Optical Module

Abstract

The optical module comprises: a metal tube seat (10); a signal pin (13) which passes through a through hole (10c) of the tube seat (10); a ground pin (14) which comprises a pin portion (14a) and a joint portion (14b) which is larger in diameter than the pin portion (14a) and is joined to an outer plane (10b) of the tube seat (10); a flexible wiring substrate which comprises a wiring pattern (32) on the front side and a ground pattern (33) on the back side, wherein the ground pattern (33) has an exposed surface at a position opposite to the outer plane of the tube seat (10), and the flexible wiring substrate is formed with an outer lead for the signal pin (13). A first through hole (36) through which the lead portion (13b) of the signal pin (13) passes, the front end portion of the outer lead portion (13b) of the signal pin (13) passing through the first through hole (36) being electrically connected to the wiring pattern (32), a second through hole (37) formed on the flexible wiring substrate for the pin portion (14a) of the ground pin (14) to pass through, the front end portion of the pin portion (14a) of the ground pin (14) passing through the second through hole (37) being electrically connected to the second through hole on the front side; and a metal plate (4) having a back side bonded to the outer plane (10b) of the tube seat (10) and a front side bonded to the exposed surface of the ground pattern (33).

Description

Technical Field

[0001] The present disclosure relates to an optical module including a flexible printed circuit board (FPC). Background Art

[0002] Patent Document 1 is known as an optical module including a flexible printed circuit board (FPC).

[0003] Patent document 1 shows a TO-CAN (Transistor Outlined CAN) type TOSA (Transmitter Optical Sub-Assembly) module, in which the ground plane of the stem contacts the ground plane of the flexible wiring substrate in order to suppress energy loss at the junction of the stem and the flexible wiring substrate.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2011-108940 Summary of the invention

[0007] Problems to be solved by the invention

[0008] On the other hand, an optical module is also known in which a ground pin is fixed to the outer surface of a stem by soldering and the ground pin is connected to a ground plane of a flexible wiring substrate.

[0009] In this optical module, the ground pin is thin. If the ground pin is welded to the outer surface of the tube holder in a thin state, the fixation between the outer surface of the tube holder and the ground pin is likely to become insufficient. Therefore, a welding portion with a larger diameter than the diameter of other portions is generally provided at the welding portion welded to the outer surface of the tube holder, that is, the root portion of the ground pin.

[0010] If the technique of making the ground plane of the stem contact the ground plane of the flexible wiring board as shown in Patent Document 1 is applied to this type of optical module, the diameter of the through hole provided in the flexible wiring board through which the ground pin passes needs to be increased in accordance with the soldering portion of the ground pin.

[0011] If the diameter of the through hole is increased, there is a problem that the area available for wiring formed on the flexible wiring substrate is reduced, and the degree of freedom in wiring design is reduced.

[0012] The present disclosure is completed in view of the above-mentioned points, and its purpose is to obtain an optical module, which includes a flexible wiring substrate and a ground pin, wherein the front end portion of the pin portion of the ground pin is electrically connected to the ground pattern of the flexible wiring substrate, and a joint portion having a diameter larger than the diameter of the pin portion and joined to the outer surface of the stem is provided at one end of the pin portion. In the optical module, the diameter of the through hole for the ground pin can be made to match the diameter of the pin portion without impairing the freedom of wiring design in the flexible wiring substrate.

[0013] Means for solving problems

[0014] The optical module disclosed in the present invention comprises: a metal stem, which has an inner plane and an outer plane, and a through hole formed therein that passes through the inner plane and the outer plane; a signal pin that passes through the through hole of the stem and is fixed to the stem in an electrically insulated manner, and comprises an inner lead portion that protrudes from the inner plane of the stem and an outer lead portion that protrudes from the outer plane of the stem; a ground pin that comprises a pin portion, and a bonding portion that has a larger diameter than the pin portion and is bonded to the outer plane of the stem at one end of the pin portion; and a flexible wiring substrate that has a wiring pattern on the front surface and a ground pattern on the back surface, the ground pattern The pattern has an exposed surface at a position opposite to the outer plane of the tube holder, a first through hole is formed at a position opposite to the signal pin on the wiring pattern, the outer lead portion of the signal pin passes through the first through hole, and the front end portion of the outer lead portion of the signal pin is electrically connected to the wiring pattern, a second through hole is formed at a position opposite to the ground pin on the exposed surface of the ground pattern, the pin portion of the ground pin passes through the second through hole, and the front end portion of the pin portion of the ground pin is electrically connected to the second through hole on the front side; and a metal plate, the back side of which is bonded to the outer plane of the tube holder and the front side is bonded to the exposed surface of the ground pattern.

