Abstract:
A printed circuit board and a method of manufacturing the printed circuit board, in which the printed circuit board includes an insulating layer, a circuit layer embedded in the insulating layer and having a connection pad that is embedded in the insulating layer such that one side of the connection pad is flush with a surface of the insulating layer, and insulating materials configured to protect the circuit layer from an external environment and having an opening through which the connection pad is exposed. The manufacturing process includes a step of pressing the circuit layer and the insulating material into the insulating layer to form a level surface while leaving the connection pads flush at the surface. The method makes the printed circuit board slim, and increases reliability and the degree of design freedom.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2009-0001971, filed Jan. 9, 2009, entitled “A printed circuit board and a fabricating method the same”, which is hereby incorporated by reference in its entirety into this application. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a printed circuit board and a method of manufacturing the printed circuit board. 
     2. Description of the Related Art 
     Recently, demands for a technology which directly mounts a semiconductor chip on a printed circuit board has been increasing in response to the development of highly-densified semiconductor chips and the high-speed transmission of signals. Consequently, the development of printed circuit boards of a high density and high reliability which are suitable to highly-densified semiconductor chips is required. 
     Requirements for a printed circuit board of a high density and reliability are closely related to the specifications of the desired semiconductor chip. The printed circuit board having high density and high reliability must further be developed to have many characteristics such as the implementation of fine circuits, excellent electrical properties, structure for high-speed transmission of signals, high reliability, high performance, slimness and the like. Accordingly, a technology for printed circuit board which is capable of forming fine circuit patterns and micro via-holes is required in order to meet these needs. 
       FIGS. 1 to 5  are cross-sectional views showing a conventional process of manufacturing a printed circuit board. The conventional process of manufacturing a printed circuit board will now be described with reference to the drawings. 
     First, as shown in  FIG. 1 , a copper clad laminate which comprises an insulating layer  12  and copper layers  14  disposed on the insulating layer  12  is prepared. 
     As shown in  FIG. 2 , a via-hole  16  for the interlayer electrical connection is formed in the copper clad laminate using mechanical drilling or laser machining. 
     As shown in  FIG. 3 , a plated layer  18  is applied on the inner wall of the via-hole  16  as well as the copper layer  14 . In this regard, the plated layer  18  includes an electroless plated layer formed by an electroless plating process and an electrolytic plated layer formed by an electrolytic plating process. For the convenience of explanation, the plated layer  18  is shown in  FIG. 3  as being composed of a single plated layer. 
     As shown in  FIG. 4 , the copper layer  14  and the plated layer  18  are patterned to create a circuit layer  20 . 
     Finally, as shown in  FIG. 5 , a solder resist layer  22  having an opening  24  through which a pad part of the circuit layer  20  is exposed is disposed on the insulating layer  12 , thus finishing a printed circuit board  50 . 
     The printed circuit board which is manufactured through the conventional process is configured such that the circuit layer  20  including the pad part is formed on the insulating layer  12  and the solder resist layer  22  for protecting the outermost circuit layer  20  is formed on the insulating layer  12 . Consequently, the printed circuit board  50  configured in this manner is problematic in that its thickness is increased and reliability of the high density circuit is deteriorated. 
     Furthermore, since the printed circuit board is configured such that the pad part and the solder resist layer  50  are formed on the insulating layer  12 , stepped portions occur in the course of machining the openings  24  through which the pad part is exposed, thus making printability of external connection terminals uneven. In addition, since the openings must be machined while taking into consideration manufacturing error, the openings  24  are inevitably made larger than the pad part, thus reducing a degree of freedom in the design of the openings  24 . 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and the present invention provides a printed circuit board and a method of manufacturing the same which enable configuration into a slim structure and improving the reliability of a high-density circuit. 
     Furthermore, the present invention provides a printed circuit board and a method of manufacturing the same in which a circuit layer and a solder resist layer are embedded in an insulating layer such that there is no stepped portion between a pad part and the solder resist layer, thus increasing a degree of freedom of design. 
     In an aspect, the present invention provides a printed circuit board including: an insulating layer; at least one circuit layer embedded in the insulating layer and having a connection pad that is embedded in the insulating layer such that one side of the connection pad is flush with a surface of the insulating layer; and a insulating materials configured to protect the circuit layer from an external environment and having an opening through which the connection pad is exposed. 
     The at least one circuit layer may include a first circuit layer disposed on one side of the insulating layer and a second circuit layer disposed on the other side of the insulating layer, and the insulating layer may include a bump for connecting the first circuit layer with the second circuit layer. 
