Abstract:
Disclosed is a laser diode having a PCB type lead frame. In the laser diode, a luminous element functions to emit a laser beam. A frame unit has an upper section mounted with the luminous element and functions to radiate heat generated during creation of the laser beam. A housing has an internal space for receiving the frame unit and an exit hole communicating with the internal space for allowing the laser beam to pass through the same. A Printed Circuit Board (PCB) has a plurality of pattern electrodes formed on an upper face of the PCB, the pattern electrodes being electrically connected with the luminous element. The semiconductor laser diode of the invention has a simple structure to facilitate an assembling process, improve productivity, save manufacturing cost and increase radiating surface area thereby improving heat radiation characteristics. The invention can further prevent a finger of a worker from direct contact with a luminous element when a worker handles components in an assembly line so that precision components are not polluted or damaged.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an improved semiconductor laser diode having a PCB type lead frame, more particularly, which has a simple structure to facilitate an assembling process, improve productivity, save manufacturing cost and increase radiating surface area thereby improving heat radiation characteristics.  
         [0003]     2. Description of the Related Art  
         [0004]     In general, semiconductor laser diodes are operated based upon electric and optical characteristics of p-n junction semiconductor devices which create laser oscillation via forward current. The semiconductor laser diodes are used in a pointer, a laser printer, a scanner and data storages such as a CD-P, CD-ROM, CD-RW, DVD-P and DVD-ROM and optical pickups.  
         [0005]     The semiconductor laser diodes are classified into a can type diode, a resin mold type diode and a lead frame type diode. As shown in  FIGS. 1A and 1B , a can type laser diode  10  comprises a submount  11 , a laser chip LC mounted on an upper portion of the submount  11  to emit a laser beam, a disk-shaped stem  12  having a heat-radiating member  13  projected from an upper face of the stem  12  to a predetermined height and mounted with the submount  11 , a photodiode PD mounted on the upper face of the stem  12  and three leads  14  extended downward from the stem  12  for facilitating electric connection of the laser diode  10  with a main board (not shown).  
         [0006]     In the can type laser diode  10 , the leads  14  are connected respectively with the laser chip LC and the photodiode PD via wire members  15 . There is provided a cap member  16  above the stem  12  to protect the laser chip LC and the photodiode PD from the external environment. In an upper central portion of the cap member  16 , there is provided a glass member  17  for allowing a laser beam to pass through the same.  
         [0007]      FIG. 2  is a perspective view of a resin mold type laser diode. As shown in  FIG. 2 , the laser diode  20  comprises a submount  21  mounted with a laser chip LC for emitting a laser beam, a central lead frame  24   a  having a seating section  24   c  which is widened at a top portion of the central lead frame  24   a  to mount the submount  21  and two auxiliary lead frames  24   b  arranged at both sides of the central lead frame  24   a.  In the laser diode  20 , the laser chip LC is electrically connected with the auxiliary lead frames  24   b  via wire members  25 . A packaging material  22  such as transparent epoxy resin is molded around the seating section  24   c  of the central lead frame  24   a  and top portions of the auxiliary lead frame  24   b  into a configuration as shown in  FIGS. 1A and 1B  where the cap member  16  is placed on the stem  12 .  
         [0008]      FIGS. 3A and 3B  illustrate a lead frame type laser diode. As shown in  FIGS. 3A and 3B , a laser diode  30  comprises a photodiode PD, a laser chip LC for emitting a laser beam mounted on an upper portion of the photodiode PD, a central lead frame  34   a  having a seating section  24   c  of a relatively large surface area for mounting the photodiode PD which is bonded to the seating section  24   c  via an adhesive such as epoxy, auxiliary lead frames  34   b  arranged at both sides of the central lead frame  34   a  and a guide holder  32  for securing the central and auxiliary lead frames  34   a  and  34   b  in vertical positions while exposing the photodiode PD from the front.  
         [0009]     The photodiode PD and the laser chip LC are electrically wire-bonded with the auxiliary lead frames  34   b  via wire members  35 . The guide holder  32  is arranged in an internal space  37  of a housing member  36  which is perforated with an exit hole  37   a  for allowing a laser beam to pass through the same.  