[0015] Effects of the Invention

[0016] According to the present disclosure, there is an effect that the degree of freedom of wiring design in the flexible wiring substrate is not impaired due to the ground pin having a bonding portion bonded to the outer surface of the stem. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a cross-sectional view showing the optical module according to the first embodiment.

[0018] Figure 2 This is an enlarged view showing the connection between the stem and the flexible wiring board in the optical module according to the first embodiment.

[0019] Figure 3 This is a cross-sectional view showing the positional relationship between the flexible wiring board and the plate in the optical module according to the first embodiment.

[0020] Figure 4This is a plan view showing the positional relationship between the flexible wiring board and the plate in the optical module according to the first embodiment.

[0021] Figure 5 This is a diagram showing frequency characteristics in the optical module according to the first embodiment. DETAILED DESCRIPTION

[0022] Implementation Method 1

[0023] use Figures 1 to 4 , the optical module of implementation mode 1 is described.

[0024] In addition, in each figure, the same reference numerals represent the same or corresponding parts.

[0025] The optical module targeted by the present disclosure is a CAN packaged optical module including an optical transmitting module equipped with a semiconductor laser for optical communication as a light-emitting element, an optical receiving module equipped with a photodiode for optical communication as a light-receiving element, and an optical transceiver module equipped with a semiconductor laser for optical communication and a photodiode for optical communication.

[0026] In the first embodiment, the optical transmission module is used as an example for explanation, but the relationship among the stem, flexible printed circuits (FPC), signal pins, ground pins, and the board is the same in the optical reception module and the optical transceiver module.

[0027] The optical module includes an optical module body 1 , a flexible wiring board 3 , and a board 4 .

[0028] The optical module body 1 includes a stem 10 , a lens cover 11 , a lens 12 , a signal pin 13 , a ground pin 14 , a thermoelectric cooler 15 , a base 16 , an auxiliary mount 17 , a semiconductor light emitting element 18 as a semiconductor laser, a terminal resistor 19 , and a dielectric substrate 20 .

[0029] The stem 10 is made of a disk-shaped metal and has an inner flat surface 10 a and an outer flat surface 10 b . A through hole 10 c is formed between the inner flat surface 10 a and the outer flat surface 10 b .

[0030] The stem 10 functions as a heat sink for the semiconductor light emitting element 18, and the inner surface 10a serves as a region for mounting components.

[0031] The stem 10 is not limited to a disc shape, and may be a cylindrical shape or a quadrangular prism shape as long as it is a flat plate shape having an inner flat surface 10 a and an outer flat surface 10 b parallel to the inner flat surface 10 a .

[0032] The lens cover 11 is formed of a cylindrical metal having a bottom and a side wall with one end open. A lens mounting opening is formed at the bottom of the lens cover 11 for mounting, i.e. mounting, a glass spherical lens 12. The lens 12 is mounted in the lens mounting opening at the bottom in a manner that airtightness is maintained inside and outside the lens cover 11.

[0033] The end surface of the side wall portion of the lens cover 11, that is, the one open end surface, is in contact with the peripheral end portion of the inner plane 10a of the stem 10 and fixed by soldering or the like. The one open end surface of the lens cover 11 is fixed to the inner plane 10a of the stem 10 in a manner that airtightness is maintained inside and outside the lens cover 11. This fixing and mounting is performed at the end of the manufacturing process.

[0034] The stem 10 and the lens cover 11 form a CAN type package.

[0035] The signal pin 13 passes through the through hole 10c of the stem 10 and is fixed to the stem 10 by the insulating glass 21 filled and cured between the signal pin 13 and the through hole 10c. The insulating glass 21 electrically insulates the signal pin 13 from the stem 10 and seals the through hole 10c of the stem 10 to maintain the airtightness in the CAN type package.

