Abstract:
The present invention relates to a manufacturing method of a semiconductor device having a lid implemented on a semiconductor chip. The semiconductor device and the semiconductor device unit are capable of maintaining high thermal dissipation efficiency as well as the semiconductor chip having improved reliability. Specifically, upon manufacturing the above semiconductor device having a semiconductor chip mounted on a substrate and a lid thermally connected to this semiconductor chip, a stiffener, which controls the deformation of the semiconductor chip, is implemented on the side of the semiconductor chip that accommodates the lid; after which heating is performed so as to bond the semiconductor chip accommodating the stiffener to the substrate; followed by the bonding of the lid to the stiffener.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a semiconductor device manufacturing method, a semiconductor device, and a semiconductor device unit, and particularly to a manufacturing method of a semiconductor device having a structure in which a lid is implemented on a semiconductor chip, a semiconductor device, and a semiconductor device unit. 
     2. Description of the Related Art 
     With the high-level densification of the semiconductor device in recent years, there is a growing tendency towards an increase in heat generated by the semiconductor chip. In response, a lid is implemented on the semiconductor chip in order to efficiently cool the semiconductor chip. 
     On the other hand, high reliability is also demanded in a semiconductor device. Thus, the desired semiconductor device is a highly reliable semiconductor device that is provided with a lid but does not suffer stress or separation in between said lid and the semiconductor chip. 
     The semiconductor of the BGA (Ball Grid Array) type having a structure in which a semiconductor chip is mounted on a substrate and external terminals such as solder balls are implemented on the surface opposite the surface that accommodates the semiconductor chip, is well-know in the conventional art. Also, in response to the increase in the heat generation of the semiconductor chip due to the speed-up and high-level densification of the semiconductor chip, a semiconductor device with a lid for efficient thermal dissipation implemented on the upper portion of the semiconductor chip is provided in the conventional art. 
     FIG.  1  and FIG. 2 show the above-described semiconductor device according to the conventional art. The semiconductor device  1 A shown in FIG. 1 has a semiconductor chip  2  mounted on the upper surface of a multi-layered resin substrate  3  and solder balls  4 , which are the external terminals, implemented on the lower surface of the substrate  3 . 
     The semiconductor chip  2  is provided with bumps  6  and is bonded to the substrate  3  through flip chip bonding. Also, in order to strengthen the bonding between the semiconductor chip  2  and the substrate  3 , an under fill material  7  is placed in between the semiconductor chip  2  and the substrate  3 . 
     Lid  5 A is, for example, made of metal, which has high thermal conductivity. In the conventional art, this lid  5 A is bonded directly onto the upper surface of the semiconductor chip  2  using bonding material  8 . 
     On the other hand, the semiconductor device  1 B shown in FIG. 2 has a lid  5 B with a protrusion  9  at its center portion. By providing the protrusion  9  on the lid  5 B, the distance between the substrate  3  and the lid  5 B can be augmented so that other electronic components such as a condenser (not shown in the drawing) can be implemented between the substrate  3  and the lid  5 B. 
     Also, in the semiconductor device  1 B shown in FIG. 2, a frame  10 , supporting the lid  5 B, is placed on the outer perimeter of the substrate  3 . By providing the frame  10 , the lid receives support not only from the semiconductor chip  2  but also from this frame  10  so that the load applied to the semiconductor chip can be reduced. 
     As mentioned above, the substrate  3  forming the semiconductor device  1 A and  1 B is a resin substrate, and the semiconductor chip  2  is made of semiconductor material such as silicon. Therefore, the coefficient of thermal expansion of the semiconductor chip  2  and the substrate  3  are different. Also, upon the flip chip bonding of the semiconductor chip  2  to the substrate  3 , a heating process is performed on the bumps  6  for melting said bumps  6 , and in the heating process for the flip chip bonding, the heat also ends up being applied to the semiconductor chip  2  and the substrate  3 . Thus, warping occurs in the semiconductor chip  2  due to the difference in the coefficient of thermal expansion between the semiconductor chip  2  and the substrate  3 . 
