KR100810916B1 - Optical waveguide and method of the same - Google Patents

Abstract

The present invention provides a method for forming an optical waveguide of a PCB, wherein a cladding step of laminating a PDMS stamp having an optical waveguide die groove formed on a lower clad and a core on the laminated clad The core filling step of filling the material with gravitational gradient and capillary force and the ultrasonic application step of applying the vibration by ultrasonic wave to the core filling step and the ultrasonic application step of hermetically filling the core inside the clad and exposing the UV to the clad filled core And a core curing step of curing the core and a PDMS stamp removing step of preparing to stack the upper clad by removing the PDMS stamp when the core is cured by the core curing step. A method for forming an optical waveguide of a PCB.

According to the present invention, the surface roughness of the core to which the optical signal is directly guided is improved through a method of directly heat-treating the cured core, thereby eliminating light scattering loss at the core and clad interface in the optical waveguide. There is an advantage that the optical waveguide forming method of the PCB to solve the problem of unfilled material is provided.

Optical ratio, optical waveguide, core, clad, surface roughness, heat treatment, glass transition temperature

Description

Optical waveguide and method of the same}

Figure 1 is a perspective view of the step of the PDMS stamp laminated to the lower clad in the practice of the present invention

Figure 2 is a perspective view of the step of curing the core with ultraviolet light after filling the core material in the clad in accordance with the present invention

Figure 3 is a perspective view of the step of removing the PDMS stamp from the cured core in the practice of the present invention

Figure 4 is a plan photo substitute for the drawing of the optical waveguide produced by the practice of the present invention

5 is a drawing substitute photograph of the unfilled defect of the core generated by the prior art method

Figure 6 is a surface photograph for the drawing of the core produced by the prior art method

Figure 7 is a drawing surface photo of the core surface improved surface roughness by the practice of the present invention

8 is a surface roughness graph improved by the practice of the present invention

* Explanation of symbols on main parts of drawings *

10: PDMS stamp 20: lower clad

30: core

Patent Registration 10-0536486-0000

Embossing Polymer Waveguides for Intergrated Optical Devices / Meather Mcknight / NNUN REU Research Accomplishment. 2003

The present invention provides a method for forming an optical waveguide of a PCB, wherein a cladding step of laminating a PDMS stamp having an optical waveguide die groove formed on a lower clad and a core on the laminated clad The core filling step of filling the material with gravitational gradient and capillary force and the ultrasonic application step of applying the vibration by ultrasonic wave to the core filling step and the ultrasonic application step of hermetically filling the core inside the clad and exposing the UV to the clad filled core And a core curing step of curing the core and a PDMS stamp removing step of preparing to stack the upper clad by removing the PDMS stamp when the core is cured by the core curing step. A method for forming an optical waveguide of a PCB.

In general, an optical PCB (PCB) refers to an optical printed circuit board in which an optical wiring assembly technology capable of greatly improving data processing speed by converting an electrical wiring of a computer into an optical wiring is implemented. Although the processing speed of the computer central processing unit (CPU) has improved from Pentium 1 to 4 by nearly 50 times, the user's sensation speed has not increased so much. This is because the transmission speed cannot be kept up, and the computer industry is currently conducting research on replacing electric wiring with optical wiring to overcome this limitation.

The optical optical waveguide (PCB), which is a substrate for transmitting the optical signal, is formed with a polymer optical waveguide, and the basic concept of the optical waveguide is the same as that of an optical fiber, but in the world, efforts are being made to implement it on a PCB substrate with high efficiency.

In the following, the optical fiber is composed of a core made of high purity acrylic resin (PMMA: Poly methylmethacrylate) and a thin clad layer made of special fluoropolymer (F-PMMA: Fluorinated Poly methyl methacrylate). Since the refractive index of the clad is lower than that of the core, the light coming from one end of the optical fiber exits to the end of the optical fiber by causing total reflection at the connection surface between the core and the clad.

One of the advantages of the plastic optical fiber is that the ratio of the core to the cross-sectional area of the optical fiber is very large. For example, 1mm Out-dia standard fiber dia is 0.98mm, Clad dia is 0.02mm, so the ratio of core to fiber cross-sectional area is 98%. This shows that the light transmission efficiency of the plastic optical fiber is very high.

