Abstract:
Provided is a reliable optical pick-up which can prevent deterioration of a performance of a component, shortening of a service life or malfunctioning due to heat generation of an laser driver IC, wherein a metallic pattern is provided on a flexible printed board, having an area wider than the external shape of the laser driver IC and having an exposed outer surface, and made of the same material as that of a wiring pattern. It is preferable to bent the flexible printed board in a mounting part for the laser driver IC so that the metallic pattern is faced to and superposed with a surface of the flexible printed board on the side remote from the surface on which the laser driver IC is mounted.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an optical pick-up for reproducing data recorded on a recording surface of a disc, or recording data thereon, and a disc unit using thereof.  
         [0003]     2. Description of the Related Art  
         [0004]     An optical pick-up used in general is mainly composed of three blocks, that is, an objective lens drive device, an optical system and a flexible printed board. The objective lens drive device drives an objective lens in a focusing direction and a tracking direction so as to follow the rotation of an optical disc in order to precisely record or reproduce data. The optical system is composed of an optical component for converging a laser beam by means of the objective lens so as to reproduce data on the disc with the use of a reflected beam, or concentrating the energy of the laser beam onto a recording layer of the disc so as to record date thereon. The flexible printed board connects the lens drive device and the optical system, electrically to an external circuit board.  
         [0005]     The above-mentioned optical pick-up is incorporated therein, as main heat generating components, a semiconductor laser for emitting a laser beam, a laser driver IC for controlling the drive of the semiconductor laser, a front monitor for monitoring a laser power upon recording, a photo detector for detecting a reflection beam from a disc and a coil for driving the objective lens in the focusing direction and the tracking direction. Due to heat generation from these components, the temperature of the optical pick-up is raised. In particular, with a writable optical pick-up capable of recording data on a disk such as DVD-RAM/R/RW, CD-R/RW or the like, the heat generation from the semiconductor laser and the laser driver IC is larger. Further, the higher the recording speed, the higher the power of the semiconductor laser is required. Further, in order to ensure the transmission characteristic, it is required to locate the semiconductor laser and the laser driver IC adjacent to each other. In particular, in the case of a DVD recording speed not less than 8×, a circuit, the so-called write strategy, for creating a recording signal waveform has to be incorporated in the laser drive IC in order to transmit a satisfactory high frequency signal to the semiconductor laser. This circuit which has been conventionally incorporated in an IC in a circuit board on the optical disc unit side, causes the heat generation of the laser driver IC to be further increased. Thus, there would be caused detdeterioration of its performance, lowering of its service life and malfunctioning and the like.  
         [0006]     In order to solve the above-mentioned problem of heat generation, there has be presented an optical pick-up in which a heat spreader for the laser driver IC is connected by soldering to a copper foil pattern on a mounting surface of the laser driver IC provided on the flexible printed board and connected to a copper foil on the rear surface the latter through a through hole, and the copper foil on the rear surface thereof is connected to a pick-up cover made of a copper alloy (Refer to an example shown in FIG. 10, which is an application of “Perfect Manual of Thermal Design for Electronics” Nikkan Kogyo Shinbun Co. Jul. 18, 1997 by Naoki Kunimine, Vo., p 130 to 131 and FIG. 11-11). With this configuration, a heat generated from the laser driver IC is dissipated over a sufficiently wide area by the copper foil on the rear surface and the pick-up cover, and accordingly, it is said that the temperature of the laser driver IC can be restrained to a low value.  
         [0007]     The above-mentioned conventional technology has caused such a problem that a sufficiently wide area of the copper foil pattern for a wiring patter by which the laser driver IC is mounted, has not been able to be ensured since the copper foil pattern is used for mounting the laser driver IC if the flexible printed board has a single copper foil layer. Further, in the case of using a stainless group metal having a low heat conductivity for the pick-up cover, a heat from the laser driver IC cannot be dissipated in-planewise, and accordingly, sufficient heat radiation cannot be expected.  
       SUMMARY OF THE INVENTION  
       [0008]     An object of the present invention is to provide a reliable optical pick-up which can prevent its components from deteriorating their performances, lowering service lives, malfunctioning and so forth caused by heat generation from a laser driver IC.  
