embodiments of the invention will now be described with reference to the attached drawings , in which like elements are indicated by like reference characters . referring to fig5 , a circuit board 100 in the first embodiment of the invention includes an embedded wcsp component 101 , semiconductor devices 110 , 111 , and a chip component 112 . the embedded wcsp component 101 is attached to a substrate 113 by means of a die bonding adhesive 114 and is sealed with a dielectric layer 115 on which a further dielectric layer 116 is formed . the two dielectric layers 115 , 116 may be formed simultaneously as a single layer . the embedded wcsp component 101 is an integrated circuit with circuit elements and interconnections ( not shown ) disposed near the upper surface in the drawing . dielectric layer 116 forms the first surface of the circuit board 100 , on which semiconductor device 110 and chip component 112 are mounted . the undersurface of the substrate 113 forms the second surface of the circuit board 100 , on which semiconductor device 111 is mounted . semiconductor device 110 and chip component 112 make electrical contact with a wiring pattern 117 formed on dielectric layer 116 on the first surface of the circuit board 100 ; semiconductor device 111 makes electrical contact with a wiring pattern 119 formed on the second surface of the circuit board 100 . the semiconductor devices 110 , 111 are , for example , semiconductor integrated circuits . the chip component 112 may be an active electronic component such as a transistor or a semiconductor integrated circuit chip , or a passive electronic component such as a capacitor or a resistor . semiconductor device 110 is electrically coupled to semiconductor device 111 through the wiring patterns 117 , 119 and a conductor 118 formed in a hole extending from the first surface to the second surface of the circuit board 100 . fig6 shows an enlarged sectional view of the embedded wcsp component 101 and the surrounding area in fig5 . the wcsp component 101 has a first surface on which electrode pads 124 are formed and a second surface , opposite the first surface , on which an electrode pad 125 is formed . the circuitry formed in the wcsp component 101 is disposed near its first surface and is electrically connected to wiring pattern 117 through the electrode pads 124 formed on that surface . in the substrate 113 , a conductor 126 is disposed in a hole opened so as to expose the electrode pad 125 on the second surface of the wcsp component 101 . the wcsp component 101 additionally has a conductor 120 formed in a hole extending through the wcsp component 101 from its first surface to its second surface , aligned with one of the electrode pads 124 on the first surface and the electrode pad 125 on the second surface . an electronic circuit element ( not shown ) in the wcsp component 101 is electrically coupled to the semiconductor device 111 mounted on the second - surface of the circuit board 100 through the conductor 120 formed in this hole , the electrode pads 124 , 125 at the ends of the hole , conductor 126 , and wiring pattern 119 . the arrow 121 in fig5 indicates the path of the electrical connection between the wcsp component 101 and the semiconductor device 111 . as described above , according to the first embodiment , the circuit board 100 includes an embedded wcsp component 101 that has a conductor 120 formed in a hole extending through the wcsp component 101 from its first surface to its second surface , thereby enabling an electrode pad 124 on the first surface to be electrically connected to a semiconductor device 111 on the far side of the circuit board 100 without requiring the connection path to detour around the wcsp component 101 through a separate via hole in the circuit board 100 . the length of the electrical connection between the wcsp component 101 and the semiconductor device 111 mounted on the second surface of the circuit board 100 is thereby reduced , improving the electrical characteristics of the connection and reducing the signal propagation delay between the wcsp component 101 and semiconductor device 111 . the number of via holes that must be formed in the circuit board 100 is also reduced , and the amount of wiring in the wiring patterns 117 , 119 on the surfaces of the circuit board 100 is reduced , providing additional layout space on the surfaces of the circuit board 100 so that the component mounting density can be increased . the invention can also be practiced in multi - layer circuit boards . fig7 to 10 show steps in the fabrication of a four - layer circuit board 300 including a pair of embedded wcsp components 306 . referring to fig7 , a substrate 301 is prepared . the substrate 301 has two major surfaces : a first surface on which a wiring pattern 302 and a plurality of electrode pads 304 are formed , and a second surface , opposite the first surface , on which a wiring pattern 303 is formed . the substrate 301 additionally has conductors 305 disposed in holes extending through the substrate 301 from the first surface to the second surface . each wcsp component 306 has a first surface on which a plurality of electrode pads 307 and external terminals 308 are formed , and a second