Abstract:
An optical module shown in FIG.  2  is disclosed having following components. 
     (1) A substrate on which optical parts and an optical fiber are mounted. An optical fiber is fixed in the V-groove formed on the substrate so that the optic axis of the optical parts and the fiber is adjusted. 
     (2) A bottom plastic package having a concave surface for the substrate mounted thereon and several leads pins being fixed to the first plastic package. 
     (3) A upper plastic package for sealing optical parts and the fiber being fixed to the bottom plastic package, the outer surface of the upper plastic package being plated by metal, and the upper plastic package and at least one of the lead pins conducted. 
     According to this, it is possible to provide optical transmission module or optical module having advantage of capable of using plastic package and electromagnetic interference free with simplified structure.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an optical module and more particularly, the optical module that is useful in cost reduction and improvement of reliability. 
     Recently, it is strongly required to reduce the cost of an optical module to realize the optical subscriber network. To answer the requirement, a lot of studies have been reported for simplifying the alignment process between an optical device and an optical fiber and decreasing number of the parts of an optical package. In connection with this, for example, in “The Journal of Japan Institute for Interconnecting and Packaging Electronic Circuits, Vol. 10, No.5, pp302-305 and pp325-329 (1995), it is described passive alignment and packaging technology for optical devices. 
     Optical receiver modules are key devices in the optical communication system. It is composed of several components such as optical semiconductor devices, an optical fiber and/or an optical waveguide, lens for the optical coupling, electronic devices, substrate, lead pins, and package. 
     Regarding the packaging, the hermetic sealed metal or ceramic package is described in “The Journal of Japan Institute for Interconnecting and Packaging Electronic Circuits, Vol. 10, No.5, pp320-324 (1995)”. The MCF (Multilayer Ceramic Frame) package that has both good frequency response equal to metal package and mass productivity equal to ceramic package is also described. 
     The plastic resin package is expected to be the substitution of these packages because the plastic package is suitable for low cost mass production, but the plastic package has high transmission of moisture, which is general weak point nevertheless. To improve the problem, the encapsulation with transparent organic materials or grass lid covering of optical semiconductor devices have been proposed as simple sealing methods. 
     However, the plastic package has another weak point; the package is more transmissive to electromagnetic wave than that of metal package and ceramic package, and is more sensitive to EMI (Electromagnetic Interference). Though the problem can be improved by attaching electromagnetic shield to the module, the conventional sealing method with wholly covered metal is not suitable for practical use, because the cost is high. Therefore, it is the subject to realize electromagnetic sealing keeping the plastic package&#39;s advantage in low cost. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an optical module with plastic package and to improve the problem of the electromagnetic interference. 
     It is another object of the present invention to provide an optical module having simple structure and to improve the problem of the electromagnetic interference. 
     The present invention has invented by paying an attention to the point that lead frame is a component of an optical module. Lead frame is a thin metal plate and composed of the plate on which devices and a substrate are mounted and lead pins for input/output the electric signal. Lead frame has the function of holding a substrate, heat radiation, and connector. The invented optical module is using the lead frame as a part of electromagnetic shielding. 
     The object of our invention can be achieved by using an optical module comprising a lead frame molded by the first resin molded part, a substrate mounted on the lead frame with optical devices, the second resin molded part (the substrate is sealed by the first and second resin molded part.) and a electric conductive parts connected with the lead frame covering the substrate. According to the structure, the optical parts in the module are covered with the lead frame and the conductive parts; therefore, the optical parts are electromagnetic shielded. According to the invention, an optical module using plastic package and with electromagnetic interference free can be obtained. 
     Although metal parts, which provided between the first and the second packages, are useful for conductive parts, and, for example, metal plating layer formed on the second package is also useful for it. Moreover, fabricated conductive metal parts, which provided in inside of the second package and a fabricated conductive metal parts in order to cover outside of the second package are also useful. 
     The above object also can be achieved by using an optical module comprising a lead frame molded by the first resin encapsulating package, a substrate mounted on the lead frame, optical devices mounted on the substrate, and electric conductive parts connected with the lead frame. The substrate is inserted between the first resin molded package and the conductive parts. In the case, the conductive parts have the function of the second resin-molded package. The conductive parts are adjacent to a fiber holding component. 
