Patent Abstract:
A printed circuit board (PCB) having at least one embedded capacitor and a method of fabricating the same is provided. A dielectric layer is formed using a ceramic material having a high capacitance, thereby assuring that the capacitors each have a high dielectric constant corresponding to the capacitance of a decoupling chip capacitor.

Full Description:
BACKGROUND OF THE INVENTION 
   INCORPORATION BY REFERENCE 
   The present application claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 2004-67487 filed on Aug. 26, 2004. The content of the application is incorporated herein by reference in its entirety. 
   1. Field of the Invention 
   The present invention relates, in general, to a printed circuit board (PCB) including embedded capacitors and a method of fabricating the same and, more particularly, to a PCB including embedded capacitors, in which a dielectric layer is formed using a ceramic material having a high capacitance, thereby assuring that the capacitors each have a high dielectric constant corresponding to the capacitance of a decoupling chip capacitor, and a method of fabricating the same. 
   2. Description of the Prior Art 
   Typically, discrete chip resistors or discrete chip capacitors have been frequently mounted on most printed circuit boards (PCB), but, recently, PCBs are developing in which passive components, such as resistors or capacitors, are embedded. 
   A technology for fabricating the PCBs including the passive components embedded therein, achieves substitution of conventional chip resistors or chip capacitors by mounting the passive components, such as the resistors or capacitors, on an external surface of a PCB or in an internal layer of the PCB according to a novel process employing a novel material (substance). In other words, the PCB including the passive component embedded therein has a structure in which the passive component, for example, the capacitor, is embedded in the internal layer of the PCB or mounted on the external surface of the PCB, and if the capacitor as the passive component is integrated with the PCB to act as one part of the PCB regardless of the size of a substrate, the capacitor is called an “embedded capacitor” and the resulting PCB is called “PCB including embedded capacitor”. One of the most important features of the PCB including the capacitor embedded therein is that since the capacitor is already mounted as part of the PCB in the PCB, it is not necessary to mount the capacitor on a surface of the PCB. 
   On the whole, the technology of fabricating a PCB including a capacitor embedded therein may be classified into three methods, and a description will be given of the three methods, below. 
   Firstly, there is a method of fabricating a polymer thick film type of capacitor, in which application of a polymer capacitor paste and thermal hardening, that is, drying, are conducted to fabricate a capacitor. In the above method, after the polymer capacitor paste is applied on an internal layer of a PCB and dried, a copper paste is printed on the resulting PCB and dried so that electrodes are formed, thereby making an embedded capacitor. 
   A second method is to apply a ceramic filled photosensitive resin on a PCB to fabricate a discrete type of embedded capacitor, and Motorola Inc. in USA holds a patent for related technologies. In detail, the photosensitive resin containing ceramic powder is applied on the PCB, a copper foil is laminated on the resulting PCB to form upper and lower electrodes, a circuit pattern is formed, and the photosensitive resin is etched to fabricate the discrete type of capacitor. 
   A third method is to insert an additional dielectric layer having a capacitance characteristic in an internal layer of a PCB so as to substitute for a decoupling capacitor conventionally mounted on a surface of a PCB, thereby fabricating a capacitor, and Sanmina Corp. in USA holds a patent for related technologies. According to the third method, the dielectric layer including a power supply electrode and a grounded electrode is inserted into the internal layer of the PCB to fabricate a power distribution type of decoupling capacitor. 
   The above three methods have been achieved through various processes, and each process is realized in a different manner. However, a market for PCBs including embedded capacitors is not yet activated. Accordingly, standardization of the above methods has not been achieved yet, but commercialization of the methods is under development. 
   Hereinafter, a detailed description will be given of a conventional PCB including an embedded capacitor and a method of fabricating the same, referring to the drawings. 
   Firstly, a conventional technology of  FIGS. 1   a  to  1   e  will be described, below. 
     FIGS. 1   a  to  1   e  illustrate the production of the conventional PCB including the polymer thick film type of embedded capacitors. A polymer capacitor paste is applied and heat-dried (or hardened) to create the PCB including the polymer thick film type of embedded capacitors. 
   In a first step, a dry film is applied on copper foils of an internal layer  42 , made of FR-4, of the PCB, exposed and developed, and the resulting copper foils are etched to form copper foils  44   a,    44   b  for a positive electrode (+), copper foils  43   a,    43   b  for a negative electrode (−), and clearances (refer to  FIG. 1   a ). 
   In a second step, capacitor pastes  45   a,    45   b,  which are made of a polymer containing ceramic powder having a high dielectric constant, are applied on the copper foils  43   a,    43   b  for the negative electrode (−) using a screen printing technology, and then dried or hardened (refer to  FIG. 1   b ). In this regard, the screen printing technology is a method of passing a medium, such as an ink, through a stencil screen using a squeeze to transcribe a pattern to the surface of a substrate. 
   At this time, the capacitor pastes  45   a,    45   b  are packed into the clearances between the copper foils  44   a,    44   b  for the positive electrode (+) and the copper foils  43   a,    43   b  for the negative electrode (−). 
   In a third step, positive electrodes (+)  46   a,    46   b  are formed using a conductive paste, such as silver or copper, according to a screen printing technology, dried and hardened (refer to  FIG. 1   c ). 
