WO2014196043A1

WO2014196043A1 - Optical module and method for manufacturing optical module

Info

Publication number: WO2014196043A1
Application number: PCT/JP2013/065632
Authority: WO
Inventors: 進石田; 松嶋　直樹
Original assignee: 株式会社日立製作所
Priority date: 2013-06-05
Filing date: 2013-06-05
Publication date: 2014-12-11

Abstract

The purpose of the present invention is to provide an optical module with a compact and simple structure such that even when the temperature of the optical module changes, a fiber block will not shift in position. The optical module comprises: an optical element that is a transmission element or a receiving element; a semiconductor for driving an optical element or amplifying the output of the optical element; a wiring substrate electrically connected to the optical element and the semiconductor; and a fiber block optically connected to the optical element. The wiring substrate includes a plurality of first projections in contact with the fiber block, and a second projection shorter than the first projection. The second projection and the fiber block are connected with a photocurable adhesive.

Description

Optical module and optical module manufacturing method

The present invention relates to an optical module and an optical module manufacturing method, and more particularly to an optical module that transmits or receives an optical signal and an optical module manufacturing method.

In recent years, with the rapid spread of the Internet, the transmission capacity of the service provider's backbone optical network is rapidly increasing. Therefore, in a station where a large-capacity router and an optical multiplex transmission apparatus are placed, there is an increasing demand for a large-capacity, low-cost, low-power-consumption optical module that connects the apparatuses or between apparatuses.

An optical module that satisfies such requirements is represented by a PIN photodiode as well as a surface light emitting device represented by a VCSEL (Vertical / Cavity / Surface / Emitting / Laser) as a light source from the viewpoint of low cost and low power consumption. A method using a surface light receiving element is employed. Further, from the viewpoint of increasing the capacity, an array type optical element in which a plurality of channels of these optical elements are arranged at a pitch of 250 μm is used. The VCSEL is driven and modulated by an electrically connected IC. On the other hand, the electrical signal photoelectrically converted by the surface light receiving element is amplified and output by the connected IC.

In the optical module disclosed in Non-Patent Document 1, the optical coupling between the fiber fixed to the V-groove of the optical connector and the optical element fixed to the transparent resin substrate is easily achieved by fitting the guide pin and the guide hole. It can be performed with an accuracy of about μm. For this reason, the optical module has no fear that an optical signal leaks into an adjacent channel. This optical module can also prevent optical coupling deterioration due to aberrations in the lens of the ray lens substrate. Note that Non-Patent Document 1 does not disclose a method of mounting an optical module on a transparent resin substrate on a ceramic substrate.

However, the optical module disclosed in Non-Patent Document 1 has the following problems.
An area is required to install the mating pin on the fiber block and the mating hole on the board for optical coupling between the fiber fixed in the V groove of the optical connector and the optical element fixed on the transparent resin substrate. It is. For this reason, it becomes a problem to reduce the size of the optical module.
In addition, in order to perform alignment with an accuracy of about several μm by the mating structure, high processing accuracy of the mating pin and the mating hole is required. Furthermore, the “play”, which is an extra space, is made as small as possible.

When the optical module is in operation, the IC generates heat and the temperature of the optical module itself rises. When the temperature rises with a small play between the fitting pin and the fitting hole, stress is applied to the fitting hole due to a difference in thermal expansion corresponding to the temperature change. This stress causes cracks in the substrate or distortion in the substrate. As a result, problems occur in the long-term reliability of the optical module.

An object of the present invention is to provide an optical module that minimizes the positional deviation of the fiber block in the z direction even when the temperature of the optical module changes.

The problems described above include an optical element that is a transmission element or a reception element, a semiconductor that drives the optical element or amplifies the output of the optical element, an optical element and a wiring board that is electrically connected to the semiconductor, an optical element, and an optical element. In the optical module configured to include the optically connected fiber blocks, the wiring board is disposed between the plurality of first protrusions contacting the fiber block and the first protrusions and the other first protrusions. And a second protrusion having a height lower than that of the first protrusion, and the second protrusion and the fiber block can be solved by an optical module connected with a photo-curable adhesive.

Also, an optical element that is a transmission element or a reception element, a semiconductor that drives the optical element or amplifies the output of the optical element, a wiring board that is electrically connected to the optical element and the semiconductor, and an optical connection to the optical element And a plurality of first protrusions in contact with the fiber block, the first protrusions and the other first protrusions, wherein the first protrusions are arranged between the first protrusions and the first protrusions. Preparing a wiring board having a second protrusion having a height lower than that of the protrusion, applying a photocurable adhesive to the second protrusion, positioning the wiring board and the fiber block And a step of irradiating the irradiation light from the upper surface of the fiber block and solidifying the adhesive by the irradiation light transmitted through the inside of the fiber block. It can be.

