made of solder or gold formed on the outer electrodes provided on the bottom surface of the semiconductor chip  3 , i.e., the semiconductor chip  3  is mounted on the substrate  2  by flip-chip mounting. An underfilling  6  is charged and cured a space formed between the substrate  2  and the semiconductor chip  3 . The roof portion  4   b  of the metal cap  4  is adhered to the top surface of the semiconductor chip  3  by a conductive adhesive  7  and the edge portions  4   a  are fixed to electrodes (not shown) on the substrate  2  by conductive adhesive or solder  8 .  
           [0006]    The high frequency module shown in FIG. 1 has the following problems.  
           [0007]    First, the connection between the semiconductor chip  3  and the substrate  2  is established by the microbumps  5  but the height of the microbumps  5  varies depending on the manufacturing conditions. As a result, the spaces between the semiconductor chip  3  and the substrate  2  varies from product to product. Therefore, the edge portions  4   a  of the metal cap  4  fixed on the semiconductor chip  3  may not reach the surface of the substrate  2  or, to the contrary, the roof portion  4   a  of the cap  4  may not reach to the top surface of the semiconductor chip  3 .  
           [0008]    Second, it is difficult to form the lower edges of the edge portions  4   a  of the metal cap  4  so as to lie exactly parallel with the roof portion  4   b . The lower edges of the edge portions  4   a  of the metal cap  4  may therefore be formed to have a small angle with the roof portion  4   b . When such a metal cap  4  is used, gaps are formed between the lower edges of the edge portions  4   a  of the metal cap  4  and the substrate  2  because the lower edges of the edge portions  4   a  of the metal cap  4  slantingly touch the substrate  2 .  
           [0009]    Each of these problems results in degradation of heat dissipation performance from the semiconductor chip  3  to the substrate  2  via the metal cap  4 . In the case where the semiconductor chip  3  processes a signal having large electric power, so that the semiconductor chip  3  generates a lot of heat, heat dissipation from the semiconductor chip  3  to the substrate  2  via the metal cap  4  is particularly important. Such degradation of the heat dissipation performance therefore becomes a serious problem.  
           [0010]    It is therefore an object of the present invention to provide an improved high frequency module.  
           [0011]    Another object of the present invention is to provide a high frequency module which can efficiently dissipate heat generated by a semiconductor chip.  
           [0012]    The above and other objects of the present invention can be accomplished by a high frequency module for mounting on a motherboard, comprising: a substrate, a semiconductor chip fixed on the substrate, and a cap provided above the semiconductor chip, the cap having a flat portion to which heat generated by the semiconductor chip is transferred and extended portions led out from opposite edges of the flat portion, the extended portions of the cap being in contact with the side surfaces of the substrate.  
           [0013]    According to this aspect of the present invention, because the extended portions of the cap are in contact with side surfaces of the substrate, a wide area of contact between the extended portions of the cap and the side surfaces of the substrate can be ensured even if the height of the semiconductor chip deviates slightly from standard or the shape of the cap deviates slightly from standard. Heat transferred to the flat portion of the cap from the semiconductor chip is therefore efficiently conducted to the substrate via the extended portions.  
           [0014]    In a preferred aspect of the present invention, the extended portions are connected to electrodes formed on the motherboard.  
           [0015]    According to this preferred aspect of the present invention, because the extended portions of the cap are connected to electrodes formed on the motherboard, heat generated by the semiconductor chip is efficiently conducted to the motherboard, which has a large heat capacity. Thus, the heat dissipation performance is further enhanced.  
           [0016]    In a further preferred aspect of the present invention, the high frequency module further comprises a roof plate provided between the semiconductor chip and the flat portion of the cap.  
           [0017]    According to this preferred aspect of the present invention, the roof plate provided between the semiconductor chip and the flat portion of the cap works as a heat sink to further enhance the heat dissipation performance.  
           [0018]    In a further preferred aspect of the present invention, the roof plate is thicker than the flat portion of the cap.  
           [0019]    According to this preferred aspect of the present invention, because the roof plate is thicker than the flat portion of the cap, the roof plate has a large heat capacity. The heat dissipation performance is therefore further enhanced.  
           [0020]    In a further preferred aspect of the present invention, the roof plate contains aluminum.  
           [0021]    According to this preferred aspect of the present invention, the aluminum content of the roof plate makes it advantageous in the electric and thermal conductivity and low in cost. Thus, the heat generated by the semiconductor chip  13  can be thoroughly dissipated and the cost of the high frequency module can be minimized.  
           [0022]    In a further preferred aspect of the present invention, the semiconductor chip is mounted on the substrate in a flip-chip manner.  
           [0023]    According to this preferred aspect of the present invention, because the semiconductor chip is mounted on the substrate in a flip-chip manner, the size of the high frequency module can be minimized.  
           [0024]    In a further preferred aspect of the present invention, the high frequency module further comprises a non reciprocal circuit element mounted on the substrate, the upper surface of the non reciprocal circuit element being in contact with the flat portion of the cap.  
           [0025]    According to this preferred aspect of the present invention, because the upper surface of the non reciprocal circuit element is in contact with the flat portion of the cap, the non reciprocal circuit element works as a heat sink. Thus, the heat dissipation performance is further enhanced.  
           [0026]    In a further preferred aspect of the present invention, a side surface of the non reciprocal circuit element is in contact with an extended portion of the cap.  