   In a fourth step, capacitor layers formed on the internal layer  42  of the PCB according to the first to third steps are interposed between insulating layers  47   a,    47   b,  and subjected to a lamination process (refer to  FIG. 1   d ). 
   In a fifth step, capacitors on the internal layer of the PCB are connected to positive terminals (+)  51   a,    51   b  and negative terminals (−)  50   a,    50   b  of integrated circuit chips (IC chip)  52   a,    52   b,  mounted on an external side of the substrate, through THs (through holes) and LBVHs (laser blind via holes)  49   a,    49   b,  thereby acting as the embedded capacitors (refer to  FIG. 1   e ). 
   A description will be given of a conventional second technology, referring to  FIGS. 2   a  to  2   f.    
     FIGS. 2   a  to  2   f  illustrate the production of a conventional PCB including a discrete type of embedded capacitors which are formed by application of a photosensitive resin. The discrete type of embedded capacitors are formed by applying a ceramic filled photosensitive resin on the PCB as disclosed in U.S. Pat. No. 6,349,456 which is granted to Motorola Inc. 
   In a first step, a photosensitive dielectric resin  14  containing ceramic powder is applied on a PCB  10 , on which a conductive layer  12  is already formed, exposed and heat-dried (refer to  FIG. 2   a ). 
   In a second step, a copper foil  16  is laminated on the dried photosensitive dielectric resin  14  (refer to  FIG. 2   b ). In this respect, reference numeral  18  denotes a sacrificial layer which is formed by plating tin on an upper side of the copper foil  16  to be used as a copper etching resist. 
   In a third step, the dry film is laminated on an upper side of the sacrificial layer  18 , exposed and developed to etch a portion of the sacrificial layer  18  and the copper foil  16 , thereby forming upper electrodes  20  (refer to  FIG. 2   c ). 
   In a fourth step, the photosensitive dielectric resin  14  positioned below the upper electrodes  20  is exposed and then etched. At this time, the upper copper electrodes  20  are used as a photomask of the photosensitive dielectric resin  14  (refer to  FIG. 2   d ). 
   In a fifth step, the conductive layer  12  below the etched photosensitive dielectric resin  22  is etched to form lower electrodes  24  (refer to  FIG. 2   e ). 
   In a sixth step, capacitor layers  32  of an internal layer of the PCB  10  formed through the first to fifth steps are interposed between insulating layers  26 , and metal layers  30  are laminated on the resulting structure (refer to  FIG. 2   f ). 
   Capacitors  32  in an internal layer of the PCB are connected to power supply terminals and grounded terminals of integrated circuit chips, mounted on an external side of the PCB through THs (through holes) and LBVHs (laser blind via holes), thereby creating the PCB including the discrete type of embedded capacitors. 
   A third conventional technology will be described, referring to  FIGS. 3   a  to  3   c.    
     FIGS. 3   a  to  3   c  illustrate the production of a conventional PCB including embedded capacitors which are formed by insertion of an additional dielectric layer having a capacitance characteristic. The additional dielectric layer having the capacitance characteristic is inserted into an internal layer of the PCB to create an embedded capacitor as a substitute of a decoupling capacitor mounted on a surface of the PCB as disclosed in U.S. Pat. Nos. 5,079,069, 5,261,153, and 5,800,575 which are granted to Sanmina Corp in the USA. 
   In a first step, a copper coated laminate  61 , which has a high dielectric constant and is interposed between copper foils  63   a,    63   b,  is coated with a dry film, exposed and developed to etch the copper foils  63   a,    63   b,  thereby forming power supply electrodes of capacitors and clearances (refer to  FIG. 3   a ). 
   In a second step, an internal layer  61  of the PCB subjected to the first step is interposed between insulating layers  64   a,    64   b  and subjected to a lamination process, and external copper foils  65   a,    65   b  are laminated on the resulting PCB (refer to  FIG. 3   b ). 
   In a third step, the capacitors in the internal layer of the PCB are connected to power supply terminals and grounded terminals of integrated circuit chips  68   a,    68   b , mounted on an external side of the PCB, through THs (through holes) and LBVHs (laser blind via holes), thereby acting as a power distribution type of decoupling capacitor (refer to  FIG. 3   c ). In this regard, reference numerals  67   a,    67   b  denote clearances between the grounded and power supply electrodes. The clearances each have a predetermined width so that the copper foils do not meet with the through holes or the via holes when the through holes or the via holes are formed through the PCB. 
   Meanwhile, since the embedded capacitors have a structure in which the capacitors are embedded in the PCB, an area which is occupied by the chip capacitors may be reduced. Thus, the embedded capacitors are advantageous in that a mounting density of chips may increase and it is unnecessary to mount the chip capacitors on a surface of the PCB. 
   In conventional technologies, a long connection length between devices at a high frequency brings about occurrence of an electric parasitic load, thereby reducing the electric performances of goods. Additionally, the number of connections increases due to a solder, causing poor reliability of goods. However, a conventional embedded capacitor is advantageous in that the connection length between the devices is reduced, resulting in suppressed occurrence of the electric parasitic element. Thus, the electric performance is improved. 
   However, a material of the conventional embedded capacitor is, for example, a polymer or a photosensitive resin filled with ceramic. Thus, it is usefully applied to a PCB process, but has a dielectric constant too low to be used as a substitute for a chip capacitor. 
   Generally, capacitance depends on the area and thickness of a capacitor, and is calculated according to the following Equation 1. 
   
