Optical module

Abstract

A carrier (3) is bonded to a thermoelectric cooler (2) by a first bonding material (4). A submount (5) is mounted on a side surface of the carrier (3) by means of a second bonding material (6). A semiconductor laser element (7) is mounted on the submount (5). A protrusion (8) is provided between the thermoelectric cooler (2) and the submount (5) on the side surface of the carrier (3). The height of the protrusion (8) is lower than the height of the submount (5).

Description

Optical Module

[0001] The present disclosure relates to optical modules.

[0002] In a CAN-type optical module, a carrier is bonded to a thermoelectric cooler, a submount is mounted on the side of the carrier, and a semiconductor laser element is mounted on the submount (see, for example, Patent Document 1). Conventionally, a photodiode for monitoring the light emission intensity of the semiconductor laser element is disposed behind the semiconductor laser element. A mounting portion for the photodiode is provided on the carrier between the thermoelectric cooler and the submount. The bonding material bonding the thermoelectric cooler and carrier is blocked by the mounting portion for the photodiode and does not flow into the mounting portion for the submount. Even when a photodiode is not mounted, a thermistor or wire exists between the thermoelectric cooler and the submount. Therefore, the submount cannot be brought close to the thermoelectric cooler, and the flow of bonding material does not pose a problem.

[0003] Japanese Patent Application Publication No. 2019-140390

[0004] To shorten the optical module, the submount needs to be mounted close to the thermoelectric cooler. However, if the adhesive that joins the thermoelectric cooler and carrier flows out onto the mounting area of ​​the submount, the flatness decreases, causing the submount to tilt and resulting in variations in the direction of the optical output. This reduces the mountability of the submount, which is a problem.

[0005] The present disclosure has been made to solve the above-mentioned problems, and its object is to obtain an optical module that can improve the mountability of a submount.

[0006] The optical module according to the present disclosure comprises a thermoelectric cooler, a carrier joined to the thermoelectric cooler with a first bonding material, a submount mounted on a side surface of the carrier with a second bonding material, and a semiconductor laser element mounted on the submount, and is characterized in that a protrusion is provided on the side surface of the carrier between the thermoelectric cooler and the submount, and the height of the protrusion is shorter than the height of the submount.

[0007] In the present disclosure, a protrusion is provided on the side surface of the carrier between the thermoelectric cooler and the submount, which prevents the bonding material from flowing out to the mounting portion of the submount, thereby improving the mountability of the submount.

[0008] FIG. 1 is a cross-sectional view showing an optical module according to a first embodiment; FIG. 2 is a cross-sectional view showing a mounting method of a submount; FIG. 3 is a top view showing an optical module according to the first embodiment; FIG. 4 is a cross-sectional view showing an optical module according to a second embodiment; FIG. 5 is a cross-sectional view showing an optical module according to the second embodiment; FIG. 6 is a cross-sectional view showing an optical module according to a third embodiment; FIG. 7 is a cross-sectional view showing an optical module according to a fourth embodiment; FIG. 8 is a cross-sectional view showing an optical module according to a fifth embodiment; FIG. 9 is a cross-sectional view showing a modified example of the optical module according to the fifth embodiment.

[0009] An optical module according to an embodiment will be described with reference to the drawings. The same or corresponding components are designated by the same reference numerals, and repeated description may be omitted.

[0010] 1 is a cross-sectional view showing an optical module according to a first embodiment. This optical module is a CAN-type optical module. However, the lens cap is not shown. A thermoelectric cooler 2 (TEC: ThermoElectric Cooler) is mounted on a metal stem 1. The thermoelectric cooler 2 has a Peltier element 2a sandwiched between a heat-absorbing substrate 2b and a heat-generating substrate 2c. The Peltier element 2a is made of BiTe, and the heat-absorbing substrate 2b and the heat-generating substrate 2c are made of AlN.

[0011] A carrier 3 is joined to a thermoelectric cooler 2 with AuSn solder 4. The carrier 3 is made of CuW. A submount 5 is mounted on the side of the carrier 3 with SnAgCu solder 6. The submount 5 is made of alumina. A semiconductor laser element 7 is mounted on the submount 5. The semiconductor laser element 7 is made of InP.

[0012] Here, the melting point of the SnAgCu solder 6 is 213°C, and the melting point of the AuSn solder 4 is lower than 283°C. First, the stem 1 and the thermoelectric cooler 2 are joined using the AuSn solder 4, and then the thermoelectric cooler 2 is joined to the carrier 3. Next, the submount 5 is joined to the carrier 3 using the SnAgCu solder 6. At this time, by setting the temperature to be equal to or higher than 213°C and lower than 283°C, the submount 5 can be solder-joined while maintaining the bond between the thermoelectric cooler 2 and the carrier 3.

