Abstract:
A holding fixture that holds a component and mounts the component on an electronic circuit board includes a holding member that holds the component at a side of a first surface of the electronic circuit board, a first fixing member that includes a first base that is engageable with the holding member, and an elastic member that is pivotally attached to the base, sandwiches the electronic circuit board at a side of a second surface of the electronic circuit board, and elastically supports the holding member at the side of the first surface, the second surface opposing to the first surface, and a second fixing member that includes a second base that is engageable with the holding member, and a projection member that projects from the second surface of the electronic circuit board and is engageable with the elastic member.

Description:
[0001]     This application claims the right of foreign priority under 35 U.S.C. §119 based on Japanese Patent Application No. 2004-232921, filed Aug. 10, 2004, which is hereby incorporated by reference herein in its entirety as if fully set forth herein.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates generally to a heat radiating mechanism, and more particularly to a heat radiating mechanism that transmits the heat generated from an exoergic circuit element (referred to as “exoergic element” hereinafter) mounted on an electronic apparatus. The present invention is suitable, for example, for a heat spreader that radiates a CPU mounted on a printed board (also referred to as a “system board” or “motherboard”) in a personal computer (referred to as “PC” hereinafter). Here, the “heat spreader” is a metal plate that efficiently transmits the heat from the exoergic element to the outside.  
         [0003]     A Ball Grid Array (“BGA”) package, one type of package board soldered to the printed board, has conventionally been proposed in order to meet recently increasing demands for supplies of high-performance electronic apparatuses. The BGA package realizes a narrower pitch and more pins (i.e., high-density leads) without enlarging the package than a Quad Flat Package (“QFP”) that has the Gullwing type leads at four sides. Thus, the BGA package provides the high-performance electronic apparatus through the high density of the package.  
         [0004]     The BGA package is mounted with an IC and an LSI that generally serve as a CPU, and the improved performance and larger size of the LSI swells the calorific value, for example, up to 100 W to 150 W. Accordingly, in order to thermally protect the electronic circuit in the LSI, a radiator called a heat sink is thermally connected to the LSI via a heat spreader. The heat sink has cooling fins, is located near the CPU, and radiates the LSI through the natural cooling. Use of a material having a high coefficient of thermal conductivity (e.g., about 16.5×10 −6 /° C.), such as copper, for the heat spreader would result in a significant difference in coefficient of thermal conductivity between the heat spreader and the LSI made of silicon (which has a coefficient of thermal conductivity of about 4.2×10 −6 /° C.). In addition, there is also a significant difference in thickness between them because the LSI has a thickness of several hundred microns whereas the heat spreader has a thickness of several millimeters.  
         [0005]     Prior art includes, for example, Japanese Patent Applications, Publication Nos. 6-169037, 2-47895, 62-183150 and 2002-184914, and Japanese Utility-Model Application, Publication No. 2-101535.  
         [0006]     A jointing layer joints the LSI to the heat spreader, and is typically made of a material having no elasticity, such as epoxy resin and solder. For example, a Cu heat spreader is arranged on a Si chip via a heat-hardening adhesive as a jointing layer, and the jointing layer is hardened, for example, at 150° C. and then returned to the room temperature. Then, the heat spreader and the LSI generate thermal strains, but the heat spreader is thicker than the LSI and hard to deform in the thickness direction. Therefore, a large thermal stress is applied to and can break the LSI and the jointing layer. In particular, the influence of the thermal stress applied to the LSI becomes conspicuous for the increased chip size.  
         [0007]     One conceivable solution for this problem is to use for the jointing layer an elastic adhesive, such as a silicon adhesive, or a sheet or paste jointing material. However, the metallic jointing material, such as solder, has a coefficient of thermal conductivity of about 40 W/° C.·m, whereas these materials have such a small coefficient of thermal conductivity as 1 to 2 W/° C.·m, lowering the radiation efficiency of the CPU. The non-operating LSI can endure the temperature up to about 200° C., but the operating LSI&#39;s electronic circuit should be maintained at about 100° C. and protected thermally. The low radiation efficiency would cause the operating LSI&#39;s temperature to exceed 100° C. and possibly result in the thermal breakdown of the electronic circuit. In particular, as the CPU has recently increased the calorific value, it is undesirable to use the jointing material having a low coefficient of thermal conductivity for the CPU and the heat spreader.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     Accordingly, it is an exemplary object to provide a semiconductor package, a printed board having the semiconductor package, and an electronic apparatus, which thermally protects the exoergic element and jointing layer due to the thermal stress associated with the junction with the heat spreader, while maintaining the heat radiation effect for the exoergic element.  
