Abstract:
Disclosed is a PCB which includes an insulating layer. At least one via hole is formed through the insulating layer. A first electroless plating layer is formed on a wall of the via hole and on at least one side of the insulating layer so as to have a predetermined pattern, and is etched at its edge portion corresponding to an edge portion of the pattern in a dimension that is in proportion to a thickness thereof. A second electroless plating layer is formed on the first electroless plating layer. An electrolytic plating layer is formed on the second electroless plating layer, and is etched at its edge portion in a dimension that is in proportion to the thickness of the first electroless plating layer.

Description:
INCORPORATION BY REFERENCE  
       [0001]     The present application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 2004-79132 filed on Oct. 5, 2004. The content of the application is incorporated herein by reference in its entirety.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates, in general, to a printed circuit board (PCB) and a method of fabricating the same and, more particularly, to a PCB and a method of fabricating the same, in which an electroless copper plating process is repeated twice to prevent interruption of an internal circuit of a via hole and to form a fine circuit pattern.  
         [0004]     2. Description of the Prior Art  
         [0005]     As a technology for coping with a highly dense semiconductor chip and a high signal transmission speed of the semiconductor chip, demand for direct mounting of a semiconductor chip on a PCB is lately growing instead of CSP (chip-sized package) or wire bonding mounting technologies. To directly mount the semiconductor chip on the PCB, it is necessary to develop a highly dense and reliable PCB capable of dealing with a highly dense semiconductor.  
         [0006]     Requirements for a highly dense and reliable PCB have a close relationship with the specifications of a semiconductor chip, and are exemplified by fineness of circuits, excellent electric characteristics, structures providing high-speed signal transmission, high reliability, and high performance. There remains a need to develop a PCB technology of forming fine circuit patterns and micro-via holes so as to solve such requirements.  
         [0007]     Generally, a process of forming a circuit pattern on a PCB is classified into a subtractive process, a full additive process, and a semi-additive process. Of them, the semi-additive process is being pursued with interest, which can make the circuit pattern fine.  
         [0008]      FIGS. 1   a  to  1   g  are sectional views illustrating a procedure of fabricating a conventional PCB, which shows the semi-additive process, and  FIGS. 2   a  and  2   b  are sectional views illustrating a via hole formed through the procedure of  FIGS. 1   a  to  1   g.  In the drawings, only one side of the PCB is illustrated. However, in practice, both sides of the PCB are processed.  
         [0009]     As shown in  FIG. 1   a,  a copper clad laminate  100 , in which a circuit pattern  112  and a lower land  113  of the via hole are formed on an insulating resin layer  111 , is provided. Subsequently, an insulating layer  120  is laminated on the copper clad laminate  100 .  
         [0010]     As shown in  FIG. 1   b,  the insulating layer  120  is processed using a laser to form the via hole (a) to provide a circuit connection between the layers.  
         [0011]     As shown in  FIG. 1   c,  an electroless copper plating layer  130  is formed to a thickness of about 1 μm or more on the insulating layer  120 , a wall  121  of the via hole, and the lower land  113  so as to achieve electric connection between the layers and to form the circuit pattern on a surface of the insulating layer  120 .  
         [0012]     As shown in  FIG. 1   d,  a dry film  150  is applied on the electroless copper plating layer  130 , exposed, and developed to form a plating resist pattern, in which a circuit pattern  131 , a wall  132  of the via hole, an upper land  133 , and a lower land  134  are partially developed, in the dry film  150 .  
         [0013]     As shown in  FIG. 1   e,  an electrolytic copper plating layer  141 ,  142  is formed on portions of the circuit pattern  131 , the wall and the bottom of the via hole (a), the upper land  133 , and the lower land  134 , on which the plating resist pattern is not formed, to a thickness of about 10-20 μm.  
         [0014]     As shown in  FIG. 1   f,  the dry film  150  is stripped and thus removed.  
         [0015]     As shown in  FIG. 1   g,  an etchant is sprayed onto the electroless copper plating layer  130  and the electrolytic copper plating layer  141 ,  142  to remove a portion of the electroless copper plating layer  130  other than the circuit pattern  131 ,  141 , and via hole regions  132 ,  133 ,  134 ,  142 .  
