Abstract:
A radiating-plate mounting structure for mounting a radiating plate on a semiconductor integrated circuit installed on a printed circuit board is arranged to have a pin disposed on the printed circuit board in the neighborhood of the semiconductor integrated circuit and to fix the radiating plate to the semiconductor integrated circuit by pressing the radiating plate with a spring member using a lock part of the pin as a fulcrum. At this time, the middle part of the radiating plate can be reliably fixed to the semiconductor integrated circuit by a hole provided in the spring member for allowing a fin part of the radiating plate to escape through the hole. The structural arrangement effectively eliminates the possibility of having the radiating plate caused to peel off by some impact inflicted thereon.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a structure for mounting a radiating plate which is provided on a semiconductor integrated circuit to be installed in a printed circuit board. 
     2. Description of Related Art 
     Semiconductor integrated circuits have recently come to be prepared to have a high degree of density. As a result, the heat build-up amount of flat-package-type semiconductor integrated circuits is trending upward. It has become difficult to sufficiently lower the temperature of these semiconductor integrated circuits by natural cooling. The semiconductor integrated circuits, however, must be cooled, because exposing them to high temperature tends to cause them to malfunction. 
     Known methods for cooling the flat-package-type semiconductor integrated circuits include air cooling by mounting a radiating plate (a heat sink), forcible cooling with a cooling fan, and cooling by Peltier effect attained with a Peltier element. 
     The methods of using a cooling fan or a Peltier element give an excellent cooling effect. However, these methods have necessitated securing a power source for operating the cooling fan or the Peltier element and also have incurred an inevitable increase in cost due to the addition of the cooling fan or the Peltier element. 
     The method of mounting a radiating plate permits cooling the semiconductor integrated circuit at a lower cost than the methods of using a cooling fan or a Peltier element. For mounting the radiating plate on the flat-package-type semiconductor integrated circuit, it has been practiced to secure the radiating plate to the semiconductor integrated circuit by bonding with an adhesive, a double-sided adhesive tape or the like. 
     However, in cases where a shake or a downfall happens to inflict an impact on the radiating plate which is bonded with an adhesive, the bonded part of radiating plate tends to peel off. In such a case, the radiating plate would part from the semiconductor integrated circuit, becoming incapable of fulfilling its cooling function. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is directed to the solution of the above-stated problem of the prior art. An object of the invention is, therefore, to provide a structure for mounting a radiating plate on a semiconductor integrated circuit in such a way as to ensure that the radiating plate is never caused to peel off by any impact inflicted thereon. 
     To attain the above object, in accordance with an aspect of the invention, there is provided a radiating-plate mounting structure, comprising, a printed circuit board, a semiconductor integrated circuit installed on the printed circuit board, a radiating plate provided on the semiconductor integrated circuit, and spring urging means for pressing and fixing the radiating plate onto the semiconductor integrated circuit. 
     The above and other objects and features of the invention will become apparent from the following detailed description of preferred embodiments taken in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEW OF THE DRAWING 
     FIG. 1 is a perspective view showing a printed circuit board on which a semiconductor integrated circuit to which a radiating plate is fixed is mounted, according to a first embodiment of the invention. 
     FIG. 2 is a sectional view showing a radiating-plate mounting part shown in FIG.  1 . 
     FIGS.  3 ( a ),  3 ( b ) and  3 ( c ) are diagrams for explaining procedures for mounting pins, a QFPIC (flat-package-type semiconductor integrated circuit), a radiating plate and a spring member shown in FIG.  1 . 
     FIG. 4 is a plan view showing the pin shown in FIG.  2 . 
     FIGS.  5 ( a ) and  5 ( b ) are a plan view and a front view, respectively, showing the spring member shown in FIG.  2 . 
     FIGS.  6 ( a ) and  6 ( b ) are a side view and a front view, respectively, showing the radiating plate shown in FIG.  2 . 
     FIG. 7 is a plan view showing a pin whose shape is different from that of the pin shown in FIG. 4, according to a second embodiment of the invention. 
