preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings . fig1 is a front view of a polishing machine 20 , and fig2 is a partial sectional view of a press head 22 . a polishing pad 24 , which is made of , for example , polyurethane foam , a hard nonwoven fabric , is adhered on an upper face of a polishing plate 23 . shallow grooves ( not shown ), which are mutually crossed like a grid , or small holes ( not shown ) may be formed in an upper face of the polishing pad 24 . for example , a polishing pad suba800 ( d52 ), which is manufactured by rodel nitta company and whose grid size of the shallow grooves is 20 mm × 20 mm , may be used as the polishing pad 24 as well as a polishing machine for polishing silicon wafers . the polishing plate 23 is rotated about a rotary shaft ( not shown ), by a known driving mechanism ( not shown ), in a horizontal plane . the press head 22 is fixed at a lower end of a shaft 26 , which can be rotated about its own axis , and rotated together with the shaft 26 . the shaft 26 is pierced through a block 25 , which is provided on an arm 27 , and capable of moving in the vertical direction . a cylinder unit 28 is provided on the arm 27 . a supporting block 30 is fixed at an upper end of a cylinder rod 29 of the cylinder unit 28 . the shaft 26 is rotatably held by the supporting block 30 . a rotary joint 31 is connected to an upper end of the shaft 26 . a rotary cylinder ( not shown ), in which a gear is provided on an outer circumferential face , is provided in the block 25 , and the shaft 26 is pierced through the rotary cylinder and capable of moving in the vertical direction . the rotary cylinder is connected with the shaft 26 by a key ( not shown ) and a key groove ( not shown ). the shaft 26 can be freely moved in the vertical direction with respect to the rotary cylinder , but the shaft 26 is compulsorily rotated if the rotary cylinder is rotated about its own axis . a motor 32 is provided on the arm 27 . a gear ( not shown ) is fixed to a motor shaft of the motor 32 and engaged with the gear of the rotary cylinder . the arm 27 is fixed on a movable table 34 , which is moved along rails 33 . a substrate 36 to be polished is held on a bottom face of the press head 22 . when the movable table 34 is moved along the rails 33 by a driving mechanism ( not shown ), the press head 33 holding the substrate 36 is moved between a first position , which is outside of the polishing plate 23 , and a second position , which is above the polishing plate 23 . by moving the cylinder rod 29 of the cylinder unit 28 downward , the press head 22 is also moved downward , so that the substrate 36 contacts the polishing pad 24 of the polishing plate 23 . further , the substrate 36 is pressed onto the polishing pad 24 , by a press mechanism ( described later ), with prescribed pressure , and the slurry is supplied onto the polishing pad 24 from the nozzle 37 . the polishing plate 23 and the press head 23 are respectively rotated about their own axes , so that the substrate 36 can be polished . the press head 22 will be explained in detail with reference to fig2 . a sectional shape of a body proper 40 of the press head 22 is formed into an inverted u - shape . a bottom face is opened , and a space 41 is formed in the body proper 40 . symbols 40 a indicate side wall sections of the body proper 40 . a plate 42 , which is made of , for example , ceramic , is provided in a lower part of the body proper 40 so as to close the space 41 . a diaphragm 44 , which is made of an elastic sheet , e . g ., a rubber sheet , is fixed on an upper face of the plate 42 . an outer edge of the diaphragm 44 is fixed to a bottom face of a step section 43 . with this structure , the plate 42 is suspended by the diaphragm 44 . further , the space 41 in the body proper 40 is divided by the diaphragm 44 . compressed air is supplied into the space 41 via an air tube 46 provided in the shaft 26 . the compressed air is introduced to the air tube 46 from air supplying means ( not shown ), e . g ., a compressor , via the rotary joint 31 . an o - ring 47 is provided between a step section formed on an outer circumferential face of the plate 42 and step sections formed in lower parts of the side wall sections 40 a . a backing pad 48 is exchangeably adhered on a bottom face of the plate 42 by , for example , an adhesive ( not shown ). asker c hardness of the backing pad 48 is 75 - 95 , and compressibility thereof is 10 % or less . for example , a backing pad bp201 ( compressibility 3 . 