     
       
         
           
             
               
                 C 
                 = 
                 
                   
                     ɛ 
                     r 
                   
                   ⁢ 
                   
                     
                       ɛ 
                       0 
                     
                     ⁡ 
                     
                       ( 
                       
                         A 
                         D 
                       
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                 Equation 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 1 
               
             
           
         
       
     
   
   Wherein, ε r  is the dielectric constant of a dielectric, ε 0  is a constant having a value of 8.855×10 −8 , A is the surface area of the dielectric, and D is the thickness of the dielectric. The dielectric constant of the dielectric must be high in order to assure a capacitor having a high capacitance, and a smaller thickness and a larger surface area of the dielectric bring about higher capacitance of the capacitor. 
   A conventional bimodal polymer ceramic complex has a capacitance of 5-7 nF/cm 2  if the thickness is 10 μm. 
   For example, U.S. Pat. No. 6,274,224 granted to 3M Co. employs a thin film type composite having a thickness of 8-10 μm which includes BaTiO 3  ceramic powder and a thermosetting plastic epoxy or polyimide mixed with each other between copper foils used as power supply and grounded electrodes. At this time, capacitance per unit area is 10 nF/in 2 . 
   Furthermore, in the third conventional technology, capacitance is low due to a low dielectric constant of an embedded capacitor layer. For instance, in a thin film type capacitor having a thickness of 10-50 μm as shown in  FIG. 3   a,  a material employed by Sanmina Corp. is made of an FR-4 dielectric substance having a thickness of 25 μm or 50 μm between copper foils used as power supply and grounded electrodes. At this time, since the dielectric constant of FR-4 is 4-5, the capacitance per unit area is 0.5-1 nF/in 2  in practice. 
   As described above, the capacitance per unit area of the conventional embedded capacitor is 0.5-1 nF/in 2  or 10 nF/in 2 , which is significantly lower than that of a traditional decoupling discrete chip capacitor, that is, 100 nF/in 2 . Accordingly, there are many limits to the realization of the conventional embedded capacitor. 
   Furthermore, in the conventional technologies, a dielectric layer is laminated on a whole side of a substrate and electrodes are formed during a circuit forming process, or patterning is conducted using a photosensitive insulating layer through an exposure process. However, these procedures result in increased production costs because the formation of upper and lower electrodes, and exposure and etching processes for patterning the insulating layer are additionally carried out. 
   SUMMARY OF THE INVENTION 
   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 including embedded capacitors, in which a dielectric layer is formed using a ceramic material having a high capacitance, thereby providing capacitors each having a high dielectric constant corresponding to the capacitance of a decoupling chip capacitor, and a method of fabricating the same. 
   Another object of the present invention is to provide a PCB including embedded capacitors each having a high dielectric constant and a method of fabricating the same, in which only a desired part is made of a ceramic material to form a dielectric thin film (or thick film), thereby creating the embedded capacitors. Accordingly, a loss of costly raw materials is reduced and unnecessary processes, such as a process of etching a dielectric, may be omitted, consequently, material costs are reduced and ease of production is assured. 
   The above objects can be accomplished by providing a PCB including embedded capacitors each having a high dielectric constant, which comprises a first insulating layer made of an insulating material to electrically insulate upper and lower parts from each other. The PCB also comprises a circuit layer made of a first conductive material, which is laminated on one side of the first insulating layer and in which circuit patterns including a plurality of lower electrodes of the embedded capacitors are formed. A plurality of second insulating layers are laminated on the lower electrodes of the circuit layer, and made of a ceramic material. A plurality of upper electrodes are laminated on the second insulating layers, and made of a second conductive material. A third insulating layer is laminated on the circuit layer and upper electrodes, and includes through holes for electrically connecting the upper electrodes to external elements. 
