next , a description will be given of embodiments of the present invention . fig1 is a cross sectional view of a semiconductor device according to a first embodiment of the present invention . the semiconductor device according to the first embodiment of the present invention includes a package board 2 , a redistribution board 4 connected with the package board 2 , a first semiconductor element 6 and a second semiconductor element 8 . the first and second semiconductor elements 6 and 8 are mounted on the redistribution board 4 . further , the number of the semiconductor elements mounted on the redistribution board 4 may be one , or three or more . additionally , in this embodiment , a heat spreader 10 is fixed to back surfaces of the first and second semiconductor elements by an adhesive 12 . the heat spreader 10 functions so as to accelerate heat dissipation from the semiconductor elements 6 and 8 . however , the heat spreader 10 is not always necessary and provided in case of need . the package board 2 is structured by a glass ceramic board , an alumina board or a built - up board . on a top surface 2 a of the package board 2 , electrode pads connected with solder bumps 14 are formed . on an under surface 2 b of the package board 2 , electrode pads are formed where solder balls 16 are formed as external terminals . the package board 2 is a multilayered structure . the electrode pads on the top surface 2 a are electrically connected with the corresponding electrode pads on the under surface 2 b by vias or the like which penetrate through layers . as shown in fig1 , the redistribution board 4 has a multilayerd structure . built - in capacitors 18 that function as the bypass condensers are formed inside the redistribution board 4 . electrode pads formed by a first electric conductive layer are exposed from an under surface 4 b of the redistribution board 4 and connected with the corresponding electrode pads of the package board 2 via the solder bumps 14 . additionally , electrode pads formed by a fourth electric conductor are exposed from a top surface 4 a of the redistribution board 4 and using these electrode pads , the first and second semiconductor elements 6 and 8 are mounted on the redistribution board 4 by flip chip mounting . fig2 a and 2b respectively are cross sectional views for explaining the structure of the redistribution board 4 and manufacturing process . first , as shown in fig2 a , electrode pads are formed by forming a pattern of platinum thin film as the first electric conductor 22 on a base board 20 such as a silicon board or the like . next , a bst film ( barium / strontium / titanium filter ) having a high dielectric constant is formed as a first insulating layer 24 . then , after forming first vias 26 at necessary positions , electrode pads are formed by forming a pattern of the platinum thin film as a second electric conductive layer 28 on the first insulating layer 24 . among the electrode pads formed on both sides of the first insulating layer 24 , pairs of the electrode pads connected by the first vias 26 function as electrically conductive parts . on the other hand , pairs of the electrode pads facing without the first via 26 function as capacitors since the bst film having the high dielectric constant stands between . these capacitors become the incorporated capacitors 18 and function as the bypass condensers when incorporated in the semiconductor device . next , as shown in fig2 b , a second insulating layer 30 is formed on the second electric conductive layer 28 . a copper wiring pattern is formed on the second insulating layer 30 as a third electric conductive layer 32 . the second insulating layer 30 is formed by polyimide , bcb film or the like . viaholes are formed in corresponding positions of the electrode pads of the second electric conductive layer 28 . a third electric conductive layer 32 is formed by copper ( cu ) plating , for example , and second vias 34 are formed in the viaholes . thus , the copper wiring pattern 32 formed on the second insulating layer 30 and the platinum thin film wiring pattern formed as the second electric conductive layer 28 are electrically connected by the second vias 34 . the copper wiring pattern as the third electric conductive layer 32 becomes a wiring pattern for redistribution . next , a third insulating layer 36 is formed on the third electric conductive layer 32 . a copper wiring pattern is formed on the third insulating layer 36 as a fourth electric conductive layer 40 . the third insulating layer 36 is formed by polyimide , bcb film or the like . viaholes are formed in corresponding positions of the copper wiring pattern of the third electric conductive layer 32 . a fourth electric conductive layer 40 is formed by copper ( cu ) plating , for example , and third vias 38 are formed in the viaholes . thus , the copper wiring formed on the second insulating layer 30 and the copper wiring pattern formed on the third insulating layer 36 are electrically connected by the third vias 38 . the copper wiring pattern as the fourth