reference will now be made in detail to the present preferred embodiments of the invention , examples of which are illustrated in the accompanying drawings . wherever possible , the same reference numbers are used in the drawings and the description to refer to the same or like parts . fig2 a through 2g are schematic cross - sectional views showing the steps for fabricating a circuit board according to one preferred embodiment of the present invention . as shown in fig2 a , the process of fabricating a circuit board in the present invention includes providing a dielectric layer 212 and two conductive layers 222 a and 224 a . the conductive layers 222 a and 224 a are disposed on each side of the dielectric layer 212 . the conductive layers 222 a and 224 a are copper foils disposed on the surfaces of the dielectric layer 212 by the lamination method , for example . as shown in fig2 b , photolithographic and etching techniques are applied to pattern the conductive layer 222 a and 224 a into a first circuit layer 222 and a second circuit layer 224 respectively . as shown in fig2 c , a dielectric layer 214 and a circuit layer 226 are sequentially laminated over the circuit layer 224 . the dielectric layer 214 is disposed between the circuit layer 226 and the circuit layer 224 . the dielectric layer 214 includes none of the conductive via that only passes through a single dielectric layer . obviously , the circuit layer 226 is formed in the same way as the circuit layers 222 and 224 , that is , by patterning a conductive layer . in fact , all subsequently formed circuit layers are formed in a similar way . thereafter , a through hole o 1 that passes through the circuit layers 222 , 224 , 226 and the dielectric layers 212 , 214 are formed . the method of forming the through hole o 1 includes mechanical drilling , for example . as shown in fig2 d , a conductive material is deposited to fill the through hole o 1 and form a first plated through hole d 1 . the first plated through holes d 1 form a path for electrically connecting various circuit layers 222 , 224 and 226 . as shown in fig2 e , a dielectric layer 216 and a circuit layer 228 are sequentially laminated over the circuit layer 222 . the dielectric layer 216 is disposed between the circuit layer 222 and the circuit layer 228 . the dielectric layer 216 includes none of the conductive via that only passes a single dielectric layer . thereafter , at least a through hole o 2 that passes through the dielectric layers 212 , 214 , 216 and the circuit layers 222 , 224 , 226 and 228 is formed . the method of forming the through hole o 2 includes mechanical drilling , for example . as shown in fig2 f , a conductive material is deposited to fill the through hole o 2 and form a second plated through hole d 2 . thus , the process of forming the circuit board is almost complete . as shown in fig2 g , solder mask layers 232 and 234 are formed on the top circuit layer 226 and the bottom circuit layer 228 respectively . the solder mask layers 232 and 234 expose a portion of each of the circuit layer 226 and 228 respectively , wherein the exposed portions of the circuit layer 226 and 228 form a plurality of bonding pads for electrical connection with a chip or other carriers in a subsequent operation . as shown in fig2 g , the circuit board 200 according to one preferred embodiment of the present invention essentially comprises a first laminated structure l 1 , a first plated through hole d 1 , a second laminated structure l 2 , a dielectric layer 216 and a second plated through hole d 2 . the first laminated structure l 1 is disposed above the second laminated structure l 2 . the first laminated structure l 1 comprises a lamination of circuit layers 222 , 224 , 226 and dielectric layers 212 , 214 . the first plated through hole d 1 passes through the three circuit layers 222 , 224 and 226 of the first laminated structure l 1 . the second laminated structure l 2 comprises a circuit layer 228 . the second plated through hole d 2 passes through the first laminated structure l 1 and the second laminated structure l 2 . the dielectric layers 212 and 214 have none of the conductive via that only passes through a single dielectric layer . in addition , the dielectric layer 212 is fabricated using a mixture containing fiberglass and a resin so that the circuit board 200 is structurally reinforced . moreover , the dielectric layers 214 and 216 are fabricated using a resin , for example . because the first plated through hole d 1 passes through the first laminated structure l 1 , the area labeled ‘ b ’ in fig2 g can be used for routing other circuits . hence , the circuit board 200 can have a higher degree of wiring integration . fig3 a and 3b are schematic cross - sectional views showing the steps for fabricating a circuit board according to another preferred embodiment of the present invention . as shown in fig3 a and 3b , the process of fabricating the circuit board according to the present embodiment includes providing a first laminated structure l 3 and a second laminated structure l 4 . as shown in fig3 a , the first laminated structure l 3 comprises three circuit layers 322 , 324 and 326 and two dielectric layers 312 and 314 alternately laminated together . the dielectric layers 312 and 314 have none of the conductive via that only passes through a single dielectric layer . the first laminated structure l 3 has a plurality of first plated through holes d 3 that passes through the first laminated structure l 3 . the second laminated structure l 4 comprises three circuit layers 328 , 330 and 332 and two dielectric layers 318 and 320 alternately laminated together . the dielectric layers 318 and 320 have none of the conductive via that only passes through a single dielectric layer . the second laminated structure l 4 has a plurality of second plated through holes d 4 that passes through the second laminated structure l 4 . thereafter , the first laminated structure l 3 and the second laminated structure l 4 are laminated on each side of a dielectric layer 316 . the dielectric layer 316 has none of the conductive via that passes through a single dielectric layer . then , at least one third plated through hole d 5 that passes through the first laminated structure l 3 , the second laminated structure l 4 and the dielectric layer 316 is formed . up to this stage , the process of fabricating a circuit board 300 is almost complete . as shown in fig3 b , the circuit board 300 in another preferred embodiment of the present invention essentially comprises a first laminated structure l 3 , a dielectric layer 316 , a second laminated structure l 4 and a plurality of third plated through holes d 5 . the second laminated structure l 4 is disposed over the first laminated structure l 3 . the third plated through holes d 5 passes through the first laminated structure l 3 , the dielectric layer 316 and the second laminated structure l 4 . the first laminated structure l 3 and the second laminated structure l 4 have a fine structure identical to the aforementioned description . the dielectric layers 314 and 318 are fabricated using a mixture containing fiberglass and a resin so that the circuit board 300 is structurally reinforced . moreover , the dielectric layers 312 , 316 and 320 are fabricated using a resin , for example . because the first plated through holes d 3 and the second plated through holes d 4 do not pass through the entire circuit board 300 , other areas of the circuit board 300 can be used for routing other circuits . hence , the circuit board 300 can have a higher degree of wiring integration . it should be noted that the four - layered circuit board and the six - layered circuit board in the aforementioned embodiments served as an illustration only and should not be used to limit the scope of the present invention . the present invention can be applied to a circuit board having five layers or seven and more layers . in addition , the spirit of the present invention is to form conductive material filled plated through holes in various laminated structures before laminating the laminated structures together . after that , through holes passing through the laminated structures are formed and then the through holes are filled to form plated through holes that pass through all the laminated structures . therefore , there is no blind via between various neighboring circuit layers in the circuit board of the present invention . in summary , because some of the plated through holes in the present invention do not pass through the entire circuit board , the emptied space can accommodate the connection between two neighboring circuit lines that carry an identical signal , or the routing for other circuits . thus , the difficulty of routing circuit lines is reduced significantly and the wiring density can be increased . in some cases , a conventional package having a six - layered circuit board can even be replaced by a four - layered circuit board according to the present invention , thereby reducing the production time and saving production cost . moreover , with an increase in the available space inside the circuit board , the length , width and separation of various circuit lines inside the circuit board can be flexibly adjusted on demand and the integrity of the ground plane and the power plane is increased . ultimately , the circuit board can have a better electrical performance . it will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention . in view of the foregoing , it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents .