JP2005017388A - Optical module and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To establish an optical module that is inexpensive and is excellent in mass-productivity and high-frequency characteristics. <P>SOLUTION: The optical module is characterized by comprising a light emitting element 110 for emitting light such as a semiconductor laser and a light emitting diode, an optical fiber 120, a V-grooved substrate electrode 140a electrically connected to a light emitting element electrode formed on the surface not processed for the light emitting element 110, a V-grooved substrate electrode 140b electrically connected to the light emitting element electrode 150, the light emitting element electrode 150 formed on the surface processed for the light emitting element 110, a wire 160 for electrically connecting between the V-grooved substrate electrode 140b and the light emitting element electrode 150, a V-groove 170 precisely formed on a V-groove substrate 130 for precisely mounting the optical fiber 120 thereon, and alignment markers 180 formed by the mask-pattern technique. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical module mounting technique and structure.
[0002]
[Prior art]
In recent years, development of optical active devices and optical functional modules typified by semiconductor lasers has been rapidly progressing toward an advanced information society such as an optical subscriber network. In the future, the spread of optical communication terminals to each home is expected by laying optical fibers up to homes. For the spread of optical communication terminals, it is important to realize an optical module that is inexpensive and excellent in mass productivity, and the realization of such an optical module is desired.
[0003]
However, there are several problems in realizing the optical module as described above. In particular, optical coupling (hereinafter referred to as optical coupling) between an optical element (for example, a semiconductor laser, a light emitting element such as a light emitting diode, a light receiving element such as a photodiode, an optical waveguide, an optical amplifier, etc.) and an optical fiber with high accuracy. When trying to realize a simple optical coupling method, there are the following problems. As an optical coupling method, the light emitting element is made to emit light, the x, y, and z positions of the optical fiber are moved, the output light intensity after passing through the optical fiber is confirmed on a monitor, and a good light intensity and optical coupling efficiency can be obtained. In general, an active alignment mounting method for fixing a table holding an optical fiber is generally used. However, this method requires a large-scale manufacturing facility and takes a long time to adjust the optical axis, which causes problems in cost and mass productivity.
[0004]
As a prior example for solving such a problem, there is a passive alignment mounting technique (see Patent Document 1). According to this document, optical coupling without optical axis adjustment as in the active alignment mounting method is realized by using a V-groove formed in advance on a semiconductor substrate.
[0005]
FIG. 8A is a perspective view of a conventional optical module, FIG. 8B is a cross-sectional view of a light emitting element mounting portion on which the light emitting element 810 of the optical module is mounted, and FIG. FIG. 5 is a cross-sectional view of an optical fiber mounting portion on which an optical fiber 820 of an optical module is mounted.
[0006]
As shown in FIGS. 8A, 8B, and 8C, the conventional optical module includes a light emitting element 810 that emits light such as a semiconductor laser and a light emitting diode, an optical fiber 820, and a V-groove substrate 830. An electrical wiring 840, a V-groove 850 formed with high accuracy in the V-groove substrate 830 for mounting the optical fiber 820 with high accuracy, an alignment marker 860 formed by a mask pattern technique, and a light-emitting element 810 A light emitting region 870 that is a light emitting region and an optical fiber core 880 are configured. Here, the V-groove substrate 830 is a semiconductor substrate with good flatness.
[0007]
In the optical module having the above-described configuration, optical coupling between the light emitting element 810 and the optical fiber 820 is performed by mounting the optical fiber 820 in the V groove 850 and then using the alignment marker 860 to form a plane of the light emitting region 870 in the V groove substrate 830. The position is determined with high accuracy, the light emitting element 810 is mounted on the upper surface of the V-groove substrate 830 by junction down mounting, and the height of the light emitting region 870 with respect to the upper surface of the V-groove substrate 830 is determined with high accuracy.
[0008]
As described above, in the conventional optical module, since the V-groove substrate 830 is a semiconductor substrate with good flatness, high-precision mounting in the planar direction can be obtained by the alignment marker 860, and the light-emitting element 810 can be obtained by junction-down mounting. Is mounted on the V-groove substrate 830 and the angle of the V-shaped etching groove of the semiconductor substrate formed by anisotropic etching is determined, so that high-precision mounting in the height direction can be obtained. Furthermore, since the optical coupling is performed by mechanically mounting the light emitting element 810 and the optical fiber 820, a low cost optical module can be realized.
[0009]
Here, when the light emitting element 810 is mounted on the upper surface of the V groove substrate 830 by junction down mounting, the height of the light emitting region 870 of the light emitting element 810 with respect to the upper surface of the V groove substrate 830 can be determined with high accuracy with reference to FIG. To do.
[0010]
9A is a perspective view of the light emitting element 810, and FIGS. 9B and 9C are cross-sectional views of the optical module in the light emitting element mounting portion. The same elements as those in FIG. 8 are denoted by the same reference numerals, and detailed description thereof will be omitted here.
[0011]
As shown in FIG. 9A, the light emitting element 810 is formed on the surface where the light emitting element alignment marker 910 and the process of the light emitting element 810 are processed, that is, the surface close to the light emitting region 870 of the light emitting element 810. 9B. The stripe-down mounting is configured by a stripe groove 920 that suppresses the spread of the actual current and performs optical confinement. As shown in FIG. 9C is a mounting in which the upper surface of the groove substrate 830 is brought into contact with the surface of the light emitting element 810 shown in FIG. 9C, that is, the surface far from the light emitting region 870 of the light emitting element 810 and the upper surface of the V groove substrate 830. Junction-up mounting that contacts with is an opposite mounting. At this time, the electrode pad 930 used in the junction-down mounting has a larger area than the electrode pad 930 used in the junction-up mounting, and the size of the parasitic capacitance 940 is determined by the area of the electrode pad 930. The parasitic capacitance 940 formed in is larger than the parasitic capacitance 940 formed in the junction-up mounting.
[0012]
As described above, junction down mounting is performed by bringing the surface of the light emitting element 810 processed and the upper surface of the V-groove substrate 830 into contact with each other, and thus the distance between the light emitting region 870 and the upper surface of the V groove substrate 830 is set at the light emitting element 810. Therefore, the thickness of the light emitting region 870 of the light emitting device 810 with respect to the upper surface of the V-groove substrate 830 can be determined with high accuracy by junction down mounting.