     A description of the problem arising from bonding the lid  5 A to the above-described warped semiconductor chip  2  is given with reference to FIG.  3 . As previously mentioned, in the conventional art the lid  5 A is directly bonded to the semiconductor chip  2  using bonding material  8 . Thermosetting resin is normally used as the bonding material  8 , and a curing process (heating process) is performed upon the bonding. 
     When the curing process is performed upon the bonding of the lid  5 A as described above, the semiconductor chip  2  is re-straightened from its warped form. Specifically, the semiconductor chip  2  attempts to change shape from its warped state (the state shown in FIG. 3) to the position (shape) indicated by the chain line A shown in the same drawing. 
     Since the bonding material  8  is placed in between the semiconductor chip  2  and the lid  5 A, a compression force from the above described changing of shape of the semiconductor chip  2  works on the outer portion of the bonding material  8  (referred to as outer perimeter bonding portion  8 A hereinafter). Additionally, a stretching force works on the inner portion of the bonding material  8  (referred to as inner perimeter bonding portion  8 B hereinafter). 
     When differing forces work in the bonding material  8  upon the bonding of the semiconductor chip  2  and the lid  5 A as described above, internal stress and voids may be generated therefrom. When internal stress is generated in the bonding material  8 , cracks can be formed in the areas where the internal stress is generated. 
     Also, when voids are formed within the bonding material  8 , a fissure may occur in the bonding material, or in the worst case the lid  5 A may be separated from the semiconductor chip. This problem can be slightly ameliorated by making the bonding material  8  thicker; however, this also lowers the thermal conductivity of the bonding material layer  8  thereby causing a decrease in thermal dissipation efficiency with regard to the semiconductor chip  2 . 
     SUMMARY OF THE INVENTION 
     The present invention has been developed in response to the above-described problems, and its object is to provide a semiconductor device manufacturing method, a semiconductor device, and a semiconductor device unit, capable of maintaining high thermal dissipation efficiency of the semiconductor device as well as improving its reliability. 
     To this end, the present invention resorts to each of the following measures. 
     First, the present invention provides a manufacturing method of a semiconductor device having a semiconductor chip mounted on a substrate, and a lid thermally connected to said semiconductor chip, the method including steps of: 
     implementing a stiffener, which prevents the deformation of the semiconductor chip, on the side of the semiconductor chip that accommodates the lid; 
     bonding the semiconductor chip accommodating the stiffener to the substrate through heating; and, 
     bonding the stiffener to the lid with a bonding material after bonding the semiconductor chip accommodating the stiffener to the substrate. 
     Preferably, the stiffener is selected from a material that has substantially the same coefficient of thermal expansion as that of the semiconductor chip. 
     Second, the present invention provides a semiconductor device having a semiconductor chip provided with bumps, a stiffener bonded to the semiconductor chip by a first bonding material and preventing the deformation of the semiconductor chip, a substrate on which the semiconductor chip is mounted via the bumps, and a lid bonded to said stiffener with a second bonding material, wherein the relation between the melting point of the first bonding material denoted as T1, the melting point of the bumps denoted as Tb, and the melting point of the second bonding material denoted as T2 can be described as T1&gt;Tb&gt;T2. 
     Preferably, the stiffener is made of material that has substantially the same coefficient of thermal expansion as that of said semiconductor chip. 
     Third, the present invention provides a semiconductor device unit comprising a motherboard on top of which a plurality of the above semiconductor devices each having a semiconductor chip provided with bumps, a stiffener bonded to the semiconductor chip by a first bonding material and preventing the deformation of the semiconductor chip, a substrate on which the semiconductor is mounted via the bumps, and a lid bonded to said stiffener with a second bonding material is implemented. 
     Additionally, each of the above-described inventions produces the following effects. 
     According to the semiconductor device manufacturing method of the present invention, a semiconductor chip, provided with a stiffener, which prevents the deformation of the semiconductor chip, is bonded to a substrate so that warping does not occur in the semiconductor chip upon the bonding process. Thus, upon the bonding of the lid, the lid can be bonded to a stiffener that is not warped, and this prevents internal stress or voids from being generated in the bonding material placed between the lid and the stiffener. In consequence, the lid and the stiffener can be securely bonded and the reliability of the manufactured semiconductor device can be improved. 