         [0009]     The above-mentioned object can be achieved by the provision of a metallic pattern having an area which is wider than an external shape of the laser driver IC having an exposed outer surface and made of a material the same as that of a wiring pattern, on a flexible printed board. Further, the flexible printed board is preferably bent in a part where the laser driver IC is mounted so that the metallic pattern is faced to and superposed with the surface of the flexible printed board thereof on the side remote from the surface on which the laser driver IC is mounted.  
         [0010]     Further, the above-mentioned object can also be achieved by the provision of a metallic pattern having an area which is wider than the outer shape of the laser river IC by extending a ground wiring pattern of the laser driver IC and having an exposed outer surface, on the flexible printed board. Further, the flexible printed board is preferably bent in a part where the laser driver IC is mounted, so that the metal pattern is faced to and superposed on the surface of the flexible printed board on the side remote from the surface thereof on which the laser driver IC is mounted. Further, after the metal pattern is folded, the metal pattern may be cut at its bent part.  
         [0011]     Moreover, the above-mentioned object can be achieved by the provision of a metal member having a heat conductivity not less than that of a pick-up housing (it is more preferable if the heat conductivity is larger than that of the pick-up housing), on the flexible printed board in a part where the laser driver IC is mounted, at a surface on the side remote from the surface on which the laser driver IC is mounted.  
         [0012]     According to the present invention, there is provided such a configuration that a metal member or a metal pattern made of aluminum, copper or the like is interposed between the flexible printed board and the cover in the part where the laser driver IC is mounted. Thus, a heat which is generated from the laser driver IC and which is then transmitted to the metal member or the metal pattern, is widely dissipated in-planewise of the metal member or the metal pattern. Thereafter, the heat is transmitted to the cover, and is then radiated into the atmosphere around the pick-up. Thus, since the heat from the laser driver IC can be radiated through a wide area, the laser driver IC can be restrained from raising its temperature, thereby it is possible to prevent occurrence of deterioration of its performance, lowering of its service life and malfunctioning. Thus, there can be provided a reliable optical pick-up.  
         [0013]     Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     Explanation will be made of preferred embodiments of the present invention with reference to the accompanying drawings in which:  
         [0015]      FIG. 1  is a plan view partially illustrating a flexible printed board in an embodiment of the present invention;  
         [0016]      FIG. 2  is a sectional view partially illustrating a mounting part for a laser driver IC in the embodiment of the present invention;  
         [0017]      FIG. 3  is a plan view partially illustrating the flexible printed board in an embodiment of the present invention;  
         [0018]      FIG. 4  is a sectional view partially illustrating a part of a mounting part for a laser driver IC in an embodiment of the present invention;  
         [0019]      FIG. 5  is a sectional view partially illustrating a mounting part for a laser driver IC in an embodiment of the present invention;  
         [0020]      FIG. 6  is a sectional view partially illustrating a mounting part for a laser driver IC in an embodiment of the present invention;  
         [0021]      FIG. 7  is an exploded perspective view illustrating a mounting part of a laser driver in an embodiment of the present invention;  
         [0022]      FIG. 8  is a perspective view illustrating an optical pick in an embodiment of the present invention;  
         [0023]      FIG. 9  is an exploded perspective view illustrating an optical disc unit in an embodiment of the present invention; and  
         [0024]      FIG. 10  is a sectional view partially illustrating a mounting part of a conventional laser driver IC. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]     Preferred embodiments of the present invention will be made of the present invention with reference to the accompanying drawings.  
       Embodiment 1  
       [0026]     Referring to  FIG. 9  which is an exploded perspective view illustrating a disc unit in which an optical pick-up according to the present invention is applied, the disc unit  10  is mainly composed of a bottom casing  10 , a disc tray  4  for loading and unloading a disc serving as a data recording medium into and from the disc unit  10 , and a circuit board  9  mounted thereon with semiconductor components for driving and controlling electronic components mounted in the disc unit, and processing signals. The bottom casing  10  is provided thereto with a top casing  2  and a front panel  3  at the upper surface and the front surface thereof, respectively, so as to cover the upper surface and the front surface of the bottom casing  10 .  