     Moreover, the optical module of the present invention also has at least a lead frame, a substrate mounted on the lead frame, an optical module mounted on the substrate, a conductive parts electrically connected with the lead frame and covering or packing the substrate, and a resin molded package which molds at least the substrate and the conductive parts. Bending part of the lead frame can make the conductive parts. 
     The optical module of the present invention is manufactured by following steps: mounting optical devices on a substrate, mounting the substrate on the lead frame molded by the first resin molded package, covering the optical device with transparent resin, and fixing the second package having a conductive parts to the first package. The following method is also useful: mounting an optical device on a substrate, mounting the substrate on the lead frame, connecting a conductive parts for covering the substrate to the lead frame, and molding at least the substrate and the conductive parts. 
     According to the constitution described above, the optical module having plastic package, characteristics of electromagnetic interference free, and simple structure can be obtained. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a bard view of the first embodiment of an optical module of the present invention. 
     FIG. 2 shows a bard view of the second embodiment of an optical module of the present invention. 
     FIGS.  3 ( a )-( c ) shows a bard view of the third to fifth embodiments of optical modules of the present invention. 
     FIG. 4 shows a bard view of the sixth embodiment of an optical module of the present invention. 
     FIG. 5 shows a bard view of the seventh embodiment of an optical module of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a bard view of the first embodiment of an optical module of the present invention. This figure also shows an exploded view for easy to understand the inside appearance. The module has at least optical device  110 , a preamplifier  120 , a capacitor  121 , an optical fiber  130 , a substrate with a V-groove  140 , a lead frame  150 , conductive material parts  160 , a transparent resin  170  which fills into space of a bottom plastic package  180 , and a upper plastic package  190  which is used as a upper lid to the bottom plastic package  180 . The lead frame  150  is resin-molded and composed of the bottom plastic package  180 . The bottom plastic package  180  is constituted as a dual in-line package (DIP) having 8 outer lead pins. The bottom and the upper packages  180 ,  190  have an outer length of 14.6 mm (The length includes an outer length of 5 mm of the fiber holder part.), an outer width of 6.3 mm, and a height of 3 mm. 
     Each one of the optical device  110  and the preamplifier  120  are die-bonded to the substrate  140 . The optical fiber  130  is fixed by adhesive to the V-groove  141  of the substrate  140 , and coupled to the optical device  110 . The transparent resin  170  covers at least on the optical device  110 , the preamplifier  120 , and one end of the optical fiber  130 . 
     The optical assembly consists of the substrate  140 , optical device  110 , preamplifier  120  and the fiber  130  are mounted on the plastic package  180  as shown in FIG.  1 . The lead frame  150  is fabricated in the plastic package  180 . The bottom plastic package  180  is constituted as a dual in-line package (DIP) having 8 outer lead pins. The substrate  140  is fixed on the lead frame  150  by the conductive adhesive  195 . The lead frame  150  is connected to the terminal for ground, and for example, bonding wire  147  led from the optical assembly is connected to another lead terminal. The optical fiber with and without cover  131 ,  130  is fixed to U-groove  181  and  182  formed on the bottom plastic package  180  respectively. 
     The conductive metal parts  160  are fixed to the lead frame  150  by conductive epoxy resin so that the substrate  140  is covered with the parts  160  for electromagnetic shielding. The conductive metal parts  160  have the opening  162  for lo the fiber  130 . The conductive metal parts  160  also have the two side-openings for avoiding the bonding wire  147 . The bottom plastic package  180  and the lead frame  150  electromagnetically shield the optical assembly. The bottom and the upper packages  180 ,  190  are fixed by epoxy resin. Further, the bottom package  180  and lead flame  150  are fixed by epoxy resin with high conductivity. 
     For example, an optical waveguide type photodiode-having InP based semiconductor can be used as the optical device  110 . Alignment markers (not shown) to align to the substrate  140  are formed on the surface of the junction side of the optical device  110 . For example, Au-Sn is used for die-bonding the optical device  110  to the substrate  140 . A thickness of Au-Sn soldering layer is 3˜5 μm, and it is adjusted so that the height of the absorption layer of the optical device  110  from the surface of the substrate  140  becomes 8-10 μm. A single mode glass fiber is used as the fiber  130  whose outer diameter is 125 μm and spot size is 5 μm. 
