Patent Publication Number: US-2012025210-A1

Title: Optical module enclosing lead frame and semiconductor optical device mounted on the lead frame with transparaent mold resin

Description:
TECHNICAL FIELD 
     The present invention relates to an optical module applicable to the optical communication system, in particular, the invention relates to an optical module that encloses a read frame and a semiconductor optical device mounted on the read frame with resin transparent for light subject to the semiconductor optical device. 
     BACKGROUND ART 
     An optical module with transparent resin to mold a semiconductor optical device has been well known in the fields. For example, Japanese Patent Applications published as JP-2007-142278A and JP-2001-074985A have disclosed an optical module that encloses a semiconductor optical device with resin transparent for light subject to the semiconductor optical device and provides a lens to concentrate light fowled by an outer shape of the molding resin. Because the transparent resin contains no filler to adjust the thermal expansion thereof, the resin has a large thermal expansion coefficient, although it becomes transparent. Consequently, the resin causes a large thermal stress against components enclosed therein. Especially, bonding wires that electrically connect the lead frame with the semiconductor device are the weakest for the stress among components within the resin; accordingly, the thermal stress caused by a large thermal expansion coefficient of the transparent resin breaks the bonding wire, or degrades the reliability of the wire at a portion where the cross section thereof narrows. 
     The present invention provides an improved arrangement that may reduce the thermal stress caused by the transparent resin with no filler to compensate the thermal expansion co-efficient where the semiconductor devices and electrical components are molded with such a resin. 
     SUMMARY OF INVENTION 
     One aspect of the present invention relates to an optical module in which a semiconductor optical device and a lead frame mounting the semiconductor optical device, where they are electrically connected with a bonding wire, are molded with resin transparent to light subject to the semiconductor optical device. Because the resin is free from filler to compensate the performance thereof, the thermal expansion co-efficient becomes considerably greater than those ordinarily used. Therefore, a stress is induced against the components molded therein by the change of the ambient temperature and/or the thermal process such as soldering the lead frame. The stress concentrates on a portion with physically intolerant components in particular, when the stress concentrates on the bonding wire, it sometimes results in the breakage. 
     The optical module according to the present invention provides a screen to compensate the stress induced in the bonding wire. The screen of the invention is a portion of the lead frame and is apart from a distance comparable to a physical dimension of the semiconductor optical device. The screen may be formed so as not only to extend along one edge of the device but to surround the semiconductor optical device, and/or to cover a space immediately above the semiconductor optical device. 
     The optical module of the present invention may provide the resin with a pillar portion that encloses the semiconductor optical device and so on, and a planar portion that extracts the lead frame. The optical module may further provide a tubular member that covers the pillar portion in adhered thereto. The tubular member may physically restrict the expansion of the pillar portion; the stress induced in the bonding wire may be compensated. 
     Furthermore, the planar portion of the transparent resin may provide a window that exposes the lead frame molded within the resin. Soldering the read frame as a member comes in contact with the lead frame exposed in the window; the heat due to the soldering may be effectively restricted to conduct inside of the resin. Moreover, the characteristic impedance of the lead frame may be substantially unvaried by filling a material with the dielectric constant thereof substantially equal to the transparent resin after the soldering is carried out. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The foregoing and other purposes, aspects and advantages will be better understood from the following detailed description of a preferred embodiment of the invention with reference to the drawings, in which: 
         FIG. 1A  is a perspective view of an optical module according to the first embodiment of the present invention, in which dotted lines denote the shape of the transparent resin; and  FIG. 1B  magnifies a primary portion that mounts a semiconductor optical device on the lead frame; 
         FIG. 2  illustrates the lead frame, which mounts the semiconductor optical device thereon shown in  FIG. 1A , viewed from a side opposite to the primary portion shown in  FIG. 1B ; 
         FIG. 3  shows a first modified example of the optical module shown in  FIG. 1A ; 
         FIG. 4  shows parameters to evaluate an effect of the new arrangement appeared in the first embodiment shown in  FIG. 1A ; 
         FIG. 5  shows parameters to evaluate an effect of the first modified embodiment shown in  FIG. 3 ; 
         FIG. 6  shows a second modified example of the optical module shown in  FIG. 1A  and parameters to evaluate an effect of the modified arrangement thereof; 
         FIGS. 7A to 7C  show results of the effect in the first embodiment shown in  FIG. 1 , where  FIGS. 7A to 7C  show relations of the stress caused in the bonding wire against a distance from the wire, the height, and the width of the screen; 
