Abstract:
A semiconductor device includes a semiconductor element mounted on a substrate; at least one electronic part arranged around the semiconductor element; and a heat radiation member bonded to a backside of the semiconductor element by a bonding material. The heat radiation member has an isolation part extending between an outer circumference of the semiconductor element and the electronic part.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 11/500,879 filed on Aug. 9, 2006. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention generally relates to semiconductor devices and, more particularly, to a semiconductor having chip part such as a capacitor arranged near a semiconductor element and a heat radiation member such as a heat spreader attached to such a semiconductor device. 
         [0004]    2. Description of the Related Art 
         [0005]    In recent years, a semiconductor element has become being operated at a higher frequency, and an amount of heat generated during operation has increased. In order to cool the semiconductor element by radiating heat from the semiconductor element, a heat spreader as a heat radiation member is provided to a backside of the semiconductor element mounted on a substrate in many cases. In order to radiate heat efficiently, a heat spreader is formed to have an outer configuration larger than that of the semiconductor element so as to cover the entire semiconductor element. Then, the heat spreader is bonded to the backside of the semiconductor element by a heat transfer bonding material 
         [0006]      FIG. 1  is a cross-sectional view of a semiconductor device having a conventional heat spreader. As shown in  FIG. 1 , a semiconductor element  1  is mounted on a printed circuit board  2 , and a heat spreader  3  is provided to cover the semiconductor element  1 . The heat spreader  3  has a leg part  3   a  which extends to the printed circuit board  2 , and a concavity  3   b  is formed so as to accommodate the semiconductor element  1  therein. 
         [0007]    Chip parts (electronic parts)  4  such as a capacitor are mounted on the printed circuit board  2  in a surrounding area of the semiconductor element  1 . Thus, the concavity  3   b  of the heat spreader  3  is formed in a size which can also accommodate the chip parts  4 . 
         [0008]    The heat spreader  3  is formed by a metal having excellent heat transfer property such as, for example, copper (Cu), and is bonded to the backside of the semiconductor element  1  by a bonding material  5 . As for the bonding material  5 , although a heat transfer resin, which is a resin added with heat transfer particles, may be used, a metal bonding material such as a solder or a silver paste has become used so as to further improve the heat transfer property. 
         [0009]    A surrounding portion of the concavity  3   b  of the heat spreader  3 , that is, an end surface of the leg part  3   a  is bonded to the printed circuit board  2 . Thereby, the heat spreader  3  is fixed to the printed circuit board  2 , and an effect that the printed circuit board  2  is reinforced by the heat spreader  3  is obtained. 
         [0010]    If a solder, which is a metal bonding material, is used as the bonding material  5 , the heat spreader  3  is placed and temporarily fixed on the printed circuit board  2  in a state where the solder is inserted between the backside of the semiconductor element  1  and a bottom surface of the concavity  3   b  of the heat spreader  3 . The thus-assembled printed circuit board  2  and the heat spreader  3  are put in a reflow furnace and heated to melt the solder, and, thereafter, the melted solder is solidified. 
         [0011]    When reflowing the solder as the bonding material  5 , if an amount of the solder is excessive, the melted solder may be extruded from the backside of the semiconductor element  1  as shown in  FIG. 2 . Additionally, when a pressure is applied to the melted solder and an oxide film on the surface of the melted solder is broken, solder particles may scatter from the broken point of the oxide film. In such a case, the extruded solder or scattered solder may contact the chip parts  4  arranged near the semiconductor element  1 , which may result in short-circuiting of the chip parts  4 . 
         [0012]    In order to solve such a problem, there is suggested a technique to cover the chip parts  4  by an under-fill  6 , which is filled between the semiconductor element  1  and the printed circuit board  2 , by supplying a generous amount of the under-fill  6  (for example, refer to Patent Documents 1 and 2). 
         [0013]    Patent Document 1: Japanese Laid-Open Patent Application 2000-200870 
         [0014]    Patent Document 2: Japanese Laid-Open Patent Application 2001-267473 
         [0015]    As mentioned above, the under-fill  6  filled between the semiconductor element  1  and the printed circuit board  2  is supplied as a liquefied resin having a relatively low viscosity. Thus, even if the under-fill  6  is supplied so as to cover the chip parts  4 , there may be a case where the chip parts are not covered completely. Additionally, if many chip parts  4  are arranged, it takes time and effort to supply the under-fill  6  since the under-fill  6  must be supplied to each of the chip parts  4 . Moreover, since a large amount of the under-fill  6 , which is relatively expensive, must be used, there is a problem that the manufacturing cost of the semiconductor device is increased. 