         [0010]     Each of the conventional laser diodes  10 ,  20  and  30  generates heat when the laser beam is created from the energized laser chip LC in response to application of external electric power. Heat is transferred to the submount  11  or  21  mounted with the laser chip LC and the integral photodiode PD, and then radiated to the outside via the heat-radiating member  13  provided on the stem  12  or via the central lead frames  24   a  or  34   a.    
         [0011]     According to the prior art, however, the area for radiating heat to the outside is not large enough. In the case of the can type laser diode  10 , heat from the laser chip LC raises the temperature of the stem  12  and the heat-radiating member  13  on which the laser chip LC as a heat source is mounted, thereby thermally distorting the same. In the case of the resin mold and lead frame type laser diodes  20  and  30 , heat from the laser chip LC raises the temperature of the packaging material  22  and the guide holder  32  in direction contact with the central lead frames  24   a  and  34   b,  thereby thermally distorting the same.  
         [0012]     Further, although the can type laser diode  10  can correctly emit the laser beam, it has a large number of components and a complicated assembly structure, thereby raise fabrication cost, prolong manufacturing time excessively and degrade productivity.  
         [0013]     On the other hand, since the resin mold type laser diode  20  has a simpler structure compared with the can and lead frame type diodes  10  and  30 , the manufacturing cost of the resin mold type laser diode  20  is less expensive than those of the can and lead frame type diodes  10  and  30 . However, the resin mold type laser diode  20  has a lower optical density per unit area, and the luminescent center of the luminous element can be changed since the packaging material  22  tends to be thermally distorted.  
         [0014]     Further, the can and lead frame type laser diodes  10  and  30  have a problem that when the stem  12  and the guide holder  32  are assembled to the cap member  16  and the housing member  36 , a finger of a worker tends to directly contact the luminous element such as the laser chip LC that is a precision component thereby polluting the same.  
       SUMMARY OF THE INVENTION  
       [0015]     The present invention has been made to solve the foregoing problems and it is therefore an object of the present invention to provide a semiconductor diode having a Printed Circuit Board (PCB) lead frame which is simplified in structure to save manufacturing cost, improve productivity and increase radiating surface area thereby improving radiation characteristics.  
         [0016]     It is another object of the invention to provide a semiconductor laser diode having a PCB type lead frame which can prevent a finger of a worker from direct contact with a luminous element when a worker handles components in an assembly line.  
         [0017]     According to an aspect of the invention for realizing the object, there is provided a laser diode having a PCB type lead frame. The laser diode of the invention comprises: a luminous element for emitting a laser beam; a frame unit having an upper section mounted with the luminous element and functioning to radiate heat generated during creation of the laser beam; a housing having an internal space for receiving the frame unit and an exit hole communicating with the internal space for allowing the laser beam to pass through the same; and a Printed Circuit Board (PCB) having a plurality of pattern electrodes formed on an upper face of the PCB, the pattern electrodes being electrically connected with the luminous element.  
         [0018]     It is preferred that the luminous element includes a photodiode which is die bonded to an upper section of the frame unit and a laser chip which is die bonded to an upper face of the photodiode.  
         [0019]     It is preferred that the frame unit comprises a metal plate having an excellent heat conductivity.  
         [0020]     It is also preferred that the frame unit has a wing section formed at both sides thereof, and is mounted within the internal space of the housing.  
         [0021]     It is preferred that the housing has holding grooves formed axially in inner peripheral portions of the internal space of the housing, and wherein the wing section includes wings which are extended laterally from both lateral peripheral portions of the frame unit to be inserted into the holding grooves and fixed therein.  
         [0022]     Also it is preferred that each of the holding grooves has a fitting groove extended radially in a top portion thereof.  
         [0023]     It is preferred that the wing section includes arc-shaped wings which are elastically contacted with inner peripheral portions of the internal space of the housing.  
         [0024]     It is preferred that the arc-shaped wings are projected forward or backward perpendicular to a front or rear face of the frame unit.  
         [0025]     It is also preferred that the frame unit has arc-shaped protective wings formed at both lateral peripheral portions of the frame unit to surround and protect the luminous element.  
