JP2011237504A - Wiring board with optical waveguide and method of manufacturing the same - Google Patents

Abstract

To provide a wiring board with an optical waveguide that can reduce a loss by reducing a loss of light transmission and prevent a core material from flowing out to improve a yield.
A wiring substrate with an optical waveguide is formed by laminating a wiring layer and insulating layers, and includes an optical waveguide in a hole extending along the thickness direction of the substrate. The optical waveguide 82 has a core 83 that serves as an optical path through which an optical signal propagates, and a clad 84 that surrounds the core 83. The refractive index of the clad 84 is smaller than the refractive index of the core 83, and the relative refractive index difference between the core 83 and the clad 84 is 1.4% or more. The core material for forming the core 83 and the clad material for forming the clad 84 have a contact angle of 35 ° or more when the core material is dropped in an uncured state on a sheet made of a cured product of the clad material. The combination is such that
[Selection] Figure 4

Description

  The present invention relates to a wiring board with an optical waveguide having a structure in which an optical signal propagates and a method for manufacturing the same.

  In recent years, with the development of information communication technology represented by the Internet and the dramatic improvement in the processing speed of information processing apparatuses, there is an increasing need for transmitting and receiving large-capacity data such as images. An information transmission speed of 10 Gbps or higher is desirable to exchange such a large amount of data freely through an information communication facility, and great expectations are placed on optical communication technology as a technology that can realize such a high-speed communication environment. On the other hand, in recent years, signal transmission paths at relatively short distances such as connections between wiring boards in devices, connections between semiconductor chips in wiring boards, connections within semiconductor chips, and the like have recently been transmitted at high speed. It is desired. For this reason, it is thought that it is ideal to shift from the conventionally common metal cable or metal wiring to optical transmission using an optical waveguide or the like.

  In recent years, various substrates with optical waveguides including optical waveguides that perform optical communication with optical elements have been proposed (see, for example, Patent Documents 1 to 4). In Patent Documents 1 to 3, for example, after removing the central portion of the transparent resin (material for forming the clad) filled in the holes of the substrate, a material (core) having a higher refractive index than the first filled material There has been proposed a technique for forming an optical waveguide having a refractive index distribution by, for example, filling a removal portion with a material for forming an optical waveguide. Patent Document 4 proposes a technique of providing a substrate with a through hole (via hole) for propagating an optical signal.

JP 2008-158388 A ([0038], [0039], FIG. 1 etc.) Japanese Patent Laying-Open No. 2009-180861 ([0039], [0040], FIG. 2 etc.) JP 2009-133967 A ([0050], [0051], FIG. 2 etc.) JP 2007-4043 A ([0053], FIG. 1 etc.)

  By the way, in the prior art described in Patent Document 4, since the optical path through which the optical signal propagates is a simple through-hole having no core and cladding, a part of the optical signal propagating in the through-hole is part of the inner circumference of the through-hole. Reflects on the surface. However, the inner peripheral surface of the through hole is rough because it is formed by drilling or laser processing. In this case, the optical signal is scattered without being reflected well on the inner peripheral surface of the through hole, or is absorbed by the inner peripheral surface of the through hole, resulting in a large loss and a light transmission loss.

  On the other hand, in the prior art described in Patent Documents 1 to 3, since the optical waveguide has a core serving as an optical path through which the optical signal propagates and a clad surrounding the core, the optical signal is the inner peripheral surface of the through hole. It becomes difficult to reach. As a result, since scattering and absorption of the optical signal are prevented, the loss is reduced and the light transmission loss is reduced. However, as shown in FIG. 11, when the core material 111 for forming the core is hardened by filling the core material 111 in the core hole 113 penetrating the center portion of the clad 112 and curing the core material 111, There is a possibility of outflow (bleed out) from the core hole 113. In this case, there is a problem in that the recesses 114 are generated at the upper end and the lower end of the core 115 formed by the core material 111, the defective product generation rate increases, and the yield decreases.

  The present invention has been made in view of the above problems, and its purpose is to reduce loss and light transmission loss, and to prevent the core material from flowing out and improve yield. Another object of the present invention is to provide a wiring substrate with an optical waveguide and a method for manufacturing the same.

  As a means (means 1) for solving the above-mentioned problem, in a wiring substrate with an optical waveguide comprising a plurality of wiring layers and an insulating layer laminated, and having an optical waveguide in a hole extending along the substrate thickness direction The optical waveguide has a core serving as an optical path through which an optical signal propagates and a clad surrounding the core, the refractive index of the clad is smaller than the refractive index of the core, and the relative refractive index difference between the core and the clad Is 1.4% or more, and the core material for forming the core and the clad material for forming the clad are dripped in an uncured state on the core material on a sheet made of a cured product of the clad material There is a wiring board with an optical waveguide characterized in that the contact angle is 35 ° or more.

  Therefore, according to the wiring substrate with an optical waveguide of the means 1, the refractive index of the cladding is smaller than the refractive index of the core, and the relative refractive index difference between the core and the cladding is 1.4% or more. It propagates only, and it becomes difficult to reach the inner peripheral surface of the hole. That is, since the scattering and absorption of the optical signal are prevented, the loss is reduced and the light transmission loss is reduced. The core material and the clad material are combined such that the contact angle when the core material is dropped in an uncured state on a sheet made of a cured clad material is 35 ° or more. That is, since the core material is made of a material having low wettability to the resin and difficult to flow, the core material is unlikely to flow out of the core hole when the core material is filled into the core hole penetrating the central portion of the clad and cured. As a result, dents are less likely to occur in the core formed by the core material. Therefore, since the defective product occurrence rate is suppressed to a low level, the yield of manufactured wiring boards with optical waveguides is increased.

  As the wiring substrate with an optical waveguide (wiring substrate), for example, a resin wiring substrate, a ceramic wiring substrate, a glass wiring substrate or a metal wiring substrate can be used, but a resin wiring substrate is preferable in consideration of cost. If it does in this way, the hole extended along the board | substrate thickness direction of a wiring board can be formed easily. When using a ceramic wiring board with higher thermal conductivity than a resin wiring board, the generated heat is efficiently dissipated. A shift in the emission wavelength due to deterioration can be avoided, and a wiring board excellent in operational stability and reliability can be realized.

  Preferable examples of such ceramic wiring boards include wiring boards made of alumina, aluminum nitride, silicon nitride, boron nitride, beryllia, mullite, low-temperature fired glass ceramic, glass ceramic and the like. Moreover, as a suitable example of a resin wiring board, the wiring board which consists of EP resin (epoxy resin), PI resin (polyimide resin), BT resin (bismaleide-triazine resin), PPE resin (polyphenylene ether resin) etc. is mentioned, for example. be able to. In addition, a wiring board made of a composite material of these resins and organic fibers such as glass fibers (glass woven fabric or glass nonwoven fabric) or polyamide fibers may be used. Preferable examples of the metal wiring board include a wiring board made of copper, a wiring board made of a copper alloy, a wiring board made of a single metal other than copper, and a wiring board made of an alloy other than copper.

  The optical waveguide-equipped wiring board is a multilayer wiring board formed by laminating a plurality of wiring layers and insulating layers. In order to achieve interlayer connection between these wiring layers, through-hole conductors may be formed inside the substrate. The wiring layer and the through-hole conductor are made of, for example, a conductive metal paste made of gold (Au), silver (Ag), copper (Cu), platinum (Pt), tungsten (W), molybdenum (Mo), or the like. It is formed by printing or filling. An electrical signal flows through such a wiring layer. In addition to such a multilayer wiring board, for example, it is allowed to use a build-up multilayer wiring board having a build-up layer formed by alternately laminating wiring layers and insulating layers on the lower end or both surfaces of the core board. The This makes it easy to increase the density of the wiring board.