         [0009]     A semiconductor package according to one aspect of the present invention that can be mounted on a printed board includes a package board that is mounted with an exoergic circuit element, a heat spreader that transmits heat from the exoergic circuit element, and a jointing layer that joints the exoergic circuit element to the heat spreader and is made of a solid jointing material that has substantially no elasticity, wherein the heat spreader includes a first surface jointed to the exoergic circuit element, and a second surface as a rear surface of the first surface, and wherein the heat spreader has a slit that extends in a substantially radial direction from an inner side to an outer side with respect to a first area that is jointed to the exoergic circuit element on the first surface or a second area that is an orthogonal projection of the first area onto the second surface, when the heat spreader is transparently viewed from the first or second surface. The slits enables the heat spreader of the semiconductor package to easily deform, and reduces the residue stress that affects the exoergic circuit element after the jointing layer made of a epoxy resin or another metal jointing material, such as solder, is hardened. On the other hand, the metal jointing material, such as solder, which has a large coefficient of thermal conductivity strongly adheres the exoergic circuit element made of silicon, etc. to the heat spreader made of copper having a large coefficient of thermal conductivity, and improve the heat radiation efficiency.  
         [0010]     Preferably, plural slits are arranged substantially symmetrical with respect to a center of the exoergic circuit element, like a substantially cross or asterisk shape. The symmetry can prevent the stress from partially concentrating on the exoergic circuit element. The slit may perforate through the heat spreader. Since the slit assists the heat spreader in deforming, its shape, size and the number are not limited as long as the heat radiation efficiency can be maintained. In other words, as the slit area is larger, the heat spreader becomes easily deformable. However, it is preferable that the slit is spaced from a center of the exoergic circuit element by a predetermined distance. This is because that the center of the exoergic circuit element is generally a heat source, and the heat radiation effect can deteriorate greatly if the slit is formed in the center.  
         [0011]     Preferably, the slit substantially follows beat flux of the heat, formed on the heat spreader, because the heat radiation effect can deteriorate greatly if the slit crosses the heat flux for radiating the exoergic circuit element. If the package board is mounted with plural exoergic circuit elements the heat spreader is commonly used for the plural exoergic circuit elements, the heat flux is a composite heat flux formed on the heat spreader by the plural exoergic circuit elements.  
         [0012]     The heat spreader may serve as part of a heat sink that naturally radiates the heat. Alternatively, the semiconductor package may further include a heat sink that naturally radiates the heat, and the heat spreader may be jointed to the heat sink so that the heat spread can deform. A joint between the heat spreader and the heat sink can use the grease, etc. When the heat spreader is strongly adhered to the heat sink, the heat spreader becomes hard to deform consequently, and the thermal stress received by the exoergic circuit element cannot be reduced. The semiconductor package has, for example, a BGA structure. A printed board mounted with the above semiconductor package and an electronic apparatus including the above printed board also constitute one aspect of the present invention.  
         [0013]     Other objects and further features of the present invention will become readily apparent from the following description of the preferred embodiments with reference to accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a schematic perspective view of an electronic apparatus according to the present invention.  
         [0015]      FIG. 2  is a schematic perspective view showing an internal structure of the electronic apparatus shown in  FIG. 1 .  
         [0016]      FIG. 3  is a schematic perspective view showing a package module shown in  FIG. 2 .  
         [0017]      FIG. 4A  is a schematic sectional view of a CPU, jointing layer and heat spreader shown in  FIG. 2 ,  FIG. 4B  is a partially exploded sectional view of  FIG. 4A , and  FIG. 4C  is a transparent plane view of a heat spreader.  
         [0018]      FIGS. 5A and 5B  are schematic plane views showing a relationship between the heat flux and slits on the heat spreader.  
         [0019]      FIG. 6  is a schematic plane view of the heat spreader commonly used for plural heat sources.  
         [0020]      FIG. 7  is a schematic sectional view as a variation of  FIG. 4A .  