         [0026]     It is preferred that each of the protective wings has an end which is formed higher than the uppermost portion of the luminous element.  
         [0027]     It is preferred that the pattern electrodes of the PCB are connected with the luminous element via wire members.  
         [0028]     It is also preferred that the pattern electrodes of the luminous element are extended to an upper peripheral portion of the PCB in close proximity of the luminous element to form upper terminals in contact with lower ends of the wire members.  
         [0029]     Also it is preferred that the PCB comprises a single sided PCB having a front face on which the pattern electrodes are formed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]     The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0031]      FIG. 1A  is a perspective view of a general can type semiconductor laser diode;  
         [0032]      FIG. 1B  is an exploded view of  FIG. 1A ;  
         [0033]      FIG. 2  is a perspective view of a general resin mold type semiconductor laser diode;  
         [0034]      FIG. 3A  is a perspective view of a general lead frame type semiconductor laser diode;  
         [0035]      FIG. 3B  is a partial magnification of  FIG. 3A ;  
         [0036]      FIG. 4  is an exploded perspective view of a semiconductor laser diode having a PCB type lead frame according to a first embodiment of the invention;  
         [0037]      FIG. 5  is a perspective view of an assembly including a luminous element, a frame unit and a PCB in the semiconductor laser diode having a PCB type lead frame according to the first embodiment of the invention;  
         [0038]      FIG. 6A  is a magnified perspective view of the semiconductor laser diode having a PCB type lead frame according to the first embodiment of the invention;  
         [0039]      FIG. 6B  is a plan view of  FIG. 6A ;  
         [0040]      FIG. 7  is a longitudinal sectional view of the semiconductor laser diode having a PCB type lead frame according to the first embodiment of the invention;  
         [0041]      FIG. 8  is an exploded perspective view of a semiconductor laser diode having a PCB type lead frame according to a second embodiment of the invention;  
         [0042]      FIG. 9A  is a magnified perspective view of the semiconductor laser diode having a PCB type lead frame according to the second embodiment of the invention;  
         [0043]      FIG. 9B  is a plan view of  FIG. 9A ;  
         [0044]      FIG. 10  is a perspective view of an assembly including a luminous element, a frame unit and a PCB in the semiconductor laser diode having a PCB type lead frame according to the second embodiment of the invention;  
         [0045]      FIGS. 11A and 11B  illustrate a process of assembling the frame unit to the housing in the semiconductor laser diode having a PCB type lead frame according to the first embodiment of the invention;  
         [0046]      FIGS. 12A and 12B  illustrate a process of assembling the frame unit to the housing in the semiconductor laser diode having a PCB type lead frame according to the second embodiment of the invention; and  
         [0047]      FIGS. 13A through 13C  illustrate a process of fabricating a luminous element used in the semiconductor laser diode having a PCB type lead frame of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0048]     The following detailed description will present preferred embodiments of the invention in reference to the accompanying drawings.  
         [0049]      FIG. 4  is an exploded perspective view of a semiconductor laser diode having a PCB type lead frame according to a first embodiment of the invention,  FIG. 5  is a perspective view of an assembly including a luminous element, a frame unit and a PCB in the semiconductor laser diode having a PCB type lead frame according to the first embodiment of the invention,  FIG. 6A  is a magnified perspective view of the semiconductor laser diode having a PCB type lead frame according to the first embodiment of the invention,  FIG. 6B  is a plan view of  FIG. 6A , and  FIG. 7  is a longitudinal sectional view of the semiconductor laser diode having a PCB type lead frame according to the first embodiment of the invention.  
         [0050]     As shown in  FIGS. 4 through 7 , a laser diode  100  according to the first embodiment of the invention comprises a luminous element  110 , a frame unit  120 , a housing  130  and a Printed Circuit Board (PCB)  140 , and can be simply assembled by inserting the frame unit  120  having the luminous element  110  into the housing  130 .  
         [0051]     That is, the luminous element  110  for creating and outwardly emitting a laser beam in response to application of electric power is provided in the form of an integral die chip so that a laser chip  111  and a photodiode  112  can be die bonded to a front face of the frame unit  120 .  