         FIGS. 8A and 8B  show results of the effect appeared in the first modified embodiment shown in  FIG. 3 , where the stress appeared in the wire are shown against the length of the sub-screen, and the gap between the sub-screens; 
         FIG. 9  shows an effect by the second modified embodiment shown in  FIG. 6 , where the stress caused in the wire is shown against the width of the ceiling of the screen; 
         FIGS. 10A to 10D  show an optical module according to the second embodiment of the present invention, where  FIG. 10A  is an exploded drawing of the optical module and the sleeve member,  FIG. 1013  is a perspective view of the optical subassembly that assembles the optical module with the sleeve member,  FIG. 10C  is a cross section taken along the optical axis of the optical sub-assembly, and  FIG. 10D  is a plan view showing the lead frame in the optical module and devices mounted on the lead frame; 
         FIGS. 11A to 11D  shows the arrangement of the optical module shown in  FIGS. 10A to 10D , where  FIG. 11A  is a perspective view,  FIG. 11B  is a plan view,  FIG. 11C  is a cross section of the pillar portion of the transparent resin, and  FIG. 11D  shows a tube covering the pillar portion of the transparent resin; 
         FIGS. 12A and 12B  show effects of the tube, where  FIG. 12A  shows a stress caused in the bonding wire against the thickness of the tube, while,  FIG. 12B  shows a stress against the width of the tube along the longitudinal direction of the module; 
         FIG. 13  shows a modified arrangement of a lead frame shown in  FIGS. 10A to 10D , where the modified lead frame has a portion bent upward to show a function of a mirror that reflects light coming from the laser diode toward the monitor PD; 
         FIGS. 14A to 14C  show processes to manufacture the optical module of the second embodiment shown in  FIGS. 10A to 10D ; 
         FIG. 15  is a perspective view of a transparent resin modified from the resin shown in  FIG. 1  or  FIGS. 10A to 10D ; 
         FIG. 16  is a plan view of the modified resin shown in  FIG. 15 ; and 
         FIG. 17  shows an assembly including the optical sub assembly shown in  FIG. 15  electrically connected with a flexible printed circuit board. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       FIG. 1A  is a perspective view of an optical module according to the first embodiment of the present invention; while,  FIG. 1B  magnifies a primary portion of the optical module  10  where the LD  13  is mounted on the lead frame  12 . The optical module  10  of the present embodiment comprises the mold resin  11  transparent to the light subject to the semiconductor optical device molded therein, the lead frame  12 , the semiconductor optical device  13 , and the sub-mount  14 . The semiconductor device  13  is mounted on the lead frame  12  through the sub-mount  14 . The semiconductor device  13  may be a laser diode (hereafter denoted as LD), or a photodiode (hereafter denoted as PD). The description presented below primarily concentrates on an optical module that encloses the LD therein, however, the subjects of the present invention may be applicable in a similar manner to an optical module that encloses the PD, or to an optical module that encloses the LD and the PD. 
     The optical module  10  shown in  FIG. 1A  encloses the LD  13  mounted on the sub-mount  14  with the transparent resin  11 . The mold resin  11  includes a planar portion  11   a  and a pillar portion  11   b . The LD  13  is molded in the pillar portion  11   b , while, the planar portion  11   a  extrudes the lead frame  12  in the end opposite to the pillar portion  11   b . A center of the pillar portion  11   b  provides a lens  11   c  formed by the outer shape of the mold resin  11  to concentrate the light emitted from the LD  13 . The mold resin  11  of the present embodiment, each of the planar portion  11   a  and the pillar portion  11   b , has a function transparent to the light subject to the LD  13 . 
     The lead frame  12  is extracted from the end of the planar portion  11   a . The lead frame  12  includes signal leads  12   a  electrically connected with the LD  13  via the bonding wire  15 , the ground lead  12   b  that mounts the LD  13  through the sub-mount  14 , and another lead  12   c  through which a signal generated by a monitor PD, which is not shown in  FIG. 1A , that monitors the magnitude of the light emitted from the LD  13 . The signal leads  12   a  is put between the ground leads  12   b  to reduce the external noise affected to the signal leads  12   a . The signal leads  12   a  are bent  12   d  in a side close to the LD  13  to shorten the length of the bonding wire  15  drawn from the lead  12   a  to the LD  13 . 
     The optical module  10  according to the present embodiment provides a screen  12   e , which is a portion of the lead frame  12  bent upward by about 90° at a portion close to the LD  13  so as to be along the edge of the LD  13 . As explained later, the screen  12   e  very close to the LD  13  may reduce the stress induced in the bonding wire  15  connected to the LD  13 . That is, the screen  12   e  may compensate the stress caused between the mold resin  11  and the lead frame  12  to prevent the bonding wire  15  from breaking. 