[0013]
[Patent Document 1]
JP-A-10-311936
[0014]
[Problems to be solved by the invention]
By the way, in recent years, the speed of optical communication devices has been rapidly increased, and in ultra-high speed optical communication devices, characteristic degradation at high frequencies has become a problem. However, in the conventional optical module, when the light emitting element 810 is mounted on the upper surface of the V-groove substrate 830, junction down mounting is used, so that a large parasitic capacitance 940 is formed in the electrode pad 930 region, and the light emitting element 810 is driven. The speed cannot be increased and the speed of the optical communication device cannot be coped with. At this time, the parasitic capacitance 940 can be reduced by reducing the area of the electrode pad 930 as much as possible. However, in junction down mounting, the bonding strength between the V-groove substrate 830 and the light emitting element 810 is weakened and peeled off. A somewhat large electrode region is required, and the driving speed of the light emitting element 810 cannot be increased.
[0015]
Further, as device speed increases, deterioration of device characteristics due to an increase in the amount of heat generated by the device becomes a problem. However, in the conventional optical module, since the V-groove substrate 830 is limited to a semiconductor substrate with good flatness, the heat generated in the light emitting element 810 cannot be released, and the light generated in the light emitting element 810 is caused by the heat generated in the light emitting element 810. The oscillation frequency of this changes and oscillation becomes unstable.
[0016]
Accordingly, in view of the above problems, the first object of the present invention is to realize an optical module that is low in price, excellent in mass productivity, and excellent in high frequency characteristics.
Another object of the present invention is to realize an optical module that prevents deterioration of device characteristics due to heat generation of the device, that is, has excellent long-term stability and reliability.
[0017]
[Means for Solving the Problems]
In order to achieve the above object, an optical module according to the present invention is an optical module including an optical fiber and an optical element that are optically coupled, and a mounting substrate on which the optical fiber and the optical element are mounted. Has two upper surfaces having steps, and the optical fiber is mounted in a V-groove formed on the first upper surface of the two upper surfaces of the mounting substrate, and the optical element is mounted on the mounting surface. It is mounted on the lower second upper surface of the two upper surfaces of the substrate, and the first upper surface of the mounting substrate and the upper surface of the optical element are substantially flush with each other.
[0018]
As a result, the optical fiber is mounted in the V-groove, and the optical element is mounted on a surface lower than the surface on which the V-groove is formed, so that the optical element can be mounted on the mounting substrate by junction-up mounting. The effect that an optical module excellent in mass productivity can be realized is exhibited.
[0019]
The optical element may be mounted on the second upper surface by junction-up mounting.
As a result, the parasitic capacitance formed by the junction-down mounting can be removed, so that an effect of realizing an optical module excellent in high frequency characteristics is exhibited.
[0020]
The mounting substrate may include a first substrate having a surface on which the V-groove is formed, and a second substrate having a surface in contact with the optical element.
As a result, the mounting substrate on which the optical element is mounted is not required to be flat, and a mounting substrate with good thermal conductivity can be used, thereby preventing deterioration of the optical element characteristics caused by the heat generation of the optical element, that is, long-term The effect that an optical module excellent in stability and reliability can be realized is exhibited.
[0021]
The optical module may further include a first fixing member that fixes a relative position of the optical element with respect to the mounting substrate between the first substrate and the second substrate. Here, the optical module may further include a second fixing member that fixes a relative position of the optical element with respect to the mounting substrate between the optical element and the mounting substrate.
[0022]
Thereby, the effect that the optical element can be fixed at the optimum relative position with respect to the mounting substrate is exhibited.
The second fixing member may have adhesiveness, and the mounting substrate and the optical element may be bonded.
[0023]
Thereby, the effect that the mounting substrate and the optical element can be bonded is exhibited.
The second fixing member may have thermosetting property or photo-curing property.
Thereby, the effect that the mounting substrate and the optical element can be integrated is exhibited.
[0024]
The second fixing member may have thermal conductivity.
Thereby, the effect that the heat generated in the optical element can be released to the mounting substrate is exhibited.
[0025]
The present invention is also a method of manufacturing an optical module comprising an optical fiber and an optical element that are optically coupled, and a mounting substrate on which the optical fiber and the optical element are mounted. An optical element mounting step of mounting an optical element on the upper surface of the mounting reference substrate to be coupled, and the upper surface of the mounting reference substrate and the upper surface of the mounting substrate on which the V-groove is formed are opposed to each other. A mounting substrate mounting step of mounting the mounting substrate on the upper surface of the reference substrate; bringing the mounting reference substrate and the mounting substrate into contact with each other; and contacting the mounting reference substrate of the optical element with the upper surface of the mounting substrate. A method of manufacturing an optical module, comprising a step of making the surfaces substantially flush and an optical fiber mounting step of mounting an optical fiber in the V-groove can be provided.
[0026]
As a result, the optical fiber is mounted in the V-groove, and the upper surface of the optical element mounted on the mounting substrate and the upper surface of the mounting substrate are substantially flush, so that the optical element can be mounted on the mounting substrate by junction-up mounting. The effect that an optical module excellent in mass productivity at a price can be produced is exhibited.
[0027]
In the optical element mounting step, the upper surface of the mounting reference substrate and the surface subjected to the process of the optical element are opposed to each other, the optical element is mounted on the upper surface of the mounting reference substrate, and the surface In one step, the surface subjected to the process of the optical element and the upper surface of the mounting substrate may be substantially flush.
[0028]
Thus, since the optical element is mounted on the mounting substrate by junction-up mounting, an effect that an optical module excellent in high frequency characteristics can be manufactured is exhibited.
[0029]
The mounting substrate includes an optical fiber substrate having a surface on which a V-groove is formed, and an optical element substrate not having a surface on which a V-groove is formed, and the method for manufacturing the optical module further includes the optical fiber A step of bonding the substrate and the optical element substrate, wherein the surface opposite to the surface contacting the reference substrate for mounting of the optical element may be in contact with the optical element substrate.
[0030]
As a result, the mounting substrate on which the optical element is mounted is not required to have flatness, and a mounting substrate with good thermal conductivity can be used, thereby preventing deterioration of the optical element characteristics caused by the heat generation of the optical element. The effect that the optical module excellent in long-term stability and reliability can be manufactured is exhibited.