     The one side of the connection pad which is flush with the insulating layer may act as an exposed surface to which an external terminal is bonded. 
     The insulating materials may be flush at one side with the insulating layer and may be embedded at the other side in the insulating layer. 
     The at least one circuit layer may be formed on the other side of the insulating materials and may be embedded in the insulating layer. 
     The at least one circuit layer may be embedded in the insulating materials. 
     The insulating layer may include photosensitive insulating material. 
     In another aspect, the present invention provides a method of manufacturing a printed circuit board, including: (A) forming at least one circuit layer on a semi-cured insulating layer, the circuit layer having a connection pad; (B) forming insulating materials on the insulating layer, the insulating materials having an opening through which the connection pad is exposed; and (C) pressing and embedding the circuit layer and the insulating materials into the insulating layer. 
     The circuit layer may include: (A1) printing a first metal layer with a bump; (A2) applying a semi-cured insulating layer on the first metal layer printed with the bump; and (A3) applying a second metal layer on the insulating layer and patterning the first and second metal layers to form first and second circuit layers each having a connection pad. 
     In (C) pressing and embedding the circuit layer and the insulating materials, one side of the connection pad, which is flush with the insulating layer, may act as an exposed surface to which an external terminal is bonded. 
     The insulating materials may be flush at one side with the insulating layer and may be embedded at the other side in the insulating layer. 
     The at least one circuit layer may be formed on the other side of the insulating materials and may be embedded in the insulating layer. 
     The at least one circuit layer may be embedded in the insulating materials. 
     In (C) pressing and embedding the circuit layer and the insulating materials, the pressing may be executed while the insulating layer is in a semi-cured state. 
     The insulating materials may be made of photosensitive insulating material. 
     In the method, (B) forming the insulating materials may include: (B1) applying a photosensitive insulating material on the insulating layer; and (B2) subjecting the photosensitive insulating material to exposure and development processes to form an opening through which the connection pad is exposed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIGS. 1 to 5  are cross-sectional views showing a conventional process of manufacturing a printed circuit board; 
         FIG. 6  is a cross-sectional view of a printed circuit board according to an embodiment of the present invention; and 
         FIGS. 7 to 14  are cross-sectional views showing a process of manufacturing the printed circuit board shown in  FIG. 6 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Various advantages and features of the invention will become apparent from the following description of embodiments with reference to the accompanying drawings. 
     The terms and words used in the present specification and claims should not be interpreted as being limited to typical meanings or dictionary definitions, but should be interpreted as having meanings and concepts relevant to the technical scope of the present invention based on the rule according to which an inventor can appropriately define the concept of the term to best describe the method he or she knows for carrying out the invention. 
     Concerning the designations of reference numerals in this description, it should be noted that the same reference numerals are used throughout the different drawings to designate the same or similar components. Also, in the description of the present invention, when it is considered that the detailed description of a related prior art may obscure the gist of the present invention, such a detailed description is omitted. 
     Hereinafter, an embodiment of the present invention will be described in greater detail with reference to the accompanying drawings. 
     Printed Circuit Board 
       FIG. 6  is a cross-sectional view of a printed circuit board according to an embodiment of the present invention. The printed circuit board  100  according to this embodiment is described below with reference to  FIG. 6 . 
     As shown in  FIG. 6 , the printed circuit board  100  according to this embodiment comprises an insulating layer  106 , circuit layers  102   a ,  108   a  embedded in the insulating layer  106 , and insulating materials  110   a ,  110   b  embedded in the surface regions of the insulating layer  106  to protect the circuit layers  102   a ,  108   a  from the external environment. 
     The circuit layers  102   a ,  108   a  are configured such that the first circuit layer  102   a  is formed on a side of the insulating layer  106  and the second circuit layer  108   a  is formed on the other side of the insulating layer  106 . The first and second circuit layers  102   a ,  108   a  are connected to each other via bumps  104  passing through the insulating layer  106 . 
     Connection pads  102   b  and  108   b  of the circuit layers  102   a ,  108   a  are embedded in the insulating layer  106  such that external surfaces of the connection pads are flush with the external surfaces of the insulating layer  106 . Specifically, one side of the connection pad is flush with the external surface of the insulating layer  106  to offer an exposed surface to which an external connection terminal such as solder ball is bonded, and the other side of the connection pad is embedded in the insulating layer  106 . 
     The insulating materials  110   a ,  110   b  are also embedded in the insulating layer  106  such that external sides thereof are flush with the external surfaces of the insulating layer  106  in order to protect the first circuit layer  102   a  and/or the second circuit layer  108   a  from the external environment. Specifically, one side of each of the insulating materials  110   a ,  110   b  is flush with the external surface of the insulating layer  106 , and the other side of the insulating materials is embedded in the insulating layer  106 . 
