Patent Publication Number: US-7712975-B2

Title: Photoelectric coupling assembly and manufacturing method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a division of and claims priority to U.S. patent application Ser. No. 11/866,596, filed on Oct. 3, 2007, which claims priority to Japanese Patent Application No. 2006-284845, filed on Oct. 19, 2006. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a photoelectric coupling assembly for connecting an electrical circuit and an optical fiber and a method for manufacturing the photoelectric coupling assembly. 
   2. Description of the Background Arts 
   With the development of broadband communication systems, higher speeds and larger capacities are increasingly in demand for networked household electric appliances as well as for routers at network nodes. Consequently, the investigation and implementation of optical interconnections is on the rise. An optical interconnection is a connection arrangement contrived to carry out a photoelectric conversion at a boundary section (interface) between a signal processing section and a signal transmission section such that the broadband capacity of optical fiber technology can be utilized to accomplish high-speed, high-capacity transmissions. Japanese Laid-Open Patent Application Publication No. 2005-43622, for example, discloses a technique in which an electrical circuit and an optical fiber are coupled together at a photoelectric conversion section using a photoelectric coupling assembly that includes a photoelectric conversion element (a light-emitting element or a light-receiving element) and an optical fiber holding member. 
     FIG. 11  is a cross sectional view showing the assembled state of an optical fiber cable connected to a photoelectric coupling assembly in accordance with the disclosure of Japanese Laid-Open Patent Application Publication No. 2005-43622. The photoelectric coupling assembly  100  includes a molded article  104  having holding holes  102  each configured to mechanically hold an optical fiber  101  such that an optical input/output end surface  103  of each optical fiber  101  is exposed at a main surface. An electrical wiring pattern  105  is provided on the main surface and a side surface of the molded article  104  such that the portion of the electrical wiring pattern  105  on the main surface is connected to the portion of the electrical wiring pattern  105  on the side surface. A photo-semiconductor element  107  is provided in front of the optical fiber  101  with an insulating film  106  disposed there-between. The photo-semiconductor element  107  is connected to the electrical wiring pattern  105  with bumps  108 . The same patent publication claims that the degree of freedom with which the photo-electric coupling assembly can be arranged is increased by having the kind of electrical wiring pattern just described. However, it is inherently difficult to form an electrical wiring pattern in a continuous manner on the surface of an object such that the wiring pattern is accurately positioned in three dimensions. 
   SUMMARY OF THE INVENTION 
   The object of the present invention is to provide a photoelectric coupling assembly and a manufacturing method thereof that are contrived such that the electrical wiring pattern can be positioned accurately in three dimensions. 
   In order to achieve the object, the invention provides a photoelectric coupling assembly that comprises: (1) a photoelectric conversion unit equipped with a photoelectric conversion element; and (2) a molded article. The molded article includes a front surface on which the photoelectric conversion unit is mounted and an optical fiber insertion hole configured and arranged to have an optical fiber inserted there-through such that a distal end of the optical fiber faces an active layer of the photoelectric conversion element. A lead is insert molded into the molded article. The lead has a first surface that is exposed at the front surface of the molded article and electrically connected to the photoelectric conversion element, a second surface that is exposed at a side surface of the molded article that continuously adjoins the front surface of the molded article, and an engaging portion having a width that increases in a direction away from the front surface of the molded article. At least a portion of the engaging portion is contained inside the resin that forms the molded article. The “width” of the lead is the dimension of the lead in a direction perpendicular to the lengthwise direction of the lead and the direction away from the front surface of the molded article. 
   Another aspect of the present invention provides a method for manufacturing a photoelectric coupling assembly that comprises: (1) a photoelectric conversion unit equipped with a photoelectric conversion element; and (2) a molded article equipped with an optical fiber insertion hole that is configured and arranged to have an optical fiber inserted there-through such that a distal end of the optical fiber faces an active layer of the photoelectric conversion element, a front surface on which the photoelectric conversion unit is mounted, and a lead that is electrically connected to the photoelectric conversion element and has an engaging portion having a width that increases in a direction away from the front surface of the molded article. In this manufacturing method, (1) a lead frame is insert molded to the front surface of the molded article such that the engaging portion is contained inside the resin forming the molded article and a first surface of the lead is exposed at the front surface of the molded article and (2) the lead frame is cut such that a second surface of the lead is exposed at a side surface of the molded article that contiguously adjoins the front surface of the molded article. 
