Optical Module

Abstract

Disclosed is an optical module comprising: an electric circuit board (E) having an electric circuit provided on a light-transmissive resin substrate (1); and an optical element (11) joined on the electric circuit board (E). The optical module is configured such that: the optical element (11) is joined to the electric circuit board (E) in a state where a light-emitting unit or a light-receiving unit (11a) of the optical element (11) faces an electric circuit surface side of the electric circuit board (E); a light-transmissive resin cured product (X) is embedded between the light-emitting unit or the light-receiving unit (11a) of the optical element (11) and the light-transmissive resin substrate (1); and the relative refractive index difference between the light-transmissive resin cured product (X) and the light-transmissive resin substrate (1) is 20% or less. In this way, light propagation loss can be reduced with a simple structure.

Description

[Technical Field]

[0001] The present invention relates to an optical module in which an optical element such as a light emitting element or a light receiving element is mounted on an electric circuit board (the optical element is joined to the electric circuit board). [Background technology]

[0002] As an optical module in which optical elements such as light-emitting elements and light-receiving elements are mounted on an optical waveguide, for example, the following optoelectronic hybrid board (first conventional example) has been proposed. This optoelectronic hybrid board includes an electric circuit board having electrical wiring formed on the surface of an insulating layer, an optical waveguide (first cladding layer, core (optical wiring), second cladding layer) laminated on the back surface of the insulating layer of the electric circuit board (the surface opposite to the surface on which the electrical wiring is formed), and a light-emitting element and a light-receiving element mounted on portions of the surface on which the electrical wiring is formed corresponding to both ends of the optical waveguide. In this optoelectronic hybrid board, both ends of the optical waveguide are formed on inclined surfaces inclined at 45° with respect to the longitudinal direction of the core (the direction of light propagation), and the portions of the core located on the inclined surfaces serve as light-reflecting surfaces (mirrors). The insulating layer is optically transparent, allowing light to propagate through the insulating layer between the light-emitting element and the light-reflecting surface at one end and between the light-receiving element and the light-reflecting surface at the other end.

[0003] Light propagates in the above-mentioned opto-electric hybrid board as follows. First, light is emitted from the light-emitting element toward the light-reflecting surface at one end. After passing through the insulating layer, the light passes through the first cladding layer at one end of the optical waveguide, is reflected by the light-reflecting surface at one end of the core (changing its optical path by 90°), and travels longitudinally within the core. The light that has propagated within the core is then reflected by the light-reflecting surface at the other end of the core (changing its optical path by 90°) and travels toward the light-receiving element. Next, the light passes through the first cladding layer at the other end, is emitted, passes through the insulating layer, and is received by the light-receiving element.

[0004] However, there is a problem in that the light emitted from the light-emitting element is diffused or reflected before it reaches the light-receiving element, reducing the amount of light that is effectively propagated, resulting in a decrease in the output of the optical-electrical hybrid board.

[0005] Therefore, various proposals have been made to reduce the propagation loss of light by providing a lens between an optical element such as a light-emitting element or a light-receiving element and an optical waveguide in the configuration shown in the first conventional example (second conventional example) (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-40011 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, the lens-equipped device as in the second conventional example has a complex structure, a large number of parts, and a complicated manufacturing process, which creates a problem in terms of cost, and there is room for improvement in this regard.

