Abstract:
A laser apparatus comprises: a lead frame comprising a first outer lead and a first inner lead connected to the first outer lead; mold resin that has a top surface, does not seal the first outer lead but does seal the first inner lead and cleaves part of the first inner lead exposed on the top surface; a sub-mount comprising a mounting surface and a back surface facing each other, the mounting surface facing the top surface of the mold resin and the back surface being not covered with the mold resin; and a laser element mounted on the mounting surface of the sub-mount and electrically connected to the exposed part of the first inner lead.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a low-cost laser apparatus with high heat dissipation efficiency and a manufacturing method thereof. 
     2. Background Art 
     There is proposed such a laser apparatus that a recessed part is formed in mold resin in which a lead frame is sealed and a laser element and a sub-mount are mounted in this recessed part (e.g., see Japanese Patent No. 3973348). In a conventional laser apparatus, a laser element and a sub-mount are mounted in a die pad section of the lead frame and electrically connected to an inner lead by wire bonding. 
     SUMMARY OF THE INVENTION 
     For the conventional laser apparatus, it is necessary to use a thick Cu lead frame to dissipate heat of the laser element to the back side via the die pad section. Furthermore, relatively thick Au plating needs to be applied to the outermost surface of the inner lead to execute wire bonding. The costs of the Cu lead frame and Au plating are increasing with soaring prices of Au and Cu in recent years. 
     The present invention has been implemented to solve the above-described problems and it is an object of the present invention to provide a low-cost laser apparatus with high heat dissipation efficiency and a manufacturing method thereof. 
     According to one aspect of the present invention, a laser apparatus comprises: a lead frame comprising a first outer lead and a first inner lead connected to the first outer lead; mold resin that has a top surface, does not seal the first outer lead but does seal the first inner lead and makes part of the first inner lead exposed on the top surface; a sub-mount comprising a mounting surface and a back surface facing each other, the mounting surface facing the top surface of the mold resin and the back surface being not covered with the mold resin; and a laser element mounted on the mounting surface of the sub-mount and connected to the exposed part of the first inner lead. 
     The present invention can realize a low-cost laser apparatus with high heat dissipation efficiency and a manufacturing method thereof. 
     Other and further objects, features and advantages of the invention will appear more fully from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a laser apparatus according to Embodiment 1. 
         FIG. 2  is an enlarged view of the section enclosed by dotted line in  FIG. 1 . 
         FIG. 3  is a cross-sectional view along A-A′ of  FIGS. 1 and 2 . 
         FIG. 4  is a cross-sectional view along B-B′ of  FIGS. 1 and 2 . 
         FIG. 5  is a cross-sectional view along C-C′ of  FIGS. 1 and 2 . 
         FIG. 6  is a perspective view showing the lead frame according to Embodiment 1. 
         FIG. 7  is a perspective view showing a sub-mount according to Embodiment 1. 
         FIGS. 8 to 10  are cross-sectional views showing a laser apparatus according to Embodiment 2. 
         FIGS. 11 to 13  are cross-sectional views showing a laser apparatus according to Embodiment 3. 
         FIGS. 14 to 16  are cross-sectional views showing a laser apparatus according to Embodiment 4. 
         FIGS. 17 to 19  are cross-sectional views to illustrate a method of manufacturing a laser apparatus according to Embodiment 5. 
         FIG. 20  is a perspective view showing a laser apparatus according to Embodiment 6. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
       FIG. 1  is a perspective view showing a laser apparatus according to Embodiment 1 and  FIG. 2  is an enlarged view of the section enclosed by dotted line in  FIG. 1 .  FIG. 3  is a cross-sectional view along A-A′ of  FIGS. 1 and 2  and  FIG. 4  is a cross-sectional view along B-B′ of  FIGS. 1 and 2  and  FIG. 5  is a cross-sectional view along C-C′ of  FIGS. 1 and 2 . 
       FIG. 6  is a perspective view showing the lead frame according to Embodiment 1. The lead frame  10  has an outer lead  12  (first outer lead), an inner lead  14  (first inner lead) connected to the outer lead  12 , outer leads  16  (second outer leads), inner leads  18  (second inner leads) connected to the outer leads  16 , frames  20  and radiating fins  22  connected to the frames  20 . The lead frame  10  is a low-cost, thin  42  alloy (e.g., 0.15 mm thick) molded through press work or the like. Ag plating is applied to the surface of the lead frame  10 . 
     Mold resin  24  seals the inner leads  14 ,  18  and frame  20 . However, the outer leads  12  and  16  are not sealed. A recessed part  26  is formed on a top surface  24   a  of the mold resin  24 . Part of the inner leads  14  and  18 , and part of the frames  20  are exposed from the recessed part  26  of this top surface  24   a . Protrusions  28  are formed in the recessed part  26  of the mold resin  24  and a notch  30  is formed at an end of the recessed part  26 . 
