Abstract:
A semiconductor device which has a preferable construction for downsizing, in which chip part(s) and a cap are not short-circuited, is provided. The semiconductor device includes: a substrate having a first surface with a cavity and a second surface opposite to the first surface; a semiconductor chip arranged in the cavity; a chip part mounted on the second surface of the substrate; a heat sink which is mounted on the second surface of the substrate and transfers heat liberated from the chip; a cap which is fitted to the substrate, covers the second surface of the substrate, and is joined to the heat sink; and an insulator provided between the cap and the chip part. By providing the insulator, short-circuiting of the chip part and the cap is prevented. Consequently, a distance between the cap and chip part can be shortened to downsize the size of semiconductor device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor device with parts mounted on a surface of a substrate and with a cap for radiating heat provided over the parts. 
     2. Description of the Background Art 
     Conventionally, semiconductor modules with parts mounted on surfaces of respective multi-layer substrates have been known. For this kind of semiconductor modules, a requirement exists that parts are mounted in an efficient mounting area. Therefore, some of semiconductor modules have cavities provided on rear surfaces of respective multi-layer substrates so that semiconductor chips can be arranged in the cavities. This kind of semiconductor module has a heat sink located on another surface of the multi-layer substrate opposite to the surface where the semiconductor chip is provided. The heat sink is joined to the cap of semiconductor module. Because the cap is formed by metal with high thermal conductivity, heat liberated from the semiconductor chip is radiated via the heat sink and the cap. According to this arrangement, the semiconductor module stably operates. 
     In recent years, requests for downsizing products such as cellular phones have increased, and as a result, a need to still further downsizing semiconductor modules such as power amplifier modules arises. 
     In the arrangement of the conventional semiconductor module, the module cannot be downsized because the size of heat sink is respectively large. The reason is that a fear of short-circuiting the cap and chip parts arises, when the heat sink and the cap are downsized to suppress size of the module. 
     For example, consider the case to change the heat sink from type 1608 (1.6 mm×0.8 mm) to type 1005 (1.0 mm×0.5 mm) that bulk feeders can operate. Level of the heat sink reaches the same as that of other 1005 chip parts (for example, L, C, R). Depending on tolerances of chip parts, the cap and chip parts may electrically short-circuiting. Note that the term “tolerances” means a difference in size between maximum and minimum values allowed from the viewpoint of specifications. 
     Although it is possible to change all the chip parts to type 0603 (0.6 mm×0.3 mm), some of the parts of type 0603 do not satisfy necessary characteristics. Thus, cost increases as a result. In addition, in the case caps are not used and heat is radiated through, for example, molds, shielding capability for preventing leakage of electric power as well as influence on peripheral parts is required for current products. To provide shielding capability, further different configuration is required, and as a result, downsizing is unable to be achieved and the cost increases. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a semiconductor device of an arrangement in which chip parts and caps are not short-circuited and at the same time which achieves downsizing. 
     The first semiconductor device according to the present invention includes a substrate, a semiconductor chip, at least one chip part, a heat sink, a cap and an insulator. The substrate has a first surface with a cavity and a second surface on the opposite side of the first surface. The semiconductor chip is arranged in the cavity and electrically connected to the substrate. The at least one chip part is mounted on the second surface of the substrate and electrically connected to the substrate. The heat sink is mounted on the second surface of the substrate and transfers heat liberated from the semiconductor chip. The cap is fitted to the substrate, covers the second surface of the substrate, and is joined to the heat sink. The insulator is provided between the cap and the at least one chip part. 
     By providing the insulator, for example, thermoplastic resin, short-circuiting of the chip part and the cap is prevented. Consequently, a distance between the cap and chip part can be shortened to downsize the size of semiconductor device. The size of the semiconductor device can be further and more effectively downsized by reducing size of the heat sink. 