[0008] The present invention has been made in view of the above circumstances, and provides an optical module that has a simple structure and can reduce the propagation loss of light. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to solve the above-mentioned problems. During the course of their research, the inventors have investigated the use of a light-transmitting resin composition as an underfill for optical elements such as light-emitting elements and light-receiving elements in the configuration shown in the first conventional example. That is, they have investigated the use of the light-transmitting resin composition as an underfill to simplify the structure and manufacturing process for reducing light propagation loss, and further investigated the use of the underfill to reinforce the joint between the optical element and the electric circuit board. In the first conventional example, as shown in Fig. 4, for example, a void (space filled with air) 20 is formed between the light-emitting portion (or light-receiving portion) 11a of the optical element 11 and the insulating layer (light-transmitting resin substrate 1) of the electric circuit board E. Because the difference between the refractive index of air and the refractive index of the light-transmitting resin substrate 1 is large, a part of the optical signal L is reflected at the interface between the void 20 and the light-transmitting resin substrate 1, as indicated by the white arrow, resulting in a large propagation loss of light. Therefore, the present inventors investigated suppressing the propagation loss of light by filling the void 20 with a light-transmitting resin cured product X as shown in Fig. 2 and further reducing the difference between the refractive index of the light-transmitting resin cured product X and the refractive index of the light-transmitting resin substrate 1 of the electric circuit board E. Then, the inventors calculated the relative refractive index difference shown in the following formula (1), where n1 is the higher refractive index and n2 is the lower refractive index of the refractive index of the cured light-transmitting resin X and the light-transmitting resin substrate 1 of the electric circuit board E, and found that when this value is 20% or less, the reflection of the optical signal L at the interface between the cured light-transmitting resin X and the light-transmitting resin substrate 1, as shown in FIG. 2, is suppressed more than the reflection of the optical signal L at the interface between the void portion 20 and the light-transmitting resin substrate 1, as shown in FIG. 4, thereby reducing the propagation loss of light. Therefore, when an optical waveguide W is provided, as shown in FIGS. 2 and 4, for example, the output efficiency of the optical signal L propagating through the core 7 can be increased. Relative refractive index difference [%] = [(n1-n2) / n1] × 100 ……(1)

[0010] That is, the gist of the present invention is the following [1] to [5]. [1] An optical module comprising an electric circuit board having an electric circuit provided on a light-transmitting resin substrate, and an optical element bonded to the electric circuit board, wherein the optical element is bonded to the electric circuit board with the light-emitting portion or the light-receiving portion of the optical element facing the electric circuit surface of the electric circuit board, the space between the light-emitting portion or the light-receiving portion of the optical element and the light-transmitting resin substrate is filled with a light-transmitting resin cured product, and the relative refractive index difference between the light-transmitting resin cured product and the light-transmitting resin substrate is 20% or less. [2] The optical module according to [1], wherein the optically transparent resin cured product has a 400 nm light transmittance of 40% or more when the thickness is set to 100 μm. [3] The optical module according to [1] or [2], wherein the cured optically transparent resin is a cured thermosetting resin composition that is cured by heating at 100°C for 3 hours. [4] The optical module according to any one of [1] to [3], wherein the light-transmitting resin substrate is made of a polyimide resin. [5] An optical module described in any one of [1] to [4], wherein the electrical circuit board has an optical waveguide on the side opposite to the side to which the optical element is bonded, and the core of the optical waveguide is optically coupled to the light emitting portion or the light receiving portion of the optical element. [Effects of the Invention]

[0011] As described above, the optical module of the present invention has a simple structure and can reduce light propagation loss, thereby increasing the light extraction efficiency (output efficiency of the optical module). Furthermore, the optical module of the present invention has excellent durability because the joints between the electric circuit board and the optical element are reinforced with underfill. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a longitudinal sectional view schematically showing an example of an optical module of the present invention. [Figure 2] FIG. 2 is a vertical cross-sectional view schematically showing the flow of an optical signal in the optical module. [Figure 3]5(a) to 5(d) are explanatory views schematically showing the steps of forming the optical module of the present invention. [Figure 4] FIG. 1 is a vertical cross-sectional view schematically showing an example of a conventional optical module. DETAILED DESCRIPTION OF THE INVENTION

[0013] Next, an embodiment of the present invention will be described in detail, but the present invention is not limited to this embodiment.

[0014] The optical module of the present invention is an optical module including an electric circuit board having an electric circuit formed on a transparent resin substrate, and an optical element bonded to the electric circuit board, wherein the optical element is bonded to the electric circuit board with its light-emitting or light-receiving portion facing the electric circuit surface of the electric circuit board, and the space between the light-emitting or light-receiving portion of the optical element and the light-transmitting resin substrate is filled with a cured light-transmitting resin. The optical module is characterized in that the relative refractive index difference (relative refractive index difference (%) shown in formula (1) below) between the cured light-transmitting resin and the light-transmitting resin substrate is 20% or less. In the present invention, the "light transparency" of the light-transmitting resin substrate refers to a light transmittance of 60% or more at a wavelength of 850 nm, preferably a light transmittance of 65% or more, and more preferably a light transmittance of 70% or more. Furthermore, the "light transmittance" of the above-mentioned light-transmitting resin cured product means that the light transmittance at a wavelength of 400 nm when the thickness is 100 μm is 40% or more, preferably the light transmittance is 60% or more, and more preferably the light transmittance is 80% or more. The light transmittance was measured using, for example, a JASCO V ultraviolet-visible-near infrared spectrophotometer manufactured by JASCO Corporation. -670".