surface , opposite the first surface , on which an electrode pad 322 is formed . a hole extends through each wcsp component 306 from the first surface to the second surface . a conductor 309 is formed in this hole , electrically coupling the electrode pad 322 on the second surface to one of the electrode pads 307 on the first surface . the external terminals 308 make electrical contact with respective electrode pads 307 on the first surface of the wcsp components 306 . the external terminals 308 may be solder bumps formed on the respective electrode pads 307 . the electrode pad 307 that is electrically connected through the hole in each wcsp component 306 to the electrode pad 322 its the second surface does not have an external electrode 308 . referring to fig8 , flux or solder paste is applied to the electrode pads 304 on the first surface of the substrate 301 by a screen printing technique ; then the wcsp components 306 are mounted on the first surface of the substrate 301 so that the external terminals 308 on the first surfaces of the wcsp components 306 align with the electrode pads 304 on the first surface of the substrate 301 . the external terminals 308 of the wcsp components 306 are then mechanically and electrically joined to the electrode pads 304 of the substrate 301 by reflow soldering . if necessary , flux residue and the like are removed in a cleaning process after the reflow process . the remaining space between the wcsp components 306 and the substrate 301 is filled with , for example , an epoxy resin filler 310 . three prepregs are now prepared : a first prepreg 313 that has openings 330 for the wcsp components 306 ; a second prepreg 314 clad with copper foil 315 on one surface ; and a thin third prepreg 312 likewise clad with copper foil 311 on one surface . referring to fig9 , the first prepreg 313 is laminated onto the first surface of the substrate 301 , the wcsp components 306 fitting into the openings in the first prepreg 313 . the second prepreg 314 is laminated onto the second surface of the substrate 301 , so that the second surface of the substrate 301 meets the unclad surface of the second prepreg 314 ( the surface that is not clad with copper foil ). the third prepreg 312 is laminated onto the first prepreg 313 , so that the first prepreg 313 meets the unclad surface of the third prepreg 312 . thus the substrate 301 is disposed between prepregs 313 and 314 , and the wcsp components 306 are embedded between the substrate 301 and the thin prepreg 312 . referring to fig1 , to complete the four - layer circuit board 300 , holes extending to the electrode pads 322 on the second surfaces of the wcsp components 306 are opened by cutting the thin prepreg 312 by laser , and conductors 320 are formed in these holes . in addition , via holes are formed in the circuit board 300 , extending through the prepregs 312 , 313 , 314 and the substrate 301 , and conductors 316 are formed in these via holes , making electrical contact with the wiring patterns 302 , 303 on the substrate 301 and copper foil conductors formed on the surfaces of the circuit board 300 . the upper copper foil conductor ( the copper foil cladding 311 of the thin prepreg 312 ) is patterned to form a wiring pattern 319 with lands 317 to which external terminals such as solder balls 318 can be attached . this wiring pattern 319 is electrically coupled to the electrode pads 322 of the wcsp components 306 through the conductors 320 disposed in the holes . besides the solder balls 318 formed on the lands 317 , a chip component 321 is mounted on the thin prepreg 312 , making electrical contact with the wiring pattern 319 . one of the embedded wcsp components 306 is electrically connected to the chip component 321 through the conductor in the hole extending through the wcsp component , the electrode pad 322 on its surface , the conductor 320 disposed in the corresponding laser - cut hole in the thin prepreg 312 , and the wiring pattern 319 . the other embedded wcsp component 306 is electrically connected in a similar fashion to one of the solder balls 318 . as in the first embodiment , these connections are comparatively short : they do not have to be routed through the wiring patterns on the substrate 301 , detour around the wcsp components 306 , or pass through via holes external to the wcsp components 306 ; instead , they pass directly through holes in the wcsp components 306 themselves . the use of a prepreg 313 having openings 330 that accommodate the wcsp components 306 enables the circuit board 300 including the embedded wcsp components 306 to be formed in a simple laminating process , irrespective of surface irregularities of the substrate 301 , whereby the productivity of the circuit board manufacturing process can be improved . in a variation of the second embodiment , the orientation of the wcsp components 306 is vertically reversed , so that the first surface with electrode pads 307 and external terminals 308 is adjacent the thin prepreg 312 and the second surface with electrode pad 322 is adjacent the substrate 301 . the external terminals 308 are joined to electrode pads on the thin prepreg 312 by reflow soldering , and the electrode pads 322 at the ends of the holes