     The second semiconductor device according to the present invention includes a substrate, a semiconductor chip, at least one chip part, a heat sink and a cap. The substrate has a first surface with a cavity and a second surface on the opposite side of the first surface. The semiconductor chip is arranged in the cavity and electrically connected to the substrate. The at least one chip part mounted on the second surface of the substrate and electrically connected to the substrate. The heat sink is mounted on the second surface of the substrate and transfers heat liberated from the semiconductor chip. The cap is fitted to the substrate, covers the second surface of the substrate, and is joined to the heat sink. Further, the cap is bent in the substrate direction at an outer edge of a region where the cap is joined to the heat sink. According to the above arrangement, short-circuiting between the cap and chip parts can be avoided without providing insulation film between the cap and chip parts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This and other objects and features of the present invention will become clear from the subsequent description of a preferred embodiment thereof made with reference to the accompanying drawings, in which like parts are designated by like reference numerals and in which: 
     FIG. 1 is a perspective view of a semiconductor module according to embodiment 1; 
     FIG. 2 is a cross-sectional view of the semiconductor module cut along line A—A′ of FIG. 1; 
     FIG. 3 is a development of a cap; 
     FIG. 4 is a development of a cap by the second example with insulation film affixed; 
     FIG. 5 is a cross-sectional view of a semiconductor module by the second example with insulation film affixed; 
     FIG. 6 is a development of a cap by the third example with insulation film affixed; 
     FIG. 7 is a development of semiconductor module with insulation film affixed over the whole surface; 
     FIG. 8 is a cross-sectional view of semiconductor module according to embodiment 2; 
     FIG. 9 is a development of a cap with insulation film affixed over the whole surface except fitting pawls; 
     FIG. 10 is a perspective view of semiconductor module according to embodiment 3; 
     FIG. 11 is a cross-sectional view of semiconductor module cut on line A—A′ of FIG. 10; 
     FIG. 12 is a perspective view of semiconductor module according to another example of embodiment 3; 
     FIG. 13 is a cross-sectional view of semiconductor module cut on line A—A′ of FIG. 12; 
     FIG. 14 is a cross-sectional view of semiconductor module related to a modified example of embodiments 1 and 2; and 
     FIG. 15 is a view showing a semiconductor module using filletless chip parts. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the attached drawings, preferred embodiments 1 through 3 of the present invention will be described as follows. In the drawings, the same reference characters are designated to elements with same or similar functions. Semiconductor modules described in the following embodiments are intended such as power amplifier modules and small-size high-frequency modules. 
     Embodiment 1 
     FIG. 1 is a perspective view of semiconductor module  100  according to embodiment 1. Semiconductor module  100  is formed with cap  10  fitted over multi-layer substrate  30 . As described later, on a rear surface of multi-layer substrate  30 , a cavity, that is, a hollow section, or a recessed section from the rear surface of the substrate is provided, in which one or more semiconductor chips (not illustrated) are mounted. On the other hand, on the opposite side of multi-layer substrate  30  of the semiconductor chip, heat sink  20  is provided. Cap soldering material  40  is applied to heat sink  20 , by which heat sink  20  and cap  10  are physically fixed. As a result, heat liberated from the semiconductor chip is transmitted to the surface of multi-layer substrate  30  and radiated to outside via heat sink  20 , cap soldering material  40 , and cap  10 . 
     One of primary features of semiconductor module  100  is that insulation film  11  is affixed to the surface of the rear side (opposite side of outer surface) of cap  10 . To explain more in detail, cap  10  is formed with metal with high thermal conductivity, such as copper, aluminum, etc., in order to function as a shield for preventing leakage of electric power and influence on peripheral parts to improve heat radiation performance. Consequently, if cap  10  is short-circuited with one or more chip parts (hereinafter referred to as “chip parts”) on multi-layer substrate  30 , element destruction and overheat would occur, causing danger and at the same time preventing them from exhibiting their originally intended performance. 
     Because of the above reason, insulation film  11  is affixed to the rear surface of cap  10  facing multi-layer substrate  30  so that short-circuiting between chip parts (not illustrated) and cap  10  is prevented. Film  11  is affixed to, for example, a strip-form section including one or more regions facing chip parts  80 . Insulation film  11  may be made of publicly known materials, such as epoxy resin (for example, Obi-One Coat) as thermosetting resin, polyimide resin (for example, PIMET of Sumitomo Electric Industries), etc. However, because cap soldering material  40  on heat sink  20  must come in direct contact with cap  10 , no insulation film is affixed to a strip-form region at the upper part of heat sink  20 . The thickness of heat insulation film is, for example, 50-200 μm. 
