JP6260167B2 - Photoelectric fusion module - Google Patents

Description

  The present invention relates to an optoelectronic module including an optical integrated circuit board and an electric integrated circuit board, and in particular, an optical waveguide and a photodiode (hereinafter referred to as PD) or a laser diode (hereinafter referred to as LD) for high-speed optical communication. ), Etc., and an electrical integrated circuit board on which an electro-optic / photoelectric conversion component is mounted, an LD driver (hereinafter referred to as LDD, also referred to as a drive circuit), a transimpedance amplifier (hereinafter referred to as TIA), and the like. The present invention relates to an optoelectronic module including an integrated circuit board.

  Currently, a PON (Passive Optical Network) system is widely adopted among FTTH (Fiber to the Home) systems that are being introduced. In the PON system, a large number of subscribers share a station-side apparatus OLT (Optical Line Terminal) by branching a single optical fiber from a station by a splitter. An OLT or an ONU (Optical Network Unit) which is a user terminal device uses optical signals of different wavelengths in order to perform bidirectional communication using a single optical fiber.

  This optical component for optical communication is configured to perform electro-optical / photoelectric conversion by being mounted in a module or package together with the electrical component. Non-Patent Document 1 discloses a single-core bidirectional communication module as an example of a photoelectric fusion module (see FIG. 5). This single-core bidirectional communication module has been downsized by mounting electrical components such as LD and PD, which have been individually mounted, on an optical circuit board. In the single-core bidirectional communication module, electrical components and optical components are mounted on the same substrate, whereby wiring is shortened and high-speed and high-frequency characteristics are improved. Patent Document 1 discloses an optoelectronic circuit board in which a double-sided high-density mounting electric circuit board and an optical circuit board are multilayered (see FIG. 6 of the present application).

JP 2006-140178 A (FIG. 5A)

Daisuke Shimura, Hiroko Kotani, Hiroyuki Takahashi, Hideaki Okayama, Hiroki Yaezaki, OKI Technical Review, April 2010 / No. 216 Vol.77 No.1, "Silicon Photonics Photoelectric Fusion Module Technology", p.4-p.7

  The optoelectronic circuit board described in Patent Document 1 (see FIG. 6 of the present application) includes an optical circuit board 32 on which an optical circuit other than communication is mounted and an electric circuit board 31 in a multilayer structure. A component 33 c (for example, LDD) is also provided in the gap 30. Therefore, one electrode of the element or component 35 mounted on the optical circuit board 32 can be brought close to the element or component 33c, but the other electrode is separated from the element or component 33c, and Are connected via vias 42 and 45. For this reason, the length of wiring will become long.

  In the photoelectric circuit board described in Patent Document 1, since the LDD as the element or component 33c serves as a heat generation source, the characteristics of the LDD deteriorate and the reliability decreases. For this reason, the optoelectronic circuit board described in Patent Document 1 has lower reliability due to the temperature rise of peripheral components. In addition, the optoelectronic circuit board described in Patent Document 1 requires high mounting accuracy, which increases the mounting and assembly costs, and various components need to be mounted. To do. In addition, in order to avoid this problem, it is necessary to verify whether it is strictly calculated or prototyped multiple times.

  In the technique of Non-Patent Document 1, the LD as the light emitting element is mounted on the same substrate as the optical integrated circuit, but the LDD as the drive circuit is not mounted on the same substrate. For this reason, there is a problem that the wiring between the LD and the LDD becomes long, and the response characteristic of the LD deteriorates. It is also conceivable that the LDD is mounted on the same substrate as the optical circuit or LD. In this case, when the LDD is mounted on the same substrate, the technology of Non-Patent Document 1 causes the LDD, which is a heat source, to change the characteristics of the LD, PD, etc. on the same substrate, and the characteristics deteriorate due to the temperature rise of the LD. In addition, there is a problem that causes a decrease in reliability. In addition, since LDD is a heat source, it is difficult to individually control the temperature of LD and PD.

  In the technique of Non-Patent Document 1, since the optical circuit and the electric circuit are formed on the same substrate, the mounting cost can be reduced and the characteristics can be improved. However, manufacturing on the same substrate is also a problem that the chip size becomes large. The chip size of the IC affects the yield, and an increase in the chip size causes a decrease in yield. That is, the technique of Non-Patent Document 1 makes an optical circuit and an electric circuit, respectively, and thus tends to cause a yield reduction rather than mounting them individually.