         [0016]     In the PCB fabricated using the semi-additive process, an electroless plating liquid does undesirably flow in the via hole (a) in  FIG. 1   c.  Accordingly, as shown in  FIG. 2   a,  the electroless copper plating layer  132  formed on the wall  121  of the via hole may be thinner than the electroless copper plating layer  133  formed on the insulating layer  120 , or the electroless copper plating layer may not be formed on a portion of the wall of the via hole. Hence, as shown in  FIG. 2   b,  undesirably, an internal circuit of the via hole (a) is interrupted after the electrolytic copper plating layer  142  is formed.  
         [0017]     To prevent the interruption of the via hole (a) connection, the electroless copper plating layer  130  may be thickly formed in  FIG. 1   c.  However, since an etching process is conducted for a relatively long time in order to remove unnecessary electrolytic copper plating layer  130  in  FIG. 1   g,  the circuit pattern  131 ,  141  (particularly, edge portions of the circuit pattern  131 ,  141 ) is over-etched. Therefore, delamination of the circuit pattern  131 ,  141  occurs, or morphology of the circuit pattern  131 ,  141  is not flat.  
         [0018]     To avoid the above problems, Japanese Pat. Laid-Open Publication No. 2002-252466 suggests the following process.  
         [0019]      FIGS. 3   a  to  3   e  are sectional views illustrating the fabrication of another conventional PCB. As in the procedure of  FIGS. 1   a  to  1   g,  only one side of the PCB is illustrated in  FIGS. 3   a  to  3   e,  but in practice, both sides of the PCB are processed.  
         [0020]     As shown in  FIG. 3   a,  an epoxy resin layer  13  is laminated on a double-sided copper clad laminate  11 , in which a circuit pattern  12  is formed on a surface of an epoxy layer reinforced with a glass fiber, and a via hole  15  is then formed using a laser. Subsequently, the double-sided copper clad laminate  11  is dipped in a mixed solution of 10% H 2 SO 4  and 10% H 2 O 2  to form an activated region  17 .  
         [0021]     As shown in  FIG. 3   b,  an electroless copper plating layer  18  is formed on the activated region  17  acting as a self-catalyst.  
         [0022]     As shown in  FIG. 3   c,  a Pd catalyst  19  adheres to the circuit pattern and an exposed portion of the epoxy resin layer  13  of the double-sided copper clad laminate  11 .  
         [0023]     As shown in  FIG. 3   d,  the double-sided copper clad laminate  11  is dipped in a copper sulfate-based electroless copper plating solution to form an electroless copper plating layer  20  on the circuit pattern and the exposed portion of the epoxy resin layer  13 .  
         [0024]     As shown in  FIG. 3   e,  an electrolytic copper plating layer  21  is formed on the electroless copper plating layer  20  of the double-sided copper clad laminate  11 .  
         [0025]     In the PCB disclosed in Japanese Pat. Laid-Open Publication No. 2002-252466 as described above, the electroless copper plating layer  18  is formed using the activated region  17 , preventing the internal circuit of the via hole  15  from being interrupted.  
         [0026]     However, in the PCB disclosed in Japanese Pat. Laid-Open Publication No. 2002-252466, since the circuit pattern is formed on the electroless copper plating layer  20  and the electrolytic copper plating layer  21  using a subtractive process, it is more difficult to make a fine circuit pattern than when using the semi-additive process.  
         [0027]     To avoid the above disadvantages, in a method of fabricating the PCB disclosed in Japanese Pat. Laid-Open Publication No. 2002-252466, the circuit pattern is formed using the semi-additive process. However, since the thick electroless copper plating layer  20  (growing for 30 min at a growth speed of about 10 μm/h) must be etched, undesirably, the circuit pattern is over-etched.  
       SUMMARY OF THE INVENTION  
       [0028]     Therefore, the present invention has been made keeping in mind the above disadvantages occurring in the prior arts, and an object of the present invention is to provide a PCB, in which an internal circuit of a via hole is not interrupted, and a method of fabricating the same.  
         [0029]     Another object of the present invention is to provide a PCB, in which a fine circuit pattern is formed, and a method of fabricating the same.  