   Furthermore, the present invention provides a PCB including embedded capacitors each having a high dielectric constant, which comprises a first insulating layer made of a first insulating material to electrically insulate upper and lower parts from each other. The PCB also comprises a first circuit layer made of a first conductive material, which is laminated on one side of the first insulating layer, and in which first circuit patterns including a plurality of lower electrodes of the embedded capacitors are formed and a second insulating material is packed between the first circuit patterns. A second insulating layer is laminated on the first circuit layer, and made of a ceramic material. A second circuit layer made of a second conductive material is laminated on the second insulating layer. At this time, second circuit patterns, including a plurality of upper electrodes corresponding to the lower electrodes, are formed on the second circuit layer. A third insulating layer is laminated on the second circuit layer, and includes through holes for electrically connecting the upper electrodes to external elements. 
   Furthermore, the present invention provides a method of fabricating a PCB including embedded capacitors each having a high dielectric constant, which comprises a first step of forming circuit patterns including a plurality of lower electrodes of the embedded capacitors on a copper foil on one side of a copper clad laminate; a second step of laminating a mask, in which portions corresponding to the lower electrodes are opened, on the copper clad laminate to form insulating layers of the embedded capacitors, and spraying a ceramic dielectric through a thermal spray process to form ceramic films; a third step of forming upper electrodes on the ceramic films formed in the second step and subsequently removing the mask; and a fourth step of laminating the insulating layers on the copper clad laminate, on which the embedded capacitors are formed, and forming through holes for electrically connecting the upper electrodes to external elements. 
   Additionally, the present invention provides a method of fabricating a PCB including embedded capacitors each having a high dielectric constant, which comprises a first step of forming first circuit patterns including a plurality of lower electrodes of the embedded capacitors on a copper foil on one side of a copper clad laminate, and packing an insulating material between the first circuit patterns; a second step of spraying a ceramic dielectric on the copper clad laminate through a thermal spray process to form ceramic films; a third step of forming second circuit patterns including upper electrodes on a portion of the ceramic films, which correspond to the lower electrodes, formed in the second step; and a fourth step of laminating insulating layers on the second circuit patterns formed in the third step, and forming through holes for electrically connecting the upper electrodes to external elements. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
       FIGS. 1   a  to  1   e  illustrate the production of a conventional PCB including the polymer thick film type of embedded capacitors; 
       FIGS. 2   a  to  2   f  illustrate the production of a conventional PCB including the discrete type of embedded capacitors which are formed by application of a photosensitive resin; 
       FIGS. 3   a  to  3   c  illustrate the production of a conventional PCB including embedded capacitors, which are formed by insertion of an additional dielectric layer having a capacitance characteristic; 
       FIGS. 4   a  and  4   b  are sectional views of PCBs including embedded capacitors having high dielectric constants according to the first and second embodiments of the present invention, respectively; 
       FIGS. 5   a  to  5   e  illustrate the production of a PCB including embedded capacitors each having a high dielectric constant according to the first embodiment of the present invention; 
       FIGS. 6   a  and  6   b  illustrate a thermal spray process adopted in the present invention; 
       FIGS. 7   a  to  7   f  illustrate the production of a PCB including embedded capacitors each having a high dielectric constant according to the second embodiment of the present invention; and 
       FIGS. 8   a  to  8   f  illustrate the production of a PCB including embedded capacitors each having a high dielectric constant according to the third embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Hereinafter, a description will be given of a PCB including embedded capacitors each having a high dielectric constant and a method of fabricating the same according to the present invention, referring to the drawings. 
     FIG. 4   a  is a sectional view of a PCB including embedded capacitors each having a high dielectric constant according to the first embodiment of the present invention. 
   Referring to  FIG. 4   a,  circuit layers  112   a,    112   b  including patterned copper foils are formed on both sides of an insulating layer  111  constituting a core layer  110 . 
   At this time, lower electrodes  121   a,    121   b,    121   c,    121   d  of the embedded capacitors  120   a,    120   b,    120   c,    120   d  are formed in the circuit layers  112   a,    112   b.    
   The embedded capacitors  120   a,    120   b,    120   c,    120   d  include the lower electrodes  121   a,    121   b,    121   c,    121   d  formed in the circuit layers  112   a ,  112   b , insulating layers  122   a ,  122   b ,  122   c ,  122   d  made of ceramic materials and laminated on the lower electrodes  121   a ,  121   b ,  121   c ,  121   d , and upper electrodes  123   a ,  123   b ,  123   c ,  123   d  laminated on the insulating layers  122   a ,  122   b ,  122   c ,  122   d.    
