Abstract:
In a compact radio frequency module, a first chip forms a heater element and a second chip forms a device whose operating characteristics vary with temperature change or whose maximum operating temperature is lower than the maximum operating temperature of the first chip. A multilayer substrate has a plurality of dielectric layers and a plurality of conductor layers and mechanically supports the first chip and the second chip with some of the conductor layers electrically connected with these chips. The module can conduct the heat generated by the first chip throughout the module; guide the heat generated by the first chip from the module&#39;s top face side to its bottom face side; and interrupt the heat conduction from the first conductor pattern on which the first chip is placed to the second conductor pattern on which the second chip is placed.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to wireless communications and particularly to radio frequency components for use in mobile communication terminals such as mobile phones and wireless communication terminals such as wireless LAN, which feature increased function, high integration, reduced size and low price.  
         [0003]     2. Description of the Related Art  
         [0004]     With the growing tendency towards more compact wireless communication terminals, there is demand for radio frequency components for wireless communication terminals that fit into a smaller packaging area. Conventionally, circuit of radio frequency parts have been divided into several blocks by function and the blocks have been manufactured separately as modules while efforts have been made to improve reliability, reduce size and increase integrtaion for each module. For example, methods of heat dissipation in power amplifier (hereinafter referred to as PA) modules including power amplifiers as heater elements are disclosed in JP-A No. 27570/1997 and JP-A No. 147349/1995.  
         [0005]     In recent years, JP-A No. 8584/1997 and JP-A No. 266546/1999 disclose techniques which produce more compact radio frequency components with higher integration in function by combining modules which would be separately manufactured in the former methods.  
         [0006]     PA requires a heat dissipation structure because it consumes much electric power and generates heat. For this reason, various PA module structures for effective heat dissipation are disclosed: one example is a multilayer substrate which has, on its surface layer, an electrically isolated metallized layer or a metallized layer connected to a grounding layer (JP-A No. 147349/1995) and another example concerns a structure of a substrate in which the almost whole surface of the ceramic substrate is covered with a metal layer and through holes for heat dissipation are uniformly distributed almost all over the substrate (JP-A No. 27570/1997).  
         [0007]     However, these conventional techniques have the following drawback: in a module which integrates a power amplifier and a device whose operating characteristics vary with rise in temperature, namely a device having sensitive temperature dependence of characteristics, on a substrate, the influence of the heat generated by the PA on the device having sensitive temperature dependence of characteristics is not taken into consideration, or though it is taken into consideration to mount a PA and a deveice having sensitive temperature dependence of characteristics together in a module, attention is not paid to the fact that part of the heat is conducted in the module substrate and then to the above-said device having sensitive temperature dependence of characteristics.  
         [0008]     Therefore, in the conventional techniques, when a device having sensitive temperature dependence of characteristics is mounted together with a power amplifier on a substrate, the fair distance between both the devices was needed to avoid the influence of the heat generated by the power amplifier. Furthermore, a deterioration in electrical characteristics which is caused by change in characteristics with temperature rise has been unavoidable. For this reason, it has been impossible to produce a compact, high performance radio frequency module in the form of both a power amplifier, which generates heat, and a device having sensitive temperature dependence of characteristics are mounted together.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention introduces a new concept of suppressing temperature rise in the part of a substrate where the above-mentioned device having sensitive temperature dependence of characteristics is placed for a radio frequency module where a power amplifier and the device having sensitive temperature dependence of characteristics are integrated, thereby solving the above problem and realizing a compact, high-performance radio frequency module.  
         [0010]     The present invention focuses the structure of a radio frequency module which solves the above problem and particularly the arrangement of conductor layers.  