  An optical element can be mounted on the wiring substrate with the optical waveguide. One or more optical elements are mounted on the wiring board. As the mounting method, for example, a method such as wire bonding or flip chip bonding, a method using an anisotropic conductive material, or the like can be employed. In addition, as an optical element (namely, light emitting element) which has a light emission part, for example, a light emitting diode (Light Emitting Diode; LED), a semiconductor laser diode (Laser Diode; LD), a surface emitting laser (Vertical Cavity Surface Emitting Laser; VCSEL) Etc. These light emitting elements have a function of converting an inputted electric signal into an optical signal and then emitting the optical signal from a light emitting portion toward a predetermined portion. On the other hand, examples of the optical element having a light receiving portion (that is, a light receiving element) include a pin photodiode (pin PD) and an avalanche photodiode (APD). These light receiving elements have a function of causing an optical signal to be incident on the light receiving unit, converting the incident optical signal into an electric signal, and outputting the electric signal. The optical element may be a light emitting / receiving element having both a light emitting unit and a light receiving unit. The light emitting / receiving element may have a plurality of light emitting / receiving units. Each light emitting / receiving unit may be arranged in a line, or may be arranged in a plurality of lines. Such a light emitting / receiving element is operated by an operation circuit. Specifically, the operation circuit for the light emitting element is called, for example, a driver IC, and the operation circuit for the light receiving element is called, for example, an amplifier or a transimpedance amplifier (TIA). The optical element and the operation circuit are electrically connected via, for example, a wiring layer (metal wiring layer) formed on the wiring board. In addition, as a suitable material used for an optical element, Si, Ge, InGaAs, GaAsP, GaAlAs, InP etc. can be mentioned, for example.

  Moreover, the wiring board with an optical waveguide includes an optical waveguide. Here, as the optical waveguide, an optical via having an optical path that penetrates the wiring board in the thickness direction and an optical signal propagates along the thickness direction of the board, or on the main surface of the wiring board or inside the wiring board, etc. A film having an optical path that is disposed and through which an optical signal propagates along the plane direction of the substrate is conceivable. The optical waveguide of the means 1 refers to a so-called optical via formed in a hole having a core serving as an optical path through which an optical signal propagates and a cladding surrounding the core. For example, an organic system made of a polymer material or the like There are inorganic optical waveguides made of quartz glass, compound semiconductors, and the like. As the polymer material, a photosensitive resin, a thermosetting resin, a thermoplastic resin, or the like can be selected. Specifically, a polyimide resin such as a fluorinated polyimide, an epoxy resin, a silicone resin, a UV curable epoxy resin, PMMA (polymethyl methacrylate), deuterated PMMA, acrylic resin such as deuterated fluorinated PMMA, polyolefin resin, and the like are suitable. The clad is formed by applying and curing a clad material in the hole, and the core is formed by filling and curing the core material in the center of the clad. Also good. In this way, since the clad material and the core material can be selected from the many types of materials described above, the optical waveguide can be formed using an inexpensive material.

  The refractive index of the cladding is smaller than the refractive index of the core. In addition, as a method of changing the refractive index of a core and a clad, many methods described below are mentioned, It is also possible to combine several methods. One of them is to change the density of the core and cladding. Other methods for changing the refractive index of the core and cladding include halogen (F, Cl, Br, I, etc.), oxygen (O), nitrogen (N), sulfur (S), silicon (Si), boron Examples thereof include changing the content of (B) and changing the abundance ratio of unsaturated bonds (benzene ring, double bond, etc.). Furthermore, another method for changing the refractive index of the core and the clad is to change the average molecular weight and molecular weight distribution before curing in the core material for forming the core and the clad material for forming the clad. Can be mentioned. In addition, when the composition of the core material and the clad material is determined, as a method of changing the refractive index of the core and the clad material, the degree of cure of the core material and the clad material (curing temperature, curing time, core material and clad material For a photosensitive resin, the exposure amount) may be changed. When the core and the clad are made of an epoxy resin, the epoxy resin may contain antimony (Sb) as a curing agent. In this case, the refractive index of the core and the clad can also be changed by changing the content of antimony.

  In addition, the relative refractive index difference between the core and the clad is preferably 1.4% or more and 15.0% or less, and particularly preferably 2.0% or more and 12.0% or less. If the relative refractive index difference is higher than 15.0%, it is difficult to find a suitable combination of the core material and the clad material. The contact angle when the core material is dropped in an uncured state on a sheet made of a cured clad material is preferably 35 ° or more and 80 ° or less. If the contact angle is larger than 80 °, it is difficult to find a suitable combination of the core material and the clad material. In addition, when the relative refractive index difference is higher than 15.0% and the contact angle is larger than 80 °, even if the combination of the core material and the clad material can be found, the adhesion between the core and the clad after curing is achieved. Since the strength is lowered, there is a possibility that a problem may occur in terms of long-term reliability.

  The hole penetrates the wiring board and has irregularities on the inner peripheral surface, and the arithmetic average roughness (Ra) of the inner peripheral surface is 0.1 μm or more, and the cladding has a thickness that covers the irregularities. It is preferable to be formed. Further, the clad preferably has an arithmetic average roughness (Ra) of the inner peripheral surface of 0.1 μm or less. With the above configuration, the adhesive strength between the clad and the hole (processed hole) is improved, and the clad covers the unevenness on the inner peripheral surface of the hole, and the inner peripheral surface of the clad becomes smooth. As a result, since the optical signal propagating through the core can propagate through the core without being scattered on the inner peripheral surface of the cladding, the loss is reduced and the light transmission loss is reduced.

  As another means (means 2) for solving the above-mentioned problem, there is provided a method for manufacturing a wiring board with an optical waveguide according to the above means 1, wherein a hole forming step for forming a hole in the wiring board, and the hole A clad forming step of forming a hollow clad by applying and curing the clad material therein, and a core forming step of forming a core by filling and curing the core material in the center of the clad. There is a method for manufacturing a wiring board with an optical waveguide, characterized in that

  Therefore, according to the manufacturing method of the wiring board with an optical waveguide of means 2, the core and the clad in which the refractive index of the clad is smaller than the refractive index of the core and the relative refractive index difference between the core and the clad is 1.4% or more are used. Thus, the optical waveguide can be formed such that the optical signal propagating through the core hardly reaches the inner peripheral surface of the hole. As a result, scattering and absorption of the optical signal are prevented, so that light transmission loss is reduced. Also, using a core material and a clad material that are combined such that the contact angle is 35 ° or more when the core material is dropped in an uncured state on a sheet produced by curing the clad material on a flat plate, for example. Since the core forming step is performed, the core material is less likely to flow out of the core hole penetrating the center portion of the clad during the core forming step, and as a result, the core formed by the core material is less likely to be depressed. Therefore, since the defective product occurrence rate is suppressed to a low level, the yield of manufactured wiring boards with optical waveguides is increased.

  Hereinafter, the manufacturing method of the wiring board with an optical waveguide will be described along the steps.

