Patent Publication Number: US-2017357063-A1

Title: Optical module and optical module manufacturing method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2016-117271, filed on Jun. 13, 2016, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiment discussed herein is related to an optical module and an optical module manufacturing method. 
     BACKGROUND 
     In recent years, for example, a system with multiple Central Processing Units (CPUs) being connected to execute parallel processing spreads with increasing information capacity. It is preferable to transfer information among such CPUs at a high speed, but no sufficient transfer speed may be obtained in a case where multiple CPUs are connected by a metal cable. Accordingly, multiple CPUs may be connected by an optical cable with a high transfer speed. An optical module that converts information that is processed in a state of an electrical signal into an optical signal or converts a transferred optical signal into an electrical signal is used in order to transfer information through an optical cable. 
     For example, an optical element member that emits light to transmit an optical signal or an optical element member that receives an optical signal is mounted on an optical module. Specifically, an optical module is formed in such a manner that, for example, an optical element member such as a Vertical Cavity Surface Emitting LASER (VCSEL) or a Photo Diode (PD) is mounted on a printed circuit board. In a case where an optical element member is mounted on a printed circuit board, the optical element member may be arranged in such a manner that a surface on a back side of a light receiving or emitting surface is opposite to the printed circuit board, and be connected to the printed circuit board by a wire bonding method. In such an arrangement, a light receiving or emitting surface of an optical element member is oriented in a direction opposite to that of a printed circuit board, so that light is not blocked by the printed circuit board and an optical signal is transmitted or received reliably. 
     In a wire bonding method, an optical element member is connected to a printed circuit board by wires that extend around the optical element member, so that a size of the optical element member is increased in order to provide a needed number of wires and the wires also extend around the optical element member to increase a surface area for mounting thereof. Accordingly, flip-chip mounting may be adopted recently, where a light receiving or emitting surface of an optical element member is arranged to be opposite to a printed circuit board and the optical element member is directly connected to the printed circuit board by a bump. In a case where flip-chip mounting is adopted, a light receiving or emitting surface of an optical element member is opposite to a printed circuit board, so that a through-hole is formed in the printed circuit board and an optical signal passes through the through-hole to be transmitted or received. 
     Japanese Laid-open Patent Publication No. 2001-033666 
     Japanese Laid-open Patent Publication No. 2002-098863 
     In a case where an optical element member is flip-chip-mounted on a printed circuit board, an underfill material is caused to fill a gap between the optical element member and the printed circuit board in order to protect a state of bonding between the optical element member and the printed circuit board. However, a light receiving or emitting part of an optical element member is opposite to a printed circuit board in flip-chip mounting, so that there is a problem in that the light receiving or emitting part may be covered by an underfill material that is caused to fill a gap between the optical element member and the printed circuit board. As a light receiving or emitting part is covered by an underfill material, light is blocked by the underfill material, so that normal transmitting or receiving of an optical signal is difficult. 
     Hence, as filling with an underfill material is executed, an inefficient method may be used in such a manner that, for example, the underfill material is warmed to increase a viscosity thereof and the underfill material with an increased viscosity is manually accumulated around an optical element member in increments of a less amount thereof. As a result, a manufacturing cost of an optical module is increased. 
     SUMMARY 
     According to an aspect of an embodiment, an optical module includes a substrate with a through-hole formed therein, an optical element member that includes a light receiving or emitting part that receives light or emits light at a position on a surface that is opposite to the substrate, the position corresponding to the through-hole, and a post that is formed of a transparent material, covers the light receiving or emitting part and is inserted into the through-hole. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a configuration of an optical module according to an embodiment; 
         FIG. 2  is a cross-sectional schematic diagram illustrating a configuration of a photoelectric conversion part; 
         FIG. 3  is an enlarged view illustrating a periphery of an optical element member; 
         FIG. 4  is a plan view illustrating a periphery of an optical element member; 
         FIGS. 5A, 5B, 5C, 5D, 5E, and 5F  are diagrams illustrating a method for manufacturing an optical element member; and 
         FIGS. 6A, 6B, and 6C  are diagrams illustrating a method for fixing an optical element member to a substrate. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     Preferred embodiments of the present invention will be explained with reference to accompanying drawings. Additionally, the present invention is not limited by such an embodiment. 