           [0027]    According to this preferred aspect of the present invention, because a side surface of the non reciprocal circuit element is in contact with an extended portion of the cap, the non reciprocal circuit element and the cap are in contact over a wide area. The heat dissipation performance is therefore further enhanced.  
           [0028]    The above and other objects of the present invention can be also accomplished by a high frequency module for mounting on a motherboard, comprising: a substrate, a semiconductor chip fixed on the substrate, a heat sink having a projecting portion in contact with the semiconductor chip, and means for conducting heat transferred to the heat sink to the substrate.  
           [0029]    According to this aspect of the present invention, the total heat capacity of the heat sink is increased by the projecting portion formed to make contact with the semiconductor chip. Thus, heat generated by the semiconductor chip is efficiently conducted to the substrate. Further, because the heat sink is in contact with the semiconductor chip only at the projecting portion, a space is formed between the other portions of the heat sink and the substrate. Thus, this space can be utilized to mount other electronic components-on the substrate.  
           [0030]    In a preferred aspect of the present invention, the projecting portion of the heat sink is formed from one end to the other end of the heat sink.  
           [0031]    According to this preferred aspect of the present invention, because the projecting portion of the heat sink is formed from one end to the other end of the heat sink, the heat sink can be easily fabricated at low cost. Further, because the projecting portion of the heat sink is formed from one end to the other end of the heat sink, the substrate and the projecting portion of the heat sink are close to each other also at portions other than where the semiconductor chip is mounted. Thus, the substrate and the heat sink can be strongly fixed by providing an adhesive at portions where they are close to each other.  
           [0032]    In a further preferred aspect of the present invention, the heat sink is fabricated by extruding aluminum metal.  
           [0033]    According to this preferred aspect of the present invention, because the heat sink is fabricated by extruding aluminum metal, the fabrication cost of the heat sink can be decreased.  
           [0034]    In a further preferred aspect of the present invention, the heat conducting means is a cap having a flat portion covering the heat sink and extended portions leaded out from opposite edges of the flat portion.  
           [0035]    According to this preferred aspect of the present invention, because the means for conducting heat transferred from the heat sink to the substrate is configured by the cap having the flat portion covering the heat sink and the extended portions led out from opposite edges of the flat portion, heat accumulated in the heat sink is conducted from the flat portion of the cap to the substrate via the extended portions of the cap.  
           [0036]    In a further preferred aspect of the present invention, an extended portion of the cap is in contact with a first side surface of the substrate.  
           [0037]    According to this preferred aspect of the present invention, because an extended portion of the cap is in contact with the first side surface of the substrate, a wide area of contact between the extended portion of the cap and the first side surface of the substrate can be ensured even if the height of the semiconductor chip deviates slightly from standard or the shape of the cap deviates slightly from standard. Heat transferred to the flat portion of the cap from the semiconductor chip is therefore efficiently conducted to the substrate via the extended portion.  
           [0038]    In a further preferred aspect of the present invention, the extended portions of the cap are connected to electrodes formed on the motherboard.  
           [0039]    According to this preferred aspect of the present invention, because the extended portions of the cap are connected to electrodes formed on the motherboard, heat generated by the semiconductor chip is efficiently conducted to the motherboard which has a large heat capacity. Thus, the heat dissipation performance is further enhanced.  
           [0040]    In a further preferred aspect of the present invention, the high frequency module further comprises an electronic component provided in a space formed between the heat sink and the substrate.  
           [0041]    According to this preferred aspect of the present invention, a space formed between the heat sink and the substrate at portions other than the projecting portion is effectively utilized.  
           [0042]    In a further preferred aspect of the present invention, the electronic component is thicker than the semiconductor chip.  
           [0043]    According to this preferred aspect of the present invention, the space formed between the heat sink and the substrate at portions other than the projecting portion, which space is taller than the space formed between the projecting portion of the heat sink and the substrate, is effectively utilized to accommodate an electronic component thicker than the semiconductor chip.  
           [0044]    In a further preferred aspect of the present invention, the upper surface of the non reciprocal circuit element is in contact with the flat portion of the cap.  
           [0045]    According to this preferred aspect of the present invention, because the upper surface of the non reciprocal circuit element is contact with the flat portion of the cap, the non reciprocal circuit element works as a heat sink. Thus, the heat radiation performance is further enhanced.  
           [0046]    In a further preferred aspect of the present invention, a first side surface of the non reciprocal circuit element is in contact with a second side surface of the substrate opposite to the first side surface thereof.  
           [0047]    According to this preferred aspect of the present invention, the non reciprocal circuit element is not mounted on the substrate but fixed to the substrate such that first side surface of the non reciprocal circuit element is contact with a second side surface of the substrate. The total height of the high frequency module is therefore not equal to the sum of the thicknesses of the non reciprocal circuit element and the substrate but can be substantially set to only the thickness of the non reciprocal circuit element. The total height can therefore be made small. As a result, the high frequency module can be preferably utilized in a mobile phone or the like.  
           [0048]    In a further preferred aspect of the present invention, the second side surface of the substrate and the first side surface of the non reciprocal circuit element have substantially the same length.  
           [0049]    According to this preferred aspect of the present invention, because the second side surface of the substrate and the first side surface of the non reciprocal circuit element have substantially the same length, the high frequency module can be formed in the overall shape of a rectangle. This not only makes handling of the high frequency module easy but also makes it unnecessary for the cap to have a complex structure. Cost can therefore be decreased.  