         [0021]      FIG. 8  is a flowchart for explaining a manufacturing method of a package module shown in  FIG. 3 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     Referring now to accompanying drawings, a description will be given of a package module  100  as a semiconductor package according to one embodiment of the present invention, a printed circuit board  200  mounted with the package module  100 , and an electronic apparatus  300  that includes the printed circuit board  200 . Here,  FIG. 1  is a schematic perspective view of the electronic apparatus  300 .  FIG. 2  is a perspective overview of a system board as the printed circuit board  200  included in the electronic apparatus  300 .  
         [0023]     As shown in  FIG. 1 , the electronic apparatus  300  of the instant embodiment is exemplarily implemented as a rack mount type UNIX server. The electronic apparatus  300  is screwed onto a rack (not shown) by a pair of attachment parts  302 , and includes the printed circuit board  200  shown in  FIG. 2  in a housing  310 .  
         [0024]     The housing  310  is provided with a fan module  320 , which rotates a built-in cooling fan to generate airflow and compulsorily cools a heat sink  150 , to which a heat spreader  140  is connected which will be described later. The fan module  320  has a power section (not shown), and a propeller section (not shown) fixed onto the power section. The power section may use any structure known in the art, which typically includes a rotary shaft, a bearing around the rotary shaft, a bearing house, a magnet for a motor, etc., and a detailed description thereof will be omitted. The propeller section includes a number of angled, isogonally or non-isogonally arranged rotors, which have a predetermined size. The power section and the propeller section may or may not be separable.  
         [0025]     As shown in  FIG. 2 , the printed circuit board  200  includes a package module  100 , an LSI module  210  around the package module, a plurality of block plates  220  for receiving a plurality of memory cards  240 , and a connector  230  for an external device, such as a hard disc and a LAN.  
         [0026]     The package module  100  serves as a BGA package that is mounted with a CPU  102  and connected to the printed circuit board  200  via BGAs  120 . More specifically, the package module  100  includes, as shown in  FIGS. 2 and 3 , a package board  110 , BGAs  120 , a jointing layer  130 , a heat spreader  140  and a heat sink  150 . Here,  FIG. 3  is a schematic sectional view of the package module  100  shown in  FIG. 2 , although  FIG. 3  omits the heat sink  150 .  
         [0027]     The package board  110  is made, for example, of ceramic, because ceramic and the CPU  102  have such close coefficients of thermal conductivity that the CPU  102  and the package board  110  do not deform when the CPU  102  is mounted onto the package board  110 . Alternatively, the package board  110  may be made of resin, because the resin board is thinner than a ceramic board, and thus the resin board is superior in electric characteristic to, less expensive than, and more easily processed than the ceramic board.  
         [0028]     The package board  110  is mounted with the CPU  102  made of an LSI and another circuit element  108 , such as a capacitor, on its top surface, and the BGAs  120  on its bottom surface. Of course, this configuration is illustrative. For example, the circuit element  108  may be mounted on the bottom surface of the package board  110 . While the package board  110  of the instant embodiment is a single chip type mounted with one CPU  102 , the present invention does not exclude a multi-chip type package board that is mounted with plural CPUs  102 .  
         [0029]     The CPU  102  is an LSI (or an exoergic element) soldered to the package board  110  by bumps  104  as terminals, and resin underfill  106  that is usually used for a flip chip (or a chip that has bumps) is filled between the CPU  102  and the package board  110  to seal the bumps  104  and maintain connection reliability of the bumps  104 .  
         [0030]     The BGA  120  is a ball-shaped soldering bump (or a soldering ball), and arranged at a connection portion between the package board  110 &#39;s bottom surface and the printed board  200 . In other words, the BGA  120  serves as a terminal and is connected to the printed board  200  strongly by soldering balls (or solder). The BGA package thus uses the BGAs for connections instead of the leads provided at four sides of the QFP package. The BGA package can narrow the pitch between terminals, arrange many terminals, and realize the high density, high performance and miniaturization without enlarging the package. The BGA  120  may arrange soldering bumps on the entire bottom surface of the package board  110 , or arrange soldering bumps in an approximately square shape having an approximately square hollow if there is the circuit element  108  on the bottom surface of the package board  110 . The heat spreader  140  of this embodiment is suitable for the BGA package, because the BGA package often makes the heat spreader of a material different from that for the LSI.  