  Therefore, an object of the present invention is to provide a photoelectric fusion module that can shorten the wiring connecting the light emitting element and the drive circuit.

To solve the above problems, the present invention provides optoelectronic module comprising the optical integrated circuit board mounted, including a light emitting element, a driving circuit for driving the light emitting element, and an electrical integrated circuits that integrate the control circuit An anisotropic conductive sheet in which a plurality of metal wires are arranged in the thickness direction is interposed between the optical integrated circuit substrate and the electric integrated circuit, and the electrode of the light emitting element and the drive circuit The electrode is connected via a specific plurality of the metal wires, and any other plurality of the metal wires are in contact with the SiO ₂ surface of the optical integrated circuit substrate .

According to this, since the anisotropic conductive sheet is interposed between the optical integrated circuit substrate and the electric integrated circuit, the light emitting element and the drive circuit are arranged to face each other. For this reason , the wiring connecting the light emitting element and the drive circuit is shortened, and the response characteristics of the light emitting element are improved. In addition , since the optical integrated circuit board is formed on the SiO ₂ surface as an insulator except for electrodes such as light emitting elements, a special insulating sheet is inserted between the anisotropic conductive sheet and the electric integrated circuit board. There is no need to do.

  According to the present invention, the wiring connecting the light emitting element and the drive circuit can be shortened.

1 is a structural diagram of a photoelectric fusion module according to a first embodiment of the present invention. It is a structural diagram of the photoelectric fusion module which is 2nd Embodiment of this invention. It is a structural diagram of an anisotropic conductive sheet. It is a structure figure of the photoelectric fusion module which is 3rd Embodiment of this invention. It is a block diagram of the photoelectric fusion module of a 1st comparative example. It is sectional drawing of the photoelectric fusion module of a 2nd comparative example.

  Hereinafter, an embodiment of the present invention (hereinafter referred to as “the present embodiment”) will be described in detail with reference to the drawings. Each figure is only schematically shown so that the present invention can be fully understood. Therefore, the present invention is not limited to the illustrated example. Moreover, in each figure, the same code | symbol is attached | subjected about the common component and the same component, and those overlapping description is abbreviate | omitted.

(First embodiment)
(Description of configuration)
FIG. 1 is a structural diagram of a photoelectric fusion module according to the first embodiment of the present invention.
The optoelectronic module 10 </ b> A is disposed in close contact with the electrical integrated circuit substrate 11, the optical integrated circuit substrate 13, the heat sink 16 disposed in close contact with the back surface of the electrical integrated circuit substrate 11, and the back surface of the optical integrated circuit substrate 13. A heat sink 17, an electric signal input / output unit 20, a lens 22, an upper case 18 for fixing the heat sink 16, and a lower case 19 for fixing the heat sink 17 are provided. The upper case 18 and the lower case 19 serve as cases. It is fixed by the fixing member 26.

  The upper case 18 and the heat sink 17 can be selected according to cost, such as aluminum and stainless steel. In addition, by combining different materials, it is possible to reduce costs and improve performance. For example, it is preferable to use stainless steel for the upper case 18 and aluminum for the heat sink 17.

  The fixing member 26 is preferably made of a material having a low thermal conductivity such as plastic so that the upper case 18 and the lower case 19 can be thermally separated. Note that the space between the heat sinks 16 and 17 and the upper case 18 and the heat sink 17 is filled with, for example, silver paste, silicon grease, gold-tin eutectic solder, or the like to reduce the contact thermal resistance. In addition, when heat_generation | fever is large, the cases 18 and 19 can also add a cooling mechanism to the exterior.

  The electrical integrated circuit substrate 11 is a rectangular substrate on which a drive circuit (LDD) and a control circuit are integrated as the electrical circuit 12. The optical integrated circuit substrate 13 is a rectangular substrate on which a light emitting element and a light receiving element driven by the drive circuit are mounted as the optical circuit 14 and other optical circuits are integrated. That is, the optical circuit 14 is mainly composed of an optical waveguide, but is mounted with a laser diode LD as a light emitting element and a photodiode PD as a light receiving element, and a plurality of electrodes are formed. The electrodes of the optical circuit 14 and the electrodes of the electric circuit 12 are connected by a connection medium 15 and fixed by a sealing resin 23.