  In the hole forming step, holes are formed in the wiring board. Here, a well-known technique can be adopted as the hole forming method, and specific examples include drilling, punching, laser processing, and electric discharge machining. However, from the viewpoint of low cost, mechanical processing such as drilling or punching is preferable. Moreover, it is more preferable that the mechanical processing performed here is a precision drilling process using a precision drill etc., for example. This is because if the hole is formed by such a processing method, the optical axis can be aligned with high accuracy. Precision drilling may be performed directly on the wiring board. In addition, after filling a material that can be easily drilled into a large hole formed in the wiring board by another method in advance, the material may be drilled precisely.

  In the subsequent clad forming step, a hollow clad is formed by applying and curing a clad material in the hole. In the subsequent core formation step, the core is formed by filling the core material in the center of the clad and curing. At this point, a desired wiring board with an optical waveguide can be obtained.

The schematic perspective view which shows the opto-electric hybrid module of one Embodiment which actualized this invention. The schematic sectional drawing which shows an opto-electric hybrid module. The principal part sectional drawing which shows a photoelectric mixed module. The principal part sectional drawing which shows the wiring board with an optical waveguide, and an optical connector. Explanatory drawing which shows the manufacturing method of an opto-electric hybrid module. Explanatory drawing which shows the manufacturing method of an opto-electric hybrid module. Explanatory drawing which shows the manufacturing method of an opto-electric hybrid module. Explanatory drawing which shows the manufacturing method of an opto-electric hybrid module. Explanatory drawing which shows the method of measuring a contact angle when a core material is dripped in the uncured state on the sheet | seat which consists of a hardened | cured material of a clad material. Explanatory drawing which shows the method of measuring a contact angle when a core material is dripped in the uncured state on the sheet | seat which consists of a hardened | cured material of a clad material. Sectional drawing for demonstrating the problem of a prior art.

  Hereinafter, an embodiment embodying the present invention will be described in detail with reference to the drawings. The dimensions, material, number of channels, and the like are not limited to the present embodiment, and can be changed as appropriate.

  As shown in FIGS. 1 to 4, the opto-electric hybrid module 1 of the present embodiment is connected to a mother board 61 (mother board), three sockets 71 provided on the mother board 61, and each socket 71. A wiring board 10 with an optical waveguide (hereinafter referred to as “wiring board 10”), a plurality of optical connectors 91, and the like are provided. In this embodiment, the wiring board 10 is a pin grid array (PGA) type semiconductor package in which pins 49 are attached to pads 48, and the socket 71 is also used for the pin grid array. However, even if the wiring substrate 10 is a land grid array (LGA) type semiconductor package to which the pins 49 are not attached, the socket 71 can be used. In this case, the pad 48 is connected to the conductor pillar 75 of the socket 71 via a pin array (not shown).

  The mother board 61 of the present embodiment is a plate-like member that has a top surface 62 and a bottom surface 63 and has a substantially rectangular shape in plan view. As shown in FIG. 3, the substrate body 69 constituting the mother board 61 is constituted by a resin insulating layer 64 and a metal conductor layer 65. The resin insulating layer 64 is, for example, about 30 μm thick, and various insulating sheets such as a resin-resin composite material obtained by impregnating continuous porous PTFE with an epoxy resin, and an epoxy resin containing a filler such as silica particles. Consists of.

  Through holes 66 for internal conduction penetrating in the thickness direction of the resin insulation layer 64 are formed at a plurality of locations in the resin insulation layer 64. These through-hole portions 66 serve to electrically connect metal conductor layers 65 of different layers. A pad 67 is disposed at a position where the upper end surface of each through-hole portion 66 is located on the upper surface 62 of the mother board 61.

  As shown in FIGS. 2 and 3, the socket 71 has a substantially rectangular flat plate shape and has an upper surface 73 and a lower surface 74. The socket 71 is formed with a plurality of conductor pillars 75 penetrating between the upper surface 73 and the lower surface 74. A substantially hemispherical solder bump 72 is provided on the lower end surface of each conductor column 75. These solder bumps 72 are connected to pads 67 on the mother board 61 side. Further, a connector housing recess 76 for housing the optical connector 91 is provided on the upper surface 73 side of the socket 71.

  As shown in FIGS. 1 to 4, the wiring board 10 has a main surface 12 and a back surface 13 located on the opposite side, and is 50.0 mm long × 50.0 mm wide × 0.4 mm thick (400 μm). It has a square plate shape. Further, the wiring board 10 has a substantially rectangular plate-shaped core substrate 14 made of glass epoxy, and has a first buildup layer 31 on the core main surface 15 (upper surface in FIG. 4), and the core back surface 16 (FIG. 4 is a build-up multilayer wiring board having a second build-up layer 32 on its lower surface.

  As shown in FIG. 4, through-hole conductors 17 that penetrate the core main surface 15 and the core back surface 16 are formed at a plurality of locations on the core substrate 14. These through-hole conductors 17 connect and conduct the core main surface 15 side and the core back surface 16 side of the core substrate 14. Note that the inside of the through-hole conductor 17 is filled with a closing body 18 such as an epoxy resin. A lid-like conductor 19 made of a copper plating layer is formed in the opening of the through-hole conductor 17, and as a result, the through-hole conductor 17 is closed. A wiring pattern (not shown) made of a copper plating layer is formed at a location where the through-hole conductor 17 does not exist on the core main surface 15 and the core back surface 16 of the core substrate 14.

  The second buildup layer 32 has a structure in which two metal wiring layers 42 made of copper and two resin insulation layers 34 made of a thermosetting resin (for example, epoxy resin) are alternately laminated. . In addition, inner layer connection via conductors 47 connected to the metal wiring layer 42 are formed at a plurality of locations in each resin insulating layer 34 by copper plating. Also, pads 48 (PGA pads) that are electrically connected to the metal wiring layer 42 are formed at a plurality of locations on the lower surface of the second resin insulating layer 34. Further, the lower surface of the second resin insulating layer 34 is almost entirely covered with a solder resist 38. An opening 40 for exposing the pad 48 is formed at a predetermined portion of the solder resist 38. On the surface of the pad 48, a plurality of pins 49 for socket mounting are joined by soldering. The wiring board 10 is connected to the socket 71 by each pin 49.

  As shown in FIG. 4, the first buildup layer 31 has substantially the same structure as the second buildup layer 32 described above. That is, the first buildup layer 31 has a structure in which two metal wiring layers 42 made of copper and two resin insulating layers 33 made of a thermosetting resin (epoxy resin) are alternately laminated. Yes. In addition, inner layer connection via conductors 43 connected to the metal wiring layer 42 are formed by copper plating at a plurality of locations in each resin insulating layer 33.

  A plurality of CPU connection terminals (not shown) and a plurality of driver IC connection terminals 57 are formed on the surface of the second resin insulation layer 33. Each CPU connection terminal is arranged in a region which becomes the central portion of the substrate on the main surface 12 side of the wiring substrate 10 (specifically, on the surface of the second resin insulating layer 33). Each driver IC connection terminal 57 is arranged on the main surface 12 side of the wiring board 10 in a region closer to the outer periphery of the board than each CPU connection terminal. Further, on the surface of the second resin insulating layer 33, a first wiring pattern 58 that connects each CPU connection terminal and each driver IC connection terminal 57 is formed. A semiconductor integrated circuit element mounting region 23 is set in a region to which each CPU connection terminal and each driver IC connection terminal 57 belong on the main surface 12 of the wiring board 10.