           [0050]    In a further preferred aspect of the present invention, the second side surface of the non reciprocal circuit element opposite to the first side surface thereof is in contact with an extended portion of the cap.  
           [0051]    According to this preferred aspect of the present invention, because the second side surface of the non reciprocal circuit element opposite to first side surface thereof is in contact with an extended portion of the cap, a wide area of contact between the cap and the non reciprocal circuit element is established. The heat dissipation performance is therefore further enhanced.  
           [0052]    In a further preferred aspect of the present invention, the cap has bent portions led out from other opposite edges of the flat portion.  
           [0053]    According to this preferred aspect of the present invention, because the cap has bent portions led out from other opposite edges of the flat portion, the mechanical strength of the cap is enhanced.  
           [0054]    In a further preferred aspect of the present invention, the bent portion are led out from the flat portion by a shorter distance than the extended portions are led out therefrom.  
           [0055]    In a further preferred aspect of the present invention, the bent portions extended to points to short of side surfaces of the substrate to leave openings between the ends thereof and the substrate.  
           [0056]    According to this preferred aspect of the present invention, because openings are formed between the ends of the bent portions and the substrate, the inside of the high frequency module can be visually inspected via the openings.  
           [0057]    The above and other objects of the present invention can be also accomplished by a high frequency module, comprising:  
           [0058]    a high frequency amplifier portion including a substrate having first and second side surfaces, a semiconductor chip mounted on the substrate, and a heat sink provided above the semiconductor chip;  
           [0059]    a non reciprocal circuit element having first and second side surfaces; and  
           [0060]    a cap having a flat portion, a first extended portion, and a second extended portion,  
           [0061]    the high frequency amplifier portion being fixed to the non reciprocal circuit element such that the first side surface of the substrate is contact with the first side surface of the non reciprocal circuit element,  
           [0062]    the cap being fixed to the high frequency amplifier portion and the non reciprocal circuit element such that the flat portion of the cap is in contact with at least the heat sink of the high frequency amplifier portion, that the first extended portion of the cap is contact with the second side surface of the substrate, and that that the second extended portion of the cap is contact with the second side surface of the non reciprocal circuit element.  
           [0063]    According to this aspect of the present invention, the non reciprocal circuit element is not mounted on the substrate, which is part of the high frequency amplifier portion, but fixed to the substrate such that the first side surface of the non reciprocal circuit element is in contact with the first side surface of the substrate. The total height of the high frequency module is therefore not equal to the sum of the thicknesses of the non reciprocal circuit element and the substrate but can be substantially set to only the thickness of the non reciprocal circuit element. The total height can therefore be made small. As a result, the high frequency module can be preferably utilized in a mobile phone or the like. Moreover, because the high frequency amplifier portion and the non reciprocal circuit element are both covered with the cap, the high frequency module is made easy to handle.  
           [0064]    In a preferred aspect of the present invention, the first side surface of the substrate and the first side surface of the non reciprocal circuit element have substantially the same length.  
           [0065]    According to this preferred aspect of the present invention, because the first side surface of the substrate and the first side surface of the non reciprocal circuit element have substantially the same length, the high frequency module can be formed in the overall shape of a rectangle. This not only makes handling of the high frequency module easy but also makes it unnecessary for the cap to have a complex structure. Cost can therefore be decreased.  
           [0066]    In a further preferred aspect of the present invention, the first side surface of the non reciprocal circuit element is longer than the distance between the first side surface and the second side surface of the non reciprocal circuit element.  
           [0067]    According to this preferred aspect of the present invention, the length of first side surface of the non reciprocal circuit element is made greater than the distance between the first side surface and the second side surface thereof and is preferably made the same as the length of first side surface of the substrate. A permanent magnet of large size in plan view can therefore be included in the non reciprocal circuit element. As a result, a strong magnetic force can be obtained without changing the thickness of the non reciprocal circuit element. Since this means that the thickness of the permanent magnet can be minimized while still obtaining the required magnetic force, the total height of the high frequency module can be reduced.  
           [0068]    In a further preferred aspect of the present invention, the first extended portion of the cap is electrically connected to a motherboard on which the high frequency module is mounted.  
           [0069]    According to this preferred aspect of the present invention, because the first extended portion of the cap is electrically connected to the motherboard on which the high frequency module is mounted, heat generated by the semiconductor chip is efficiently conducted to the motherboard, which has a large heat capacity. Further, a predetermined potential can be applied to the semiconductor chip via the cap.  
           [0070]    In a further preferred aspect of the present invention, the non reciprocal circuit element further has an upper surface, the flat portion of the cap being in contact with the upper surface of the non reciprocal circuit element.  
           [0071]    According to this preferred aspect of the present invention, because the flat portion of the cap is in contact with the upper surface of the non reciprocal circuit element, the non reciprocal circuit element works as a heat sink. Thus, the heat dissipation performance is enhanced. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0072]    [0072]FIG. 1 is a schematic sectional diagram showing a prior-art high frequency module described in U.S. Pat. No. 5,831,836.  
         [0073]    [0073]FIG. 2A is a perspective view showing a high frequency module that is a preferred embodiment of the present invention. FIG. 2B is a sectional view showing the high frequency module mounted on a motherboard. FIG. 2C is an enlarged sectional view of a part of FIG. 2B.  
         [0074]    [0074]FIG. 3 is an exploded schematic perspective view showing the high frequency module of FIG. 2A.  