     The transparent resin  11  includes no additive, which is often called as filler, to make the resin transparent for the light subject to the LD  13 . Because the filler may reduce the thermal expansion co-efficient of the resin, the transparent resin  11  of the present embodiment has an expansion co-efficient about four (4) times greater than that of the components molded therein, such as metal lead frame  12 , and causes a large thermal stress against such components due to the ambient temperature of the optical module  10  and the heat generated by the LD  13 . When such thermal stress is applied to the bonding wire  15 , which is one of the weakest components within the resin  11 , the wire  15  probably and easily breaks. 
       FIG. 1B  schematically illustrates a shape of the bonding wire  15  that is bonded to the pad on the LD  13  and that on the sub-mount  14 . An ordinary wire bonding extends the bonding wire  15  in a direction perpendicular to the bonding pad. Moreover, when the bond strength between the bonding wire  15  and the bonding pad satisfies an ordinary condition, the stress caused by the discrepancy of the thermal expansion co-efficient concentrates on a neck portion of the bonding wire  15 , that is, a portion immediately close to the bonding pad and a portion where the diameter of the wire drastically varies. The screen  12   e  may reduce the stress concentrated on the neck portion of the bonding wire  15 . 
     The screen  12   e  provides an opening  12   f  in a center thereof to pass the light emitted from the LD  13  therethrough. Although the embodiment shown in  FIG. 1  forms an opening  12   f  with a circular shape, it is unrestricted for the opening  12   f  to be circular. A V-shaped cut or a U-shaped cut formed from the edge of the screen  12   e  toward the center thereof may be applicable. The light emitted from the LD  13  passes the opening  12   f  and is concentrated or collimated by the lens  11   c  formed in the surface of the transparent resin  11  to be provided outside of the module  10 . The lead frame  12  of the present embodiment may be made of cupper alloy or Fe—Ni alloy with a thickness of 0.1 to 0.2 mm. 
     Referring to  FIG. 2 , the lead frame  12  further provides a thinned portion  12   g  in the back side of the screen  12   e , which facilitates the bend of the screen  12   e . Forming a thinned portion  12   g  in the back surface of the lead frame  12  with a chisel first, the lead frame  12  is to be bent upward along the thinned portion  12   g  after the wire bonding between the LD  13  and the lead frame  12  is carried out. As explained later, the present embodiment is preferable for the screen  12   e  as close as possible to reduce the stress induced in the bonding wire  15 , for instance, the screen  12   e  is preferably close to the LD  13  within a distance substantially equal to a size of the LD  13 . Accordingly, it is exceedingly effective to make the thinned portion  12   g  in the back surface of the lead frame  12  in advance to bend it. 
     Next, a process to manufacture the optical module  10  of the present embodiment will be described. The optical module  10  may be completed through processes below: first, the LD  13  and other components are mounted on the lead frame  12  through the sub-mount  14  or directly thereon, where the lead frame  12  has a plurality of inner leads,  12   a  to  12   c , supported by an support lead surrounding the inner leads,  12   a  to  12   c . Because the inner leads,  12   a  to  12   c , are supported by the support lead with tie bars, the inner leads,  12   a  to  12   c , could not be disassembled. Next, the wire bonding connects respective bonding pads of the LD  14 , the PD and the sub-mount  14  with the lead frame  12 . Thermo-compression bonding or the ultrasonic bonding, or using them concurrently may be applicable. Then, thus assembled lead frame  12  with the components thereof is bent upward in the screen  12   e  along the thinned portion  12   g , and is set within a cavity of the molding die. The molding die generally comprises an upper die, a lower die and a lens die, where they form the cavity into which the lead frame  12  is set. The shape of the cavity corresponds to the outer shape of the transparent resin  11 . 
     Then, a molding resin is injected within the cavity. One of the upper and lower dies provides a port to inject the resin, while, the other or the same die provides another port to deflate the air or the inert atmosphere. When the screen  12   e  provided in immediate to the LD  13  is substantially perpendicular to the injection port, the injected resin occasionally is insufficiently filled within the cavity by the existence of the screen  12   e . Accordingly, the screen  12   e  is preferably to be set so as to be in substantially parallel to the injection port. Further, in order to reduce the stress to the bonding wire  15  caused by the flow of the injected resin, the injection port preferably locates in a direction extending the bonding wire  15 , that is, in a direction substantially perpendicular to the primary surface of the lead frame  12 . Injecting resin and solidifying them, the lens die is firstly removed then the upper and lower dies are detached to complete the resin molding. Finally, cutting the tie bars supporting the inner leads,  12   a  to  12   c , the optical module  10  with the transparent resin to enclose the optical and electrical components therein is completed. 
       FIGS. 7A to 7C  evaluate the function of the screen  12   e  according to the embodiment of the invention. Physical parameters used in the evaluation are shown in  FIG. 4  and listed in the table blow; in which the width of the screen  12   e  is denoted as w, the height from the primary surface of the lead frame  12  is shows as h, and the distance from the bonding wire  15  at the pad of the LD  13  is shown as l. The evaluation is done through the stress caused in the bonding wire  15 . 
     