     The substrate  140  is constituted by of silicon which has {100} crystal surface. The substrate  140  has the V-groove  141  for high precision alignment of the fiber  130  and the optical device  110 , and a wiring layer  145  to connect the optical device  110  to outer devices. More, the substrate  140  has markers (not shown) in a position that the optical device  110  should be fixed. The alignment can be carried out preciously using both the markers of the substrate  140  and the optical device  110 . The side of the V-groove  141  and the marker is constituted by {111} of crystal surface and these surfaces are formed at a time using KOH solution and orientation dependent anisotropic etching method. A width of the V-groove is 138-143 μm and the V-groove is formed so that the height of the optical axis of tip of the fiber  130  measured from the surface of the substrate  40  is equal to the height of the active layer and the absorption layer of the optical device  110 . 
     The wiring layer  145  is made of, for example, Au/Pt/Ti film layer or Au/Ni/Cr film layer and is formed by evaporation method on surface of insulating layer formed on the substrate  140 . Although, in FIG. 1, the wiring layer pattern is shown as a simplified sketch, width and thickness of the wiring  145  and thickness of the optical device  110  are determined by considering load capacitance of the optical device  110 . The silicone resin is used for this transparent resin  170 . The transparent resin  170  is filling the optical device  110  and the optical fiber  130  and adheres to them. The reflective index of the transparent resin  170  is 1.4 at wavelength of 1.3 μm, and it is almost adjusted to reflective index of the fiber  130 . If it is required higher reliability, the transparent resin  170  must be filled all over the optical fiber  130 . Thermoplastic resin, for example, liquid crystal polymer(LPC) is used as a material of the bottom and the upper packages  180 ,  190 . 
     A manufacturing process of the optical module of the first embodiment is summarized as follows: (1) the markers formed on the optical device  110  and substrate  140  are detected by using imaging device with infrared light and then, alignment is carried out between them. (2) A load is put on the optical device  110  and pre-bonds it to the preheated substrate  140 . (3) Die-bonds the optical device  110  to the substrate  140  by reflowing the Au-Sn solder. (4) Preamplifier  120  is fixed to the substrate  140  by adhesive. (5) Wire bonding the optical device  110 , preamplifier  120  to the wiring layer  145  of the substrate  140 . (6) The substrate  140  is fixed to the lead frame  150  using epoxy resin  195  with conductivity and high thermal conductivity. (7) The optical fiber  130  is fixed to the V-groove  141  by ultraviolet ray hardening resin. (8) The boxy conductive metal parts  160  formed by press manufacturing is fixed to the lead frame  150  using epoxy resin  195  with conductivity and high thermal conductivity. (9) The transparent resin  170  is dropped down on the optical device  110  and the optical fiber  130  and they are heat hardened. (10) The bottom and the upper packages  180 ,  190  are fixed each other by filling between them with epoxy resin. 
     According to the embodiment, low cost optical module is obtained by constituting dual in-line package and using the lead frame as a part of the maintaining electromagnetic shield. 
     FIG. 2 shows an optical module of second embodiment of the present invention. Internal structure of package of this embodiment is similar to that of first embodiment with the exception of that the second embodiment does not have the conductive metal parts  160  of FIG.  1 . In this embodiment, thermoplastic resin that is possible to plate, for example, liquid crystal polymer is used as material of the bottom and the upper packages  280 ,  290 . Copper plating for electromagnetic shielding and Nickel plating for prevention of oxidization is carried out to the upper package  290  surface by using electroless plating method. The copper plating is not required to the bottom package  280  because the lead frame of the bottom package  280  has the function of electromagnetic shielding. 
     As shown in FIG. 2, electric connecting part  291 - 1  is provided at the upper package. It is connected to a lead pin for the ground  250 - 1  with conductive adhesive  295 - 1 . By using this structure, it is possible to electrically connect the upper package  290  to the lead frame  150 . Another structure for electric connection between them is also shown in FIG.  2 . Extending the die-pad of the lead frame forms the expanded part  250 - 2 , and it is electrically connected to the corresponding part  291 - 2  of the upper package  290  using the conductive adhesive  295 - 2 . By using these structures, insulation of the other lead pins used as power supply line or signal line can be maintained easily because these pins are not electrically connected with the upper package  290 . Because the gap between these pins and the top part of the bottom package  280  is not more than 2 mm, there is durability against electromagnetic noise up to about 2-3 GHz. Adhesive of epoxy thermal hardening resin type is used for connecting between the bottom and upper package  280 ,  290  except for the part of the electric connection. 