         [0075]    [0075]FIG. 4A is a perspective view showing a high frequency module that is another preferred embodiment of the present invention. FIG. 4B is a sectional view showing the high frequency module mounted on a motherboard.  
         [0076]    [0076]FIG. 5 is an exploded schematic perspective view showing a high frequency module that is another preferred embodiment of the present invention.  
         [0077]    [0077]FIG. 6A is a perspective view showing a high frequency module that is a further preferred embodiment of the present invention. FIG. 6B is a sectional view showing the high frequency module mounted on a motherboard.  
         [0078]    [0078]FIG. 7 is an exploded schematic perspective view showing the high frequency module of FIG. 6.  
         [0079]    [0079]FIG. 8 is a sectional view showing a section along line X-X in FIG. 6A.  
         [0080]    [0080]FIG. 9 is a sectional view showing a section along line Y-Y in FIG. 6A.  
         [0081]    [0081]FIG. 10 is a sectional view showing the high frequency module shown in FIGS.  6  to  9  from which an isolator has been eliminated.  
         [0082]    [0082]FIG. 11 is a schematic plan view showing a high frequency amplifier portion and an isolator. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0083]    Preferred embodiments of the present invention will be explained with reference to the drawings.  
         [0084]    [0084]FIG. 2A is a perspective view showing a high frequency module that is a preferred embodiment of the present invention. FIG. 2B is a sectional view showing the high frequency module mounted on a motherboard. FIG. 2C is an enlarged sectional view of a part of FIG. 2B. FIG. 3 is an exploded schematic perspective view showing the high frequency module of FIG. 2A.  
         [0085]    As shown in FIGS. 2 and 3, the high frequency module  10  according to this preferred embodiment is constituted of a substrate  11 , a plurality of electrodes  12  formed on the back surface of the substrate  11 , a semiconductor chip  13  and electronic components  14 , such as capacitors, each mounted on the main surface of the substrate  11 , a roof plate  15  mounted on the upper surface of the semiconductor chip  13 , and a cap  16 . The high frequency module  10  having such a configuration is mounted on a motherboard  23  as shown in FIG. 2B.  
         [0086]    The substrate  11  is a single layered insulating substrate or a multilayered substrate with elements are incorporated therein. Electrodes  19  are formed on the main surface of the substrate  11  to establish electrical connection with the semiconductor chip  13  and the electronic components  14 , and the electrodes  19  are electrically connected to the electrodes  12  formed on the back surface of the substrate  11  via through holes (not shown).  
         [0087]    The electrodes  12  are electrically connected to electrodes  24  formed on the motherboard  23  as shown in FIG. 2B.  
         [0088]    The semiconductor chip  13  processes a high frequency signal and has a plurality of electrodes  20  provided thereon. Microbumps  17  made of solder or gold are formed on the electrodes  20 . The microbumps  17  are electrically and mechanically connected to the electrodes  19  formed on the substrate  11  to establish electrical connection between the electrodes  19  formed on the substrate  11  and the electrodes  20  formed on the semiconductor chip  13  so that the semiconductor chip  13  is fixed on the main surface of the substrate  11  in a flip-chip manner. As shown in FIG. 2C, an underfilling resin  18  is charged and cured in a space formed between the semiconductor chip  13  and the substrate  11  so that the semiconductor chip  13  and the substrate  11  are strongly fixed to each other. It is preferable to use a low viscosity resin such as an epoxy type resin for the underfilling resin  18  because the underfilling resin  18  is required to be charged into the entire space between the semiconductor chip  13  and the substrate  11 .  
         [0089]    The roof plate  15  is a plate-shaped component made of aluminum, copper or the like. As shown in FIG. 2C, the roof plate  15  is electrically connected to an electrode  13   a  formed on the upper surface of the semiconductor chip  13  via solder or conductive adhesive  21 . Further, an insulating resin  22  is provided between the roof plate  15  and the substrate  11  at the portion where the semiconductor chip  13  is mounted so that the semiconductor chip  13 , the roof plate  15 , and the substrate  11  are fixed to one another and the semiconductor chip  13  is passivated. It is preferable to use a high viscosity resin such as a silicon type resin for the resin  22  because the resin  22  is required to sufficiently passivate the semiconductor chip  13 .  
         [0090]    The cap  16  is formed by bending a tape-shaped metal component made of aluminum, copper or the like. The cap  16  has a flat portion  16   a  and extended portions  16   b  led out from the both edges. The flat portion  16   a  of the cap  16  is electrically connected and fixed to the roof plate  15  by solder, conductive adhesive, or spot welding (not shown). The extended portions  16   b  contact the both of side surfaces of the substrate  11  as though pinching it. Ground electrodes (not shown) are formed on both side surfaces of the substrate  11 . The ground electrodes and the extended portions  16   b  are electrically connected and fixed to each other by conductive adhesive or solder (not shown).  
         [0091]    As described above, a plurality of electrodes  24 , which are connected to the electrodes  12  on the substrate  11 , are formed on the motherboard  23  on which the high frequency module  10  is mounted. Further, ground electrodes  25  are formed on the motherboard  23 . The ground electrodes  25  and lower portions of the extended portions  16   b  of the cap  16  are connected by solder  26 .  