         [0016]    Additionally, if the under-fill  6  is supplied after the chip parts  4  are soldered and when electrodes of opposite ends of each chip part  4  are soldered, there may be many cases where a narrow air gap (indicated by a reference numeral  7  in  FIG. 2 ) is formed between the bottom of the chip part  4  and the printed circuit board  2 . If the under-fill  6  is supplied to the chip parts  4  after the chip parts  4  are soldered in the above-mentioned state, there may be a case where the under-fill  6  cannot enter the air gap and the air gap cannot been filled by the under-fill  6 . 
         [0017]    In such a case, when the semiconductor device is heated in a reflow furnace so as to melt the bonding material  5  to bond the heat spreader  3 , the solder on the opposite ends of the chip part  4  is also temporarily heated. At that time, the melted solder may flow into the air gap under the chip part  4  since the upper side of the chip part  4  is covered by the under-fill  6 . In such a case, there is a problem in that electrodes on opposite ends of the chip part  4  are short-circuited. 
       SUMMARY OF THE INVENTION 
       [0018]    It is a general object of the present invention to provide an improved and useful semiconductor device in which the above-mentioned problems are eliminated. 
         [0019]    A more specific object of the present invention is to provide a semiconductor device in which a melted bonding material is prevented from contacting electronic parts arranged around a semiconductor element when bonding a heat radiation member to the semiconductor element, and a heat radiation member having such a function to prevent the bonding material from being brought into contact with electronic parts near the semiconductor element. 
         [0020]    In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a semiconductor device comprising: a semiconductor element mounted on a substrate; at least one electronic part arranged around the semiconductor element; and a heat radiation member bonded to a backside of the semiconductor element by a bonding material, wherein the heat radiation member has an isolation part extending between an outer circumference of the semiconductor element and the electronic part. 
         [0021]    In the semiconductor device according to the present invention, the isolation part may be formed integrally with the heat radiation member, and may be formed in a frame shape so as to surround an entire circumference of the semiconductor element. The bonding material may be a metal bonding material, which joins the backside of the semiconductor element to the heat radiation member by being melted by heat and thereafter solidified, and may be arranged inside the frame-shaped isolation part. The heat radiation member and the isolation part may be formed by a material having a wetting characteristic to the metal bonding material. The metal bonding material may be one of a solder and a silver paste. 
         [0022]    Additionally, in the semiconductor device according to the present invention, the heat radiation member may have a concavity accommodating the semiconductor element and the electronic part, a peripheral part of the concavity being bonded to the substrate, and the isolation part may extend toward the substrate from the heat radiation member, and a predetermined air gap may be formed between an extreme end of the isolation part and the substrate. 
         [0023]    Further, in the semiconductor device according to the present invention, the isolation part may be a member different from the heat radiation part and attached to the heat radiation member, and may be formed in a frame shape so as to surround an entire circumference of the semiconductor element. The heat radiation member may have a concavity accommodating the semiconductor element and the electronic part, and the isolation part may be formed by bending a metal plate and fitted into the concavity of the heat radiation member. The bonding material may be a metal bonding material, which joins the backside of the semiconductor element to the heat radiation member by being melted by heat and thereafter solidified, and may be arranged inside the frame-shaped isolation part. The isolation part may be formed by a material having a wetting characteristic to the metal bonding material. The metal bonding material may be one of a solder and a silver paste. A peripheral part of the concavity of the heat radiation member may be bonded to the substrate, and the isolation part extends toward the substrate from the heat radiation member, and a predetermined air gap may be formed between an extreme end of the isolation part and the substrate. 
         [0024]    Additionally, there is provided according to another aspect of the present invention a heat radiation member configured and arranged to be bonded by a bonding material to a backside of a semiconductor element around which at least one electronic part is arranged, the heat radiation member including an isolation part formed to extend between an outer circumference of the semiconductor element and the electronic part. 
         [0025]    In the heat radiation member according to the present invention may include a concavity accommodating the semiconductor element and the electronic part, wherein the isolation part may be a frame-shaped member having a size larger than an outer configuration of the semiconductor element. An extreme end of the isolation member may be lower than a height of a peripheral part of the concavity from a bottom part of the heat radiation member. The isolation part may be formed by bending a metal plate, and may be fixed to the concavity by being fitted therein. 
         [0026]    According to the present invention, when bonding the heat radiation member to the semiconductor element, the melted bonding material does not go beyond the isolation part. Thus, the melted bonding material does not contact the electronic part arranged in the surrounding area of the semiconductor element, which improves reliability of the semiconductor device and also improves yield rate of the semiconductor device. 