[0015] 1 shows an example of an optical module of the present invention, with 11 being an optical element, 11a being a light-emitting portion (or a light-receiving portion), and 11b being a bump. As shown in the figure, the optical element 11 is mounted with its light-emitting portion (or light-receiving portion) 11a facing the electric circuit board E, so as to be connected to the electric circuit of the electric circuit board E via the bump 11b and the mounting pad 2a. The electric circuit board E is formed by forming an electric circuit (not shown) and the mounting pad 2a on the surface of an optically transparent resin substrate 1.

[0016] The optical module of the present invention shown in FIG. 1 is an opto-electrical hybrid board having an optical waveguide W on the surface of the electric circuit board E opposite to the surface to which the optical element 11 is bonded. The core 7 of the optical waveguide W is optically coupled to the light-emitting portion (or light-receiving portion) 11a of the optical element 11 via the optically transparent resin cured product X and the optically transparent resin substrate 1. The optical waveguide W is formed by laminating a first cladding layer 6, a core 7, and a second cladding layer 8. As shown in the figure, one end of the optical waveguide W corresponding to the optical element 11 is formed on an inclined surface inclined at 45° with respect to the longitudinal direction of the core 7, and the portion of the core 7 located on the inclined surface serves as a light-reflecting surface 7a. With this configuration, the light-emitting portion (or light-receiving portion) 11a of the optical element 11 is optically coupled to the core 7. When 11a is the light-emitting portion, an optical signal L propagates through the core 7 of the optical waveguide W in the direction indicated by the arrow in the figure. When 11a is a light receiving section, the optical signal L propagates in the direction opposite to the arrow shown in the figure. In this embodiment, a reinforcing metal layer M is provided between the electric circuit board E and the optical waveguide W. The metal layer M is provided with a through hole 5 so as not to interfere with the optical signal L transmitted and received at the light emitting section (or light receiving section) 11a of the optical element 11, and a first clad layer 6 is inserted in the through hole 5 to fill it.

[0017] 1, the space between the light-emitting section (or light-receiving section) 11a of the optical element 11 and the light-transmitting resin substrate 1 of the electric circuit board E is filled with a light-transmitting resin cured product X, and as mentioned above, the relative refractive index difference between the light-transmitting resin cured product X and the light-transmitting resin substrate 1 is 20% or less. The relative refractive index difference is preferably 0 to 15%, more preferably 0 to 10%. This can increase the light extraction efficiency (output efficiency of the optical module). The relative refractive index difference is a value shown in the following formula (1), where n1 is the higher refractive index and n2 is the lower refractive index of the optically transparent resin cured product X and the optically transparent resin substrate 1 of the electric circuit board E. Relative refractive index difference [%] = [(n1-n2) / n1] × 100 ……(1) In the present invention, the refractive index is measured by a prism coupler method to measure the refractive index for light of 850 nm, and can be measured, for example, by a 2010 / M prism coupler manufactured by Metricon. The refractive index of the optically transparent resin cured product X is preferably 1.30 to 1.90, more preferably 1.40 to 1.65. The refractive index of the optically transparent resin substrate 1 of the electric circuit board E is preferably 1.30 to 1.90, more preferably 1.50 to 1.85.

[0018] Examples of materials for forming the light-transmitting resin substrate 1 in the electric circuit board E include synthetic resins such as polyimide, polyethernitrile, polyethersulfone, polyethylene terephthalate, polyethylene naphthalate, and polyvinyl chloride, as well as silicone-based sol-gel materials. These may be used alone or in combination of two or more. Among these, polyimide resin is preferred. From the viewpoint of light transmittance, the thickness of the light-transmitting resin substrate 1 is preferably within a range of 5 to 100 μm, and from the same viewpoint, more preferably within a range of 10 to 30 μm.