[0031]
The manufacturing method of the optical module further includes a step of applying a first fixing member between the optical element substrate and the optical fiber substrate, and the substantially fixed surface is formed by the first fixing member in the surface step. One state may be fixed. Here, the method for manufacturing the optical module further includes a step of applying a second fixing member between the optical element and the mounting substrate, and in the step, the surface is substantially flush with the second fixing member. The state may be fixed.
[0032]
As a result, the effect that the optical module in which the relative position of the optical element with respect to the mounting substrate is fixed in an optimal relationship can be manufactured is exhibited.
Further, the second fixing member may have adhesiveness, and the optical element and the mounting substrate may be bonded in the same step.
[0033]
As a result, the effect that an optical module in which the optical element and the mounting substrate are bonded can be produced.
The second fixing member may be thermosetting or photocurable, and the method for manufacturing the optical module may further include a step of curing the second fixing member with ultraviolet rays or heat.
[0034]
As a result, an effect that an optical module in which the mounting substrate and the optical element are integrated can be produced.
[0035]
The mounting reference board includes an optical element alignment marker, a mounting board alignment marker, and a fixing unit. In the optical element mounting step, the light on the upper surface of the mounting reference board is formed by the optical element alignment marker. The mounting position of the element is determined, and the optical element mounted on the upper surface of the mounting reference substrate is temporarily fixed by the fixing means, and the mounting substrate alignment marker is used to mount the mounting device in the mounting substrate mounting step. The mounting position of the mounting board on the upper surface of the reference board for use may be determined. Here, the mounting reference substrate is a light transmissive substrate, and in the optical element mounting step, the optical element alignment marker is confirmed from a surface opposite to the upper surface of the mounting reference substrate, and the mounting is performed. In the substrate mounting step, the mounting substrate alignment marker may be confirmed from a surface opposite to the upper surface of the mounting reference substrate.
[0036]
As a result, an effect of being able to manufacture an optical module in which the planar position of the optical element on the mounting substrate is determined with high accuracy is exhibited.
[0037]
The present invention also includes an optical fiber and an optical element that are optically coupled, an optical fiber substrate having a surface on which a V-groove is formed, and an optical element substrate that does not have a surface on which a V-groove is formed. An optical module manufacturing method comprising an optical fiber and a mounting substrate on which the optical element is mounted, the optical element mounting step for mounting the optical element on an upper surface of the optical element substrate, the optical element and the optical fiber, An optical fiber substrate placement step of placing the optical fiber substrate on the upper surface of the mounting reference substrate so that the upper surface of the mounting reference substrate that optically couples the optical fiber substrate and the upper surface of the optical fiber substrate on which the V-groove is formed are opposed to each other. And an optical element mounting step of placing an optical element on the upper surface of the mounting reference substrate, with the upper surface of the mounting reference substrate facing the surface on which the process of the optical element has been performed, and the optical element; Contact the mounting reference board, A step of making the surface of the optical recording element substantially flush with an upper surface of the optical fiber substrate, and an optical fiber mounting step of mounting the optical fiber in the V-groove. It can also be set as the manufacturing method of the optical module to do.
[0038]
With this, by using the optical element mounted in advance on the optical element substrate, the optical element characteristic test and the reliability test can be performed during the manufacturing of the optical module, so that only good optical elements can be selected. The effect that a low-cost optical module can be manufactured is exhibited.
[0039]
The manufacturing method of the optical module further includes a step of applying a fixing member between the optical fiber substrate and the optical element substrate, and the substantially flush state is fixed by the fixing member in the surface step. May be.
As a result, the effect that the optical module in which the relative position of the optical element with respect to the mounting substrate is fixed in an optimal relationship can be manufactured is exhibited.
[0040]
Further, the fixing member may have adhesiveness, and the optical fiber substrate and the optical element substrate may be bonded in the same step.
Thereby, an effect that an optical module in which the optical fiber substrate and the optical element substrate are bonded can be produced.
[0041]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an optical functional material according to an embodiment of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a perspective view of an optical module according to the present embodiment.
[0042]
The optical module of the present embodiment is intended to realize an optical module that is low in price, excellent in mass productivity, and excellent in high frequency characteristics, and emits light from a semiconductor laser, a light emitting diode, or the like. Light-emitting element 110, optical fiber 120, V-groove substrate 130, and V-groove substrate electrode electrically connected to the light-emitting element electrode (not shown) formed on the surface of the light-emitting element 110 that has not been subjected to the process. 140a, a V-groove substrate electrode 140b electrically connected to the light-emitting element electrode 150, a light-emitting element electrode 150 formed on the surface of the light-emitting element 110, a V-groove substrate electrode 140b and the light-emitting element electrode 150 for electrically connecting 150, V-groove 170 formed on the V-groove substrate 130 with high accuracy for mounting the optical fiber 120 with high accuracy, and mask pattern technology. Composed of the alignment markers 180. formed Ri. In the optical module of the present invention, the light-emitting element 110 is mounted on the V-groove substrate 130 by junction-up mounting, and the surface on which the light-emitting element 110 is mounted on the V-groove substrate 130 is more than the top surface of the V-groove 170. The conventional light is that the surface of the light-emitting element 110 that contacts the V-groove substrate 130, that is, the surface opposite to the surface subjected to the process is substantially flush with the top surface of the V-groove substrate 130. Different from module.
[0043]
Here, the V-groove substrate 130 is a semiconductor substrate with good flatness, for example, a silicon semiconductor substrate. The V-groove substrate 130 may be a metal substrate or a resin substrate.
[0044]
Next, a method for manufacturing the optical module having the above-described configuration will be described with reference to a cross-sectional view shown in FIG. 2 (a cross-sectional view of the mounting portion of the light-emitting element 110 in the perspective view) and a flowchart shown in FIG. The same elements as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted here.