         [0092]    According to the high frequency module  10  having the above described configuration, heat generated by the semiconductor chip  13  is conducted through the roof plate  15  and the cap  16  to the substrate  11  and the ground electrodes  25  of the motherboard  23 . In this case, because the extended portions  16   b  of the cap  16  lie along the side surfaces of the substrate  11 , the flat portion  16   a  of the cap  16  can contact the entire upper surface of the roof plate  15  and the extended portions  16   b  of the cap  16  can contact the side surfaces of the substrate  11  without leaving a gap. Thus, extremely good heat dissipation performance can be obtained.  
         [0093]    Further, in the high frequency module  10 , the roof plate  15  can work as a heat sink to accumulate heat because the roof plate  15  is inserted between the semiconductor chip  13 , a heat source, and the cap  16 . Heat accumulated in the roof plate  15  is conducted through the flat portion  16   a  of the cap  16  to the substrate  11  and the motherboard  23  via the extended portions  16   b . Thus, the heat dissipation performance is markedly improved because the roof plate  15  works as a heat sink. Further, as shown in FIGS. 2 and 3, therefore the roof plate  15  is thicker than the cap  16 . The roof plate  15  therefore has good heat sink capability, so that even if the semiconductor chip  13  processes a signal having relatively large electric power, as in the case of a high frequency power amplifier, and thus generates a large amount of heat, the heat can be sufficiently dissipated. Moreover, as shown in FIGS. 2 and 3, the contact area of the roof plate  15  with the cap  16  is greater than the contact area of the roof plate  15  with the electrode  13   a  formed on the upper surface of the semiconductor chip  13 . Heat accumulated in the roof plate  15  can therefore be efficiently conducted to the substrate  11  and the motherboard  23 . It is worth noting that the material of the roof plate  15  is not limited to metal but can be resin or ceramic covered with a conductor.  
         [0094]    Although most of the heat generated by the semiconductor chip  13  is conducted to the motherboard  23  via the roof plate  15  and cap  16 , part of heat is conducted to the substrate  11  via the microbumps  17  and the resin  18 . Heat conducted to the substrate  11  is also conducted to the motherboard  23  via the electrodes  12 .  
         [0095]    Because the high frequency module  10  according to this embodiment can be used in a high frequency band over 1 GHz, for example, a predetermined potential must be applied to the electrode  13   a  formed on the upper surface of the semiconductor chip  13 . The potential of the electrode  13   a  formed on the upper surface of the semiconductor chip  13  can be reliably made the same potential as the ground potential applied to the motherboard  23  because the electrode  13   a  formed on the upper surface of the semiconductor chip  13  is connected to the ground electrodes  25  on the motherboard  23  via the roof plate  15  and the cap  16 .  
         [0096]    Furthermore, because the cap  16  is thinner than the roof plate  15 , it is easy to bend. If the cap  16  and the roof plate  15  should be constituted as a single component, the component would be difficult to form because of its complex shape. In the high frequency module  10 , the cap  16 , which is easy to bend because it is thin, and the roof plate  15 , which has good heat accumulation performance because it is thick, are separate members. The high frequency module  10  can therefore be easily fabricated at low cost. Moreover, in the high frequency module  10 , the fact that the roof plate  15  and the cap  16  are separate members enables use of the same cap  16  with various semiconductor chips  13  of different thickness and various substrates  11  of different thickness simply selecting a roof plate  15  of appropriate thickness. Thus, flexibility is enhanced and the cost can be decreased.  
         [0097]    Furthermore, because the roof plate  15  can be thickened by thinning the cap  16  while staying within the allowable total thickness of the high frequency module  10 , the heat sink performance of the roof plate  15  can be enhanced. It is preferable to use aluminum or copper as the material of the cap  16 , as mentioned above. Taking cost, thermal conductivity, and electric conductivity into consideration, however, it is most preferable to use aluminum.  
         [0098]    Use of aluminum as the material of the roof plate  15  is advantageous in the points of electric conductivity, thermal conductivity, and cost. In addition, use of aluminum enables the connection and heat conduction between the semiconductor chip  13  and the ground electrodes (not shown) formed on the substrate  11  to be sufficiently performed. This also lowers cost.  
         [0099]    In the high frequency module  10  according to the embodiment, because the cap  16  does not entirely cover the semiconductor chip  13  and the electronic components  14 , the semiconductor chip  13  and the electronic components  14  can be visually observed after the high frequency module  10  is mounted on the motherboard  23 . This makes it easy to find and repair defects if any malfunctions are detected after the high frequency module  10  is mounted on the motherboard  23 . However, it is not an essential feature of this invention that the cap  16  does not entirely cover the semiconductor chip  13  and the electronic components  14 . Therefore, the extended portions  16   b  can if desired be led out from the all edges of the flat portion  16   a  to cover all sides of the substrate  11 .  
         [0100]    Another preferred embodiment of the present invention will be explained.  
         [0101]    [0101]FIG. 4A is a perspective view showing a high frequency module that is another preferred embodiment of the present invention. FIG. 4B is a sectional view showing the high frequency module mounted on a motherboard. FIG. 5 is an exploded schematic perspective view showing the high frequency module of FIG. 4A.  
         [0102]    The high frequency module  30  according to this preferred embodiment is constituted of a substrate  11 , a plurality of electrodes  12  formed on the back surface of the substrate  11 , a semiconductor chip  13  and electronic components  14 , such as capacitors, each mounted on the main surface of the substrate  11 , an isolator  31  that is taller than the semiconductor chip  13 , a roof plate  15  mounted on the upper surface of the semiconductor chip  13 , and a cap  16 . The high frequency module  30  having such a configuration is mounted on a motherboard  23  as shown in FIG. 4B.  