   In a photoelectric coupling assembly and manufacturing method thereof according to the present invention, it is acceptable to form the engaging portion by using etching to form a lead forming pattern in the lead frame. It is also acceptable for the lead to be configured such that a thickness thereof varies. The thickness variation of the lead can be formed by etching or plating. It is acceptable for a width of the first surface to vary with respect to a direction perpendicular to the width. The “thickness” of the lead is the longitudinal dimension of the lead in a direction perpendicular to the front surface of the molded article. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a molded article of a photoelectric coupling assembly in accordance with an embodiment of the present invention. 
       FIG. 2  is a partial cross sectional view of the photoelectric coupling assembly at the section line II-II in  FIG. 1  and shows the distal end of the photoelectric coupling assembly. 
       FIG. 3  is a top plan view of a lead frame used in a photoelectric coupling assembly in accordance with the present invention. 
       FIGS. 4A and 4B  are cross sectional views showing examples of leads used in a photoelectric coupling assembly in accordance with the present invention. 
       FIGS. 5A and 5B  are cross sectional views showing the insert molded states of the leads shown in  FIGS. 4A and 4B . 
       FIGS. 6A and 6B  are cross sectional views showing examples of leads with plated surfaces used in a photoelectric coupling assembly in accordance with the present invention. 
       FIG. 7  is a longitudinal cross sectional view of a molded article of a photoelectric coupling assembly in accordance an embodiment of the present invention. The cross section lies in a plane that is parallel to an optical fiber insertion hole and includes a lead. 
       FIGS. 8A and 8B  are cross sectional views showing other examples of leads used in a photoelectric coupling assembly in accordance with the present invention. 
       FIGS. 9A and 9B  are frontal views showing other examples of leads used in a photoelectric coupling assembly in accordance with the present invention as seen from the front surface of the molded article. 
       FIG. 10  is a cross sectional view illustrating a photoelectric coupling assembly being insert molded in accordance with an embodiment of a manufacturing method for a photoelectric coupling assembly in accordance with the present invention. 
       FIG. 11  is a cross sectional view showing a conventional photoelectric coupling assembly with optical fibers assembled thereto. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The above-mentioned features and other features, aspects, and advantages of the present invention will be better understood through the following description, appended claims, and accompanying drawings. In the explanation of the drawings, identical reference numerals are applied to identical elements and duplicate explanations are omitted. 
     FIG. 1  is a perspective view of a molded article of a photoelectric coupling assembly in accordance with an embodiment of the present invention. The photoelectric coupling assembly  10  includes a main unit (molded article)  20  whose overall shape is generally cuboids and a photoelectric conversion unit  40  that is mounted to a front surface  21  of the main unit  20 . The main unit  20  has a plurality of optical fiber insertion holes  24 , each of which is configured and arranged to receive an optical fiber  11  there-through with a distal end  11   b  of the optical fiber facing an active layer of a photoelectric conversion element of the photoelectric conversion unit  40 . The main unit  20  also has a front surface  21  on which the photoelectric conversion unit  40  is mounted. An electrical wiring pattern section  23  is provided across the front surface  21  of the main unit  20  and a side surface  22  (e.g., top and bottom surfaces) that is contiguous with the front surface  21 . The electrical wiring pattern section  23  comprises alternately arranged short electrical wires  23   a  and long electrical wires  23   b . The optical fiber insertion holes  24  are arranged between the short electrical wires  23   a.    
     FIG. 2  is a partial cross sectional view of the photoelectric coupling assembly  10  at the section line II-II in  FIG. 1  and shows the distal end of the photoelectric coupling assembly  10 . The photoelectric conversion unit  40  has a photoelectric conversion element  41  and an active layer  42  of the photoelectric conversion unit  40  is positioned so as to face the optical fiber insertion holes  24  of the main unit  20 . The photoelectric conversion unit  40  is provided with electrodes  43  for supplying electricity to the active layer  42  or transmitting a signal from the active layer  42 . When the photoelectric conversion unit  40  is mounted to the front surface  21  of the main unit  20 , the electrodes  43  contact the electrical wiring pattern section  23  of the main unit  20 . 
     FIG. 3  is a top plan view of a lead frame used in a photoelectric coupling assembly in accordance with the present invention. The lead frame  30  has a lead forming pattern  31  to be the electrical wiring pattern section  23 . The lead forming pattern  31  has short leads  31   a  to be the short electrical wires  23   a  and long leads  31   b  to be the long electrical wires  23   b . Spaces  33  where the lead frame  30  has been cut out are disposed between and on the outsides of the leads  31   a  and  31   b . During molding, resin  59  fills the spaces  33  and the lead frame  30  is insert molded into the main unit  20 . Positioning holes  32  for positioning the lead frame  30  are provided at the four corners of the lead forming pattern  31 . 
   The leads  31   a  and  31   b  are fine (very narrow). For example, if the pitch at which the optical fibers  11  are arranged is 250 μm, then the widths of the leads  31   a  and  31   b  will be approximately 50 μm. Consequently, it is difficult to ensure the shear strength of the insert-molded leads. Additionally, the leads  31   a  and  31   b  are cut in accordance with the shape of the molded article  20  after the insert molding process and the cut surfaces of the leads  31   a  and  31   b  are exposed at the side surface  22  so as to form electrode terminals  36 . Since the surface area of the cut surface of each electrode terminal  36  is only the product of the lead thickness and the lead width, there is the possibility that poor electrical connections would result in the completed photoelectric coupling assembly if these cut surfaces alone were used as contacts. 
   Therefore, in a photoelectric coupling assembly in accordance with this embodiment, the leads  31   a  and  31   b  are each configured and arranged to have a first surface that is exposed at the front surface  21  of the molded article  20  and electrically connected to the photoelectric conversion element and a second surface that is exposed at a side surface  22  of the molded article  20 , the side surface  22  being contiguous with the front surface  21 . Additionally, by providing each of the leads  31   a  and  31   b  with a wide section  34  having a width W 1  that is wider than the width W 0  at the front surface  21  of the molded article  20 , an engaging portion is formed that has a width that increases in a direction away from the front surface  21  of the molded article  20 . The leads  31   a  and  31   b  are insert molded into the front surface  21  of the molded article  20  such that at least a portion of the engaging portion of each is contained inside the resin  20   a  forming the molded article  20 . The leads  31   a  and  31   b  are also cut from the lead frame  30  such that an end face of each (which constitutes a portion of each) is exposed at the side surface  22  of the molded article  20 , which is contiguous with the front surface  21 . 
     FIGS. 4A and 4B  are cross sectional views showing examples of leads used in a photoelectric coupling assembly in accordance with the present invention and  FIGS. 5A and 5B  are cross sectional views showing the insert molded states of the leads.  FIGS. 4A and 5A  show a lead  31   a  or  31   b  having a trapezoidal cross sectional shape. The bottom side of the trapezoid has a larger width than the top side and constitutes the wide section  34 . Thus, the entire lead  31   a  or  31   b  forms the engaging portion  37 . The top side of the insert molded lead  31   a  or  31   b  is exposed from the resin  20   a , and a portion of the engaging portion  37  is embedded in the resin  20   a . In this way, the lead  31   a  or  31   b  is reliably insert molded into the front surface  21  of the molded article  20 . 
     FIGS. 4B and 5B  show a lead  31   a  or  31   b  having a hexagonal cross sectional shape. The wide section  34  is provided in the middle such that the portion from the front surface  21  to the middle corms the engaging portion  37 . The top side of the insert molded lead  31   a  or  31   b  is exposed from the resin  20   a , and a portion of the engaging portion  37  is embedded in the resin  20   a . In this way, the lead  31   a  or  31   b  is reliably insert molded into the front surface  21  of the molded article  20 . 
   The engaging portion of the lead  31   a  or  31   b  shown in  FIG. 4A  can be formed easily by, for example, forming a mask film on one side of a thin copper plate and etching the copper plate from one side. The engaging portion of the lead  31   a  or  31   b  shown in  FIG. 4B  can be formed easily by, for example, forming a mask film on both sides of a thin copper plate and etching the copper plate from both sides. 
   It is preferred to apply plating onto the surface of the leads  31   a  and  31   b  after insert molding in preparation for wire bonding.  FIGS. 6A and 6B  show cross sectional views of each of the leads  31   a  or  31   b  shown in  FIGS. 4 and 5  with a plating  35  applied to the surface thereof. The plating  35  comprises a layer of nickel (Ni) (applied first) and a layer of gold (Au) (applied second) that are applied to the surface of the lead  31   a  or  31   b  with a non-electrolytic plating method. 
