JP4810911B2 - Epoxy resin composition, epoxy resin film, optical waveguide, optical / electrical hybrid wiring board, and electronic device - Google Patents

Description

  The present invention provides a photo-curing or thermosetting epoxy resin composition suitably used for forming an optical waveguide used integrally with an electric wiring such as a printed wiring board or sealing a light emitting / receiving element, the epoxy An epoxy resin sheet formed of a resin composition, an optical waveguide for performing optical transmission formed of the epoxy resin composition, an optical / electrical hybrid wiring board including an optical wiring section including the optical waveguide, In addition, the present invention relates to an electronic device using the epoxy resin composition as a sealing material.

  The amount and speed of information transmission has been increasing inside consumer devices, and optical communication that has been used only in the field of long-distance communication is now being used inside consumer devices. In this application, in order to reduce the cost, the light receiving / emitting element uses infrared light on the short wavelength side, which is different from 1.3 μm and 1.55 μm used in long-distance optical communication, such as a wavelength used around 850 nm. The development of surface mount type VCSELs and photodiodes is progressing.

  A multimode optical waveguide made of a polymer molded body has been developed as a member for guiding light. As a method proposed for forming a multimode optical waveguide, a liquid curable resin is used to harden a necessary portion as a core, and an unnecessary portion is developed and removed, and then wrapped with a clad resin (Patent Document 1). ), A method of increasing the refractive index of the exposed portion by utilizing diffusion of monomers contained in the thermoplastic resin sheet (Patent Document 2), lowering the refractive index of the exposed portion using polysilane, and non-exposure with a high refractive index A method using a part as a core (Patent Document 3), and a method in which various acrylates are subjected to pattern exposure by applying a technique employed in a resist material such as a dry film and developed with a solvent or an aqueous developer (Patent Document 4, Patent Document) 5) etc.

In addition, light receiving and emitting elements that transmit and receive light via these optical waveguides are also sealed with a transparent sealing material in order to increase the reliability of the elements. For example, in a form in which a light emitting surface of a VCSEL (surface emitting laser element) is mounted in a flip chip type with a substrate side facing, there is one that is sealed with a transparent resin using an underfill. As the sealing material, a cationic curable epoxy resin that causes self-polymerization of the epoxy resin is often used in order to increase transparency.
Japanese Patent No. 30603903 JP-A-1-302308 JP 2004-12635 A JP 2000-081520 A JP 2003-128737 A

  In forming the optical waveguide as described above, in the method using a liquid curable resin, the epoxy resin is photocured and the non-exposed portion is washed away with a solvent and developed, but a liquid resin is used. Therefore, it is necessary to carry out projection exposure, and there is a problem that it is difficult to increase the area or productivity is low.

  In addition, according to the method of increasing the refractive index of the exposed portion by utilizing the diffusion of the monomer contained in the thermoplastic resin sheet, the resin is used at the temperature received in the process of being integrated with the printed wiring board or the subsequent solder reflow process. There is a disadvantage that the heat resistance of the waveguide itself is low and the waveguide portion is deformed.

  In addition, since the clad layer formed so as to wrap the resin, particularly the core, has a large coefficient of thermal expansion (CTE), a CTE mismatch with the substrate occurs, and reliability such as temperature cycleability There was a problem with sex.

  On the other hand, there is a method using polysilane as the curable resin, but since a heat treatment of about 300 ° C. is necessary to eliminate the exposure property of the polysilane after exposure, the printed wiring board which is an organic material can withstand that temperature. However, it is difficult to use it integrally.

  In addition, in the method using various acrylates by applying the technique adopted for resist materials such as dry film, the transparency of the resin itself cannot be increased, so that the waveguide loss becomes as large as about 0.3 dB / cm or more. In addition, there is a problem in reliability because the CTE is large.

  Also, in sealing applications of light emitting and receiving elements, CTE is large because most of the cationic curing epoxy resins that do not use an addition type curing agent do not contain a filler, so that the CTE is large and the reliability including temperature cycleability is unsatisfactory. There is a problem of enough.

  The present invention has been made in view of the above points. The formation and reception of an optical waveguide used for optical transmission in which CTE is reduced while maintaining transparency to improve reliability such as temperature cycleability. It aims at providing the epoxy resin composition used suitably as a sealing material for light emitting elements.

  At the same time, in order to make it possible to put into practical use a multimode waveguide that can be integrated with a printed wiring board, it is a film material with a processing temperature that is easy to introduce into the printed wiring board manufacturing process. It is an object of the present invention to provide an epoxy resin film that has heat resistance that can withstand the temperature of the process of mounting components and optical elements and that has low transmission loss when formed as an optical waveguide.

  Furthermore, the present invention provides an optical waveguide formed of the epoxy resin composition or the epoxy resin film, an optical / electrical hybrid wiring board having an optical wiring section provided with the optical waveguide, and the epoxy resin composition as a sealing material. It aims at providing the electronic device used as.

The epoxy resin composition according to the present invention, an epoxy resin, a cationic polymerization initiator, and epoxidized polybutadiene having a hydroxyl group and an inorganic filler an epoxy resin composition containing the inorganic filler, an epoxy resin composition The difference in refractive index from the cured resin , which is a cured product of the component excluding the inorganic filler in the product, is 0.01 or less and the average particle size is 0.5 μm or less.

  The inorganic filler is preferably an inorganic filler obtained by sol-gel reaction of a mixture of alkoxysilane and alkoxytitanium acetylacetonate or titanium acetylacetonate.

  Moreover, the epoxy resin film 1 according to the present invention is formed by molding the above epoxy resin composition into a film shape.

  Moreover, the optical waveguide according to the present invention is formed of the clad layer 2 formed by curing the epoxy resin composition or the epoxy resin film 1 as described above, and a photocurable resin composition not containing an inorganic filler. And a core 4 having a refractive index higher than that of the cladding layer.

  Another optical waveguide according to the present invention is a photocuring containing a clad layer 2 formed by curing the epoxy resin composition or the epoxy resin film 1 as described above, and silica particles having an average particle diameter of 100 nm or less. And a core 4 having a higher refractive index than that of the clad layer 2 formed of a conductive resin composition.

  Moreover, the optical / electrical hybrid wiring board according to the present invention is characterized in that the optical wiring part provided with the optical waveguide as described above and the electric wiring part provided with the conductor wiring 24 are integrally provided. is there.

  The electronic device according to the present invention includes a light emitting element or a light receiving element and an optical waveguide, and a gap between the light emitting element or the light receiving element and the optical waveguide is sealed with the epoxy resin composition as described above. It is characterized by that.

  In the epoxy resin composition according to the present invention, the epoxidized polybutadiene having a contained hydroxyl group has a chain transfer effect in a cationic curing system because the molecular chain easily moves and has a hydroxyl group, and the polymerization rate (curing rate) is increased. In addition to being able to remarkably increase, since it is an aliphatic non-glycidyl ether epoxy resin having a large molecular weight, the reactivity of the epoxy group is the same as that of the alicyclic epoxy and is incorporated into the curing system. It is difficult to deteriorate the hygroscopicity and heat resistance, and the compatibility with the epoxy resin is good and the transparency can be maintained. Furthermore, since the specific inorganic filler is contained, the linear expansion coefficient of the cured product can be reduced without inhibiting the transparency of the cured product of the epoxy resin composition. . Therefore, the epoxy resin composition can be suitably used as a material for forming an optical waveguide, an optical / electrical hybrid wiring board, or a sealing material in an electronic device.

  In particular, when an inorganic filler obtained by sol-gel reaction of a mixture of alkoxysilane and alkoxytitanium acetylacetonate or titanium acetylacetonate is used as the inorganic filler, such an inorganic filler has a refractive index higher than that of amorphous silica. While being able to adjust highly, a linear expansion coefficient can be restrained low, the transparency of the hardened | cured material of an epoxy resin composition can be maintained, and a linear expansion coefficient can be reduced further.