         [0011]     According to one aspect of the present invention, a radio frequency module comprises at least: a first chip forming a heater element; a second chip forming a device whose operating characteristics vary with temperature change or whose maximum operating temperature is lower than the maximum operating temperature of the first chip; and a multilayer substrate which is comprised of a plurality of dielectric layers and a plurality of conductor layers and mechanically supports the first chip and the second chip with some of the conductor layers electrically connected with these chips, wherein the first chip is located on a conductor layer provided on the top face of the multilayer substrate or on a first conductor pattern made on a conductor layer inside a cavity made in the multilayer substrate; the second chip is located on a conductor layer provided on the top face of the multilayer substrate or on a second conductor pattern made on a conductor layer inside a cavity made in the multilayer substrate; and when the multilayer substrate is fixed on another substrate, it is fixed with its bottom face in contact with the other substrate, and the module has at least one of the following means: means for conducting the heat generated by the first chip throughout the module; means for guiding the heat generated by the first chip from the module&#39;s top face to its bottom face; and means for interrupting heat conduction from the first conductor pattern to the second conductor pattern.  
         [0012]     According to another aspect of the invention, a radio frequency module comprises at least: a first chip forming a heater element; a second chip forming a device whose operating characteristics vary with temperature change or whose maximum operating temperature is lower than the maximum operating temperature of the first chip; and a multilayer substrate which is comprised of a plurality of dielectric layers and a plurality of conductor layers and mechanically supports the first chip and the second chip with some of the conductor layers electrically connected with these chips, wherein the first chip is located on a conductor layer provided on the top face of the multilayer substrate or on a first conductor pattern made on a conductor layer inside a cavity made in the multilayer substrate; the second chip is located on a conductor layer provided on the top face of the multilayer substrate or on a second conductor pattern made on a conductor layer inside a cavity made in the multilayer substrate; and when the multilayer substrate is fixed on another substrate, it is fixed with its bottom face in contact with the other substrate and the first conductor pattern and another conductor pattern electrically connected with the first conductor pattern are isolated from the second conductor pattern and another conductor pattern electrically connected with the second conductor pattern at the conductor layer in which the second conductor pattern is formed and conductor layers closer to the top face of the multilayer substrate than the conductor layer in which the second conductor pattern is formed.  
         [0013]     According to a further aspect of the invention, the first conductor pattern and another conductor pattern electrically connected with the first conductor pattern are isolated from the second conductor pattern and another conductor pattern electrically connected with the second conductor pattern at the conductor layer in which the second conductor pattern is formed and conductor layers closer to the top face of the multilayer substrate than the conductor layer in which the second conductor pattern is formed and the former conductor patterns are connected with the latter ones at least at one of the conductor layers located closer to the bottom face of the multilayer substrate than the conductor layer in which the second conductor pattern is formed.  
         [0014]     According to a further aspect of the invention, a radio frequency module comprises a first chip; a second chip whose heat value per unit time may be smaller than that of the first chip; and a multilayer substrate comprised of a plurality of conductor layers and a plurality of dielectric layers, wherein the first chip and the second chip are electrically connected with any of the conductor layers, and there are a first structure for conducting the heat generated by the first chip horizontally in the module and a second structure for conducting the heat vertically in the module.  
         [0015]     A conductor layer may be used for the first structure. The conductor layer can conduct the heat generated by the first chip horizontally. When the conductor layer extends to the substrate&#39;s outer edge area, it realize easier heat conduction in a substrate. One approach to controlling the heat conductivity of the conductor layer is to cut off patterns in the conductor layer. To this end, part of the conductor layer may be removed or a groove may be made.  
         [0016]     The first chip, for example a power amplifier, does not always generate heat but turns on and off periodically in some cases. The primary object of the invention is to prevent the second chip from being affected by the heat generated by the first chip which is operating.  
         [0017]     According to a further aspect of the invention, as a method for preventing heat conduction from the first chip to the second chip, a heat isolation zone which crosses the line connecting the first chip and the second chip is specified on the main surface of the multilayer substrate and the conductor layer area corresponding to the projection from the heat isolation zone is removed or a groove is made in the area corresponding to the projection from the heat isolation zone. The conductor layer area corresponding to the projection from the heat isolation zone may be removed in all the conductor layers or in a single conductor layer. Also, the whole area corresponding to the projection or part of the area may be removed.  
         [0018]     One example of the second structure is a via hole.  
         [0019]     To put the first chip and the second chip at the different conductor layer each other is effective to reduce the thermal effect to the second chip, because the distance between the first chip and the second chip becomes longer than that in case of mounting them on the same layer.  