  As shown in FIG. 4, a plurality of optical element connection terminals 55 are formed on the surface of the second resin insulating layer 33. Each optical element connection terminal 55 is located on the main surface 12 side of the wiring substrate 10 on the outer peripheral side of the substrate with respect to each driver IC connection terminal 57, that is, on the outer peripheral side of the substrate with respect to the semiconductor integrated circuit element mounting region 23. Arranged in the area. A second wiring pattern 59 is formed on the surface of the second resin insulating layer 33 to connect each driver IC connection terminal 57 and each optical element connection terminal 55.

  Further, the surface of the second resin insulating layer 33 is almost entirely covered with a solder resist 37. An opening 46 for exposing the CPU connection terminal, the driver IC connection terminal 57 and the optical element connection terminal 55 is formed at a predetermined location of the solder resist 37. On the surfaces of the CPU connection terminal, the driver IC connection terminal 57, and the optical element connection terminal 55, the surface-side solder bumps 45 are respectively disposed.

  As shown in FIGS. 1 to 3, an IC chip 21 (CPU), which is a semiconductor integrated circuit element, is bonded to each surface side solder bump 45 disposed on the surface of the CPU connection terminal. The IC chip 21 having a function as an MPU has a rectangular plate shape of 10.0 mm long × 7.5 mm wide × 0.7 mm thick. Circuit elements (not shown) are formed on the lower surface layer of the IC chip 21. A plurality of element-side terminals (not shown) are provided in a grid pattern on the lower surface side of the IC chip 21.

  As shown in FIG. 4, each surface-side solder bump 45 disposed on the surface of the optical element connection terminal 55 has a VCSEL 24, which is a kind of optical element (light emitting element), with a light emitting surface below (wiring). Bonded in a state directed toward the substrate 10 side). The VCSEL 24 of the present embodiment has a substantially rectangular flat plate shape of 3.0 mm long × 0.25 mm wide. The VCSEL 24 has a plurality of (here, 12) light emitting units 25 arranged in a line along the longitudinal direction of the VCSEL 24 in the light emitting surface. These light emitting sections 25 emit laser light (optical signals) having a predetermined wavelength in a direction orthogonal to the main surface 12 of the wiring board 10 (that is, a downward direction in FIG. 4). Further, the plurality of terminals 29 included in the VCSEL 24 are respectively joined to the front surface side solder bumps 45.

  Furthermore, a driver IC 22, which is a semiconductor integrated circuit element for driving the VCSEL 24, is joined to each surface-side solder bump 45 disposed on the surface of the driver IC connection terminal 57. The driver IC 22 is disposed in the vicinity of the VCSEL 24 on the main surface 12 of the wiring board 10. The driver IC 22 of the present embodiment has a substantially rectangular flat plate shape of 3.5 mm long × 2.5 mm wide. Circuit elements (not shown) are formed on the lower surface layer of the driver IC 22. Further, the plurality of terminals 28 of the driver IC 22 are respectively joined to the front surface side solder bumps 45. Accordingly, the driver IC 22 and the VCSEL 24 are electrically connected via the second wiring pattern 59 and the like.

  A plurality of surface-side solder bumps 45 are also formed on the main surface 12 of the wiring board 10 on the right side in FIG. A photodiode 27, which is a kind of optical element (light receiving element), is bonded to each surface-side solder bump 45 with the light receiving surface facing downward (wiring board 10 side). The photodiode 27 of the present embodiment has a substantially rectangular flat plate shape of 3.0 mm length × 0.25 mm width. The photodiode 27 has a plurality of (here, 12) light receiving portions (not shown) arranged in a line along the longitudinal direction of the photodiode 27 in the light receiving surface. Therefore, these light receiving sections are configured to easily receive laser light (optical signal) from the lower side to the upper side in FIG.

  A receiver IC 26 that is a semiconductor integrated circuit element that amplifies the photocurrent output from the photodiode 27 is disposed in the vicinity of the photodiode 27 on the main surface 12 of the wiring board 10. The receiver IC 26 of the present embodiment has a substantially rectangular flat plate shape of 3.5 mm long × 2.5 mm wide. Circuit elements (not shown) are formed on the lower surface layer of the receiver IC 26. In addition, a plurality of terminals (not shown) of the receiver IC 26 are respectively joined to the front surface side solder bumps 45. Therefore, the photodiode 27 and the receiver IC 26 are electrically connected via a wiring pattern (not shown).

  As shown in FIGS. 3 and 4, a plurality of positioning guide holes 51 are formed at a plurality of locations (eight locations per wiring substrate 10) in the wiring substrate 10. Each positioning guide hole 51 has a circular cross section and an equal cross section, and penetrates the main surface 12 and the back surface 13 of the wiring substrate 10. In the case of this embodiment, the diameter of each positioning guide hole 51 is set to about 0.7 mm. An upper end portion of a guide pin 52 having a circular cross section can be fitted into each positioning guide hole 51. When the guide pins 52 are inserted into the positioning guide holes 51, both end portions of the guide pins 52 protrude toward the main surface 12 side and the back surface 13 side of the wiring substrate 10, respectively. These guide pins 52 are made of stainless steel and have flat surfaces at both ends perpendicular to the axial direction. Specifically, in this embodiment, a guide pin “CNF125A-21” (diameter 0.699 mm) defined in JIS C 5981 is used. That is, the diameter of the guide pin 52 is set to be substantially the same as that of the positioning guide hole 51.

  As shown in FIGS. 3 and 4, the main surface 12 side of the wiring board 10 is covered with a metal lid 11. Note that the main surface side end portion of the guide pin 52 protrudes higher than the VCSEL 24 on the main surface 12 side of the wiring substrate 10 and is in contact with the inner surface of the metal lid 11.

  In the wiring substrate 10, a plurality of optical waveguide holes 80 are formed in a region closer to the outer periphery of the substrate than the semiconductor integrated circuit element mounting region 23. Each optical waveguide hole 80 extends along the substrate thickness direction, and penetrates the main surface 12 and the back surface 13 of the wiring substrate 10. In the present embodiment, the optical waveguide hole 80 has a circular cross section and an equal cross section, and the diameter is set to 50 μm for the light emitting element and the diameter is set to 80 μm for the light receiving element. Each of the optical waveguide holes 80 is a processed hole having irregularities 81 (see FIGS. 6 and 7) on the inner peripheral surface and an arithmetic average roughness (Ra) of the inner peripheral surface of 0.13 μm.

  As shown in FIGS. 3 and 4, an optical waveguide 82 is formed in each optical waveguide hole 80. Each optical waveguide 82 has a core 83 and a clad 84 surrounding it. It should be noted that the core 83 substantially becomes an optical path through which the optical signal propagates. The number of cores 83 serving as an optical path is twelve, the same as the number of light emitting portions 25 of the VCSEL 24 and the number of light receiving portions of the photodiode 27, and they are formed so as to extend linearly and in parallel to each other. .

  In the case of this embodiment, the core 83 and the clad 84 are formed of transparent resins having different refractive indexes. Specifically, the core 83 is formed of an epoxy resin having a refractive index of 1.570 (Loctite 3335 manufactured by Henkel), and the clad 84 is a silicone resin having a refractive index of 1.410 (Toray Dow Corning Co., Ltd.). EG-6301). That is, the refractive index of the clad 84 is smaller than the refractive index of the core 83. The relative refractive index difference between the core 83 and the clad 84 is calculated from {(refractive index of the core 83) − (refractive index of the clad 84)} / (refractive index of the core 83). %.