   It is also acceptable for the lead to be configured such that a thickness thereof varies.  FIG. 7  is a longitudinal cross sectional view of a molded article  20  of a photoelectric coupling assembly  10 . The cross section lies in a plane that is parallel to an optical fiber insertion hole  24  and includes a lead  31   a  or  31   b . The thickness T 1  of the top and bottom end sections of the lead  31   a  or  31   b  is larger than the thickness T 0  of the general section such that the electrode terminal  36  exposed on the side surface  22  of the molded article  20  is larger. Increasing the thickness of the lead  31   a  or  31   b  in at the top and bottom in this way makes the lead  31   a  or  31   b  less likely to become detached from the molded article  20  when a vertical force (upward or downward force) acts on the lead  31   a  or  31   b . The increased thickness also makes it easier to accomplish wire bonding and enables three-dimensional wiring to be accomplished in a reliable manner, thereby increasing the degree of freedom with respect to packaging configurations. Thus, when the photoelectric coupling assembly  10  is mounted on a substrate (not shown), the end faces of the leads  31   a  and  31   b , i.e., the electrode terminals  36 , contact the terminals of the substrate in a reliable manner. 
   The thickness variation of the lead can be formed by etching or plating. When the thickness variation is formed by etching, half etching is applied to the lead frame such that the portions other than the end sections of the leads  31   a  and  31   b  are made to be thinner. 
     FIGS. 8A and 8B  are cross sectional views showing other examples of leads used in a photoelectric coupling assembly in accordance with the present invention. The lead  31   a  or  31   b  shown in  FIG. 8A  is configured to have a narrow section  60  having a width W 2  that is smaller than the width W 0  at the surface  30   a  of the lead frame  30 . The lead  31   a  or  31   b  shown in  FIG. 8B  has a bellows-like cross sectional shape. In either case, an engaging portion  37  whose width increases in a direction away from the front surface  21  is obtained. The method of manufacturing the leads shown in  FIGS. 8A and 8B  is the same as the method of manufacturing the leads shown in  FIG. 4 . 
     FIGS. 9A and 9B  are frontal views showing other examples of leads used in a photoelectric coupling assembly in accordance with the present invention as seen from the front surface  21  of the molded article  20  (first surface of the lead). It is acceptable for the width of the first surface to vary with respect to a direction perpendicular to the width. In the example shown in  FIG. 9A , the leads  31 A are arranged in the front surface  21  of the molded article  20  with a prescribed spacing between one another and the optical fiber insertion holes  24  are provided in-between the leads  31 A. Each of the leads  31 A is configured such that the width thereof at the front surface  21  varies as one moves along a direction perpendicular to the widthwise direction in the plane of the front surface  21 . More specifically, each of the leads  31 A has a wide section D 1  at an upper side and a wide section D 2  at a lower side along said perpendicular direction (vertical direction in  FIG. 9 ). Additionally, each lead  31 A has a narrow section D 3  at an intermediate portion along the vertical direction. Conversely, in the example shown in  FIG. 9B , each of the leads  31 B is configured to have a narrow section D 4  at an upper side and a narrow section D 5  at a lower side along said perpendicular direction (vertical direction in  FIG. 9 ). Additionally, each lead  31 B has a wide section D 6  at an intermediate portion along the vertical direction. 
   Configuring the leads  31 B such that the widths thereof vary as one moves along a direction perpendicular to the width of the lead  31 B in the plane of the lead surface makes the leads  31 B less likely to become detached from the molded article  20  when a force acts on a lead  31 B in a direction perpendicular to the widthwise direction of the lead  31 B in the plane of the lead surface. It is acceptable for the variation of the lead width to be either continuous or discontinuous. A lead having a varied width can be fabricated, for example, by etching. 
   A mold used in a manufacturing method for a photoelectric coupling assembly in accordance with the present invention will now be explained.  FIG. 10  is a cross sectional view illustrating a photoelectric coupling assembly being insert molded in accordance with an embodiment of a manufacturing method for a photoelectric coupling assembly in accordance with the present invention. The mold  50  has an upper die  51  and a lower die  52 . When the upper and lower dies  51  and  52  are joined together, a cavity  53  is formed inside for forming the main unit  20  of the photoelectric coupling assembly  10 . A second slide core  56  is positioned on the frontward side (leftward side in  FIG. 10 ) of the upper and lower dies  51  and  52  with positioning pins  57  such that it faces toward a first slide core  55 . The second slide core  56  forms a front surface  21  on the molded article  20  from which the distal ends  11   a  of the optical fibers  11  are exposed. 