electric conductive layer 40 is formed as the electrode pads . on these electrode pads , the above - described first and second semiconductor elements 6 and 8 are mounted by flip chip mounting . when forming the above - described third and fourth electric conductive layers 32 and 40 by copper plating , it is desirable to form sputter thin films of such as ti , cr , w or the like prior to the copper plating in order to secure adhesion with the respective insulating layers below the third and fourth electric conductive layers 32 and 40 , and to enable electrolytic plating . additionally , a thickness of the second and third insulating layers 30 and 36 is 2 μm to 10 μm . a thickness of the copper wiring patterns 32 and 40 is approximately several micrometers . in addition , the wiring pattern as the fourth electric conductive layer 40 corresponds to the electrode pads mounting the semiconductor elements 6 and 8 by flip chip packaging . thus , it is preferable to perform barrier metal plating such as ni plating or the like and plating of such as au , pd , sn or the like to the fourth electric conductive layer . as shown in fig2 b , the redistribution board 4 is formed on the base board 20 . however , the base board 20 is removed when manufacturing the semiconductor device using the redistribution board 4 . since the redistribution board 4 is thin , it may be easily deformed or damaged when separated from the base board 20 . further , the above - described redistribution board 4 may be manufactured by a method proposed in japanese laid - open patent application no . 2001 - 274036 . next , a description will be given of the manufacturing process of the semiconductor device according to the present invention with reference to fig3 a , 3 b , 3 c and 4 . first , as shown in a flow chart of fig4 , the redistribution board 4 is prepared . in step s 1 , the first electric conductive layer 22 formed by a platinum thin film is formed on a silicon wafer referred to as the base board 20 . next , in step s 2 , the bst film as the first insulating layer 24 is formed on the first electric conductive layer 22 . then , in step s 3 , the second electric conductive layer 28 formed by the platinum film is formed on the bst film . next , in step s 4 , a polyimide film as the second insulating layer 30 is formed on the second electric conductive layer 28 . in step s 5 , the third electric conductive layer 32 made of copper plating is formed on the polyimide film . in step s 6 , a polyimide film as the third insulating layer 36 is formed on the third electric conductive layer 32 . in step s 7 , the fourth electric conductive layer 40 made of copper plating is formed on the polyimide film . the steps s 1 through s 7 are the processes for preparing the redistribution board 4 . further , by repeating steps s 5 and s 6 , the number of layers of the redistribution board 4 can be further increased . when the preparation of the redistribution board 4 is completed , a process is performed for mounting the semiconductor elements 6 and 8 on the redistribution board 4 by flip chip packaging . that is , in step s 8 , ni plating is performed as the barrier metal on the electrode pads of the fourth electric conductive layer 40 of the redistribution board 4 , and another plating of such as au , pd , sn or the like is performed thereafter . then , in step s 9 , the semiconductor elements 6 and 8 to which solder bumps are previously formed are mounted on the fourth electric conductive layer 40 of the redistribution board 4 by flip chip mounting . instead of solder bonding , au — sn bonding may be employed by forming au stud bumps to the semiconductor elements 6 and 8 , and performing tin - plating on the redistribution board 4 side . next , in step s 10 , an under fill material 44 fills between the redistribution board 4 and the semiconductor elements 6 and 8 , respectively so as to secure reliability of the flip chip mounting . in this embodiment , the semiconductor elements 6 and 8 are mounted on the redistribution board 4 by flip chip mounting . however , the number of the semiconductor elements mounted may alternately be one , or three or more . as shown in fig3 a , the redistribution board 4 assumes a state where the first and second semiconductor elements 6 and 8 are mounted after the above - described processes . the steps s 1 through s 10 are performed while the redistribution board 4 is formed on the base board 20 . accordingly , the base board 20 functions to reinforce the thin redistribution board 4 . thus , it is possible to perform flip chip mounting of the semiconductor elements 6 and 8 easily , and to prevent the redistribution board 4 from being deformed or damaged . in step 11 , the base board 20 made of a silicon board is removed after the semiconductor elements 6 and 8 are mounted on the redistribution board 4 and fixed by the under fill material 44 . the base board 20 can be removed by etching or back grind ( grinding ). the etching and the back grind may be used together . by removing the base board 20 , the first