     Also, since internal stress and voids are prevented from being generated in the bonding material connecting the lid and the stiffener, the bonding material can be made thinner. Thus, the thermal conductivity of the bonding material layer can be raised and the heat generated in the semiconductor chip can be efficiently transferred through the stiffener and the bonding material. 
     Additionally, the stiffener is selected from a material that has substantially the same coefficient of thermal expansion as that of the semiconductor chip so that deformation such as warping upon heat application can be prevented from occurring in either the stiffener or the semiconductor chip, or in both of these elements due to the difference in the thermal expansion rate between the stiffener and the semiconductor chip. In consequence, the stiffener and the lid can be securely bonded and the reliability of the manufactured semiconductor device can be improved. 
     Also, in the semiconductor device according to the present invention, the relation between the melting point of the first bonding material T1, the melting point of the bumps Tb, and the melting point of the second bonding material T2 is arranged to be T1&gt;Tb&gt;T2; thus, the first bonding material and the bumps will not melt upon the bonding of the lid to the stiffener with the second bonding material. Also, the first bonding material will not melt upon the bonding of the semiconductor chip to the substrate via the bumps. Thus, when the semiconductor chip is bonded to the substrate and to the lid, the stiffener is securely bonded to the semiconductor chip by the first bonding material so that deformation such as warping will not occur in the semiconductor chip and the reliability of the semiconductor device can be increased. 
     Also, in the semiconductor device unit according to the present invention, a plurality of the semiconductor devices each having a semiconductor chip provided with bumps, a stiffener bonded to the semiconductor chip by a first bonding material and preventing the deformation of the semiconductor chip, a substrate on which the semiconductor is mounted via the bumps, and a lid bonded to said stiffener with a second bonding material are implemented on a motherboard, thereby realizing a multi-chip module with excellent heat dissipation characteristics as well as high reliability. 
     Additionally, in the present invention, the stiffener may be structured to have a concave portion into which a portion of the semiconductor chip is inserted. In this way, the positioning of the semiconductor chip and the stiffener can be easily determined, and the bonded area between the semiconductor chip and the stiffener is increased, thereby strengthening the bonding between these two elements. 
     Also, the stiffener may have chamfers formed at its corners. The chamfered portions of the stiffener are positioned at the corners of the semiconductor chip where stress is likely to be concentrated, and the stress can be prevented from concentrating on the bonding material situated in these areas. Particularly, this prevents damage such as cracks from occurring in the bonding material situated around the corners of the semiconductor chip and the lid. 
     Further, the stiffener may be structured to have a plurality of stiffener layers. In this way, the characteristics of the stiffener may vary for each layer so that, for example, a stiffener layer having characteristics that are close to those of the semiconductor chip can be selected for the stiffener layer implemented on the semiconductor chip side and a stiffener layer having characteristics that are close to those of the lid can be selected for the stiffener layer implemented on the lid side. Thus, the stiffener can strengthen the bonding between the semiconductor chip and the lid and deformation such as warping can be controlled. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a semiconductor device according to the conventional art (version 1); 
     FIG. 2 shows a semiconductor device according to the conventional art (version 2); 
     FIG. 3 is a diagram for illustrating the problems arising in the conventional art; 
     FIG. 4 shows a semiconductor device according to an embodiment of the present invention; 
     FIG. 5 shows a semiconductor device unit implementing the semiconductor devices according to the embodiment of the present invention; 
     FIG. 6 is a diagram for illustrating the manufacturing method of the semiconductor device according to the embodiment of the present invention; 
     FIG. 7 is a diagram for illustrating the first modification of the semiconductor device shown in FIG. 4; 
     FIG. 8 is a diagram for illustrating the second modification of the semiconductor device shown in FIG. 4; 
     FIG. 9 is a diagram for illustrating the third modification of the semiconductor device shown in FIG. 4; and, 
     FIG. 10 is a diagram for illustrating the fourth modification of the semiconductor device shown in FIG.  4 ; 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following, a description of the preferred embodiment of the present invention is given with reference to the accompanying drawings. 
