Patent Application
20190097735
This application is based upon and claims priority to Japanese Patent Application No. 2017-188251, filed on Sep. 28, 2017, the entire contents of which are incorporated herein by reference.
The disclosures herein generally relate to an optical module.
Optical communications are becoming widely used in the field of supercomputers and high-end servers supporting high-speed signal transmission via high-speed interfaces. In particular, for next-generation interfaces currently developed, such as InfiniBand Trade Association (IBTA) EDR (registered trademark) and 100G Ethernet (registered trademark), optical communications are used because of a long signal transmission distance. In optical communications, optical modules are used to convert an electrical signal into an optical signal. The optical module converts an input optical signal into an electrical signal. Also, the optical module converts an input electrical signal into an optical signal.
The optical module includes a light emitter that converts an electrical signal into an optical signal, a light receiver that converts an optical signal into an electrical signal, a drive IC (integrated circuit) that drives the light emitter, and a TIA (transimpedance amplifier) that converts an electrical current into voltage. The light emitter, the light receiver and semiconductor devices such as the drive IC and the TIA are mounted on a FPC (flexible printed circuit).
The devices mounted on the FPC generate heat when the optical module is in operation, resulting in an elevated temperature. In order to prevent a failure due to such heat, Patent Document 1 discloses a heat dissipation sheet disposed above a surface of a FPC on which devices are mounted, and is interposed between an upper cover and a lower cover. Accordingly, the dissipation sheet is brought into contact with the upper cover, and compressive stress is applied. This improves the efficiency of heat dissipation from the photoelectric conversion devices and the semiconductor devices.
When compressibility of the dissipation sheet is within a range of approximately 30% to 50%, the efficiency of heat dissipation improves. Thus, the dissipation sheet is preferably placed in the housing while being pressed such that the compressibility falls within the predetermined range. However, in Patent Document 1, because there are a number of parts between which the dissipation sheet is positioned, assembly dimensional tolerance becomes large, and a pressuring force applied to the dissipation sheet may become too weak or too strong. In this case, the compressibility falls outside the predetermined range and the photoelectric conversion devices and the semiconductor devices may fail to have a sufficient heat dissipation effect, and characteristics of the photoelectric conversion devices and the semiconductor devices may decrease.
According to an embodiment, an optical module includes a housing having an upper cover and a lower cover; a substrate having a circuit device mounted on its first surface; a heat dissipation member configured to be in contact with the circuit device mounted on the substrate; and at least one inner case having stiffness, wherein the upper cover is disposed facing the first surface of the substrate, and the lower cover is disposed facing a second surface of the substrate, and the inner case is disposed so as to press the substrate from the second surface of the substrate toward the upper cover.
According to at least one embodiment, it is possible to provide an optical module having high efficiency of heat dissipation from a circuit device, such as a photoelectric conversion device and a semiconductor device, disposed in a housing.
In the following, embodiments of the present invention will be described with reference to the accompanying drawings. For convenience of explanation, the same elements are denoted by the same reference numerals in the drawings, and a duplicate description thereof will be omitted.
Referring to
In the following, three axes (an x-axis, a y-axis, and a z-axis) perpendicular to each other are used as references to describe shapes of elements and positional relationships between the elements of the optical module 1. As illustrated in
As illustrated in
A FPC connector 11 to which to connect the FPC 12 (a substrate) is provided on the printed circuit board 10. The light emitter 13 such as a vertical-cavity surface-emitting laser (VCSEL) that converts an electrical signal into an optical signal, the light receiver 14 such as a photodiode that converts an optical signal into an electrical signal, a drive IC 15 that drives the light emitter 13, and a TIA 16 that converts an electrical current from the light receiver 14 into voltage are mounted on the upper surface of the FPC 12. Also, a connection terminal 17 for external connection is provided on +x side. The printed circuit board 10 is placed on the lower cover 51.