       FIG. 1  is a schematic diagram illustrating a configuration of an optical module  100  according to an embodiment. The optical module  100  is disposed on, for example, a connector at an end of an optical cable, or the like. The optical module  100  as illustrated in  FIG. 1  is put into, for example, a connector  210  that is included in a substrate  200  of another device such as a server. Furthermore, the optical module  100  includes an optical waveguide  110 , a photoelectric conversion part  120 , a Flexible Printed Circuit (FPC) connector  130 , and a FPC  140 . 
     The optical waveguide  110  is a transmission path that transmits an optical signal. The optical waveguide  110  is composed of a core and a clad that surrounds the core, and transmits an optical signal through the core. The optical waveguide  110  is connected to the photoelectric conversion part  120 . 
     The photoelectric conversion part  120  executes photoelectric conversion between an optical signal that is transmitted by the optical waveguide  110  and an electrical signal. That is, the photoelectric conversion part  120  converts an electrical signal into an optical signal and transmits it to the optical waveguide  110 , or converts an optical signal received from the optical waveguide  110  into an electrical signal. A configuration of the photoelectric conversion part  120  will be described in detail later. 
     The FPC connector  130  connects the photoelectric conversion part  120  to the FPC  140  that is a circuit board. That is, the FPC connector  130  transmits an electrical signal generated by a circuit on the FPC  140  to the photoelectric conversion part  120  or transmits an electrical signal converted from an optical signal by the photoelectric conversion part  120  to a circuit on the FPC  140 . 
     The FPC  140  is a flexible printed circuit board where a wiring pattern is printed or a variety of circuits are formed on a surface thereof. An electrical signal is transmitted by a wiring pattern or a circuit on the FPC  140 . 
     Next, a configuration of the photoelectric conversion part  120  will be described with reference to  FIG. 2 .  FIG. 2  is a schematic diagram illustrating a cross section of the optical module  100  along a line I-I as illustrated in  FIG. 1 . 
     As illustrated in  FIG. 2 , the photoelectric conversion part  120  is connected to the FPC  140  through the FPC connector  130 . Furthermore, the optical waveguide  110  is inserted into a gap between the photoelectric conversion part  120  and the FPC  140  and connected to the photoelectric conversion part  120 . Moreover, a mirror  121  is provided in the optical waveguide  110  at a position where the photoelectric conversion part  120  is connected thereto. The photoelectric conversion part  120  is formed in such a manner that an optical element member  123  and a conversion control member  124  are mounted on a substrate  122 . 
     The mirror  121  changes a traveling direction of an optical signal transmitted through the optical waveguide  110  to a direction toward the optical element member  123 . Furthermore, the mirror  121  changes a traveling direction of an optical signal that is emitted from the optical element member  123  to a direction of extension of the optical waveguide  110 . That is, the mirror  121  changes a traveling direction of an optical signal so that the optical element member  123  can transmit or receive the optical signal through the optical waveguide  110 . 
     The substrate  122  is, for example, a printed circuit board capable of printing a wiring pattern of a conductor on a surface of a core member made of a resin. As described later, a through-hole that passes an optical signal therethrough is formed at a position where the substrate  122  is interposed between the mirror  121  and the optical element member  123 . 
     The optical element member  123  is an optical element that includes a light receiving or emitting part. Specifically, the optical element member  123  includes, for example, a Vertical Cavity Surface Emitting LASER (VCSEL) to emit light or includes, for example, a Photo Diode (PD) to receive light. The optical element member  123  is flip-chip-mounted on the substrate  122 . Therefore, a light receiving or emitting part of the optical element member  123  is opposite to the substrate  122  and transmits or receives an optical signal through a through-hole formed in the substrate  122 . 
     Thus, the optical element member  123  is flip-chip-mounted on the substrate  122 , so that the optical element member  123  is bonded to the substrate  122  by an underfill material. In other words, an underfill material is caused to fill a gap between the optical element member  123  and the substrate  122 . However, in the present embodiment, a light receiving or emitting part of the optical element member  123  is protected by a transparent post as described later, so that the light receiving or emitting part is not covered by an underfill material. As a result, light is not blocked between a light receiving or emitting part of the optical element member  123  and the mirror  121 , so that traveling of an optical signal is not prevented. 