electric conductive layer 40 is exposed from a surface of the redistribution board 4 as shown in fig3 b . further , although the base board 20 is removed , since the semiconductor elements 6 and 8 are fixed on the opposite side of the redistribution board 4 by the under fill material 44 , the semiconductor elements 6 and 8 function to reinforce the redistribution board 4 so as to prevent the redistribution board 4 from being deformed or damaged . next , in step 12 , solder bumps are formed on the electrode pads made of the first electric conductive layer 22 of the redistribution board 4 . the redistribution board 4 is mounted on the package board 2 made of such as glass ceramic board , built - up board or the like . then , the reliability of the mounting is secured by filling an under fill material 46 between the redistribution board 4 and the package board 2 . then , in step s 13 , the heat spreader 10 is fixed to the semiconductor elements 6 and 8 , respectively , via the adhesive 12 . last , in step s 14 , solder balls 16 are formed as external terminals to the electrode pads provided on a bottom face side of the package board 2 , and the semiconductor device shown in fig3 c is accomplished . when it is not necessary to provide the heat spreader 10 in step s 13 , step s 13 may be skipped to advance to step 14 . additionally , with regard to steps s 13 and s 14 , either step may be performed first . further , in the above embodiment , the silicon wafer is used for the base board 20 . however , when the base board 20 is in a state of a wafer , it is also possible to form a plurality of redistribution boards 4 on the wafer . in this case , it is preferable that a process of individualizing such as dicing or the like be performed after the process of step s 7 ends , or after the process of either step s 9 or s 10 ends . next , a description will be given of a second embodiment of the present invention with reference to fig5 . fig5 is a cross sectional view of a semiconductor device according to the second embodiment of the present invention . in fig5 , those components which are the same as those corresponding components in fig1 are designated by the same reference numerals , and a description thereof will be omitted . the semiconductor device according to the second embodiment of the present invention uses the same components as the semiconductor device according to the first embodiment of the present invention . however , there is a difference between the semiconductor device according to the second embodiment of the present invention and the semiconductor device according to the first embodiment of the present invention in that the redistribution board 4 is placed upside down . that is , the electrode pads made of the fourth electric conductive layer 40 of the redistribution board 4 are connected with the electrode pads of the package board 2 . the semiconductor elements 6 and 8 are mounted on the electrode pads made of the first electric conductive layer 22 . fig6 a , 6 b and 6 c are cross sectional views for explaining the manufacturing process of the semiconductor device shown in fig5 . fig7 is a flow chart of the manufacturing process of the semiconductor device shown in fig5 . in fig7 , steps s 21 through s 27 are processes for forming the redistribution board 4 the same as the processes of steps s 1 through s 7 in fig4 . in this embodiment , after the redistribution board 4 is formed on the base board 20 , a preprocessing is performed for mounting the redistribution board 4 on the package board in step s 28 . that is , when the redistribution board 4 is mounted by the solder bonding , the solder bumps are formed to the package board . alternatively , when the redistribution board 4 is mounted by the au — sn bonding , au stud bumps are formed to the electrode pads of the package board 2 and tin - plating process is performed to the electrode pads of the redistribution board 4 . next , in step s 29 , as shown in fig6 a , the redistribution board 4 is mounted on the package board 2 . in step s 30 , the under fill material 46 is injected between the redistribution board 4 and the package board 2 . thereafter , in step s 31 , as shown in fig6 b , the base board 20 is removed . the base board 20 is removed by the same method as the above - described first embodiment . as described above , in this embodiment , the redistribution board 4 is mounted on the package board 2 before the base board 20 is removed from the redistribution board 4 . thus , the redistribution board 4 is always reinforced by the base board 20 or the package board 2 . therefore , the deformation of or the damage to the redistribution board 4 due to the redistribution board 4 being by itself without any reinforcement can be prevented . when the base board 20 is removed in step s 31 , the first electric conductive layer 22 is exposed from a surface of the redistribution board 4 . then , in step s 32 , the semiconductor elements 6 and 8 are mounted on the redistribution board 4 by flip chip mounting , and under fill material 