         [0027]     The above-mentioned disc tray  4  is attached thereto with a module type mechanical portion (which will be referred to as “unit mechanism”)  6 , and is covered over its lower surface with an under cover  8 . The unit mechanism  6  is incorporated therein with a spindle motor  5  for rotating the disc, an optical pick-up  7  for recording and reproducing data onto and from the disc, and an optical pick-up feed mechanism for displacing the optical pick up  7 , radially of the disc, along a guide shaft (which is not shown).  
         [0028]     Referring to  FIG. 8  which is a perspective view illustrating the optical pick-up  7 , the optical pick-up  7  is mainly composed of three components, that is, an objective lens drive device  74 , an optical system and a flexible printed board  75 . The objective lens drive device  74  is a mechanism for driving an objective lens in an focusing direction and a tracking direction in order to precisely record and reproduce data to and from the disc so as to follow the rotation of the disc. The optical system is composed of a semiconductor laser  71  for emitting a laser beam, a laser driver IC  72  for driving and contracting the semiconductor laser  7 , a lens and a mirror (which are not shown) for diverging a laser beam from the semiconductor laser and focusing the same onto the disc, a photo detector  73  for receiving a reflection beam from the disc and the like. The flexible printed board  75  electrically connects the objective lens drive device  74  and the optical system to the circuit board  9  through the intermediary of a plurality of wiring patterns. This flexible printed bard  75  is coated over its surfaces with a polyimide film for ensuring insulation therefor, and is laid along the outer surface of a pick-up housing  70 , and is fixed by a cover set thereon.  
         [0029]     It is noted that the upward and downward directions of the pick-up are defined by the arrows shown in  FIG. 8 . That is, the upward direction is toward the side where a first upper cover  76   a  and a second upper cover  76   b  are attached to the pick-up housing  70  while the downward direction is toward the side where a lower cover  76   c  is attached.  
         [0030]     Referring to  FIG. 1  which is a plan view partially illustrating the flexible printed board  75  in the optical pick-up  7 , and  FIG. 2  is a sectional view partially illustrating a mounting part of a laser driver IC  72 . The laser driver IC  72  is mounted on the flexible printed circuit board  75  on the side which is front of the sheet of  FIG. 1 , with the use of soldering  79 . The laser driver IC  72  is attached thereto with a heat spreader  72   a  for dissipating heat generated from an internal chip. In this embodiment, the heat spreader  72   a  is electrically and thermally connected to the ground wiring pattern  75   a  of the flexible printed board  75  by the soldering  79 . With this configuration, the thermal resistance between the heat spreader  7   a  and the ground wiring pattern  75   a  of the flexible printed board  75  can be reduced, and in addition, it is possible to aim at enhancing the grounding of the laser driver IC  72 , and satisfactorily holding an electric characteristic.  
         [0031]     Further, in this embodiment, a metallic pattern  75   c  is interposed between a connecter terminal part  75   d  of the flexible printed board  75  and the mounting part of the laser driver IC  72 , having an area larger than the external shape of the laser drive IC  72  and having an exposed outer surface. This metallic pattern  75   c  is made of the same material as that of other wiring patterns  75   e , such as copper. Further, a plurality of wiring patterns  75   e  is present in the mounting part for the laser driver IC  72  on the printed board  75 , and accordingly, it is difficult to surely hold the metallic pattern in this part. Thus, in this embodiment, the metallic pattern  75   c  is located at a position where the external shape of the laser driver IC  72  and that of the metallic pattern  75   c  are superposed with each other as shown in  FIG. 2  when the mounting part for the laser driver IC  72  is folded in an angled shape along a crease line shown in  FIG. 1 . It is noted here that the wiring patterns  75   e  are coated over their outer surfaces with a polyimide film, other than the ground wiring pattern  75   c , on the surface of the flexible printed board  75  (which is rear of the mounting surface for the laser driver IC  72 ) which makes contact with the metallic pattern  75   c , and accordingly, the metallic pattern  75   c  and the wiring pattern  75   e  are prevented from being conducted with each other. Further, since the metallic pattern  75   c  is bent in a direction opposite to the mounting surface for the laser driver IC  72 , the metallic pattern  75   c  and any of terminals of the laser driver IC  72  are prevented from being conducted from each other. With this configuration, the metallic pattern  75   c  can ensure a wider area, and accordingly, even though the first upper cover  76   a  is made of stainless steel or the like having a heat conductivity which is less than that of aluminum and copper, heat generated from the laser drive IC  72  can be dissipated over a wide area through the metallic pattern  75   c . Thereareter, the heat generated from the laser driver IC  72  is transmitted through the first upper cover  76   a  and is radiated from the outer surface of the first upper cover  76   a  into the atmosphere therearound. Thus, since the wide heat radiation area can be ensured, the temperature of the laser driver IC  72  can be restrained to a low value in comparison with a proof temperature of the laser driver IC  72 .  