     FIG. 2 is a cross-sectional semiconductor module  100  cut along line A—A′ in FIG.  1 . As clear from the figure, semiconductor module  100  has parts (Surface Mounted Device; SMD) mounted on multi-layer substrate  30 , and is formed by fitting cap  10  into multi-layer substrate  30  as a shield. In addition, a cavity is provided on the rear side of multi-layer substrate  30 , and semiconductor chip  50  is electrically connected to multi-layer substrate  30  by bonding wire  60 . When connection is secured by bonding wire  60 , the cavity is filled with potting material  70  and semiconductor chip  50  is sealed. 
     Insulation film  11  lies between cap  10  and chip parts  80  which are mounted on multi-layer substrate  30 . According to this configuration, short-circuiting can be prevented. In addition, it is understood that no insulation film  11  is affixed at the upper part of region  20  and cap soldering material  40  is fixed directly in contact with cap  10 . To spaces where no insulation film  11  is affixed, chip parts  80  may be mounted if levels of chip parts  80  are lower than heat sink  20 . Note that chip parts with the same levels as the heat sink  20  or with levels higher than heat sink  20  cannot be mounted on the spaces depending on parts tolerances. Further note that soldering material  41  is used to connect multi-layer substrate  30  and heat sink  20 , and to connect multi-layer substrate  30  and chip parts  80  parts. 
     In the case that size of heat sink  20  is reduced from type 1608 (1.6 mm×0.8 mm) to type 1005 (1.0 mm×0.5 mm, height 0.5 mm±0.05 mm), inductors of type 1005 (height 0.45 mm±0.05 mm) can be used. This is because short-circuiting may not occur because of presence of insulation film  11 . Accordingly, the distance between chip parts  80  and cap  10  can be reduced. At the same time, since the mounting area of heat sink  20  and its size in the height direction can be reduced, height of semiconductor module  100  in the direction vertical to multi-layer substrate  30  can also be reduced. Consequently, the whole size of semiconductor module  100  can be reduced. 
     FIG. 3 is a development of cap  10 . By folding in the same direction at a dotted line, cap  10  of FIG. 2 can be obtained. Insulation film  11  is affixed to both sides of cap  10 . Cap soldering material  40  is connected to cap  10  in strip-form portion  9  between insulation films  11 . That is, on the rear surface of cap  10 , insulation film  11  is affixed on stripes. Affixing insulation film  11  in the form of stripe is extremely convenient and consequently, it can be achieved at a low cost. Note that, in this example, insulation film  11  is not affixed to fitting pawl  12  of cap  10  for fitting cap  10  into multi-layer substrate  30 . This allows solder to climb up a rear surface of cap fitting pawl to enhance mounting strength when customers mounts the semiconductor module. 
     FIG. 4 is a development of cap  10  according to the second affixing example of insulation film  11 . The difference from FIG. 3 lies in that insulation film  11  is affixed even to fitting-pawl  12  of cap  10 . According to this configuration, the same advantages as an example shown in FIG. 3 are obtained. What is more advantageous as compared to the case in which insulation film  11  is affixed except for the portion of fitting pawl  12  is that it is no longer necessary to be aware of the accuracy of the outer periphery of stripe. Consequently, insulation film  11  can be affixed at still lower cost and therefore, the cap can be manufactured at lower cost. 
     FIG. 5 is a cross-sectional view of semiconductor module  100  according to the second affixing example of insulation film  11 . Although Insulation film  11  is affixed even to fitting pawl  12  of cap  10 , such configuration affects no influence on operations of semiconductor module  100 . Note that, since multi-layer substrate  30 , soldering material  41 , semiconductor chip  50 , bonding wire  60 , potting material.  70 , and chip parts  80  are exactly same as those of FIG.  2 . Therefore, explanations on these elements will be omitted. 
     FIG. 6 is a development of cap  10  according to the third affixing example of insulation film  11 . Insulation film  11  is affixed to cap  10  in all the area except for region  9  where cap soldering material  40  and cap  10  come into contact. In other words, insulation film  11  with the portion of region  9  removed (cut away) is affixed. According to this configuration, not only the same advantages as those shown in FIG. 3 are obtained but also a wider insulated portion can be obtained, and the degree of design freedom can be increased. Note that region  9  may not be exactly the region where cap soldering material  40  and cap  10  come in contact and may be varied as necessary if changes are required from the viewpoint of manufacturing. 
     Embodiment 2 
     In embodiment 2, a semiconductor module will be described, in which cap soldering material on a heat sink comes in contact with a cap via insulation film to radiate heat. 