         [0103]    The isolator  31  of the type is widely used as a non reciprocal circuit element at the stage following a high frequency amplifier. The isolator  31  tends to be taller than other components because it includes a ferrite core made of a YIG or the like, a permanent magnet mounted on the ferrite core, and a metal plate made of iron or the like wrapped around them as a magnetic yoke.  
         [0104]    In the high frequency module  30 , the roof plate  15  is electrically connected to an electrode  13   a  (not shown in FIGS. 4 and 5) formed on the upper surface of the semiconductor chip  13  by solder or conductive adhesive  21  (not shown in FIGS. 4 and 5). The upper surface of the roof plate  15  is coplanar with or slightly higher than the upper surface of the isolator  31 . The reason for setting the upper surface of the roof plate  15  coplanar with or slightly higher than the upper surface of the isolator  31  is to avoid forming a gap between the roof plate  15  and the cap  16 , since otherwise the upper surface of the roof plate  15  might become lower than the upper surface of the isolator  31  owing to a fabrication error.  
         [0105]    The cap  16  has a flat portion  16   a  and extended portions  16   b . The flat portion  16   a  of the cap  16  is electrically connected and fixed to the roof plate  15  by solder, conductive adhesive, or spot welding (not shown), and retains the upper surface of the isolator  31 . The extended portions  16   b  contact both side surfaces of the substrate  11  as though pinching it therebetween. Ground electrodes (not shown) are formed on both side surfaces of the substrate  11 . The ground electrodes and the extended portions  16   b  are electrically connected and fixed to each other by conductive adhesive or solder (not shown).  
         [0106]    The roof plate  15  can adhere to the flat portion  16   a  of the cap  16  because the upper surface of the roof plate  15  is set coplanar with or slightly higher than the upper surface of the isolator  31 . The electrical connection and the fixing between the substrate  11  and the semiconductor chip  13 , between the cap  16  and the substrate  11 , and between the cap  16  and the motherboard  23  are the same as in the high frequency module  10  of the embodiment explained earlier and will not be explained again here.  
         [0107]    The high frequency module  30  according to this embodiment has the following advantages in addition to the advantages obtained from the high frequency module  10 . Specifically, because the single cap  16  covers the semiconductor chip  13  and the isolator  31  both mounted on the same substrate  11 , a nozzle of a mounter (not shown) can chuck at the flat portion  16   a  of the roof plate  16  to handle the high frequency module  30  when the high frequency module  30  including the substrate  11 , the semiconductor chip  13 , the roof plate  16 , and the isolator  31  is mounted on the motherboard  23 . With the high frequency module  30 , therefore, handling is simplified during the mounting process despite the integration of the semiconductor chip  13  and the isolator  31  that are of different heights.  
         [0108]    A further preferred embodiment of the present invention will be explained.  
         [0109]    [0109]FIG. 6A is a perspective view showing a high frequency module that is further preferred embodiment of the present invention. FIG. 6B is a sectional view showing the high frequency module mounted on a motherboard. FIG. 7 is an exploded schematic perspective view showing the high frequency module of FIG. 6. FIG. 8 is a sectional view showing a section along line X-X in FIG. 6A. FIG. 9 is a sectional view showing a section along line Y-Y in FIG. 6A.  
         [0110]    As shown in FIGS.  6  to  9 , the high frequency module  40  according to this preferred embodiment is constituted of a substrate  41 , a plurality of electrodes  42  formed on the back surface of the substrate  41 , a semiconductor chip  43  and electronic components  44 , such as capacitors, each mounted on the main surface of the substrate  41 , a heat sink  45  mounted on the upper surface of the semiconductor chip  43 , an isolator  47  as a non reciprocal circuit element, and a cap  46  covering the heat sink  45  and the isolator  47 . The substrate  41 , the semiconductor chip  43 , the electronic components  44 , and the heat sink  45  constitute a high frequency amplifier portion  70 . The high frequency module  40  having such a configuration is mounted on a motherboard  23  as shown in FIG. 6B.  
         [0111]    The substrate  41 , which is part of the high frequency amplifier portion  70 , is a multilayered substrate in which a number of conductive layers  48  are incorporated. Electrodes  49  are formed on the main surface of the substrate  41  to establish electrical connection with the semiconductor chip  43  and the electronic components  44 , and the electrodes  49  are electrically connected to the electrodes  42  formed on the back surface of the substrate  41  via the conductive layers  48  incorporated in the substrate  41 .  
         [0112]    The electrodes  42  are electrically connected to electrodes  51  formed on the motherboard  23  via solder  50  as shown in FIG. 6B.  
         [0113]    The semiconductor chip  43 , which is part of the high frequency amplifier portion  70 , is a chip composed of a Ga—As substrate, for example, for processing a high frequency signal. The semiconductor chip  43  employs a plurality of electrodes (not shown) on which microbumps  52  made of solder or gold are provided. The microbumps  52  are electrically and mechanically connected to the electrodes  49  formed on the main surface of the substrate  41  to establish electrical connection between the electrodes  49  formed on the substrate  41  and the electrodes (not shown) formed on the semiconductor chip  43  so that the semiconductor chip  43  is fixed on the main surface of the substrate  41  in a flip-chip manner. As shown in FIGS.  6  to  9 , an underfilling resin  53  is charged and cured in a space formed between the semiconductor chip  43  and the substrate  41  so that the semiconductor chip  43  and the substrate  41  are strongly fixed to each other. It is preferable to use a low viscosity resin such as an epoxy type resin for the underfilling resin  53  because the underfilling resin  53  is required to be charged into the entire space between the semiconductor chip  43  and the substrate  41 .  