         [0020]     According to the present invention, even when a first device which has a power amplifying function and a second device which has sensitive temperature dependence of characteristics such as a surface acoustic wave device (hereinafter referred to as a “SAW” device) are integrated on a substrate, the temperature rise of the area in which the second device is placed can be suppressed and its thermal interference with the first device can be reduced so that it is possible to provide a compact radio frequency module with higher integration in function which allows the first device and the second device to operate normally and stably.  
         [0021]     The use of a radio frequency module according to the present invention enables to realize of a more compact wireless communication terminal or if the size of a wireless communication terminal is fixed, it offers more space for new additional functions. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     The invention will be more particularly described with reference to the accompanying drawings, in which:  
         [0023]      FIG. 1  is a sectional view showing a first embodiment of the present invention;  
         [0024]      FIG. 2  is a sectional view showing a second embodiment of the present invention;  
         [0025]      FIG. 3A  is a top view showing a conductor pattern on a conductor layer  5   a  according to the second embodiment of the present invention and  FIG. 3B  is a top view showing a conductor pattern on a conductor layer  5   b  according to the second embodiment of the present invention;  
         [0026]      FIG. 4C  is a top view showing a conductor pattern on a conductor layer  5   c  according to the second embodiment of the present invention and  FIG. 4D  is a top view showing a conductor pattern on a conductor layer  5   d  according to the second embodiment of the present invention;  
         [0027]      FIG. 5E  is a top view showing a conductor pattern on a conductor layer  5   e  according to the second embodiment of the present invention and  FIG. 5F  is a top view showing a conductor pattern on a conductor layer  5   f  according to the second embodiment of the present invention;  
         [0028]      FIG. 6  is a sectional view showing a third embodiment of the present invention;  
         [0029]      FIG. 7  is a sectional view showing a fourth embodiment of the present invention;  
         [0030]      FIG. 8  is a sectional view showing a fifth embodiment of the present invention;  
         [0031]      FIG. 9  is a top view showing a conductor layer pattern according to the fifth embodiment of the present invention;  
         [0032]      FIG. 10  is a sectional view showing a sixth embodiment of the present invention;  
         [0033]      FIG. 11  is a sectional view showing a variation of the sixth embodiment of the present invention;  
         [0034]      FIG. 12  is a perspective view showing a seventh embodiment of the present invention;  
         [0035]      FIG. 13  is a perspective view showing an eighth embodiment of the present invention;  
         [0036]      FIG. 14  is a sectional view showing a ninth embodiment of the present invention;  
         [0037]      FIG. 15  is a perspective view showing a tenth embodiment of the present invention;  
         [0038]      FIG. 16  is a sectional view showing the tenth embodiment of the present invention; and  
         [0039]      FIG. 17  is another sectional view showing the tenth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0040]     Next, preferred embodiments of the present invention will be described in detail referring to the accompanying drawings. In the figures which illustrate the embodiments, components which have the same functions are designated by the same reference numerals and components which are once explained will not be explained again.  
         [0041]      FIG. 1  is a sectional view showing a radio frequency module according to a first embodiment of the present invention. The first embodiment is a radio frequency module in which a power amplifier  1  and a SAW device  2  ( ) are mounted on a ceramic multilayer substrate  3 . The SAW device  2  in this embodiment has a function as a transmitting filter. The multilayer substrate  3  is composed of six dielectric layers  4   a ,  4   b ,  4   c ,  4   d ,  4   e ,  4   f  and seven conductor layers  5   a ,  5   b ,  5   c ,  5   d ,  5   e ,  5   f ,  5   g . According to the first embodiment, the power amplifier  1  is mounted by silver paste or solder on a conductor pattern  10  formed on the conductor layer  5   a . The SAW device  2  is mountd by silver paste or solder on a conductor pattern  13  formed on the conductor layer  5   e  inside a cavity  6  made by partially removing the dielectric layers  4   a  to  4   d . The conductor pattern on the surface of each device and the relevant conductor layer of the multilayer substrate are connected by bonding wires  7 . The cavity, in which the SAW device  2  is located, is hermetically sealed by a cover  40 . With a passive device  8  and the like on the top face of the multilayer substrate, the substrate top is covered by a lid  50 .  