   The embedded capacitors  120   a ,  120   b ,  120   c ,  120   d  may also include an adhesive metal layer, which consists of an adhesive metal such as Cr, Pt, or Ta, between the lower electrodes  121   a ,  121   b ,  121   c ,  121   d , formed in the circuit layers  112   a ,  112   b , and the insulating layers  122   a ,  122   b ,  122   c ,  122   d  so as to increase interfacial adhesion between the lower electrodes and the insulating layers. Furthermore, the embedded capacitors  120   a ,  120   b ,  120   c ,  120   d  may also include an adhesive metal layer, which consists of an adhesive metal such as Cr, Pt, Ta, between the insulating layers  122   a ,  122   b ,  122   c ,  122   d  and the upper electrodes  123   a ,  123   b ,  123   c ,  123   d  so as to increase interfacial adhesion between the insulating layers and the upper electrodes. 
   Insulating layers  131   a ,  131   b  are formed on the circuit layers  112   a ,  112   b  and the embedded capacitors  120   a ,  120   b ,  120   c ,  120   d , and blind via holes  134   a ,  134   b ,  134   c ,  134   d , for providing electrical connection between the upper electrodes  123   a ,  123   b ,  123   c ,  123   d  and external elements, are formed through the insulating layers  131   a ,  131   b.    
   Resins  133   a ,  133   b ,  133   c ,  133   d  are packed into the blind via holes  134   a ,  134   b ,  134   c ,  134   d , and nickel-gold plating layers  136   a ,  136   b ,  136   c ,  136   d  and photoresists  135   a ,  135   b  are formed outside the blind via holes  134   a ,  134   b ,  134   c ,  134   d.    
     FIG. 4   b  is a sectional view of a PCB including embedded capacitors each having a high dielectric constant according to the second embodiment of the present invention. 
   Referring to  FIG. 4   b , circuit layers  112   a ,  112   b  including patterned copper foils are formed on both sides of an insulating layer  111  constituting a core layer  110 . Insulators  113   a ,  113   b  such as resins are packed into a portion of the circuit layers  112   a ,  112   b  on which circuit patterns are not formed. 
   At this time, lower electrodes  121   a ,  121   b ,  121   c ,  121   d  of the embedded capacitors  120   a ,  120   b ,  120   c ,  120   d  are formed in the circuit layers  112   a ,  112   b.    
   Insulating layers  122   a ,  122   b  made of ceramic materials are laminated on the circuit layers  112   a ,  112   b.    
   Circuit layers  125   a ,  125   b  on which circuit patterns are formed are formed on the insulating layers  122   a ,  122   b , and upper electrodes  123   a ,  123   b ,  123   c ,  123   d  that correspond to the lower electrodes  121   a ,  121   b ,  121   c ,  121   d  are formed on the circuit layers  125   a ,  125   b.    
   Embedded capacitors  120   a ,  120   b ,  120   c ,  120   d  comprise the lower electrodes  121   a ,  121   b ,  121   c ,  121   d  formed in the circuit layers  112   a ,  112   b , the insulating layers  122   a ,  122   b  made of ceramic materials and laminated on the circuit layers  112   a ,  112   b , and the upper electrodes  123   a ,  123   b ,  123   c ,  123   d  formed in the circuit layers  125   a ,  125   b  laminated on the insulating layers  122   a ,  122   b.  Additionally, the embedded capacitors may also include an adhesive metal layer consisting of an adhesive metal between the lower electrodes and insulating layers, and between the insulating layers and upper electrodes so as to increase interfacial adhesion between the lower electrodes and insulating layers, and between the insulating layers and upper electrodes. 
   Insulating layers  131   a ,  131   b  are formed on the circuit layers  112   a ,  112   b  and embedded capacitors  120   a ,  120   b ,  120   c ,  120   d , and blind via holes  134   a ,  134   b ,  134   c ,  134   d , for providing electrical connection between the upper electrodes  123   a ,  123   b ,  123   c ,  123   d  and external elements, are formed through the insulating layers  131   a ,  131   b.    
   Resins  133   a ,  133   b ,  133   c ,  133   d  are packed into the blind via holes  134   a ,  134   b ,  134   c ,  134   d , and nickel-gold plating layers  136   a ,  136   b ,  136   c ,  136   d  and photoresists  135   a ,  135   b  are formed outside the blind via holes  134   a ,  134   b ,  134   c ,  134   d.    
     FIGS. 5   a  to  5   e  illustrate the production of a PCB including embedded capacitors each having a high dielectric constant according to the first embodiment of the present invention. 
   As shown in  FIG. 5   a , a copper clad laminate  210 , which includes an insulating layer  211  and copper foils  212   a ,  212   b  formed on both sides of the insulating layer  211 , is provided to fabricate a PCB including embedded capacitors each having a high dielectric constant according to the first embodiment of the present invention. 
   The insulating layer  211  of the copper clad laminate  210  is made of a resin. Even though the resin has excellent electrical properties, it has poor mechanical strength and its dimensional variation depending on temperature is undesirably ten times as great as metal. To avoid the disadvantages, papers, glass fibers, glass non-woven fabrics and the like are used as a reinforcing material. Use of the reinforcing material serves to increase longitudinal and transversal strengths of the resin and to reduce the dimensional variation depending on the temperature. 