         [0114]    Each of the electronic components  44 , which are part of the high frequency amplifier portion  70 , is a discrete capacitor, for example. As shown in FIGS.  6  to  8 , the upper surfaces of the electronic components  44  are higher than the upper surface of the semiconductor chip  43  when mounted on the substrate  41 .  
         [0115]    The heat sink  45 , which is part of the high frequency amplifier portion  70 , is made of aluminum metal. As shown in FIGS.  6  to  8 , the heat sink  45  has a projecting portion  45   a  at the approximately center thereof. The projecting portion  45   a  has a constant width from one end to the other end of the heat sink  45 . The heat sink  45  can therefore be easily and cheaply mass-produced by means of extruding of aluminum metal and cutting. The projecting portion  45   a  of the heat sink  45  is electrically connected to an electrode (not shown) formed on the upper surface of the semiconductor chip  43  by solder or a conductive adhesive  54 . Further, an adhesive  55  is provided between the projecting portion  45   a  of the heat sink  45  and the substrate  41  so that the semiconductor chip  43 , the heat sink  45 , and the substrate  41  are fixed to one another and the semiconductor chip substantially throughout the region between the projecting portion  45   a  of the heat sink  45  and the substrate  41 , so that the heat sink  45  and the substrate  41  are strongly fixed.  
         [0116]    The upper surface of the heat sink  45  is coplanar with or slightly higher than the upper surface of the isolator  47 . The reason for setting the upper surface of the heat sink  45  coplanar with or slightly higher than the upper surface of the isolator  47  is to avoid forming a gap between the heat sink  46  and the cap  46 , since otherwise the upper surface of the heat sink  45  might become lower than the upper surface of the isolator  47  owing to a fabrication error. Because the heat sink  45  has the projecting portion  45   a , a space  69  is formed between the heat sink  45  and the substrate  41 . As shown in FIGS. 6 and 8, the electronic components  44  are provided in the space  69 .  
         [0117]    The cap  46  covers both the high frequency amplifier portion  70  and the isolator  47  and is formed by bending a tape-shaped metal component made of aluminum, copper or the like. The cap  46  has a flat portion  46   a , extended portions  46   b  and  46   c , and bent portions  46   d  and  46   e . The flat portion  46   a  of the cap  46  is electrically connected and fixed to the upper surface of the heat sink  45  and the upper surface of the isolator  47  by solder, conductive adhesive, or spot welding  56 . The extended portion  46   b  of the cap  46  covers one side surface of the heat sink  45  and one side surface of the substrate  41 . The extended portion  46   c  of the cap  46  covers one side surface of the isolator  47 . Thus, the extended portions  46   b  and  46   c  of the cap  46  contact one side surface of the substrate  41  and one side surface of the isolator  47  as though pinching them therebetween. Ground electrodes (not shown) are formed on the side surface of the substrate  41 . The ground electrodes and the extended portion  46   b  are electrically connected and fixed to each other by conductive adhesive or solder (not shown).  
         [0118]    As shown in FIG. 8, the isolator  47  is constituted of a support body  57 , an insulating substrate  58 , a ferrite core  59  made of a YIG or the like, a resonation conductor  60  covering the ferrite core  59 , a permanent magnet  61 , and a yoke  62  wrapping and integrating them. The insulating substrate  58  has an input terminal  63  for connection with the high frequency amplifier portion  70 , a ground terminal (not shown), and electrodes  64  and  65  for connection with the electrodes  51  formed on the motherboard  23 . The electrodes  64  and  65  formed on the isolator  47  and the electrodes  51  formed on the motherboard  23  are electrically connected to each other via solder  50 .  
         [0119]    The high frequency amplifier portion  70  and the isolator  47  having the above described configuration are adhered and integrated side by side to constitute the high frequency module  40 . Electrical connections between the high frequency amplifier portion  70  and the isolator  47  are established by solder  66 .  
         [0120]    Prior to integration, each of the high frequency amplifier portion  70  and the isolator  47  is an intermediate product which can be inspected and trimmed independently. Therefore, after the high frequency amplifier portion  70  and the isolator  47  are fabricated, they can be inspected and trimmed before integration.  
         [0121]    As described above, a plurality of electrodes  51  for connection with the electrodes  42  on the substrate  41  are formed on the motherboard  23  on which the high frequency module  40  is mounted. Further, ground electrodes  67  are formed on the motherboard  23 . The ground electrodes  67  and lower portions of the extended portions  46   b  and  46   c  of the cap  46  are connected by solder  68 .  
         [0122]    Because the high frequency module  40  having the above described configuration employs the heat sink  45  having the projecting portion  45   a , there is formed the space  69  for accommodating the electronic components  44 , whose thickness is usually greater than that of the semiconductor chip  43  located between the projecting portion  45   a  of the heat sink  45  and the substrate  41 . According to the high frequency module  40  of this preferred embodiment, therefore, even if the electronic components  44  are thicker than the semiconductor chip  43  that generates heat transferred to the heat sink  45 , they can still be mounted on the same substrate  41 .  