  Note that the refractive indexes of the core 83 and the clad 84 are measured as follows. First, a chromium mirror is created by sputtering chromium (Cr) on the surface of a glass plate (not shown). Next, using a conventionally known film forming method such as spin coating or screen printing, a transparent resin for forming the core 83 or a transparent resin for forming the clad 84 is applied onto the chromium mirror and cured. In addition, as a method for curing the transparent resin, ultraviolet irradiation, heat treatment, and the like can be mentioned, but curing is appropriately performed by a method that matches the curing conditions and the material of the transparent resin when manufacturing the actual wiring board 10. Is preferred. Then, after the transparent resin is cured, the chrome mirror is divided into a plurality of measurement samples (vertical 25 mm, horizontal 8 mm). Then, if the refractive index of the measurement sample at a wavelength of 850 nm is measured using a multiwavelength Abbe refractometer (DR-M2 manufactured by Atago Co., Ltd.), the refractive index of the core 83 and the clad 84 is measured.

  As shown in FIG. 4, the clad 84 is formed by filling the optical waveguide hole 80 with a paste clad material 85 (see FIG. 6) and curing it. The clad 84 is formed with a thickness (about 5 μm) covering the irregularities 81. The central portion of the clad 84 is a core hole 86 (see FIG. 6) that penetrates the upper end surface (the end surface on the main surface 12 side of the wiring substrate 10) and the lower end surface (the end surface on the back surface 13 side of the wiring substrate 10). It has become. The clad 84 has an outer diameter of 50 μm, an inner diameter (of the core hole 86) of 40 μm, and an arithmetic average roughness (Ra) of the inner peripheral surface of 0.06 μm. That is, the arithmetic average roughness (Ra) of the inner peripheral surface of the clad 84 is smaller than the arithmetic average roughness (Ra) of the inner peripheral surface of the optical waveguide hole 80. The core 83 is formed by filling the core hole 86 with a pasty core material 87 (see FIG. 7) and curing it. The core 83 has a diameter of 40 μm. The core material 87 and the clad material 85 have a contact angle θ1 (see FIG. 10) of 69 ° when the core material 87 is dropped in an uncured state on a sheet 88 made of a cured product of the clad material 85. It is a combination.

  As shown in FIGS. 1 to 4, each optical connector 91 is housed in a connector housing recess 76 of the socket 71. The optical connector 91 of this embodiment is constituted by an upper housing 96 and a lower housing 97, and has a substantially rectangular flat plate shape of 8 mm long × 15 mm wide × 2.5 mm thick. The upper housing 96 is formed with a slit 98 for allowing an optical signal propagating through the core 83 of the optical waveguide 82 to pass therethrough. On the other hand, an optical fiber fitting groove 99 is formed in the lower housing 97. In the optical fiber fitting groove 99, a tip end portion of an optical fiber 92 serving as an optical path through which an optical signal propagates is fitted. The optical connector 91 includes an optical path conversion unit 93 that converts the path of light propagating in the optical path. The optical path conversion section 93 is an inclined surface having an angle of about 45 ° with respect to the optical fiber installation surface 94 which is the inner bottom surface of the optical fiber fitting groove 99, and the light can be totally reflected on the inclined surface. A thin film made of metal is deposited. As a result, an optical path changing unit 93 that reflects light at an angle of 90 ° is configured. In addition, for example, a JPCA (Japan Electronics Circuit Association) standard PT connector can be used for the optical connector 91 of the present embodiment. Further, instead of fitting the optical fiber 92 into the optical fiber fitting groove 99, a multi-channel optical waveguide having a 45 ° inclined surface may be used. In this case, if the other of the inclined surfaces is air, light can be reflected at an angle of 90 ° without depositing a metal thin film, and therefore the presence or absence of the thin film can be selected as appropriate.

  As shown in FIGS. 3 and 4, a circular guide hole 95 is formed in the optical connector 91 at two locations. These guide holes 95 are set to have a diameter of about 0.7 mm corresponding to the size of the guide pins 52. Each guide pin 52 protruding from the back surface 13 side of the wiring board 10 can be fitted into each guide hole 95. When the guide pin 52 is inserted into the guide hole 95, the optical connector 91 and the optical waveguide 82 are fixed in a state of being aligned. Here, “fixed in an aligned state” specifically means that the optical connector 91 is supported and fixed when the optical axis of each optical fiber 92 and the optical axis of each core 83 of the optical waveguide 82 are aligned. It means being done.

  A general operation of the opto-electric hybrid module 1 configured as described above will be briefly described.

  The VCSEL 24 and the photodiode 27 become operable by supplying power via the metal conductor layer 65 of the mother board 61, the metal wiring layer 42 of the wiring board 10, and the like. When an electrical signal is output from the driver IC 22 on the wiring board 10 to the VCSEL 24, the VCSEL 24 converts the input electrical signal into an optical signal (laser light), and then converts the optical signal into an optical path conversion unit 93 in the optical connector 91. The light is emitted from the light emitting unit 25 toward. The laser light emitted from the light emitting unit 25 travels in the core 83 of the optical waveguide 82, passes through the slit 98 of the optical connector 91, and enters the optical path changing unit 93. The laser light incident on the optical path changing unit 93 changes its traveling direction by 90 °. For this reason, the laser light passes through the optical fiber 92 and is emitted from the upper surface side of the optical waveguide 82 of another wiring substrate 10, and further enters the light receiving portion of the photodiode 27. The photodiode 27 converts the received laser light into an electrical signal and outputs the converted electrical signal to the receiver IC 26.

  Next, a manufacturing method of the opto-electric hybrid module 1 having the above configuration will be described.

  First, the wiring board 10 is prepared by a conventionally known method and prepared in advance. The wiring board 10 is manufactured as follows. First, a copper clad laminate (not shown) in which a copper foil is pasted on both sides of a base 50 mm long × 50 mm wide × 0.3 mm thick is prepared. Then, laser drilling is performed using a YAG laser or a carbon dioxide gas laser, and a through hole penetrating the copper-clad laminate is formed in advance at a predetermined position. Next, after the through-hole conductor 17 is formed by performing electroless copper plating and electrolytic copper plating according to a conventionally known method, the closing body 18 is filled in the through-hole conductor 17. Further, the copper conductor is formed to form the lid-like conductor 19, and the copper foil on both sides of the copper-clad laminate is etched to pattern a wiring pattern (not shown). Specifically, after electroless copper plating, exposure and development are performed to form a predetermined pattern of plating resist. In this state, after electrolytic copper plating is performed using the electroless copper plating layer as a common electrode, first, the resist is dissolved and removed, and further unnecessary electroless copper plating layer is removed by etching. As a result, the core substrate 14 is obtained.

  Next, a photosensitive epoxy resin is applied to the core main surface 15 and the core back surface 16 of the core substrate 14, and exposure and development are performed, so that blind holes are formed at positions where the inner layer connection via conductors 43 and 47 are to be formed. The first resin insulation layers 33 and 34 are formed. The first resin insulation layers 33 and 34 having blind holes are formed at positions where the inner layer connection via conductors 43 and 47 are to be formed by applying a thermosetting epoxy resin and performing laser processing. May be. Further, electrolytic copper plating is performed in accordance with a conventionally known method (for example, a semi-additive method) to form inner layer connection via conductors 43 and 47 in the blind holes and to form a metal wiring layer 42 on the resin insulating layers 33 and 34. To do.