   Generally, an electrolytic copper foil is used for the copper foils  212   a ,  212   b.  The copper foils  212   a ,  212   b  are formed in such a way that the copper foils  212   a ,  212   b  chemically react with the resin to partially penetrate into the resin in order to increase interfacial adhesion to the resin. 
   As shown in  FIG. 5   b , a wiring pattern is formed on the copper foils  212   a ,  212   b  according to a photolithography process. At this time, lower electrodes  221   a - 221   d  of embedded capacitors  220   a - 220   d  are formed simultaneously. 
   The photolithography process is conducted in the order of lamination for application of a photosensitive material, exposure, and development. The photolithography process may be classified into a photograph process and a screen printing process. 
   The wiring pattern is transferred onto the copper foils  212   a ,  212   b  using a photosensitizer such as D/F according to the photolithography process, and the copper foils  212   a ,  212   b  are patterned using the wiring pattern employing the photosensitizer as an etching resist. In other words, the photolithography process is conducted to form the pattern of the etching resist employing the photosensitizer on a substrate, and an etchant is sprayed on the resulting substrate to remove the copper foils other than a portion of the copper foils which is protected by the etching resist (i.e. a portion which forms the wiring pattern). The used etching resist is then stripped, thereby creating the patterned copper foils  212   a ,  212   b.    
   As shown in  FIG. 5   c , capacitor patterning masks  215   a ,  215   b  are laminated on both sides of the copper clad laminate  210  (it is possible to conduct the lamination on one side as well as on both sides) to pattern the capacitors  220   a - 220   d.  At this time, the capacitor patterning masks  215   a ,  215   b  may be made of metals, glasses, plastics or the like. 
   Additionally, dielectric ceramic powder is melted and sprayed onto the capacitor patterning masks  215   a ,  215   b  through a thermal spray process to form dielectric thin films (or thick films)  222   a - 222   d  of the embedded capacitors  220   a - 220   d.    
   The thermal spray process is a process which includes melting nano-sized spraying material powder using a high temperature heat source, and subsequently spraying the molten powder onto a mother material in a high speed to form a thin film on the mother material. 
     FIGS. 6   a  and  6   b  illustrate the thermal spray process adopted in the present invention. 
   With reference to  FIG. 6   a , molten nano-sized powder is sprayed using a thermal spray gun  310  to a mother material  320 , in which capacitor patterning masks  322   a ,  322   b  are applied on a copper clad laminate  321 , to form a thin film. 
   At this time, cleaning, blasting, and bond coating processes are conducted as a pretreatment process. In this regard, an adhesive metal such as Cr, Pt, or Ta may be used as a raw material in the bond coating process. 
   Furthermore, the spray process is conducted using the thermal spray gun  310 . At this time, a distance between the gun  310  and mother material  320 , and a moving speed of the gun or mother material are controlled in the spray process so as to adjust a thickness of the film. Particularly, the distance between the nozzle of the gun  310  and the mother material  320  is very important during the spray process, and depends on the type of device, the level of power, the type of spraying material, and the like. 
   As well, interfacial adhesion between the mother material  320  and dielectric thin film depends on the cleaning process, roughness, and chemical affinity between a surface of the mother material  320  and fused thin film. 
   For example, it is preferable that the distance between the gun  310  and mother material  320  be 3-4 inches, the moving speed of the gun  310  or mother material  320  be 1-2 m/sec, an air filter be used for the cleaning process, and the roughness be about ⅕ of a size of the nano-sized powder. 
   A description will be given of transformation of the nano-sized powder (ceramic powder having a high dielectric constant in the present invention) caused by the spraying of molten nano-sized powder onto the mother material  320  using the thermal spray gun  310 , referring to  FIG. 6   b.    
   Dielectric particles from a few μm to a few μm (ceramic powder) are melted in the thermal spray gun  310 , and then sprayed onto the mother material  320  at high temperature and pressure. 
   The molten dielectric particles adhere to the mother material  320 , and are exposed to room temperature, resulting in sintered crystalline dielectric thin films  222   a - 222   d.    
   At this time, examples of material for the dielectric ceramic powder include SrTiO 3 , BaTiO 3 , (Ba, Sr)TiO 3 , Pb(Zr, Ti)O 3 , (Pb, La) (Zr, Ti)O 3 , Pb(Ti 1/3 Nb 2/3 )O 3 , Ta 2 O 5 , and Al 2 O 3 . 
   Meanwhile, after the dielectric thin films  222   a - 222   d  are formed on the lower electrodes  221   a - 221   d  according to the thermal spray process, upper electrodes  223   a - 223   d  are formed according to the thermal spray process. 
