Abstract:
An optical wiring board having a core, the optical wiring board including: a lower cladding; a side cladding formed over the lower cladding and having an indentation formed therein, the indentation being in correspondence with the core; a core embedded in the indentation; and an upper cladding covering the core, wherein a height of the core is different from a depth of the indentation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. divisional application filed under 37 USC 1.53(b) claiming priority benefit of U.S. Ser. No. 12/149,952 filed in the United States on May 9, 2008, which claims earlier priority benefit to Korean Patent Application No. 10-2007-0117286 filed with the Korean Intellectual Property Office on Nov. 16, 2007, the disclosures of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    The present invention relates to an optical wiring board and a method of manufacturing the optical wiring board. 
         [0004]    2. Description of the Related Art 
         [0005]    The technology of manufacturing a printed circuit board using copper wiring is reaching its limit, because of the increasing speeds and capacities required for transferring and storing data. Accordingly, the optical wiring board, which includes optical wiring, is receiving attention as an alternative for overcoming the problems of electrical copper wiring. 
         [0006]    An optical waveguide, which can deliver optical signals using polymers or optical fibers, may be inserted in the optical wiring board. This is referred to as an EOCB (Electro-Optical Circuit Board). The EOCB can be used in the transceiving equipment and switching equipment of a communication network, the switches and servers of a data communication system, the mobile base stations of an UMTS (Universal Mobile Telecommunication System), or in the backplanes and daughter boards of a super computer. 
         [0007]    One method of forming the optical waveguide includes forming a lower cladding, forming a core over the lower cladding, and forming an upper cladding over the core. According to this method, however, the core may be polluted, and it is difficult to form the upper cladding to a uniform thickness. 
       SUMMARY 
       [0008]    An aspect of the invention provides an optical wiring board and a method of manufacturing the optical wiring board, with which the thickness of the core can be controlled easily. 
         [0009]    Another aspect of the invention provides a method of manufacturing an optical wiring board that includes a core. The method includes forming a lower cladding over an insulating layer; forming a side cladding, which has an indentation corresponding with the core, over the lower cladding; filling a core material in the indentation; and forming an upper cladding such that the core material is covered. 
         [0010]    Additionally, the method may further include forming a pad over an upper side or a lower side of the insulating layer, before forming the lower cladding. 
         [0011]    The forming of the side cladding may include forming a cladding layer over the lower cladding and forming an indentation by processing the cladding layer. 
         [0012]    Here, the operation of hardening the lower cladding may be performed additionally before the forming of the cladding layer, and the indentation may be formed by wet etching. 
         [0013]    The core material may be filled by an ink-jet method, and a height of the core material filled in the indentation may be smaller than a depth of the indentation. In certain embodiments, the upper cladding may be formed only in the indentation. 
         [0014]    Conversely, a height of the core material filled in the indentation may be greater than a depth of the indentation, and the lower cladding and the side cladding may be made from different materials. 
         [0015]    Yet another aspect of the invention provides an optical wiring board having a core. The optical wiring board can include a lower cladding; a side cladding, which is formed over the lower cladding, and in which an indentation corresponding with the core is formed; a core embedded in the indentation; and an upper cladding covering the core. Here, a height of the core may be different from a depth of the indentation. 
         [0016]    The height of the core may be smaller than the depth of the indentation, and in certain embodiments, the upper cladding may be formed only in the indentation. 
         [0017]    Additional aspects and advantages of the present invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a flowchart of a manufacturing method of an optical wiring board according to an embodiment of the present invention. 
           [0019]      FIG. 2 ,  FIG. 3 ,  FIG. 4 ,  FIG. 5 ,  FIG. 6 , and  FIG. 7  are cross-sectional views representing processes of a method of manufacturing an optical wiring board according to an embodiment of the present invention. 
           [0020]      FIG. 8 ,  FIG. 9 , and  FIG. 10  are cross-sectional views of an optical wiring board according to another embodiment of the present invention. 
           [0021]      FIG. 11 ,  FIG. 12 ,  FIG. 13 ,  FIG. 14 ,  FIG. 15 , and  FIG. 16  are cross-sectional views representing processes of a manufacturing method of an optical wiring board according to still another embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0022]    As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to particular modes of practice, and it is to be appreciated that all changes, equivalents, and substitutes that do not depart from the spirit and technical scope of the present invention are encompassed in the present invention. In the description of the present invention, certain detailed explanations of related art are omitted when it is deemed that they may unnecessarily obscure the essence of the invention. 