  Next, a photosensitive epoxy resin is deposited on the first resin insulation layers 33 and 34, and exposure and development are performed, whereby blind holes are formed at positions where the inner layer connection via conductors 43 and 47 are to be formed. Second resin insulation layers 33 and 34 are formed. The second resin insulation layers 33 and 34 having blind holes are formed at positions where the inner layer connection via conductors 43 and 47 are to be formed by applying a thermosetting epoxy resin and performing laser processing. May be. Further, electrolytic copper plating is performed according to a conventionally known method to form inner layer connection via conductors 43 and 47 inside the blind holes. Further, a pad 48 is formed on the second resin insulation layer 34, and a CPU connection terminal, an optical element connection terminal 55, a driver IC connection terminal 57 and a wiring are formed on the second resin insulation layer 33. Patterns 58 and 59 are formed.

  Thereafter, solder resists 37 and 38 are formed on the second resin insulation layers 33 and 34. Next, exposure and development are performed with a predetermined mask placed, and the openings 40 and 46 are patterned in the solder resists 37 and 38. As a result, the desired wiring board 10 having the build-up layers 31 and 32 on both sides is completed. The final thickness of the wiring board 10 is about 0.4 mm.

  Further, a substrate body 69 constituting the mother board 61 is prepared and prepared by a conventionally known method. As a specific example, a copper-clad laminate is used as a starting material, and copper foil etching, electroless copper plating, or the like is performed to form a resin insulating layer 64 having a metal conductor layer 65 and a through-hole portion 66. Next, a resin insulating layer 64 is further laminated on the surface layer of the resin insulating layer 64, and a pad 67 is formed on the upper surface 62 of the uppermost resin insulating layer 64.

  Further, the socket 71 is prepared and prepared by a conventionally known method. To give a specific example, first, a rectangular epoxy resin plate is prepared, and a number of vias penetrating the front and back are formed on the epoxy resin plate by, for example, laser processing using a carbon dioxide laser. To do. Of course, vias may be formed by a drilling method other than laser processing, such as drilling. Next, the epoxy resin plate with vias is transferred to a paste printing device (not shown) to perform solder paste printing. After this step, the solder paste is filled in each via. Next, reflow is performed at a predetermined temperature and a predetermined temperature to form the conductive pillar 75. Further, the epoxy resin plate on which the conductive pillars 75 are formed is set in a screen printing apparatus, and a predetermined mask having an opening corresponding to a position where the conductive pillars 75 are provided is disposed on the lower surface of the epoxy resin board. To do. In this state, the solder paste is printed on the epoxy resin plate, and a solder paste print layer is formed on the lower end surface of the conductor pillar 75 through the opening of the mask. Next, the epoxy resin plate is transferred to a reflow furnace where it is heated to a predetermined temperature to reflow the solder paste printed layer. As a result, a substantially hemispherical solder bump 72 is directly formed on the lower end surface of each conductor column 75, and the socket 71 shown in FIG. 2 is completed.

  In the subsequent hole forming step, a precision drilling process using a precision drill is performed to form a positioning guide hole 51 in the wiring board 10. Next, the wiring board 10 is set in a surface polishing apparatus, and the main surface 12 and the back surface 13 are polished. By this polishing, the excess resin protruding from the opening of the positioning guide hole 51 and the resin adhering to the substrate surface are removed. When this polishing process is performed, unevenness on the main surface 12 and the back surface 13 of the wiring substrate 10 is eliminated and the wiring substrate 10 is flattened. Further, finishing is performed by a known method, and the hole diameter of the positioning guide hole 51 is finely adjusted to be 0.700 mm. Specifically, the accuracy required for processing at this time is ± 0.001 mm.

  In the hole forming step, a precision drilling process using the precision drill 101 is performed to form the optical waveguide hole 80 in the wiring board 10 (see FIG. 5). Next, if necessary, the wiring board 10 may be set in a surface polishing apparatus and the main surface 12 and the back surface 13 may be polished. By this polishing, surplus resin protruding from the opening of the optical waveguide hole 80 and the resin adhering to the substrate surface are removed. When this polishing process is performed, unevenness on the main surface 12 and the back surface 13 of the wiring substrate 10 is eliminated and the wiring substrate 10 is flattened.

  In the subsequent clad formation step, a clad material 85 is applied and cured in the optical waveguide hole 80 to form a hollow clad 84 (see FIG. 6). In the present embodiment, conventionally known castellation printing is performed, and the clad material 85 is attached to the inner peripheral surface of the optical waveguide hole 80. Specifically, the back surface 13 side of the wiring substrate 10 is placed on the stage 102 and the metal mask 103 is placed on the main surface 12 side of the wiring substrate 10. Next, the paste clad material 85 is filled into the optical waveguide hole 80 through the opening of the metal mask 103. In this state, if the pressure on the back surface 13 side of the wiring substrate 10 is reduced, the clad material 85 flows along the inner peripheral surface of the optical waveguide hole 80 toward the back surface 13 side of the wiring substrate 10 (in the direction of arrow F1 in FIG. 6). The clad material 85 adheres to the entire inner peripheral surface of the optical waveguide hole 80. Thereafter, the clad material 85 is cured by heat treatment, ultraviolet irradiation, or the like, so that the clad 84 having the core hole 86 provided at the center is obtained.

  In the subsequent core forming step, the core 83 is filled in the core hole 86 and cured to form the core 83 (see FIG. 7). Specifically, first, the metal mask 104 is placed on the side of the main surface 12 of the wiring substrate 10 in a state of being separated from the main surface 12. Next, using the dispenser 105, the core material 87 in a paste form is filled into the core hole 86 through the opening of the metal mask 104. In the present embodiment, the core material 87 is filled by hole filling printing. Thereafter, the core material 87 is cured to form the core 83 by performing heat treatment or ultraviolet irradiation, and the optical waveguide 82 is formed (see FIG. 8). In the core formation process, it is necessary to manufacture the core 83 so that the core material 87 does not flow out and cause a dent defect.

  In the subsequent solder bump forming step, the surface-side solder bumps 45 are respectively formed on the CPU connection terminal, the driver IC connection terminal 57 and the optical element connection terminal 55. Next, the pins 49 are attached onto the pads 48 by soldering. Further, the IC chip 21 is mounted on the semiconductor integrated circuit element mounting region 23 of the wiring board 10. At this time, the CPU connection terminal and the element side terminal of the IC chip 21 are aligned to perform reflow. As a result, the CPU connection terminal and the element side terminal are joined together, and the wiring substrate 10 and the IC chip 21 are electrically connected.

  In the subsequent optical element mounting step, the driver IC 22 and the VCSEL 24 are mounted on the main surface 12 side of the wiring board 10 on the left side in FIG. In addition, a receiver IC 26 and a photodiode 27 are mounted on the main surface 12 side of the wiring board 10 on the right side in FIG. More specifically, when the positions of the driver IC 22 and the VCSEL 24 are determined, they are lowered and pressed against the surface-side solder bump 45 to be temporarily fixed. In this state, solder reflow is performed, and the terminal 28 of the driver IC 22 and the terminal 29 of the VCSEL 24 are soldered to the surface-side solder bump 45. The receiver IC 26 and the photodiode 27 are also mounted on the main surface 12 side of the wiring substrate 10 through the same process as the driver IC 22 and the VCSEL 24.

  Next, one end of the guide pin 52 is fitted and supported in the positioning guide hole 51. As a result, a part of the guide pin 52 protrudes on the main surface 12 side and the back surface 13 side of the wiring substrate 10. Further, the guide pins 52 protruding from the back surface 13 of the wiring board 10 are fitted into the guide holes 95 of the optical connector 91. As a result, it is possible to support and fix the optical connector 91 to the wiring substrate 10 while aligning the optical axes of the optical connector 91 and the optical waveguide 82.