       
         
           
               
             
               
                 TABLE 
               
             
            
               
                   
               
               
                 Physical parameters used in evaluation 
               
            
           
           
               
               
               
               
            
               
                   
                   
                   
                 linear expansion 
               
               
                 element 
                 material 
                 Young&#39;s Modulus 
                 co-efficient 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 LD 
                 InP 
                 82.7 
                 4.50 × 10 −6   
               
               
                 Sub-mount 
                 AlN 
                 320.0 
                 4.70 × 10 −6   
               
               
                 PD 
                 InP 
                 82.7 
                 4.50 × 10 −6   
               
               
                 Lead frame 
                 Cu-alloy 
                 125.0 
                 1.75 × 10 −5   
               
               
                 Au wire 
                 Au 
                 78.0 
                 1.42 × 10 −5   
               
               
                 mold resin 
                 epoxy 
                 3.2 
                 6.50 × 10 −5   
               
               
                 adhesive 
                 epoxy 
                 7.0 
                 3.00 × 10 −5   
               
               
                   
               
            
           
         
       
     
     Referring to  FIGS. 7A to 7C , conditions where the distance  1  from the bonding wire  15  is large enough, the width of the screen  12   e  becomes 0, and the height h thereof becomes 0 are corresponding to the case where no screen  12   e  is formed. The function of the screen  12   e  may be evaluated through how the stress caused in the bonding wire  15  may be reduced compared with the case where no screen  12   e  is provided. 
     Referring to  FIG. 7A , a stress of about 550 MPa is induced in the bonding wire  15  for the case of no screen  12   e . Setting the screen  12   e  in a distance of about 0 5 mm, which is about twice of the dimensions of the LD  13 , the stress may be reduced to 500 MPa, and setting the screen  12   e  closer to the LD  13 , about 0.4 mm from the LD  13 , the stress may be reduced to 450 MPa, which means the 18% reduction from the initial condition. The bonding wire  15  is not always broken even in the case without the screen  12   e . Exposing the module  10  under a condition of 85° C. and 85% of the humidity, the breakage of the bonding wire  15  is found in only a few modules. Therefore, the reduction of the stress from 550 MPa to 500 MPa may result in an extremely increase of the reliability of the module. Closing the screen  12   e  to about 0.2 mm, which is comparable to the size of the LD  13 , the stress may decrease to 400 MPa or less. 
       FIG. 7B  shows the evaluation of the stress against the height of the screen  12   e . In this evaluation, the distance from the bonding wire  15  is set to be 0.4 mm and the width of the screen  12   e  is assumed to be 1 mm. Referring to  FIG. 7B , the stress monotonically decreases as the height h increases. But, the effect thereof reduces when the height exceeds 1 mm and saturates over 1.5 mm. To increase the height h of the screen  12   e  means that the diameter of the pillar portion  11   b  of the molding resin  11  increases. Based on the continuous requests to make the size of the module smaller, the diameter of the pillar portion  11   b  is probably 5 mm in a maximum. Accordingly, the height h of the screen  12   e  is restricted to be 5 mm, a half of the possibly maximum diameter. The evaluation shown in  FIG. 7B  enough satisfies the restriction, that is, the stress induced in the bonding wire  15  may be reduced without expanding the diameter of the pillar portion  11   b  of the molding resin  11 . 
       FIG. 7C  evaluates the effect of the width w of the screen  12   e  to the stress appeared in the bonding wire  15 , where the height h and the distance  1  to the bonding wire  15  are assumed to be 1 mm and 0.4 mm, respectively. Setting the width w of the screen  12   e  at least 0.75 mm, the stress may be decreased by at least 18% compared with the case of no screen  12   e . But, even further increasing the width w of the screen  12   e , the reduction of the stress is restricted. An enough wide screen  12   e  may reduce the stress only by about 20%. Thus, based on the evaluation shown in  FIGS. 7A to 7C , the screen  12   e  as closer to the LD  13  or the bonding wire  15  as possible is most effective to reduce the stress induced in the bonding wire  15 . However, a condition of the zero (0) distance is physically impossible, while, taking the process to bend the screen  12   e  after the wire bonding into account, the screen  12   e  may be practically set apart from the LD  13  by about 0.4 mm, which is comparable to the size of the LD  13 . 