  In addition, the epoxy resin film according to the present invention is easy to introduce into a printed wiring board manufacturing process, and it becomes easy to apply such a printed wiring board manufacturing process to produce an optical waveguide or an optical / electrical mixed wiring board. is there.

  In addition, since the optical waveguide according to the present invention has the clad layer formed of the epoxy resin composition or the epoxy resin film, the clad layer has excellent transparency without adversely affecting the transparency due to the inorganic filler. The optical loss of the cladding layer is reduced, the waveguide efficiency of the entire optical waveguide can be made extremely excellent, and the linear expansion coefficient of the cladding layer occupying most of the volume of the optical waveguide is reduced. Thus, reliability such as temperature cycle characteristics as the entire optical waveguide affected by the linear expansion coefficient can be improved.

  Furthermore, by forming the core with a photocurable resin composition that does not contain an inorganic filler, the core can be easily formed into a desired shape by exposure / development processing and the like, and the transparency of the core is increased. This is particularly suitable for applications where low waveguide loss is required.

  Further, when the core is formed of a photocurable resin composition containing silica particles having an average particle size of 100 nm or less, the core can be easily formed into a desired shape by exposure / development processing, etc. Silica particles can exhibit the characteristics of so-called nano-sized silica, while suppressing deterioration of the transparency of the core and lowering the linear expansion coefficient of the core, significantly reducing the waveguide loss of the optical waveguide. The reliability such as temperature cycle characteristics influenced by the linear expansion coefficient of the optical waveguide can be further improved.

  In addition, since the optical / electrical hybrid wiring board according to the present invention includes the optical wiring part including the optical waveguide as described above, it has a high affinity with the printed wiring board method and mounts electronic components and optical elements. It has heat resistance that can withstand the temperature of the manufacturing process, is easy to manufacture, has low loss as an optical waveguide, and can realize high heat cycle resistance and moisture resistance reliability from the time of component mounting to the use environment It is.

  In addition, the electronic device according to the present invention has serious problems such as deterioration of light receiving / emitting efficiency due to contamination of the light receiving surface or light emitting surface of the surface mount type light emitting / receiving element, and electric conduction due to corrosion. It is possible to improve the reliability by preventing the occurrence, and to prevent the surface on the optical waveguide side and the surface on the light receiving and emitting element side in the gap between the light emitting and receiving element and the optical waveguide from being contaminated. It is possible to prevent problems such as light propagation loss and light propagation impossibility, and furthermore, sealing with an epoxy resin composition having a large refractive index and high transparency reduces loss due to light reflection in the gap. It can be significantly reduced, and sealing with an epoxy resin composition with a low coefficient of linear expansion prevents connection failures such as disconnection due to thermal stress even when the electronic device is exposed to a thermal cycle. Bets are made, in which it is possible to improve the reliability of the thermal stress caused.

  Embodiments of the present invention will be described below.

[Epoxy resin composition]
The epoxy resin composition according to the present invention contains an epoxy resin, a cationic polymerization initiator, and an epoxidized polybutadiene having a hydroxyl group, and further has a refractive index difference of 0.01 or less and an average particle diameter from the cured resin. Contains an inorganic filler of 0.5 μm or less. The resin cured product means a cured product of components other than the inorganic filler in the epoxy resin composition.

  The epoxy resin is not particularly limited as long as it has a plurality of epoxy groups in one molecule as long as the transparency is not significantly impaired, and a commercially available liquid epoxy resin or solid epoxy resin can be used. It can be used as appropriate.

  Specific examples of the epoxy resin include alicyclic epoxy resin, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, biphenyl type epoxy resin having biphenyl skeleton, naphthalene ring-containing epoxy resin, dicyclopentadiene Dicyclopentadiene type epoxy resin having a skeleton, phenol novolac type epoxy resin, cresol novolac type epoxy resin, triphenylmethane type epoxy resin, bromine-containing epoxy resin, aliphatic epoxy resin, triglycidyl isocyanurate, etc. From these, only one type or two or more types can be selected and used in combination. Of these, alicyclic epoxy resins are preferred from the viewpoint of excellent transparency.

  Among such epoxy resins, specific examples of liquid epoxy resins include bifunctional ones sold by Daicel Chemical Industries, Ltd. under the trade names “Celoxide 2021” and “Celoxide 2081”, and hydrogenated bisphenol A. Type epoxy resin, hydrogenated bisphenol F type epoxy resin, and the like. As a specific example of the solid epoxy, 1,2-epoxy-polyfunctional 2,2-bis (hydroxymethyl) -1-butanol sold by Daicel Chemical Industries, Ltd. under the trade name “EHPE3150” Examples include 4- (2-oxiranyl) cyclosoxane adducts. From the viewpoint of suppressing the hydrolyzability of the cured product and improving the moisture resistance reliability, an alicyclic epoxy resin having no ester group in the molecular skeleton is more preferable.

In the present invention, the cationic polymerization initiator is not particularly limited as long as it generates Lewis acid or Bronsted acid by light, heat, electron beam, etc., and does not impair transparency. You can use what you have. Specific examples include aryldiazonium salts having PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , SbCl ₆ ²⁻ , BF ₄ ⁻ , SnCl ₆ ⁻ , FeCl ₄ ⁻ , BiCl ₅ ^2−, etc. as anions; PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , SbCl ₆ ²⁻ , BF ₄ ⁻ , ClO ₄ ⁻ , CF ₃ SO ₃ ⁻ , FSO ₃ ⁻ , F ₂ PO ₂ ⁻ , B (C ₆ F ₅ ) ₄ ^- diaryl iodonium salt with like, triarylsulfonium salts, triarylselenonium salts and the like; PF as anions ₆ ^-, AsF ₆ ^-, SbF ₆ ^- dialkyl phenazine Gilles sulfonium salts with such, dialkyl-4-hydroxy-phenylsulfanyl Phonium salt, etc .; α-hydroxymethylbenzoin sulfonate ester, N monohydroxyimide sulfonate, α-sulfonyloxyketone, β-sulfonyloxyketo Allene compound of iron; sulfonic acid esters and the like silanol over Noto aluminum complex; o-nitrobenzyl - can be exemplified triphenylsilyl ether. These cationic polymerization initiators may be used alone or in combination. In addition, a photo-curing type and a thermosetting type may be used in combination.

  A preferable addition amount of the cationic polymerization initiator is 0.5 to 3 phr, and more preferably 0.6 to 1.5 phr. If the added amount is too small, it is difficult to cure, and if it is excessive, there is a possibility that the moisture resistance reliability of the cured product is impaired.

  When the cationic polymerization initiator is of a type that initiates curing by light (photocuring type), the initiator initiates curing even with light having a wavelength longer than the wavelength of light that most efficiently generates acid. A sensitizer can be used in combination. Specific examples of the sensitizer include benzophenone, acridine orange, perylene, anthracene, phenothiazine, and 2,4-diethylthioxanthone.

  In such a cationic curing system, a chain transfer agent can be used in combination for the purpose of increasing the polymerization rate and preventing the unreacted epoxy resin from remaining. In general, polyfunctional alcohols are used, and examples include ethylene glycol, butanediol, trimethylolpropane trionyl, pentaerythritol, and polyvinyl alcohol. However, the use of these increases the hygroscopicity of the cured product. In addition, there is a possibility that a problem that the heat resistance is lowered may be caused. Therefore, it is preferable to use in a range that does not cause these problems.

  Further, the epoxidized polyptadiene having a hydroxyl group used in the present invention is represented by CAS number 68441-49-6, and for example, in the main chain of a liquid polybutadiene having a hydroxyl group as shown in the following structural formula. Some have a structure in which a double bond is epoxidized and have a hydroxyl group at the end of the molecular chain. This product is manufactured by Daicel Chemical Industries, Ltd. under the trademark “Evolid” and has a product number “PB3600” (number average molecular weight 5900) having a hydroxyl group in the molecular chain and at the molecular chain end, and a hydroxyl group in the molecular chain. The product number “PB4700” can be exemplified. In addition, a product number “Adeka Resin EPB1200” manufactured by Asahi Denka Kogyo Co., Ltd. is also included.

