Patent Publication Number: US-2021191048-A1

Title: Optical module

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2019-228686, filed on Dec. 18, 2019, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein are related to an optical module. 
     BACKGROUND 
     In recent years, with miniaturization and speeding up of optical modules that perform predetermined optical processes, attention has been focused on high-density component mounting on a substrate in an optical module. As such an optical module, for example, there is one that uses bridge mounting for mounting components as a bridge type. 
     In an optical module using the bridge mounting, for example, an optical component that performs a predetermined optical process according to an electrical signal is arranged in a recess formed in a substrate, and an electrical component that supplies an electrical signal to the optical component is connected in a bridge form across the optical component and the substrate. For example, the electrical component is connected to an electrode on the optical component and an electrode on the substrate across a gap between the optical component and an inner wall surface of the recess of the substrate. 
     The optical component is bonded to the inner wall surface of the recess of the substrate with, for example, a thermosetting adhesive in the entire gap between the optical component and the inner wall surface of the recess of the substrate. For example, the entire gap between the optical component and the inner wall surface of the recess of the substrate is filled with an uncured adhesive. Then, by thermally curing the uncured adhesive, the optical component arranged in the recess of the substrate is bonded to the inner wall surface of the recess of the substrate. For example, Japanese Laid-open Patent Publication No. 2004-216649 and the like are disclosed as related art. 
     SUMMARY 
     According to an aspect of the embodiments, an optical module includes a substrate in which a through hole or a recess is formed; a first component that is arranged in the through hole or the recess of the substrate, and is bonded to an inner wall surface of the through hole or the recess by a thermosetting adhesive in a portion of a gap between the first component and the inner wall surface of the through hole or the recess; and a second component that is connected to an electrode on one surface of the first component and an electrode on one surface of the substrate, across the gap between the first component and the inner wall surface of the through hole or the recess. 
     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. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional side view illustrating a configuration of an optical module according to an embodiment; 
         FIG. 2  is a diagram illustrating an example of a bonding portion between an optical component and an inner wall surface of a through hole; 
         FIG. 3  is a cross-sectional side view illustrating a configuration of an optical module according to a comparative example; 
         FIGS. 4A to 4C  are diagrams for explaining a flow of a method for manufacturing the optical module according to the present embodiment; 
         FIG. 5  is a diagram illustrating modification example 1 of a bonding region of the optical component with an adhesive; 
         FIG. 6  is a diagram illustrating modification example 2 of the bonding region of the optical component with the adhesive; 
         FIG. 7  is a diagram illustrating modification example 3 of the bonding region of the optical component with the adhesive; 
         FIG. 8  is a diagram illustrating modification example 4 of the bonding region of the optical component with the adhesive; 
         FIG. 9  is a diagram illustrating modification example 5 of the bonding region of the optical component with the adhesive; 
         FIG. 10  is a diagram illustrating modification example 6 of the bonding region of the optical component with the adhesive; 
         FIG. 11  is a diagram illustrating modification example 7 of the bonding region of the optical component with the adhesive; 
         FIG. 12  is a diagram illustrating an example of results of simulating stress on connecting portions of an electrical component to electrodes on a substrate; 
         FIG. 13  is a diagram illustrating an example of results of simulating stress on the connecting portions of the electrical component to the electrodes on the substrate; and 
         FIG. 14  is a diagram illustrating an example of results of simulating stress on the connecting portions of the electrical component to the electrodes on the substrate. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Incidentally, when the adhesive filled in the entire gap between the optical component and the inner wall surface of the recess of the substrate is thermally cured, thermal expansion and thermal contraction of the substrate are caused simultaneously, and thereby stress is applied to the entire circumference of the optical component from the entire inner wall surface of the recess of the substrate via the adhesive. When the stress is applied to the entire circumference of the optical component from the entire inner wall surface of the recess of the substrate via the adhesive, while the optical component is pulled upward by the electrical component connected in the bridge form to the electrode on the optical component and the electrode on the substrate, the substrate is pulled upward near the recess, consequently, there is a problem that the stress concentrates on connecting portions of the electrical component to the electrode on the optical component and the electrode on the substrate, and the component is damaged or peeled off at these connecting portions. 