     FIGS.  8 ( a ) and  8 ( b ) are a plan view and a front view, respectively, showing a spring member arranged in combination with the pin shown in FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings. 
     First, a first embodiment of the invention is described with reference to FIG. 1 to FIGS.  6 ( a ) and  6 ( b ). FIG. 1 shows a printed circuit board on which a semiconductor integrated circuit to which a radiating plate is fixed is mounted. In FIG. 1, there are illustrated a pin  101  which is formed approximately in a U shape, a spring member  102 , a radiating plate  103  (or a heat sink), a flat-package-type semiconductor integrated circuit  104  (hereinafter referred to as QFPIC), and a printed circuit board  105 . 
     FIG. 2 is a sectional view taken along a line I—I in FIG. 1 to show a mount part where the radiating plate  103  is mounted. Referring to FIG. 2, metal pins  101   a  and  101   b  each of which is formed approximately in a U shape are soldered to the printed circuit board  105 . The radiating plate  103  is fixed to the QFPIC  104  in a state of being pushed to the QFPIC  104  by the urging force of the spring member  102  with the upper sides of the metal pins  101   a  and  101   b  used as fulcra. 
     FIGS.  3 ( a ),  3 ( b ) and  3 ( c ) are diagrams for explaining procedures for mounting the approximately-U-shaped pins  101 , the QFPIC  104 , the radiating plate  103  and the spring member  102 . 
     Referring to FIG.  3 ( a ), the approximately-U-shaped metal pins  101   a  and  101   b  are fixed by soldering to the printed circuit board  105  at through-hole parts  302   a  and  302   b  thereof. The QFPIC  104  has its lead wire parts soldered to the printed circuit board  105  at its parts  301   a  and  301   b.  The soldering is performed by the same process by which other parts are fixed by soldering to the printed circuit board  105 . With the printed circuit board  105  designed to have the through-hole parts  302   a  and  302   b  connected at this time to the signal ground of the printed circuit board  105 , the soldered approximately-U-shaped pins  101   a  and  101   b  are connected to the signal ground of the printed circuit board  105 . 
     Referring to FIG.  3 ( b ), next, the radiating plate  103  is temporarily fixed to the QFPIC  104  with an adhesive, a double-sided adhesive tape or the like. The adhesive or the double-sided adhesive tape to be used at that time, of course, must have a good thermal conductivity. 
     Referring to FIG.  3 ( c ), next, the spring member  102  is mounted in such a way as to push the radiating plate  103  against the QFPIC  104  with the approximately-U-shaped pins  101   a  and  101   b  used as fulcra. The radiating-plate mounting steps are as follows. The spring member  102  is first set in an approximately vertical posture to have its one end  303  in touch with the approximately-U-shaped pin  101   a.  Then, the spring member  102  is swung in this state in the direction of an arrow  350 . At this time, a fin  601  which is formed at the center of the radiating plate  103  as shown in FIG.  6 ( a ) comes into a hole  50  provided in the center part of the spring member  102  as shown in FIG.  5 ( a ), so that the spring member  102  is prevented from colliding with the radiating plate  103 . With the swinging motion of the spring member  102  made further, when the spring member  102  comes to be approximately in parallel to the printed circuit board  105 , the tip  306  of a V-shaped part  305  provided in the center part of the spring member  102  comes to abut on the radiating plate  103 . Then, the spring member  102  is further swung in a pushing manner until the other end  304  thereof comes to touch the approximately-U-shaped pin  101   b.  After that, the spring member  102  is slid in the direction of an arrow  351  (to the right as viewed in FIG.  3 ( c )). In this state, a pushing force is exerted on the radiating plate  103  at the tip  306  of the V-shaped part  305  of the spring member  102 . 