  Since the epoxidized polybutadiene having a hydroxyl group is liquid and has a hydroxyl group because the molecular chain easily moves, it has a chain transfer effect in a cationic curing system, and can significantly increase the polymerization rate (curing rate). Unlike the above polyfunctional alcohol, since it is an aliphatic non-glycidyl ether epoxy resin having a large molecular weight, the reactivity of the epoxy group is the same as that of the alicyclic epoxy and is incorporated into the curing system. It is difficult to deteriorate hygroscopicity and heat resistance. Furthermore, the compatibility with the epoxy resin is good and the transparency can be maintained.

  The epoxidized polybutadiene having a hydroxyl group is preferably blended in the range of 1 to 30% by weight in all resins having an epoxy group in the composition. If it is less than 1% by weight, the effect of increasing the polymerization rate cannot be exhibited. On the other hand, when it exceeds 30% by weight, the heat resistance of the cured product is lowered, and the tackiness of the film is deteriorated. A more preferable range of the blending amount is 2 to 15% by weight.

  The inorganic filler used in the present invention having a refractive index difference from the resin cured product of 0.01 or less and an average particle diameter of 0.5 μm or less maintains transparency in the cured product of the composition. , Has the effect of reducing the coefficient of linear expansion. When the refractive index difference is larger than 0.01, there arises a problem that transparency is lowered. Also, if the average particle size is larger than 0.5 μm, it will approach or be larger than the wavelength of light used in this application, 0.85 μm, and the diffraction and scattering of light will increase, resulting in a minute refractive index. Even if it is a difference, there exists a problem of reducing transparency. Such a filler can be prepared by pulverizing and spraying various kinds of glass, or by a sol-gel method.

  In producing the resin composition of the present invention, it is preferable to produce a composition in which an epoxy resin other than the epoxidized polybutadiene having a hydroxyl group and a cationic polymerization initiator are mixed in advance with the epoxidized polybutadiene having a hydroxyl group. . When manufactured by this method, a uniform cured product can be formed from the obtained resin composition, and a high Tg can be stably realized. The reason for this is not clear, but it is assumed that a slight difference in compatibility between the epoxy resin and the epoxidized polybutadiene having a hydroxyl group has an effect.

  In addition to this method, for example, a cationic polymerization initiator may be added to a mixture of epoxidized polybutadiene having an acid group and other epoxy resin, but the cured product obtained may be uneven. Since the Tg may be lowered, it is more preferable to employ the above method.

  Note that there is no particular problem even if the inorganic filler is added at any point.

  The resin composition of the present invention may be liquid at room temperature, and may be in the form of a so-called varnish dissolved or dispersed in some solvent when it becomes solid at room temperature. The solvent used for preparing the varnish can be volatile and dry, and can be a general one as long as it does not deteriorate the transparency or inhibit the curing of the epoxy resin in the resin composition after drying. Can be used.

  In addition, in the present invention, other monomers and polymers can be used in combination with the above as long as the transparency is not deteriorated.

  As another example of the monomer, an oxetane resin may be used in combination. An oxetane resin is a compound having a 4-membered ring consisting of three saturated carbon atoms and one oxygen atom, which has one more carbon than an epoxy ring, and is supplied by Toa Gosei Co., Ltd. 3- (2-ethylhexyloxymethyl) oxetane (product name “10XT-212”), 3-ethyl-3-hydroxymethyloxetane (product name “OXT-101”), or 1,4-bis {[( 3-ethyl-3-ogisetanyl) methoxy] methyl} benzene (product name “◯ XT-121”), oxetanyl-silsesquioxane (product name “10X-SQ”), and the like.

  When such an oxetane is used in combination with an epoxy resin, a highly transparent cured product can be obtained, and the advantages of a fast curing start rate of the epoxy resin and a rapid polymerization growth rate of the oxetane are manifested, thereby further improving the curability. An excellent composition can be obtained.

  In addition, as the other polymer, an appropriate polymer can be used in combination as long as it can be dissolved in a resin or varnish, and specific examples include phenoxy resin, polyamide resin, PPE resin, and the like. A butyral resin, which is a polymer but regarded as a rubber component, an acrylonitrile-butadiene copolymer resin, an acrylonitrile-butadiene copolymer resin having a carboxyl group or an amino group, and the like can be used in combination.

  As an inorganic filler having a refractive index difference of 0.01 or less and an average particle size of 0.5 μm or less contained in the epoxy resin as described above and having an average particle diameter of 0.5 μm or less, alkoxysilane and alkoxytitanium acetylacetonate or titanium acetyl Those obtained by sol-gel reaction of a mixture of acetonates are particularly preferred. The composite oxide of silica-titania obtained in this way can adjust the refractive index higher than that of amorphous silica and can keep the linear expansion coefficient low.

  Such an inorganic filler is, for example, an aqueous solution or alcohol solution of a hydrolysis initiator added dropwise to a mixture of an ethanol solution of tetraethoxysilane and an ethanol solution of diethoxy diacetylacetonate titanium or tetraacetylacetonate titanium with stirring. Then, a sol-gel reaction is caused, and the porous silica-titania particles as a product are washed with water, and then recovered and fired at around 1000 ° C. Here, when tetraalkoxytitanium is used as the titanium source, the rate of hydrolysis is increased and particles of only titania are produced, making it difficult to obtain homogeneous silica-titania composite oxide particles.

[Epoxy resin film]
The epoxy resin composition as described above can be formed into a film shape. A general method can be adopted for film forming. For example, an epoxy resin composition prepared in a liquid or varnish form can be applied to the base film 10 and dried, and the cover film 11 can be further adhered to the surface of the resulting epoxy resin film 1 (FIG. 1). reference). In order to improve the coating property in this processing process, it is preferable to mix various surfactants in the epoxy resin composition. Moreover, a leveling agent for improving the wettability to the base film 10 or an antifoaming agent for preventing the generation of bubbles can be blended. In forming the film, care must be taken because the solvent itself remaining in the epoxy resin after drying may impair the curability depending on the type of the solvent. Moreover, since the uneven | corrugated state of the surface may be transcribe | transferred to the surface of the core 4 or a clad | crud, it is preferable to use the base film 10 with few flatness and high flatness.

[Optical waveguide]
By forming the clad layer 2 using the epoxy resin composition or the epoxy resin film 1 as described above and forming the core 4 having a refractive index larger than that of the clad layer 2 adjacent to the clad layer 2, the optical A waveguide can be obtained.

  Here, when light propagates in the optical waveguide, most of the light is guided through the core 4, but a certain proportion of the light is distributed and guided also in the cladding layer 2. It is known. For this reason, when light dissipation occurs in the cladding layer 2, there arises a problem that the optical loss increases as a whole of the optical waveguide. Therefore, it is natural that the core 4 needs to have high transparency, but the cladding layer 2 also needs high transparency. On the other hand, since the inorganic filler contained in the epoxy resin composition has the predetermined refractive index and the average particle diameter, the inorganic filler may adversely affect the transparency of the cured product. Therefore, the clad layer 2 formed by the epoxy resin composition or the epoxy resin film 1 obtained from the epoxy resin composition has excellent transparency, and light loss in the clad layer 2 is reduced. The waveguide efficiency of the entire optical waveguide is extremely excellent. The cladding layer 2 surrounding the core 4 occupies most of the volume of the optical waveguide, but the linear expansion coefficient of the cladding layer 2 can be kept low, and the temperature cycle characteristics of the entire optical waveguide affected by the linear expansion coefficient. The reliability of such can be improved.