         [0030]     The above objects can be accomplished by providing a PCB which includes an insulating layer. At least one via hole is formed through the insulating layer. A first electroless plating layer is formed on a wall of the via hole and on at least one side of the insulating layer so as to have a predetermined pattern, and is etched at its edge portion corresponding to an edge portion of the pattern in a dimension that is in proportion to a thickness thereof. A second electroless plating layer is formed on the first electroless plating layer. An electrolytic plating layer is formed on the second electroless plating layer, and is etched at its edge portion in a dimension that is in proportion to the thickness of the first electroless plating layer.  
         [0031]     It is preferable that the first electroless plating layer be thinner than the second electroless plating layer.  
         [0032]     It is preferable that a thickness of the first electroless plating layer be about 0.1-0.5 μm and a thickness of the second electroless plating layer be about 1-5 μm.  
         [0033]     It is preferable that each of the first electroless plating layer, the second electroless plating layer, and the electrolytic plating layer comprises a material, selected from the group consisting of Cu, Au, Ni, Sn, and an alloy thereof, as a main component.  
         [0034]     Furthermore, the present invention provides a method of fabricating a PCB, which includes (A) laminating an insulating layer on a substrate, on which a circuit pattern is formed, and forming a via hole through the insulating layer for connection to the circuit pattern; (B) forming a first electroless plating layer on an exposed portion of the circuit pattern, the insulating layer, and a wall of the via hole; (C) forming a predetermined plating resist pattern on the first electroless plating layer, and forming a second electroless plating layer on a portion of the first electroless plating layer, on which the plating resist pattern is not formed; (D) forming an electrolytic plating layer on the second electroless plating layer, and removing the plating resist pattern; and (E) removing the remaining portion of the first electroless plating layer, on which the second electroless plating layer and the electrolytic plating layer are not formed.  
         [0035]     It is preferable that the first electroless plating layer be formed using a catalyst precipitation process in the step (B).  
         [0036]     It is preferable that the first electroless plating layer be formed using a sputtering process in the step (B).  
         [0037]     It is preferable that the second electroless plating layer be formed using the first electroless plating layer as a self-catalyst in the step (C).  
         [0038]     It is preferable that the electrolytic plating layer be formed using the first electroless plating layer as an incoming line for plating in the step (D).  
         [0039]     It is preferable that the first electroless plating layer be formed thinner than the second electroless plating layer of the step (C) in the step (B).  
         [0040]     It is preferable that a thickness of the first electroless plating layer be about 0.1-0.5 μm and a thickness of the second electroless plating layer be about 1-5 μm.  
         [0041]     It is preferable that each of the first electroless plating layer, the second electroless plating layer, and the electrolytic plating layer comprise a material, selected from the group consisting of Cu, Au, Ni, Sn, and an alloy thereof, as a main component.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0042]     The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0043]      FIGS. 1   a  to  1   g  are sectional views illustrating a procedure of fabricating a conventional PCB;  
         [0044]      FIGS. 2   a  and  2   b  are sectional views illustrating a via hole formed through the procedure of  FIGS. 1   a  to  1   g;    
         [0045]      FIGS. 3   a  to  3   e  are sectional views illustrating the fabrication of another conventional PCB;  
         [0046]      FIGS. 4   a  and  4   j  are sectional views illustrating the fabrication of a PCB according to the present invention; and  
         [0047]      FIG. 5  is a partially enlarged view of a portion B which is marked by a dotted circle of  FIG. 4   j.   
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0048]     Hereinafter, a detailed description will be given of a PCB and a method of fabricating the same according to the present invention with reference to the drawings.  
         [0049]      FIGS. 4   a  and  4   j  are sectional views illustrating the fabrication of a PCB according to the present invention, and  FIG. 5  is a partially enlarged view of a portion B which is marked by a dotted circle of  FIG. 4   j.  In the drawings, only one side of the PCB is illustrated, but in practice, both sides of the PCB are processed.  
         [0050]     As shown in  FIG. 4   a,  a substrate, that is, a copper clad laminate  1100 , is provided, in which a first circuit pattern  1120  and a lower land  1130  are formed on an insulating resin layer  1110 . Subsequently, an insulating layer  1200  (for example, prepreg) is laminated on the substrate  1100 .  