[0045]
First, as shown in FIG. 2A, the surface on which the process of the light emitting element 110 is performed, that is, the surface near the light emitting region 210 of the light emitting element 110 and the upper surface of the mounting reference substrate 220 are opposed to each other. The mounting position of the light emitting element 110 on the upper surface of the mounting reference substrate 220 is determined by the alignment marker formed on the surface subjected to the process 110 and the alignment marker for mounting the light emitting element formed on the upper surface of the mounting reference substrate 220. Determine with high accuracy (S300). Then, the light emitting element 110 is placed on the upper surface of the mounting reference substrate 220 (S310). Then, the light emitting element 110 is fixed to the upper surface of the mounting reference substrate 220 by the vacuum chuck 230 (S320). And the fixing member 240 is apply | coated to the surface on the opposite side to the surface in which the process of the light emitting element 110 was given (S330). Although the mounting position of the light emitting element 110 on the upper surface of the mounting reference substrate 220 is determined with high accuracy by the alignment marker formed on the surface where the process of the light emitting element 110 is performed, the mounting position of the light emitting element 110 is determined. The light-emitting element 110 is not limited to that as long as it can be determined with high accuracy, and other methods, for example, the unevenness of the stripe groove formed on the surface of the light-emitting element 110 or the alignment unevenness formed by etching or the like. May be determined with high accuracy. In addition, the light emitting element 110 is fixed to the upper surface of the mounting reference substrate 220 by the vacuum chuck 230. However, the light emitting element 110 is not limited to this as long as the light emitting element 110 can be fixed to the upper surface of the mounting reference substrate 220. You may fix to the board | substrate 220 upper surface.
[0046]
Here, the mounting reference board 220 is used when the optical module of the present embodiment is manufactured, and has a configuration as shown in FIG.
FIG. 4 is a top view of the mounting reference board 220. The same elements as those in FIGS. 1 and 2 are denoted by the same reference numerals, and detailed description thereof will be omitted here.
[0047]
The mounting reference substrate 220 includes a light emitting element placement alignment marker 410 that controls the placement position of the light emitting element 110 on the upper surface of the mounting reference substrate 220 with high accuracy, and a V-groove substrate 130 on the upper surface of the mounting reference substrate 220. The V-groove substrate mounting alignment marker 250 and the vacuum chuck 230 for controlling the mounting position with high accuracy. Note that the mounting reference substrate 220 is preferably a light-transmitting substrate such as a quartz substrate.
[0048]
The fixing member 240 is a conductive material having adhesiveness and thermosetting, and is, for example, Ag paste or cream solder. Note that the fixing member 240 is used for adjusting the relative height position of the light emitting element 110 with respect to the V-groove substrate 130 by the adjustment external pressure in mounting, and is used to fix the position. It is preferable to have power. The fixing member 240 is assumed to have thermosetting properties. However, the fixing member 240 may not be thermosetting but may be photocurable.
[0049]
Next, as shown in FIG. 2B, the upper surface of the V-groove substrate 130 on which the V-groove 170 is formed and the upper surface of the mounting reference substrate 220 are opposed to each other, and the alignment marker 250 for mounting the V-groove substrate and the alignment marker are used. By 180, the mounting position of the V-groove substrate 130 on the upper surface of the mounting reference substrate 220 is determined (S340).
[0050]
Next, as shown in FIG. 2C, the V-groove substrate 130 is placed on the upper surface of the mounting reference substrate 220 (S350). Then, the V-groove substrate 130 and the mounting reference substrate 220 were brought into strong contact, the light emitting element 110 and the V-groove substrate 130 were bonded by the fixing member 240, and the upper surface of the V-groove substrate 130 and the light emitting element 110 were processed. The surface is made substantially flush (S360). Then, the fixing member 240 is cured by heating, and the light emitting element 110 and the V-groove substrate 130 are integrated (S370).
[0051]
Next, as shown in FIG. 2D, the integrated light emitting element 110 and V-groove substrate 130 are separated from the mounting reference substrate 220 (S380).
[0052]
Next, as shown in FIG. 2 (e), the V-groove substrate electrode 140 b and the light emitting element electrode 150 are electrically connected by the wire 160, the optical fiber 120 is mounted in the V-groove 170, and the optical fiber 120 The optical fiber core 260 and the light emitting region 210 of the light emitting element 110 are matched (S390).
[0053]
As described above, according to the present embodiment, optical coupling is performed by using the V groove 170 formed on the V groove substrate 130 in advance. Therefore, since the optical axis adjustment as in the active alignment mounting method is not performed, the optical module of the present embodiment can realize an optical module that is inexpensive and excellent in mass productivity.
[0054]
Further, according to the present embodiment, the light emitting element 110 is mounted on the V-groove substrate 130 by junction-up mounting. Therefore, since the parasitic capacitance formed by the junction-down mounting can be removed, the optical module of the present embodiment can realize an optical module excellent in high frequency characteristics.
[0055]
Further, according to the present embodiment, the mounting reference substrate 220 used in the optical module manufacturing process is a light-transmitting substrate, and the alignment marker formed on the upper surface of the light emitting element 110 and the upper surface of the V-groove substrate 130 are formed. The alignment marker 180 can be confirmed from the surface opposite to the upper surface of the mounting reference substrate 220. Therefore, since the alignment marker can be confirmed by a simple device such as a CCD camera instead of using an X-ray or infrared camera, the optical module of the present embodiment simplifies the adjustment and reduces the cost of the implementation equipment. An optical module that can be realized can be realized.
[0056]
In the present embodiment, the optical module optically couples the optical fiber 120 and the light emitting element 110. However, the optical module may optically couple another optical element such as a light receiving element, an optical waveguide, or an optical amplifier with an optical fiber.
[0057]
In this embodiment, fixing member 240 has adhesiveness and plasticity, and light emitting element 110 and V-groove substrate 130 are bonded and integrated by fixing member 240. However, the fixing member 240 does not have adhesiveness and plasticity, and the light emitting element 110 and the V-groove substrate 130 may be bonded and integrated by another fixing member having adhesiveness and plasticity. The integration of the light emitting element 110 and the V-groove substrate 130 using such another fixing member fixes the relative position of the light emitting element 110 with respect to the V-groove substrate 130 by the fixing member 240 having no adhesiveness and plasticity. Thereafter, another fixing member having adhesiveness and plasticity is applied between the V-groove substrate 130 and the light emitting element 110, and the light emitting element 110 and the V groove substrate 130 are bonded and integrated.