     (First Modification) 
       FIG. 3  shows a modification of the first embodiment. The optical module  10 A shown in  FIG. 3  provides another lead frame  12 A different from the lead frame  12  of the first embodiment shown in  FIG. 1A . That is, the present lead frame  12 A provides sub-screens  12   h  in addition to the screen  12   e  so as to put the LD  13  therebetween, but the screen  12   e  of the present embodiment also provides, as that in the first embodiment, the opening  12   f  to pass the light emitted from the LD  13 . 
       FIGS. 8A and 8B  evaluate the function of the screen  12   e  and the sub-screens  12   h  shown in  FIG. 3 , where parameters appeared in  FIGS. 8A and 8B  correspond to those denoted in  FIG. 5 . The width w of the screen  12   e  is a gap between the sub-screens  12   h , while, the length l of the sub-screen  12   h  corresponds to the outer length thereof. Referring to  FIGS. 8A and 8B , the sub-screen  12   h  shows substantial effect to the reduction of the stress induced in the bonding wire  15 , but, the effectiveness thereof is slighter than that of the screen  12   e . Increasing the length l of the sub-screen  12   h  from 0 to 0.6 mm, where the length l equal to 0 corresponds to a case without any sub-screen  12   h , the stress may be compensated by about 10%, but, it indicates to saturate over 0.5 mm. Similarly, even when the gap w between the sub-screens  12   h  decreases, the stress becomes not less than 400 MPa. In those evaluations, the distance from the screen  12   e  to the bonding wire  15  and the height of the screen  12   e  and that of the sub-screens  12   h  are assumed to be 0.4 mm and 1 mm, respectively: 
     (Second Modification) 
       FIG. 6  shows still another modification of the optical module  10 . The optical module of the present embodiment provides another lead frame  12 B that has an overhang  12   j  to cover the upper space of the LD  13 . The overhang  12   j  is bent at the end of the screen  12   e  rearward by about 90° to cover the upper space of the LD  13 . 
       FIG. 9  evaluates the effect of the overhang  12   j  in a length l thereof against the stress induced in the bonding wire  15 . The length l equal to 0 mm corresponds to a case of the screen  12   e  without any overhang, at which the stress becomes about 450 MPa substantially equal to cases shown in  FIGS. 7A to 7C . Expanding the length l of the overhang  12   j , the stress may be equal to 400 MPa or lower at the length l equal to 1 mm, which means that the existence of the overhang  12   j  may be effective independent of the length thereof to compensate the stress induced in the wire  15 . The evaluation above assumes that the distance from the bonding wire  15 , the height and the width of the screen  12   e  are 0.4 mm, 1 mm and 1 mm, respectively. 
     Second Embodiment 
       FIGS. 10A to 10D  show an optical module according to the second embodiment of the present invention. The optical module  10 C shown comprises a lead frame  12 C, a molding resin  11  and a tubular member  16 , and the optical module  10 C constitutes an optical subassembly  1  assembled with the coupling member  17 . The tubular member  16  may be made of metal including copper alloy and nickel-iron alloy that covers the pillar portion  11   b  of the molding resin  11 . As described later, the tubular member  16  may be assembled with the transparent resin  11  at the molding process, no air or no gap is put between the tubular member  16  and the transparent resin  11 . The optical subassembly  1  may be formed by inserting thus assembled optical module  10 C with the tubular member  16  into a bore of the coupling member  17  and gluing them. The function of the tubular member  16  to reduce the stress to the bonding wire  15  will be described later. 
       FIG. 10D  is a plan view of the lead frame  12 C installed in the optical module  10 C of the present embodiment. The lead frame  12 C provides the ground leads  12   b  having the U-plane shape putting the signal lead  12   a  with in the U-shape. The ground lead  12   b  mounts the LD through the sub-mount  14  in a position corresponding to the bottom of the U-shape. One of the ground lead  12   b  directly mounts the monitor PD  18  without a sub-mount  14 . The signal generated by the monitor PD  18  is lead through the other lead  12   c . The electrical connections of the LD  13 , the sub-mount  14  and the monitor PD  18  with the corresponding lead are performed by the bonding wires  15 . 