         [0031]     If necessary, the reinforcing metal is provided on the top surface of the package board and reinforces the package board. The reinforcing metal straightens the torsion of the package board  110 , and made, for example, of aluminum, copper, etc.  
         [0032]     The jointing layer  140  strongly joints the CPU  102  to the heat spreader  140 . The jointing layer  140  is made of a jointing material that has a high coefficient of thermal conductivity and substantially no elasticity, such as epoxy resin high thermal conductive adhesive and solder. The jointing layer  130  strongly adheres the CPU  102  to the heat spreader  140 , and efficiently transmits the heat from the CPU  102  to the heat spreader  140 . The jointing layer  130  never causes a temperature gap between the CPU  102  and the heat spreader  140 .  
         [0033]     The heat spreader  140  is arranged between the package board  110  and the heat sink  150 , and connected to the CPU  102  via the jointing layer  130 . The heat spreader  140  serves to transmit the heat from the CPU  102  to the heat sink  150 , and is made of a material having a high coefficient of thermal conductivity, such as copper, aluminum carbide, aluminum, aluminum silicon carbide (aluminum that contains silicon), silicon carbide.  
         [0034]     The heat spreader  140  has a surface  141  jointed to the CPU  102 , and a surface  142  as a rear surface of the surface  141 . As shown in  FIGS. 4B and 4C , the heat spreader  140  has slit  144  each of which extends in a radial direction from an inner side to an outer side with respect to an area  143   a  that is jointed to the CPU  102  on the first surface  141  or a second area  143   b  that is an orthogonal projection of the area  143   a  onto the second surface  142 , when the heat spreader  140  is transparently viewed from the first surface  141  or the second surface  142 . Here,  FIG. 4A  is a schematic sectional view showing a joint state of the CPU  102 , the jointing layer  130 , and the heat spreader  140 .  FIG. 4B  is a partially exploded sectional view that separates the CPU  102  and the jointing layer  130  from the heat spreader  140  in  FIG. 4A  so as to illustrate the areas  143   a  and  143   b .  FIG. 4C  is a transparent plane view of a heat spreader  140  viewed from the surface  141  or  142 . The areas  143   a  and  143   b  are the same when viewed from the surface  141  or  142  transparently, and  FIG. 4C  encloses the area  143  by broken line.  
         [0035]     The heat spreader  140  has a thickness, for example, of several millimeters although  FIGS. 3 and 4 A- 4 C exaggerate the heat spreader  140  for illustration convenience. The CPU  102  has a thickness, for example, of 300 μm to 600 μm. The heat spreader  140  is made of a material having a high coefficient of thermal conductivity, such as copper that has a coefficient of thermal conductivity of about 16.5×10 −6 /° C., and a difference in coefficient of thermal conductivity is very significant between the heat spreader  140  and the CPU  102  made of silicon (which has a coefficient of thermal conductivity of about 4.2×10 −6 /° C.).  
         [0036]     Therefore, when the package is heated up to 150° C. and then returned to the room temperature in order to harden the jointing layer  130 , the large thermal stress is applied to the CPU  102  due to a difference between the thermal shrinkage and coefficient of thermal conductivity of the heat spreader  140 . In particular, the heat spreader  140  is thicker than the CPU  102 , and less easily deforms than the CPU  102  in the thickness direction. This causes a problem that the large thermal stress is applied to the CPU  102 , and breaks the CPU  102  and the jointing layer  130 . The influence of the thermal stress applied to the CPU  102  becomes conspicuous for a large chip size of 10 mm to 20 mm.  
         [0037]     One conceivable solution for this problem is use for the jointing layer  130  an elastic adhesive, such as a silicon adhesive, or a sheet or paste jointing material. However, these materials have smaller coefficients of thermal conductivity or larger thermal resistances than the metallic jointing material, lowering the radiation efficiency of the CPU. The non-operating CPU  102  can endure the temperature up to about 200° C., but the operating CPU  102 &#39;s electronic circuit should be maintained at about 100° C. and protected thermally. The low radiation efficiency would cause the operating LSI&#39;s temperature to exceed 100° C. and possibly result in the thermal breakdown of the electronic circuit. In particular, along with the recently increasing calorific value of the CPU to 100 W to 150 W, it is not preferable to joint the CPU  102  to the heat spreader  140  with an adhesive having a low coefficient of thermal conductivity.  