[0058]
(Second Embodiment)
In the optical module according to the first embodiment, the light emitting element electrode formed on each of the non-processed surface and the processed surface of the light emitting element and the electrode of the V-groove substrate are electrically connected. It was supposed to be connected. However, even if only the light emitting element electrode formed on the surface subjected to the process of the light emitting element is electrically connected to the electrode of the V-groove substrate, the surface and process where the process of the light emitting element is not performed are performed. The same effect as when the light emitting element electrode formed on each of the surfaces and the electrode of the V-groove substrate are electrically connected can be obtained, and in this case, the light emitting element is not formed on the surface. Since it is not necessary to electrically connect the formed light emitting element electrode and the electrode of the V-groove substrate, the fixing member does not need to have conductivity, and the material of the fixing member can be selected with a high degree of freedom. . Therefore, in the optical module according to the second embodiment, only the light emitting element electrode formed on the surface subjected to the process of the light emitting element is electrically connected to the electrode of the V-groove substrate. The following description will focus on differences from the first embodiment.
[0059]
FIG. 5 is a perspective view of the optical module in the present embodiment. 5, the same elements as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted here.
[0060]
The optical module of the present embodiment includes a light emitting element 110, an optical fiber 120, a V groove substrate 130, a V groove 170, an alignment marker 180, and V grooves electrically connected to the light emitting element electrodes 520a and 520b. Substrate electrodes 510a and 510b, light emitting element electrodes 520a and 520b formed on the surface subjected to the process of the light emitting element 110, a wire 530a that electrically connects the V groove substrate electrode 510a and the light emitting element electrode 520a, It is comprised from the wire 530b which electrically connects the V-groove board | substrate electrode 510b and the light emitting element electrode 520b.
[0061]
The optical module of the present embodiment having the above-described configuration is manufactured by the same method as that of the first embodiment. However, in S330 of the flowchart shown in FIG. In addition, a non-conductive fixing member is applied to the surface opposite to the surface subjected to the process of the light emitting element 110, and in S390, the V-groove substrate electrode 140b and the light emitting element electrode 150 are electrically connected by the wire 160. In the first embodiment, the V groove substrate electrode 510a and the light emitting element electrode 520a, and the V groove substrate electrode 510b and the light emitting element electrode 520b are electrically connected by the wires 530a and 530b. Different from the manufacturing method of the form.
[0062]
Here, the fixing member of the present embodiment is a material having adhesiveness and thermosetting properties, such as silicone or polyethylene. The fixing member is used for adjusting the relative height position of the light emitting element 110 with respect to the V-groove substrate 130 by the adjustment external pressure in mounting, and is used for fixing the position, so that the moderately high viscosity or repulsive force is used. It is preferable to have. Moreover, it is preferable that the fixing member of the present embodiment has high thermal conductivity. The fixing member is assumed to have thermosetting properties. However, the fixing member is not thermosetting and may have photocuring property.
[0063]
As described above, according to the present embodiment, the fixing member does not need to have conductivity. Therefore, the optical module of the present embodiment can realize an optical module that can select a fixing member with a high degree of freedom.
[0064]
Moreover, according to this Embodiment, the fixing member which has high heat conductivity can be used as a fixing member. Therefore, the optical module of the present embodiment can release heat generated in the light emitting element 110 to the V-groove substrate 130.
[0065]
(Third embodiment)
In the optical module according to the second embodiment, the light emitting element and the optical fiber are mounted on the same V-groove substrate. However, even when the light-emitting element and the optical fiber are mounted on separate V-groove substrates, the same effect as when the light-emitting element and the optical fiber are mounted on the same V-groove substrate is obtained. Since the V-groove substrate to be mounted does not require flatness, the material of the V-groove substrate on which the light emitting element is mounted can be selected with a high degree of freedom. Therefore, in the optical module according to the third embodiment, the light emitting element and the optical fiber are mounted on separate V-groove substrates. Hereinafter, a description will be given focusing on differences from the second embodiment.
[0066]
FIG. 6A is a perspective view of the optical module in the present embodiment, and FIG. 6B is a cross-sectional view of the optical module taken along line AA ′ in the perspective view. 6, the same elements as those in FIG. 5 are denoted by the same reference numerals, and detailed description thereof will be omitted here.
[0067]
The optical module of the present embodiment includes a light emitting element 110, an optical fiber 120, a V groove 170, an alignment marker 180, V groove substrate electrodes 510a and 510b, light emitting element electrodes 520a and 520b, and wires 530a and 530b. The first V-groove substrate 610 on which the optical fiber 120 is mounted, the second V-groove substrate 620 on which the light emitting element 110 is mounted, and the light emitting element 110 and the second V groove substrate 620. The relative height position of the light emitting element 110 with respect to the first V-groove substrate 610 is adjusted, the position is fixed, and the light emitting element 110 and the second V-groove substrate 620 are bonded and integrated. And a fixing member 630. Note that the fixing member 630 may also be provided between the first V-groove substrate 610 and the second V-groove substrate 620, or between the light emitting element 110 and the second V-groove substrate 620. There may be no gap between the first V-groove substrate 610 and the second V-groove substrate 620, or between the light emitting element 110 and the first V-groove substrate 610.
[0068]
Here, the first V-groove substrate 610 is a semiconductor substrate with good flatness, for example, a silicon semiconductor substrate. Note that the first V-groove substrate 610 may be a metal substrate or a resin substrate.
The second V-groove substrate 620 is a metal substrate with high thermal conductivity. Note that the first V-groove substrate 610 may be a semiconductor substrate or a resin substrate.
[0069]
The fixing member 630 is a material having adhesiveness, thermosetting property and high thermal conductivity, and is made of, for example, silicone or polyethylene. The fixing member is used for adjusting the relative height position of the light emitting element 110 with respect to the first V-groove substrate 610 and fixing the position with an external pressure for adjustment in mounting, so that the viscosity is appropriately high. Or it is preferable to have a repulsive force. The fixing member is assumed to have thermosetting properties. However, the fixing member is not thermosetting and may have photocuring property.
[0070]
The optical module of the present embodiment having the above-described configuration is manufactured by the same method as that of the second embodiment, but is shown in FIG. 7A in S340 of the flowchart shown in FIG. As described above, the mounting position on the upper surface of the mounting reference substrate 220 of the V-groove substrate in which the first V-groove substrate 610 and the second V-groove substrate 620 are joined instead of the V-groove substrate 130 is determined. It is different from the manufacturing method of the second embodiment.