         [0123]    Further, because the heat sink  45  has the projecting portion  45   a , the heat capacity thereof is enhanced, so that the heat dissipation performance is enhanced. Moreover, because the adhesive  55  is provided between the projecting portion  45   a  and the semiconductor chip  43 , the projecting portion  45   a  and the side surface of the semiconductor chip  43  can also be adhered to enhance the bonding strength therebetween is enhanced.  
         [0124]    Furthermore, because the projecting portion  45   a  of the heat sink  45  is rail-shaped from one end to the other end of the heat sink  45 , the heat sink  45  can be easily formed by extruding aluminum metal and cutting. The cost of fabricating the heat sink  45  is therefore low.  
         [0125]    Further, in the high frequency module  40 , the extended portions  46   b  and  46   c  of the cap  46  are soldered to the ground electrodes  67  on the motherboard  23 . Heat generated by the semiconductor chip  43  is therefore conducted to the ground electrodes  67  on the motherboard  23  via the heat sink  45  and the cap  46 . Because the heat sink  45  and the cap  46  constitute a heat storage having a large heat capacity and the neat accumulated therein is conducted to the ground electrodes  67 , good heat dissipation performance can be obtained. Of the extendednportions  46   b  and  46   c  in the high frequency module  40 , only the extended portion  46   b  touching the heat sink  45  and the substrate  41  is absolutely required to be soldered to the motherboard  23 . However, taking the heat dissipation performance into consideration, it is preferable that both of the extended portions  46   b  and  46   c  be soldered to the motherboard  23 .  
         [0126]    Furthermore, in the high frequency module  40  of this preferred embodiment, the cap  46  and the yoke  62  of the isolator  47  are connected by the conductive adhesive or solder  56 . Heat dissipation performance is therefore enhanced because heat generated by the semiconductor chip  43  is conducted to the yoke  62  via the heat sink  45  and the cap  46 .  
         [0127]    Further, in the high frequency module  40  of this preferred embodiment, the opposite ends of the cap  46  are formed with the narrow bent portions  46   d  and  46   e  (see FIG. 9) that meet the flat portion  46   a  at right angles. The mechanical strength of the cap  46  is therefore improved so that warping thereof can be avoided. Moreover, because the bent portions  46   d  and  46   e  have small width, visual observation of the high frequency amplifier portion  70  and the isolator  47  covered with the cap  46  is not obstructed to inspect visually the interfitting condition of the high frequency amplifier portion  70  and the isolator  47  with the cap  46  and, when necessary, to perform various operations, including, for example, using a dispenser to supply a solder paste or a conductive adhesive into the interfitting portion of the high frequency amplifier portion  70  and the isolator  47  with the cap  46 . Moreover, because the high frequency amplifier portion  70  and the isolator  47  can be visually observed even after the high frequency module  40  is mounted on the motherboard  23 , defects can be easily detected and repaired even after the high frequency module  40  has been mounted on the motherboard  23 .  
         [0128]    Furthermore, in the high frequency module  40  of this preferred embodiment, the isolator  47  is not mounted on the substrate  41  but is fixed to the side surface of the substrate  41 . The total height of the high frequency module  40  is therefore not equal to the sum of the thicknesses of the isolator  47  and the substrate  41  but can be substantially set to only the thickness of the isolator  47 . The total height can therefore be made small. As a result, the high frequency module  40  can be preferably utilized in a mobile phone or the like.  
         [0129]    Further, in the high frequency module  40  of this preferred embodiment, because the cap  46  is in contact with the isolator  47 , heat generated by the semiconductor chip  43  is also conducted to the isolator  47  via the cap  46 , so that the heat dissipation performance is enhanced.  
         [0130]    The high frequency module  40  according to the above described embodiment employs the high frequency amplifier portion  70  and the isolator  47  connected to each other and covered with the cap  46 . However, as shown in FIG. 10, the high frequency module according to the present invention can be embodied as a high frequency module  80  obtained by eliminating the isolator  47  from the high frequency module  40 .  
         [0131]    The lateral length of the high frequency amplifier portion  70  and the lateral length of the isolator  47  are generally different from each other. However, in the high frequency module  40  according to the above described embodiment, because the plan shape of the isolator  47  is a rectangle measuring by L1×L2 in which L2 is coincident with the lateral length of the high frequency amplifier portion  70  as shown in FIG. 11, the high frequency module  40  can be formed in the overall shape of a rectangle. This not only makes handling of the high frequency module  40  easy but also makes it unnecessary for the cap  46  to have a complex structure. Cost can therefore be decreased. Further, because the lateral length of the isolator  47  is extended to be coincident with the lateral length L2 of the high frequency amplifier portion  70 , the permanent magnet  61  can be enlarged in plan view to generate a stronger magnetic force without increasing the thickness thereof. Since this means that the thickness of the permanent magnet  61  can be minimized while still obtaining the required magnetic force, the total height of the high frequency module  40  can be reduced. Because the lateral length of the isolator  47  is coincident with the side length L2 of the high frequency amplifier portion  70 , the overall shape of the high frequency module  40  can be made rectangular merely by connecting them. Thus, the isolator  47  need not be mounted on the substrate  41 . This enables reduction of the total height of the high frequency module  40  and eliminates the need for various processing steps, such as forming via holes, that would be required if the isolator  47  were mounted on the substrate  41 .  
       INDUSTRIAL APPLICABILITY  
       [0132]    As described in the foregoing, the high frequency module according to the present invention can be preferably utilized in various communication apparatuses, particularly in mobile phones, owing to its superior heat dissipation performance, small size, and low cost.

Technology Category: h