In the present embodiment, the light emitter 13 and the light receiver 14 are collectively referred to as a “photoelectric conversion device”. Further, the drive IC 15 and the TIA 16 are collectively referred to as a “semiconductor device”. The photoelectric conversion device and the semiconductor device are collectively referred to as a “circuit device”.
The optical waveguide 20 is a flexible sheet-shaped optical waveguide and extends in x-direction. A +x side end of the optical waveguide 20 is connected to the FPC 12. A −x side end of the optical waveguide 20 is connected to the lens ferrule 31. A connection part of the optical waveguide 20 and the lens ferrule 31 is protected by a ferrule boot (not illustrated).
The ferrule 30 includes the lens ferrule 31 and a mechanically transferable (MT) ferrule 32. The lens ferrule 31 and the MT ferrule 32 are connected to each other along x-direction and are held by the clip 40 so as to be fixed. The MT ferrule 32 is a ferrule that can hold a multi-core optical fiber. The lens ferrule 31 is designed to have higher density than the MT ferrule 32. For example, in a Quad Small Form-factor Pluggable (QSFP) optical connector, by connecting and aligning the MT ferrule 32 with the lens ferrule 31, the optical cable 60 connected to the MT ferrule 32 and the optical waveguide connected to the lens ferrule 31 are coupled to each other.
The ferrule 30 is disposed above the lower cover 51. The clip 40 has two screw holes 40a. Once two threads 51a provided on the lower cover 51 are positioned to match the screw holes 40a, screws 53 are inserted. By screwing the clip 40 to the lower cover 51, the ferrule 30 is fixed to the lower cover 51 via the clip 40.
The FPC 12 is interposed between an upper inner case 81 and a lower inner case 82 and is held from above and below. The upper inner case 81 covers the upper surface of the FPC 12, and the lower inner case 82 covers the lower surface of the FPC 12. The upper inner case 81 and the lower inner case 82 are harder than the FPC 12, and are formed of a material having high heat dissipation efficiency. Also, the upper inner case 81 and the lower inner case 82 are formed of a material having stiffness. As used herein, “stiffness” means the extent to which a material resists a deformation in response to an applied force such as in bending or torsion. Having stiffness means less deformation and high stiffness under an applied force. Stiffness includes axial stiffness, bending stiffness, shear stiffness, and torsional stiffness.
Examples of the material of the upper inner case 81 and the lower inner case 82 include metal, ceramics, and plastic containing metal filler. For example, the upper inner case 81 and the lower inner case 82 may be manufactured by processes such as die-cast molding, cutting, press working, or bending.
A heat dissipation sheet 83 is placed above the upper surface of the FPC 12 on which the circuit devices are mounted. The heat dissipation sheet 83 conducts heat generated by the circuit devices toward the upper cover 52, such that heat is released. The heat dissipation sheet 83 is designed to have a size that allows the heat dissipation sheet 83 to make contact with at least upper surfaces of the circuit devices and cover the upper surfaces. The heat dissipation sheet 83 is inserted between the upper inner case 81 and the upper surface of the FPC 12. The heat dissipation sheet 83 is formed mainly of a silicon material and has flexibility.
An electric wave absorption sheet 84 for absorbing electric wave, an example of a wave absorption member, is placed between the lower surface of the FPC 12 and the lower inner case 82. The wave absorption sheet 84 has a cutout so as not to overlap the optical waveguide 20. Accordingly, when the wave absorption sheet 84 is inserted between the FPC 12 and the lower inner case 82, the wave absorption sheet 84 does not overlap the optical waveguide 20 in z-direction, as illustrated in
As illustrated in
The upper inner case 81, the heat dissipation sheet 83, the FPC 12, the wave absorption sheet 84, and the lower inner case 82 are stacked in this order, and fixed to the upper cover 52. As illustrated in
Further, a leaf spring 86 is placed between the lower inner case 82 and the printed circuit board 10 located therebelow. The leaf spring is disposed approximately at the center of the lower inner case 82, and is preferably disposed right below the heat dissipation sheet 83. The leaf spring 86 is sandwiched between the lower inner case 82 and the printed circuit board 10 so as to apply a pressing force toward the upper cover 52.