  The solder bumps 72 are reflowed in a state where the solder bumps 72 of the socket 71 are in close contact with the upper surface 62 of the mother board 61. As a result, the solder bump 72 and the pad 67 of the mother board 61 are joined, and the socket 71 is soldered to the mother board 61.

  Then, the pins 49 on the wiring board 10 side are inserted into the conductor pillars 75 from the upper surface 73 side of the socket 71, and the wiring board 10 is placed on the socket 71. As a result, the pad 48 and the pad 67 of the mother board 61 are electrically connected via the pin 49 and the socket 71, and the wiring board 10 is attached to the mother board 61. As described above, the opto-electric hybrid module 1 of this embodiment shown in FIGS. 1 and 2 is completed.

  Next, an optical waveguide evaluation method and the results will be described.

  First, a measurement sample was prepared as follows. The same wiring substrate 10 as that of the present embodiment was prepared, and this was taken as Example 1. A wiring board was prepared in which the core material 87 forming the core 83 of Example 1 was changed to a core material made of acrylic resin A having a refractive index of 1.600. A wiring board in which the core material 87 of Example 1 was changed to a core material made of acrylic resin B having a refractive index of 1.580 was prepared. The core material 87 of Example 1 is changed to a core material made of acrylic resin C having a refractive index of 1.565, and the clad material 85 of Example 1 is changed to clad material made of acrylic resin F having a refractive index of 1.502. A modified wiring board was prepared, and this was designated as Example 4.

  Further, a wiring board in which the clad material of Example 2 was changed to a clad material made of acrylic resin F was prepared, and this was designated as Comparative Example 1. A wiring board in which the clad material of Example 3 was changed to a clad material made of acrylic resin E having a refractive index of 1.524 was prepared, and this was designated as Comparative Example 2. A wiring board in which the clad material of Example 3 was changed to a clad material made of acrylic resin D having a refractive index of 1.559 was prepared, and this was designated as Comparative Example 3. A wiring board in which the cladding material of Example 3 was changed to a cladding material made of acrylic resin F was prepared, and this was designated as Comparative Example 4. A wiring board in which the clad material of Example 3 was changed to a clad material made of acrylic resin G having a refractive index of 1.487 was prepared, and this was designated as Comparative Example 5.

Next, in each measurement sample (Examples 1 to 4 and Comparative Examples 1 to 5), the relative refractive index difference between the core and the clad was calculated. The results are also shown in the “relative refractive index difference” column of Table 1.

  As a result, the relative refractive index difference is 6.1% in Comparative Example 1, the relative refractive index difference is 3.5% in Comparative Example 2, and the relative refractive index difference is 1.3% in Comparative Example 3. 4, the relative refractive index difference was 4.9%, and in Comparative Example 5, the relative refractive index difference was 5.9%. On the other hand, the relative refractive index difference is 10.2% in Example 1, the relative refractive index difference is 11.8% in Example 2, and the relative refractive index difference is 10.8% in Example 3. Then, the relative refractive index difference was 4.0%.

  Moreover, the optical loss of each measurement sample was measured by the following method. More specifically, a light source (not shown) that emits an optical signal toward the core of the optical waveguide is disposed on the main surface side of the wiring board that is a measurement sample. Specifically, an LED light source (manufactured by Advantest) is arranged, and a multimode with a core diameter of 50 μm is provided so that an optical signal from the LED light source can be irradiated toward the core of the optical waveguide on the main surface side of the wiring board. An optical fiber was disposed (not shown). Further, a light intensity measuring device for measuring the light intensity (dB) of the optical signal propagating through the core is disposed on the back side of the wiring board. Then, an optical signal was incident on the core from the light source, and an optical signal propagated through the core was incident on the optical intensity measurement device, and the optical intensity at the exit (lower end) of the optical waveguide was measured. Since the light receiving surface of the light intensity measuring device has a size of 10 mm square, it is possible to receive an optical signal propagating through the core so that no coupling loss occurs. Furthermore, the amount of decrease in light intensity was calculated based on the light intensity of the optical signal before propagating through the core and the light intensity of the optical signal after propagating through the core.

  As a result, it was confirmed that in Comparative Example 3 where the relative refractive index difference is less than 1.4%, the amount of decrease in light intensity is greater than 2 (dB), that is, the light loss is increased. On the other hand, in Examples 1-4 and Comparative Examples 1, 2, 4 and 5 in which the relative refractive index difference is 1.4% or more, the amount of decrease in light intensity is less than 2 (dB), that is, optical loss. Was confirmed to be small. From the above, it was confirmed that the optical loss can be reduced by setting the relative refractive index difference to 1.4% or more.

  In addition, in order to make the relative refractive index difference 1.4% or more, as a method of changing the refractive index of the core and the clad, changing the density of the core and the clad can be mentioned. Other methods for changing the refractive index of the core and cladding include halogen (F, Cl, Br, I, etc.), oxygen (O), nitrogen (N), sulfur (S), silicon (Si), boron Examples thereof include changing the content of (B) and changing the abundance ratio of unsaturated bonds (benzene ring, double bond, etc.). For example, when the content of fluorine (F) is increased, the refractive index of the core or cladding can be reduced. Further, when the content of bromine (Br) or sulfur (S) is increased, the refractive index of the core or cladding can be increased. Furthermore, another method for changing the refractive index of the core and the clad is to change the average molecular weight and molecular weight distribution before curing in the core material for forming the core and the clad material for forming the clad. Can be mentioned. In addition, when the composition of the core material and the clad material is determined, as a method of changing the refractive index of the core and the clad material, the degree of cure of the core material and the clad material (curing temperature, curing time, core material and clad material For a photosensitive resin, the exposure amount) may be changed. When the core and the clad are made of an epoxy resin, the epoxy resin may contain antimony (Sb) as a curing agent. In this case, the refractive index of the core and the clad can also be changed by changing the content of antimony.

  Furthermore, in each measurement sample, the contact angle θ1 when the core material was dropped in an uncured state on a sheet made of a cured clad material was measured. The results are also shown in the “contact angle” column of Table 1. The contact angle θ1 is measured by the following method. First, a transparent resin (cladding material 85) having a relatively low refractive index is applied onto a white alumina substrate 89 by using a conventionally known film formation method such as spin coating or screen printing, and then cured. Thus, a flat sheet 88 is formed (see FIG. 9). Examples of the method for curing the transparent resin include ultraviolet irradiation and heat treatment, but it is preferable that the transparent resin is appropriately cured by an actual production method or a method suited to the material of the transparent resin. Further, the substrate 89 is not particularly limited to being made of alumina as long as the sheet 88 can be formed. Next, the formed sheet 88 is installed in a contact angle meter (DM-501 manufactured by Kyowa Interface Science Co., Ltd.), and a transparent resin (core material 87) having a relatively high refractive index is used with a syringe (not shown). It is dropped on the sheet 88. Since the core material 87 starts to flow immediately after landing on the sheet 88, the core material 87 is left for 3 minutes until it becomes a droplet having a stable shape. Thereafter, an angle (contact angle θ1) formed by the surface of the sheet 88 and the spherical surface of the droplet (core material 87) is measured by a contact angle meter (see FIG. 10).

  As a result, in Comparative Examples 1 and 2, the contact angle θ1 is 33 °, in Comparative Example 3 the contact angle θ1 is 23 °, in Comparative Example 4 the contact angle θ1 is 22 °, and in Comparative Example 5 the contact angle θ1 is 7 °. It became °. On the other hand, in Example 1, the contact angle θ1 is 69 °, in Example 2, the contact angle θ1 is 72 °, in Example 3, the contact angle θ1 is 57 °, and in Example 4, the contact angle θ1 is 45 °. It was.