     In view of the above, it is desirable to suppress damage or peeling of the component connected in the bridge form. 
     Hereinafter, an embodiment of an optical module disclosed in the present application will be described in detail with reference to the drawings. Note that this embodiment does not limit the disclosed technology. 
     EMBODIMENT 
       FIG. 1  is a cross-sectional side view illustrating a configuration of an optical module  100  according to the embodiment. Hereinafter, for convenience of description, a surface on an upper side of the paper surface of  FIG. 1  is referred to as an upper surface, and a surface on a lower side of the paper surface is referred to as a lower surface. However, the optical module  100  may be used upside down, for example, and may be used in any posture. The optical module  100  illustrated in  FIG. 1  has a substrate  110 , an optical component  120 , and an electrical component  130 . 
     The substrate  110  is, for example, a glass epoxy substrate, and is a component on which various components forming the optical module are mounted. Electrodes for electrically connecting various components are formed on an upper surface  110   a  of the substrate  110 . Further, in the substrate  110 , a substantially rectangular through hole  111  arranging the optical component  120  is formed. 
     The optical component  120  is a chip component that has an optical waveguide and an electrode on an upper surface  120   a , propagates light from a light source through the optical waveguide, and performs optical modulation based on an electrical signal supplied to the electrode. The optical component  120  performs optical modulation based on, for example, an electrical signal supplied from the electrical component  130  to the electrode. 
     Further, the optical component  120  is arranged in the through hole  111  of the substrate  110 . For example, by connecting the electrode on the upper surface  120   a  of the optical component  120  to a lower surface of the electrical component  130 , the optical component  120  is arranged in the through hole  111  in a state that the gap  125  is formed between the optical component  120  and an inner wall surface of the through hole  111 . 
     The optical component  120  is bonded to the inner wall surface of the through hole  111  with a thermosetting adhesive  205  in a portion of the gap  125  between the optical component  120  and the inner wall surface of the through hole  111 . For example, the optical component  120  is partially bonded to the inner wall surface of the through hole  111  by the adhesive  205  in a state that a portion not filled with the adhesive  205  remains in the gap  125  between the optical component  120  and the inner wall surface of the through hole  111 . A region where the optical component  120  is bonded to the inner wall surface of the through hole  111  by the adhesive  205  will be described later. The optical component  120  is an example of a first component. 
     The electrical component  130  is, for example, a chip component such as a driver that supplies an electrical signal to the optical component  120 , and is connected in a bridge form across the optical component  120  and the substrate  110 . For example, the electrical component  130  is connected to the electrode on the upper surface  120   a  of the optical component  120  and an electrode on the upper surface  110   a  of the substrate  110  across the gap  125  between the optical component  120  and the inner wall surface of the through hole  111 . The connection of the electrical component  130  to the electrode on the upper surface  120   a  of the optical component  120  is achieved by, for example, flip-chip connecting the electrical component  130  to the electrode on the upper surface  120   a  by a solder ball  201 , and filling an adhesive  202  between the electrical component  130  and the optical component  120 . The connection of the electrical component  130  to the electrode on the upper surface  110   a  of the substrate  110  is achieved by, for example, flip-chip connecting the electrical component  130  to the electrode on the upper surface  110   a  by a solder ball  203 , and filling an adhesive  204  between the electrical component  130  and the substrate  110 . The electrical component  130  is an example of a second component. 
     Here, the bonding portion between the optical component  120  and the inner wall surface of the through hole  111  will be described with reference to  FIG. 2 .  FIG. 2  is a diagram illustrating an example of a bonding portion between the optical component  120  and the inner wall surface of the through hole  111 . In  FIG. 2 , a plan view of the optical module  100  as viewed from above is schematically illustrated. A cross-sectional view taken along a line I-I of  FIG. 2  corresponds to  FIG. 1 . 
     As illustrated in  FIG. 2 , the substrate  110 , the optical component  120 , and the gap  125  between the optical component  120  and the inner wall surface of the through hole  111  partially overlap with the electrical component  130  when viewed from a direction perpendicular to the upper surface  120   a  of the optical component  120 . Then, as described above, the optical component  120  is bonded to the inner wall surface of the through hole  111  by the thermosetting adhesive  205  in a portion of the gap  125 . For example, the optical component  120  is bonded by the adhesive  205  in a portion of the gap  125 , the portion overlapping with the electrical component  130  when viewed from the direction perpendicular to the upper surface  120   a  of the optical component  120 . 