Also, as illustrated in
The vicinity of the end of the optical cable 60 to which to connect the MT ferrule 32 is covered by cable boots 71 and 72 from above and below, and further, a latch is attached thereto.
The ferrule 30 is fixed to the lower cover 51 via the clip 40, and the printed circuit board 10 is mounted on the lower cover 51. Then, the upper cover 52 having the FPC 12 fixed to its lower surface is placed over the lower cover 51. In this state, two screw holes 52a of the upper cover 52 are positioned to match two threads 51b, and the upper cover 52 is screwed to the lower cover 51 with screws 54.
The optical module 1 according to the first embodiment includes the housing having the upper cover 52 and the lower cover 51, the FPC 12 on which the circuit devices are mounted, and the heat dissipation sheet 83 in contact with the light emitter 13, the light receiver 14, the drive IC 15, and the TIA 16 mounted on the FPC 12. The optical module 1 also includes the upper inner case 81 and the lower inner case 82 respectively disposed at the upper surface and the lower surface of the FPC 12. The upper inner case 81 and the lower inner case 82 are placed so as to apply a pressing force to the FPC 12 toward the upper cover 52.
In the optical module disclosed in Patent Document 1, the heat dissipation sheet is held by 6 parts corresponding to the upper cover 52, an electronic component such as the drive IC 15, the FPC 12, the wave absorption sheet 84, the printed circuit board 10, and the lower cover 51, and receives a pressing force from these parts. The parts holding the heat dissipation sheet 83 each have tolerances. When the number of parts is large, tolerance stacking increases in accordance with the number of parts. As a result, the final assembly dimensional tolerance becomes large. If the assembly dimensional tolerance is large, a range in which the heat dissipation sheet receives the pressing force expands. This may cause the pressing force to become too weak or too strong. In this case, compressibility of the heat dissipation sheet falls outside of a range of approximately 30% to 50%, failing to sufficiently release heat from the photoelectric conversion device and the semiconductor device mounted on the FPC. As a result, characteristics of the circuit devices decrease. Alternatively, when excessive force is applied to the circuit devices, the devices may be damaged.
Conversely, in the optical module 1, the heat dissipation sheet 83 is held by 5 parts of the upper inner case 81, the electronic component such as the drive IC 15, the FPC 12, the wave absorption sheet 84, and the lower inner case 82. Accordingly, as compared to the conventional configuration, the optical module 1 according to the first embodiment can reduce the number of parts involved in applying a pressing force to the heat dissipation sheet 83. As the number of parts decreases, assembly dimensional tolerance can be reduced. Thus, compressibility of the dissipation sheet 83 can be easily maintained in the appropriate range, and efficiency of heat dissipation from the photoelectric conversion device and the semiconductor device mounted on the FPC 12 inside the housing can be improved.
Further, in the first embodiment, the upper inner case 81 covers the upper surface of the FPC 12, and the lower inner case 82 covers the lower surface of the FPC 12. Although the FPC 12 is very thin and flexibly deforms, the upper inner case 81 and the lower inner case 82 have stiffness and are formed of a material harder than that of the FPC 12. Accordingly, by interposing the FPC 12 between the upper inner case 81 and the lower inner case 82, the FPC 12 can be surrounded by a rigid body. Thus, the flexibility of the FPC 12 can be suppressed such that the FPC 12 is not distorted. Accordingly, in an assembly process, the FPC 12 can be prevented from unnecessarily bending and can be easily placed, allowing yield and reliability to improve.
Further, in the first embodiment, because the wave absorption sheet 84 is inserted into a space between the lower surface of the FPC 12 and the lower inner case 82, an effect of electromagnetic interference (EMI) can be suppressed.