[0071]
When the fixing member 630 is between the light emitting element 110 and the second V-groove substrate 620 and further between the first V-groove substrate 610 and the second V-groove substrate 620, the optical module is In S340 of the flowchart shown in FIG. 3, as shown in FIG. 7B, the upper surface of the first V-groove substrate 610 on which the V-groove 170 is formed and the upper surface of the mounting reference substrate 220 are opposed to each other. The mounting position of the first V-groove substrate 610 on the upper surface of the mounting reference substrate 220 is determined by the V-groove substrate mounting alignment marker 250 and the alignment marker 180, and in S350, the mounting position on the upper surface of the mounting reference substrate 220 is determined. The first V-groove substrate 610 is placed, and in S360, fixing members 710a and 710b are applied to the surface opposite to the upper surface of the first V-groove substrate 610, and the second V-groove substrate 620 The V-groove substrate 610, the second V-groove substrate 620, and the light emitting element 110 are brought into strong contact with each other, and the second V-groove substrate 620 and the first V-groove substrate 610 are fixed to the fixing member 630 by the fixing members 710a and 710b. To bond the second V-groove substrate 620 and the light emitting element 110 so that the upper surface of the first V-groove substrate 610 and the surface subjected to the process of the light emitting element 110 are substantially flush with each other. The fixing members 630, 710 a, and 710 b are cured, and the light emitting element 110, the first V-groove substrate 610, and the second V-groove substrate 620 are integrated.
[0072]
When the fixing member 630 is not between the light emitting element 110 and the second V-groove substrate 620 but between the first V-groove substrate 610 and the second V-groove substrate 620, the optical module is In S330 of the flowchart shown in FIG. 3, the fixing member 630 is not applied to the surface opposite to the surface subjected to the process of the light emitting element 110, and in S340, as shown in FIG. The upper surface of the first V-groove substrate 610 on which the V-groove 170 is formed and the upper surface of the mounting reference substrate 220 are opposed to each other, and the upper surface of the mounting reference substrate 220 is aligned by the alignment marker 250 and the alignment marker 180 for mounting the V-groove substrate. The mounting position of the first V-groove substrate 610 is determined. In S350, the first V-groove substrate 610 is mounted on the upper surface of the mounting reference substrate 220. In S360, the light emission is performed. The light emitting element 110 and the second V-groove substrate 620 are bonded in a state where the surface of the child 110 opposite to the surface on which the process has been performed and the upper surface of the second V-groove substrate 620 are opposed to each other. The fixing members 710 a and 710 b are applied to the surface opposite to the upper surface of the groove substrate 610, and the light emitting element 110 and the second light emitting element 110 are connected to the second surface of the mounting reference substrate 220 in a state where the surface of the light emitting element 110 is subjected to the process. The bonding substrate formed by bonding the V-groove substrate 620 and the mounting reference substrate 220 are brought into strong contact, and the first V-groove substrate 610 and the bonding substrate are bonded by the fixing members 710a and 710b. The upper surface of the groove substrate 610 and the surface subjected to the process of the light emitting element 110 are substantially flush with each other, and in S370, the fixing members 710a and 710b are cured by heating, and the first V groove substrate 610 and the bonding substrate are bonded. Unite It is produced by.
[0073]
When the fixing member 630 is not between the light emitting element 110 and the second V groove substrate 620 but between the light emitting element 110 and the first V groove substrate 610, the optical module is shown in FIG. In step S330 of the flowchart, the fixing member 630 is not applied to the surface opposite to the surface on which the process of the light emitting element 110 is performed. In step S340, as illustrated in FIG. The upper surface of the groove substrate 610 in which the V-groove 170 is formed and the upper surface of the mounting reference substrate 220 are opposed to each other, and the first alignment mark on the upper surface of the mounting reference substrate 220 is aligned by the alignment marker 250 for mounting the V-groove substrate and the alignment marker 180. The mounting position of the V-groove substrate 610 is determined. In S350, the first V-groove substrate 610 is mounted on the upper surface of the mounting reference substrate 220. In S360, the light-emitting element 1 is placed. The light emitting element 110 and the second V groove substrate 620 are bonded in a state where the surface opposite to the surface subjected to the process 0 and the upper surface of the second V groove substrate 620 are opposed to each other. A bonding substrate formed by bonding the light emitting element 110 and the second V-groove substrate 620 is placed on the upper surface of the mounting reference substrate 220 in a state where the surface provided with the surface and the upper surface of the mounting reference substrate 220 face each other. The fixing members 720a and 720b are applied between the first V-groove substrate 610 and the bonding substrate, the first V-groove substrate 610 and the bonding substrate are bonded, and the first V-groove substrate 610 and the mounting reference are mounted. The substrate 220, the bonding substrate, and the mounting reference substrate 220 are brought into strong contact with each other so that the upper surface of the first V-groove substrate 610 and the surface subjected to the process of the light emitting element 110 are substantially flush with each other. Fixing members 720a, 72 by heating b curing the is produced by integrating the bonding substrate and the first V-groove substrate 610.
[0074]
Here, the fixing members 710 a, 710 b, 720 a, and 720 b are the same material as the fixing member 630.
[0075]
As described above, according to the present embodiment, the second V-groove substrate 620 is a metal substrate having high thermal conductivity, and the fixing members 630, 710a, and 710b have high thermal conductivity. Therefore, heat generated in the light emitting element 110 can be released through the fixing members 630, 710a, 710b and the second V-groove substrate 620, and instability of oscillation such as a change in the oscillation frequency of the light emitting element 110 can be removed. Therefore, the optical module of the present embodiment can prevent the deterioration of the characteristics of the light emitting element 110 caused by the heat generation of the light emitting element 110, that is, can realize an inexpensive optical module excellent in long-term stability and reliability. it can.
[0076]
Further, according to the present embodiment, the second V-groove substrate 620 does not require flatness. Therefore, the optical module of the present embodiment can realize an optical module that can select the V-groove substrate on which the light emitting element is mounted with a high degree of freedom.
[0077]
Further, according to the present embodiment, a ceramic substrate having excellent high frequency characteristics can be used as the second V-groove substrate 620. Therefore, the optical module of the present embodiment can realize an optical module with excellent high frequency characteristics.
[0078]
Further, according to the present embodiment, an optical module can be manufactured using a bonded substrate in which the second V-groove substrate 620 and the light emitting element 110 are bonded in advance. Therefore, it is possible to select only good light emitting elements by conducting light emitting element characteristic tests and reliability tests during the manufacturing of the optical module, so that the optical module of this embodiment greatly reduces yield and other damages. Thus, a low-cost optical module can be realized.