According to the present invention, when the adhesive for fixing the fiber block to the substrate is expanded or contracted due to a change in heat or humidity, the stress of the adhesive on the substrate generated by the expansion or contraction of the adhesive is reduced at room temperature. By doing so, the positional deviation of the fiber block can be reduced.

It is sectional drawing of zx surface of an optical module. It is sectional drawing of yz surface of an optical module. It is sectional drawing (the 1) which shows the manufacturing process of an optical module. It is sectional drawing (the 2) which shows the manufacturing process of an optical module. It is a graph explaining the relationship between the internal stress and temperature in an optical module. It is sectional drawing of the xz surface in the assembly process in Example 2 of an optical module. It is sectional drawing of the xz surface in the final shape in Example 2 of an optical module. It is sectional drawing in Example 3 of an optical module.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings. The coordinates in the figure are defined by the z-axis direction as the upward direction in which the substrate overlaps the fiber block, and the x-axis and y-axis are defined by the right-handed system.

The cross-sectional structure of the optical module will be described with reference to FIG. FIG. 1 is a cross-sectional view in the length direction of a fiber of an optical module. In the embodiment, a transmission optical module will be described as the optical module 100. However, it can also be applied to a reception optical module by replacing the surface light emitting element with a surface light receiving element and replacing the drive device with a transimpedance amplifier (TIA). At this time, the arrows in FIG. 1 are reversed.

1, the optical module 100 includes a substrate 1, an LD (laser diode) 6, an LD driver IC 7, and a fiber block 3. The substrate 1 has electrical wiring. The LD 6 is a surface light emitting element. The LD driver IC 7 is a drive device that controls the optical element.

The fiber block 3 is connected to the optical fiber 8. In the fiber block 3, a condensing lens 4, a reflecting mirror 5, and a fiber positioning V-groove 9 are arranged and designed so as to optimize optical characteristics, and are integrally molded.

On the substrate 1, a recess 10 is provided, and a conductive wiring 11 for inputting and outputting an electric signal is provided. A driver IC 7 for electrically controlling the LD 6 is mounted face down on the substrate 1 and connected to the conductive wiring 11. The conductive wiring 11 is connected to the LD 6 by wire bonding.

A plurality of LDs 6 arranged in an array in the y-axis direction are also mounted on the substrate 1. Each LD 6 is connected to the conductive wiring 11 and is electrically connected to the driver IC 6. On the fiber block 3, the reflection mirror 5, the lens 4, and the V-shaped groove 9 for positioning the fiber are formed at a pitch of 250 μm, and a plurality of fibers 8 are fixed accurately in parallel at intervals of 250 μm. The end face of the fiber 8 is arranged and fixed so as to be in contact with the end face 13 of the fiber block 3 so that no optical loss occurs.

In the position adjustment of the fiber block 3, the optical loss of the optical element 6 installed on the substrate 1 and the lens 4 installed in the fiber block 3 is minimized with respect to the rotation angle in the x direction, the y direction, and the xy plane. It has been adjusted to be.

The optical path in the optical module 100 will be described. The optical signal spread from the LD 6 in the z direction and output at an angle 2θ is converted to the fiber end face direction by the optical path conversion mirror 5 through the converging convex lens 4 having the diameter d and propagates through the fiber block 3. The optical fiber 8 positioned in the V groove 9 is optically connected. Conversely, the path of incident light when the optical element 6 is a PD is the same as the optical design, although the light direction is opposite to that of the LD.

Referring to FIG. 2, the zy cross section of the optical module will be described. FIG. 2 is a cross-sectional view taken along the line A-A ′ of FIG. In FIG. 2, the fiber block bottom surface 31 is placed in direct contact with the top surface of the protrusion 15 installed on the substrate 1. An adhesive 14 is sandwiched between the upper surface of the protrusion 16 installed on the substrate 1 and the fiber block bottom surface 31 facing the protrusion 16. The fiber block 3 is fixed to the substrate 1 by the adhesive 14.

The bonding structure between the substrate 1 and the fiber block 3 will be described in detail. On the outside of the substrate 1, there is a protrusion 15 having a height H_b1 of 200 μm to several mm. In addition, a protrusion 16 having a height H_b2 of 200 μm to several mm is provided inside the substrate 1. The protrusion height has a relationship of H_b1> H_b2.