  The core 4 is formed of a transparent material having a refractive index higher than that of the clad layer 2. In particular, when the optical waveguide is used as a multimode ridge waveguide for passing a high-speed optical signal, the clad is used. The difference in refractive index between the layer 2 and the core 4 is preferably in the range of 0.5% to 5% of the refractive index of the cladding layer 2. If this difference in refractive index is small, it is difficult to take light into the core 4 when light emitted from the light emitting element is introduced into the optical waveguide, and the loss at the light incident portion may increase. Conversely, if this refractive index difference is too large, the radiation angle when light is derived from the optical waveguide becomes large, and when the derived light is received by the light receiving element, all light is irradiated to the light receiving portion. There is a possibility that the loss becomes large due to difficulty, or the pulse pattern of the optical signal deteriorates during high-speed transmission.

  Moreover, it is preferable to form the core 4 with the photocurable resin composition which does not contain an inorganic filler. As such a photocurable resin composition, an appropriate one can be used. For example, as with the epoxy resin composition for forming the clad layer 2, an epoxy resin, a photocationic polymerization initiator, and an epoxy having a hydroxyl group are used. However, it is necessary to adjust the composition so that the refractive index of the cured product is in a desired range larger than that of the cladding layer 2. When the core 4 is formed of such a photocurable resin composition that does not contain an inorganic filler, the transparency of the core 4 can be increased, and it is particularly suitable for applications where low waveguide loss is required. .

  Moreover, it is also preferable to form the core 4 with the photocurable resin composition containing a silica particle with an average particle diameter of 100 nm or less. When the silica particles having such an average particle diameter are contained in the core 4, the characteristics as so-called nano-sized silica can be expressed, and the transparency of the core 4 is deteriorated because it is sufficiently shorter than the wavelength of light used. In addition, the linear expansion coefficient of the core 4 can be reduced. Thereby, the temperature cycle in which the linear expansion coefficient of the optical waveguide influences without significantly deteriorating the waveguide loss of the optical waveguide as compared with the case where the core 4 is formed of the photocurable resin composition containing no inorganic filler. Reliability such as characteristics can be remarkably improved.

  As such a photocurable resin composition containing silica particles having an average particle diameter of 100 nm or less, an appropriate one can be used as such a photocurable resin composition, for example, for forming the cladding layer 2. Similar to the epoxy resin composition, an epoxy resin, a cationic photopolymerization initiator, an epoxidized polybutadiene having a hydroxyl group, and the like, and further containing the specific silica particles can be used. Therefore, it is necessary to adjust the composition so that the desired range is larger than that of the cladding layer 2. Specifically, for example, the product name “NANOPOX”, which is a nano silica-dispersed epoxy resin manufactured by Hanse-Chemi, Germany, is used, or after further mixing with silica sol of an alcohol solvent, the alcohol is removed by distillation under reduced pressure. Can be used. In the product name “NANOPOX”, a product number “XP22 / 0314” in which 40% by weight of silica having an average particle diameter of 5.0 nm is contained in an epoxy resin corresponding to “Celoxide 2021” which is the alicyclic epoxy described above, There is a product number “XP22 / 0516” in which 40 wt% of silica having an average particle diameter of 50 nm is contained in bisphenol A diglycidyl ether.

  The weight content of silica having an average particle diameter of 100 nm or less in the photocurable resin composition for forming the core 4 is preferably in the range of 5 to 20% by weight. Then, the linear expansion coefficient can be significantly reduced without significantly deteriorating the transparency.

  An example of a specific method for manufacturing the optical waveguide will be described. First, the epoxy resin composition is coated on a flat member 12 such as glass, film, resin plate, metal plate, etc. by a method such as a bar coater, spin coater, comma coater, die coater, curtain coater, screen printing, gravure printing, and the like. Alternatively, the cover film 11 is peeled off from the epoxy resin film 1 and laminated on the member 12 (see FIG. 2A). When the epoxy resin film 1 is used, the base film 10 is further peeled from the epoxy resin film 1. This epoxy resin composition coating or epoxy resin film 1 is photocured or thermally cured by applying a treatment such as light irradiation or heating according to the cationic polymerization initiator contained in the composition, and cured. A base layer 2a is formed (see FIG. 2B). When photocuring is performed, it is preferable to perform after-curing by heating.

  The surface of the base layer 2a thus formed is subjected to ozone treatment or plasma treatment in order to improve the adhesion with the core 4, so that the surface of the base layer 2a has reactivity such as carboxyl groups and hydroxyl groups. It is preferable to generate a functional group.

  Next, the photocurable resin composition as described above is applied to the surface of the base layer 2a by an appropriate coating method similar to that for forming the base layer 2a, or the photocurable property as described above. The photocurable film 3 obtained by forming the resin composition into a film is laminated. The photocurable film 3 can be formed using the base film 10 and the cover film 11 in the same manner as the epoxy resin film 1, and the cover film 11 can be peeled and laminated. Subsequently, by exposing the coating film or the photocurable film 3 of the photocurable resin composition through the negative mask 13 according to the curing characteristics of the composition with ultraviolet rays or the like as indicated by an arrow 14, a desired pattern can be obtained. Curing is performed (see FIG. 2C). When the photocurable film 3 is used, it can be exposed through the base film 10 as shown. Further, the non-exposed portion is washed away with a developing solution to form a core 4 in a ridge shape (see FIG. 2D).

  Thereafter, using the epoxy resin composition or the epoxy resin film 1 as described above, the coating layer 2b is formed on the surface of the base layer 2a using the same method as the formation of the base layer 2a so as to enclose the core 4. When the epoxy resin film 1 is used (see FIG. 2 (e)), the base film 10 is peeled off, and the clad layer 2 surrounding the core 4 is formed by the base layer 2a and the covering layer 2b (FIG. 2 ( f)). Thereby, an optical waveguide can be obtained. The flat member 12 is peeled off from the optical waveguide as necessary.

  Further, instead of the flat member 12 such as the metal plate, a member in which a metal foil 17 such as a copper foil is attached to the surface of the member 12 is used and laminated on the metal foil 17 as described above. An optical waveguide may be formed (see FIG. 3). The metal foil 17 at this time can be used for forming the conductor wiring 24 when forming the optical / electrical hybrid wiring board as described later.

[Optical / electric mixed wiring board]
The optical wiring section provided with the optical waveguide as described above and the electric wiring section provided with the conductor wiring 24 can be integrated to obtain an optical / electrical mixed wiring board (see FIG. 5B).

  Specifically, for example, a substrate in which an optical wiring portion is constituted by an optical waveguide having the cladding layer 2 and the core 4 as described above, and a conductor wiring 24 such as copper is provided on an insulating layer 22 made of an insulating resin or the like. The electrical wiring part can be configured with In integrating the optical wiring portion and the electrical wiring portion, an appropriate method can be adopted. For example, an optical wiring portion made of an optical waveguide is formed, and an insulating layer 22 and a conductor wiring 24 are separately laminated. By forming an electrical wiring portion made of a printed wiring board or the like and laminating and bonding the insulating layer 22 of the electrical wiring portion and the cladding layer 2 of the optical wiring portion, the two can be integrated. Alternatively, after forming an optical wiring portion made of an optical waveguide, a conductor wiring 24 such as copper may be directly laminated on the surface of the cladding layer 2 of the optical wiring portion.

  In addition, after forming an optical wiring portion made of an optical waveguide, an insulating resin tank and a conductor wiring 24 are sequentially laminated and formed on the surface of the cladding layer 2 of this optical wiring portion by a so-called build-up method. May be formed in an integrated state with the optical wiring portion.

  In addition, this optical / electrical mixed wiring board may have an electrical wiring part formed on one side and an optical wiring part formed on the other side, but the electrical wiring part is provided on both sides of the optical wiring part. You may make it integrate. In any case, in order to ensure sufficient adhesion between the electrical wiring portion and the optical wiring portion, the insulation layer 22 constituting the electrical wiring portion and the cladding layer 2 constituting the optical wiring portion are provided. It is necessary to consider adhesion.