         [0052]     The laser chip  111  is made of GaAlAs based material containing an active layer and a cladding layer surrounding the active layer, AlGaIP and AlGaInPAs based material used in a red semiconductor laser device of a high density optical disk, GaN based material used in electronics and so on. A rear electrode is bonded onto a surface electrode of the photodiode  112  via a bonding layer  113 .  
         [0053]     For the purpose of epoxy die boding, the bonding layer  113  may be made of Au or Ag. Alternatively, the bonding layer  113  may comprise a bonding adhesive made of Sn.  
         [0054]     Further, the integral photodiode  112  having the laser chip  111  bonded to the upper face thereof has surface and rear electrodes formed in a silicon-based crystal of a P—I—N structure, and the surface electrode is in ohmic contact with a light receiving section having a P diffusion area.  
         [0055]     The laser chip  112  is bonded to the surface electrode of the photodiode  111  via the bonding layer  113 . The rear electrode is bonded to a front portion of an upper section  120   a  of the frame unit  120  above a central lead frame  121  via the bonding layer  114  made of Au—Sn or Sn according to eutectic die bonding technique.  
         [0056]     Further, in addition to the central lead frame  121  bonded with the luminous element  110 , the frame unit  120  comprises auxiliary lead frames  122  arranged at both sides of the central lead frame  121 . The central lead frame  121  mounted with the luminous element  110  is integrally provided with heat-radiating sections  123  for outwardly radiating heat which is generated during creation of a laser beam in the luminous element  110 .  
         [0057]     The housing  130  has an internal space  131  formed in a central body portion communicating with an exit hole  132  for allowing the laser beam from created the luminous element  110  to pass through the same. The frame unit  120  is arranged within the internal space  131  to protect the luminous element  110  mounted on the frame unit  120  from the external environment.  
         [0058]     The frame unit  120  is shaped as a quadrangular plate made of metal such as copper, iron and alloys thereof having excellent heat conductivity, machinability and bending ability. The housing  130  is made of resin through injection molding to form the internal space  131  and the exit hole  132  in the central body portion.  
         [0059]     As a result, high temperature heat from the laser beam which is generated in actuation of the luminous element  110  can be transferred through the entire area of the frame unit  120  to be uniformly radiated, and the frame unit  120  can be machined or worked easily.  
         [0060]     At both sides of the frame unit  120 , there is provided a laterally symmetric wing section  121  for mounting the frame unit  120  within the internal space  131  of the housing  130 .  
         [0061]     The wing section  121  comprises two wing pieces  121   a  which are extended laterally from right and left peripheral portions of the frame unit  120 . On the other hand, the housing  130  has holding grooves  134  formed in inner peripheral portions of the internal space  131  to a predetermined depth in an exit direction X of the laser beam so that the wing pieces  121   a  are inserted into the holding grooves  134  and then fixed thereto.  
         [0062]     As a result, the wing pieces  121   a  are aligned with the holding grooves  134  formed in the internal space  131  of the housing  130  and then the frame unit  120  is inserted into the internal space  131  of the housing  130  in the laser beam exit direction X in order to assemble the frame unit  120  having the right and left wing pieces  121   a  to the housing  130 .  
         [0063]      FIG. 8  is an exploded perspective view of a semiconductor laser diode having a PCB type lead frame according to a second embodiment of the invention,  FIG. 9A  is a magnified perspective view of the semiconductor laser diode having a PCB type lead frame according to the second embodiment of the invention,  FIG. 9B  is a plan view of  FIG. 9A , and  FIG. 10  is a perspective view of an assembly including a luminous element, a frame unit and a PCB in the semiconductor laser diode having a PCB type lead frame according to the second embodiment of the invention.  
         [0064]     The wing section  121  provided at the both sides of the frame unit  120  according to the first embodiment of the invention can be substituted by arc-shaped wing pieces  121   b  according to the second embodiment of the invention which are elastically contacted with inner peripheral portions of an internal space  131  of a housing  130  as shown in  FIGS. 8 through 10 .  