     The conversion control member  124  is electrically connected to the optical element member  123  and controls the optical element member  123  or converts an output signal from the optical element member  123 . Specifically, the conversion control member  124  includes a driver that drives a VCSEL of the optical element member  123  or includes a Trance-Impedance Amplifier (TIA) that converts a current signal that is output from a PD of the optical element member  123  into a voltage signal. The conversion control member  124  transmits to or receives from a circuit on the FPC  140  through the FPC connector  130 , an electrical signal. 
     Next, a part A around the optical element member  123  will be described in detail with reference to  FIGS. 3 and 4 .  FIG. 3  is an enlarged view illustrating a part A in  FIG. 2 . Furthermore,  FIG. 4  is a plan view of a periphery of the optical element member  123  when viewed in a direction of II as illustrated in  FIG. 3 . 
     As illustrated in  FIG. 3 , the optical element member  123  includes a light receiving or emitting part  123   a  and is flip-chip-mounted on the substrate  122 . That is, a light receiving or emitting surface of the light receiving or emitting part  123   a  that receives light or emits light is opposite to the substrate  122 , and the optical element member  123  is electrically connected to a wiring pattern  122   a  on a surface of the substrate  122  by a bump  302 . Furthermore, a through-hole is formed at a position where the substrate  122  is interposed between the light receiving or emitting part  123   a  and the mirror  121 . An optical signal that travels between the light receiving or emitting part  123   a  and the mirror  121  passes through a through-hole formed in the substrate  122 . 
     The light receiving or emitting part  123   a  of the optical element member  123  is covered by a transparent post  301 , and the transparent post  301  is inserted into a through-hole formed in the substrate  122 . The transparent post  301  is provided by molding a resin that is transparent and has a less amount of attenuation of light, and is formed of, for example, a ultraviolet ray curable resin that is cured by irradiating it with an ultraviolet ray, or the like. The transparent post  301  covers a whole of the light receiving or emitting part  123   a  of the optical element member  123 , is positioned between the light receiving or emitting part  123   a  and the mirror  121 , and provides a passage for an optical signal. 
     An underfill material  303  is caused to fill a gap between the optical element member  123  and the substrate  122  to bond the optical element member  123  to the substrate  122 . Herein, the light receiving or emitting part  123   a  of the optical element member  123  is covered by the transparent post  301 , so that the light receiving or emitting part  123   a  is not covered by the underfill material  303 . Hence, at the light receiving or emitting part  123   a , light is not blocked by the underfill material  303 . That is, light that is received or emitted by the light receiving or emitting part  123   a  passes through an inside of the transparent post  301 , so that traveling of an optical signal between the light receiving or emitting part  123   a  and the mirror  121  is not prevented. 
     Specifically, an optical signal transmitted through the optical waveguide  110  is reflected from the mirror  121  and is incident on the transparent post  301 . Then, an optical signal that travels inside the transparent post  301  is received by the light receiving or emitting part  123   a.  Furthermore, an optical signal that is emitted from the light receiving or emitting part  123   a  travels inside of the transparent post  301  and is output from an end of the transparent post  301  to the mirror  121 . Then, an optical signal is reflected from the mirror  121  and transmits through the optical waveguide  110 . 
     Thus, the light receiving or emitting part  123   a  is covered by the transparent post  301 , so that the transparent post  301  that is transparent and has a less amount of attenuation of light is a passage for an optical signal and blocking of light by the underfill material  303  can be prevented. 
     Additionally, as illustrated in  FIG. 4 , the optical element member  123  may include multiple light receiving or emitting parts  123   a,  where each of the light receiving or emitting parts  123   a  may be a light emitting part that includes a VCSEL or may be a light receiving part that includes a PD. Light emitting or light receiving by the light receiving or emitting parts  123   a  are controlled by the conversion control member  124  that is connected to the optical element member  123  through the wiring pattern  122   a.    
     Any of these light receiving or emitting parts  123   a  is protected by the transparent post  301 . Herein, for the multiple light receiving or emitting parts  123   a , separate transparent posts  301  may be provided respectively, or one transparent post  301  may be provided collectively. 
     Next, a method for manufacturing the optical element member  123  will be described with reference to  FIGS. 5A, 5B, 5C, 5D, 5E, and 5F .  FIGS. 5A, 5B, 5C, 5D, 5E, and 5F  are diagrams illustrating steps (A) to (F) in a case where the optical element member  132  is manufactured. 