  Further, when this optical / electrical mixed wiring board is formed as a multilayer wiring board having a plurality of layers of conductor wiring 24, a via hole (Via Ho1e) or a through hole (through hole) penetrating the optical wiring portion constituted by the optical waveguide. Through Ho1e) may be formed.

  In addition, a light emitting element such as a surface emitting laser (VCSEL) that makes light incident on the optical waveguide of the optical wiring portion, or a surface mount photodiode that receives light derived from the optical waveguide, on such an optical / electrical hybrid wiring board. When mounting a light receiving element such as (PD), the optical axis of the light guided through the optical waveguide is bent and received during the optical wiring portion forming process or after the optical wiring portion is formed. It is also possible to provide a light input / output portion 21 for bending the optical axis of light incident on the light receiving surface of the element or emitted from the light emitting surface of the light emitting element toward the core 4 and guiding it to the optical waveguide. . At this time, the light entrance / exit section 21 is provided with, for example, a micromirror 20 (see FIG. 4) provided in the core 4 so as to be inclined at 45 °, or femtosecond laser irradiation or interference exposure on the core 4. By providing a polarizer that changes the direction of the optical axis, such as a formed grating, it can be formed on the surface of the optical waveguide directly above the polarizer (see FIGS. 5B and 5C). .

  The optical / electrical hybrid circuit board obtained in this way is easy to manufacture because of its high compatibility with the printed wiring board construction method, and has a low loss as an optical waveguide, and has a high resistance against the use environment from the time of component mounting. It can realize heat cycle performance and moisture resistance reliability.

[Electronic device]
The epoxy resin composition as described above is used to obtain an optical device having an optical waveguide and a light emitting element that enters light into the optical waveguide and a light receiving element that receives light emitted from the optical waveguide. It can also be used to seal between the waveguide and the light receiving element or the light emitting element (see FIG. 5C). Hereinafter, the light emitting / receiving element 26 refers to a light receiving element or a light emitting element.

  This electronic device can be formed, for example, by mounting the light emitting / receiving element 26 on the optical / electrical hybrid wiring board having the light input / output portion 21 as described above. Further, in the above optical / electrical hybrid wiring board, the optical waveguide clad layer 2 and the core 4 constituting the optical wiring portion may be formed by adopting other appropriate materials and methods.

  In mounting the light receiving / emitting element 26 on the optical / electrical hybrid wiring board, for example, the light receiving / emitting element 26 may be mounted on the conductor wiring 24 provided directly laminated on the cladding layer 2 of the optical waveguide. A conductor wiring 24 may be formed on the cladding layer 2 via an insulating layer 22 made of a transparent resin or the like, and the light emitting / receiving element 26 may be mounted on the conductor wiring 24.

  The light emitting / receiving element 26 can be mounted by surface mounting such as flip chip mounting. At this time, for example, bumps 27 such as solder balls are provided on the light emitting surface side or light receiving surface side of the light emitting / receiving element 26, and the light emitting surface or light receiving surface of the light receiving / emitting element 26 is opposed to the light input / output portion 21 of the optical waveguide. In this state, the bump 27 can be mounted on the electrode pad portion pre-coated with the eutectic solder in the conductor wiring 24 on the optical / electrical mixed wiring board side and subjected to a reflow process.

  Next, a gap formed between the light emitting / receiving element 26 and the optical waveguide (for example, when the light emitting / receiving element 26 is mounted on the conductor wiring 24 provided by being directly laminated on the cladding layer 2 of the optical waveguide, the clad A gap between the layer 2 and the light emitting / receiving element 26. A conductor wiring 24 is formed on the cladding layer 2 of the optical waveguide via an insulating layer 22 made of a transparent resin or the like, and the light receiving / emitting element 26 is formed on the conductor wiring 24. In the case of mounting, an epoxy resin composition is injected into the gap between the insulating layer 22 and the light emitting / receiving element 26. In this state, the epoxy resin can be cured by heating, exposing to light, and the like, so that the cured product 28 can be sealed.

  If such sealing is performed, the light receiving surface of the surface mount type light emitting / receiving element 26 or the light emitting surface and the electrode are contaminated, so that the light receiving / emitting efficiency is deteriorated or the electric conduction is not caused by corrosion. Can be prevented and reliability can be improved. Further, the surface on the optical waveguide side and the surface on the light receiving / emitting element 26 side in the gap between the light receiving / emitting element 26 and the optical waveguide are prevented from being contaminated. In serious cases, it is possible to prevent the occurrence of problems such as the inability to transmit light.

  Further, when air having a refractive index of 1 is interposed in the gap between the light emitting / receiving element 26 and the optical waveguide, the refractive index is generally in the range of 1.5 to 1.6, and the refractive with respect to the optical waveguide. The difference in rate increases and light is reflected at the interface, resulting in loss. However, if the gap is sealed with an epoxy resin composition having a high refractive index and high transparency, the loss of light is significantly reduced. It becomes possible to do.

  In addition, the epoxy resin composition has a low coefficient of linear expansion, and can prevent connection failures such as disconnection due to thermal stress even when the electronic device is exposed to a thermal cycle. It can be improved.

  Hereinafter, the present invention will be specifically described by way of examples. In the following description, “parts” means parts by weight.

〔raw materials〕
As the alicyclic epoxy resin, “Celoxide 2021P” (manufactured by Daicel Chemical Industries, liquid at room temperature, abbreviated as CEL2021P) and “EHPE3150” (manufactured by Daicel Chemical Industries, solid at room temperature) were used.

  As the bisphenol A type epoxy, “Epicron 840S” (Dainippon Ink Industries, Ltd., liquid at room temperature) and “Epicoat 1006” (Japan Epoxy Resins, Inc., solid at room temperature) were used.

  As the epoxidized polybutadiene having a hydroxyl group, “PB3600” (manufactured by Daicel Chemical Industries) was used.

  As the nano silica-dispersed resin, “XP22 / 0516” (manufactured by Hanse Chemie, bisphenol A epoxy resin containing 40% by weight of silica having an average particle diameter of 50 nm) was used.

  “SP-170” (manufactured by Asahi Denka Kogyo Co., Ltd.) was used as the UV cationic polymerization initiator, and “SI-160L” (manufactured by Sanshin Chemical Industry Co., Ltd.) was used as the thermal cationic polymerization initiator.

  As the solvent, propylene glycol monomethyl ether acetate (abbreviated as PGMEA), an industrial reagent was used.

[Synthesis of inorganic filler]
The raw materials used for the synthesis of each inorganic filler used all industrial reagents.

(1) Inorganic filler a
While stirring 93 parts of tetraalkoxysilane, 7 parts of diacetylacetonate-diethoxytitanium, and 200 parts of ethanol, 50 parts of 10% aqueous hydrochloric acid was slowly added dropwise at room temperature. After completion of the dropping, stirring was continued for 1 hour, and decantation was performed by centrifuging with ion-exchanged water 5 times, followed by washing with ethyl alcohol in the same manner.

  The obtained wet paste was dried at 100 ° C. and then calcined at 1000 ° C. for 3 hours to obtain an inorganic filler a which is silica titania particles having an average particle diameter of 0.4 μm and a refractive index of 1.51.

(2) Inorganic filler b
While stirring 93 parts of tetraalkoxysilane, 7 parts of diacetylacetonate-diethoxytitanium, and 400 parts of ethanol, 100 parts of 5% aqueous hydrochloric acid was slowly added dropwise at room temperature. After completion of the dropping, stirring was continued for 1 hour, and decantation was performed by centrifuging with ion-exchanged water 5 times, followed by washing with ethyl alcohol in the same manner.

  The obtained wet paste was dried at 100 ° C. and then fired at 1000 ° C. for 3 hours to obtain an inorganic filler b which is silica titania particles having an average particle diameter of 0.8 μm and a refractive index of 1.51.