         [0038]     Accordingly, this embodiment makes the jointing layer  130  of a jointing material having a coefficient of thermal conductivity, and maintains the radiation efficiency. On the other hand, this embodiment provides the heat spreader  140  with the slits  144  so as to make the heat spreader  140  easily deformable in a thickness direction, reducing the influence of the thermal stress applied to the CPU  102 .  
         [0039]     As a result, the operating CPU  102 &#39;s electronic circuit is protected from the thermal breakdown, and the CPU  102  and the jointing layer  130  are protected from breakdown due to the thermal distortion break at the jointing time between the CPU  102  and the heat sink  140 .  
         [0040]     The slits  144  extend in radial directions, as shown in  FIG. 4C , from the center C of the CPU  102 , because the heat flux HF approximately extends in the radial direction from the center of the CPU  102  as a heat source. Here,  FIGS. 5A and 5B  are schematic plane views showing a relationship between the heat flux HF from the heat source and the slit S.  
         [0041]     The heat spreader  140  spreads the heat from the CPU  102 . The heat spread is precluded on the heat spreader  140  as the heat flux is obstructed. In other words, in order to maintain the radiation efficiency of the CPU  102 , it is necessary to form the slit  144  without obstructing the heat flux. When the slit S is arranged as shown in  FIG. 5B , the heat flux HF 1  is obstructed and the effective heat radiation from the CPU is interrupted. The term “radial” in instant specification does not necessarily mean a line that extends straightforward from the center but covers an eddy and other shapes as long as the shape follows the heat flux.  
         [0042]     While the instant embodiment regards the heat source as the center of the CPU  102 , the heat source actually has a certain area and the heat flux formed by the heat from the CPU  102  does not perfectly extend in a radial direction from the center of the CPU  102 . Therefore, it is necessary to calculate the heat flux using a simulation, experiment, etc., and then to determine an effective arrangement of the slit(s). Of course, the present invention does not require the slit&#39;s shape and arrangement to perfectly accord with the heat flux, in light of the fact that the manufacturing convenience does not permit a complexly shaped slit.  
         [0043]     In addition, the present invention does not require the extension line to pass the center C of the CPU  102 . For example, the extension lines of the slits  144   a  and  144   b  can intersect at a position apart from the center C by a predetermined distance in  FIG. 4C . In this context, it is sufficient that the slit extends in an approximately radial direction from the center C of the CPU  102 . The phrase “approximately radial” means that the slit is arranged along the heat flux and the number of heat fluxes cut by the slit is small. The slit is preferably formed along the heat flux and the heat flux generally extends from the center to the outside but its extending direction may not perfectly accord with the radial direction. The phrase “approximately radial” covers a case the heat flux does not perfectly extend in the radial direction as long as the slit follows the heat flux. That “the number of heat fluxes cut by the slit is small” means that an angle between the slit and the heat flux is within 45°, preferably within 30°. The angle between the slit and the heat flux of 45° cuts about 50% of the heat flux, and the angle between the slit and the heat flux of 30° cuts about 33% of the heat flux.  
         [0044]     The slits are arranged substantially symmetrical with respect to the center C of the CPU  102 , like a substantially cross or asterisk shape or every 30° intervals. The symmetry can prevent the stress from partially concentrating on the CPU  102 . For example, when the slits  144  are formed only at the right side of the heat spreader shown in  FIG. 4C , the thermal stress does not reduce at the left side of the CPU  102 .  
         [0045]     Of course, when the heat flux is not formed symmetrically and biased, the slits  144  can be formed asymmetrically. For example, the heat flux appears asymmetrically when the package board  110  has a deviation in its temperature distribution, for example, if the package board  110  is mounted with plural CPUs or includes a CPU and another package board  110  mounted with another CPU adjacently.  
         [0046]     The slits  144  extend, as shown in  FIG. 4C , from the inner side to the outer side of the area  143 . In other words, the slit  144  extends across the outline that defines the area  143 . The area  143  is an area  143   a  jointed to the CPU  102  or the area  143   b  as a rear surface of the area  143   a , and the CPU  102  generally receives the thermal stress from the heat spreader. It is undesirable that the slit  144  extends from the inside of the area  143  only to the outline of the area  143 , i.e., not to the outside of the area  143 , because the stress concentrates on the outline.  