     Furthermore, the circuit layers  102   a ,  108   a  excluding the connection pads are also embedded in the insulating layer  106  so as not to be exposed to the outside. In this context, there are two manners in which the circuit layers  102   a ,  108   a  excluding the connection pads may be embedded in the insulating layer  106  such that the external surfaces thereof are disposed on the other sides, i.e., internal surfaces of the insulating materials  110   a ,  110   b  for the protection from the external environment (see  FIG. 6 ) or they are embedded in the insulating materials  110   a ,  110   b  (see  FIG. 14 ). In other words, the circuit layers  102   a ,  108   a  may have any embedded configuration as long as the circuit layers  102   a ,  108   a  are protected from the external environment by the insulating materials  110   a ,  110   b . Although the circuit layers  102   a ,  108   a  are shown in  FIG. 14  as being entirely embedded in the insulating materials  110   a ,  110   b , circuit layers which are at least partially embedded in the insulating materials  110   a ,  110   b  should also be construed as falling within the scope of the present invention. 
     In this embodiment, the insulating layers  110   a ,  110   b  may be composed of photosensitive insulating material. 
     Although the printed circuit board  100  is shown in  FIG. 6  as having a two-layered structure, this is no more than a single exemplary structure. Accordingly, it will be appreciated that the scope of the present invention may include any of various structures wherein a multilayered buildup layer is formed, a connection pad formed on the outermost layer is embedded in an insulating layer so as to be flush with an outermost insulating layer, and an outermost circuit layer is protected by insulating materials embedded in the outermost insulating layer. 
     Process of Manufacturing the Printed Circuit Board 
       FIGS. 7 to 14  are cross-sectional views showing a process of manufacturing the printed circuit board shown in  FIG. 6 . The process is described below with reference to the drawings. 
     First, as shown in  FIG. 7 , a first metal layer  102  is prepared. As this first metal layer  102 , a copper layer typically used in the creation of a circuit layer of a printed circuit board may be used. 
     As shown in  FIG. 8 , bumps  104  are formed on the first metal layer  102 . 
     In this regard, the bumps  104  may be formed using a screen print technology. The screen print technology is executed in a manner such that conductive paste is transferred to the metal layer through openings of a mask. Specifically, openings of the mask are aligned with the metal layer  102 , and then conductive paste is applied onto the mask. Subsequently, the conductive paste is wiped using a squeegee, so that the conductive paste is extruded through the openings of the mask and is then transferred to the first metal layer  102  into a pattern having the desired shape and height. Of course, it is to be noted that a process of forming the bumps  104  through any other of known technologies also falls within the scope of the present invention. 
     The conductive paste that constitutes the bumps  104  may include any conductive material, for example, one selected from among Ag, Pd, Pt, Ni and Ag/Pd. 
     As shown in  FIG. 9 , an insulating layer  106  is applied onto the first metal layer  102  on which the bumps  104  were formed. 
     At this point, the insulating layer  106  may be configured such that its thickness is less than the height of the bumps  104 , and may be formed in a contact or noncontact way. 
     The process of contact way formation is executed in a manner such that the insulating layer  106  is applied onto the first metal layer  102  on which the bumps  104  were formed. At this point, the bumps  104  may have a rigidity higher than that of the insulating layer  106  such that the bumps  104  penetrate through the insulating layer  106 , and the insulating layer  106  may be embodied as a semi-cured prepreg made of thermosetting resin. In this embodiment, since the insulating layer  106  has a thickness less than the height of the bumps  104 , the bumps protrude from the insulating layer  106  by the difference therebetween. 
     The process of noncontact way formation is executed in a manner such that the metal layer is coated with insulating resin powder using an ink-jet print technology. This process is advantageous in that it minimizes problems such as deformation of the bumps and generation of fine gaps between the bumps  104  and the insulating layer  16  which may otherwise occur in the process of the contact way in which the bumps  104  are under pressure from the insulating layer  106  while penetrating through the insulating layer  106 . 
     As shown in  FIG. 10 , second metal layers  108  are applied onto the insulating layer  106 . 
     At this point, the second metal layer  108  is formed in a manner such that the insulating layer  106  and the bumps  104  are heated to a temperature higher than a softening temperature thereof under a vacuum condition and are thus semi-cured, and then the second metal layer  108  is pressed onto the semi-cured components using a press plate such as a stainless steel plate with a flat surface. By the pressing of the second metal layer  108 , the second metal layer  108  is connected to the bumps  104 . 