The substrate 1 is preferably free from warping and distortion in order to achieve optimum optical coupling between the lens 4 and the optical element 6. For this purpose, the projection heights H_b1 and H_b2 that affect the rigidity of the substrate are preferably 200 μm to several mm.

Since the upper surface of the protrusion 15 is in direct contact with the bottom surface of the fiber block, the optical coupling in the z direction between the optical element 6 and the lens 4 is optimized. For this purpose, the light spread of the optical element is made smaller than the diameter of the lens. Therefore, if the thickness of the substrate is H_b3 and the thickness of the optical element 6 (not shown) is H_b4, the optical distance (H_b1-H_b3-H_b4) to the optical element 6 installed on the substrate 1 Preferably, the relationship of (Equation 1) is satisfied between the spread angle 2θ of the optical element and the diameter d of the lens.

d / 2 <(H_b1-H_b3-H_b4) · tan θ (Formula 1)
The height of (H_b1-H_b2), that is, the thickness of the adhesive is less than 100 μm, and desirably 50 μm or less. This is because a light-solidifying adhesive is used as the adhesive, and the thinner the adhesive, the easier it is to solidify.

From the above, the ratio of the thicknesses of H_b1 and (H_b1-H_b2) is 10 times or more.
The adhesive 14 exists between the upper surface of the protrusion 16 and the adhesive surface 32 of the fiber block 3. On the bottom surface of the fiber block 3, the bonding portion 32 that is in contact with the adhesive 14 is in a flat state (planar surface) without a step. This is because the fiber block 3 moves due to thermal expansion or contraction of the adhesive if there is a step in the bonding portion 32.

As for the shape in the xy plane of the upper surface of the protrusion 16, a circular shape is desirable as a shape for canceling the stress generated in the xy plane of the adhesive. However, a shape having high rotational symmetry in the xy plane such as a hexagon or an octagon may be used. As a result, the total stress acting on the xy in-plane fiber block is cancelled. There is an air layer 18 between the side surface of the projection 15 and the side surface of the projection 16, and the adhesive 14 is not in contact with the side surface of the projection 15. Note that the shape of the spread adhesive 14 in the upper surface of the protrusion 16 may be circular. Moreover, a some circular shape may be sufficient. The shape of the upper surface of the protrusion 15 in the xy plane preferably extends below the fiber block 3 as shown in FIG.

The material of the substrate 1 is an electronic circuit substrate using an organic material such as ceramic, glass or glass epoxy. Since the fiber block 3 transmits an optical signal, the transmittance is preferably 70% or more with respect to the wavelength of the signal light from 600 nm to 1300 nn. Further, a material having a transmittance of about 30% even at a wavelength of 365 nm used for the photo-curing adhesive, specifically, PMMA (acrylic), polycarbonate, polyetherimide, or the like is preferable.

Referring to FIG. 3 and FIG. 4, the assembly process of the fiber block in the optical module will be described. 3 and 4 are both A-A 'cross-sectional views of FIG. In FIG. 3, after supplying the liquid adhesive 14 onto the protrusion 16, the fiber block 3 is gripped by a manipulator 19 capable of fine alignment. In the xy plane, the manipulator 19 is operated to adjust the position so that the optical coupling between the optical element 6 mounted on the substrate and the lens 4 on the fiber block 3 is the best (arrow B).

4, next, the manipulator 19 is moved in the −Z direction so that the bottom surface 31 of the fiber block 3 is in contact with the protrusion 15 of the substrate 1 (arrow C). At this time, the adhesive 14 is sandwiched between the substrate protrusion 16 and the fiber block 3. UV light is irradiated from a UV light source 24 installed above the fiber block 3, and the UV light passes through the fiber block 3 to cure the adhesive 14. After the adhesive 14 is completely cured, the gripping of the fiber block 3 with the manipulator 19 is released. By irradiation with UV light, the adhesive 14 undergoes volume shrinkage of about 5% accompanying cure shrinkage.

When the adhesive 14 is solidified with curing shrinkage, the thickness of the adhesive in the z direction cannot shrink because the fiber block 3 is in direct contact with the protrusion 15 as shown in FIG. Thereby, after the adhesive 14 is solidified, the shrinkage pressure is included in the adhesive 14.