         [0027]    Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1  is a cross-sectional view of a semiconductor device having a conventional heat spreader; 
           [0029]      FIG. 2  is a cross-sectional view of the semiconductor device shown in  FIG. 1  in a state where a bonding material is extruded; 
           [0030]      FIG. 3  is a cross-sectional view of a semiconductor device according to a first embodiment of the present invention; 
           [0031]      FIG. 4  is a perspective view of a heat spreader shown in  FIG. 3 ; 
           [0032]      FIG. 5  is a cross-sectional view of a semiconductor device according to a second embodiment of the present invention; and 
           [0033]      FIG. 6  is a perspective view of an isolation member shown in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0034]    A description will now be given, with reference to  FIG. 3 , of a semiconductor device according to a first embodiment of the present invention.  FIG. 3  is a cross-sectional view of the semiconductor device according to first embodiment of the present invention. 
         [0035]    As shown in  FIG. 3 , a semiconductor element  1  is flip-chip mounted to a printed circuit board  2 , and a heat spreader  10  is provided to cover the semiconductor element  1 . An under-fill  6  is filled between the semiconductor element  1  and the printed circuit board  2 . 
         [0036]    The heat spreader  10  as a heat radiation member has a leg part  10   a  extending to the printed circuit board  2  so that a concavity  10   b  is formed to accommodate the semiconductor element  1 . That is, the concavity  10   b  is formed by the leg part  10   a  of the peripheral portion of the heat spreader  10 . 
         [0037]    Chip parts (electronic parts) such as a capacitor or a resistor are mounted on the printed circuit board  2  around the semiconductor element  1 . Thus, the concavity  10   b  of the heat spreader  10  is formed in a size which can accommodate the chip parts  4 . 
         [0038]    The heat spreader  10  is formed of a metal such as copper (Cu) or aluminum (Al) having an excellent heat transfer property, and is bonded to a backside of the semiconductor element  1  by a bonding material  5 . As for the bonding material  5 , for example, a heat transfer resin, which is prepared by adding heat transfer particles into a resin, may be used. In order to improve the heat transfer property, it is preferable to use a metal bonding material such as a solder, a silver paste or the like. In the present embodiment, the heat spreader  10  is formed of copper (Cu), and a solder, which is bondable to copper and has an excellent heat transfer property, is used for the bonding material  5 . 
         [0039]    A peripheral part of the concavity  10   b  of the heat spreader, that is, an end surface of the leg part  10   a  is bonded to the printed circuit board  2  by an adhesive  8 . Thereby, the heat spreader  10  is fixed to the printed circuit board  2  and also an effect that the printed circuit board  2  is reinforced by the heat spreader  10  is obtained. 
         [0040]    Here, in the present embodiment, the heat spreader  10  has an isolation part  12  as a portion extending between the semiconductor element  1  and the chip parts  4 , when fixed to the semiconductor element  1  and the printed circuit board  2 . In the present embodiment, the isolation part  12  is integrally formed with the heat radiation member  10 .  FIG. 4  is a perspective view of the heat spreader  10 . For example, when fabricating the heat spreader  10  by a copper plate, the concavity  10   a  is formed by machining or etching so as to let the isolation part  12  remaining in a frame-shape. 
         [0041]    The frame-shaped isolation part  12  is processed so that an inner size thereof is slightly larger than an outer size of the semiconductor element  1 . Additionally, the end part  12   a  of the isolation part  12  is formed to be slightly lower than the leg part  10   b . That is, when the heat spreader  10  is fixed to the printed circuit board  2 , as shown in  FIG. 3 , a height relationship is achieved so that the end part  12   a  is separated from the printed circuit board and a predetermined small gap is formed therebetween. By providing the gap, the isolation part  12 , which is electrically conductive, is prevented from being brought into contact with wirings on the printed circuit board  2  and also the solder as the bonding material  5  is prevented from being extruded outside the isolation part  12 . 
         [0042]    The heat spreader  10  having the above-mentioned structure has an excellent wetting characteristic to a solder when a solder is used as the bonding material  5  since the portion bonded to the semiconductor element  1  (the bottom of the concavity  10   a  inside the isolation part  12 ) and the inner surface of the frame-shaped isolation part  12  are made of copper (Cu). 
         [0043]    A description will now be given of a process of bonding the heat spreader  10  to the semiconductor element  1  and fixing the heat spreader  10  to the printed circuit board  2 . 
         [0044]    The heat spreader  10  is turned over (set in a state shown in  FIG. 4 ) and an appropriate amount of solder paste or solder grains is applied inside the isolation part  12 . Then, the adhesive  8  is applied to the end surface of the leg part  10   b  of the heat spreader  10 . Thereafter, the printed circuit board  2  having the semiconductor element  1  and the chip parts  4  mounted thereon is turned over, and is placed on the heat spreader  10  so that the semiconductor element  1  and the chip parts  4  are accommodated in the isolation part  12 . Then, the printed circuit board  2  and the heat spreader  10  are tentatively fixed to each other by clamping by a clip or the like, and are put into a reflow furnace in that state to be heated. According to the heating by the reflow furnace, the solder between the backside of the semiconductor element  1  and the bottom surface of the concavity  10   a  of the heat spreader  10  inside the isolation part  12  is melted. 