[0079]
Further, according to the present embodiment, the fixing members 720a and 720b can be poured between the first V-groove substrate 610 and the bonding substrate, and the bonding substrate can be fixed on the side surface. Therefore, when the fixing members 720a and 720b are cured, there is no alignment change in the height direction of the light emitting element 110 due to shrinkage or the like, and thus the optical module of the present embodiment realizes an optical module with excellent reliability. Can do.
[0080]
【The invention's effect】
As is apparent from the above description, according to the optical module of the present invention, optical coupling is performed by using a V-groove formed in advance on a V-groove substrate, and optical axis adjustment as in the active alignment mounting method is performed. Therefore, there is an effect that it is possible to realize an optical module that is inexpensive and excellent in mass productivity. In addition, since the light emitting element is mounted on the V-groove substrate by junction-up mounting and the parasitic capacitance formed by junction-down mounting can be removed, an effect of realizing an optical module with excellent high frequency characteristics can be realized. Played. Also, according to the optical module of the present invention, the mounting reference substrate is a light-transmitting substrate, so that it is formed on the light emitting device from the surface opposite to the surface on which the light emitting device and the V-groove substrate are placed. The alignment marker and the alignment marker formed on the V-groove substrate can be confirmed, and the alignment marker can be confirmed by a simple method such as a camera instead of using an X-ray or infrared camera. There is an effect that an optical module capable of simplifying the adjustment and reducing the cost of the implementation facility can be realized. In addition, according to the optical module of the present invention, since the fixing member does not need to have conductivity, there is an effect that an optical module that can select the fixing member with a high degree of freedom can be realized.
[0081]
In addition, according to the optical module of the present invention, the light emitting element and the optical fiber are mounted on separate V-groove substrates, a metal substrate having high thermal conductivity is used as the V-groove substrate on which the light emitting elements are mounted, and the fixing member is used. By using a fixing member having high thermal conductivity, heat generated in the light emitting element can be released to the V-groove substrate, and oscillation instability such as a change in the oscillation frequency of the light emitting element can be removed. There is an effect that an inexpensive optical module excellent in stability and reliability can be realized. According to the optical module of the present invention, the light emitting element and the optical fiber are mounted on separate V-groove substrates, and a ceramic substrate having excellent high frequency characteristics is used as the V-groove substrate on which the light emitting elements are mounted. Therefore, an effect that an optical module excellent in high frequency characteristics can be realized is achieved. Further, according to the optical module of the present invention, since the light emitting element and the optical fiber can be mounted on separate V-groove substrates, the light that can select the V-groove substrate on which the light emitting elements are mounted with a high degree of freedom. There is an effect that a module can be realized. In addition, according to the optical module of the present invention, the light emitting device and the optical fiber are mounted on separate V-groove substrates, and the optical module is manufactured by using the V-groove substrate and the light-emitting device previously bonded. This makes it possible to carry out characteristic tests and reliability tests of light emitting elements during the manufacturing of optical modules, and to select only good light emitting elements, greatly reducing yield and other damage and realizing a low-cost optical module The effect that it can be done is produced. According to the optical module of the present invention, the light emitting element and the optical fiber are mounted on separate V groove substrates, and the V groove substrate on which the light emitting elements are mounted and the V groove substrate on which the optical fiber is mounted are disposed. Since the fixing member is applied and the V-groove substrate on which the light emitting element is mounted and the light emitting element are fixed on the side surfaces, there is no alignment change in the height direction of the light emitting element due to shrinkage or the like when the fixing member is cured. As a result, an effect that an optical module excellent in reliability can be realized is produced.
[0082]
Therefore, according to the present invention, it becomes possible to realize an optical module having excellent mass productivity and excellent high frequency characteristics, and also having excellent long-term stability and reliability, and the practical value of the optical module of the present invention. Is extremely expensive.
[Brief description of the drawings]
FIG. 1 is a perspective view of an optical module according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view of the optical module showing the method of manufacturing the optical module in the embodiment.
FIG. 3 is a flowchart showing a manufacturing method of the optical module in the embodiment.
FIG. 4 is a top view of a mounting reference substrate 220 used in the method for manufacturing an optical module in the embodiment.
FIG. 5 is a perspective view of an optical module according to a second embodiment of the present invention.
FIG. 6A is a perspective view of an optical module according to a third embodiment of the present invention.
(B) is sectional drawing of the optical module in the embodiment.
FIG. 7 is a cross-sectional view of the optical module showing a manufacturing process of the optical module in the same embodiment.
FIG. 8A is a perspective view of a conventional optical module.
(B) is sectional drawing in the light emitting element mounting part in which the light emitting element 810 of the same optical module was mounted.
(C) is sectional drawing in the optical fiber mounting part in which the optical fiber 820 of the same optical module was mounted.
FIG. 9A is a perspective view of a light emitting element 810. FIG.
(B), (c) is sectional drawing of the optical module in a light emitting element mounting part.