         [0051]     In this respect, the copper clad laminate used as the substrate  1100  may be classified into a glass/epoxy copper clad laminate, a heat-resistant resin copper clad laminate, a paper/phenol copper clad laminate, a high-frequency copper clad laminate, a flexible copper clad laminate, and a composite copper clad laminate, depending on the application. However, it is preferable to use the glass/epoxy copper clad laminate, in which copper foil layers are formed on both sides of the insulating resin layer, and which is most frequently employed in the course of fabricating PCBs.  
         [0052]     In the present invention, the substrate has a structure in which a circuit layer is formed on one side of the substrate  1100 . However, a substrate  1100  having a multi-layered structure, in which a predetermined circuit pattern, a via hole and the like are formed on an internal layer, may be used depending on the purpose or application.  
         [0053]     As shown in  FIG. 4   b,  the insulating layer  1200  is bored using a laser to form a via hole (A) for circuit connection between the layers.  
         [0054]     In this regard, the laser may be exemplified by a YAG (yttrium aluminum garnet) laser and a carbon dioxide (CO 2 ) laser.  
         [0055]     In the present invention, after formation of the via hole (A) using the laser, it is preferable to further conduct a desmear process so as to remove a smear which is formed on a wall  1210  of the via hole by melting the insulating layer  1200  due to heat generated in the course of forming the via hole.  
         [0056]     As shown in  FIG. 4   c,  a very thin first electroless copper plating layer  1300  is formed on the insulating layer  1200 , wall  1210  of the via hole, and a lower land  1130  so as to electrically connect the layers to each other and to form the circuit pattern on a surface of the insulating layer  1200 .  
         [0057]     At this time, it is preferable that the first electroless copper plating layer  1300  be about 0.1-0.5 μm in thickness. When the thickness of the first electroless copper plating layer  1300  is less than about 0.1 μm, the first electroless copper plating layer  1300  may not be formed on a portion of the resulting substrate, affecting a subsequent electrolytic copper plating process. On the other hand, when the thickness of the first electroless copper plating layer  1300  is more than about 0.5 μm, since the first electroless copper plating layer  1300  is thick, over-etching may occur in an etching process.  
         [0058]     For example, the first electroless copper plating layer  1300  may be formed using a catalyst precipitation method including a degreasing step, a soft etching step, a pre-catalyst treating step, a catalyst treating step, an acceleration step, an electroless copper plating step, and an anti-oxidizing step.  
         [0059]     In the degreasing step, oxides, impurities, and particularly oils and fats are removed from the surfaces of the insulating layer  1200 , the wall  1210  of the via hole, and the lower land  1130  using a chemical containing acid or alkaline surfactants, and the resulting substrate is rinsed to completely remove the surfactants therefrom.  
         [0060]     The soft etching step makes the surfaces of the insulating layer  1200 , the wall  1210  of the via hole, and the lower land  1130  slightly rough (for example, a roughness of about 1-2 μm) to uniformly deposit copper particles on the surfaces during the electroless copper plating step, and to remove contaminants which are not removed during the degreasing step.  
         [0061]     In the pre-catalyst treating step, the substrate  1100  is dipped in a dilute first catalyst-containing chemical to prevent a second catalyst-containing chemical used in the catalyst treating step from being contaminated or to prevent the concentration of the second catalyst-containing chemical from changing. Moreover, because the substrate  1100  is preliminarily dipped in the first chemical, having the same components as the second chemical, prior to treating the substrate using the second chemical, the treating of the substrate using the catalyst is preferably achieved. At this stage, it is preferable that the chemical diluted in a concentration of 1-3% be used in the pre-catalyst treating step.  
         [0062]     In the catalyst treating step, catalyst particles are applied on the surfaces of the insulating layer  1200 , the wall  1210  of the via hole, and the lower land  1130 . The catalyst particles may be preferably exemplified by a Pd-Sn compound, and Pd 2   −  dissociated from the Pd-Sn compound helps promote the plating of the substrate in conjunction with Cu 2   +  plated on the substrate.  