  The heat sinks 16 and 17 are made of a material such as aluminum, copper, or copper tungsten, and are subjected to surface treatment such as gold plating according to the purpose. Since the space between the heat sink 16 and the electric integrated circuit substrate 11 and the space between the heat sink 17 and the optical integrated circuit substrate 13 are filled with, for example, silver paste or gold-tin eutectic solder, the contact thermal resistance is reduced. It has been.

  The electric signal input / output unit 20 means, for example, a pin connected to the outside, a flexible cable, or the like. The lens 20 constitutes an optical signal input / output unit, and the optical signal input / output unit may include an optical fiber connected to the outside.

(Description of operation)
The optical circuit (optical waveguide or LD, PD) 14 produced on the surface of the optical integrated circuit substrate 13 has a large temperature dependency, and in particular, the characteristics of the LD deteriorate with increasing temperature. On the other hand, the electric circuit (particularly LDD) 12 manufactured on the electric integrated circuit substrate 11 generates a large amount of heat.

  By the way, the thermal conductivity is 168 [W / (m · K)] when the general sealing resin 23 is 1 [W / (m · K)] and the electrical integrated circuit substrate 11 is silicon. . That is, the thermal conductivity of the electrical integrated circuit board 11 is higher than that of the sealing resin 23. For this reason, the heat flow generated in the electric circuit 12 flows to the heat sink 16 via the electric integrated circuit board 11 and is transferred from the upper case 18 to the air. A cooling mechanism can be added outside the upper case 18 according to the amount of heat generated.

  The optical integrated circuit board 13 is affected by the heat generated in the electric circuit 12 through the sealing resin 23 and the connection medium 15, but is cooled by the heat sink 17 and the lower case 19 connected to the optical integrated circuit board 13. Therefore, the temperature rise of the optical integrated circuit board 13 is reduced. Further, since the connection medium 15 has a higher thermal conductivity than the sealing resin 23, it can be said that the heat flow is connected at a point.

(Explanation of effect)
According to the optoelectronic module 10A of the present embodiment, since the optical integrated circuit board 13 and the electric integrated circuit board 11 face each other, the mounting area can be almost halved. Further, since the substrate sizes of the integrated circuit substrates 11 and 13 are reduced, a decrease in process yield due to an increase in chip size can be reduced.

In the optoelectronic module 10A, the optical circuit 14 (specifically, LD) and the electric circuit 12 (specifically, LDD) are arranged so as to face each other, so that LD and LDD elements are formed on the same substrate. The effect of heat is less than placing it. For this reason, especially in the case of a transmission rate exceeding 10 Gbps, the electrical characteristics can be improved. That is, the electrical integrated circuit board 11 and the optical integrated circuit board 13 can be thermally separated, and the influence of the heat generated in the electrical circuit 12 on the optical circuit 14 can be reduced. Further, since the electrical integrated circuit board 11 and the optical integrated circuit board 13 are thermally separated from each other, individual temperature control becomes easy. As a result, the optoelectronic module 10A can keep the temperature of the LD mounted on the optical integrated circuit board 13 low, and the characteristics can be improved and stable operation can be achieved.

(Second Embodiment)
(Description of configuration)
FIG. 2 is a structural diagram of a photoelectric fusion module according to the second embodiment of the present invention.
The photoelectric fusion module 10B has the same basic configuration as that of the photoelectric fusion module 10A shown in FIG. 1, but instead of the connection medium 15 and the sealing resin 23, an anisotropic conductive sheet 24 as shown in FIG. It differs in that it is provided. That is, in the optoelectronic module 10 </ b> B, the electrical integrated circuit substrate 11 and the optical integrated circuit substrate 13 are disposed to face each other with the anisotropic conductive sheet 24 interposed therebetween. Thus, the photoelectric fusion module 10B needs to connect the electrical integrated circuit board 11 and the optical integrated circuit board 13 with the connection medium 15 (FIG. 1) or seal with the sealing resin 23 (FIG. 1). Absent.