According to the optical module 100 having the above structure, the z-axis direction of the fiber block 3 due to thermal expansion and thermal contraction of the adhesive 14 that bonds and fixes the substrate 1 and the fiber block 3 with an increase in temperature. Can be suppressed.

Referring to FIG. 5, the effect of suppressing the displacement of the fiber block 3 in the z direction due to the temperature rise will be described. As described with reference to FIG. 4, after the adhesive 14 is solidified at the time of curing, the shrinkage pressure is included in the adhesive (arrow D). When the temperature rises in the optical module 100, the adhesive 14 is stressed in the direction extending in the + z direction due to thermal expansion. However, since the adhesive 14 contains a shrinkage stress, it simply releases the compressive stress as the temperature rises, and does not expand (arrow E). The thermal expansion coefficient of the adhesive 14 is about 50 PPM / ° C. Therefore, a temperature increase of 125 ° C. is necessary to completely release the shrinkage stress. On the other hand, since the upper limit temperature of the optical module 100 is 100 ° C. or lower, the shrinkage stress is always applied to the adhesive at the operating temperature of the optical module. Therefore, the height change of the fiber block 3 in the z direction does not occur.

On the other hand, when a temperature drop occurs in the optical module, the adhesive 14 undergoes heat shrinkage. However, in the structure of FIG. 2, since the fiber clock 3 is in contact with the protrusion 15, the optical distance (H_b1-H_b3-H_b4) between the optical element 6 installed on the substrate 1 does not change.

Next, the effect of suppressing the displacement of the fiber block in the xy plane will be described. The adhesive 14 provided on the upper surface of the protrusion 16 is bonded to the fiber block 3 with a flat bonding surface 32 having no step in the z direction. There is an air layer 18 between the side surface of the projection 15 and the side surface of the projection 16, and the adhesive 14 is not in contact with the side surface of the projection 15. When the adhesive expands due to the temperature rise, the side surface of the adhesive 14 is not restrained because it is in contact with the air 18 and can expand freely. From this, the adhesive 14 does not apply stress to the fiber block 3. The bonding surface 32 of the fiber block is in a flat state without a step. For this reason, the force that the bonding surface 32 receives from the expansion of the adhesive 14 is only the shear stress from the bonding interface. Since the adhesive interface 32 has a circular shape, the force received from the adhesive interface is isotropic, and the sum of stresses that cause displacement in the xy plane of the fiber block 3 is cancelled. Therefore, no positional deviation occurs in the xy plane.

The optical module of Example 2 will be described with reference to FIGS. In FIG. 6, the board 1 of the optical module 100 </ b> A is provided with a fitting hole 22 in the protrusion 15 in addition to the protrusion 15 and the protrusion 16.

On the other hand, the fiber block 3 is also provided with a fitting hole 20. The optical element 6 and the lens 4 can be aligned by passing the fitting pin 21 through both the fitting hole 20 and the fitting hole 22. Accordingly, the alignment of the fiber block 3 in the xy direction can be easily performed without using the manipulator 19 as shown in FIGS. 4 and 5 of the first embodiment.

The adhesive 14 exists between the upper surface of the protrusion 16 and the adhesive surface 32 of the fiber block 3 as described in the first embodiment. The bonding surface on the bottom surface of the fiber block is flat without a step in the z direction. The upper surface of the protrusion 15 is in direct contact with the fiber block bottom surface 31. Thereby, the height of the fiber block in the z direction is determined by H_b1.

In the structure of Example 2 described above, it is possible to include compressive stress inside the adhesive by curing the adhesive 14 in the assembly process described in FIGS. 3 and 4 of Example 1. The positional deviation of the fiber block in the z direction is the same as that of the first embodiment described with reference to FIG.

In FIG. 7, it is desirable that the fitting pin 21 can be removed. The optical module 100 </ b> A can align the fiber block 3 using the fitting pin 21, and can pull out the fitting pin 21 after fixing by fixing the adhesive 14. Therefore, in the optical module 100A, as shown in FIG. 7, the fitting pin 21 does not exist, but the fitting hole 20 and the fitting hole 22 remain.

The fiber block 3 is aligned with the fitting pin 21, and the fitting pin 21 is pulled out after the fixing with the adhesive 14 is completed. Further, even if the temperature changes after the fitting pin 21 is extracted, no stress in the xy plane is applied to the substrate 1.
According to the second embodiment, an optical module that does not require the use of a manipulator in its manufacture can be obtained.