[0036] The signal pin 13 includes an inner lead portion 13 a protruding from an inner plane 10 a of the stem 10 and an outer lead portion 13 b protruding from an outer plane 10 b of the stem 10 .

[0037] In the figure, only the semiconductor light emitting element 18 is shown, but a light receiving element as a photodiode that receives back light from the semiconductor light emitting element 18 and monitors output light, and a temperature adjustment device that adjusts the temperature of the semiconductor light emitting element 18 are also installed in the CAN type package.

[0038] Although not shown, there are power supply pins for the semiconductor laser 18 and the light receiving element, etc., and these are fixed to the stem 10 in an electrically insulated manner, similarly to the signal pins 13 .

[0039] The ground pin 14 includes a pin portion 14a and a joint portion 14b having a larger diameter than the pin portion 14a and joined to the outer plane 10b of the stem 10 at one end. The pin portion 14a has the same diameter as the signal pin 13.

[0040] The ground pin 14 has a step between the pin portion 14 a and the bonding portion 14 b , and the bonding portion 14 b is a stepped portion with respect to the pin portion 14 a .

[0041] The joint surface of the joint portion 14b in the ground pin 14 is joined to the outer plane 10b of the stem 10 by welding.

[0042] Thermoelectric cooler 15 is mounted on inner plane 10a of stem 10 to cool semiconductor light emitting element 18. Heat generated by cooling semiconductor light emitting element 18 is dissipated to the outside from stem 10. Thermoelectric cooler 15 is, for example, a Peltier element as a cooling element. In addition, thermoelectric cooler 15 is not essential.

[0043] A flat plate-shaped base 16 is vertically fixed to the thermoelectric cooler 15. When the thermoelectric cooler 15 is not required, the base 16 is vertically fixed to the inner plane 10a of the stem 10.

[0044] The submount 17 is mounted, ie, attached, on one plane of the base 16. The submount 17 is a ceramic substrate made of aluminum nitride having a thermal linear expansion coefficient close to that of the semiconductor light emitting element 18.

[0045] A semiconductor light emitting element 18 is mounted on one plane of the auxiliary mount 17 .

[0046] The semiconductor light emitting element 18 is mounted by die bonding with solder or a conductive adhesive on a first electrode connection region provided on one plane of the auxiliary mount 17 by vapor deposition or the like, and is mounted and fixed on the one plane of the auxiliary mount 17 .

[0047] Thus, one electrode of the semiconductor light emitting element 18 , that is, one signal terminal, is electrically connected to the first electrode connection region.

[0048] Furthermore, the other electrode of the semiconductor light emitting element 18, that is, the other signal terminal is electrically connected to a second electrode connection region provided on one plane of the auxiliary mount 17 by vapor deposition or the like, through a gold wire 22a.

[0049] A terminal resistor 19 is provided on one plane of the auxiliary bracket 17 by vapor deposition or the like.

[0050] The terminal resistor 19 is a resistor for achieving impedance matching with the IC driving the semiconductor light emitting element 18 , and is connected to the other signal terminal of the semiconductor light emitting element 18 via a gold wire 22 b .

[0051] The dielectric substrate 20 is mounted in the CAN type package, that is, is arranged on the inner plane 10 a of the stem 10 , and has a high-frequency line connected between the semiconductor light emitting element 18 and the signal pins 13 for the semiconductor light emitting element 18 formed by vapor deposition or the like.

[0052] The dielectric substrate 20 functions as a bridge substrate between the semiconductor light emitting element 18 and the signal pin 13 .

[0053] That is, the dielectric substrate 20 has: a first signal line region, which is connected to a first electrode connection region of a signal terminal connected to the semiconductor light emitting element 18 via a gold wire 22c; and a second signal line region, which is connected to a second electrode connection region of another signal terminal connected to the semiconductor light emitting element 18 via a gold wire 22d, and the first signal line region and the second signal line region are respectively connected to different signal pins 13 via gold wires (not shown).

[0054] The first signal line region and the second signal line region are other high-frequency lines.

[0055] The semiconductor light emitting element 18 receives a modulation signal from the signal pin 13 and emits laser light corresponding to the modulation signal. The laser light emitted from the semiconductor light emitting element 18 is converted into convergent light or parallel light by the lens 12 and irradiated to the outside.