       FIG. 7  is a perspective view showing a sub-mount according to Embodiment 1. The sub-mount  32  has a mounting surface  32   a  and a back surface  32   b  facing each other. Wiring patterns  34  and  36  are formed on the mounting surface  32   a  of the sub-mount  32 . A laser element  38  is mounted on the mounting surface  32   a  of the sub-mount  32  and connected to the wiring pattern  34  with AuSn solder (melting point 280° C.) or the like. 
     A Cu film  40  (metal film) with excellent heat dissipation and having a thickness of 10 μm or more, for example, 200 μm is formed on the exposed back surface  32   b  of the sub-mount  32  through plating or brazing. The outermost surface is plated with Ni/Au. 
     The pre-bonded laser element  38  and sub-mount  32  are mounted face down in the recessed part  26  of the mold resin  24 . That is, the mounting surface  32   a  of the sub-mount  32  faces the top surface  24   a  of the mold resin  24 , and the laser element  38  and the sub-mount  32  are accommodated in the recessed part  26 . However, the back surface  32   b  of the sub-mount  32  is not covered with the mold resin  24 . In this condition, part of the laser element  38  and the exposed part of the inner lead  14  face each other and are bonded together via SnAgCu solder  42  (first conductive material). Part of the wiring pattern  34  and the exposed part of the inner leads  18  face each other and are bonded together via SnAgCu solder  44  (second conductive material). Part of the frames  20  is bonded to the wiring pattern  36  of the mounting surface  32   a  of the sub-mount  32  via SnAgCu solder  46 . 
     The method of manufacturing the above-described laser apparatus will be explained. First, the lead frame  10  as shown in  FIG. 6  is formed. Steps corresponding in thickness to the laser element  38  and sub-mount  32  are formed in this lead frame  10  through bending. Next, the inner leads  14 ,  18  and frames  20  are sealed with the mold resin  24 . However, the outer leads  12  and  16  are not sealed. Furthermore, the recessed part  26  is formed on the top surface  24   a  of the mold resin  24  and part of the inner leads  14  and  18 , and part of the frames  20  are exposed in the recessed part  26  of this top surface  24   a.    
     Next, as shown in  FIG. 7 , the wiring patterns  34  and  36  are formed on the mounting surface  32   a  of the sub-mount  32 . The laser element  38  is then mounted on the mounting surface  32   a  of the sub-mount  32  and connected to the wiring pattern  34 . 
     Next, the SnAgCu solder  42  is supplied to part of the laser element  38 , the SnAgCu solder  44  to part of the wiring pattern  34  and the SnAgCu solder  46  to the wiring pattern  36  of the sub-mount  32  respectively beforehand using vapor deposition or the like. 
     Next, the mounting surface  32   a  of the sub-mount  32  on which the laser element  38  is mounted is placed so as to face the top surface  24   a  of the mold resin  24 . Part of the laser element  38  and the exposed part of the inner lead  14  are placed so as to face each other and bonded together via the SnAgCu solder  42 . Part of the wiring pattern  34  and the exposed part of the inner leads  18  are made to face each other and bonded together via the SnAgCu solder  44 . Part of the wiring pattern  36  and part of the frames  20  are made to face each other and bonded together via the SnAgCu solder  46 . The laser apparatus according to the present embodiment is manufactured in these steps. 
     In the present embodiment, the laser element  38  is mounted on the mounting surface  32   a  of the sub-mount  32  and the back surface  32   b  facing the mounting surface  32   a  is exposed without being covered with the mold resin  24 . Therefore, it is possible to dissipate heat of the laser element  38  without going through the lead frame  10 . This avoids using a costly thick Cu lead frame, and can thereby reduce the manufacturing cost. Furthermore, it is possible to secure a heat dissipation path of small thermal resistance and thereby efficiently dissipate heat generated at the high output laser element  38 , too. Therefore, a low-cost laser apparatus with good heat dissipation can be realized. 
     Furthermore, part of the laser element  38  and the exposed part of the inner lead  14  face each other and are bonded together via the SnAgCu solder  42  such as solder or conductive adhesive. Part of the wiring pattern  34  and the exposed part of the inner leads  18  face each other and are bonded together via the SnAgCu solder  44 . This eliminates the necessity for wire bonding and the necessity for applying costly surface treatment such as Au plating to the inner lead  14  and inner leads  18 . Therefore, it is possible to further reduce the manufacturing cost. 
     Moreover, the radiating fins  22  are connected to the mounting surface  32   a  of the sub-mount  32  on which the laser element  38  is mounted via the frames  20 . This makes it possible to effectively use the mounting surface  32   a  of the sub-mount  32  which has not been conventionally used for heat dissipation and realize high heat dissipation. 
     Furthermore, forming the recessed part  26  in the mold resin  24  makes it easier to position and mount the laser element  38  and the sub-mount  32 . It is also possible to protect the mounted laser element  38  and sub-mount  32 . 