  Moreover, the optical waveguide of each measurement sample was observed. As a result, in Comparative Examples 1 to 5 in which the contact angle θ1 is less than 35 °, it was confirmed that dents (see the dents 114 in FIG. 11) were generated in the upper end portion and the lower end portion of the core (Table 1). "Yes" in the "Dent" column). On the other hand, in Examples 1 to 4 in which the contact angle θ1 is 35 ° or more, generation of dents in the upper end portion and the lower end portion of the core was not confirmed. From the above, it was confirmed that the formation of dents can be prevented by setting the contact angle θ1 to 35 ° or more.

  Therefore, in Examples 1 to 4 in which the relative refractive index difference is set to 1.4% or more and the contact angle θ1 is set to 35 ° or more, the optical loss can be reduced and the generation of the dent can be prevented. Was confirmed.

  Therefore, according to the present embodiment, the following effects can be obtained.

  (1) According to the wiring substrate with an optical waveguide 10 of the present embodiment, the refractive index of the clad 84 is smaller than the refractive index of the core 83, and the relative refractive index difference between the core 83 and the clad 84 is 10.2%. The optical signal propagates only in the core 83 and does not easily enter the clad 84 or reach the inner peripheral surface of the optical waveguide hole 80. That is, since scattering and absorption of the optical signal are prevented, the loss (the degree to which the light intensity decreases) is reduced and the light transmission loss is reduced. The core material 87 and the clad material 85 are combined such that the contact angle θ1 when the core material 87 is dropped on the sheet 88 in an uncured state is 69 °. That is, since the core material 87 is made of a material that has low wettability with respect to the resin that becomes the clad 84 and does not flow easily, the core material 87 formed by the clad material 85 is filled when the core material 87 is filled and cured. The core material 87 is less likely to flow out of the hole 86, and as a result, the recess 114 (see FIG. 11) is less likely to occur in the core 83 formed by the core material 87. Therefore, since the defective product occurrence rate is kept low, the yield of the manufactured wiring board 10 is increased.

  (2) The VCSEL 24 of the present embodiment is configured to emit an optical signal in a direction orthogonal to the main surface 12 of the wiring board 10 from the light emitting unit 25 (that is, downward in FIGS. 3 and 4). The main surface 12 of the wiring board 10 is mounted. In addition, the photodiode 27 of the present embodiment has a configuration in which the light receiving portion easily receives an optical signal from the lower side to the upper side in FIG. 2, and is similarly mounted on the main surface 12 of the wiring board 10. Therefore, since the VCSEL 24 and the photodiode 27 can be mounted by a conventional technique such as flip chip bonding, the opto-electric hybrid module 1 can be manufactured at low cost.

  (3) For example, if the optical waveguide 82 is exposed to the outside, the light is easily scattered, so that the quality of the optical signal is deteriorated. On the other hand, the optical waveguide 82 of the present embodiment is formed in an optical waveguide hole 80 that penetrates the wiring substrate 10. Therefore, even if a part of the optical signal enters the clad 84 and reaches the inner peripheral surface of the optical waveguide hole 80, the optical signal that has reached the optical waveguide is reflected on the inner peripheral surface of the optical waveguide hole 80. Since it propagates in the 82, loss and scattering can be minimized. Therefore, it is possible to prevent the quality deterioration of the optical signal.

  In addition, you may change this embodiment as follows.

  The optical waveguide hole 80 of the above embodiment has the unevenness 81 on the inner peripheral surface, but may not have the unevenness 81 on the inner peripheral surface. In this case, finishing is performed by a well-known method after the hole forming step, and the hole diameter of the optical waveguide hole 80 is finely adjusted to be 0.050 mm so that the optical waveguide hole 80 does not have the unevenness 81. It will be a thing. Note that the accuracy required for the processing at this time is specifically ± 0.005 mm.

  -You may change the clad formation process of the said embodiment. For example, in the clad forming process, after filling (coating) and hardening a liquid clad material in the optical waveguide hole 80, precision drilling using a precision drill is performed to penetrate the center of the clad material. A hollow clad 84 may be formed by forming the core hole 86. The core hole 86 may be formed by performing laser processing using a YAG laser or a carbon dioxide laser to penetrate the center of the clad material.

  Next, the technical ideas grasped by the embodiment described above are listed below.

  (1) In the above means 1, a light source that emits an optical signal toward the core is disposed on the main surface side of the wiring board, and the optical signal propagated through the core on the back surface side of the wiring board. In a state where a light intensity measuring device for measuring light intensity is arranged, an optical signal is made incident on the core from the light source, and an optical signal propagated through the core is made incident on the optical intensity measuring device. Measure the light intensity at the end of the back surface of the waveguide, and calculate the light intensity based on the light intensity of the optical signal before propagating through the core and the optical intensity of the optical signal after propagating through the core The wiring board with an optical waveguide, wherein the amount of decrease is less than 2 (dB).

  (2) In the said means 2, in the said core formation process, the said core which does not have a dent in the edge part of the said main surface side and the edge part of the said back surface side is formed, The manufacturing of the wiring board with an optical waveguide characterized by the above-mentioned. Method.

  (3) A mother board, a socket provided on the mother board, a wiring board with an optical waveguide according to the above-described means 1 connected to the socket, and an optical fiber tip serving as an optical path through which an optical signal propagates An opto-electric hybrid module, comprising: an optical connector having an optical path conversion unit that is connected and converts a path of light propagating in the optical path.

10: Wiring board with optical waveguide (wiring board)
33, 34 ... Resin insulating layer 42 as an insulating layer ... Metal wiring layer 80 as a wiring layer ... Optical waveguide hole 81 as a hole ... Unevenness 82 ... Optical waveguide 83 ... Core 84 ... Cladding 85 ... Cladding material 87 ... Core material 88 ... sheet θ1 ... contact angle

Claims (4)

In a wiring substrate with an optical waveguide comprising a plurality of wiring layers and an insulating layer, and having an optical waveguide in a hole extending along the thickness direction of the substrate,
The optical waveguide has a core serving as an optical path through which an optical signal propagates and a clad surrounding the core, the refractive index of the clad is smaller than the refractive index of the core, and the relative refractive index difference between the core and the clad is 1.4% or more,
The core material for forming the core and the clad material for forming the clad have a contact angle of 35 ° or more when the core material is dropped in an uncured state on a sheet made of a cured product of the clad material. A wiring board with an optical waveguide, characterized in that the combination is as follows.   The hole penetrates the wiring board and has irregularities on the inner peripheral surface, and the arithmetic average roughness (Ra) of the inner peripheral surface is a processed hole of 0.1 μm or more, and the cladding has the irregularities The wiring board with an optical waveguide according to claim 1, wherein the wiring board is formed to have a covering thickness.   The wiring substrate with an optical waveguide according to claim 2, wherein the clad has an arithmetic average roughness (Ra) of an inner peripheral surface of 0.1 μm or less. A method for manufacturing a wiring board with an optical waveguide according to any one of claims 1 to 3,
Forming a hole in the wiring board; and
A clad forming step of forming a hollow clad by applying and curing a clad material in the hole;
A method of manufacturing a wiring board with an optical waveguide, comprising: a core forming step of forming a core by filling a core material in a central portion of the clad and curing the core material.

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