[0056] The dielectric substrate 20 is not necessary. When the dielectric substrate 20 is not required, the first electrode connection region connected to one signal terminal of the semiconductor light emitting element 18 and the second electrode connection region connected to the other signal terminal of the semiconductor light emitting element 18 are directly connected to different signal pins 13 via gold wires.

[0057] The flexible wiring substrate 3 includes: a flexible insulating substrate 31 such as polyimide; a wiring pattern 32 formed on the front side of the insulating substrate 31 by vapor deposition or the like; a ground pattern 33 formed on the back side of the insulating substrate 31 by vapor deposition or the like; a power wiring layer (not shown) formed on the front side of the insulating substrate 31 by vapor deposition or the like; a front protective film 34; and a back protective film 35.

[0058] The wiring pattern 32 has a plurality of signal wiring layers for transmitting high-frequency signals. The front surface of the wiring pattern 32 is covered with a front surface protection film 34 for protection.

[0059] The insulating substrate 31 has a first through hole 36 formed at a position in the wiring pattern 32 that is opposite to the signal pin 13. Figure 4 As shown, in the first embodiment, three first through holes 36a to 36c are arranged along the circumference.

[0060] That is, in Figure 4 In the figure, the following example is shown: a semiconductor light emitting element 18, a light receiving element and a temperature adjustment device are installed in a CAN type package, and there are signal pins 13 for the semiconductor light emitting element 18, the light receiving element and the temperature adjustment device, and first through holes 36 corresponding to the signal pins 13 are formed.

[0061] In order to simplify the description, the suffixes of the reference numerals in the first through holes 36 a to 36 c may be omitted in the description.

[0062] In this first embodiment, the through hole has a conductive portion on the inner wall of a hole opened in the substrate, a front pad is provided on the front surface of the substrate, and a back pad is provided on the back surface, and the front pad and the back pad are electrically connected through the conductive portion.

[0063] The outer lead portion 13 b of the signal pin 13 is in contact with the via portion and penetrates the first through hole 36 , and the tip end portion of the outer lead portion 13 b of the signal pin 13 is electrically connected to the wiring pattern 32 .

[0064] The tip end of the outer lead portion 13 b is fixed to the front pad of the first through hole 36 by solder 39 , whereby the signal pin 13 is electrically connected to the wiring pattern 32 via the first through hole 36 .

[0065] The ground pattern 33 is formed on substantially the entire surface of the back surface of the insulating substrate 31. The ground pattern 33 has an exposed surface at a position facing the outer surface of the stem 10, and the surface other than the exposed surface is covered with a back surface protection film 35 for protection.

[0066] The insulating substrate 31 has a second through hole 37 formed at a position facing the ground pin 14 on the exposed surface of the ground pattern 33 .

[0067] The pin portion 14 a of the ground pin 14 is grounded to the conductive portion and penetrates the second through hole 37 . The front end portion of the pin portion 14 a of the ground pin 14 is fixed to the front pad of the second through hole 37 by solder 40 .

[0068] As a result, the ground pin 14 is electrically connected to the ground pattern 33 via the front-side pad-conductive portion-back-side pad of the second through hole 37 .

[0069] The insulating substrate 31 has a third through hole 38 formed at a position facing the power pin.

[0070] The outer lead portion of the power pin is connected to the conductive portion and penetrates the third through hole 38 , and the front end portion of the outer lead portion of the power pin is electrically connected to the power pattern.

[0071] The front end portion of the outer lead portion of the power pin is fixed to the front surface pad of the third through hole 38 by solder, so that the power pin is electrically connected to the power pattern via the third through hole 38 .

[0072] The plate 4 is a flat metal having a flat front surface and a flat back surface. The back surface is bonded to the outer plane 10 b of the stem 10 , and the front surface is bonded to the exposed surface of the ground pattern 33 of the flexible wiring board 3 .

[0073] like Figure 4 As shown, the planar shape of the plate 4 is a shape whose outer shape follows the outer shape of the outer plane 10b of the stem 10 except for the surface through which the signal pins 13 and the ground pins 14 are separately penetrated.

[0074] That is, the plate 4 is obtained by continuously cutting out the parts through which the signal pins 13, the ground pins 14 and the power pins pass through the disc-shaped metal. In addition, the plate 4 can also be obtained by drilling holes in the parts through which the signal pins 13, the ground pins 14 and the power pins pass through the disc-shaped metal.