         [0042]     In this embodiment, the multilayer substrate  3  has two areas: a first area  100  and a second area  200 . The first area  100  includes the power amplifier  1 , the passive device  8  for its operation, a wiring pattern  101  which connects them, and a conductor pattern  102  which serves as the ground for the power amplifier  1 ; the second area  200  includes the SAW device  2  and a passive device  80  for its operation, a wiring pattern  201  which connects them and a conductor pattern  202  which serves as the ground for the SAW device  2 .  
         [0043]     The heat generated by the power amplifier  1  is conducted partially from the module surface and partially through the conductor pattern  10  holding the power amplifier  1 , then through conductor layers and dielectric layers or via holes  11  down to the bottom face  12  of the module while being cconducted horizontally and vertically. From the bottom face  12 , the heat goes, for example, through a motherboard (not shown) on which the module is mounted, before being forced out of the module (for example, dissipated into the air).  
         [0044]     In the present invention, the SAW device  2 , which has sensitive temperature dependence of characteristics, and the power amplifier  2  are integrated on the same multilayer substrate  3  so it is necessary to minimize temperature rise of the conductor pattern  13  holding the SAW device  2  in order to prevent or reduce the possibility of deterioration in the SAW device  2 .  
         [0045]     For this purpose, preferably the module should have either of the following structures or a combination of them: one structure is such that the heat is conducted throughout the module to reduce rise in the overall temperature of the module; another structure is such that the heat can easily emanate from the conductor pattern  10  holding the power amplifier  1  or from the conductor pattern  13  holding the SAW device; and a further structure is such that the heat from the power amplifier  1  is hardly transfered to the conductor pattern holding the SAW device  2 .  
         [0046]     In the first embodiment of the present invention, in order to facilitate heat conduction inside the module, as many conductors as possible are provided in each of the first area  100  and the second area  200 . In the first embodiment there is an area  300  where conductors are not connected between the area  100  and the area  200  at the following conductor layers; conductor layers between the conducter layer in which the conductor pattern  13  is formed and the conductor layer in which the conductor pattern  10  is formed, namely conductor layer  5   a ,  5   b , 5   c , 5   d  and  5   e . Therefore, as the heat conducted from the conductor pattern  10  passes mainly through conductors or via holes  11  and enters the first area  100 , the heat conductivity becomes low in the area  300  and the heat is hardly conducted into the second area  200 . As a result, the amount of heat which is conducted into the second area  200  decreases. Also in the second area  200 , as many conductors as possible are provided in order to conduct the incoming heat throughout the second area  200 . Therefore, the amount of heat which is conducted to the conductor pattern  13  holding the SAW device  2  decreases so that the temperature rise of the conductor pattern  13  can be suppressed, resulting in a reduction in the temperature rise of the SAW device  2 .  
         [0047]     Consequently, even when the power amplifier  1  and SAW device  2  are ingtegrated into one module, the SAW device  2  can operate with stability.  
         [0048]     Next, a second embodiment of the present invention is described referring to  FIG. 2 .  FIG. 2  is a sectional view showing a radio frequency module according to the second embodiment. The structure of the second embodiment is the same as that of the first embodiment except that the multilayer substrate  3  is composed of five dielectric layers and six conductor layers and a cavity in which the SAW device  2  is located extends from the dielectric layer  4   b  to the dielectric layer  4   e.    
         [0049]     In this embodiment, a conductor pattern electrically connected with the conductor pattern  10  holding the power amplifier  1  is connected with another conductor pattern electrically connected with the conductor pattern  13  holding the SAW device  2  at the conductor layers  5   e  and  5   f  which are located below the conductor pattern  13 . Between the conductor layers  5   a  to  5   d , there is an area  300  in which the conductor pattern  10  holding the power amplifier  1  and the other conductor pattern electrically connected with the conductor pattern  10  are not connected with the conductor pattern  13  holding the SAW device  2  and the other conductor pattern electrically connected with the conductor pattern  13 .  