       FIG. 13  shows another arrangement to mount the monitor PD  18  on the lead frame  12 D. In the arrangement shown in  FIG. 13 , the ground lead  12   b  with the U-shape, a pair of signal leads, and the signal lead  12   c  for the monitor PD  18  are substantially same with those of the lead frame  12 C. The lead frame LW in  FIG. 13  has a feature that the monitor PD  18  is mounted on the other ground lead  12   b , not the ground lead  12   b  adjacent to the signal lead  12   c , and this ground lead  12   b  mounting the PD  18  provides a tab  12   k  picked upward behind the PD  18 . The light emitted from the back facet of the LD  13  enters the monitor PD  18  by being reflected at the surface of this tab  12   k . Because the light emitted from the LD  13  is dispersive, the arrangement of the monitor PD  18  shown in  FIG. 1  or  FIG. 10 , where no optical members reflecting the light from the LD  18  is placed, may receive the dispersive light from the LD  18 . However, the optical member  12   k  to reflect the light provided behind the LD  13  may strengthen the magnitude of the light which the monitor PD  18  is detectable. 
     Referring back to  FIGS. 10B and 10C , the optical module  10 C with the tubular member  16  is inserted into the bore  17   h  of the coupling member  17 . The coupling member  17  with a co-axial shape provides a first tube  17   d  that forms a first bore  17   f  extending from an end so as to receive a ferrule attached in a tip of the external fiber, while, another tube  17   a  in the other end that forms the bore  17   h  to receive the optical module  40 C. These two bores,  17   f  and  17   h , are connected with the third bore  17   g  whose diameter is smaller than those of two bores,  17   f  and  17   h . Furthermore, between two tubes,  17   a  and  17   d , is fowled with a neck  17   b  and a flange  17   c , which may optically align the optical subassembly  1 . The end  17   e  of the first bore  17   f  is chamfered to facilitate the insertion of the ferrule. 
     The optical module  10 C may be assembled with the coupling member  17  by applying an adhesive on the outer surface of the tubular member  16  and inserting it into the bore  17   h . The optical module  10 C may be optically aligned by adjusting a depth of the insertion into the bore  17 , which performs the alignment along the optical axis, and by slightly shifting the module  10 C within the bore  17   h , which performs the alignment in a plane perpendicular to the optical axis. Because a slight gap is formed between the tubular member  16  and the inner surface of the bore  17   h , the optical module  10 C may be slightly moved within the bore  17   h . Solidifying the adhesive after the optical alignment described above, the optical module  10 C may be assembled with the coupling member  17 . 
     (Third Modification) 
       FIGS. 11A to 11D  illustrate a modified tubular member  16 A. This tubular member  16 A also covers the pillar portion  11   b  of the transparent resin  11 . The tubular member  16 A has a feature compared with the tubular member  16  shown in  FIGS. 10A to 10D  that the tubular member  16 A of the present embodiment provides two openings  16   a  and two slits  16   b , where they are alternately formed with a rotation of about 90°. 
     Two openings  16   a  are prepared to receive the positional pins when the tubular member  16 A is set within the molding cavity. That is, referring to  FIG. 11C , after mounting components on the lead frame  12 C and electrically connecting the components with the lead frame  12 C, the intermediate assembly is set within the molding cavity. In an example, the upper die  20   a  and the lower die  20   b  each provides a pin  20   c . The pin in the lower die  20   b  is inserted into one of the opening  16   a  of the tubular member  16 A, while, the other opening  16   a  receives the pin  20   c  prepared in the upper die  20   a  when the upper and lower dies,  20   a  and  20   b , are joined. Thus, the tubular member  16 A may be aligned with the dies, then, the injection port  20   d  provided in the upper die  20   a  may be aligned with one of the slit  16   b  of the tubular member  16 A, while the other slit  16   b  may be aligned with the deflation port  20   e  automatically, which may facilitate the injection of the molding resin into the cavity and the tubular member  16 A fully covers the pillar portion  11   b  of the molding resin to compensate the stress induced in the bonding wire  15 . 
     The function of the tubular member  16 A with dimensions shown in  FIG. 11D  is evaluated.  FIG. 12A  evaluates the thickness t of the tubular member  16 A against the stress, where a condition t=0 mm corresponds to a case without the tubular member. Referring to  FIG. 12A , even the thickness t of the tubular member  16 A is only 0.1 mm, enough compensation may be anticipated for the bonding wire  15 , but, the effectiveness of the compensation is restricted or saturates even when the thickness t is greater than 2 mm. The thickness t of 2 mm is comparable with that of the lead frame  12 ; accordingly, the tubular member  16 A is quite effective even when the member  16 A is made of material same with that of the lead frame  12 A. 