   The first slide core  55  has a plurality of core pins  54  for forming the insertion holes  24  (through which the optical fibers  11  will be passed) in the molded article  20  and is inserted between the upper and lower molds  51  and  52 . A protruding part  58  for adjusting the height of the first slide core  55  is fitted inside a middle portion of the lower die  52  such that the vertical position thereof can be adjusted. The protruding part  58  is arranged to adjust the height of the first slide core  55  by supporting the first slide core  55  from underneath. The protruding part  58  also forms an adhesive injection port through which an adhesive is injected to fasten the optical fiber  11  inside the photoelectric coupling assembly. 
   A manufacturing method for a photoelectric coupling assembly in accordance with the present invention will now be explained. In this manufacturing method, leads each of which has an engaging portion and supplies electricity to a photoelectric conversion element arranged facing toward the respective optical fiber are insert molded into a front surface and a side surface, which is contiguous with respect to the front surface, of the molded article which is configured to have optical fibers passed there-through such that the distal ends of the optical fibers are exposed at the front surface. A lead frame  30  is insert molded into the front surface  21  of the molded article  20  such that at least a portion of the engaging portion of each lead is contained inside the resin  20   a  that forms the molded article  20  and a first surface of each lead is exposed at the first surface  21 . In this way, the leads  31   a  and  31   b  can be prevented from detaching from the front surface  21  of the molded article  20 . Also, the lead frame  30  is cut such that a second surface of each lead  31   a  or  31   b  is exposed at a side surface  22  of the molded article  20  that is contiguous with the front surface  21  of the molded article  20 . As a result, a three dimensional wiring pattern can be fabricated with ease. 
   The manufacturing method will now be explained in more detail. As shown in  FIG. 10 , the mold  50  is set by assembling the two dies  51  and  52  such that a cavity  53  for forming the molded article  20  is formed. The lead frame  30  and the second slide core  56  are mounted to the front surfaces  51   a  and  52   a  of the upper and lower dies  51  and  52  and are positioned there by the positioning pins  57 . The height of the protruding part  58  is adjusted to a prescribed height and the first slide core  55  is inserted. The first slide core  55  is positioned by inserting the distal end of the core pin  54  into a core pin positioning hole  56   b  provided in the second slide core  56 . Then, resin  20   a  is injected into the cavity  53  inside the mold  50  and the lead frame  30  is insert molded so as to form the molded article  20 . When this is done, as described previously, the wide sections  34  of the leads  31   a  and  31   b  are contained inside the resin  20   a.    
   When the resin  20   a  is injected and the insert molding of the lead frame  30  has been completed, the first slide core  55  and the second slide core are moved away from each other and the molded article  20  is removed from the mold  50 . Next, the lead frame  30  insert molded in the front surface  21  of the molded article  20  is cut in accordance with the size of the front surface  21 . The end faces exposed at the side surface  22  are then polished and plated with nickel followed by gold so as to form electrode terminals  36 . Finally, the photoelectric conversion unit  40  is mounted to the front surface  21  of the molded article  20  such that the active layer  42  of the photoelectric conversion element  41  is positioned directly in front of the optical fiber insertion holes  24  and the electrodes  43  contact the electrical wiring pattern section  23 , i.e., the leads  31   a  and  31   b . By manufacturing the photoelectric coupling assembly  10  in this manner, the front surface  21  of the main unit  20  is formed to be slanted and the transmission properties can be improved. 
   As described above, in a photoelectric coupling assembly and manufacturing method thereof in accordance with the present invention, engaging portions are provided in the cross sections of the leads serving to electrically connect to the photoelectric conversion unit and the leads are insert molded into the front surface of the molded article. The leads are formed such that at least a portion of the engaging portion is contained inside the resin of the molded article. As a result, the resin can prevent the leads from becoming detached after the leads are insert molded. Also, since a portion of each of the leads is arranged such that it is exposed at a side surface that is contiguous with the front surface of the molded article, a three-dimensional electrical wiring pattern can be formed easily and reliably. 
   A photoelectric coupling assembly and manufacturing method thereof in accordance with the present invention can be used as a photoelectric coupling assembly and a manufacturing method for a photoelectric coupling assembly that serves to connect a plurality of optical fibers passed through insertion holes provided in a molded article to a photoelectric conversion unit provided on a front surface of the molded article such that it faces the insertion holes. 
   While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, the invention is not limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 
   The entire disclosure of Japanese Patent Application No. 2006-284845 filed on Oct. 19, 2006 including specification, claims, drawings, and summary are incorporated herein by reference in its entirety.