     FIG. 7 is a development of cap  10  to which insulation film  11  is affixed to the whole surface. Region  9  is the position corresponding to the upper part of heat sink. In this example, insulation film  11  is affixed to region  9 . In addition, to fitting pawl  12  of cap  10 , insulation film  11  is affixed. 
     FIG. 8 is a cross-sectional view of semiconductor module  102  according to embodiment 2. Semiconductor module  102  differs from that in FIG. 2 in the arrangement of the portion between cap  10  and heat sink  20 . Description will be primarily made on the relevant different portion. Note that, since multi-layer substrate  30 , soldering material  41 , semiconductor chip  50 , bonding wire  60 , potting material  70 , and chip parts  80  are exactly the same as those of FIG. 2, explanations on these elements will be omitted. 
     In embodiment 2, between cap  10  and heat sink  20 , insulation  11  and thermoplastic resin  40  are provided in this order from the side of cap  10 . Thermosetting resin  40  is provided in place of cap soldering material. Thermosetting resin  40  also provides high thermal performance and is sufficient to transfer heat liberated from heat sink  20  to cap  10 . In this example, since insulation film  11  is affixed to the whole surface of cap  10 , as compared to the case in which insulation film  11  is affixed except for the upper position of heat sink, a trimming process of insulation film  11  can be omitted. Consequently, cap  10  can be manufactured conveniently and inexpensively. In addition, reduction of parts contact, heat radiation performance, and parts size can be achieved similar to embodiment 1. 
     Note that, in this example, since insulation film  11  is affixed to fitting pawl  12  of cap  10 , the insulation film affixing accuracy is no longer required to be intentionally improved, and cap  10  can be manufactured more conveniently and inexpensively. However, needless to say, even if insulation film  11  is not affixed to fitting pawl  12 , reduction of parts contact, heat radiation performance, and parts size can be achieved. FIG. 9 is a development of cap  10  with insulation film  11  affixed to all the surfaces except fitting pawl  12 . In order to affix insulation film  11  as illustrated, an affixing accuracy of insulation film  11  must be improved. However, since no insulation film  11  exists, solder climbs up the rear surface of cap fitting pawl  12  at the time of mounting at customers and increase of mounting strength can be expected. 
     Embodiment 3 
     In embodiment 3, a semiconductor module that has a cap with a portion joined to a heat sink recessed will be described. By recessing a part of the cap, it is no longer necessary to provide the insulation film described in embodiments 1 and 2. 
     FIG. 10 is a perspective view of semiconductor module  110  according to embodiment 3. As shown in the figure, recess  13  folded and set back from the periphery to the multi-layer substrate  30  side is provided to cap  10 . The recess designated as cap recess  13  will be discussed hereinafter. Cap recess  13  is located at the upper part of a heat sink (not illustrated). 
     FIG. 11 shows a cross-sectional view of semiconductor module  110  cut along line A—A′ of FIG.  10 . Semiconductor module  110  differs from the semiconductor module of FIG. 2 in configuration of cap  10  as well as in that no insulation film  11  is affixed to cap  10  of semiconductor module  110 . In the following section, description will be primarily made on the relevant different portion. Note that, since multi-layer substrate  30 , soldering material  41 , semiconductor chip  50 , bonding wire  60 , potting material  70 , and chip parts  80  are exactly the same as those in FIG. 2, explanations on these elements will be omitted. 
     As clear from the figure, cap  10  has cap recess  13  at the upper part of heat sink  20 . In other words, cap recess  13  is provided to be bent in the substrate direction of cap  10  at the outer edge of the region joined to the heat sink. Depending on set back amount (i.e. bent amount) from the surface of cap  10 , clearance at the upper part of heat sink  20  can be adjusted. For example, assume that the set back amount of cap recess  13  is 0.05 mm from the surface of cap  10 . Then, it is possible to gain clearance of at least 0.05 mm in the case height of heat sink  20  is 0.5±0.05 mm and inductor height which is one of peripheral chip parts  80  is 0.45±0.05 mm. Conversely, if the set back amount from the surface of cap recess  13  is increased, the height of heat sink  20  can be lowered in accordance with the increase. Therefore, heat sink  20  can be downsized and at the same time, short-circuiting of cap  10  and chip parts  80  can be avoided. The use of cap  10  described in this embodiment can eliminate a need to affix insulation film  11  as shown in FIG. 2, semiconductor modules can be manufactured at still lower cost. 