         [0050]      FIGS. 3A  to  5 F respectively show the respective conductor patterns on the conductor layers  5   a  to  5   f . The power amplifier  1  is mounted on the conductor pattern  10  as shown in  FIG. 3A  and the heat generated by the power amplifier  1  is conducted through conductor patterns (shown in  FIG. 3A  to  FIG. 5F ) horizontally or mainly through the via holes  11  vertically. In this embodiment, the power amplifier is held by the conductor pattern  10  (as shown in  FIG. 3A ) while the SAW device  2  is held by the conductor pattern  13  (as shown in  FIG. 3B ). The module is designed so that the conductor pattern  14  ( FIG. 3B ), conductor pattern  15  ( FIG. 4C ) and conductor pattern  16  ( FIG. 4D ), which are electrically connected through the via holes  11  to the conductor pattern  10 , are not connected with the conductor pattern  31  ( FIG. 4C ) and conductor pattern  32  ( FIG. 4D ) which are electrically connected through via holes  30  to the conductor pattern  13  holding the SAW device, at the same layer level. On the other hand, as shown in  FIGS. 5E and 5F , the conductor pattern electrically connected with the conductor pattern  10  and the conductor pattern electrically connected with the conductor pattern  13  are connected with each other at the conductor layers  5   e  and  5   f , by a conductor pattern  17  and a conductor pattern  18 , respectively.  
         [0051]     As a consequence, the heat generated by the power amplifier  1  is hardly conducted to the conductor layer  5   b  holding the SAW device  2  and the conductor layers located adjacent to it,  5   a ,  5   c  and  5   d , which curbs the temperature rise of the conductor pattern  13  and enables the SAW device  2  to operate with stability.  
         [0052]     The wiring which carries signals from the power amplifier  1  to the SAW device  2  crosses the boundary zone between the first area  100  to the second area  200  through a wiring pattern  60  provided on the conductor layer  5   d  as shown in  FIG. 4D . The area of wiring which carries signals from the power amplifier  1  to the SAW device  2  is smaller than that of the conductor patterns  10  and  14  and thus the amount of heat which is conducted from the first area  100  to the second area  200  is smaller. Accordingly, the influence of the heat conducted through the wiring pattern  60  on the SAW device  2  is not considerable so the wiring pattern  60  need not always be provided on the conductor layer  5   d ; instead it may be provided on a layer above or below the conductor layer  5   d.    
         [0053]     Therefore, even when the power amplifier  1  and SAW device  2  are mounted on the same multilayer substrate  3 , the adoption of the structure as defined by the present invention reduces the influence of the heat generated by the power amplifier  1  on the SAW device  2 , so it is possible to provide a radio frequency module which allows the SAW device  2  to operate with stability even when both the devices are densely integrated in the substrate.  
         [0054]     Next, a third embodiment of the present invention is described, referring to  FIG. 6 .  FIG. 6  is a sectional view showing the third embodiment. The structure of the radio frequency module in the third embodiment is the same as that in the second embodiment except that via holes  70  are provided between the conductor pattern  10  holding the power amplifier  1  and the conductor pattern  13  holding the SAW device  2 , in addition to the via holes  11  located beneath the power amplifier  1 . These via holes  70  further encourage the heat to be conducted vertically, thereby decreasing the amount of heat to be conducted towards the conductor pattern  13  holding the SAW device  2 . As a consequence, the influence of the heat generated by the power amplifier  1  on the SAW device  2  is reduced so it is possible to provide a radio frequency module which allows the SAW device  2  to operate with stability even when both the devices are densely integrated in the substrate.  
         [0055]     Next, a fourth embodiment of the present invention is described, referring to  FIG. 7 .  FIG. 7  is a sectional view showing the fourth embodiment. The structure of the radio frequency module in the fourth embodiment is the same as that in the second embodiment except that there is a groove  80  between the conductor pattern  10  holding the power amplifier  1  and the conductor pattern  13  holding the SAW device  2 . The groove  80  decreases the amount of heat to be conducted horizontally. As a consequence, the influence of the heat generated by the power amplifier  1  on the SAW device  2  is reduced so it is possible to provide a radio frequency module which allows the SAW device  2  to operate with stability even when both the devices are densely integrated in the substarate.  