       FIG. 12B  evaluates the stress to the bonding wire  15  against the width w of the tubular member  16 A. The stress may be compensated by about 70% by the existence of the tubular member  16 A with the width thereof only 3 mm. The tubular member  16  whose width w is only 1 mm may reduce the stress about 35%. As already described, the bonding wire  15  is not always broken even in a case of no tubular member, which corresponds to the width of 0 mm. Reliability of a level, in which the possibility for the wire to be broken substantially increases by iterating the harsh environment conditions, is subject to the present invention. The compensation of a few tens of percentages be accomplished by the tubular member  16 A would bring an extreme increase in the reliability of the optical module  10 C. In the evaluations shown in  FIGS. 12A and 12B , physical constants of the components are used listed in the table above, and the tubular member  16 A has a material made of cupper alloy. 
     Additionally, the compensation of the stress by the tubular member  16 A is far greater than that due to the screen  12   e  formed in the lead frame  12  according to the first embodiment shown in  FIG. 1 . Because the tubular member  16 A covers and tightens the whole outer surface of the transparent resin  11 , which effectively restricts the swell of the resin  11 , in particular, the swelling toward a direction of the extension of the bonding wire  15 . 
     (Fourth Modification) 
       FIGS. 14A to 14C  describe the fourth modified example according to the present invention. The optical module  10 A according to the second embodiment shown form  FIG. 10  to  FIG. 12  provides the tubular member,  16  or  16 A, so as to cover the outer surface of the transparent resin  11 . The optical module  10 B of the present embodiment implements the tubular member  16  within the transparent resin  11 .  FIGS. 14A to 14C , each describes the process to manufacture the optical module  10 B that provides the lead frame  12 D. The lead frame  12 D provides a pair of slits  12   n  in the outsides of the ground leads  12   b . An interval between the slits  12   n  is substantially equal to the diameter of the tubular member  16 . The process is carried out as follows: first inserting the tubular member  16  into the slits  12   n  as shown in  FIG. 14B , then setting the intermediate assembly of the tubular member  16  with the lead frame  12 D on which the components are mounted and wire-bonded on the lower die  20   b . Because the space between the slits  12   n  is substantially equal to the diameter of the tubular member  16 , the tubular member  16  may be assembled with the lead frame  12 D only by inserting it into the slits  12   n.    
     The lower die  20   b  extrudes the pin that passes through the opening  12   m  formed in the lead frame  12 D. This pin in the lower die  20   b  has a function to align the upper die  20   a  with the lower die  20   b , accordingly, setting the upper die  20   a  as receiving the pin in the hole provided therein, the cavity  20   f  for the molding is formed into which the lead frame  12 D with the tubular member  16  is set. Then, injecting the resin from the injection port  20   d  as exhausting the air left in the cavity  20   f  from the deflation port  20   e , the transparent resin is molded. As illustrated in  FIG. 14C , the center of the tubular member  16  is offset from the center of the pillar portion  11   b  of the resin because the center of the pillar portion  11   b  is necessary to be aligned with the optical axis of the LD  13  which is mounted on the lead frame  12 D through the sub-mount  14 . Moreover, the pillar portion  11   b  of the molding resin practically has an outer shape of an expanded circular with linear edges. This is because the upper and lower dies,  20   a  and  20   b , are easily removed from the module  10 A after the molding. 
     The tubular member  16  molded within the resin  11  according to this modified embodiment may also effectively compensate the stress induced in the bonding wire  15 . 
     Third Embodiment 
       FIG. 15  is a perspective view of an optical module  10 C according to the third embodiment of the present invention. The optical module  10 C provides the transparent resin  11 A which also has the planar portion  11   a  and the pillar portion  11   b . But, the transparent rein DA of the present embodiment has features different from those of the foregoing resin  11  that the planar portion  11   a  of the present resin  11 A provides a window  11   d  that exposes the ground lead  12   b  of the lead frame  12 E in the bottom thereof, and the ground lead  12   b  provides another window  12   k.    