   At this time, the cleaning, blasting, and bond coating processes are conducted as a pretreatment process so as to improve an interfacial adhesion between the dielectric thin films  222   a - 222   d  and upper electrodes  223   a - 223   d.  In this regard, an adhesive metal such as Cr, Pt, and Ta may be used as a raw material in the bond coating process. 
   At this time, the upper electrodes  223   a - 223   d  may be formed through electroless and electrolytic copper plating processes instead of the thermal spray process. 
   An electroless plating process is the only plating process that provides conductivity to the surface of an insulator such as resins, ceramics, and glasses. 
   Since the electroless copper plating process is a process of plating an insulator, it is difficult to expect a reaction caused by ions with electricity. The electroless copper plating process is achieved by a deposition reaction, and the deposition reaction is promoted by a catalyst. 
   After the electroless copper plating process is conducted to provide the conductivity, the electrolytic copper plating process is carried out using electrolysis. The electrolytic copper plating process is advantageous in that it is easy to form a thick plating film and physical properties of an electrolytic copper-plating layer are superior to those of an electroless copper-plating layer. 
   Referring to  FIG. 5   d , after the embedded capacitors  220   a - 220   d  are formed on the copper clad laminate  210 , the masks  215   a ,  215   b  are removed. 
   Furthermore, RCCs  230   a ,  230   b , in which copper foils  232   a ,  232   b  are each formed on one side of each insulating layer  231   a ,  231   b , are laminated on both sides of the resulting copper clad laminate. 
   Referring to  FIG. 5   e,  via holes  233   a - 233   d  and copper plating layers  234   a - 234   d  are formed to provide conductivity to the upper electrodes  223   a - 223   d.    
   Additionally, circuit patterns are formed on the copper foils  232   a ,  232   b , solder resists  235   a ,  235   b  are formed, and nickel-gold plating layers  236   a - 236   d  are formed to increase the conductivity of the via holes  233   a - 233   d.    
     FIGS. 7   a  to  7   f  illustrate the production of a PCB including embedded capacitors each having a high dielectric constant according to the second embodiment of the present invention. 
   As shown in  FIG. 7   a , a copper clad laminate  410 , which includes an insulating layer  411  and copper foils  412   a ,  412   b  formed on both sides of the insulating layer  411 , is provided to fabricate the PCB including embedded capacitors each having a high dielectric constant according to the second embodiment of the present invention. 
   As shown in  FIG. 7   b , a wiring pattern is formed on the copper foils  412   a ,  412   b  according to a photolithography process. At this time, lower electrodes  421   a - 421   d  of embedded capacitors  420   a - 420   d  are formed simultaneously. 
   As shown in  FIG. 7   c , capacitor patterning masks  415   a ,  415   b  are laminated on both sides of the copper clad laminate  410  (it is possible to conduct the lamination on one side as well as on both sides) to pattern the capacitors  420   a - 420   d.  At this time, the capacitor patterning masks  415   a ,  415   b  may be made of metals, glasses, plastics or the like. 
   Additionally, dielectric ceramic powder is melted and sprayed onto the capacitor patterning masks  415   a ,  415   b  through a thermal spray process to form dielectric thin films (or thick films)  422   a - 422   d  of the embedded capacitors  420   a - 420   d.    
   At this time, cleaning, blasting, and bond coating processes are conducted as pretreatment processes. In this regard, an adhesive metal such as Cr, Pt, and Ta may be used as a raw material in the bond coating process. 
   Furthermore, examples of material for the dielectric ceramic powder include SrTiO 3 , BaTiO 3 , (Ba, Sr)TiO 3 , Pb(Zr, Ti)O 3 , (Pb, La) (Zr, Ti)O 3 , Pb(Ti 1/3 Nb 2/3 )O 3 , Ta 2 O 5 , and Al 2 O 3 . 
   Meanwhile, after the dielectric thin films  422   a - 422   d  are formed on the lower electrodes  421   a - 421   d  by the thermal spray process, upper electrodes  423   a - 423   d  are formed according to the thermal spray process. 
   At this time, the cleaning, blasting, and bond coating processes are conducted as a pretreatment process so as to improve an interfacial adhesion between the dielectric thin films  422   a - 422   d  and upper electrodes  423   a - 423   d.  In this regard, an adhesive metal such as Cr, Pt, or Ta may be used as a raw material in the bond coating process. 
   At this time, the upper electrodes  423   a - 423   d  may be formed through electroless and electrolytic copper plating processes instead of the thermal spray process. 
   Referring to  FIG. 7   d , after the embedded capacitors  420   a - 420   d  are formed on the copper clad laminate  410 , the masks  415   a ,  415   b  are removed. 
   Furthermore, resins  425   a ,  425   b  are uniformly applied on the copper clad laminate using a vacuum printing process unlike the first embodiment. This functions to prevent some problems that occur in the first embodiment, that is to say, generation of cracks caused by a bias of forces applied to the embedded capacitors  420   a - 420   d  due to a stress partially occurring in the lamination of the RCCs, or generation of pore defects or voids caused by the lamination of the B-stage RCCs disturbing the packing of the resin into edge portions of corners of the embedded capacitors  420   a - 420   d.    