(3) Inorganic filler c
While stirring 90 parts of tetraalkoxysilane, 10 parts of diacetylacetonate-diethoxytitanium, and 200 parts of ethanol, 50 parts of 10% aqueous hydrochloric acid was slowly added dropwise at room temperature. After completion of the dropping, stirring was continued for 1 hour, and decantation was performed by centrifuging with ion-exchanged water 5 times, followed by washing with ethyl alcohol in the same manner. The obtained wet paste was dried at 100 ° C. and then calcined at 1000 ° C. for 3 hours to obtain an inorganic filler c which is silica titania particles having an average particle diameter of 0.3 μm and a refractive index of 1.55.

[Formulation Examples 1-5, Comparative Formulation Examples 1-3]
About each compounding example and the comparative compounding example, the epoxy resin composition was prepared by the raw material compounding shown in the following Table 1.

  In the preparation, first, components other than “PB3600” and the cationic polymerization initiator were weighed, mixed with stirring, and then dispersed with a bead mill, and then the cationic initiator was added and stirred at room temperature. Next, “PB3600” was further added and further stirred and mixed.

  The resulting composition was filtered through a 400 mesh filter and degassed under reduced pressure to prepare an epoxy resin composition.

  The characteristic evaluation of the obtained epoxy resin composition was performed as follows.

  (1) Refractive index measurement.

  The epoxy resin composition of each blending example and comparative blending example is in a range of 0.2 to 0.5 mm in resin thickness on a smooth surface of high refractive index glass (refractive index 1.6) having dimensions of 20 mm × 10 mm × 5 mm. It applied so that it might become.

Next, with regard to Formulation Example 1 and Comparative Formulation Examples 1 to 3 which do not contain a solvent and contain a cationic photopolymerization initiator, the UV light of the ultra-high pressure mercury lamp is exposed at a light amount of ² J / cm ² and then heat treatment at 160 ° C. for 30 minutes. Cured.

Moreover, about the compounding examples 2-5 containing a solvent, it dries by heating for 30 minutes at 80 degreeC, followed by heating for 30 minutes at 120 degreeC, and also the mixing example 2 which mix | blended the photocationic polymerization initiator among these. , 4-5, UV light from an ultra-high pressure mercury lamp is exposed at a light amount of ² J / cm ² and then cured by heat treatment at 160 ° C. for 30 minutes. In Formulation Example 3 containing a thermal cationic polymerization initiator, 1 at 160 ° C. Heat treatment curing for hours was performed.

  And after grind | polishing in order to make the surface of the obtained hardened | cured material smooth, the refractive index was measured with the refractive index measuring apparatus made from Atago.

  Moreover, about the composition containing an inorganic filler, although the refractive index was measured similarly to the above also about the resin cured material of the composition which has the same composition except having excluded the inorganic filler, the measurement result is an inorganic filler. It became the same as the case of containing.

(2) Transmission loss measurement In Formulation Example 1 and Comparative Formulation Examples 1 to 3 which do not contain a solvent and contain a cationic photopolymerization initiator, the epoxy resin composition is cast into a 3 cm × 5 cm × 2 mm frame sandwiched between glass plates. Then, after UV light from an ultra-high pressure mercury lamp was exposed at a light amount of ² J / cm ² , the mold was removed and cured by heat treatment at 160 ° C. for 30 minutes to produce a test piece having a thickness of 3 mm.

Also, in Formulation Examples 2 to 5 containing a solvent, the epoxy resin composition was applied to the base film 10 (PET film having a thickness of 25 μm) with a bar coater, and after primary drying at 80 ° C. for 5 minutes, then at 120 ° C. for 5 minutes. Is then dried to prepare a resin film having a coating film thickness of 60 μm, and then two similarly formed resin films are bonded to each other, vacuum laminated at 70 ° C., and one base film 10 is peeled off. A resin film having a thickness of 120 μm was prepared. Further, the same operation was repeated to produce a sheet having a thickness of 1.9 mm. Next, in Formulation Examples 2 and 4 to 5 including the cationic photopolymerization initiator “SP170”, UV light from an ultrahigh pressure mercury lamp is further exposed at a light amount of ² J / cm ² , and then heat treatment is performed at 160 ° C. for 30 minutes. In Formulation Example 3 containing a thermal cationic polymerization initiator, heat treatment curing at 160 ° C. for 1 hour was performed. Next, the base film 10 was peeled off to produce test pieces. Then, using these test pieces, a spectrophotometer “UV-3100PC” manufactured by Shimadzu Corporation with an integrating sphere mounted, the light transmittance at a wavelength of 850 nm (T: unit is%) and surface reflectance (R: unit is%) measured by shifting this incident angle by 7 ° were measured, and transmission loss was calculated based on these results. Here, when the thickness of the test piece is t (unit: mm), the transmission loss is calculated by the following equation.

Transmission loss [dB / cm] =-10 × 1 og (T / (100-R)) / (t / 10)
(3) Measurement of linear expansion coefficient (CTE) The epoxy resin compositions of the respective blending examples and comparative blending examples were applied to a PET film having a thickness of 25 μm by a bar coater with a wet thickness of 80 μm.

Next, in Formulation Example 1 and Comparative Formulation Examples 1 to 3 which do not contain a solvent and contain a cationic photopolymerization initiator, the UV light of the ultra-high pressure mercury lamp is exposed at a light amount of ² J / cm ² and then heat treated at 160 ° C. for 30 minutes. To obtain an epoxy resin film 1.

In addition, in Formulation Examples 2 to 5 containing a solvent, after performing heat treatment at 80 ° C. for 30 minutes and then 120 ° C. for 30 minutes for drying, Formulation Examples 2 and 4 to which a photocationic polymerization initiator was blended. 5 is cured by heat treatment at 160 ° C. for 30 minutes after exposure with UV light of an ultra-high pressure mercury lamp at a light amount of ² J / cm ² , and heat treatment curing is performed at 160 ° C. for 1 hour in Formulation Example 3 containing a thermal cationic polymerization initiator, An epoxy resin film 1 was obtained.

  These epoxy resin films 1 are cut into strips having a size of 8 mm × 20 mm, and a linear expansion coefficient in a range of 30 ° C. to 70 ° C. is measured in a tensile mode with a TMA apparatus (“EXSTAR6000” manufactured by Seiko Instruments Inc.). did.

  The above results are summarized in Table 1.

  As seen in Table 1, in the blending examples 1 to 3, in the epoxy resin composition containing the epoxy resin, the cationic polymerization initiator, and the epoxidized polybutadiene having a hydroxyl group as essential components, compared with the comparative blending examples 1 to 3, Since it contains an inorganic filler having a refractive index difference of 0.01 or less and a mean particle size of 0.5 μm or less from the cured product, it has a low transmission loss and excellent transparency, and also has a low linear expansion coefficient Have both. On the other hand, in Comparative Formulation Example 1 containing no inorganic filler, the linear expansion coefficient is large, and in Comparative Formulation Example 2 in which the inorganic filler particle size is large and in the Comparative Formulation example in which the inorganic filler has a large refractive index, transmission loss is large. It was.

  Formulation examples 4 and 5 are epoxy resin compositions for forming the core 4. However, the blending example 4 containing an inorganic filler has a low transmission loss, and the blending example 5 containing silica having an average particle size of 100 μm or less is transparent. While the increase in loss is suppressed, the linear expansion coefficient is reduced.

[Epoxy resin film and optical waveguide]
The following cladding films a to c were formed as the epoxy resin film 1, and the following core films a and b were formed as the photocurable film 3.

(Clad film a)
Using the epoxy resin composition shown in Formulation Example 2 above, this was coated on the base film 10 (25 μm-thick PET film) with a bar coater, followed by primary drying at 80 ° C. for 5 minutes and then secondary drying at 120 ° C. for 5 minutes. Went. The thickness of the obtained film was 30 μm.