     By bonding the optical component  120  to the inner wall surface of the through hole  111  by the adhesive  205  in a portion of the gap  125 , a portion remains where the gap  125  is not filled with the adhesive  205 . Thus, even if thermal expansion and thermal contraction of the substrate  110  are caused when the adhesive  205  filled in the gap  125  is thermally cured, no stress is applied from the inner wall surface of the through hole  111  of the substrate  110  to the entire circumference of the optical component  120  via the adhesive  205 . Therefore, even if the optical component  120  is pulled upward by the electrical component  130  and the substrate  110  is pulled upward near the through hole  111 , concentration of stress on the connecting portions of the electrical component  130  to the electrode on the optical component  120  and the electrode on the substrate  110  is reduced. Consequently, damage or peeling of the electrical component  130  may be suppressed. 
       FIG. 3  is a cross-sectional side view illustrating a configuration of are optical module according to a comparative example. As illustrated in  FIG. 3 , in the optical module according to the comparative example, the optical component  120  is bonded to the inner wall surface of the through hole  111  of the substrate  110  with the thermosetting adhesive  205  in the entire gap  125 . In the optical module according to the comparative example, when the adhesive  205  is thermally cured, thermal expansion and thermal contraction of the substrate  110  are caused simultaneously, thereby applying stress from the entire inner wall surface of the through hole  111  of the substrate  110  to the entire circumference of the optical component  120  via the adhesive  205 . In  FIG. 3 , the stress applied to the entire circumference of the optical component  120  is indicated by white arrows. When the stress is applied to the entire circumference of the optical component  120 , the optical component  120  is pulled upward by the electrical component  130  connected to the electrode on the optical component  120  and the electrode on the substrate  110  in a bridge form, and the substrate  110  is pulled upward near the through hole  111 . In  FIG. 3 , directions in which the optical component  120  and the substrate  110  are pulled are indicated by black arrows. By application of the stress to the entire circumference of the optical component  120  and pulling of the optical component  120  and the substrate  110  upward, stress concentrates on each of the connecting portions of the electrical component  130  to the electrode of the optical component  120  and the electrode on the substrate  110 . Consequently, damage or peeling of the electrical component  130  occurs at these connecting portions. For example, cracks may occur around the solder balls  201 ,  203  on the lower surface of the electrical component  130 , or the electrical component  130  may peel off from the adhesives  202 ,  204 . 
     On the other hand, in the optical module  100  according to the present embodiment, as illustrated in  FIGS. 1 and 2 , the optical component  120  is bonded to the inner wall surface of the through hole  111  of the substrate  110  with the thermosetting adhesive  205  in a portion of the gap  125 . For example, in the optical module  100 , the optical component  120  is bonded to the inner wall surface of the through hole  111  of the substrate  110  by the adhesive  205  in a portion of the gap  125 , the portion overlapping with the electrical component  130  when viewed from the direction perpendicular to the upper surface  120   a  of the optical component  120 . Thus, in a portion of the gap  125  that does not overlap with the electrical component  130  when viewed from the direction perpendicular to the upper surface  120   a  of the optical component  120 , the inner wall surface of the through hole  111  of the substrate  110  and the optical component  120  do not come into direct contact with each other, and thus the stress is not applied to the entire circumference of the optical component  120 . Consequently, concentration of stress on the connecting portions of the electrical component  130  to the electrode on the optical component  120  and the electrode on the substrate  110  is reduced, and thus damage or peeling of the electrical component  130  may be suppressed. 
     Next, a method for manufacturing the optical module  100  according to the present embodiment will be described with reference to  FIGS. 4A to 4C .  FIGS. 4A to 4C  are diagrams for explaining a flow of the method for manufacturing the optical module  100  according to the present embodiment. 
     As illustrated in  FIG. 4A , first, the electrical component  130  is connected to the electrode on the upper surface  120   a  of the optical component  120 . For example, the electrical component  130  is flip-chip connected to the electrode on the upper surface  120   a  of the optical component  120  by the solder ball  201 , and the adhesive  202  is filled between the electrical component  130  and the optical component  120 . At this time, the solder ball  203  is installed on the lower surface of the electrical component  130  as needed. Once the adhesive  202  is filled between the electrical component  130  and the optical component  120 , the adhesive  202  is thermally cured. 
     Subsequently, as illustrated in  FIG. 4B , with the optical component  120  arranged in the through hole  111  formed in the substrate  110 , the electrical component  130  is connected to the electrode on the upper surface  110   a  of the substrate  110  across the gap  125  between the optical component  120  and the inner wall surface of the through hole  111 . For example, the electrical component  130  is flip-chip connected to the electrode on the upper surface  110   a  of the substrate  110  by the solder ball  203 , and the adhesive  204  is filled between the electrical component  130  and the substrate  110 . Once the adhesive  204  is filled between the electrical component  130  and the substrate  110 , the adhesive  204  is thermally cured. Note that the adhesive  204  may have the same or different thermosetting temperature as the adhesive  202 . 
     Subsequently, as illustrated in  FIG. 4C , a portion of the gap  125  between the optical component  120  and the inner wall surface of the through hole  111  is filled with the adhesive  205 . For example, the adhesive  205  is filled in a portion of the gap  125 , the portion overlapping with the electrical component  130  when viewed from the direction perpendicular to the upper surface  120   a  of the optical component  120 . Once the adhesive  205  is filled in the portion of the gap  125 , the adhesive  205  is thermally cured. At this time, even if thermal expansion and thermal contraction of the substrate  110  are caused, stress is only applied to a portion of the entire circumference of the optical component  120  from the inner wall surface of the through hole  111  of the substrate  110  via the adhesive  205 . Therefore, even if the optical component  120  is pulled upward by the electrical component  130  and the substrate  110  is pulled upward near the through hole  111 , concentration of stress on the connecting portions of the electrical component  130  to the electrode on the optical component  120  and the electrode on the substrate  110  is reduced. Consequently, damage or peeling of the electrical component  130  may be suppressed. Note that the adhesive  205  may have the same or different thermosetting temperature as the adhesives  202 ,  204 . When the thermosetting temperature differs between the adhesive  205  and the adhesives  202 ,  204 , it is preferable that the adhesive  205  has a lower thermosetting temperature than the adhesives  202 ,  204 . Thus, thermal expansion and thermal contraction of the substrate is suppressed when the adhesive  205  is thermally cured. 
     Note that in the embodiment described above, the case where the optical component  120  is bonded by the adhesive  205  in the portion of the gap  125 , the portion overlapping with the electrical component  130  when viewed from the direction perpendicular to the upper surface  120   a  of the optical component  120 , has been illustrated, but the optical component may be bonded in another portion. For example, as illustrated in  FIG. 5 , the optical component  120  may be bonded by the adhesive  205  in a portion of the gap  125 , the portion being along one side of the upper surface  120   a , the one side overlapping with the electrical component  130  when viewed from the direction perpendicular to the upper surface  120   a  of the optical component  120 . Further, for example, as illustrated in  FIG. 6 , the optical component  120  may be bonded by the adhesive  205  in a portion of the gap  125 , the portion being along one side of the upper surface  120   a  and two sides continuous to the one side, the one side overlapping with the electrical component  130  when viewed from the direction perpendicular to the upper surface  120   a  of the optical component  120 . Further, for example, as illustrated in  FIG. 7 , the optical component  120  may be bonded by the adhesive  205  in a portion of the gap  125 , the portion being along one side of the upper surface  120   a  and halves of two sides continuous to the one side, the one side overlapping with the electrical component  130  when viewed from the direction perpendicular to the upper surface  120   a  of the optical component  120 . Further, for example, as illustrated in  FIG. 8 , the optical component  120  may be bonded by the adhesive  205  in a portion of the gap  125 , the portion being along one side of the upper surface  120   a , the one side not overlapping with the electrical component  130  when viewed from the direction perpendicular to the upper surface  