FIG. 3 is a structural view of the anisotropic conductive sheet, FIG. 3 (a) is a plan view thereof, and FIG. 3 (b) is a cross-sectional view thereof.
As shown in FIG. 3A, in the anisotropic conductive sheet 24, a plurality of fine metal wires (metal wires) are two-dimensionally arranged on the silicone rubber sheet at a constant interval and a high density (approximately 0.1 mm interval). It is a pressure contact type connector. The anisotropic conductive sheet 24 has a good contact property with a low load because the gold-plated fine metal wires protrude from the surface (both sides) of the silicone rubber sheet. That is, anisotropy means having conductivity in the thickness direction of the sheet and not having conductivity between adjacent thin metal wires.

That is, the electrode (electrode pad) of the electric circuit 12 (particularly LDD) and the electrode (electrode pad) of the optical circuit 14 (particularly LD) are electrically connected by the metal thin wire bundle of the anisotropic conductive sheet 24. . At this time, the positions of the electrodes of the electric circuit 12 and the optical circuit 14 (electrodes of the light emitting element and the light receiving element) are a plurality of specific thin metal wires (a plurality of thin metal wires are also referred to as a thin metal wire bundle) in contact with the electrodes. The optical circuit 14 is an insulator such as SiO ₂ except for the electrodes of the light emitting element and the light receiving element, so that the other fine metal wires are in contact with the insulator. Yes. For this reason, when connecting the electric circuit boards with the anisotropic conductive sheet 24, it is necessary to insulate unnecessary thin metal wires by interposing an insulating sheet or the like. This insulating sheet needs to be thinner than the protruding length of the fine metal wire, but this is extremely difficult. Since the optical circuit 14 is mainly made of an insulator (SiO ₂ ), the photoelectric fusion module 10B does not need to interpose an insulating sheet between the electrical integrated circuit board 11 and the anisotropic conductive sheet 24. .

  Further, as shown in FIG. 3B, the anisotropic conductive sheet 24 is shifted by ΔL in one direction between the front surface side and the back surface side. As a result, the bundle of fine metal wires is inclined, and the tip of the inclined fine metal wires and the electrode are in contact with each other with lines or surfaces, so that the contact resistance is further reduced.

(Explanation of effect)
As described above, according to the photoelectric fusion module 10B of the second embodiment, the following effects can be expected in addition to the effects of the first embodiment.
It is not necessary to form the connection medium 15 (FIG. 1) between the electrical integrated circuit board 11 and the optical integrated circuit board 13, and assembly and member costs can be reduced. Since the anisotropic conductive sheet 24 is made of a soft material such as silicone rubber, the degree of freedom in height adjustment when the substrates are stacked and sealed with the module increases (the process can be simplified).

(Third embodiment)
(Description of configuration)
FIG. 4 is a structural diagram of a photoelectric fusion module according to the third embodiment of the present invention.
The photoelectric fusion module 10C has the same basic configuration as that of FIG. 1, but an interposer substrate 25 is interposed between the electric integrated circuit substrate 11 and the optical integrated circuit substrate 13, and each substrate is connected to the interposer substrate 25. They are connected using a medium 15 and sealed with a sealing resin 23. The interposer substrate 25 preferably has a relative dielectric constant of 3.5 or less in order to obtain an insertion effect. In particular, when the frequency band to be handled is a millimeter wave band, a silicon substrate of 2.5 or less is used. As a result, the wiring length and wiring width between chips integrated in the electric circuit 12 can be reduced, and variations in parasitic capacitance and wiring length between the chips can be reduced.

(Description of operation)
The optoelectronic module 10C operates in the same manner as the optoelectronic module 10A of the first embodiment, but electrical connections are made using via holes formed in the interposer substrate 25. At this time, it may be directly connected to the electrical connection point of each substrate through a via hole, or may be connected to the interposer substrate 25 by forming a wiring pattern.

(Explanation of effect)
As described above, according to the photoelectric fusion module 10C, the following effects are provided in addition to the first embodiment.
In the photoelectric fusion module 10C, the heat source (LDD of the electric circuit 12) is separated from the optical circuit 14, so that the effect of heat separation is improved. Further, since the interposer substrate 25 can widen the inter-terminal spacing by making the inter-terminal spacing of the electrical connection portions different from each other, the connection between the light emitting element and the light receiving element of the optical circuit 14 can be simplified. . Further, when a signal in a high frequency band such as 60 GHz is used, peripheral parasitic capacitance becomes a problem, but the photoelectric fusion module 10C responds by using an interposer substrate 25 made of a low dielectric constant material (for example, silicon). Improved characteristics.