[0019] The material for forming the optically transparent cured resin X is typically a material having thermosetting or UV-curing properties. In particular, from the perspective of better manufacturing the optical module of the present invention, it is preferable that the resin composition used as the forming material has both thermosetting and UV-curing properties. The properties are typically determined by the combination of the resin component (main component) and the curing agent component, which will be described later. The resin composition is typically a liquid that exhibits fluidity at room temperature (25°C), and is diluted with an organic solvent as needed. From the viewpoint of preventing damage to optical elements due to heat, it is preferable that the optically transparent cured resin X be a cured product of a thermosetting resin composition that cures upon heating for 3 hours at 100° C. From the same viewpoint, it is more preferable that the optically transparent cured resin X be a cured product of a thermosetting resin composition that cures upon heating for 0.5 to 1 hour at 25 to 100° C.

[0020] The resin component (main component) in the material for forming the optically transparent cured resin X may be an optically transparent resin such as an epoxy resin, a silicone resin, an acrylic resin, or a urethane resin, which may be used alone or in combination. Among these, from the viewpoint of heat resistance reliability, an epoxy resin or a silicone resin is preferred.

[0021] The epoxy resin may be, for example, a bisphenol epoxy resin, an alicyclic epoxy resin, or a novolac epoxy resin, and may be used alone or in combination. Of these, bisphenol epoxy resins and alicyclic epoxy resins are preferred. Such epoxy resins generally have an epoxy equivalent of 100 to 1000 and a softening point of 120°C or less. The proportion of the bisphenol epoxy resin and alicyclic epoxy resin is preferably set to 50% by weight or more of the total epoxy resin.

[0022] As the silicone resin, for example, methyl silicones, phenyl silicones, etc. may be used alone or in combination of two or more kinds. Among them, methyl silicones are preferred.

[0023] Examples of the curing agent component used together with the resin component include a heat curing agent, an ultraviolet curing agent (a photocationic polymerization initiator, a photoanionic polymerization initiator, a radical initiator), a moisture curing agent, etc. These may be used alone or in combination of two or more. Specific examples of the photocationic polymerization initiator include triarylsulfonium-phosphorus anion salts, triarylsulfonium borate salts, and the like. The amount of the cationic photopolymerization initiator added is preferably set in the range of 0.1 to 10 parts by weight, more preferably 0.5 to 4 parts by weight, and even more preferably 1 to 2 parts by weight, per 100 parts by weight of the resin component (main component).

[0024] The material for forming the optically transparent cured resin X may further contain, as necessary, a curing catalyst, a dye, a modifier, a discoloration inhibitor, an anti-aging agent, a release agent, a reactive or non-reactive diluent, and the like.

[0025] The resin composition that is the material for forming the optically transparent cured resin X can be prepared, for example, by blending and mixing the resin component, curing agent component, etc., and further, if necessary, kneading or melt-mixing the mixture with a kneader.

[0026] The method of underfilling the optical element 11 using the resin composition that is the material for forming the above-mentioned light-transmitting resin cured product X is not particularly limited, and can be carried out by known molding methods such as ordinary transfer molding and casting. FIG. 3 is a schematic diagram showing an example of a manufacturing process for the optical module of the present invention (the optical module shown in FIG. 1), and the process proceeds in the order of (a) to (d) shown in the figure. That is, first, as shown in (a), an optical element 11 is mounted on an electric circuit board E, and then, as shown in (b), an underfill X' (the above-mentioned resin composition) is applied. The application is carried out using a syringe or the like. Then, UV (ultraviolet rays) are irradiated in the direction of the arrow U shown in (c) to partially harden the underfill X', temporarily fixing the optical element 11, and then, as shown in (d), the underfill X' is heated. This heat cures the uncured parts of Underfill X' (the parts that were not irradiated with UV light), This results in a completely cured product (light-transmitting resin cured product X). In this way, the optical element 11 is finally fixed. The UV irradiation conditions for curing the underfill X' are as follows: 4,000~30,000mJ / cm 2 It is preferable to carry out ultraviolet irradiation of Preferably, the device is 12,000 to 24,000 J / m 2 UV irradiation is performed The heating conditions for thermally curing the underfill X' are as follows: 2 Heating is preferably carried out at 5 to 150°C for 10 to 180 minutes, and more preferably at 80 to 100°C for 30 to 120 minutes using the above-mentioned device. When an optical module is manufactured by the above-described process, the underfill X' is It is preferable that the composition has both heat-curable and ultraviolet-curable properties. Although the above-described temporary fixing step can be omitted, it is preferable to include the above-described temporary fixing step in order to improve yield.