     In this regard, since the second metal layer  108  is pressed by the press plate having a flat surface, the pressure of the press plate is evenly transmitted to the insulating layer  106 , thus preventing warping or twisting from occurring throughout the substrate. Furthermore, since the pressing is executed under vacuum conditions, there is no occurrence of voids in the insulating layer  106 . 
     As shown in  FIG. 11 , the first metal layer  102  and the second metal layer  108  are patterned to create a first circuit layer  102   a  and a second circuit layer  108   a  each having a connection pad. 
     At this point, the first circuit layer  102   a  and the second circuit layer  108   a  may be created using a typical process such as a subtractive process. Specifically, the first circuit layer  102   a  and the second circuit layer  108   a  may be created in a manner such that dry films are applied onto the first metal layer  102  and the second metal layer  108  and then the first and second metal layers  102  and  108  are subjected to exposure, development and etching processes in this order. 
     In this regard, the first circuit layer  102   a  and the second circuit layer  108   a  are formed on the semi-cured insulating layer  106 . The reason for this is because the first circuit layer  102   a , the second circuit layer  108   a  and insulating materials  110   a ,  110   b  which are described below must be embedded in the insulating layer  106 . 
     As shown in  FIG. 12 , the insulating materials  110   a ,  110   b  having openings through which the insulating layer  106  is exposed are formed on the insulating layer  106 . 
     The insulating materials  110   a ,  110   b , which are provided so as to serve as solder resist layers for protecting the first and second circuit layers  102   a ,  108   a , may be made of a photosensitive insulating material that has a higher reliability than a general solder resist material and which allows for provision of openings by a simple process. Specifically, this procedure may be implemented by applying photosensitive insulating material  110   a ,  110   b  onto the insulating layer  106  and subjecting the photosensitive insulating material to exposure and development processes to form the openings through which the connection pads are exposed. 
     Furthermore, the insulating materials  110   a ,  110   b  applied to the insulating layer  106  may have a thickness exceeding that of the first circuit layer  102   a  and the second circuit layer  108   a  so as to protect the first and second circuit layer  102   a ,  108   a  from the external environment. 
     Finally, as shown in  FIG. 13 , the first and second circuit layers  102   a ,  108   a  including the connection pads  102   b  and  108   b  and the insulating materials  110   a ,  110   b  are pressed and are thus embedded in the insulating layer  106 . 
     At this point, the embedding procedure is implemented by pressing the first and second circuit layers  102   a ,  108   a  and the insulating materials  110   a ,  110   b  into the semi-cured insulating layer  106  using a press plate such as a flat stainless steel plate. 
     In this regard, the connection pads of the first and second circuit layers  102   a ,  108   a  are embedded in the insulating layer  106  such that outer surfaces thereof are flush with the surface of the insulating layer  106 . In other words, one side of each of the connection pads is flush with the surface of the insulating layer  106  and acts as an exposed surface on which an external connection terminal such as a solder ball is bonded, and the other side of the connection pad is embedded in the insulating layer  106 . 
     The insulating materials  110   a ,  110   b  are also embedded in the insulating layer  106  with their external surfaces flush with the surface of the insulating layer  106 . In other words, one side of each of the insulating materials  110   a ,  110   b  is flush with the surface of the insulating layer  106 , and the other side of the insulating materials is embedded in the insulating layer  106 . 
     At this point, the first and second circuit layers  102   a ,  108   a  excluding the connection pads thereof are embedded in the insulating layer  106  so as not to be exposed to the external environment. In this procedure, the insulating materials  110   a ,  110   b  may be deformed by the pressing force of the press plate and the repulsion force of the insulating layer  106  against the pressing force so that the first and second circuit layers  102   a ,  108   a  are disposed on the internal surfaces of the insulating materials  110   a ,  110   b . Alternatively, the insulating materials  110   a ,  110   b  and the first and second circuit layers  102   a ,  108   a  may be embedded in the insulating layer  106  without their initial configuration being changed, as shown in  FIG. 14 . Although the first and second circuit layers  102   a ,  108   a  are shown in  FIG. 14  as being entirely embedded in the insulating materials  110   a ,  110   b , the first and second circuit layers  102   a ,  108   a  may be partially embedded in the insulating materials  110   a ,  110   b.    
     Although the preferred embodiment of the present invention has been disclosed for illustrative purposes, those skilled in the art will appreciate that the printed circuit board and the method of manufacturing the same are not limited thereto and that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. Accordingly, such modifications, additions and substitutions should also be understood as falling within the scope of the present invention.