     Furthermore, the protrusions  28  contacting the laser element  38  are formed in the recessed part  26  of the mold resin  24 . Thermally deforming the protrusions  28  during heating for soldering allows the protrusions  28  to constrain the laser element  38 . This can increase the bonding strength and improve the reliability. The protrusions  28  may also be made to constrain the sub-mount  32 . 
     Furthermore, supplying the SnAgCu solder  42  to part of the laser element  38  before bonding the laser element  38  to the inner lead  14  allows the SnAgCu solder  42  to melt and easily bond both parts during mounting and heating. It is thereby possible to secure high productivity. Likewise, supplying the SnAgCu solder  44  to part of the wiring pattern  34  before bonding the wiring pattern  34  to the inner leads  18  can obtain similar effects. A conductive adhesive, conductive adhesive film, Au stud bump or the like may also be used instead of the SnAgCu solder  42  or  44 . 
     Furthermore, forming the Cu film  40  only on the back surface  32   b  of the exposed sub-mount  32  can secure high heat dissipation while suppressing the amount of Cu used to a minimum. 
     Embodiment 2 
       FIGS. 8 to 10  are cross-sectional views showing a laser apparatus according to Embodiment 2. These  FIGS. 8 to 10  are cross-sectional views corresponding to  FIGS. 3 to 5  of Embodiment 1. 
     A Cu plate  48  (metal plate) made of a member different from the lead frame  10  is bonded to the exposed back surface  32   b  of the sub-mount  32  instead of the Cu film  40  of Embodiment 1 through Ag brazing or Ti brazing. The rest of the configuration is the same as that of Embodiment 1. 
     This makes it possible to secure high heat dissipation while suppressing the amount of Cu used to a minimum. Soldering, welding or an adhesive may be used to bond the lead frame  10  of  42  alloy to the Cu plate  48 . 
     Embodiment 3 
       FIGS. 11 to 13  are cross-sectional views showing a laser apparatus according to Embodiment 3. These  FIGS. 11 to 13  are cross-sectional views corresponding to  FIGS. 3 to 5  of Embodiment 1 respectively. The Cu plate  48  (metal plate) is connected to the sides of the radiating fins  22 . The rest of configuration is the same as that of Embodiment 2. This makes it possible to secure higher heat dissipation. 
     Embodiment 4 
       FIGS. 14 to 16  are cross-sectional views showing a laser apparatus according to Embodiment 4. These  FIGS. 14 to 16  are cross-sectional views corresponding to  FIGS. 3 to 5  of Embodiment 1 respectively. The Cu plate  48  is connected to the top surface of the radiating fin  22 . The rest of the configuration is the same as that of Embodiment 3 and can obtain effects similar to those of Embodiment 3. 
     Embodiment 5 
       FIGS. 17 to 19  are cross-sectional views to illustrate a method of manufacturing a laser apparatus according to Embodiment 5. These  FIGS. 17 to 19  are cross-sectional views corresponding to  FIGS. 3 to 5  of Embodiment 1 respectively. 
     An opening  50  (first opening) that extends from an undersurface  24   b  facing the top surface  24   a  to the inner lead  14 , openings  52  (second opening) that extend from the undersurface  24   b  to the inner leads  18  and openings  54  that extend from the undersurface  24   b  to the frames  20  are formed in the mold resin  24 . When the laser element  38  and the inner lead  14  are bonded together, the inner lead  14  is deformed by a metal needle  56  that penetrates the opening  50  and pressed against the laser element  38 . Likewise, when the wiring pattern  34  and the inner leads  18  are bonded together, the inner leads  18  are deformed by a metal needle  56  that penetrates the opening  52  and pressed against the wiring pattern  34 . When the wiring pattern  36  and the frames  20  are bonded together, the frames  20  are deformed by a metal needle  56  that penetrates the opening  54  and pressed against the wiring pattern  36 . 
     This makes it possible to absorb dimensional errors during manufacturing and satisfactorily connect the laser element  38  and the inner lead  14 , the wiring pattern  34  and the inner leads  18 , and the wiring pattern  36  and the frames  20  respectively. Furthermore, applying ultrasound through the metal needle  56  also allows bonding using an Au stud bump or the like. 
     Embodiment 6 
       FIG. 20  is a perspective view showing a laser apparatus according to Embodiment 6. As in the case of the conventional laser apparatus, the laser element  38  and the inner lead  14 , and the wiring pattern  34  on the sub-mount  32  and the inner leads  18  are connected via wires  58  respectively. However, as in the case of Embodiment 1, the Cu plate  48  is disposed only right below the sub-mount  32  requiring heat dissipation and the lead frame  10  made of a low-cost, thin  42  alloy is used for other parts. This makes it possible to realize a low-cost laser apparatus with high heat dissipation. 
     Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. 
     The entire disclosure of a Japanese Patent Application No. 2008-329680, filed on Dec. 25, 2008 including specification, claims, drawings and summary, on which the Convention priority of the present application is based, are incorporated herein by reference in its entirety.