[0027] [Formation of Electric Circuit Board E] 1, first, a metal sheet material is prepared for forming the metal layer M. Examples of materials for forming this metal sheet material include stainless steel and 42 alloy, and among these, stainless steel is preferred from the viewpoint of dimensional accuracy, etc. The thickness of the metal sheet material (metal layer M) is set within the range of 10 to 100 μm, for example.

[0028] Next, a coating liquid made of the material for forming the light-transmitting resin substrate 1 as described above is applied to the surface of the metal sheet material, and the light-transmitting resin substrate 1 having a predetermined pattern is formed by photolithography.

[0029] Next, electrical wiring (not shown) and mounting pads 2a are formed on the light-transmitting resin substrate 1 by, for example, a semi-additive method, a subtractive method or the like.

[0030] Furthermore, a photosensitive insulating resin such as polyimide resin is usually applied to the electrical wiring portion, and a coverlay is formed by photolithography. In this way, an electric circuit board E is formed on the surface of the metal sheet material.

[0031] Thereafter, the metal sheet material is subjected to etching or the like to form through holes 5 in the metal sheet material, thereby forming the metal layer M.

[0032] [Formation of optical waveguide W] 1, when forming an optical waveguide W on the back surface of a laminate of the electric circuit board E and the metal layer M, a photosensitive resin, which is a material for forming the first cladding layer 6, is first applied to the back surface (the bottom surface in the figure) of the laminate, and then the first cladding layer 6 is formed by photolithography. As shown in the figure, the first cladding layer 6 is formed in a state in which the through holes 5 of the metal layer M are filled. The thickness of the first cladding layer 6 (thickness from the back surface of the metal layer M) is set, for example, in the range of 5 to 80 μm. When forming the optical waveguide W (when forming the first cladding layer 6, the core 7 described below, and the second cladding layer 8 described below), the back surface of the laminate is faced upward. Next, a photosensitive resin, which is a material for forming the core 7, is applied to the surface (the lower surface in the figure) of the first cladding layer 6, and the core 7 is formed in a predetermined pattern by photolithography. As a result, the dimensions of the core 7 are set, for example, in the range of 20 to 100 μm in width, 20 to 100 μm in thickness, and 0.5 to 100 cm in length. Then, a material for forming the second cladding layer 8 is applied to the surface (the lower surface in the figure) of the first cladding layer 6 so as to cover the core 7, and the second cladding layer 8 is formed by a photolithography method. The thickness of this second cladding layer 8 (thickness from the interface with the core 7) is set in the range of 3 to 50 μm, for example. The material for forming the second cladding layer 8 can be, for example, the same photosensitive resin as that for the first cladding layer 6. Thereafter, an inclined surface (light reflecting surface 7a) inclined at 45° with respect to the longitudinal direction of the core 7 is formed on the optical waveguide W formed as described above, for example, by laser processing, etc. In this way, the optical waveguide W is formed on the back surface of the metal layer M. The photosensitive resins are prepared so that the refractive index of the core 7 is greater than the refractive indexes of the first cladding layer 6 and the second cladding layer 8 described below.