     FIG. 12 is a perspective view of semiconductor module  120  according to another example of embodiment 3. Unlike the preceding cap recess  13  (FIG.  10 ), a hole is provided in cap  10  of semiconductor module  120 . The figure illustrates a condition in which adhesive  40  is injected in the hole to the surface of cap  10 . 
     FIG. 13 shows a cross-sectional view of semiconductor module  120  cut at line A—A′ of FIG.  12 . Semiconductor module  120  differs from the semiconductor module of FIG. 11 in the arrangement of cap  10 . In the following section, description will be primarily made on the relevant different portion. Note that, since multi-layer substrate  30 , soldering material  41 , semiconductor chip  50 , bonding wire  60 , potting material  70 , and chip parts  80  are exactly the same as those in FIG. 11, explanations on these elements will be omitted. 
     As illustrated in FIG. 13, cap  10  of semiconductor module  120  has a hole provided in the region corresponding to the upper part of heat sink  20 . This hole is obtained by removing the bottom section of cap recess  13  (FIG. 11) and passes through from the top surface of heat sink  20  to the surface of cap  10 . By providing the hole, it becomes possible to dispense adhesives  40  from the top surface of the cap  10  to fill the hole with the adhesive, manufacturing efficiency can be improved. Furthermore, even when adhesive  40  is dispensed in excess, a predetermined volume of adhesive  40  is easily scraped away from the hole. Therefore, operating efficiency can be improved and the manufacturing efficiency can be further improved. Note that, because cap  10  in this modified example is obtained only by removing the bottom of cap recess  13  (FIG.  11 ), the advantages explained for cap  10  in FIG. 11 can be obtained as advantages of this example as they are. 
     Now, embodiments of the present invention have been described. In embodiments 1 and 2, in order to avoid short-circuiting between the cap and the chip parts, insulation film is provided to the surface of the cap facing the chip parts. However, if short-circuiting can be avoided, it is not necessary to restrict to this configuration. For example, thermosetting resin with nonconductive and heat transferring characteristics is applied on the substrate (on chip parts) and a cap may be affixed. Furthermore, such resin can be filled between cap  10  and multi-layer substrate  30  instead of or at the same time in applying on the chip parts. The resin also functions as an adhesive to affix cap  10  and multi-layer substrate  30 . 
     FIG. 14 is a cross-sectional view of semiconductor module  140  related to a modified example of embodiments 1 and 2. Semiconductor module  140  is formed by filling a space defined between facing surfaces of cap  10  and multi-layer substrate  30 , or surfaces of cap  10  and chip parts  80 , with nonconductive resin (adhesive agent)  42 . The adhesive agent is, for example, thermosetting resin such as epoxy resin. Cap  10  is brought in direct contact with nonconductive resin and fixed. According to this arrangement, electrical short-circuiting may not occur, since nonconductive resin is inserted between cap  10  and chip parts  80 . In addition, because heat generated at semiconductor chip  50  is transmitted directly to cap through nonconductive resin, the heat sink can be eliminated. Consequently, the physical dimensions of semiconductor module  140  can be extremely reduced. 
     In addition, by using one or more filletless parts for all the chip parts  80 , the semiconductor module can be downsized. “Fillet” referred to here means a solder-buildup or a shape the solder-buildup that expands from top to bottom when electrode terminal of element and mounting land are soldered. Consequently, “filletless parts” means parts free of such solder-buildup. FIG. 15 is a diagram showing semiconductor module  130  using filletless chip parts  81 . In this figure, multi-layer substrate  30 , soldering material  41 , semiconductor chip  50 , bonding wire  60 , and potting material  70  are exactly the same as those in FIG. 2, and explanations on these elements will be omitted. The use of filletless parts can lower the cap and can prevent short-circuiting because electrode terminals and the cap will not be brought into contact and no unwanted solder buildup exists. In addition, since the land width or land area can be made smaller, the mounting area of chip parts  80  can be reduced. As a result, simply downsizing conventional caps and heat sinks enables downsizing semiconductor modules without providing insulation film to the cap. If filletless parts are used in semiconductor modules of embodiments 1 through 3, advantages of each of embodiments 1 through 3 can be obtained and further downsizing can be promoted. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the cope of the following claims.