     FIG. 4 shows a semiconductor device  20 A according to an embodiment of the present invention, and FIG. 5 shows a semiconductor device unit  30  that implements the semiconductor device  20 A of FIG.  4 . The semiconductor device  20 A shown in FIG. 4 is roughly composed of a semiconductor chip  22 , a substrate  23 , a lid  25 , a stiffener  28 A, etc. 
     The semiconductor chip  22  is a highly densified semiconductor chip that has a circuit formation surface (the lower surface in the drawing) provided with a plurality of bumps  26 . In the embodiment solder balls are used as these bumps. 
     The substrate  23  is a multi-layer wiring substrate and thus comprises a plurality of conductor wiring layers. Each of the conductor wiring layers comprises a wiring membrane whose base material is an insulating resin, and the conductor wiring layers are electrically connected to each other via inter-layer wiring (e.g. conductor via). 
     Also, a bump bonding pad (not shown) is formed on the chip mounting surface (the upper surface in the drawing) of the substrate  23  on which the semiconductor chip  22  is mounted, and an external connection pad (not shown) is formed on the mount surface opposite to the chip mounting surface (the lower surface in the drawing). The bumps  26  implemented on the semiconductor chip  22  are bonded to the above-mentioned bump bonding pad. Also, the solder balls  24 , which are the external connection terminals, are bonded to the external connection pad. Here, a multi-layer wiring substrate having a plurality of conductor wiring layers can be used as the substrate  23  as described above, thereby allowing greater flexibility in the wiring design and fan out, as well as a narrower pitch in the bump bonding pad (i.e. bumps  26 ). 
     The semiconductor chip  22  is mounted on the substrate  23  having the above-described structure using the flip chip bonding technique. Thus, the semiconductor chip  22  and the substrate  23  are electrically connected. 
     Also, an under fill material  27  is implemented in between the semiconductor chip  22  and the substrate  23 . The function of this under fill  27  is to mitigate the stress applied to the bumps  26 . 
     The solder balls  24  function as external connection terminals as described above, and are bonded to the substrate  23  using, for example, the transfer method. Thus, the semiconductor chip  22  is electrically connected to the solder balls  24  via the substrate  23 . 
     The semiconductor chip  22  having the stiffener  28 A on its top surface further has the lid  25  bonded on top of the stiffener  28 A with the second bonding material  29 B in between. The lid  25  has the function of dissipating the heat generated at the semiconductor chip  22  and transmitted via the stiffener  28 A. Thus, the stiffener  28 A is made of metallic material which has high thermal conductivity (e.g. aluminum). It should be noted that although in the present embodiment the lid  25  is illustrated as being board-shaped, the lid  25  can also be structured to have fins so as to further enhance its heat dissipation characteristics. 
     As shown in FIG. 4, the stiffener  28 A is a member placed in between the semiconductor chip  22  and the lid  25 . This stiffener  28 A is made of ceramic material (e.g. BN, SiC, BeO, ALN), composite material (e.g. ALC, CW), metallic material (e.g. Cu, W, Mo, etc.), or some other material (e.g. Si, diamond). It is desirable that a material having substantially the same coefficient of thermal expansion as that of the semiconductor chip  22  be selected as the material of the stiffener  28 A. 
     In the present invention, ‘substantially the same coefficient of thermal expansion’ is defined as follows. Namely, the semiconductor chip  22  and the stiffener  28 A have ‘substantially the same coefficient of thermal expansion’ when deformation such as warping, as a result of the difference in the coefficient of thermal expansion of the two elements, does not occur in either the semiconductor chip  22  or the stiffener  28 A upon the bonding of the semiconductor chip  22  and the stiffener  28 A using the first bonding material  29 A. 