   Referring to  FIG. 7   e,  RCCs  430   a ,  430   b , in which copper foils  432   a ,  432   b  are each formed on one side of each insulating layer  431   a ,  431   b , are laminated on both sides of the resulting copper clad laminate. 
   Referring to  FIG. 7   f,  via holes  433   a - 433   d  and copper plating layers  434   a - 434   d  are formed to provide conductivity to the upper electrodes  423   a - 423   d.    
   Additionally, circuit patterns are formed on the copper foils  432   a ,  432   b , solder resists  435   a ,  435   b  are formed, and nickel-gold plating layers  436   a - 436   d  are formed to increase the conductivity of the via holes  433   a - 433   d.    
     FIGS. 8   a  to  8   f  illustrate the production of a PCB including embedded capacitors each having a high dielectric constant according to the third embodiment of the present invention. 
   As shown in  FIG. 8   a , a copper clad laminate  510 , which includes an insulating layer  511  and copper foils  512   a ,  512   b  formed on both sides of the insulating layer  511 , is provided to fabricate a PCB including embedded capacitors each having a high dielectric constant according to the third embodiment of the present invention. 
   As shown in  FIG. 8   b , a wiring pattern is formed on the copper foils  512   a ,  512   b  according to a photolithography process. At this time, lower electrodes  521   a - 521   d  of embedded capacitors  520   a - 520   d  are formed simultaneously. 
   As shown in  FIG. 8   c , resins  515   a ,  515   b  are formed on the copper clad laminate  510 , on which circuits are formed, according to a vacuum printing process. Flattening the resins  515   a ,  515   b  increases their interfacial adhesion to a ceramic material. 
   Referring to  FIG. 8   d , dielectric ceramic powder is melted and sprayed onto the copper clad laminate  510  as a mother material through a thermal spray process without using a mask to form dielectric thin films (or thick films)  522   a ,  522   b  of the embedded capacitors  520   a - 520   d , unlike the first and second embodiments of the present invention. 
   At this time, cleaning, blasting, and bond coating processes are conducted as pretreatment processes. In this regard, an adhesive metal such as Cr, Pt, or Ta may be used as a raw material in the bond coating process. 
   Furthermore, examples of material for the dielectric ceramic powder include SrTiO 3 , BaTiO 3 , (Ba, Sr)TiO 3 , Pb(Zr, Ti)O 3 , (Pb, La) (Zr, Ti)O 3 , Pb(Ti 1/3 Nb 2/3 )O 3 , Ta 2 O 5 , and Al 2 O 3 . 
   Meanwhile, after the dielectric thin films  522   a ,  522   b  are formed on the lower electrodes  521   a - 521   d  according to the thermal spray process, circuit layers  525   a ,  525   b  are formed using the thermal spray process and then patterned to form upper electrodes  523   a - 523   d.    
   At this time, the cleaning, blasting, and bond coating processes are conducted as a pretreatment process so as to improve interfacial adhesion between the dielectric thin films  522   a ,  522   b  and upper electrodes  523   a - 523   d.  In this regard, an adhesive metal such as Cr, Pt, and Ta may be used as a raw material in the bond coating process. 
   At this time, the upper electrodes  523   a - 523   d  may be formed through electroless and electrolytic copper plating processes instead of the thermal spray process. 
   Referring to  FIG. 8   f,  RCCs  530   a ,  530   b , in which copper foils  532   a ,  532   b  are each formed on one side of each insulating layer  531   a ,  531   b , are laminated on both sides of the resulting copper clad laminate. 
   Furthermore, via holes  533   a - 533   d  and copper plating layers  534   a - 534   d  are formed to provide conductivity to the upper electrodes  523   a - 523   d.    
   Additionally, circuit patterns are formed on the copper foils  532   a ,  532   b , solder resists  535   a ,  535   b  are formed, and nickel-gold plating layers  536   a - 536   d  are formed to increase the conductivity of the via holes  533   a - 533   d.    
   As described above, the present invention provides a PCB including embedded capacitors and a method of fabricating the same, in which a paste is packed only in a desired part to create the embedded capacitors. Accordingly, a loss of costly raw materials is reduced and unnecessary processes, such as an etching process of a dielectric, may be omitted, and thus, material costs are reduced and ease of production is assured. 
   Furthermore, the present invention provides a PCB including embedded capacitors and a method of fabricating the same, in which precise capacitances of capacitors having a consistent height and area are assured by use of via holes formed through a FR-4 copper clad laminate. 
   Additionally, the present invention provides a PCB including embedded capacitors and a method of fabricating the same, in which the circuits and embedded capacitors can be simultaneously formed in a commonly used PCB layer without the use of additional PCB layers for forming capacitors.

Technology Classification (CPC): 7