[0075] Figure 4 A first through hole 36 , a second through hole 37 and a third through hole 38 are shown.

[0076] The back surface of the board 4 is joined to the outer plane 10b of the stem 10 by the conductive tape 5. The board 4 is fixed to the stem 10 by the conductive tape 5, and the board 4 and the stem 10 are electrically connected.

[0077] In addition, the back surface of the plate 4 and the outer surface 10 b of the stem 10 may be bonded and fixed to each other using other conductive materials instead of the conductive tape 5 .

[0078] The front surface of the plate 4 and the exposed surface of the ground pattern 33 of the flexible wiring board 3 are bonded together by the conductive adhesive 6. The conductive adhesive 6 fixes the plate 4 to the flexible wiring board 3 and electrically connects the plate 4 and the ground pattern 33.

[0079] In addition, the front surface of the plate 4 and the exposed surface of the ground pattern 33 of the flexible wiring board 3 may be bonded and fixed by other conductive materials instead of the conductive adhesive 6 .

[0080] The stem 10 is electrically connected to the ground pattern 33 of the flexible wiring board 3 via the conductive tape 5 - plate 4 - conductive adhesive 6 , and the stem 10 and the ground pattern 33 share a common ground.

[0081] As described above, the optical module of the first embodiment includes the ground pin 14, the front end portion of the pin portion 14a of the ground pin 14 is electrically connected to the ground pattern 33 of the flexible wiring substrate 30, and the pin portion 14a has a joint portion 14b at one end thereof, the diameter of which is larger than the diameter of the pin portion 14a and is joined to the outer plane 10b of the stem 10. In this optical module, the metal plate 4 is sandwiched between the stem 10 and the exposed surface of the ground pattern 33 to perform electrical and mechanical connection, so that the diameter of the through hole 37 for the ground pin 14 can be made to match the diameter of the pin portion 14a, without impairing the freedom of wiring design in the flexible wiring substrate 30.

[0082] That is, it is not necessary to increase the diameter of the through hole 37 for the ground pin 14 in accordance with the joining portion 14 b having a larger diameter than the pin portion 14 a , and the degree of freedom in wiring design is not impeded.

[0083] The front end portion of the outer lead portion 13b of the signal pin 13 is fixed to the front pad of the first through hole 36 by solder 39, and the front end portion of the pin portion 14a of the ground pin 14 is fixed to the front pad of the second through hole 37 by solder 40, thereby the flexible wiring substrate 30, the board 4, and the stem 10 are firmly attached.

[0084] As a result, the electrical and mechanical connection between the stem 10 and the ground pattern 33 can be reliably and firmly maintained together with the conductive tape 5 and the conductive adhesive 6 .

[0085] The board 4 is joined to the exposed surface of the ground pattern 33 of the flexible wiring substrate 30 using a conductive adhesive 6, a conductive tape 5 is attached to the front surface of the board 4 joined to the flexible wiring substrate 30, and the stem 10 is joined to the board 4 using the conductive tape 5. Therefore, the optical module can be assembled without processing the optical module body 1 and the flexible wiring substrate 3.

[0086] Furthermore, the stem 10 is fixed to the flexible wiring substrate 3 by means of the conductive tape 5 and the conductive adhesive 6, so that it is easy to weld the front end portion of the outer lead portion 13b of the signal pin 13 to the solder 39 of the front pad of the first through hole 36, and to weld the front end portion of the pin portion 14a of the ground pin 14 to the solder 40 of the front pad of the second through hole 37.

[0087] Furthermore, the stem 10 and the ground pattern 33 of the flexible wiring board 30 are electrically connected to the ground potential via the metal plate 4 , so that the ground potential near the signal pin 13 is strengthened, and parallel plate resonance caused by the stem 10 and the ground pattern 33 of the flexible wiring board 30 can be suppressed.

[0088] In order to verify that the parallel plate resonance is suppressed, the transmission characteristic S21 with respect to the frequency in the optical module according to the first embodiment is calculated.

[0089] For comparison, the frequency-dependent transmission characteristic S21 of an optical module in which the plate 4 is not made of metal but is made of an insulator made of polyimide was also calculated.