     As described above, by selecting for the material of the stiffener  28 A, a material that has substantially the same coefficient of thermal expansion as that of the semiconductor chip  22 , deformation such as warping, which occurs in either the stiffener or the semiconductor chip or in both of these elements due to a difference in thermal expansion between the stiffener  28 A and the semiconductor chip  22  upon the heating process for bonding the stiffener  28 A to the semiconductor chip  22 , can be thwarted. In consequence, the stiffener  28 A and the lid  25  can be securely bonded (since the semiconductor chip  22  and the stiffener  28 A are not deformed) and the reliability of the semiconductor device  20 A can be increased. 
     Also, by constructing a semiconductor device unit  30  so as to have a plurality of the semiconductor devices  20 A implemented on a motherboard  31 , as shown in FIG. 5, a multi-chip module having excellent heat dissipation characteristics as well as high reliability can be realized. Note that connector  32  in FIG. 5 is a connector for connecting the motherboard  31  to external devices. 
     Now, the manufacturing method of the semiconductor device  20 A of FIG. 4 will be described. FIG. 6 illustrates the procedures in manufacturing the semiconductor device  20 A. 
     First, in order to manufacture the semiconductor device  20 A, the first bonding material  29 A is placed on the semiconductor chip  22 , as shown in FIG.  6 (A). Bumps  26  are implemented on the other side of the semiconductor chip  22  from the beginning. 
     The above bumps  26  are solder balls and are implemented at the electrodes of the semiconductor chip  22  using, for example, the transfer method. Also, the first bonding material  29 A is, for example, made of epoxy resin or metal with a low melting point (e.g. low-melting-point solder). In the following description, the melting point of the solder making up the bumps  26  is denoted as Tb, and the melting point of the first bonding material  29 A is denoted as T1. 
     After the bonding material  29 A is implemented on the surface of the semiconductor chip  22  as described above, the stiffener  28 A is then bonded to the semiconductor chip  22 . As previously mentioned, the stiffener  28 A has the same coefficient of thermal expansion as that of the semiconductor chip  22 , and has a higher rigidity with respect to the semiconductor chip  22 . Thus, the stiffener  28 A functions as a stiffening material for strengthening the semiconductor chip  22 . 
     The bonding of the semiconductor chip  22  and the stiffener  28 A is performed through use of the first bonding material  29 A. In the bonding process, the semiconductor chip  22  and the stiffener  28 A are heated up to the melting temperature T1, and thus, the first bonding material  29 A is melted so as to bond the semiconductor chip  22  and the stiffener  28 A. FIG.  6 (B) illustrates the state in which the semiconductor chip  22  and the stiffener  28 A are bonded together by the first bonding material  29 A. 
     After the bonding process of the semiconductor chip  22  and the stiffener  28 A, the semiconductor chip  22  is bonded to the substrate  23 . The bonding of the semiconductor chip  22  to the substrate  23  is performed using the flip chip bonding method. 
     Namely, the semiconductor chip  22  is bonded to the substrate  23  face-down in an environment where the temperature is raised to the melting temperature Tb of the bumps  26 . During the process of bonding the semiconductor chip  22  to the substrate  23 , the semiconductor chip  22  is supported by the stiffener  28 A. In other words, the stiffener  28 A has a higher rigidity than the semiconductor chip  22 . 
     Also, the degree of rigidity in the stiffener  28 A is determined by the rigidity needed in order to thwart the force working to deform the semiconductor chip  22 , caused by the difference in the thermal expansion rate between the semiconductor chip  22  and the substrate  23 . FIG.  6 (C) shows the state in which the semiconductor chip  22  and the substrate  23  are bonded. As shown in the drawing, no deformation such as warping occurs in the semiconductor chip  22  when the semiconductor chip  22  is bonded to the substrate  23 . 
     When the semiconductor chip  22  is bonded to the substrate  23  as described above, an under fill material  27  is implemented in between the semiconductor chip  22  and the substrate  23  so as to support the bumps  26 . FIG.  6 (D) shows the state in which the under fill material  27  is implemented. 