         [0056]     Next, a fifth embodiment of the present invention is described, referring to  FIG. 8 .  FIG. 8  is a sectional view showing the fifth embodiment. The structure of the radio frequency module in the fifth embodiment is the same as that in the second embodiment except that a conductor pattern  17  electrically connected with the conductor pattern  10  holding the power amplifier  1  is electrically connected with a metal lid  40  for the cavity  6  in which the SAW device  2  is located. The difference between the conductor layer  5   e  in the second embodiment and that in the fifth embodiment is explained below referring to  FIG. 5E  and  FIG. 9 .  
         [0057]      FIG. 9  illustrates the conductor pattern on the conductor layer  5   e  in the radio frequency module according to the fifth embodiment while  FIG. 5E  illustrates the conductor pattern on the conductor layer  5   e  according to the second embodiment. In the second embodiment, an area  41  which is in contact with the metal lid  40  for the cavity  6  is not electrically connected with the conductor pattern  17  surrounding it. On the other hand, in the fifth embodiment, as shown in  FIG. 9 , the conductor pattern  17  is in contact with the area  41  which is in contact with the metal lid  40 . As a result, since the heat from the power amplifier  1  is conducted to the metal lid  40 , the heat is easier to disperse inside the radio frequency module than in the second embodiment and thus the overall temperature of the module is decreased, which leads to a decrease in the temperature of the area in which the SAW device  2  is located. Accordingly, the module structure according to this embodiment makes the temperature rise of the conductor pattern  13  holding the SAW device smaller than the module structure according to the second embodiment. As a consequence, the adoption of the same module structure as defined by this embodiment reduces the influence of the heat generated by the power amplifier  1  on the SAW device  2  so it is possible to provide a radio frequency module which allows the SAW device  2  to operate with stability even when both the devices are densely integrated in the substrate.  
         [0058]     Next, a sixth embodiment of the present invention is described, referring to  FIG. 10 .  FIG. 10  is a sectional view showing the sixth embodiment. The structure of the module in this embodiment is the same as that in the first embodiment except that the conductor pattern in the first area  100  and that in the second area  200  are not connected with each other at the conductor layers  5   f  and  5   g . Thus, the conductor patterns which serve as the grounds in the first area  100  and the second area  200  are not connected at any layer, so horizontal heat conduction is smaller than in the first embodiment. This means that, although the module temperature in the first area  199  may rise a little, the amount of heat which is conducted from the power amplifier  1  to the conductor pattern  13  holding the SAW device  2  can be reduced. Consequently it is possible to provide a radio frequency module which allows the SAW device  2  to operate with stability.  
         [0059]      FIG. 11  shows a variation of the embodiment shown in  FIG. 10 . As can be seen from  FIG. 11 , in a situation that the radio frequency module according to the sixth embodiment of the present invention is mounted on a motherboard  350 , a conductor-free zone  352  which fits the conductor free area between the first area  100  and the second area  200  of the radio frequency module is made in a conductor pattern  351  on the motherboard  350  so that the heat which is conducted from the first area  100  through the conductor on the motherboard  350  to the second area  200  can be reduced. Hence, it is possible to provide a radio frequency module which allows the SAW device  2  to operate with stability even when the power amplifier  1  and the SAW device  2  are densely integrated in the substrate.  
         [0060]      FIG. 12  shows a seventh embodiment of the present invention.  
         [0061]      FIG. 13  shows an eighth embodiment of the present invention.  
         [0062]      FIGS. 12 and 13  only show the shape of the multilayer substrate  3  and the positional relationship between the power amplifier  1  and the SAW device  2  where the conductor patterns of the radio frequency module are omitted. Here, the conductor patterns on the respective layers are much the same as those in the embodiments mentioned earlier. In these embodiments, the power amplifier  1  is located on the top face of the multilayer substrate  3  and the SAW device  2  is located inside the cavity  6  made through the bottom of the substrate  3 . The multilayer substrate  3  is mounted on the motherboard  350 .  