         [0032]     Thus, in this embodiment, there can be exhibited such an advantage that the temperature of the laser driver IC  72  can be restrained from rising without increasing the number of required components. Further, the metallic pattern  75   c  is not electrically connected to the other wiring patterns. Thus, no fine wiring pattern which can hardly be manufacture is required, and accordingly, the productivity of the flexible printed board  75  can be enhanced, thereby it is possible to reduce the manufacturing costs thereof.  
         [0033]     Further, it is desirable to interpose a silicon resin layer  78  between the ground wiring pattern  72   a  and the metallic pattern  75   c  and between the metallic pattern  75   c  and the first upper cover  76   a  in order to enhance the adherence therebetween. With this configuration, the thermal resistance between the ground wiring pattern  72   a  and the metallic pattern  75   c  and the thermal resistance between the metallic pattern  75   b  and the first upper cover  76   a  can be decreased to a value which is smaller than that given by an air layer intervening therebetween, thereby it is possible to restrain the temperature of the laser driver IC  72  to a small value in comparison with the proof temperature of the laser driver IC  72 .  
         [0034]     Further, it is desirable to make holes through the ground wiring pattern  75   a  and the metallic pattern  75   c  as shown in  FIG. 3 , and then to fill the holes with the silicon resin  78 . With this configuration, the silicon resin  78  can be filled after the flexible printed board  75  is bent, thereby it is possible to enhance the working efficiency. Further, the adherence between the members can be enhanced by the silicon resin  8 , thereby it is possible to set the thermal resistance between the ground wiring pattern  72   a  and the metallic pattern  75   c  and the thermal resistance between the metallic pattern  75   b  and the first upper cover  76   a  to be lower than that given by an air layer therebetween. Thus, it is possible to restrain the temperature of the laser driver IC  72  to a small value I comparison with the proof temperature of the laser driver IC  72 .  
       Embodiment 2  
       [0035]     Next, explanation will be made of another embodiment of the present invention with reference to  FIGS. 4 and 5  in the case of the application to an optical pick-up  7 .  FIG. 4  is a plan view partially illustrating a flexible printed board  75  for the optical pick-up  7  in this embodiment of the present invention, and  FIG. 5  is a sectional view partially illustrating a mounting part for the laser driver IC  72 . The laser driver IC  72  is mounted on the flexible printed board  75  by soldering  79  on the side which is rear of the sheet surface of  FIG. 4 . The laser driver IC  72  is attached thereto with a heat spreader  72  in order to dissipate a heat generated from an internal chip. In this embodiment, the heat spreader  72   a  and the ground wiring pattern  75   a  of the flexible printed board  75  are electrically and thermally connected with each other through the intermediary of soldering  79 . With this configuration, the thermal resistance between the laser driver IC  72  and the ground wiring pattern  75   a  of the flexible printed board  75  can be reduced, and in addition, the grounding of the laser driver IC  72  can be enhanced, thereby it is possible to satisfactorily maintain the electric characteristic.  