44 is filled between the semiconductor elements 6 and 8 and the redistribution board 4 , respectively . in step s 33 , as in the first embodiment , the heat spreader 10 is connected with the semiconductor elements 6 and 8 by the adhesive 12 . in step s 34 , solder balls 16 are formed on the electrode pads on the bottom side surface of the package board 2 , and the semiconductor device shown in fig5 and 6c is completed . next , a description will be given of a third embodiment of the present invention with reference to fig8 a , 8 b , 8 c and 8 d . the semiconductor device of the third embodiment of the present invention has the same structure as the semiconductor device of the above - described first or second embodiment . however , the semiconductor device of the third embodiment of the present invention differs from the semiconductor device of the first or second embodiment in the manufacturing process . in the third embodiment of the present invention , as shown in fig8 a , the redistribution board 4 is formed on the base board 20 . thereafter , as shown in fig8 b , the base board 20 is separated or removed from the redistribution board 4 . thereafter , the redistribution board 4 is bonded to the semiconductor elements 6 and 8 and the package board 2 . as shown in fig8 c , the semiconductor elements 6 and 8 may be mounted on the redistribution board 4 previous to the package board 2 . or , as shown in fig8 d , the package board 2 may be mounted on the redistribution board 4 previous to the semiconductor elements 6 and 8 . in this case , the redistribution board 4 is formed with a thickness to have enough strength even when the base board 20 is separated or removed . alternatively , a material with enough strength is chosen to form the redistribution board 4 . next , a description will be given of a fourth embodiment of the present invention with reference to fig9 . fig9 is a cross sectional view of a semiconductor device according to the fourth embodiment of the present invention . in fig9 , those components which are the same as those corresponding components in fig1 are designated by the same reference numerals , and a description thereof will be omitted . the semiconductor device according to the present invention has the same structure as the semiconductor device of the above - described first embodiment . however , a structure of a redistribution board 4 a is different from the above - described redistribution board 4 . that is , as shown in fig9 , the redistribution board 4 a of this embodiment further includes a columnar metal member 50 ( also referred to as a metal pillar or metal post ) on the fourth electric conductive layer 40 structuring the electrode pads . then , by filling insulating resin 52 between the metal pillars 50 , the adjacent metal pillars 50 are insulated and held separate from each other . a height of the metal pillar is 100 μm , for example . a thickness of the insulating resin layer is from 70 to 80 μm . by reinforcement effect of the insulating resin layer 52 , the redistribution board 4 a has enough rigidity so as to prevent the deformation of or the damage to the redistribution board 4 a . fig1 a , 10 b , 10 c and 10 d are cross sectional views for explaining a manufacturing process of the redistribution board 4 a . in order to form the metal pillars 50 on the fourth electric conductive layer 40 , after forming the redistribution board 4 , a barrier metal layer ( an illustration thereof is omitted ) of such as ti , cr or the like is formed on the fourth electric conductive layer 40 by a sputter apparatus . then , as shown in fig1 a , a dry film made of a photo resist is attached to the barrier metal layer . through - holes corresponding the figure of the metal pillars 50 are formed to the dry film using a photolithography technology . the thickness of the dry film used is the same as the height of the metal pillars to be formed . then , as shown in fig1 b , the metal pillars 50 are formed by depositing copper in the through - holes of the dry film according to a cu electrolytic plating method . after the metal pillars 50 are formed , plated layers 54 are formed on projecting parts of the insulating resin layer 52 as shown in fig1 such that heads of the metal pillars 50 function as electrode pads for mounting the semiconductor elements 6 and 8 . it is preferable that the plated layer 54 have a double layer structure such that the barrier metal layer made of a ni plated layer is formed on a part contacting a surface of the metal pillar 50 , and a pd plated layer or a au plated layer for improving solder bonding efficiency is formed thereon . a triple layer structure may also be applied such that the pd plated layer is formed on the ni plated layer , and the au plated layer is formed thereon . after the plated layer 54 is formed , the dry film is removed as shown in fig1 c . thereafter , as shown in fig1 d , the insulating resin layer 52 is formed by filling the insulating resin between the metal pillars 50 . in filling the insulating resin , a method of injecting