[0033] The optical module of the present invention is compatible with optical communication interface standards such as QSFP (Quad Small Form-factor Pluggable) and OSFP (Octal Small Form Factor Pluggable). Used as an optical transceiver and AOC (Active Optical Cable), AOC for consumer use, and internal wiring for electrical devices such as smartphones, tablets, and PCs (Personal Computers). It is possible. [Example]

[0034] Next, examples will be described together with comparative examples, but the present invention is not limited to these examples as long as the gist of the present invention is not exceeded. The refractive indexes described in the following examples and comparative examples were all measured for light of 850 nm by the prism coupler method using a 2010 / M prism coupler manufactured by Metricon. The light transmittances described in the following examples and comparative examples were measured using a JASCO V-670 ultraviolet-visible-near-infrared spectrophotometer manufactured by JASCO Corporation. This is the specified value.

[0035] [Example 1] 100 parts by weight of epoxy resin (jER828, manufactured by Mitsubishi Chemical Corporation) and 2 parts by weight of photocationic polymerization initiator (CPI-200K, manufactured by San-Apro Co., Ltd.) were premixed, then melt-mixed by kneading in a kneader, and cooled to 23° C. In this way, a light-transmitting resin composition (underfill) was prepared, the cured product of which had a refractive index of 1.58 and a light transmittance of 95% at a wavelength of 400 nm when the cured product was 100 μm thick.

[0036] In addition, 4,4'-biphthalic anhydride (s-BPDA) is used as an acid anhydride, and diamine is used as A light-transmitting resin substrate (a polyimide resin substrate with an optical element mounting area of ​​10 μm thick, a refractive index of 1.73, and a light transmittance of 80% at a wavelength of 850 nm) was fabricated using a varnish prepared by mixing p-phenylenediamine (PDA) and 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl (TFDB), as well as a photobase generator, a reaction accelerator, a development accelerator, and a solvent. The refractive index was adjusted by adjusting the compounding ratio of the acid anhydride and diamine. An electrical circuit was then formed on the surface of the light-transmitting resin substrate to obtain a flexible printed circuit board (electrical circuit board). Then, as shown in Figure 1, a metal layer (SUS layer: thickness 20 μm) and an optical waveguide (underclad layer: thickness 30 μm (area without SUS), core: thickness 40 μm, width 40 μm) were provided on the back surface of the flexible printed circuit board.

[0037] Thereafter, the optical element was fixed to the flexible printed circuit board (electric circuit board) on which the optical waveguide and the like were formed as described above, using the above-mentioned light-transmitting resin composition (underfill) in the steps shown in (a) to (d) of FIG. 3. That is, first, a vertical-cavity surface-emitting laser (VCSEL) chip (light-emitting area: φ1 0 μm) was mounted (see FIG. 3(a)). Then, the resin composition (underfill) prepared above was applied using a syringe (see FIG. 3(b)). Next, UV (ultraviolet rays) was applied at 12,000 mJ / cm using a spot UV irradiation device (SP-9 manufactured by Ushio Inc.). 2 Irradiation The UV-irradiated portion of the underfill was cured, temporarily fixing the optical element (see FIG. 3(c)). After that, the underfill was thermally cured by heating in an oven at 100°C for 60 minutes, forming a completely cured product (cured resin for reinforcing the bond of the optical element), and the optical element was permanently fixed (see FIG. 3(d)). The thickness of the underfill was 36 μm, and the distance between the optical element and the light reflecting surface (mirror) formed on the core of the optical waveguide was 96 μm. In this way, a sample optical module was fabricated.

[0038] [Example 2] The light-transmitting resin composition (underfill) used was a resin composition ("LPS-3419", a silicone resin (adhesive) manufactured by Shin-Etsu Chemical Co., Ltd.) that has a refractive index of 1.40 after curing and a 400 nm light transmittance of 95% when the thickness of the cured product is 100 μm.

[0039] An optical module was manufactured in the same manner as in Example 1, except that the above-mentioned optically transparent resin composition was used instead of the optically transparent resin composition (underfill) of Example 1, the UV irradiation process was omitted, and the curing conditions were 150°C x 60 minutes.

[0040] [Example 3] From the composition of the light-transmitting resin substrate in Example 1, a part of s-BPDA was replaced with 4,4'-(hexafluorophosphate). and part of the PDA was replaced with 2,2'-bis(4-aminocyclohexyl)-hexafluoropropane (6FDC). By replacing the substrate, a light-transmitting resin substrate (a polyimide resin substrate with an optical element mounting portion having a thickness of 10 μm, a refractive index of 1.52, and a light transmittance of 85% for a wavelength of 850 nm) was fabricated.