     First, light receiving or emitting parts  123   a , terminals  123   b,  and the like that correspond to multiple optical element members  123  are formed on a wafer that is a semiconductor substrate (step (A)). Then, a photoresist is applied onto layers of the light receiving or emitting parts  123   a,  the terminals  123   b,  and the like to form a resist  401  (step (B)). As the resist  401  is formed, development thereof is executed at positions  402  that correspond to the light receiving or emitting parts  123   a  and the resist  401  at positions of the light receiving or emitting parts  123   a  is eliminated (step (C)). 
     In such a state, for example, a transparent resin such as an ultraviolet ray curable resin is injected at the positions  402  where the resist  401  has been eliminated, and irradiated with light such as an ultraviolet ray as needed. Thereby, transparent posts  301  are formed at positions that correspond to the light receiving or emitting parts  123   a  (step (D)). Additionally, the transparent posts  301  need not be formed of an ultraviolet ray curable resin, and may be formed of, for example, a thermosetting resin or the like, as long as such a material is transparent and has an amount of attenuation of light that is less than a predetermined reference thereof. 
     As the transparent posts  301  are formed, a surrounding resist  401  is stripped (step (E)). Thereby, multiple optical element members  123  are produced where respective light receiving or emitting parts  123   a  are protected by the transparent posts  301 . Then, these multiple optical element members  123  are cut into pieces by, for example, a diamond blade, so that the optical element members  123  are completed (step (F)). 
     Thus manufactured optical element member  123  is flip-chip-mounted on a substrate  122 . As illustrated in  FIG. 6A , a wiring pattern  122   a  is formed on the substrate  122  and a through-hole  122   b  is formed at a position that corresponds to a light receiving or emitting part  123   a  of the optical element member  123 . Moreover, a metal bump  302  is formed on the wiring pattern  122   a  in order to flip-chip-mount the optical element member  123 . The bump  302  is formed at a position that corresponds to a terminal  123   b  of the optical element members  123 . 
     Then, as illustrated in  FIG. 6B , the optical element member  123  is mounted on the substrate  122 . Herein, alignment is executed in such a manner that the transparent post  301  is inserted into the through-hole  122   b  of the substrate  122  and the terminal  123   b  contacts the bump  302 . As the optical element member  123  is mounted at a suitable position, an underfill material  303  is caused to fill a gap between the substrate  122  and the optical element member  123  as illustrated in  FIG. 6C . Herein, the light receiving or emitting part  123   a  is protected by a transparent post  301 , so that the light receiving or emitting part  123   a  is not covered by the underfill material  303 . Therefore, in a case where filling with the underfill material  303  is executed, increasing a viscosity of the underfill material  303  by warming thereof or manually accumulating the underfill material  303  in increments of a less amount thereof is not needed. Thus, filling with the underfill material  303  is readily executed by a machine operation, so that fixing of the optical element member  123  to the substrate  122  is executed efficiently. 
     As described above, according to the present embodiment, a transparent post that covers a light receiving or emitting part of an optical element member is formed, the optical element member is flip-chip-mounted on a substrate in such a manner that a light receiving or emitting surface at a side of the light receiving or emitting part is opposite to the substrate, and an undefill material is caused to fill a gap between the optical element member and the substrate. Hence, a light receiving or emitting part of an optical element member is protected by a transparent post, so that the light receiving or emitting part is not covered by an underfill material even though filling therewith is executed by, for example, a machine operation. In other words, blocking of light on a light receiving or emitting part can be prevented efficiently. 
     Additionally, it is also possible to apply a configuration as described for the embodiment as described above where a light receiving or emitting part of an optical element member is covered by a transparent post and a light receiving or emitting surface is opposite to a substrate, to a variety of optical modules as well as an optical module that is disposed on an optical cable. Specifically, it is also possible to apply a configuration of the embodiment as described above to, for example, a case where, in an optical transmitter, an optical receiver, or the like, an optical element member is flip-chip-mounted on a substrate, or the like. 
     According to an aspect of an optical module and an optical module manufacturing method as disclosed in the present application, an advantageous effect is provided in such a manner that blocking of light on a light receiving or emitting part can be prevented efficiently. 
     All examples and conditional language recited herein are intended for pedagogical purposes of aiding the reader in understanding the invention and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiment of the present invention has been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.