The optical waveguide forming process is a process for implementing the optical fiber as described above on a PCB substrate, and the manufacturing method thereof is a photolithography process, a laser direct writing process, a hot embossing process, Soft lithography.

In the photolithography process, a cladding material is coated on a substrate, baked, coated with a core material, a photoresist and a photoresist are applied, and then exposed, developed, and / or exposed by a photomask. It is a very complicated process such as etching.

In the laser direct drawing process, a polymer is coated and cured on a planar substrate to form a cladding layer and then cured to complete an optical waveguide.

Meanwhile, in the hot embossing process, a lower cladding layer is formed on a substrate, and a mold master (made of nickel or silicon) is formed on the lower cladding layer to inject a core material to cover the upper cladding layer, and then adhere the adhesive. To form an optical waveguide.

In such an optical waveguide manufactured by the conventional technique, the surface roughness of the core to which the optical signal is directly guided is maintained at the level of several tens of nanometers. However, since the optical waveguide implemented on the same principle as the optical fiber is to allow light to pass through by total reflection, the light transmission efficiency depends on the diffuse reflection at the core and clad interface in the optical waveguide, so that the surface roughness of the core There is a problem that causes serious light scattering loss.

Therefore, the current research of the optical waveguide is increasing interest in improving the core surface roughness for the efficient transmission of light, and the existing studies to improve this have been shown in the prior art document or prior patent document 10-0536486 As described above, although the surface roughness of the PDMS stamp, which is a molding mold for forming the core, and the prevention of adhesion with the core through the surface treatment of the PDMS are being progressed in the direction of improving the surface, these are optical Since it is limited to indirect surface roughness improvement of the waveguide, there is a limit to the direct surface roughness improvement of the manufactured waveguide.

On the other hand, in core molding, unfilling of the core in the core mold is a big problem. When PDMS is used for core molding, surface contact characteristics of the lower clad are different, and the core material is in contact with the filling process. There is a difference in flow velocity with respect to the face, which is a major cause of the core unfilled, which means poor core forming.

In addition, in the case of the PDMS stamp fabricated through the replication process, the surface roughness of the circular stamp generated during etching is transferred as it is, so that the natural surface roughness exists. Therefore, the core is not filled due to the difference in the contact angle due to the surface roughness, and due to the difference in the filling speed between the independent molds (hereinafter, 'channels'), the core material coming out of the first filled channel blocks the exit of the other channel. There is a problem that the filling is not generated because the core is not advanced in the channel of the exit is closed.

In order to solve the above problems, the present invention provides a direct method for improving the surface roughness of the core to which the optical signal is directly guided, through which the PCB to remove the scattering loss at the core and clad interface in the optical waveguide It is an object of the present invention to provide a method for forming an optical waveguide and an optical waveguide of a PCB.

In addition, in the core forming process, the difference in the flow velocity generated due to the difference in the surface contact characteristics between PDMS and the lower cladding, and the difference in the contact angle and the filling rate between the channels due to the native surface roughness of PDMS stamps. The purpose of the present invention is to provide a method for forming an optical waveguide of the PCB which can overcome the problem that the core material coming out of the first filled channel blocks the exit of the other channel to prevent the core from advancing in the closed channel.

In order to achieve the above object, the present invention provides a method for forming an optical waveguide of a PCB, and a cladding step of stacking a PDMS stamp in which an optical waveguide mold groove is formed on a lower clad. And a core filling step of filling the laminated clad with a gravity gradient and capillary force and an ultrasonic wave applying step of applying an ultrasonic vibration to the core filling step and hermetically filling the core inside the clad and the core filled clad. A core curing step of curing the core by exposing UV (UV) and a PDS stamp removing step of removing the PDMS stamp and preparing to stack the upper clad when the core is cured by the core curing step. An optical waveguide forming method of a PCB comprising an optical waveguide is a technical gist.

Wherein the optical waveguide forming method of the PCB comprises a surface roughness forming step of reducing the surface roughness of the core by heat-treating the optical waveguide hardened by the core curing step at a glass transition temperature (Tg). It relates to a method for forming an optical waveguide of.

In another aspect, the present invention relates to an optical optical waveguide of a PCB, characterized in that the surface roughness is improved by heat-treating the core cured by UV (UV) at a temperature within ± 10 ° C. at the glass transition temperature. Make a point.