         [0023]    While such terms as “first” and “second,” etc., may be used to describe various components, such components must not be limited to the above terms. The above terms are used only to distinguish one component from another. For example, a first component may be referred to as a second component without departing from the scope of rights of the present invention, and likewise a second component may be referred to as a first component. The term “and/or” encompasses both combinations of the plurality of related items disclosed and any item from among the plurality of related items disclosed. 
         [0024]    The terms used in the present specification are merely used to describe particular embodiments, and are not intended to limit the present invention. An expression used in the singular encompasses the expression of the plural, unless it has a clearly different meaning in the context. In the present specification, it is to be understood that the terms such as “including” or “having,” etc., are intended to indicate the existence of the features, numbers, steps, actions, elements, parts, or combinations thereof disclosed in the specification, and are not intended to preclude the possibility that one or more other features, numbers, steps, actions, elements, parts, or combinations thereof may exist or may be added. 
         [0025]    The optical wiring board and the method of manufacturing the optical wiring board according to certain embodiments of the invention will be described below in more detail with reference to the accompanying drawings. Those components that are the same or are in correspondence are rendered the same reference numeral regardless of the figure number, and redundant explanations are omitted. 
         [0026]      FIG. 1  is a flowchart of a manufacturing method of an optical wiring board according to an embodiment of the present invention, and  FIG. 2  through  FIG. 7  are cross-sectional views representing processes of a method of manufacturing an optical wiring board according to an embodiment of the present invention. In  FIG. 2  through  FIG. 7  are illustrated an insulating layer  10 , a metal layer  20 , pads  22 , a lower cladding  30 , a side cladding  40 , indentations  42 , cores  44 , and an upper cladding  50 . 
         [0027]    First, pads  22  can be formed over an upper side or a lower side of an insulating layer  10  (S 110 ). For this, an insulating  10  layer on which a metal layer  20  is formed may be prepared, as shown in  FIG. 2 , and the metal layer  20  may be selectively removed, as shown in  FIG. 3 . 
         [0028]    Next, a lower cladding  30  can be formed over the insulating layer  10  (S 120 ), and hardened (S 130 ). The lower cladding  30  may be made of materials such as polyimide, and epoxy or acrylic materials, with additives added to control the refractive index. 
         [0029]    Then, a side cladding  40  having indentations  42  formed in correspondence with the cores  44  can be formed over the lower cladding  30  (S 140 ). For this, a cladding layer (not shown) may be formed over the lower cladding  30  (S 142 ), after which the indentations  42  may be formed by processing the cladding layer (not shown) (S 144 ). 
         [0030]    A material of film-type may be stacked, or a material of ink-type may be dispensed so that the cladding layer (not shown) is formed over the lower cladding  30 . 
         [0031]    The cladding layer (not shown) may be made of materials such as polyimide, epoxy, or acrylic materials, to which additives may be added for controlling the refractive index. 
         [0032]    The indentations  42  may be formed by wet etching. That is, an exposure process may be performed for the cladding layer (not shown) with a mask (not shown) blocking the beams, after which an etchant may be provided to the cladding layer (not shown). Using wet etching to etch the unhardened or semi-hardened cladding layer formed over the already hardened lower cladding  30  reduces the risk of damage to the lower cladding  30 , thereby allowing a facilitated operation. 
         [0033]    In this way, the side cladding may  40  be formed after the lower cladding  30  is hardened. Other methods may also be used, some of which can include forming the side cladding  40  from a different material from that of the lower cladding  30 . Thus, when the wet etching is performed for forming the indentations  42 , chemical reactions between the etchant and the lower cladding  30  can be prevented. This can reduce the risk of damage to the lower cladding  30  during the forming of the indentations  42 . In certain examples, the lower cladding  30  can be made of an acrylic material, while the side cladding  40  can be made of polyimide. 
         [0034]    After forming the side cladding  40  having the indentations  42  through the processes described above, the cores  44  may be formed by filling a core material in the indentations  42  (S 150 ), as shown in  FIG. 6 . Then, as shown in  FIG. 7 , an upper cladding  50  may be formed such that the core material is covered (S 160 ). The core material can be filled in using an ink-jet method. 