[0013] Since there are no elements such as photodiodes or wiring between the thermoelectric cooler 2 and the submount 5, the submount 5 can be placed close to the thermoelectric cooler 2. A protrusion 8 is provided on the side surface of the carrier 3 between the thermoelectric cooler 2 and the submount 5. The height of the protrusion 8 relative to the side surface of the carrier 3 is lower than the height of the submount 5.

[0014] In the present disclosure, a protrusion 8 is provided on the side surface of the carrier 3 between the thermoelectric cooler 2 and the submount 5. The protrusion 8 increases the creepage distance from the thermoelectric cooler 2 to the submount 5, thereby suppressing the outflow of the AuSn solder 4 onto the mounting portion of the submount 5. This prevents the submount 5 from tilting due to a decrease in flatness caused by the outflow of the AuSn solder 4, which can cause variations in the light output direction. This improves the mountability of the submount 5.

[0015] Furthermore, by suppressing the outflow of the AuSn solder 4 using the protrusions 8, it is possible to prevent contact between the AuSn solder 4 and the SnAgCu solder 6. The Au content of the AuSn solder 4 is approximately 80%. On the other hand, the fixing strength of the SnAgCu solder 6 decreases when it contains a few percent of Au. By preventing contact between the AuSn solder 4 and the SnAgCu solder 6 using the protrusions 8, it is possible to improve reliability.

[0016] FIG. 2 is a cross-sectional view showing a submount mounting method. The collet 9 holds the submount 5 by suction. The collet 9 is vibrated to break the oxide film on the surface of the SnAgCu solder 6, soldering the submount 5 to the carrier 3. Vacuum suction of only the top surface of the submount 5 during this process would not be able to withstand the vibrations. Therefore, the collet 9 must clamp and secure the submount 5. The contact portion of the collet 9 is inclined at 45° and contacts the top corner of the submount 5. Therefore, the tip of the contact portion of the collet 9 is positioned below the top surface of the submount 5 on the side of the submount 5. Therefore, in this embodiment, the height of the protrusion 8 relative to the side of the carrier 3 is made lower than the height of the submount 5. This prevents interference between the collet 9 and the protrusion 8 during mounting of the submount 5. Therefore, the submount 5 can be mounted close to the thermoelectric cooler 2, just as if the protrusion 8 were not present, thereby achieving a shorter optical module. However, in order to more reliably avoid interference between the collet 9 and the protrusion 8, it is preferable that the height of the protrusion 8 relative to the side surface of the carrier 3 is lower than half the height of the submount 5.

[0017] 3 is a top view showing the optical module according to embodiment 1. The protrusions 8 may be provided across the entire width of the carrier 3, or may be provided across only a portion of the width of the carrier 3 as shown in FIG. 3. The protrusions 8 provided across only a portion of the width of the carrier 3 can be used as a positioning reference for the submount 5.

[0018] 4 and 5 are cross-sectional views showing an optical module according to a second embodiment. A bonding material reservoir 10 for storing AuSn solder 4 is provided on the bonding surface of the carrier 3 bonded to the thermoelectric cooler 2. In FIG. 4, the bonding material reservoir 10 is provided in the center of the bonding surface of the carrier 3, while in FIG. 5, the bonding material reservoir 10 is provided on the protrusion 8. By storing the AuSn solder 4 in the bonding material reservoir 10, it is possible to further suppress the AuSn solder 4 from flowing out onto the mounting portion of the submount 5. The bonding material reservoir 10 may be provided across the entire width of the carrier 3, or may be provided only on a portion of the width of the carrier 3. The other configurations and effects are the same as those of the first embodiment.

[0019] 6 is a cross-sectional view showing an optical module according to a third embodiment. In this embodiment, a coating film 11 is provided on the tip surface of the protrusion 8 and on the surface of the protrusion 8 opposite the thermoelectric cooler 2. The coating film 11 is, for example, a Cr plating, which has poorer wettability with the AuSn solder 4 than the Au plating provided on the entire surface of the carrier 3. This makes it possible to further suppress the AuSn solder 4 from flowing out onto the mounting portion of the submount 5.

[0020] By limiting the coating film 11 to a portion of the protrusion 8, there is no effect on the bonding of the carrier 3 and the mounting of the submount 5. The coating film 11 may be provided over the entire width of the carrier 3, or may be provided only on a portion of the width of the carrier 3. The coating film 11 provided only on a portion of the width of the carrier 3 may be used as a positioning reference for the submount 5. The other configurations and effects are the same as those of the first embodiment.

[0021] 7 is a cross-sectional view showing an optical module according to a fourth embodiment. In this embodiment, the carrier 3 includes a CuW base material 3a, a Ni plating 3b as an undercoat covering the base material 3a, and an Au plating 3c as an outermost surface covering the Ni plating 3b. Ti plating may be used instead of the Ni plating 3b. Because solder bonding is not possible with the CuW base material 3a, the Au plating 3c is provided on the outermost surface of the carrier 3. The Au plating 3c has better wettability with the AuSn solder 4 than the Ni plating 3b. Therefore, the Au plating 3c is provided on the bonding surface of the carrier 3 bonded to the thermoelectric cooler 2 and on the mounting portion of the submount 5.