an epoxy resin in liquid form or a method of filling the epoxy resin by transfer molding , for example , may be used . the semiconductor elements 6 and 8 are mounted on the redistribution board 4 a formed as described above by flip chip mounting in the same method as the above - described first embodiment . besides , the redistribution board 4 a is mounted on the package board 2 and incorporated in the semiconductor device shown in fig9 . as described above , the redistribution board 4 a according to the present invention has rigidity increased by the insulating resin layer 52 . thus , the redistribution board 4 a can prevent the deformation or damage in the manufacturing process of the semiconductor device and improve a production yield of the semiconductor device . next , a description will be given of a fifth embodiment of the present invention with reference to fig1 . fig1 is a cross sectional view of a semiconductor device according to the fifth embodiment of the present invention . in fig1 , those components which are the same as those corresponding components in fig9 are designated by the same reference numerals , and a description thereof will be omitted . the semiconductor device according to this embodiment has the same components as the semiconductor device according to the above - described fourth embodiment , except that the redistribution board 4 a is placed upside down . that is , the metal pillars 50 of the redistribution board 4 a are connected with the electrode pads of the package board 2 . the semiconductor elements 6 and 8 are mounted on the electrode pads made of the electric conductive layer 22 . a manufacturing method of the semiconductor device according to this embodiment is the same as the manufacturing method of the semiconductor device according to the above - described second embodiment , except that the redistribution board 4 is replaced with the redistribution board 4 a . thus , a detailed description thereof will be omitted . as the above - described fourth embodiment , the redistribution board 4 a of this embodiment has rigidity increased by the insulating resin layer 52 . thus , the redistribution board 4 a can prevent the deformation or damage in the manufacturing process of the semiconductor device , and improve the production yield of the semiconductor device . next , a description will be given of a sixth embodiment of the present invention with reference to fig1 . fig1 is a cross sectional view of a semiconductor device according to the sixth embodiment of the present invention . in fig1 , those components which are the same as those corresponding components in fig1 are designated by the same reference numerals , and a description thereof will be omitted . the semiconductor device according to this embodiment has basically the same structure as the semiconductor device according to the above - described first embodiment except that a structure of a redistribution board 4 b differs from the structure of the redistribution board 4 . that is , as shown in fig1 , the redistribution board 4 b of this embodiment further has micro pins 60 as columnar metal members on the fourth electric conductive layer 40 structuring the electrode pads . then , insulating resin 62 is filled between the micro pins 60 so as to insulate and hold the adjacent micro pins separate from each other . a height of a micro pin is 100 μm , for example . a thickness of the insulating resin layer 62 is from 70 to 80 μm . by reinforcement effect of the insulating resin layer 62 , the redistribution board 4 b has enough rigidity so as to prevent the deformation of or the damage to the redistribution board 4 b . as shown in fig1 a , the micro pins 60 are formed such that metal wires such as gold wires or the like are bonded to the fourth electric conductive layer 40 . then , heads of the metal wires are cut off so as to obtain a length ( height ) of 100 μm , for example , in a direction of the thickness of the redistribution board 4 . each of the micro pins 60 are provided to the fourth electric conductive layer 40 so as to extend nearly vertically therefrom and not to contact each other . when the micro pins 60 are formed , surfaces of the micro pins 60 are nickeled by an electroless plating method and gilded . the ni plating functions as the barrier metal , and the gold plating is for improving the solder bonding efficiency . next , as shown in fig1 b , insulating resin such as an epoxy resin or the like fills between the micro pins 60 so as to form the insulating resin layer 62 . the semiconductor elements 6 and 8 are mounted on the redistribution board 4 b formed as described above by flip chip mounting in the same method as the above - described first embodiment . besides , the redistribution board 4 b is mounted on the package board 2 and is incorporated in the semiconductor device shown in fig1 . as described above , the redistribution board 4 b according to this embodiment has rigidity increased by the insulating resin layer 62 . thus , the redistribution board 4 b can prevent the