(Clad film b)
A film having a thickness of 60 μm was formed in the same manner as for the film 1 except that the count of the bar coater was changed.

(Clad film c)
A film having a thickness of 20 μm was formed in the same manner as in the case of the clad film a except that the epoxy resin composition shown in Formulation Example 3 was used and the count of the bar coater was changed.

(Core film a)
Using the epoxy resin composition shown in Formulation Example 4, this was applied to the base film 10 (25 μm thick PET film) with a bar coater, followed by primary drying at 80 ° C. for 5 minutes and then secondary drying at 120 ° C. for 5 minutes. went. The thickness of the obtained film was 40 μm.

(Core film b)
Using the epoxy resin composition shown in Formulation Example 5, a film having a thickness of 40 μm was formed in the same manner as in the case of core film a.

  These films had good tackiness, and even when folded, the coating did not crack and showed good flexibility.

[Optical waveguide and optical / electrical mixed wiring board]
(Production Example 1)
A printed wiring board obtained by patterning a copper foil of a FR4 double-sided copper-clad laminate having a thickness of 4 cm × 14 cm × 1.6 mm having a copper foil with a thickness of 18 μm on both sides is used as an electric wiring portion. An optical / electrical mixed wiring board having a structure in which a copper circuit for component mounting is disposed on a surface opposite to the electric wiring portion of the optical waveguide portion provided with an optical waveguide portion made of a waveguide is manufactured.

  Specifically, first, an aluminum plate 12a having a thickness of 6 cm × 16 cm × 0.6 mm as the flat member 12 and a smooth surface of a copper foil 17a having a thickness of 6 cm × 16 cm × 35 μm as the metal foil 17 are opposed to each other. The outer peripheral portion was thermally laminated through a hot-melt type thermoplastic adhesive sheet having a width of 3 mm, and the copper foil 17a was supported on the aluminum plate 16 (FIG. 3 (a)).

The clad film a (epoxy resin coating thickness 30 μm) as the epoxy resin film 1 is vacuum laminated on the rough surface exposed on the outer surface of the copper foil 17a while being supported by the base film 10 (FIG. 3B). ) Over the entire surface of the clad film a through the base film 10, UV light from an ultra-high pressure mercury lamp is irradiated with a light amount of 2000 mJ / cm ² and cured, and then post-cured at 150 ° C. for 30 minutes. The base film 10 was peeled off to form a base layer 2a (FIG. 3C).

After the surface of the base layer 2a is treated with oxygen plasma at a high frequency output of 200 W for 1 minute, the core film a (not containing an inorganic filler and having a coating thickness of 40 μm) is applied as a photocurable film 3 to the base film 10 Then, a negative mask 13 in which 12 slits of 40 μm width and 16 cm length are arranged at a pitch of 250 μm is inserted through the base film 10 so that the slit direction is parallel to the longitudinal direction of the copper foil. The waveguide slit is disposed so as to be in the center in the short direction, and is closely adhered, and UV light (arrow 14) of an ultrahigh pressure mercury lamp is irradiated with energy of 2000 mJ / cm ² to be exposed and cured (FIG. 3 (d) ) After further heat treatment at 120 ° C. for 5 minutes, the base film 10 was peeled off and developed with toluene, and the cross section was 40 μm square and 16 cm long. The core 4 was formed (FIG. 3E).

Next, after the film 4 for clad (coating thickness 60 μm) as the epoxy resin film 1 is vacuum-laminated at 100 ° C. while being supported by the base film 10 on the surface on which the core 4 is formed (FIG. 3F). Then, the entire surface of the base film 10 was exposed and cured with an ultrahigh pressure mercury lamp at an energy of 2000 mJ / cm ² , and then post-cured under conditions of 150 ° C. for 30 minutes, and then the base film 10 was peeled off to cover the coating layer 2b. The clad layer 2 was formed by the covering layer 2b and the base layer 2a. This produced the copper foil with an optical waveguide supported by the aluminum plate 16 (FIG. 3G).

  Next, using a dicing machine equipped with a blade (abrasive grains: # 5000, tip angle: 90 degrees), a coating layer is placed 3 cm from both ends of the copper foil perpendicular to the longitudinal direction of the core 4 to a depth of 70 μm from the resin surface. A blade was inserted from the 2b side, the position of the width 6 cm in the short direction of the copper foil 17a was cut, and two mirror V-grooves 18 were formed at an interval of 10 cm (FIG. 4A). After unevenness due to grinding of the surface of the V-groove 18 is smoothed by an excimer laser, gold is vacuum-deposited only over the V-groove 18 through the metal mask 19 to form a micromirror 20 (FIGS. 4B and 4C). Then, an aluminum-reinforced copper foil with a micromirror-formed aluminum reinforcement was produced.

  Next, one of the copper foils on both sides of the 6 cm × 16 cm × 1.6 mm thick FR4 double-sided copper clad laminate is removed by etching to form a laminate of the insulating layer 22 and the metal foil 17 (copper foil 17b). The clad film c (epoxy resin coating thickness 20 μm) is vacuum laminated at 100 ° C. on the insulating layer 22, and the micromirror-formed aluminum reinforcing waveguide is provided on the surface from which the base film 10 is peeled off. The surfaces of the copper foil on the coating layer 2b side were combined and vacuum laminated at 140 ° C.

  Then, after heat treatment at 160 ° C. for 1 hour, the aluminum plate 12a is removed by cutting off the four sides with a width of 5 mm, and the insulating layer 22 and the optical waveguide are integrated with the resin layer 23 in which the cladding film c is cured. A double-sided copper-clad optical / electrical composite substrate was obtained (FIG. 5A).

  Only 1 cm is removed from the periphery of the copper foil 17a on the optical waveguide side of the substrate so that the positions of the core 4 and the micromirror 20 of the optical waveguide can be confirmed, and they are used as position markers from the optical waveguide. The positions of the intersections of the core 4 and the micromirror 20 that are the light input / output portions 21 were calculated, and guide holes for the mask necessary for copper foil patterning were provided at the four corners of the substrate based on the positions.

  Thereafter, by performing an etching process on the copper foil 17a on the optical waveguide side, an electrode pad part for mounting a light emitting element and a light receiving element immediately above the light input / output part 21, a through hole pad part to the circuit on the back of the substrate, Conductor wiring 24 such as a wiring pattern connecting them is formed, and the copper foil 17b on the side opposite to the optical waveguide is also etched to provide a through-hole pad portion, a pad portion for an electrical connection terminal with an external circuit, Conductor wiring 24 such as a wiring pattern to be connected is formed, and through holes for connecting through hole pad portions on the front and back sides are provided, and through holes 25 are formed on the inner surfaces of the through holes to form through holes 25. Was made (FIG. 5B).

  The light from the light source with a wavelength of 850 nm is 10 μm in diameter of the core 850 nm by interposing silicone oil as a matching oil from directly above one of the light input / output portions 21 of the two light input / output portions 21 in the optical / electrical mixed wiring board. Introduced by an optical fiber, silicone oil is interposed as a matching oil directly above the other light input / output part 21 and received by an optical fiber having a core 4 diameter of 200 μm, connected to a power meter, and guided through an optical waveguide. Loss was assessed.

  As a result, the entire loss (insertion) of the light (see the arrow in FIG. 5B) input from one light input / output unit 21 and guided through the optical waveguide by 10 cm and then output from the other light input / output unit 21. Loss) was 3.2 dB.

  In addition, after the solder reflow process was performed three times on this substrate under a lead-free solder reflow condition with a peak temperature of 265 ° C., the insertion loss was measured in the same manner, and was found to be 3.7 dB.

  In addition, a heat shock test in which a separate optical / electrical mixed wiring board fabricated under the same conditions is subjected to 300 times of a 5-minute immersion in a liquid phase at −50 ° C. and a 5-minute immersion in a liquid phase at 125 ° C. As a result, the insertion loss after the test increased only slightly to 3.6 dB.