[0090] The operation result is as follows Figure 5 shown.

[0091] exist Figure 5 In FIG. 1 , the horizontal axis represents the frequency, the vertical axis represents the pass characteristic S21 , the solid line represents the calculation result in the optical module according to Embodiment 1, and the dotted line represents the calculation result in the comparative example.

[0092] according to Figure 5 It can be understood that the pass characteristic S21 with respect to frequency in the optical module of the first embodiment is better than the pass characteristic S21 with respect to frequency in the comparative example.

[0093] That is, the optical module of Embodiment 1 is electrically and mechanically connected by sandwiching the metal plate 4 between the stem 10 and the exposed surface of the ground pattern 33 of the flexible wiring board 30, thereby suppressing resonance and multiple reflections between the stem 10 and the ground pattern 33 and obtaining good frequency characteristics.

[0094] Furthermore, within the scope of the invention, the present invention may modify any constituent elements of the embodiments or omit any constituent elements in the embodiments.

[0095] Industrial applicability

[0096] The optical module disclosed herein can be used as an optical transmission module for optical communication as shown in Embodiment 1, and can be used as an optical reception module for optical communication equipped with a light receiving element, and an optical transmission and reception module equipped with both a light emitting element and a light receiving element.

[0097] Description of symbols

[0098] 1: optical module body; 10: socket; 10a: inner plane; 10b: outer plane; 10c: through hole; 13: signal pin; 13a: inner lead portion; 13b: outer lead portion; 14: ground pin; 14a: pin portion; 14b: joint portion; 18: semiconductor light emitting element; 20: dielectric substrate; 3: flexible wiring substrate; 31: insulating substrate; 32: wiring pattern; 33: ground pattern; 36a~36c: first through hole; 37: second through hole; 4: plate; 5: conductive tape; 6: conductive adhesive.

Claims

1. An optical module, comprising: A metal tube seat having an inner plane and an outer plane, and a through hole penetrating between the inner plane and the outer plane; A signal pin, which passes through the through hole of the stem and is fixed to the stem in an electrically insulated manner, and includes an inner lead portion protruding from an inner plane of the stem and an outer lead portion protruding from an outer plane of the stem; A ground pin, which has a pin portion, and a bonding portion at one end of the pin portion, which has a diameter larger than that of the pin portion and is bonded to an outer plane of the stem; A flexible wiring substrate, comprising a wiring pattern on a front surface and a ground pattern on a back surface, the ground pattern having an exposed surface at a position opposite to an outer plane of the stem, a first through hole formed at a position opposite to the signal pin on the wiring pattern, an outer lead portion of the signal pin passes through the first through hole, and a front end portion of the outer lead portion of the signal pin is electrically connected to the wiring pattern, a second through hole is formed at a position opposite to the ground pin on the exposed surface of the ground pattern, a pin portion of the ground pin passes through the second through hole, and a front end portion of the pin portion of the ground pin is electrically connected to the second through hole on the front surface; and The metal plate has a back surface bonded to the outer plane of the stem and a front surface bonded to the exposed surface of the ground pattern, and electrically connects the stem and the ground pattern of the flexible wiring substrate to a ground potential.

2. The optical module according to claim 1, wherein: The exposed surface of the ground pattern is bonded to the front surface of the board by a conductive adhesive, and the outer plane of the stem is bonded to the back surface of the board by a conductive tape.

3. The optical module according to claim 1, wherein: The planar shape of the plate is a shape whose outer shape is along the outer shape of the outer plane of the stem, except for the surface through which the signal pins and the ground pins penetrate separately.

4. The optical module according to claim 2, wherein: The planar shape of the plate is a shape whose outer shape is along the outer shape of the outer plane of the stem, except for the surface through which the signal pins and the ground pins penetrate separately.

5. The optical module according to any one of claims 1 to 4, wherein: A semiconductor light emitting element, a light receiving element and a temperature adjustment device are installed in a CAN type package consisting of the stem and a lens cover connected to and fixed to the peripheral end of the inner plane of the stem. The signal pin is configured as a signal pin for the semiconductor light emitting element.

6. The optical module according to claim 5, wherein: A dielectric substrate having a high-frequency line connected between the semiconductor light emitting element and a signal pin for the semiconductor light emitting element is mounted in the CAN type package.

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