     FIG. 4 is a plan view showing each of the approximately-U-shaped pins  101  ( 101   a  and  101   b ) used in the first embodiment. Referring to FIG. 4, the pin  101  is soldered to the printed circuit board  105  by inserting parts  401  of the pin  101  into through holes of the printed circuit board  105 . Parts  402  of the pin  101  serve to keep a predetermined distance of clearance between the printed circuit board  105  and the upper side of the pin  101  which acts as a fulcrum. The approximately-U-shaped pin  101  is formed with a hard metal. 
     FIG.  5 ( a ) is a plan view of the spring member  102  used in the first embodiment. FIG.  5 ( b ) is a front view of the spring member  102 . The spring member  102  is made of an elastic metal and is provided with a hole  501  in its middle part for allowing a fin part of the radiating plate  103  to escape therethrough. 
     FIG.  6 ( a ) is a side view of the radiating plate  103  used in the first embodiment. FIG.  6 ( b ) is a front view of the radiating plate  103 . The radiating plate (heat sink)  103  excels in thermal conductivity and is made of a light metal such as aluminum or the like. To enhance its efficiency of cooling, the radiating plate  103  is provided with a plurality of fins  601 . 
     In the arrangement described above, the approximately-U-shaped pins  101   a  and  101   b  are soldered to the QFPIC  104  at positions on both sides thereof. With the approximately-U-shaped pins  101   a  and  101   b  used as fulcra, the radiating plate  103  is fixed to the QFPIC  104  in a state of being pressed against the QFPIC  104  by the spring member  102 . 
     Further, the spring member  102  can be readily dismounted and removed according to procedures which are reverse to the mounting procedures described above. Therefore, the QFPIC  104  which is soldered can be easily replaced. 
     According to the invention, each metal pin which is soldered to the printed circuit board  105  does not have to be in the approximate U shape. The metal pin may be arranged in any other suitable shape as long as the pin is provided with some lock part. FIG. 7 shows in a plan view an E-shaped pin  701  which is employed in a second embodiment of the invention. Referring to FIG. 7, the E-shaped pin  701  has a leg part  702  at which the pin  701  is soldered to the printed circuit board  105  with the leg part  702  inserted into a through hole formed in the printed circuit board  105 . Parts  703  of the pin  701  are arranged to maintain a predetermined distance of clearance between the printed circuit board  105  and the upper side of the pin  701  which is used as a fulcrum after the pin  701  is soldered to the printed circuit board  105 . 
     FIG.  8 ( a ) is a plan view of a spring member  801  which is arranged according to the shape of the E-shaped pin  701 . FIG.  8 ( b ) is a front view of the spring member  801 . Since the pin  701  has the leg part  702  formed at the center thereof, a cut-in part  803  is provided in each end of the spring member  801  for preventing the spring member  801  from touching the center leg part  702  of the pin  701 . Further, as in the first embodiment, the spring member  801  has a hole  802  formed in its middle part for allowing the fin of the radiating plate  103  to escape therethrough. 
     The procedures for mounting the parts of the second embodiment described above are identical with the mounting procedures of the first embodiment and are, therefore, omitted from the description. Although the second embodiment has the E-shaped pin  701  and the spring member  801  arranged as described above, the E-shaped pin  701  is soldered to a position on each of two sides of the QFPIC  104  and the spring member  801  is mounted thereon. With the spring member  801  thus mounted, the radiating plate  103  can be fixed in position in a state of being pushed against the QFPIC  104  as in the case of the first embodiment. 
     According to the invention, as described in the foregoing, the radiating plate, i.e., a heat sink, which is mounted on the semiconductor integrated circuit is fixed in position with a spring member. Therefore, the radiating plate, i.e., the heat sink, is never caused to peel off the semiconductor integrated circuit by vibrations or shakes nor by a downfall impact inflicted thereon. 
     In replacing the semiconductor integrated circuit on which the radiating plate is mounted, the replacing work can be easily carried out as the spring member and the radiating plate are removable without difficulty. 
     Further, since the heat sink can be connected to the signal ground through the metal pin and the spring member, radiant noises of the semiconductor integrated circuit can be adequately suppressed.