         [0063]     During the electroless copper plating step, the first electroless copper plating layer  1300  is formed on the insulating layer  1200 , the wall  1210  of the via hole, and the lower land  1130 . In this stage, it is preferable that a plating solution contain CuSO 4 , HCHO, NaOH, and a stabilizer. It is important to control the composition of the plating solution because chemical reactions constituting the plating process must maintain an equilibrium state in order to continuously conduct the plating process. To desirably maintain the composition of the plating solution, it is necessary to properly replenish each component constituting the plating solution, to mechanically agitate the plating solution, and to smoothly operate a cycling system of the plating solution. Furthermore, it is necessary to use a filtering device for removing byproducts resulting from the reaction, and the removal of the byproducts using the filtering device extends the life of the plating solution.  
         [0064]     An anti-oxidizing layer is formed on a copper clad to prevent oxidation of the copper clad caused by alkaline components remaining after the electroless copper plating step during the anti-oxidizing step.  
         [0065]     Alternatively, the formation of the first electroless copper plating layer  1300  may be achieved using a sputtering method, in which gas ion particles (for example, Ar + ) generated by plasma or the like collide with a copper target to form the first electroless copper plating layer  1300  on the insulating layer  1200 , the wall  1210  of the via hole, and the lower land  1130 .  
         [0066]     As shown in  FIG. 4   d,  a dry film  2000  is formed on the first electroless copper plating layer  1300 .  
         [0067]     The dry film  2000  includes three layers, that is, a cover film, a photoresist film, and a Mylar film, and the photoresist film substantially acts as a resist.  
         [0068]     As shown in  FIG. 4   e,  an art work film  3000 , having a predetermined pattern printed thereon, is attached to the dry film  2000 , and then exposed to ultraviolet rays. The ultraviolet rays are not transmitted through a black portion  3100  of the art work film  3000 , on which the pattern is printed, but through the remaining portion  3200  of the art work film  3000 , on which the pattern is not printed, hardening the dry film  2000  below the art work film  3000 .  
         [0069]     The predetermined pattern includes a second circuit pattern, the wall and the bottom of the via hole, and an upper land of the via hole to be formed in the subsequent processes.  
         [0070]     As shown in  FIG. 4   f,  after the art work film  3000  is removed, the substrate  1100  is dipped in a developing solution to remove the unhardened portions of the dry film  2000  from portions of the electroless copper plating layer  1300 , such as the second circuit pattern  1310 , the wall  1320  of the via hole, the upper land  1330 , and the lower land  1340 . The remaining hardened portion of the dry film  2000  forms a plating resist pattern.  
         [0071]     In this regard, examples of the developing solution include a sodium carbonate (Na 2 CO 3 ) aqueous solution or a potassium carbonate (K 2 CO 3 ) aqueous solution.  
         [0072]     As shown in  FIG. 4   g,  a second electroless copper plating layer  1410 ,  1420 ,  1430 ,  1440  is formed on the second circuit pattern  1310 , the upper land  1330 , the wall  1320  of the via hole, and the lower land  1340  using the patterned dry film  2000  as a plating resist.  
         [0073]     At this stage, it is preferable that the second electroless copper plating layer  1410 ,  1420 ,  1430 ,  1440  be about 1-5 μm in thickness. When the thickness of the second electroless copper plating layer  1410 ,  1420 ,  1430 ,  1440  is less than about 1 μm, since an electroless plating liquid undesirably flows in the via hole, the second electroless copper plating layer  1420  may not be formed on a portion of the wall of the via hole. In this case, undesirably, an internal circuit of the via hole (A) may be interrupted after an electrolytic copper plating layer is formed. On the other hand, when the thickness of the second electroless copper plating layer  1410 ,  1420 ,  1430 ,  1440  is more than about 5 μm, it undesirably takes a long time to form the second electroless copper plating layer  1410 ,  1420 ,  1430 ,  1440 . Additionally, since the electroless copper plating layer has physical properties poorer than the electrolytic copper plating layer, it is preferable to form the second electroless copper plating layer as thinly as possible so that the internal circuit of the via hole is not interrupted.  