         [0045]    Although the excessive solder is protruded from the backside of the semiconductor element  1  when the solder is melted, the protrusion of the solder is stopped by the inner surface of the isolation part  12 , and the solder cannot protrude beyond the isolation part  12 , which results in the melted solder being retained within the isolation part  12 . Since the inner surface of the isolation part  12  has an excellent wetting property to the solder, the melted solder adheres to the inner surface of the isolation part  12  and is effectively retained inside the isolation part  12 . Moreover, even if an oxide film on the surface of the melted solder is broken and the solder is scattered when the melted solder is being extruded, the scattered solder merely adheres to the inner surface of the isolation part  12 , and the solder does not go out of the isolation part  12 . 
         [0046]    As mentioned above, the melted solder is retained inside the isolation part  12 , and the melted solder does not reach the chip parts  4 . Thus, a problem that the chip parts are short-circuited due to the solder as the bonding material  5  can be eliminated. 
         [0047]    It should be noted that the adhesive  8  is cured by heating in the reflow furnace, and the heat spreader  10  is bonded to the printed circuit board  2 . After the heating is ended, the semiconductor device is taken out of the reflow furnace and cooled. Thus, the solder is solidified and turned to the bonding material  5  shown in  FIG. 3 , and the heat spreader  10  as a heat radiation member is bonded to the backside of the semiconductor element  1  by the bonding material  5 . 
         [0048]    As mentioned above, the semiconductor device according to the present embodiment has the heat spreader  10  as a heat radiation member so that the isolation part  12  of the heat spreader  10  suppresses protrusion of the solder. The isolation part  12  can be formed simultaneously when forming processing the heat spreader  10 . Therefore, the protrusion of the solder can be prevented merely by changing the machining form of the heat spreader without increasing a number of parts, which does not increase a manufacturing cost of the semiconductor device. Additionally, the reliability of the semiconductor device having the heat spreader is improved, and a defective rate due to protrusion of a solder can be reduced, which improves a yield rate of the semiconductor device. 
         [0049]    A description will now be given, with reference to  FIGS. 5 and 6 , of a semiconductor device according to a second embodiment of the present invention.  FIG. 5  is a cross-sectional view of the semiconductor device according to the second embodiment of the present invention.  FIG. 6  is a perspective view of an isolation member shown in  FIG. 5 . In  FIG. 5 , parts that are the same as the parts shown in  FIG. 3  are given the same reference numerals, and descriptions thereof will be omitted. 
         [0050]    The semiconductor device according to the present embodiment has basically the same structure as the semiconductor device according to the above-mentioned first embodiment except for the structure of a heat spreader  20  being different from the heat spreader  10 . The heat spreader  20  according to the present embodiment is provided with an isolation member  22  as a separate member as a member constituting the isolation part  12  of the heat spreader  10 . 
         [0051]    The isolation member  22  has a shape in which an attaching parts  22   b  are protruded around a frame-shaped part  22   a  formed of, for example, a copper plate, as shown in  FIG. 5 . A dimension of protrusion of the attaching parts  22   b  is determined in accordance with a size of inside of a concavity  20   a  of the heat spreader  20  so that the isolation member  22  is fit into the concavity  20   a  by using an elasticity of the copper plate. 
         [0052]    Although the isolation member  22  is formed to provide the same effect as the above-mentioned isolation part  12  in the present embodiment, it is not limited to a copper plate. The isolation member  22  may be formed of a metal plate other than a copper plate, or formed of an insulating material so as to prevent short-circuiting when the isolation member  22  is brought into contact with the chip parts  4  or wirings on the printed circuit board  2 . When the isolation member  22  is formed by an insulating material, gold plating or nickel plating may be applied to a portion requiring a wetting characteristic to a solder. Additionally, the frame-shaped part  22   a  and the attaching parts  22   b  of the isolation member  22  may be formed as separate parts and are bonded to each other. That is, any structure may be used if the frame-shaped part  22   a  can be attached to a predetermined position of the heat spreader  20 . 
         [0053]    The heat spreader provided with the above-mentioned isolation member  22  also provides the same effect as the heat spreader  10  according to the above-mentioned first embodiment. The heat spreader  20  according to the present embodiment can be a shape the same as a conventional heat spreader having a concavity like the concavity  20   a , and, therefore, protrusion of a solder can be prevented by merely attaching the isolation member  22  after forming the heat spreader. 
         [0054]    The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing form the scope of the present invention. 
         [0055]    The present application is based on Japanese priority application No. 2006-053227 filed Feb. 28, 2006, the entire contents of which are hereby incorporated herein by reference.