penetrating through the wcsp components 306 are electrically connected to the wiring pattern 302 on the facing surface of the substrate 301 . the prepreg method illustrated in the second embodiment can also be used to fabricate a circuit board of the type described in the first embodiment . as a third embodiment of the invention , fig1 to 14 show steps in the fabrication of such a circuit board 400 including an embedded wcsp component 101 . referring to fig1 , the wcsp component 101 has the structure described in the first embodiment , with a conductor 120 in a hole electrically connecting one of a plurality of electrode pads 124 formed on one major surface to an electrode pad 125 formed on the other major surface . as in the second embodiment , three prepregs are prepared : a first prepreg 405 clad on one surface with copper foil 406 , a second prepreg 403 having an opening 404 for the wcsp component 101 , and a third prepreg 402 clad on one surface with copper foil 401 . referring to fig1 , the wcsp component 101 is attached to the unclad surface of the first prepreg 405 by a die bonding adhesive 114 . the second prepreg 403 is laminated onto the same surface of prepreg 405 so that the opening 404 accommodates the wcsp component 101 . the third prepreg 402 is laminated onto the second prepreg 403 so that the unclad surface with the third prepreg 402 meets the second prepreg 403 . the copper foil cladding 401 is at this stage electrically isolated from the wcsp component 101 . referring to fig1 , via holes extending through all three prepregs 402 , 403 , 405 are formed , and conductors 118 are formed in these holes . a hole is formed by cutting the first prepreg 405 by laser so as to expose electrode pad 125 of the wcsp component 101 , and a conductor 126 is formed in this hole . similar holes and conductors are formed in the third prepreg 402 to provide electrical paths to the electrode pads 124 on the opposite surface of the wcsp component 101 . the copper foil cladding 401 on the third prepreg 402 is patterned to form a wiring pattern 117 , and the copper foil cladding 406 on the first prepreg 405 is patterned to form a wiring pattern 119 , which is electrically coupled to wiring pattern 117 through conductors 118 . the wcsp component 101 is electrically coupled to wiring pattern 119 through electrode pad 125 and the conductor 126 disposed in the hole in the first prepreg 405 . referring to fig1 , a semiconductor device 110 and a chip component 112 are mounted on the surface of the third prepreg 402 . another semiconductor device 111 is mounted on the surface of the first prepreg 405 . semiconductor device 110 is electrically coupled to semiconductor device 111 through wiring pattern 117 , a conductor 118 , and wiring pattern 119 . the wcsp component 101 is electrically coupled to the semiconductor device 111 through conductor 120 , electrode pad 125 , conductor 126 , and wiring pattern 119 . use of a prepreg 403 having an opening 404 accommodating a wcsp component 101 enables a circuit board 400 including an embedded wcsp component 101 to be formed in a simple laminating process , whereby the productivity of the circuit board manufacturing process can be improved . compared with the second embodiment , since the circuit board has fewer layers , the manufacturing process is simpler and the thickness of the circuit board 400 can be reduced . although a circuit board with solder balls formed on external terminals was shown in the second embodiment , the invention is not limited to this structure . a connector or socket of the type generally used on mother and daughter boards may be utilized for electrical connections to other circuit boards and components ( not shown ). although circuit boards including simple embedded wcsp components were described in the embodiments above , the embedded circuitry may be more complex . for example , an embedded wcsp component may have peripheral components , also embedded in the circuit board , to which the wcsp component is connected through the wiring patterns . alternatively , a multi - chip package or module may be embedded as a single unit . such an embedded package or module may include both active and passive electronic components . an embedded wcsp component may also include both active and passive circuitry . the embedded component is not necessarily a wcsp component . the embedded component may be , for example , a passive component with a silicon or ceramic substrate having a conductor formed in a hole in this substrate . although prepregs having surface - to - surface openings were used in the second and third embodiments , the embodiments are not limited to this structure . countersunk prepregs may be used instead , or sheet prepregs made of a resin with high fluidity may be used . the method of forming holes in the prepregs is not limited to the laser cutting method mentioned in the second and third embodiments . the thin prepregs in particular may be replaced by sheets of a photosensitive material , in which case holes may be formed by photolithography . those skilled in the art will recognize that further variations are possible within the scope of the invention , which is defined in the appended claims .