[Explanation of symbols]
110, 810 Light emitting element
120, 820 optical fiber
130,830 V-groove substrate
140a, 140b, 510a, 510b V-groove substrate electrode
150, 520a, 520b Light emitting device electrode
160, 530a, 530b wire
170, 850 V groove
180,860 Alignment marker
210,870 Light emitting area
220 Reference board for mounting
230 Vacuum chuck
240, 630, 710a, 710b, 720a, 720b fixing member
250 V-groove substrate placement alignment marker
260, 880 Optical fiber core
410 Alignment marker for light emitting element placement
610 First V-groove substrate
620 Second V-groove substrate
840 Electrical wiring
910 Light emitting element alignment marker
920 stripe groove
930 electrode pad
940 Parasitic capacitance

Claims (23)

An optical module comprising an optical fiber and an optical element that are optically coupled, and a mounting substrate on which the optical fiber and the optical element are mounted,
The mounting substrate has two upper surfaces having steps,
The optical fiber is mounted in a V-groove formed on the first upper surface of the two upper surfaces of the mounting substrate,
The optical element is mounted on the lower second upper surface of the two upper surfaces of the mounting substrate,
An optical module, wherein a first upper surface of the mounting substrate and an upper surface of the optical element are substantially flush. The optical module according to claim 1, wherein the optical element is mounted on the second upper surface by junction-up mounting. 3. The optical module according to claim 1, wherein the mounting substrate includes a first substrate having a surface on which the V-groove is formed, and a second substrate having a surface in contact with the optical element. . The optical module further includes:
The optical module according to claim 2, further comprising a first fixing member that fixes a relative position of the optical element with respect to the mounting substrate between the first substrate and the second substrate. The optical module further includes:
The optical module according to claim 1, further comprising a second fixing member that fixes a relative position of the optical element with respect to the mounting substrate between the optical element and the mounting substrate. The optical module according to claim 5, wherein the second fixing member has adhesiveness, and bonds the mounting substrate and the optical element. The optical module according to claim 5, wherein the second fixing member has thermosetting property or photo-curing property. The optical module according to claim 5, wherein the second fixing member has thermal conductivity. An optical module manufacturing method comprising an optically coupled optical fiber and an optical element, and a mounting substrate on which the optical fiber and the optical element are mounted,
An optical element mounting step of mounting the optical element on the upper surface of the mounting reference substrate for optically coupling the optical element and the optical fiber;
A mounting substrate placing step of placing the mounting substrate on the upper surface of the mounting reference substrate, with the upper surface of the mounting reference substrate facing the upper surface of the mounting substrate on which the V-groove is formed;
A step of bringing the mounting reference substrate and the mounting substrate into contact with each other, and making a surface of the optical element in contact with the mounting reference substrate substantially flush with an upper surface of the mounting substrate;
And an optical fiber mounting step of mounting an optical fiber in the V-groove. In the optical element mounting step, the upper surface of the mounting reference substrate and the surface subjected to the process of the optical element are opposed, and the optical element is mounted on the upper surface of the mounting reference substrate,
10. The method of manufacturing an optical module according to claim 9, wherein in the step of flushing, a surface on which the process of the optical element is performed and an upper surface of the mounting substrate are substantially flush with each other. The mounting substrate includes an optical fiber substrate having a surface on which a V-groove is formed, and an optical element substrate having no surface on which a V-groove is formed,
The method for manufacturing the optical module further includes:
Bonding the optical fiber substrate and the optical element substrate,
11. The method of manufacturing an optical module according to claim 9, wherein, in the one surface step, a surface opposite to a surface in contact with the mounting reference substrate of the optical element is in contact with the optical element substrate. The method for manufacturing the optical module further includes:
Applying a first fixing member between the optical element substrate and the optical fiber substrate;
The method of manufacturing an optical module according to claim 11, wherein the substantially flush state is fixed by the first fixing member in the flush step. The method for manufacturing the optical module further includes:
Applying a second fixing member between the optical element and the mounting substrate;
The method of manufacturing an optical module according to claim 9, wherein the substantially flush state is fixed by the second fixing member in the flush step. The second fixing member has adhesiveness;
The optical module according to claim 13, wherein the optical element and the mounting substrate are bonded in the flush step. The second fixing member has thermosetting property or photo-curing property,
The method for manufacturing the optical module further includes:
15. The method of manufacturing an optical module according to claim 13, further comprising a step of curing the second fixing member with ultraviolet rays or heat. The mounting reference board includes an optical element alignment marker, a mounting board alignment marker, and a fixing unit.
In the optical element placement step, the optical element placement marker determines the placement position of the optical element on the upper surface of the mounting reference substrate, and the fixing device places the optical element on the upper surface of the mounting reference substrate. Is temporarily fixed,
The light according to any one of claims 9 to 15, wherein, in the mounting substrate mounting step, a mounting position of the mounting substrate on the upper surface of the mounting reference substrate is determined by the mounting substrate alignment marker. Module manufacturing method. The mounting reference substrate is a light-transmitting substrate,
In the optical element mounting step, confirm the optical element alignment marker from the surface opposite to the upper surface of the mounting reference substrate,
17. The method of manufacturing an optical module according to claim 16, wherein in the mounting substrate mounting step, the mounting substrate alignment marker is confirmed from a surface opposite to the upper surface of the mounting reference substrate. An optical fiber and an optical element that are optically coupled, an optical fiber substrate having a surface on which a V-groove is formed, and an optical element substrate that does not have a surface on which a V-groove is formed. An optical module manufacturing method comprising a mounting substrate to be mounted,
An optical element mounting step of mounting the optical element on the upper surface of the optical element substrate;
The upper surface of the mounting reference substrate for optically coupling the optical element and the optical fiber is opposed to the upper surface of the optical fiber substrate on which the V-groove is formed, and the optical fiber substrate is placed on the upper surface of the mounting reference substrate. An optical fiber substrate mounting step,
An optical element mounting step of placing an optical element on the upper surface of the mounting reference substrate, with the upper surface of the mounting reference substrate facing the surface on which the process of the optical element has been performed;
A step of bringing the optical element into contact with the mounting reference substrate and making the surface of the optical element processed and the upper surface of the optical fiber substrate substantially flush with each other;
And an optical fiber mounting step of mounting an optical fiber in the V-groove. The method for manufacturing the optical module further includes:
Applying a fixing member between the optical fiber substrate and the optical element substrate;
The method of manufacturing an optical module according to claim 18, wherein the substantially flush state is fixed by the fixing member in the flushing step. The fixing member has adhesiveness;
The optical module according to claim 19, wherein the optical fiber substrate and the optical element substrate are bonded in the flush step. The fixing member has thermosetting property or photocuring property,
The method for manufacturing the optical module further includes:
21. The method of manufacturing an optical module according to claim 19, further comprising a step of curing the fixing member by ultraviolet rays or heat. The mounting reference board includes an optical element alignment marker and a mounting board alignment marker,
In the optical fiber substrate mounting step, the mounting position of the optical fiber substrate on the upper surface of the mounting reference substrate is determined by the mounting substrate alignment marker,
The light according to any one of claims 18 to 21, wherein, in the optical element mounting step, a mounting position of the optical element on the upper surface of the mounting reference substrate is determined by the optical element alignment marker. Module manufacturing method. The mounting reference substrate is a light-transmitting substrate,
In the optical fiber substrate mounting step, confirm the mounting substrate alignment marker from the surface opposite to the upper surface of the mounting reference substrate,
23. The method of manufacturing an optical module according to claim 22, wherein in the optical element mounting step, the optical element alignment marker is confirmed from a surface opposite to the upper surface of the mounting reference substrate.

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