         [0036]     Further, in this embodiment, of the patterns on the flexible printed board  75 , the ground wiring pattern  75   a  of the laser driver IC  72  is extended in a direction opposite to the terminal part  75   d  of the flexible printed board  75 , and the metallic pattern  75   b  is provided at the distal end thereof. Since the metallic pattern  75   b  is provided outside of the body of the flexible printed board  75 , the metallic pattern  75   b  can have an enlarged area, irrespective of the other wiring patterns  75   e . Further, this metallic pattern  75   b  is made of the same material as that of the other metallic patterns  75   e , such as copper. Further, the metallic pattern  75   b  is bent in a V-like shape along a crease line shown in  FIG. 4  so as to superpose the metallic pattern  75   b  and the ground wiring pattern  75   a  with one another. In this configuration, the surfaces of the wiring patterns  75   e  other than the ground wiring pattern  75   a  are coated thereover with a polyimide film at the surface of the flexible printed board  75  (the surface which is in rear of the mounting surface for the laser driver IC  72 ) making contact with the metallic pattern  75   b , thereby the metallic pattern  75   b  and the wiring patterns  75   e  are prevented from being conducted with each other. Further, since the metallic pattern is bent, opposite to the mounting surface for the laser driver IC  72 , the metallic pattern  75   b  and any of terminals of the laser driven IC  72  can be prevented from being conducted with each other. With this configuration, even though the first upper cover  76   a  is made of stainless steel or the like having a less thermal conductivity in comparison with that of aluminum, copper or the like, a heat generated from the laser driver IC  72  is dissipated over a wide area, in-planewise. Thereafter, the heat is transmitted through the first upper cover  76   a  and is then radiated from the outer surface of the first upper cover  76   a  into the atmosphere therearound. Thus, a larger heat radiation area can be ensured, thereby it is possible to restrain the temperature of the laser driver IC  72  to a lower value in comparison with the proof temperature of the laser driver IC  72 . Thus, in this embodiment, there can be provided such an advantage that the temperature of the laser driver IC  7  is restrained from rising without increasing the number of required components.  
         [0037]     Further, in this embodiment, the metallic pattern  75   b  is continuous with the ground wiring pattern  75   a  for the laser driver IC  72 . With this configuration, a heat generated from the laser driver IC  72  is transmitted to the heat spreader  72   a  and the ground wiring pattern  75   a  of the flexible printed board  75  through the soldering  79 , and then is transmitted in an upward direction (the thicknesswise direction of the ground wiring pattern  75   a ) from a the ground wiring pattern  75   a  to the metallic pattern  75   b , and is also transmitted to the metallic pattern  75   b  through the inside of the ground wiring pattern  75   a  (in-planewise of the ground wiring pattern  75   a ). Thus, the number of heat radiation paths from the ground wiring pattern  75   a  to the metallic pattern  75   b  can be increased, thereby it is possible to restrain the temperature of the laser driver IC  72  to a lower value in comparison with the proof-temperature of the laser driver IC  72 . Thus, since the number of required components is prevented from being increased, and since the metallic pattern  75  is prevented from being deviated, it is possible to prevent the working efficiency from being lowered.  
         [0038]     It is desirable to interpose silicone resin  78  between the ground wiring pattern  75   a  and the metallic pattern  75   b  and between the metallic pattern  75   b  and the first upper cover  76   a  in order to enhance the adherence between therebetween. With this configuration, the thermal resistance between the ground wiring pattern  72   a  and the metallic pattern  75   b  and the thermal resistance between the metallic pattern  75   b  and the first upper cover  76   a  can be set to be lower than that given by an air layer therebetween, it is possible to restrain the temperature of the laser driver IC  72  to a low value in comparison with the proof temperature of the laser driver IC  72 .  
         [0039]     Further, in this embodiment, although the metallic pattern  75   b  is continuous with the ground wiring pattern  75   a  of the laser driver IC  72 , the bent part (the part A in  FIG. 3 ) of the metallic pattern  75   b  may be cut after the first upper cover  76   a  is fixed to the pick-up housing  70 .  
       Embodiment 3  
       [0040]     Next, explanation will be made of a further another embodiment of the present invention with reference to  FIGS. 6 and 7  in which  FIG. 6  is a sectional view partially illustrating a mounting part for a laser driver IC in an optical pick-up in this embodiment of the present invention, and  FIG. 7  is a perspective view illustrating the mounting part for the laser driver IC.  