         [0065]     The arc-shaped wing pieces  121   b  form portions of an imaginary circle drawn at an outside diameter which is substantially same as or slightly larger than the inside diameter of the internal space  131  so that the arc-shaped wing section  121  inserted into the internal space  131  of the housing  130  is press fit with the inner peripheral portions of the internal space  131 .  
         [0066]     The arc-shaped wing pieces  121   b  tightly contacted with the inner peripheral portions of the internal space  131  may be projected forward or backward perpendicular to a front or rear face of the frame unit  120  as shown in  FIGS. 12A and 12B .  
         [0067]     As shown in  FIGS. 11A and 11B , in lateral peripheral portions of an upper section  120   a  of the frame unit  120  to which the luminous element  110  is die bonded, there are provided protective wings  123  which are bent in the form of arcs to surround and protect the luminous element  110  as those shown in  FIGS. 4 through 6 B. The surface of the upper section  120   a  to which the luminous element is bonded is formed flat.  
         [0068]     Ends of the protective wings  123  are preferably formed higher than the uppermost portion of the luminous element  110  to the extent that a finger of a worker may not contact the luminous element  110  that is a precision component when the frame unit  120  is assembled to the housing  130  in an assembly line.  
         [0069]     Further, a PCB  140  is bonded to a lower section  120   b  of the frame unit  120  via an adhesive such as epoxy, arranged coplanar with the luminous element  110 . The PCB  140  also has a plurality of pattern electrodes  141  which are printed on a front face thereof and electrically connected with the luminous element  110 .  
         [0070]     The pattern electrodes  141  are wire bonded to be electrically connected with the luminous element  110  via wire members  142  made of metal such as Au and Ag.  
         [0071]     The pattern electrodes  141  are extended up to an upper peripheral portion of the PCB  140  in close proximity of the luminous element  110  to form upper terminals  143  which are connected with lower ends of the wire members  142  so that the wire members  142  are provided at minimum lengths to connect the pattern electrodes  141  with the luminous element  110 .  
         [0072]     The PCB  140  is provided as a single sided PCB with the pattern electrodes  141  formed on the front face of the PCB  140 , and preferably has a width smaller than that of the lower section  120   b  of the frame unit  120 .  
         [0073]     The operation of the invention having the above construction will be described as follows.  
         [0074]     According to a fabrication process of a luminous element  110  for emitting a laser beam, a bonding layer  114  made of Au—Sn or Sn is formed on one side of a substrate  200  in the form of a wafer, and then an upper face of the substrate  200  is partitioned into a matrix.  
         [0075]     Laser chips  111  are mounted on matrix-shaped partitioned sections of the substrate  200  according to die bonding technique, in which each of the laser chips  111  is mounted on each of the partitioned sections via a bonding layer  113  made of Sn. The substrate  200  mounted with the laser chips  111  is cut longitudinally to form a plurality of bars  200   a.    
         [0076]     Each of the bars  200   a  is scribed laterally and then cut along the scribed lines to form a plurality of luminous elements  110  each having a laser chip  111  and a photodiode  112  integrally bonded thereto.  
         [0077]     In subsequence, each of the luminous elements  110  is placed so that the photodiode  112  as a base is seated on an upper section  120   a  of a frame unit  120  according to any of the first and second embodiments of the invention. A heat source having a temperature of about 300° C. is provided to a junction between the luminous element  110  and the frame unit  120  having a plated layer of Au or Ag at a thickness of about 3 μm to weld the plated layer of the frame unit  120  with the bonding layer  114  of the photodiode  112  according to eutectic die bonding technique so that the each luminous element  110  is arranged in the upper section  120   a  of the frame unit  120 .  
         [0078]     Adhesive such as epoxy is coated on a front face of a lower section  120   b  of the frame unit  120  via dotting, and then a rear face of a PCB  140  having a plurality of pattern electrodes  141  formed in a front face thereof is attached to the epoxy-coated front face of the lower section  120   b.    
         [0079]     The luminous element  110  mounted on the upper section  120   a  of the frame unit  120  is electrically connected with the PCB  140  mounted on the lower section  120   b  of the frame unit  120  by connecting one ends of wire members  142  with the luminous element  110  and bonding the other ends of the wire members  142  with upper terminals  143  of the pattern electrodes  141  extended adjacent to upper peripheral portions of the PCB  120  so that electric power for generating a laser beam can be supplied to the luminous element  110  via the pattern electrodes  141  and the wire members  142 .  