         [0047]     The slit  144  does not necessarily extend to the outline of the heat spreader  140  outside the area  143 , because the CPU  102  is not jointed to the heat spreader  140  outside the area  143  and does not receive the thermal stress from the heat spreader  140  in this area. Of course, the present invention does not preclude the slit  144  from extending to the outline of the heat spreader  140 . The length by which the slit  144  extends from the outline of the area  143  outside the area  143  is determined by a simulation or an experiment based on the calorific value and size of the CPU  102  and the material and size of the heat spreader  140 .  
         [0048]     The slit  144  may or may not perforate through the heat spreader  140 . In this specification, the term “slit” covers both situations. The non-perforating slit  144  may be provided only at the side of the surface  141  or  142  or in both surfaces. The slit  144  may perforates through the surfaces  141  and  142  obliquely. The perforating and non-perforating slits  144  may exist at the same time.  
         [0049]     Since the slit  144  assists the heat spreader  140  in deforming, its shape and size and the number of slits are not limited as long as the necessary heat radiation efficiency can be maintained. The large slit area would facilitate the deformation of the heat spreader  140 , but the heat radiation would deteriorate in the slit area. A shape of the slit  144  is not limited, and the slit  144  does not have to be an elongated hole or groove. For example, the slit  144  may have a circular or sectorial shape in  FIG. 4C . The slit  144  does not have the constant depth. For example, the slit  144  is deeper in  FIG. 4C  as a distance between the slit and the center C increases.  
         [0050]     The slit  14  is formed, for example, by punching a copper sheet.  
         [0051]     It is preferable that the slit  144  is spaced from the center C of the CPU  102  by a predetermined distance, as shown in  FIG. 4C . This is because that a circle that has a certain radius and a center at the center C of the CPU  102  is generally a heat source and the heat radiation effect can deteriorate greatly if the slit is formed within this circle.  
         [0052]     The package board  110  can be mounted with plural exoergic elements (for example, a CPU and a chipset or plural CPUs) and the heat spreader can be commonly used for the plural exoergic elements. In this case, the heat flux is a composite heat flux formed on the heat spreader  140  by the plural exoergic elements. For example, when the heat flux from two heat sources C 1  and C 2  is formed on the heat spreader  140 A as shown in  FIG. 6 , the slits S that are arranged as shown in  FIG. 6  follow heat fluxes HF 2  and HF 3  preferably. While  FIG. 6  assumes that these two heat sources C 1  and C 2  have approximately the same calorific value, if one of the calorific values is larger the slits S may incline or deform accordingly.  
         [0053]     While the heat spreader  140  is a rectangular plate in this embodiment, it may have an arbitrary shape, such as a downwards convex. The heat spreader  140  can be made of two or more components, and the slits are formed one or more of the components so that the thermal stress applied to the CPU  102  can reduce.  
         [0054]     The heat spreader  140  may serve as part of a heat sink that naturally radiates the heat. For example, the heat spreader  140  may be provided with fins  145  as shown in  FIG. 7 . Here,  FIG. 7  is a variation of  FIG. 4A . Since the heat spreader  140  is slit so that it may easily deform, the plate fins  145  are formed at both ends of the heat spreader  140  so that the plate fins  145  may not prevent deformations of the heat spreader  140 . Of course, if the plate fin  145  does not originally preclude the deformation of the heat spreader  140 , for example, because the plate fin  145  has a needle shape, etc., the fin  145  may be formed above the CPU  102 .  
         [0055]     Since the slit  144  assists the heat spreader  140  in deforming, the slit does not have to be provided if the heat spreader  140  is made of an elastic member. The present invention does not preclude the heat spreader  140  from being made of an elastic material having a coefficient of thermal conductivity.  
         [0056]     The package  100  of the instant embodiment further includes the heat sink  150 , and the heat spreader  140  is jointed to the heat sink  150  so that the heat spreader  140  is deformable. For example, in attaching the heat sink  150 , a dispenser applies, in a radial direction, the thermal grease or compound onto a surface of the heat sink  150  at the side of the heat spreader  140 . Next, an applied surface of the heat sink  150  is placed on the heat spreader  140 .  
         [0057]     The heat spreader  140  and the heat sink  150  have approximately similar jointing areas, such as 16 cm 2 m and the jointing area is four times as large as the jointing area, such as 4 cm 2 , between the CPU  102  and the heat spreader  140 . Therefore, the jointing material between the heat spreader  140  and the heat sink  150  does not necessarily have a coefficient of thermal conductivity similar to that of the jointing layer  130 . If both members are strongly adhered to each other, the heat sink  150  undesirably precludes the heat spreader  140 &#39;s deformations through the slits  144 .  