[0041] An optical module was manufactured in the same manner as in Example 1, except that the light-transmitting resin substrate prepared above was used instead of the light-transmitting resin substrate of Example 1.

[0042] [Example 4] 100 parts by weight of epoxy resin (YX8034, manufactured by Mitsubishi Chemical Corporation) and 2 parts by weight of photocationic polymerization initiator (CPI-200K, manufactured by San-Apro Co., Ltd.) were premixed, then melt-mixed by kneading in a kneader, and cooled to 23° C. In this way, a light-transmitting resin composition (underfill) was prepared, the cured product of which had a refractive index of 1.53 and a light transmittance of 95% at a wavelength of 400 nm when the cured product was 100 μm thick.

[0043] In addition, from the composition of the light-transmitting resin substrate in Example 1, a part of s-BPDA was replaced with 4,4'-(hexyl)- The PDA was partially replaced with 2,2'-bis(4-aminocyclohexyl)-hexafluoropropane (6FDC) and partially replaced with 2,2'-bis(4-aminocyclohexyl)-hexafluoropropane (6FDA). ), a light-transmitting resin substrate (a polyimide resin substrate with an optical element mounting area of ​​10 μm, a refractive index of 1.52, and a light transmittance of 85% for a wavelength of 850 nm) was fabricated.

[0044] An optical module was manufactured in the same manner as in Example 1, except that the light-transmitting resin composition prepared above was used instead of the light-transmitting resin composition (underfill) of Example 1, and the light-transmitting resin substrate prepared above was used instead of the light-transmitting resin substrate of Example 1.

[0045] [Example 5] 100 parts by weight of epoxy resin (Ogsol EG-200, manufactured by Osaka Gas Chemicals Co., Ltd.) and 2 parts by weight of photocationic polymerization initiator (CPI-200K, manufactured by San-Apro Co., Ltd.) were premixed, then melt-mixed and kneaded in a kneader, and the mixture was cooled to 23° C. In this way, a light-transmitting resin composition (underfill) was prepared, the cured product of which had a refractive index of 1.62 and a light transmittance of 95% at a wavelength of 400 nm when the cured product was 100 μm thick.

[0046] Furthermore, by increasing the blending ratio of PDA to TFDB in the composition of the optically transparent resin substrate of Example 1, an optically transparent resin substrate (a polyimide resin substrate with an optical element mounting portion having a thickness of 10 μm, a refractive index of 1.85, and a light transmittance of 70% for a wavelength of 850 nm) was fabricated.

[0047] An optical module was manufactured in the same manner as in Example 1, except that the light-transmitting resin composition prepared above was used instead of the light-transmitting resin composition (underfill) of Example 1, and the light-transmitting resin substrate prepared above was used instead of the light-transmitting resin substrate of Example 1.

[0048] [Comparative Example 1] 100 parts by weight of a fluororesin (1,4-bis(2',3'-epoxypropyl)perfluoro-n-butane, manufactured by Tosoh Fine Chemicals Co., Ltd.) and 2 parts by weight of a photocationic polymerization initiator (CPI-200K, manufactured by San-Apro Co., Ltd.) were premixed, then melt-mixed and kneaded in a kneader, and cooled to 23°C. In this way, a light-transmitting resin composition (underfill) was prepared, the cured product of which had a refractive index of 1.35 and a light transmittance of 95% at a wavelength of 400 nm when the cured product was 100 μm thick.

[0049] An optical module was produced in the same manner as in Example 1, except that the light-transmitting resin composition (underfill) of Example 1 was replaced with the light-transmitting resin composition prepared above.

[0050] Comparative Example 2 No underfill was applied, and a gap was left between the electric circuit board and the optical element (see FIG. 4). Except for this, an optical module was manufactured in the same manner as in Example 1.