(First comparative example)
FIG. 5 is a configuration diagram of the photoelectric fusion module of the first comparative example.
The optoelectronic module 10D is a single-core bidirectional communication module, and includes a Si substrate 3, an optical circuit 1 and an electric circuit 2 formed on the surface of the Si substrate 3, and the electric circuit 2 serves as a light receiving element. A photodiode 2a, a laser diode 2b as a light emitting element, a transimpedance amplifier 2c, and a monitoring photodiode 2d are provided. In the optical circuit 1, a spot size converter 1b and a wavelength multiplexer / demultiplexer 1a are formed. Note that the single-core bidirectional communication module described as the first comparative example can be used as the optical circuit 14 of the first to third embodiments.

  The wavelength multiplexer / demultiplexer 1a is composed of a silicon thin wire waveguide, guides the light emitted from the laser diode 2b to the spot size converter 1b, and enters the light guided from the spot size converter 1b into the photodiode 2a. It is something to be made. In addition, since two-way communication is performed using one optical fiber, the wavelength of light incident on the photodiode 2a is cut off from the wavelength of light emitted by the laser diode provided at the other end of the optical fiber. ing. For example, when the transmission wavelength of the laser diode 2b is 1.310 nm and the reception wavelength of the photodiode 2a is 1.49 nm, the wavelength of light incident on the photodiode 2a is a laser provided at the other end of the optical fiber. The wavelength of light emitted by the diode is cut off at 1.310 nm. The silicon thin wire waveguide is an optical waveguide having a core material made of silicon and a clad material made of quartz, and the light path can be bent sharply as compared with a conventionally used quartz optical waveguide.

  The spot size converter 1b couples between an optical fiber (not shown) and a silicon fine wire waveguide, and uses a tapered taper type. That is, the spot size converter 1b has a function of converting the size of the light beam spot, and is provided in order to reduce the optical power loss in the optical input / output. Note that a taper type spot size conversion is used between the laser diode 2b and the waveguide, and a grating type is used between the photodiode 2a and the waveguide.

The photodiode 2a as the light receiving element and the laser diode 2b as the light emitting element are mounted on the surface of the Si substrate 3 by surface mounting. The transimpedance amplifier 2c converts the current generated by the photodiode 2a into a voltage while virtually grounding the voltage across the photodiode 2a.
The monitoring photodiode 2c is for monitoring the optical output of the laser diode 2b and performing feedback control, and is disposed in proximity to the laser diode 2b.

  In this optoelectronic module 10D, since the area of the electric circuit 2 formed of the Si substrate 3 and the area of the optical circuit 1 are almost the same area, the occupied area is the same as that of the optoelectronic modules 10A, 10B, and 10C of the above embodiment. About twice as much. Moreover, although the transimpedance amplifier 2c is mounted on the photoelectric fusion module 10D, the LDD that is a heating element is not mounted. For this reason, in the photoelectric fusion module 10D, the wiring between the LD and the LDD becomes longer than the photoelectric fusion modules 10A, 10B, and 10C, and the high-frequency characteristics are deteriorated.

(Second comparative example)
FIG. 6 is a cross-sectional view of the photoelectric fusion module of the second comparative example.
The optoelectronic module 10E is an optoelectronic circuit board in which an electric circuit board 31 and an optical circuit board 32 are arranged to face each other via a gap 30. The electric circuit board 31 is a multilayer board (five-layer board). The pattern of each layer is connected by a plurality of vias 41, 42, 43, 44, 45.
The electric circuit board 31 has elements or components 33 (33 a, 33 b, 33 c) mounted on both side surfaces thereof, and opposes the optical circuit board 32 through the gap 30. In the optical circuit board 32, an element or component 35 (for example, a light emitting element or a light receiving element) is mounted on the surface on the electric circuit board 31 side.

The electric circuit board 31 and the optical circuit board 32 are connected by a connection medium 34 (34a, 34b, 34c, 34d).
Since the element or component 35 (for example, LD) is disposed in proximity to the element or component 33c (for example, LDD), the element or component 33c and the connection medium 34b are disposed in proximity to each other. However, the connection media 34a and 34d are not only separated from the element or component 33c but also connected from other layers. Since the connection medium 34c and the connection medium 34b are insulated, the connection medium 34c is also connected from other layers.