         [0035]    The core material may be made of an uncured polyimide, epoxy, or acrylic material. The core material may be cured later to form the cores  44 . 
         [0036]    The cores  44  can serve as paths through which optical signals may be transferred, and can be surrounded by the lower cladding  20 , upper cladding  50 , and side cladding  40 . Here, the cores  44  may have a higher refractive index compared to the lower cladding  20 , upper cladding  50 , and side cladding  40 , for the efficient transmission of optical signals. The core may thus contain additives for controlling the refractive index. 
         [0037]    Since the cores may be formed by filling and curing the core material in the indentations  42  of the side cladding  40 , the thickness of the cores  44  may readily be controlled by controlling the thickness of the side cladding  40 . Also, by using an ink-jet method, the high-cost core materials may not be wasted. 
         [0038]    While it is possible to completely fill indentations  42  with the core material such as in the example shown in  FIG. 6 , the core material  44 - 1  may also be only partially filled in the indentations  42  before forming the upper cladding  50 - 1 , such as in the example shown in  FIG. 8 . It is also possible to overfill the core material  44 - 2  in the indentations  42  and then form the upper cladding  50 - 2 , such as in the example shown in  FIG. 9 . In other words, the height of the core material filled in the indentations  42  may be greater than the depth of the indentations  42 , or may be smaller than the depth of the indentations  42 . 
         [0039]    In addition, the core material  44 - 3  can be filled in only a part of the indentations  42 , with the upper cladding  50 - 3  formed only in the indentations  42 , as shown in  FIG. 10 . 
         [0040]      FIG. 11  through  FIG. 16  are cross-sectional views representing processes of a method of manufacturing an optical wiring board according to another embodiment of the present invention. Compared to the embodiment described above, one difference of this embodiment lies in the positions of the pads  22 ,  22 ′. 
         [0041]    That is, in the embodiment described above, the pads  22  may be buried in the lower cladding  30 , as shown in  FIG. 7 . In this embodiment, however, the pads  22 ′ may not be buried in the lower cladding  30 , but may be formed on the lower side of the insulating layer  10 , so that the pads  22 ′ may be exposed. 
         [0042]    For this, an insulating layer  10  on which a metal layer  20 ′ such as of copper is stacked may be prepared as shown in  FIG. 11 , and pads  22 ′ may be formed underneath the insulation layer  10  (S 110 ) as shown in  FIG. 12 , for example, by selectively etching the metal layer  20 ′. 
         [0043]    Then, as illustrated in  FIG. 13 , the lower cladding  30  may be formed over the insulating layer  10  (S 120 ), and the lower cladding  30  may be hardened (S 130 ). 
         [0044]    Next, the side cladding  40  having indentations  42  formed in correspondence with the core  44  can be formed over the lower cladding  30  (S 140 ), as shown in  FIG. 14 , and the core material can be filled in the indentations  42  (S 150 ), as shown in  FIG. 15 . Afterwards, as shown in  FIG. 16 , the upper cladding  50  may be formed over the side cladding  40  such that the indentations  42  are covered (S 160 ). 
         [0045]    A manufacturing method of an optical wiring board according to an aspect of the present invention is set forth above, and an optical wiring board manufactured by the method is illustrated in  FIG. 7  through  FIG. 10  and  FIG. 16 . 
         [0046]    The optical wiring board may include a lower cladding  30 , a side cladding  40  in which one or more indentations  42  can be formed, one or more cores  44 ,  44 - 1 ,  44 - 2 ,  44 - 3  embedded in the indentations  42 , and an upper cladding  50 ,  50 - 1 ,  50 - 2 ,  50 - 3  covering the cores  44 . 
         [0047]    The height of the cores  44  may be equal to the depth of the indentations  42 , as shown in  FIG. 7  and  FIG. 16 , or may be different from the depth of the indentations  42 , as shown in  FIG. 8  through  FIG. 10 . 
         [0048]    In particular, if the height of the cores  44  is smaller than the depth of the indentations  42 , it is possible to form the upper cladding  44 - 3  only in the indentations  42 . This can reduce the overall thickness of the optical wiring board. 
         [0049]    The functions of and manufacturing method for each component can be substantially the same as those of each component in the previously described embodiment. As such, the description of these will not be repeated. 
         [0050]    While the spirit of the invention has been described in detail with reference to particular embodiments, the embodiments are for illustrative purposes only and do not limit the invention. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the invention.