deformation or damage in the manufacturing process of the semiconductor device and improve the production yield of the semiconductor device . next , a description will be given of a seventh embodiment of the present invention with reference to fig1 . fig1 is a cross sectional view of a semiconductor device according to a seventh embodiment of the present invention . in fig1 , those components which are the same as those corresponding components in fig1 are designated by the same reference numerals and a description thereof will be omitted . the semiconductor device according to this embodiment has the same components as the semiconductor device according to the above - described fourth embodiment except that the redistribution board 4 b is placed upside down . that is , the metal pillars 50 of the redistribution board 4 b are connected with the electrode pads of the package board 2 . the semiconductor elements 6 and 8 are mounted on the electrode pads made of the first electric conductive layer 22 . a manufacturing method of the semiconductor device according to this embodiment is the same as the manufacturing method of the semiconductor device according to the above - described second embodiment , except that the redistribution board 4 is replaced with the redistribution board 4 b . thus , a detailed description thereof will be omitted . however , it should be noted that the insulating resin layer 62 is not provided for the redistribution board 4 b . each micro pin stands erect by itself . thus , the micro pin 60 may not contact with the adjacent micro pin 60 when the insulating resin does not fill between the micro pins 60 . accordingly , the under fill material 46 fills between the micro pins 60 after the redistribution board 4 b formed on the base board 20 is mounted on the package board 2 by soldering via the micro pins 60 . additionally , when the insulating resin layer 62 is provided , the under fill material 46 may not be necessary . further , since the micro pins have spring characteristics , the micro pins can stand a heat cycle , shock or the like when the micro pins are connected with the bumps . in each of the above - described embodiments , a silicon board is used as the base board 20 . however , a board made of other material may also be used . for example , when a sapphire board is used as the base board 20 , the base board 20 can be separated from the redistribution board by irradiation of a laser beam . that is , a thin organic film is formed on the sapphire board so as to form the redistribution board thereon . then , the sapphire board is separated from the redistribution board by irradiating the laser beam on the sapphire board and vaporizing the organic film . additionally , when the base board 20 is formed by copper or copper alloy , the base board 20 can be removed by dipping only the base board 20 in etchant and dissolving the copper or copper alloy . in this case , it is preferable to previously perform resin courting so as not to expose the copper from a wiring layer , a circuit element or the package board of the components of the semiconductor device . further , as a method of separating the base board , there is a method of forming the redistribution board on a water soluble exfoliating layer previously formed on the base board 20 . as a material of the water soluble exfoliating layer , potassium bromide kbr may be used . by forming the redistribution board on the water soluble exfoliating layer formed on the base board 20 and dipping the redistribution board and the base board 20 in water , the water soluble exfoliating layer is dissolved and the base board 20 is separated from the redistribution board . additionally , the base board 20 can be dissolved in water to be removed by forming the base board 20 itself of a water soluble material such as potassium bromide kbr . additionally , in order to separate the base board and the redistribution board ( wiring layer ) easily , the redistribution board may be formed by forming a copper ( cu ) sputter film on a ceramic board of such as aluminum nitride or the like , and forming the wiring layer or the like on the cu sputter layer by photolithography . since adhesion between the cu sputter film and the ceramic board is weak , the cu sputter layer easily exfoliates from the ceramic board . after exfoliating the ceramic board including the cu sputter film from the redistribution board , the cu sputter film is removed by the etching , and electrodes for connecting with the package board and the semiconductor elements are exposed . a forming method of the redistribution board is the same as the above - described embodiments , and a description thereof will be omitted . the present invention is not limited to the specifically disclosed embodiments , and variations and modifications may be made without departing from the scope of the present invention . the present application is based on japanese priority application no . 2001 - 335413 filed on oct . 31 , 2001 , the entire contents of which are hereby incorporated by reference .