         [0074]     In the present invention, the formation of the second electroless copper plating layer  1410 ,  1420 ,  1430 ,  1440  may be conducted using the first electroless copper plating layer  1310 ,  1320 ,  1330 ,  1340  as a self-catalyst. Therefore, the second electroless copper plating layer  1410 ,  1420 ,  1430 ,  1440  may be directly formed on the first electroless copper plating layer  1310 ,  1320 ,  1330 ,  1340  of the second circuit pattern, the wall of the via hole, the upper land, and the lower land while the catalyst treating step is not conducted. This means that many pretreatments may be omitted in the course of forming the second electroless copper plating layer  1410 ,  1420 ,  1430 ,  1440 .  
         [0075]     The second electroless copper plating layer  1410 ,  1420 ,  1430 ,  1440  is formed on the second circuit pattern  1310 , the wall  1320  of the via hole, the upper land  1330 , and the lower land  1340  using a plating solution which contains CuSO 4 , HCHO, NaOH, and a stabilizer. As in the formation of the first electroless copper plating layer  1300 , it is important to control the composition of the plating solution because chemical reactions constituting the second copper plating process must maintain an equilibrium state in order to continuously conduct the plating process. To desirably maintain the composition of the plating solution, it is necessary to properly replenish each component constituting the plating solution, to mechanically agitate the plating solution, and to smoothly operate a cycling system of the plating solution. Furthermore, it is necessary to use a filtering device for removing byproducts resulting from the reaction, and the removal of the byproducts using the filtering device extends the life of the plating solution.  
         [0076]     As shown in  FIG. 4   h,  an electrolytic copper plating layer  1510 ,  1520  is formed on a portion of the second electroless copper plating layer  1410 ,  1420 ,  1430 ,  1440 , such as the second circuit pattern, the wall and the bottom of the via hole, the upper land, and the lower land, on which the plating resist pattern of the dry film  2000  is not formed.  
         [0077]     After the substrate  1100  is dipped into a copper plating tub, the electrolytic copper plating is then conducted using a D.C. rectifier to form the electrolytic copper plating layer  1510 ,  1520 . Preferably, the electrolytic copper plating is conducted in such a way that after an area to be plated is calculated, a proper amount of electricity is applied to the D.C. rectifier to achieve the deposition of copper.  
         [0078]     The electrolytic copper plating process is advantageous in that physical properties of the electrolytic copper plating layer are superior to those of the electroless copper plating layer and it is easy to form a thick copper plating layer.  
         [0079]     An additional incoming line for the copper plating may be used to form the electrolytic copper plating layer  1510 ,  1520 . However, in the present invention, it is preferable to use the first electroless copper plating layer  1300  as the incoming line to form the electrolytic copper plating layer  1510 ,  1520 .  
         [0080]     As shown in  FIG. 4   i,  the dry film  2000  is stripped from the substrate  1100  and thus removed.  
         [0081]     At this time, the dry film  2000  is removed using a stripping solution containing sodium hydroxide (NaOH) or potassium hydroxide (KOH).  
         [0082]     In the steps of  FIGS. 4   d  to  4   i,  the dry film  2000  is used as the plating resist. However, a liquid photosensitive substance may be used as the plating resist.  
         [0083]     In this case, the liquid photosensitive substance, which is to be exposed to ultraviolet rays, is applied on the insulating layer  1200 , and then dried. Subsequently, the photosensitive substance is exposed and developed using the patterned artwork film  3000 , which includes the second circuit pattern, the via hole, and the upper land, thereby forming a predetermined pattern thereon. Next, the patterned photosensitive substance is used as the plating resist, and the electroless and electrolytic copper plating processes are sequentially conducted, thereby forming the second electroless copper plating layer  1410 ,  1420 ,  1430 ,  1440  and the electrolytic copper plating layer  1510 ,  1520  on the second circuit pattern  1310 , the wall  1320  of the via hole, the upper land  1330 , and the lower land  1340 . The photosensitive substance is then removed. The application of the liquid photosensitive substance is implemented by a dip coating process, a roll coating process, an electro-depositing process or the like.  
         [0084]     Compared to the use of the dry film  2000 , the use of the liquid photosensitive substance is advantageous in that since it is possible to form a thinner layer, a finer circuit pattern can be formed. Another advantage is that when a surface of the insulating layer  1200  is uneven, it is possible to flatten the surface by filling recesses of the insulating layer.  