     Next, a second bonding material  29 B is implemented on the upper surface of the stiffener  28 A so as to bond the lid  25 . As for the material of the second bonding material  29 B, for example, Ag paste may be used. FIG.  6 (E) shows the state in which the second bonding material  29 B is implemented on the upper surface of the stiffener  28 A. In the following descriptions, the melting point of the second bonding material  29 B is denoted as T2. 
     After the bonding material  29 B is implemented on the stiffener  28 A as described above, the lid  25  is bonded to the stiffener  28 A via the second bonding material  29 B. Specifically, the lid  25  is bonded to the stiffener  28 A in an environment where the temperature is raised to the melting point T2 of the second bonding material  29 B. In this way the semiconductor device  20 A is manufactured as shown in FIG.  6 (F). 
     The following description concerns the relation between the melting point T1 of the first bonding material  29 A, the melting point T2 of the second bonding material  29 B, and the melting point Tb of the bumps  26 . In the present embodiment, the appropriate material is selected for each of the bonding material  29 A,  29 B and the bumps  26  so that their melting points have the following relationship: T1&gt;Tb&gt;T2. 
     By arranging each of the melting points T1, T2, and Tb to have the above relationship, the first bonding material  29 A and the bumps  26  will not melt upon the bonding of the lid  25  to the stiffener  28 A via the second bonding material  29 B. Also, the first bonding material will not melt upon the bonding of the semiconductor chip  22  to the substrate  23  via the bumps  26 . 
     Thus, the process of bonding the semiconductor chip  22  to the substrate  23  and the process of bonding the lid  25  to the stiffener  28 A are performed with the stiffener  28 A being securely bonded to the semiconductor chip  22  by the first bonding material  29 A; in other words, with the semiconductor chip  22  being securely supported by the stiffener  28 A so as to avoid deformation. In this way, each of the above bonding processes can be performed with accuracy and high reliability can be achieved in the semiconductor device  20 A. 
     Also, as described above, in the present embodiment, the semiconductor chip  22  is bonded to the substrate  23  with the stiffener  28 A being implemented in order to prevent the deformation of the semiconductor chip  22 . In this way, warping can be prevented from occurring in the semiconductor chip  22  upon its bonding to the substrate  23 . 
     Thus, in bonding the lid  25  to the stiffener  28 A, the lid  25  is bonded to a stiffener  28 A that is not warped. In this way, internal stress and voids can be prevented from being generated in the second bonding material  29 B placed in between the lid  25  and the stiffener  28 A upon the bonding process. As a result, the lid  25  and the stiffener  28 A can be bonded with accuracy and high reliability can be achieved in the semiconductor device  20 A. 
     Also, since internal stress and voids can be prevented from being generated in the second bonding material by means of the above-described arrangement, the stiffener  28 A can be made thinner. In this way, the thermal conductivity of the stiffener  28 A can be raised and the heat generated in the semiconductor chip  22  can be efficiently transferred via the stiffener  28 A and the second bonding material  29 B. 
     In the following, a description of modified versions of the semiconductor device  20 A is given. 
     FIGS. 7 through 10 illustrate the above modified versions of the semiconductor device  20 A. It should be noted that in each of the above drawings, the same numerical notations are assigned to the elements that are the equivalents of the elements shown in FIGS. 4 through 6 and their descriptions are omitted. 
     FIG. 7 shows a semiconductor device  20 B, which is a first modification of the semiconductor device  20 A. The semiconductor device  20 B shown in this drawing has a frame  33 , which supports the lid  25 , placed at the outer perimeter of the substrate  23 . The lower surface of this frame  33  is bonded to the substrate  23  with adhesive  34 A, and the upper surface of the frame  33  is bonded to the lid  25  with adhesive  34 B. 
     By implementing the frame  33 , the lid  25  receives support not only from the semiconductor chip  22  but also from the frame  33 , thereby enabling a reduction in the load applied to the semiconductor chip  22 . Also, it is possible to implement other electronic devices (not shown) such as a condenser in between the semiconductor chip  22  and the frame  33 . 