         [0080]     The frame unit  120  mounted with the luminous element  110  and the PCB  140  which are wire bonded to each other is assembled to the housing  130  as follows: Where the wing section  121  has the wing pieces  121   a  extended laterally from the both lateral peripheral portions of the frame unit  120  as shown in  FIG. 4  and  FIGS. 11A and 11B , distal ends of the wing pieces  121   a  are aligned with the holding grooves  134  formed in the inner peripheral portions of the internal space  131  of the housing  130 .  
         [0081]     The frame unit  130  is inserted into the internal space  131  in the exit direction X or along the central axial of the internal space  131  with the distal ends of the wing pieces  121   a  moved upward along the holding grooves  134  until the distal ends of the wing pieces  121   a  are stopped by upper ends of the holding grooves  134 . Then, the frame unit  120  is turned to the right or the left within the internal space  131  so that the distal ends of the wing pieces  121  a are inserted into and held by fitting grooves  134   a  which are extended perpendicularly in a radial direction from the upper ends of the holding grooves  134 . As a result, the frame unit  120  is securely held within the housing  130  so that it is not released from the housing  130 .  
         [0082]     Further, where the wing section  121  comprises the arch-shaped wing pieces  121   b  which are projected from the both lateral peripheral portions of the frame unit  120  forward or backward perpendicular to the front or rear face of the frame unit  120 , the upper portion of the frame unit  120  having the arc-shaped wing pieces  121   b  is aligned with a lower end of the internal space  131  of the housing  130  as shown in  FIGS. 12A and 12B .  
         [0083]     In this position, the frame unit  130  is inserted into the internal space  131  in the exit direction X or along the central axial of the internal space  131  so that the arc-shaped wing pieces  121   b  are inserted along the internal space  131  causing outer peripheral portions of the arc-shaped wing pieces  121   b  to be elastically pressed against the inner periphery of the internal space  131 . As a result, the frame unit  120  can be securely held within the internal space  131  of the housing  130  so that it is not released from the housing  130 .  
         [0084]     Both of the arc-shaped wing pieces  121   b  of the wing section  121  can be projected forward with respect to the front face of the frame unit  120  or backward with respect to the rear face of the frame unit  120 . Alternatively, the arc-shaped wing pieces  121   b  of the wing section  121  can be alternatively projected with respect to the frame unit  120 , that is, one of the arc-shaped wing pieces  121   b  is projected forward with respect to the front face of the frame unit  120  and the other one of the arc-shaped wing pieces  121   b  is projected backward with respect to the rear face of the frame unit  120 . In the circumstances, all configurations of the arc-shaped wing pieces  121   b  provide equal areas which are pressed against the inner peripheral portions of the internal space  131  so as to impart the same securing force to the wing section  121  regardless of the configuration of the arc-shaped wing pieces  121   b.    
         [0085]     According to the present invention as set forth above, the frame unit having the luminous element and the PCB in electric connection with the luminous element which are mounted on the front face thereof is received within the internal space of the housing with the exit hole formed therein so as to simplify the structure of the assembly line thereby saving the manufacturing cost of a final product while enhancing the productivity thereof.  
         [0086]     The frame unit having the wide heat-radiating surface area can efficiently radiate high temperature heat which is generated from the luminous element during emission of the laser beam through the exit hole to the outside to enhance heating characteristics of the final product thereby improving the reliability thereof.  
         [0087]     The protective wing pieces are formed at the both lateral sides of the frame unit to surround and protect the wire members and the luminous element as precision components in order to reliably prevent the luminous element and the wire members from contacting with a finger of a worker. This resultantly prevents the components of the frame unit from malfunction or damage owing to pollutants sticking to the same.  
         [0088]     While the present invention has been described in connection with the preferred embodiments of the invention, it is also to be understood that various modifications and variations can be made without departing from the spirit or the scope of the invention, which is not restricted to the above described embodiments but shall be defined by the appended claims and equivalents thereof.