         [0058]     If necessary, a pressure mechanism, such as a spring, compresses the heat sink  150  against the heat spreader  140  so as to enhance the adhesion between them but not to break the CPU  102 .  
         [0059]     The heat sink  150  has a base and cooling fins. The base is a plate composed, for instance, of aluminum, copper, aluminum nitride, artificial diamond, plastic, or other materials of high thermal conductivity, and connected to the heat spreader  140 . The heat sink  150  is manufactured by sheet metal working, aluminum die casting, or other processes. The housing  120 , if made of plastic, may be formed, for example, by injection molding. The cooling fins include many aligned plate-shaped fins, and form a convex portion to increase a surface area thereof, thereby enhancing dissipating effects. However, the shape of the cooling fin is not limited to one like a plate, and any arrangement shapes like a pin, a curve, etc. may be adopted. The cooling fins do not necessarily have to be aligned horizontally at a regular interval, but may be placed radially or obliquely with respect to the base. Moreover, the number of the cooling fins may be set arbitrarily. The cooling fins are preferably made of a material of high thermal conductivity, such as aluminum, copper, aluminum nitride, artificial diamond, and plastic. The cooling fins are formed by molding, a press fit, brazing, welding, injection molding, or the like.  
         [0060]     A description will now be given of a method for manufacturing the package module  100 , with reference to  FIG. 8 . Here,  FIG. 8  is a flowchart showing a manufacturing method of the package module  100 . First, the heat flux formed on the slitless heat spreader is obtained by a simulation or experiment (step  1002 ). Next, the deformation amount of the heat spreader  140  is calculated in order to reduce the thermal stress applied to the CPU  102  (step  1004 ). Next, an arrangement of the slits  144  is determined based on the heat flux, the necessary deformation amount of the heat spreader  140 , and the permissible radiation efficiency loss (step  1006 ). Next, the heat spreader  140  is formed by cutting a sheet into a predetermined size after the slits  144  is formed in the sheet metal by punching etc (step  1008 ).  
         [0061]     Next, the CPU  102  is soldered onto the package board  110  by the bumps  104 , and the underfill  106  is filled between the CPU  102  and the package board  110  (step  1010 ). Next, the CPU  102  is strongly adhered to the heat spreader  140  via the jointing layer  130  (step  1012 ). For example, the step  1012  heats up to 150° C. and hardens the jointing layer  130 , and then returns to the room temperature. Then, the heat spreader  140  deforms through the slits  144 , and the thermal stress applied to the CPU  102  reduces. As a consequence, the CPU  102  is protected from breakdown, and the package  100  can be manufactured with good yield.  
         [0062]     In operation of the electronic apparatus  300 , the CPU  102  generates the heat but the slits  14  are formed along the heat fluxes and do not significantly preclude the heat radiation effect by the heat spread  140  and the heat sink  150 . The heat spreader  140  can maintain high heat spread performance, and the heat sink  150  properly radiates the heat generated from the CPU  102 . The cooling fins of the heat sink  150  are cooled by the cooling fan installed in the fan module  320 . The electronic apparatus  300  can maintain the stable operations of the CPU  102  by protecting the electronic circuit in the CPU  102  from thermal breakdown.  
         [0063]     Further, the present invention is not limited to these preferred embodiments, and various modifications and changes may be made in the present invention without departing from the spirit and scope thereof. For example, the inventive electronic apparatus is not limited to a rack mount type server, but is applicable to a bookshelf type. It is not limited to a server, and is applicable to a PC, a network device, a PDA, and other peripherals. The inventive package module is applicable to a Land Grid Array (“LGA”) package that is connected to a printed board via a LGA socket and other packages, such as a Pin Grid Array (“PGA”) package. The inventive package module is applicable to an exoergic element that does not serve as a CPU, such as a chipset.  
         [0064]     Thus, the present invention provides a semiconductor package, a printed board having the semiconductor package, and an electronic apparatus, which thermally protects the exoergic element and jointing layer due to the thermal stress associated with the junction with the heat spreader, while maintaining the heat radiation effect for the exoergic element.