     The optical module  10 C may be manufactured by processes similar to those for the first and second embodiments, that is, the LD  13  and so on are molded with the resin  11  after they are mounted on and wire-bonded with the lead frame  12 E. Then, thus molded module  10 C is electrically connected with a host system by soldering, for instance, a flexible printed circuit refer to  FIG. 17 , to a portion  12   o  of the lead frame  12 E. The lead frame  12 E as described in the foregoing shows the thermal conductivity greater than 350 [Wm/K]. Moreover, a temperature for the soldering reaches about 180 to 230° C. depending on types of the solder. Then, heat at the soldering is easily conducted to the other end of the lead frame  12 E where the wire  15  is bonded thereto, and causes a large thermal stress in the bonding wire  15  and the lead frame  12 E. The optical module  10 C according to the present embodiment provides in the planar portion of the molding resin  11 A the window  11   d  to expose the ground lead  12 , and in addition to the window  11   d , another window  12   p  in the ground lead  12   b  so as to traverse the lead  12   b . The window  12   p  in the ground lead  12   b  narrows the cross section of the ground lead  12   h , which increases the thermal resistance of the lead  12   b . Not only the window  12   p  but a notch or a groove may show the function substantially same with the window  12   p . Coming a member  21  in contact with the ground lead  12   b  when the flexible printed circuit board is soldered to the position  12   o  of the lead frame  12 E, the member  21  may effectively dissipate heat conducted from the position  12   o  to the inside of the molding resin  11 A along the lead frame  12 E. The member  21  may be a metal block made of copper alloy. The embodiment shown in  FIGS. 15 and 16  implements the window  11   d  in the planar portion  11   a  and another window  12   p  in the lead frame  12 E; however, only one of the windows,  11   d  or  12   p , may show the function to restrict the heat to be conducted into the mold resin  11 A. 
       FIG. 16  is a plan view of the module  10 C implementing two windows,  11   d  and  12   p . The first window  12   p  formed in the ground lead  12   b  has a longitudinal width w 1  of 0.15 mm; and a rest portion of the ground lead  12   b  has another width (u+v) of about 0.2 mm. To restrict the heat conduction into the inside of the mold resin  11 A, the rest portion of the ground lead is preferably as narrow as possible. However, the width of the ground lead  12   b  should be wide enough to stabilize the ground potential at high frequency regions in a case that the present module  10 C operates in giga-hertz regions. Also, taking the handling of the lead frame  12 E during the manufacturing processes of the module  10 C, the lead frame  12 E is necessary in a thickness thereof at least about 0.2 mm. 
     The module  10 C shown in  FIG. 16  provides two windows,  11   d   1  and  11   d   2 , where the former exposes the ground lead  12   b  while the latter exposes the signal lead  12   a . These two windows,  11   d   1  and  11   d   2 , each have a lateral width of 0.5 mm. When the window  11   d  has a wider lateral width, the heat dissipation through the window  11   d  becomes further effective, but the planar portion  11   a  is necessary to be expanded for such a wider window, which results in an enlarged size of the module. 
     When the operating speed of the optical module  10 C reaches or exceeds 10 GHz, the characteristic impedance of the signal lead  12   a  strongly influences the signal quality transmitting on the signal lead  12   a . The characteristic impedance of the signal lead  12   a  depends on not only the width and the thickness thereof but substances surrounding the signal lead  12   a . Providing the window  11   d  in the resin  11 A, the characteristic impedance of the signal lead  12   a  at a portion fully covered with the resin  11 A and that in the window with no substances are considerably mismatched, which degrades the signal quality transmitting on the signal lead  12   a . Therefore, the present optical module  10 C fills the window  11   d  with a material whose dielectric constant substantially equal to the transparent resin  11 A after the soldering of the circuit board to the lead frame  12 E as the member  21  comes in contact with the signal lead  12   a  and the ground lead  12   b  to facilitate the heat dissipation from the lead frame  12 E. Thus, the impedance mismatching between the portion where the window  11   d  is formed and the rest portion may be considerably compensated.  FIG. 17  illustrates the optical module  10 C according to the present embodiment with the flexible printed circuit board  22  connected to the lead frame  12 E.