         [0063]     In these embodiments, top view of the substrate of the radio frequency module is not rectangular but L-shaped or U-shaped and the power amplifier  1  and the SAW device  2  are located in the peripheral area of the module as illustrated in  FIGS. 12 and 13 . The module structures according to these embodiments make it possible to increase the distance between the power amplifier  1  and the SAW device  2  and thereby reduce heat conduction, resulting in a decrease in the temperature of the area in which the SAW device  2  is located. Part of the heat conducted to the motherboard  350  is conducted through the motherboard  350  by the conductor pattern  351 . Therefore, as illustrated in  FIG. 13 , the conductor pattern  351  on the motherboard  350  may have a conductor-free area  352  between the SAW device  2  and the power amplifier  1 .  
         [0064]     Referring to  FIG. 14 , a ninth embodiment of the present invention is explained next. The ninth embodiment is the same as the embodiments mentioned so far except that the power amplifier  1  is located inside a cavity  90  made in the multilayer substrate  3 . Like the embodiment shown in  FIG. 6 , this embodiment has via holes  70  between the power amplifier  1  and the SAW device  2  in addition to the via holes beneath the power amplifier  1  in order to help the heat conduct towards the motherboard.  
         [0065]     Referring to  FIG. 15 , a tenth embodiment of the present invention is explained next.  FIG. 15  shows a radio frequency module which combines not only the power amplifier  1  and the SAW device but also an RF-IC  400 . In  FIG. 15 , the SAW device is located in a cavity (not shown). This embodiment has different areas with different functions: a first area  100  which includes the power amplifier  1  and components of a matching circuit for the power amplifier; a second area  200  which includes filter components such as a SAW device, switch, capacitance and inductor; and a third area  500  which includes an RF-IC  400  and components related to RF-IC operation.  
         [0066]     In this case, although the conductors which serve as the grounds for the respective areas may be connected not within the multilayer substrate  3  but on the motherboard  350  as in the embodiment shown in  FIG. 10 , from the viewpoint of suppressing the module temperature rise caused by the heat generated by the power amplifier  1  it is desirable to use a structure that conducts the heat throughout the module by connecting conductor patterns as far as possible while at the same time preventing the heat from being conducted to the conductor pattern (not shown) holding the SAW device.  
         [0067]      FIG. 16  is a sectional view taken along the dotted line A-B of  FIG. 15 . In the embodiment shown in  FIG. 16 , at the conductor layer holding the SAW device  2  and the conductor layers located above it, the conductors which serve as the grounds for the first area  100  and third area  500  are continuous with each other. In addition, via holes  71  and  72  are provided under the RF-IC chip  400  and the SAW device respectively so that the heat conducted to the third area  500  and the second area  200  is guided to the motherboard (not shown). As a consequence, the temperature rise of the conductor pattern  13  holding the SAW device  2  is suppressed and thus it is possible to provide a radio frequency module which enables the SAW device  2  to operate with stability.  
         [0068]      FIG. 17  shows another example of a radio frequency module structure. Needless to say, the radio frequency module structure is not limited to that shown in  FIG. 16 ; it is acceptable to employ the radio frequency structure as shown in  FIG. 17  in which, while the conductor patterns which serve as the grounds for the second area  200  and the third area  500  are continuous with each other, the conductor patterns in the first area  100  are not connected at the conductor layer on which the conductor pattern  13  where the SAW device  2  is mounted and the conductor layers located above that layer.  
         [0069]     This approach, in which the power amplifier and SAW device are integrated in a module as described above, combined with a integration of a switch and an RF-IC in the module, makes it easier to design radio frequency curcuit parts, requires a smaller number of man-hours for assembling, provides more handling ease and thus enables production of terminals at lower cost than the conventional method in which components are individually assembled into a terminal.  
         [0070]     As discussed so far, the adoption of a module structure according to the present invention makes it possible to provide a more compact radio frequency module which assures more stable operation of a SAW device with no deterioration in the SAW device performance than existing radio frequency modules.  
         [0071]     It is apparent that the present invention is not limited to a combination of a power amplifier and a SAW device and may be applied to a combination of another type of heater element and another type of device having sensitive temperature dependence of characteristics.  
         [0072]     Furthermore, the invention may be embodied in any forms other than the above-mentioned embodiments without departing from the spirit and scope of the invention.