     In this embodiment, it is possible to maintain electromagnetic shielding by metal plating to the upper package and the lead frame  150 , therefore, the optical module becomes low cost. 
     FIGS.  3 ( a )-( c ) shows optical module as the third to the fifth embodiments of the present invention. In the third embodiment, as shown in FIG.  3 ( a ), instead of using metal plating in the second embodiment, boxy conductive metal parts  360  formed by press manufacturing is insert-fabricated into upper package  390 . The figure shows the structure by showing cross sectional view of the part of the upper package  390 . The other structural feature is similar to that of the second embodiment. 
     In the forth embodiment, as shown in FIG.  3 ( b ), instead of using metal plating in the second embodiment, it is constituted that the substrate  140  is covered by the boxy conductive metal parts  360  formed by press manufacturing. A component  392  is provided next to the conductive metal parts  360 . The component  392  is made of plastic and has a U-groove for holding an optical fiber. The optical fiber is sandwiched between the component  392  and the bottom package. The other structural feature is similar to that of the second embodiment. 
     In the fifth embodiment, as shown in FIG.  3 ( c ), instead of using the metal plating parts in the second embodiment, the boxy conductive metal parts made using press manufacturing method  360  is used. The parts  360  are mounted on a bottom package. It is possible to maintain electromagnetic shielding according to the parts  360  and electric contact between the pins of the lead frame  150  and the parts  360 . The other structural feature is similar to that of the second embodiment. 
     In the third to fifth embodiments, it is possible to maintain electromagnetic shielding by the boxy conductive metal parts  360  formed by press manufacturing method and electric contact between the pins of the lead frame  150  and the parts  360 . Therefore, the low cost optical module can be achieved. 
     In the sixth embodiment, as shown in FIG. 4, the boxy or semi-boxy conductive metal parts  460  formed by press manufacturing are electrically fixed to a lead frame  450  so that the parts  460  do not contact with bonding wires  447  and the substrate  440  is covered with the parts  460 . In this embodiment, the lead frame  450  has projecting parts  461  and holes  451  so that tips of the part  460  are inserted into the holes  451  and the tip is bent for fixing the parts  460  to the lead frame  450 . This structure has advantage of strengthening mechanical joining between the lead frame  450  and the parts  460 . 
     The package of the present embodiment has the shape shown by dashed line of FIG.  4  and is manufactured by using lump fabrication method, for example, transfer mold method. The metal parts  460  has openings  462  in front and behind portion to avoid interference with the optical fiber  430  and smooth the way for the flow of the mold resin as package material. Though the embodiment shown in FIG. 4 explaining a package using a lump fabrication method, the same method can be generally applied to a package using lead frame fabricated conductive metal. 
     In the seventh embodiment, as shown in FIG. 5, one part of the lead frame  550  is used as conductive metal part  560  to cover substrate. The part  560  and the lead frame  550  are in a body. This is manufactured by mounting substrate  540  and optical fiber  530  on the lead frame  550  and then, bending the lead frame  550 . In this embodiment, it has advantage of improvement of the ground because the part  560  and the lead frame  550  are in a body. 
     The package of the present embodiment has the shape shown by dashed line of FIG. 5, is similar to that of the sixth embodiment, and is manufactured by lump fabrication method, for example, transfer mold method. The part  560  has openings  562  in front and behind portion to smooth the way for the flow of the mold resin. Though the embodiment shown in FIG. 5 explaining a package using a lump fabrication method, the same method can be generally applied to a package using lead frame fabricated conductive metal. 
     The advantages of these embodiments are providing optical module manufactured using plastic package capable of satisfying requirement of lowering cost and having durability against electromagnetic noise with simplified assembling process. Therefore, it is possible to achieve lowering cost and high reliability by the embodiments. 
     According to the invention, it is possible to provide optical module using plastic package with high durability against electromagnetic interference by simplified structure.