  Further, a separate optical / electrical hybrid wiring board manufactured under the same conditions was cut out of the light inlet / outlet portion 21 to expose the cross section of the core 4 on the cut surface, and optical polishing was performed to obtain an optical waveguide having a core 4 length of 9 cm. Thereafter, light from a light source of 850 nm was introduced from the cross section of one core 4 of the optical waveguide through an optical fiber having a core 4 diameter of 10 μm, and the optical waveguide was guided from the cross section of the other core 4 through an optical fiber having a core 4 diameter of 200 μm. Light was derived and connected to a power meter to evaluate light loss only in the optical waveguide portion. As a result, the loss of light was 0.1 dB / cm.

  Thus, this optical / electrical hybrid circuit board is formed using a film made of an epoxy resin composition containing an epoxy resin, a cationic polymerization initiator, an epoxidized polybutadiene having a hydroxyl group, and a specific inorganic filler. An optical wiring portion formed of an optical waveguide provided with a core 4 formed of a photocurable resin composition not containing an inorganic filler and an electric wiring portion provided with a conductor wiring 24 are integrated in the clad layer 2. Because it is equipped, it has high compatibility with the printed wiring board method, it is easy to manufacture, surface mounting of electronic parts and optical parts is possible, it has extremely low loss as an optical waveguide, and it is high from the time of mounting the part to the environment of use. Reliability can be realized.

(Production Example 2)
In the formation of the core 4, an optical / electrical hybrid wiring board is produced under the same conditions as in Production Example 1 except that the core film b, which is an epoxy resin film 1 containing silica having an average particle diameter of 100 nm or less, is used. Similarly, the characteristics were evaluated.

  As a result, the total loss (insertion loss) of light input from one light input / output unit 21 and guided through the optical waveguide by 10 cm and output from the other light input / output unit 21 is 3.4 dB. The later insertion loss was 3.5 dB, the insertion loss after the heat shock test was 3.6 dB, and the waveguide loss of only the optical waveguide portion having a waveguide length of 9 cm was 0.12 dB / cm.

  Thus, this optical / electrical hybrid circuit board is formed using a film made of an epoxy resin composition containing an epoxy resin, a cationic polymerization initiator, an epoxidized polybutadiene having a hydroxyl group, and a specific inorganic filler. An optical wiring portion comprising an optical waveguide provided with a core 4 formed of a photocurable resin composition containing silica having an average particle diameter of 100 nm or less inside the clad layer 2, and an electric wiring portion provided with a conductor wiring 24 Is integrated with the printed wiring board method, making it easy to manufacture, enabling surface mounting of electronic and optical components, extremely low loss as an optical waveguide, and the usage environment from the time of component mounting. High reliability can be realized over time.

[Electronic device]
Using a photodiode (PD) package 26a, which is a light receiving element made of a 3 mm × 4 mm interposer, as the light receiving / emitting element 26, one light input / output portion 21 of the optical / electrical hybrid wiring board obtained in Production Example 1; In a state where the light receiving surface of the PD package 26a is opposed, the bump 27 (high temperature solder ball) provided on the light receiving surface side of the PD package 26a is applied with eutectic solder in the conductor wiring 24 on the optical / electrical mixed wiring board side. An electronic device that receives light introduced into the optical waveguide from the other light input / output portion 21 through the optical fiber by the PD package 26a by placing it on the precoated electrode pad portion, performing reflow processing, and flip-chip mounting. Was made.

  A laser beam having a wavelength of 850 nm is incident on the electronic device through the optical fiber having a core 4 diameter of 10 μm from the other light input / output portion 21 without sealing the PD package 26a, and the output voltage of the PD package 26a at this time ( V1) was measured.

Next, after allowing the liquid epoxy resin composition of Formulation Example 1 to penetrate into the gap between the PD package 26a and the optical / electrical hybrid wiring board and irradiating UV light obliquely from above at ² J / cm ² , Heat treatment was performed at 150 ° C. for 1 hour, and the epoxy resin composition was sealed with the cured product 28 (FIG. 5C).

  After sealing the PD package 26a in this way, the output voltage (V2) of the PD package 26a was again measured in the same manner.

  Based on these results, the total loss was derived from the following equation.

Total loss [dB] = − 10 × log (V2 / V1)
As a result, the total loss was -2.8 dB, which was significantly lower than that in the case of no sealing.

  In addition, 10 samples each sealed with the PD package 26a and 10 samples sealed with the PD package 26a are produced in the same manner as described above, and each of these samples is heated at −55 ° C. for 30 minutes at room temperature. 2000 cycles of a gas cycle temperature cycle test of 5 minutes, 125 ° C. for 30 minutes, and 5 minutes at room temperature for one cycle, and the solder ball electrical continuity between the substrate and the PD package 26a every 100 cycles The quality was judged by checking.

  And the temperature cycle property was evaluated by the number of cycles in which the number of defects in each of the 10 samples became half or more for the first time.

  As a result, in the sample in which the PD package 26a is not sealed, half of the samples are already defective in 100 cycles. When this is subjected to failure analysis, the solder bump 27 is cracked and the bump 27 is destroyed by thermal stress. I understood it. On the other hand, in the sample in which the PD package 26a was sealed, 700 cycles became half, and the temperature cycle performance was remarkably improved.

  Thus, by sealing between the light emitting / receiving element 26 and the optical waveguide with an epoxy resin composition containing an epoxy resin, a cationic polymerization initiator, an epoxidized polybutadiene having a hydroxyl group, and a specific inorganic filler. It has been revealed that the electronic device can sufficiently secure reliability while minimizing the loss of light.

An example of the manufacturing process of an epoxy resin film is shown, (a) And (b) is sectional drawing. An example of the manufacturing process of an optical waveguide is shown, (a) thru | or (f) is sectional drawing. An example of the manufacturing process of an optical waveguide, an optical / electrical hybrid board | substrate, and an electronic device is shown, (a) thru | or (g) is sectional drawing. FIG. 4 shows a step that follows the step shown in FIG. 3, and FIGS. 3A to 3C are cross-sectional views corresponding to the II cross section of FIG. FIG. 5 shows a step that follows the step shown in FIG. 4, and (a) to (c) are cross-sectional views.

Explanation of symbols

1 Epoxy resin film 2 Clad layer 4 Core 24 Conductor wiring

Claims (7)

An epoxy resin composition containing an epoxy resin , a cationic polymerization initiator, an epoxidized polybutadiene having a hydroxyl group, and an inorganic filler, wherein the inorganic filler is a component excluding the inorganic filler in the epoxy resin composition An epoxy resin composition characterized by having a refractive index difference of 0.01 or less and an average particle diameter of 0.5 μm or less from a cured resin that is a cured product.   The epoxy resin composition according to claim 1, wherein the inorganic filler is an inorganic filler obtained by subjecting a mixture of alkoxysilane and alkoxytitanium acetylacetonate or titanium acetylacetonate to a sol-gel reaction.   An epoxy resin film obtained by molding the epoxy resin composition according to claim 1 or 2 into a film shape.   A clad layer formed by curing the epoxy resin composition according to claim 1 or 2 or the epoxy resin film according to claim 3, and a clad layer formed from a photocurable resin composition containing no inorganic filler An optical waveguide comprising a core having a higher refractive index.   A photocurable resin composition comprising a clad layer formed by curing the epoxy resin composition according to claim 1 or 2 or the epoxy resin film according to claim 3, and silica particles having an average particle diameter of 100 nm or less. An optical waveguide comprising: a core having a refractive index higher than that of the clad layer formed by the step.   6. An optical / electrical hybrid wiring board, comprising: an optical wiring portion provided with the optical waveguide according to claim 4; and an electric wiring portion provided with a conductor wiring.   It has a light emitting element or a light receiving element and an optical waveguide, and a gap between the light emitting element or the light receiving element and the optical waveguide is sealed with the epoxy resin composition according to claim 1 or 2. Electronic devices.

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