         [0041]     In this embodiment, a metal member  77  is laid on the flexible printed board  75  on the upper side of the mounting part for the laser driver IC  72 , having an area which is larger the external shape of the laser driver IC  72 . This metal member  77  is made of a material such as aluminum or copper having a thermal conductivity not les than 100 W/m/K. It is noted here that the outer surfaces of the wiring patterns  75   e  other than the ground wiring pattern  75   a  are coated thereover with a polyimide film at the surface of the flexible printed board  77  (a surface which is rear of the mounting surface for the laser driver IC  72 ) making contact with the metal member  77 , and accordingly, it is possible to prevent the metal member  77  and the wiring patterns  75   e  from being conduced to each other. Further, the metal member  77  is positioned on te side remote from the mounting surface for the laser driver IC as shown in  FIG. 6 , and accordingly, it is possible to prevent the metal member  77  and terminals of the laser driver IC  72  from being conducted with each other. With this configuration, a heat generated from the laser driver IC  72  is transmitted to the metal member  77  through the ground wiring pattern  75   a , and is then dissipated in-planewise of the metal member  77 , Thereafter the heat generated from the laser driver IC  72  is transmitted to the first upper cover  76   a , and is then radiated from the outer surface of the first upper cover  76   a  into the atmosphere therearound. Accordingly, even though the first upper cover  76   a  is made of stainless steel or the like having a thermal conductivity lower than that of aluminum or copper, the heat generated from the laser driver IC  72  can be dissipated in-planewise of the metal member  77  so as to ensure a lager heat radiation area, thereby it is possible to restrain the temperature of the laser driver IC  72  to a low value in comparison with the proof temperature of the laser driver IC  72 .  
         [0042]     Further, it is desirable to interpose a silicon resin layer between the ground wiring pattern  72   a  and the metal member  77  and between the metal member  77  and the first upper cover  76   a  in order to enhance the adherence therebetween. With this configuration, the thermal resistance between the ground wiring pattern  72   a  and the metal member  77  and the thermal resistance between the metal member  77  and the first upper cover  76   a  can be restrained to a small value in comparison with that given by an air layer therebetween. Thus, it is possible to restrain the temperature of the laser driver IC in comparison with the proof-temperature of the laser driver IC  72 .  
       Embodiment 4  
       [0043]     In a further another embodiment of the present invention, with the use of a metal member  77  having one adhesive surface and having an area which is larger than the external shape of the laser driver IC  72 , the metal member  77  may be bonded to the lower surface of the first upper cover  76   a . This metal member  77  is made of a material such as aluminum or copper having a heat conductivity of not less than 100 W/m/K. Further, the first upper cover  78   a  is fixed to the pick-up housing  70  so as to cause the metal member  77  to make close contact with the flexible printed board  75  and the ground wiring pattern  72   a  thereof. With this configuration, the metal member  77  can be prevented from being positionally deviated during assembly, thereby it is possible to aim at enhancing the assembling ability. Further, even though the first upper cover  76   a  is made of a material such as stainless steel having a small thermal conductivity in comparison with that of aluminum or copper, a heat generated from the laser driver IC can be dissipated in-planewise of the metal member  77 , thereby it is possible to restrain the temperature of the laser driver IC  72  to a lower value in comparison with the proof temperature of the laser driver IC  72 .  
         [0044]     In this embodiment, although the metal member  77  having an adherence is bonded to the first upper cover  76   a , the metal member  77  having an adherence may be bonded to the ground wiring pattern  75   a  of the flexible printed board  75 . In this case, the first upper cover  76   a  is fixed to the pick-up housing  70  in order to cause the metal member  77  and the lower surface of the first upper cover  76   a  to make close contact with each other, thereby it is possible to exhibit similar technical effects and advantages.  
       INDUSTRIAL APPLICABILITY  
       [0045]     The present invention can enhance the speed of data recording onto a disc, and to enhance the recording density thereon.  
         [0046]     It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.