With reference to the drawings will be described with respect to the present invention, Figure 1 of the drawings is a perspective view of the step of the PDMS stamp is laminated to the lower clad in the embodiment of the present invention, Figure 2 is a clad in the embodiment of the present invention After filling the core material, it is a perspective view of the step of curing the core with ultraviolet light, Figure 3 is a perspective view of the step of removing the PDMS stamp from the cured core in the practice of the present invention, Figure 4 is an embodiment of the present invention Fig. 5 is a plan photo of the drawing substitute of the optical waveguide produced by the present invention, Figure 5 is a drawing substitute photo of the unfilled defect of the core generated by the prior art method, Figure 6 is a surface photo of the drawing substitute of the core produced by the prior art method. 7 is a drawing surface photograph of the core of the improved surface roughness by the implementation of the present invention, Figure 8 is a surface roughness improved by the implementation of the present invention A graph.

In the following description of the present invention together with the drawings, in the case where it is determined that the detailed description of the related well-known technology or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted, and the following terms are used in the present invention. As terms defined in consideration of functions may vary according to intentions or customs of users or operators, the definitions should be made based on the contents throughout the specification for describing the present invention.

The present invention relates to a method of implementing a low loss optical waveguide for early realization by lowering transmission loss in an information processing optical PCB (PCB).

In general, an optical waveguide is formed by placing a lower clad on a substrate, stacking an upper clad with a core path mold on the lower clad, and filling the clad with a core material and exposing a UV. In the process of hardening the core, it is not easy to penetrate the core material by the fine core path of the clad, there is a problem that the penetration of the core material in the clad stops when filling the core material. In order to solve this problem, the core is penetrated by capillary force in parallel to penetrating the core material by gravity gradient, and in addition, by applying ultrasonic wave to the cladding when the core material penetrates to amplify the penetration distance of the capillary force. It is the point to give.

To this end, the present invention is characterized by further comprising a cladding step, core filling step, ultrasonic application step, core curing step, PDMS stamp removal step and surface roughness improvement step.

In detail, the cladding step of the present invention includes laminating PDMS stamps 10 in which an optical waveguide mold groove (core mold) is formed on a lower clad 20 as shown in FIG. 1. to be.

The PDMS stamp 10 has a pattern for forming a core 30 (core mold pattern: hereinafter, each of the independent core 30 patterns is referred to as a 'channel 100'), and the lower clad (cladd) Lamination and adhesion to the core 20 to form a core mold.

The core filling step of the present invention is a process of filling a core material in the laminated clad (core mold), and has a feature of adding capillary force and ultrasonic vibration to the filling force caused by the gravity gradient. In general, in the prior art, by relying only on the gravity gradient in the core filling step, the core is unfilled and broken or micro bubbles are generated as shown in FIG. 5.

The unfilled problem is explained by the following three causes. Prior to the description, the filling rate of the core by the capillary tube is described as in Equation 1 below.

[Equation 1]

x: penetration distance D _h : hydraulic radius

σ: interfacial energy μ: viscosity of the fluid

θ: Contact angle due to surface characteristics

Therefore, the filling rate in the microchannel such as the filling of the core 30 is an important factor in the hydraulic radius (D _h ) and the interfacial energy (σ), the viscosity of the fluid (μ), the contact angle (θ) by the characteristics of the surface.

However, the PDMS stamp 10 and the lower clad 20, which are stacked to form the channel, have different surface characteristics, and thus, the flow rate of the PDMS stamp 10 and the lower clad 20 are different depending on the contact surface of the core 30 during the filling process. Differences occur, which is the main cause of unfilled.

Secondly, in the case of the PDMS stamp 10 manufactured through the copying process, the surface roughness of the circular stamp generated during etching is transferred as it is, so that the natural surface roughness exists. Therefore, unfilling of the core occurs due to the difference in contact angle due to the surface roughness.

Thirdly, due to the difference in filling speed between the channels, the core material coming out of the first filled channel blocks the exit of the other channel so that the core 30 cannot move forward in the channel in which the exit is closed, thereby causing unfilled.

In the present invention, the core unfilled problem generated in the process by the capillary force generated as described above is solved by applying the ultrasonic vibration energy and the gravitational energy due to the gradient during the core filling.