         [0085]     As shown in  FIG. 4   j,  an etchant is sprayed onto the substrate  1100  to remove the remaining portion of the first electroless copper plating layer  1300  other than the second circuit pattern, the via hole, and the upper land.  
         [0086]     Referring to  FIG. 5 , thicknesses (E 1 , E 2 ) of etched edge portions of the first electroless copper plating layer  1300  and the electrolytic copper plating layer  1510  of the second circuit pattern are proportional to a thickness of the first electroless copper plating layer  1300 . Accordingly, since the first electroless copper plating layer  1300  is very thin (about 0.1-0.5 μm), the amount of etched materials of the first electroless copper plating layer  1300  and the electrolytic copper plating layer  1510  of the second circuit pattern is very small.  
         [0087]     Subsequently, a procedure of laminating the insulating layer, and of forming the via hole, the first electroless copper plating layer, the second electroless copper plating layer, and the electrolytic copper plating layer is repeated to form a structure having desired layers. Next, a solder resist forming process, a nickel/gold plating process, and an external part forming process are implemented, thereby creating the PCB  1000  according to the present invention.  
         [0088]     As shown in  FIG. 4   j,  in the PCB  1000  according to the present invention, since the first electroless copper plating layer  1300  used as the incoming line for the copper plating is very thin (about 0.1-0.5 μm), the second circuit pattern  1310 ,  1410 ,  1510  (particularly, edge portions of the second circuit pattern  1310 ,  1410 ,  1510 ) is scarcely etched. Accordingly, it can be seen that flat morphology of the circuit pattern can be assured without delamination of the circuit pattern in the course of forming a fine circuit pattern (a line width of about 10 μm or less).  
         [0089]     Furthermore, in the PCB  1000  according to the present invention, since the second electroless copper plating layer  1420 ,  1440  having a desired thickness (about 1-5 μm) is formed in the via hole, an internal circuit of the via hole is not interrupted after the electrolytic copper plating layer  1510 ,  1520  is formed.  
         [0090]     Meanwhile, in the present invention, sections of the first electroless copper plating layer  1310 ,  1320 ,  1330 ,  1340 , the second electroless copper plating layer  1410 ,  1420 ,  1430 ,  1440 , and the electrolytic copper plating layer  1510 ,  1520 , which are sequentially formed on the second circuit pattern, the wall of the via hole, the upper land, and the lower land of the PCB  1000  according to the present invention, are observed using an analysis device, such as SEM (scanning electron microscope), thereby confirming a three-layered structure of the copper plating layer.  
         [0091]     Furthermore, the three-layered structure of the copper plating layer of the PCB  1000  according to the present invention is not limited to a layer made of pure copper, but means a plating layer consisting mostly of copper. This is confirmed by analyzing a chemical composition of the layer using an analysis device, such as EDAX (energy dispersive analysis of X-rays), which is usually provided in the scanning electron microscope.  
         [0092]     Additionally, the three-layered structure of the copper plating layer of the PCB  1000  according to the present invention is not limited to a layer made only of copper (Cu), but may be a three-layered structure consisting mostly of a conductive material, such as gold (Au), nickel (Ni), and tin (Sn), according to the purpose and the application.  
         [0093]     The present invention has been described in an illustrative manner, and it is to be understood that the terminology used is intended to be in the nature of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.  
         [0094]     As described above, a PCB and a method of fabricating the same according to the present invention are advantageous in that since a first electroless copper plating layer is very thin, the amount of an etched material of a copper plating layer of a circuit pattern is minimized.  
         [0095]     Another advantage of the present invention is that the amount of the etched material of the copper plating layer is reduced, preventing delamination of the circuit pattern due to over-etching, resulting in the formation of a very fine circuit pattern.  
         [0096]     Still another advantage of the present invention is that the amount of the etched material of the copper plating layer is reduced, thereby assuring flat morphology and a uniform circuit pattern.  
         [0097]     A further advantage of the present invention is that a second electroless copper plating layer is plated in a desired thickness in a via hole, thereby preventing interruption of an internal circuit of the via hole after an electrolytic copper plating layer is formed.  
         [0098]     Yet another advantage of the present invention is that since the fine via hole, in which the internal circuit is not interrupted, can be formed, a highly dense PCB may be provided.