[0022] The Au plating 3c is removed from the tip surface of the protrusion 8 and the surface of the protrusion 8 opposite the thermoelectric cooler 2, exposing the Ni plating 3b. For example, when plating, the relevant areas are covered with a mask to prevent the Au plating 3c from being formed. Alternatively, laser marking may be performed, in which laser light is irradiated to remove the Au plating 3c and expose the underlying Ni plating 3b. The exposed Ni plating 3b is oxidized. Because the oxidized Ni plating 3b has poor wettability with the AuSn solder 4, it is possible to further suppress the outflow of the AuSn solder 4 to the mounting portion of the submount 5.

[0023] By limiting the portion from which the Au plating 3c has been removed to a portion of the protrusion 8, there is no effect on the bonding of the carrier 3 and the mounting of the submount 5. The portion from which the Au plating 3c has been removed may be provided over the entire width of the carrier 3, or may be provided over only a portion of the width of the carrier 3. The portion from which the Au plating 3c has been removed over only a portion of the width of the carrier 3 may be used as a positioning reference for the submount 5. The other configurations and effects are the same as those of the first embodiment.

[0024] 8 is a cross-sectional view showing an optical module according to a fifth embodiment. In this embodiment, a recess 12 for storing AuSn solder 4 is provided at the corner between the bonding surface of the carrier 3 bonded to the thermoelectric cooler 2 and the side surface of the carrier 3 on which the submount 5 is mounted. By storing excess AuSn solder 4 in the recess 12, it is possible to prevent the AuSn solder 4 from flowing out onto the side surface of the carrier 3 on which the submount 5 is mounted. Note that the recess 12 may be provided across the entire width of the carrier 3, or may be provided only in a portion of the width direction of the carrier 3.

[0025] 9 is a cross-sectional view showing a modification of the optical module according to the fifth embodiment. A portion of the submount 5 protrudes above the recess 12. Because there is sufficient space below the protruding submount 5, the AuSn solder 4 does not reach the joint of the submount 5. Therefore, there is no contact between the AuSn solder 4 and the SnAgCu solder 6, which would impair reliability.

[0026] 2 Thermoelectric cooler, 3 Carrier, 3a Base material, 3b Ni plating (undercoat film), 3c Au plating (top surface film), 4 AuSn solder (first bonding material), 5 Submount, 6 SnAgCu solder (second bonding material), 7 Semiconductor laser element, 8 Protrusion, 10 Bonding material reservoir, 11 Coating film, 12 Recess

Claims

1. An optical module comprising: a thermoelectric cooler; a carrier bonded to the thermoelectric cooler with a first bonding material; a submount mounted on a side surface of the carrier with a second bonding material; and a semiconductor laser element mounted on the submount, wherein a protrusion is provided on the side surface of the carrier between the thermoelectric cooler and the submount, and the height of the protrusion is shorter than the height of the submount.

2. The optical module according to claim 1, wherein the height of said protrusion is less than half the height of said submount.

3. An optical module according to claim 1 or 2, wherein the protrusion is provided only on a part of the width of the carrier.

4. An optical module according to any one of claims 1 to 3, characterized in that a bonding material reservoir for storing the first bonding material is provided on the bonding surface of the carrier bonded to the thermoelectric cooler.

5. An optical module described in any one of claims 1 to 4, further comprising a coating film provided on the tip surface of the protrusion and on the surface of the protrusion opposite the thermoelectric cooler, the coating film having poorer wettability with the first bonding material than the surface of the carrier.

6. An optical module as claimed in any one of claims 1 to 4, characterized in that the carrier has a base material, a base film covering the base material, and a top surface film covering the base film, the top surface film having better wettability with the first bonding material than the base film, and the top surface film is removed to expose the base film at the tip surface of the protrusion and at the surface of the protrusion opposite the thermoelectric cooler.

7. An optical module comprising: a thermoelectric cooler; a carrier bonded to the thermoelectric cooler with a first bonding material; a submount mounted on a side surface of the carrier with a second bonding material; and a semiconductor laser element mounted on the submount, wherein a recess for storing the first bonding material is provided at a corner between the bonding surface of the carrier bonded to the thermoelectric cooler and the side surface of the carrier.

8. The optical module according to claim 7, wherein a portion of said submount protrudes above said recess.

9. The optical module according to claim 7 or 8, wherein the recess is provided only in a part of the width direction of the carrier.

10. The optical module according to any one of claims 1 to 9, wherein the first bonding material and the second bonding material are different.

11. The optical module according to claim 10, wherein the first bonding material is solder, and the second bonding material is solder having a lower melting point than the first bonding material.

12. The optical module according to claim 11, wherein the first bonding material is an AuSn solder, and the second bonding material is an SnAgCu solder.

13. The optical module according to any one of claims 1 to 12, wherein there are no elements or wiring between the thermoelectric cooler and the submount.

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