[0051] <Relative refractive index difference> The relative refractive index difference was calculated using the following formula (1), where the higher refractive index of the cured product of the light-transmitting resin composition that serves as the underfill and the lower refractive index of the light-transmitting resin substrate of the electric circuit board is n1 and n2, respectively, and is shown in Table 1 below. Relative refractive index difference [%] = [(n1-n2) / n1] × 100 ……(1)

[0052] The optical modules of the examples and comparative examples thus manufactured were evaluated for their characteristics according to the following criteria, and the results are shown in Table 1 below.

[0053] <Propagation loss> The above optical modules and the vertical cavity surface emitting laser (VCSEL) chips of the above optical modules An optical module was prepared in the same way as the above optical modules, except that a photodiode (PD) chip (light receiving area: φ40 μm) was mounted instead of the VCSEL chip. Next, the cores of both optical waveguides were connected with a graded index multimode optical fiber (GI50) with a core diameter of 50 μm, and the light received by the PD chip when the output power of the VCSEL chip was set to 1 W was measured. The light intensity was determined by optical simulation using simulation software (LightTools, manufactured by Cybernet Systems Co., Ltd.) For simplicity, the optical simulation considered the effects of Fresnel reflection only at the interface between the underfill and the optically transparent resin substrate and at the interface between the optoelectronic hybrid substrate and the optical fiber. Then, from the output power (W) of the VCSEL chip and the power (W) of the light received by the PD chip, The propagation loss was calculated using the following formula (2). Propagation loss (dB) = -10 × log 10 (Light intensity received by the PD chip / Light intensity emitted from the VCSEL chip) …(2) The propagation loss value obtained from the above formula (2) was evaluated according to the following criteria. ◯ (very good): Propagation loss is less than 3.75 dB. × (poor): Propagation loss is 3.75 dB or more.

[0054] [Table 1]

[0055] From the results in Table 1 above, the optical module of the example had a smaller propagation loss than the optical module of the comparative example, and therefore had a higher output efficiency than the optical module of the comparative example.

[0056] Although the above examples show specific embodiments of the present invention, the examples are merely illustrative and should not be construed as limiting. Various modifications that are obvious to those skilled in the art are intended to fall within the scope of the present invention. [Industrial Applicability]

[0057] The optical module of the present invention is compatible with optical transceivers and active optical cables (AOCs), such as those used in QSFP (Quad Small Form-factor Pluggable), which is a communication interface standard for optical communications, and OSFP (Octal Small Form Factor Pluggable), and AOCs for consumer use. Internal wiring of electrical devices such as smartphones, tablets, and PCs (Personal Computers) It can be used as such. [Explanation of symbols]

[0058] E. Electrical circuit board X Light-transparent cured resin 1 Light-transparent resin substrate 11 Optical elements 11a Light emitting part (or light receiving part)

Claims

1. An optical module comprising an electric circuit board having an electric circuit provided on a light-transmitting resin substrate, and an optical element bonded to the electric circuit board, the optical element is joined to the electric circuit board with a light-emitting portion or a light-receiving portion of the optical element facing the electric circuit surface of the electric circuit board, and the space between the light-emitting portion or the light-receiving portion of the optical element and the light-transmitting resin substrate is filled with a light-transmitting resin cured product, thereby covering the entire surface of the joint between the optical element and the electric circuit board, In the resin composition that forms the light-transmitting resin cured product, a resin component is an epoxy resin, and the resin composition contains the epoxy resin and a photocationic polymerization initiator; An optical module characterized in that the difference in relative refractive index between the cured light-transmitting resin and the light-transmitting resin substrate is 20% or less.

2. 2. The optical module according to claim 1, wherein said cured light-transmitting resin has a transmittance of 40% or more at 400 nm when the thickness of said cured light-transmitting resin is 100 [mu]m.

3. 3. The optical module according to claim 1, wherein the cured light-transmitting resin is a cured product of a thermosetting resin composition that is cured by heating at 100[deg.] C. for 3 hours.

4. 4. The optical module according to claim 1, wherein the light-transmitting resin substrate is made of a polyimide resin.

5. 5. The optical module according to claim 1, further comprising an optical waveguide on a surface of the electrical circuit board opposite to the surface to which the optical element is bonded, and a core of the optical waveguide is optically coupled to a light emitting portion or a light receiving portion of the optical element.

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