  That is, in the photoelectric fusion modules 10A, 10B, and 10C of the embodiment, the electric circuit 12 (particularly, the drive circuit (LDD)) and the optical circuit 14 (particularly, the light emitting element (LD)) are disposed to face each other. With respect to the photoelectric fusion module 10E, the wiring distance is shortened, and the response characteristics of the light emitting element are improved.

  The electric circuit board 31 is made of a glass epoxy board, and its thermal conductivity is about 0.5 [W / (m · K)]. On the other hand, the optical integrated circuit substrate 13 is made of silicon, and its thermal conductivity is about 150 [W / (m · K)]. Therefore, in the first to third embodiments, the effect of the heat sink 16 closely arranged on the back surface of the electrical integrated circuit substrate 11 is greater than that of the second comparative example.

(Modification)
The present invention is not limited to the embodiments described above, and various modifications such as the following are possible.
(1) In the embodiment, the optical integrated circuit board 13 is used to connect to the electrical signal input / output unit 20, but the electrical integrated circuit board 11 may be used to connect to the electrical signal input / output unit 20.
(2) In the first to third embodiments, the optical integrated circuit board 13 and the electric integrated circuit board 11 have been described. However, between the electric integrated circuit board 11 and the electric integrated circuit board 11, or the optical integrated circuit. It can also be used between the substrate 13 and the optical integrated circuit substrate 13.
(3) Although the first embodiment to the third embodiment have been described on the premise that they are used in a metal case, flexible materials such as TCP (Tape Carrier Package) and other materials may be used.
(4) In the first embodiment and the third embodiment, the chip is fixed using the sealing resin 23, but it can be fixed only by the connection medium 15.
(5) In the first to third embodiments, the description has been made by directly electrically connecting to the circuit forming surface of the electric circuit board. However, a component having a shape such as WL-CSP (Wafer Level Chip Size Package) is used. It can also be installed.
(6) In the third embodiment, only the interposer substrate 25 is inserted. However, the anisotropic conductive sheet 24 can be combined and inserted.
(7) In the third embodiment, the interposer substrate 25 having only electrical connection has been described, but a component-embedded substrate can also be used.

DESCRIPTION OF SYMBOLS 1 Optical circuit 1a Wavelength multiplexer / demultiplexer 1b Spot size converter 2 Electric circuit 2a Photodiode 2b Laser diode 2c Transimpedance amplifier 2d Photodiode for monitoring 3 Si substrate 10, 10A, 10B, 10C, 10D, 10E Photoelectric fusion module 12 Electrical circuit 13 Optical integrated circuit board 14 Optical circuit 15 Connection medium 16, 17 Heat sink 18 Upper case 19 Lower case 20 Electric signal input / output unit 22 Lens 23 Sealing resin 24 Anisotropic conductive sheet 25 Interposer substrate 26 Fixing member 30 Gap 31 Electrical circuit board 32 Optical circuit board 33, 35 Element or part 34 Connection medium 41, 42, 43, 44, 45 Via

Claims (4)

And an optical integrated circuit board mounted, including a light emitting element, a optoelectronic module comprising an electrical integrated circuits with an integrated driving circuit, and a control circuit for driving the light emitting element,
An anisotropic conductive sheet in which a plurality of metal wires are arranged in the thickness direction is interposed between the optical integrated circuit substrate and the electric integrated circuit,
The electrode of the light emitting element and the electrode of the drive circuit are connected via a specific plurality of the metal wires,
Any other plurality of metal lines, the optoelectronic module according to claim <br/> to contact the SiO ₂ surface of the optical integrated circuit substrate. The photoelectric fusion module according to claim 1,
  An electric circuit board on which the electric integrated circuit is mounted;
  A heat sink disposed in close contact with the back side of the electric circuit board;
  The electrical circuit board is thermally separated from the optical integrated circuit board by the anisotropic conductive sheet.
A photoelectric fusion module characterized by that. The photoelectric fusion module according to claim 2,
  The optical integrated circuit board and the electric circuit board are configured to individually control the temperature.
A photoelectric fusion module characterized by that. It is a photoelectric fusion module as described in any one of Claim 1 thru | or 3, Comprising :
The anisotropic conductive sheet is shifted in one direction on the front side and the back side,
The photoelectric fusion module , wherein the metal wire is inclined .

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