Further, in the first embodiment, the recess 52b is formed on the lower surface of the upper cover 52 such that a part of the upper inner case 81 is fitted in the recess 52b during assembly. Thus, the upper inner case 81 can be easily attached to the upper cover 52.
The heat dissipation sheet 83 is not required to have a sheet shape as long as heat generated by the FPC 12 can be conducted to the upper cover 52. Similarly, the wave absorption sheet 84 is not required to have a sheet shape as long as a wave absorption member of the other shape can suppress EMI.
Referring to
As illustrated in
The heat dissipation sheet 83, the FPC 12, the wave absorption sheet 84, and the inner case 182 are stacked in this order, and are fixed to the upper cover 52 by inserting screws 85 into two through-holes 82a, 82a of the inner case 182 and fastening the screws to the upper cover 52. Further, the leaf spring 86 is placed between the inner case 182 and the printed circuit board 10.
The optical module 1A has a configuration in which the upper cover 52, the heat dissipation sheet 83, the electronic component such as the drive IC 15, the FPC 12, the wave absorption sheet 84, and the inner case 182 are stacked and assembled. The heat dissipation sheet 83 is held by five parts, the upper cover 52, the electronic component, the FPC 12, the wave absorption sheet 84, and the inner case 182. Namely, the optical module 1A can further reduce the number of parts involved in applying a pressing force to the heat dissipation sheet 83. Accordingly, assembly dimensional tolerance can be further reduced and efficiency of heat dissipation from the circuit devices device mounted on the FPC can be further improved.
Referring to
As illustrated in
The heat dissipation sheet 83, the FPC 12, and the wave absorption sheet 84 are stacked in this order, and held by the inner cases 281 and 282 while being accommodated inside the inner cases 281 and 282. The inner cases 281 and 282 are coupled to each other at an approximately center position in the width direction of the FPC 12. The screws 85 are inserted into through-holes 281a, 282a of the inner cases 281 and 282, and are fastened to the upper cover 52. Accordingly, the inner cases 281 and 282, the heat dissipation sheet 83, the FPC 12, and the wave absorption sheet 84 are integrally fixed to the upper cover 52. Further, the leaf spring 86 is placed between the inner cases 281 and 282 and the printed circuit board 10 located below the inner cases.
Similarly to the first embodiment, the optical module 1B can also reduce the number of parts involved in applying a pressing force to the heat dissipation sheet 83. Thus, assembly dimensional tolerance can be reduced, and also efficiency of heat dissipation from the circuit device mounted on the FPC 12 can be improved.
The inner cases 281 and 282 are not limited to a configuration in which an inner case is divided into two in y-direction. Any inner case may be adopted as long as the heat dissipation sheet 83, the FPC 12, and the wave absorption sheet 84 are accommodated inside the inner case and the upper surface and the lower surface of the FPC 12 are covered by the inner case. For example, a box-shaped inner case having an inner space and also having a lid on −x side can be used. In this configuration, after the lid is opened, the heat dissipation sheet 83, the FPC 12, and the wave absorption sheet 84 are inserted into the inner space from the opening. Then, by closing the lid, the heat dissipation sheet 83, the FPC 12, and the wave absorption sheet 84 can be accommodated in the inner case.
Referring to
As illustrated in
As illustrated in
As illustrated in
Although the embodiments have been specifically described above, the present disclosure is not limited to the above-described embodiments. These specific embodiments may be modified by a person skilled in the art as long as the features of the present disclosure are included. Elements and their arrangement, conditions, and shapes are not limited to the above-described embodiments and may be modified as necessary. It should be noted that combination of the elements of the above-described embodiments may be changed as long as no technical contradiction occurs.
In the above-described embodiments, the FPC 12 has been described as an example of a substrate on which the circuit devices are mounted. However, instead of the FPC 12, a rigid substrate may be used.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-188251 | Sep 2017 | JP | national |