The optical module of Example 3 will be described with reference to FIG. In FIG. 8, in the optical module 100 </ b> B, the adhesive 23 remains between the side surface of the protrusion 15 and the side surface of the protrusion 16. The thickness H_s of the adhesive 23 is lower than the side surface height (H_b2-H_b3) of the protrusion 16, that is, there is a relationship of H_s <H_b1.

Therefore, the adhesive 23 does not contact the bottom surface 31 of the fiber block. Therefore, the upper surface of the protrusion 15 is in direct contact with the bottom surface 31 of the fiber block.

In the adhesive 23 surrounded by the

protrusions

15 and 16, even if the thermal expansion of the adhesive 23 due to a temperature rise occurs, the air layer 18 exists in the z direction. The stress applied to the fiber block 3 is the same as in the first embodiment. In the xy plane, the adhesive 23 applies stress to the side surfaces of the

protrusions

15 or 16, but does not apply stress to the fiber block 3.
According to the third embodiment, it is not necessary to accurately control the application amount of the adhesive 14 described with reference to FIG.

DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 3 ... Fiber block, 4 ... Lens, 5 ... Mirror, 6 ... Optical element, 7 ... IC, 8 ... Fiber ..., 9 ... V groove, 10 ... Recessed part, 11 ... Wiring, 13 ... End face of fiber block 14 ... adhesive, 15 ... protrusion, 16 ... protrusion, 17 ... substrate thickness, 18 ... air layer, 19 ... manipulator, 20 ... fitting hole, 21 ... fitting pin, 22 ... fitting hole ..., 23 ... adhesive ... , 24 ... UV light source, 31 ... bottom surface of the fiber block, 32 ... adhesive portion in contact with the adhesive of the fiber block, 40 ... optical element, 41 ... solder, 42 ... transparent resin substrate, 43 ... conductive pattern, 44 ... Array lens substrate, 45 ... lens holder, 46 ... optical connector, 47 ... V groove, 48 ... optical fiber, 49 ... guide pin, 50 ... guide hole, 51 ... mirror surface, 52 ... IC, 53 ... ceramic substrate, 54 ... Sul Hall, 100 ... light module.

Claims

An optical element that is a transmitting element or a receiving element; a semiconductor that drives the optical element or amplifies the output of the optical element; the optical element; a wiring board that is electrically connected to the semiconductor; the optical element and the optical element; An optical module configured to include an optically connected fiber block;
The wiring board is disposed between a plurality of first protrusions in contact with the fiber block, the first protrusion and the other first protrusions, and a second height lower than the first protrusions. A projection, and
The optical module, wherein the second protrusion and the fiber block are connected by a photocurable adhesive.
The optical module according to claim 1,
When the height of the first protrusion is H_b1, and the height of the second protrusion is H_b2,
An optical module having a relationship of H_b1 / (H_b1-H_b2)> 10.
The optical module according to claim 1 or 2, wherein
An optical module comprising a space between a first side surface of the first protrusion and a second side surface of the second protrusion.
An optical module according to any one of claims 1 to 3, wherein
A portion of the bottom surface of the fiber block that is in contact with the adhesive is a flat surface.
An optical module according to any one of claims 1 to 4, wherein
The optical module is characterized in that the fiber block has a transmittance of 10% or more with respect to a wavelength used for adhesive curing.
An optical module according to any one of claims 1 to 5, comprising:
An optical module characterized in that the fiber block has a transmittance of 70% or more in a wavelength band used by an optical element placed on a substrate.
An optical module according to any one of claims 1 to 6, comprising:
The optical module according to claim 2, wherein the bonding surface of the second protrusion is a circle or a polygon having high rotational symmetry.
An optical module according to any one of claims 1 to 7,
There is a second adhesive between the first side of the first projection and the second side of the second projection;
The optical module is characterized in that the height of the second adhesive is H_s and H_s <H_b2.
An optical element that is a transmitting element or a receiving element; a semiconductor that drives the optical element or amplifies the output of the optical element; the optical element; a wiring board that is electrically connected to the semiconductor; the optical element and the optical element; In the manufacturing method of the optical module comprised including the optically connected fiber block,
A plurality of first protrusions in contact with the fiber block; and a second protrusion disposed between the first protrusion and the other first protrusion and having a height lower than that of the first protrusion. Preparing the wiring board;
Applying a photo-curable adhesive to the second protrusion;
Positioning the wiring board and the fiber block;
Irradiating irradiation light from the upper surface of the fiber block, and solidifying the adhesive by the irradiation light transmitted through the inside of the fiber block.