When filling the core 30 by capillary force, as in the present invention, when the ultrasonic vibration energy is applied, the bubbles generated inside the channel undergo a large amplitude expansion process near the resonance radius, and thus influence of the pressure gradient. Since it is buoyant, bubbles generated inside the channel are discharged out of the channel and disappear. In addition, the unfilled at the end of the channel is compensated by the gravitational energy due to the gradient to realize the core as shown in FIG.

Core curing step of the present invention is a step of curing the core by exposing the UV (UV) to the clad (precise the laminated structure of the PDMS stamp and lower clad) filled with the core as shown in FIG. However, since the core material is a polymer having a very high molecular weight, it is difficult to arrange regularly, and thus the core material is entangled in the form of a network structure. Since the polymer material has a wide range of motion of molecules with temperature, the core layer hardened by UV exposure is fixed at a given position without moving the polymer chains at all, and flows into a long polymer chain. It is the state which formed the restrictive entanglement.

In this state of the polymer segment, the segmental motion of the vibration level is made around a fixed position such as the dynamic state of the crystalline state of the low molecular material.

On the other hand, when looking at the surface state of the core formed by the core hardening step, the PDMS stamp (10) on the surface of the core due to the surface roughness of the PDMS stamp (10) inherently ) Surface roughness is transferred as it is, the surface roughness is very coarse as shown in FIG.

When thermal energy is given to these cores, the movement of the polymer segment is gradually activated, and the given thermal energy is near the glass transition temperature (within ± 10 ° C at the glass transition temperature) where the temperature range is similar to the energy barrier required for the local translation and rotation of the polymer. Temperature) decreases the viscosity and surface tension of the core layer surface due to local diffusion and transfer to other locations of polymers that are insecurely entangled by UV curing. The illuminance can be improved as shown in FIG. Accordingly, the present invention improves the surface roughness by heat-treating the core to which light is guided after the core curing step to a temperature near the glass transition temperature, thereby improving the surface roughness of PDMS stamps and the surface treatment technique There is another advantage that can overcome the limitations of surface roughness improvement.

8 is a graph showing the degree of improvement of the surface roughness of the optical waveguide core layer through the heat treatment method devised in the present invention, the degree of improvement of the surface roughness (the lower the smoother) of the Y axis against the amount of heat applied to the X axis is clearly expressed. It can be seen that.

 Embodiments shown for the purpose of the present invention described above are only one embodiment in which the present invention is embodied, and as shown in the drawings, it can be seen that various forms of combinations are possible to realize the gist of the present invention.

Therefore, the present invention is not limited to the above-described embodiments, and various changes can be made by any person having ordinary skill in the art without departing from the gist of the present invention as claimed in the following claims. It will be said that the technical spirit of this invention is to the extent possible.

According to the present invention described above, the surface roughness of the core to which the optical signal is directly guided is improved by directly heat-treating the cured core, thereby eliminating light scattering loss at the core and clad interface in the optical waveguide. There is an advantage that an optical waveguide of the PCB and a method of forming the optical waveguide of the PCB are provided.

In addition, the flow velocity difference caused by the difference in surface contact characteristics between PDMS and the lower cladding by capillary force, gravitational force and application of ultrasonic waves is overcome, and the inherent surface roughness of PDMS stamp Due to the difference in contact angle and filling speed between channels, the core waveguide formed by the first filled channel blocks the exit of another channel, thereby overcoming the problem of the core not moving forward in the closed channel. There is an advantage.

Claims (4)

In the optical waveguide forming method of the PCB (PCB), A clad forming step of laminating a PDMS stamp having an optical waveguide mold groove formed on a lower clad; A core filling step of filling the laminated clad with a gravity gradient and capillary force; Applying an ultrasonic vibration to the core filling step to apply an airtight filling of the core to the clad; Core curing step of curing the core by exposing the UV (UV) to the core filled clad; When the core is hardened by the core hardening step, the PDMS stamp removing step of removing the PDMS stamp and preparing to stack the upper clad is performed. An optical waveguide forming method of a PCB comprising a. The optical waveguide forming method of claim 1, wherein The surface roughness improving step of improving the surface roughness of the core by heat-treating the core from which the PDMS stamp is removed to a temperature near the glass transition temperature (Tg) The optical waveguide forming method of the PCB characterized in that it further comprises. The temperature near the glass transition temperature is The optical waveguide forming method of the PCB, characterized in that the temperature within the glass transition temperature within ± 10 ℃. delete

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