     In the conventional semiconductor device  1 B shown in FIG. 2, the protrusion  9  has to be formed as a part of the lid  5 B, and this requirement causes various complications in the formation of the above lid  5 B. However, in the embodiment of the present invention, the stiffener  28 A is equipped with functions equivalent to that of the protrusion  9 ; therefore the lid  25  can be flat-shaped without any protrusions. By eliminating the necessity to form a protruding portion in the lid  25 , the manufacturing process of the semiconductor device  20 B can be facilitated. 
     FIG. 8 is an enlarged diagram of a stiffener  28 B implemented in a second modified semiconductor device. In this modification, the stiffener  28 B has a cavity  35  (a concave portion) into which a part of the upper portion of the semiconductor chip  22  is inserted. By forming the cavity  35  in the stiffener  28 B, the positioning of the semiconductor chip  22  and the stiffener  28 B can be facilitated when bonding these two elements together. Also, since the bonded area between the semiconductor chip  22  and the stiffener  28 B is increased, the bonding can be strengthened. 
     FIG. 9 is an enlarged top view diagram of a stiffener  28 C implemented in a third modified semiconductor device. In this modification, the stiffener  28 C has chamfers  36  formed at its four corners. Thus, the stiffener  28 C is octagon-shaped when viewed from the top. 
     Since the corners of the semiconductor chip  22  are approximately right-angled, they are prone to stress concentration. The chamfers of the stiffener  28 C are formed at positions corresponding to the above corners of the semiconductor chip  22  where the stress is likely to be concentrated. 
     Thus, when stress is generated in the first bonding material  29 A placed between the semiconductor chip  22  and the stiffener  28 C, the concentration of the stress on the corners of the semiconductor chip  22  can be avoided. In turn, damage such as cracks can be prevented from occurring in the first bonding material, especially in the areas corresponding to the corners of the semiconductor chip  22 . 
     FIG. 10 is an enlarged diagram of a stiffener  28 D implemented in a semiconductor device according to a fourth modification. In this modification, the stiffener  28 D comprises multiple stiffener layers (2 layers are shown in FIG. 10, referred to as first layer  37  and second layer  38 ). 
     By forming the stiffener  28 D so as to have a first layer  37  and a second layer  38 , the characteristics of the stiffener  28 D may vary for each layer. Thus, for example, for the first layer  37 , which is implemented on the side facing the semiconductor chip  22 , a layer having characteristics similar to those of the semiconductor chip  22  may be selected, and for the second layer  38 , which is implemented on the side facing the lid  25 , a layer having characteristics similar to those of the lid  25  may be selected. Thus, the bonding of the stiffener  28 D to the semiconductor chip  22  and the lid  25  can be strengthened, thereby preventing deformation such as warping from occurring in the semiconductor chip  22  and the lid  25 . 
     In the following, the various effects that can be achieved by the above-described invention are described. 
     According to the present invention, internal stress and voids are prevented from being generated in the bonding material placed in between the lid and the stiffener; therefore, the lid and the stiffener can be securely bonded and a higher reliability in the manufactured semiconductor device can be achieved. Also, the bonding material can be made thinner, thereby improving the thermal conductivity of the bonding material layer and enabling the efficient dissipation of heat generated at the semiconductor chip and transferred via the stiffener and the bonding material. 
     Also, according to the present invention, deformation such as warping in the stiffener or the semiconductor chip, or in both of these elements owing to the difference in the thermal expansion rate between the stiffener and the semiconductor chip would not occur even when heat is applied, thereby enabling a secure bonding between the stiffener and the lid and improving the reliability in the manufactured semiconductor device. 
     Additionally, according to the present invention, the bonding process of the semiconductor chip to the substrate and the bonding process of the lid are performed with the stiffener being securely bonded to the semiconductor chip by the first bonding material; therefore, deformation such as warping in the semiconductor chip can be avoided and higher reliability in the semiconductor device can be achieved. 
     Further, according to the present invention, a multi-chip module having excellent thermal dissipation characteristics as well as high reliability can be realized by implementing a plurality of the semiconductor devices on a motherboard.