120   a  of the optical component  120 . Further, for example, as illustrated in  FIG. 9 , the optical component  120  may be bonded by the adhesive  205  in portions of the gap  125 , the portions being along both two sides that are continuous to one side of the upper surface  120   a , the one side overlapping with the electrical component  130  when viewed from the direction perpendicular to the upper surface  120   a  of the optical component  120 . Further, for example, as illustrated in  FIGS. 10 and 11 , the optical component  120  may be bonded by the adhesive  205  in a portion of the gap  125 , the portion being along one of two sides that are continuous to one side of the upper surface  120   a , the one side overlapping with the electrical component  130  when viewed from the direction perpendicular to the upper surface  120   a  of the optical component  120 .  FIGS. 5 to 11  are views illustrating modification examples 1 to 7, respectively, of the bonding portion of the optical component  120  with the adhesive  205 . In any of the cases illustrated in  FIGS. 5 to 11 , the optical component  120  is bonded to the inner wall surface of the through hole  111  by the adhesive  205  in a portion of the gap  125 . Then, in any of the cases illustrated in  FIGS. 5 to 11 , concentration of stress on the connecting portions of the electrical component  130  to the electrode on the optical component  120  and the electrode on the substrate  110  is reduced, and thus damage or peeling to the electrical component  130  may be suppressed. 
       FIGS. 12 to 14  are diagrams illustrating an example of a result of simulating stress on connecting portions of the electrical component  130  to electrodes on the substrate  110 .  FIG. 12  illustrates, as a comparative example, the stress applied to the connecting portions when the optical component  120  is bonded to the entire gap  125  by the adhesive  205 . Further,  FIGS. 12 to 14  illustrate stress on the connecting portions when the optical component  120  is bonded by the adhesive  205  in the portions illustrated in  FIGS. 5 to 11  in the gap  125  as modification examples 1 to 7. 
     As illustrated in  FIGS. 12 to 14 , in the comparative example in which the optical component  120  is bonded in the entire gap  125 , the maximum value of the stress on the connecting portions of the electrical component  130  to the electrodes on the substrate  110  is 145 MPa. On the other hand, in the embodiment and the modification examples 1 to 7 in which the optical component  120  is bonded in the portion of the gap  125 , the maximum value of the stress on the connecting portions of the electrical component  130  to the electrodes on the substrate  110  is a value smaller than 145 MPa. For example, in the embodiment and the modification examples 1 to 7, it is possible to reduce the concentration of stress on the connecting portions of the electrical component  130  to the electrodes on the substrate  110 , as compared with the comparative examples. Thus, in the embodiment and the modification examples 1 to 7, it is possible to suppress damage or peeling of the electrical component  130 . 
     As described above, the optical module  100  according to the embodiment includes the substrate  110 , the optical component  120 , and the electrical component  130 . The through hole  111  is formed in the substrate  110 . The optical component  120  is arranged in the through hole  111  of the substrate  110 , and is bonded to the inner wall surface of the through hole  111  by the thermosetting adhesive  205  in the portion of the gap  125  between the optical component  120  and the inner wall surface of the through hole  111 , The electrical component  130  is connected to the electrode on the upper surface  120   a  of the optical component  120  and the electrode on the upper surface  110   a  of the substrate  110  across the gap  125  between the optical component  120  and the inner wall surface of the through hole  111 . Thus, the optical module  100  may suppress damage or peeling of the electrical components  130  connected in the bridge form. 
     Note that in the embodiment described above, the case where the optical component  120  is arranged in the through hole  111  formed in the substrate  110  has been illustrated, but the optical component  120  may be arranged in a recess formed in the substrate  110 . For example, the optical component  120  arranged in the recess of the substrate  110  may be bonded to the inner wall surface of the recess by a thermosetting adhesive in a portion of a gap between the optical component  120  and the inner wall surface of the recess. Even when the optical component  120  is arranged in the recess, concentration of stress on the connecting portion of the electrical component  130  to the electrode on the optical component  120  and the electrode on the substrate  110  is reduced, and thus damaging or peeling of the electrical component  130  may be suppressed. 
     All examples and conditional language provided herein are intended for the 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 one or more embodiments of the present invention have 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.