4 %, compression elasticity 75 %, asker c hardness 84 ), which is manufactured by fujiboseki inc ., may be used as the backing pad 48 . further , polyurethane foam may be used as the backing pad 48 . a back side ( an upper face ) of the substrate 36 contacts a bottom face of the backing pad 48 , and the substrate 36 is held by the backing pad 48 . the substrate 36 is pressed onto the backing pad 48 including water so as to purge air left between the substrate 36 and the backing pad 48 . by purging the air , negative pressure is produced between the substrate 36 and the backing pad 48 , so that the substrate 36 can be held on the bottom face of the backing pad 48 . preferably , a retainer ring ( not shown ), whose lower end is slightly projected downward from a lower end of the backing pad 48 , is provided on an outer circumferential face of the backing pad 48 . by providing the retainer ring , the substrate 36 never springs out during the polishing . the retainer ring presses the polishing pad 24 of a periphery of the substrate 36 , so that the upper face of the backing pad 48 is depressed and its level is made equal to that of a lower face ( a front side ) of the substrate 36 . with this function , over polishing of an edge of the substrate 36 can be prevented . by supplying the compressed air in the space 41 via the air tube 46 , the plate 42 and the substrate 36 held by the backing pad 48 can be pressed onto the polishing pad 24 with a prescribed force so as to polish the lower face of the substrate 36 . next , an ordinary process of manufacturing a build - up substrate will be explained with reference to fig3 - 7 . firstly , as shown in fig3 a plurality of through - holes 51 ( one of the through - holes is shown ) are formed in a core substrate 50 , e . g ., a plastic substrate including glass - cloth , whose both sides are covered with copper films by a drill or laser means . the through - holes 51 are arranged in a prescribed pattern . then , copper layers are formed on the copper films and inner faces of the through - holes 51 by non - electrolytic copper plating and electrolytic copper plating ( see fig4 ). the copper layers are etched so as to form cable patterns 52 a and 52 b on the both faces of the core substrate 50 ( see fig5 ). resin is applied to the both faces of the core substrate 50 so as to cover the cable patterns 52 a and 52 , so that insulating resin layers 53 a and 53 b are formed ( see fig6 ). in some cases , surfaces of the insulating resin layers 53 a and 53 b may be polished to make flat . this polishing may be executed by the polishing machine shown in fig1 with supplying proper polishing slurry . then , as shown in fig7 via - holes 54 a and 54 b are formed so as to partially expose the cable patterns 52 a and 52 b . if the insulating resin layers 53 a and 53 b are made of photosensitive resin , the via - holes 54 a and 54 b can be formed by exposing and developing treatments ; if the insulating resin layers 53 a and 53 b are made of non - photosensitive resin , they can be formed by , for example , laser means . copper layers 55 a and 55 b are formed in the via - holes 54 a and 54 b and on the insulating resin layers 53 a and 53 b . in some cases , the via - holes 54 a and 54 b may be filled with copper . in the present embodiment , the copper layers 55 a and 55 b of the substrate is polished to make flat . firstly , the copper layer 55 a is polished , then the substrate is inverted to polish the other copper layer 55 b . after the copper layers 55 a and 55 b are made flat , they are etched to make cable patterns . the above described process is repeated prescribed times to form a multi - layered build - up substrate . in the above described embodiment , the broad copper layers 55 a and 55 b are polished ; in another embodiment , copper bumps are polished . in fig8 copper bumps 62 , which act as connecting terminals , are formed in a substrate 60 , e . g ., a silicon wafer . the copper bumps 62 are made by the steps of : forming a resist mask having opening sections , which correspond to the copper bumps 62 , on the wafer 60 ; plating parts of circuit sections exposed in the opening sections with copper ; and removing the resist mask . with this method , the copper bumps 62 can be projected from the surface of the wafer 60 . by the method of the present invention , copper bumps formed on a circuit board ( a substrate ) can be removed . the substrate is not limited to the plastic substrate ; ceramic substrates , glass substrates , etc . can be polished . copper layers of substrates were polished by the polishing machine shown in fig1 and 2 under following conditions : note that , the uniformity of polished layer means uniformity of thickness of the copper layer , and it is standard deviation ( 1σ ) of thickness of the copper layer measured at a center and eight points near edges . the average surface roughness ( ra ) means roughness of the surface of the copper layer measured by the noncontacting measuring instrument . the stock removal rate was slightly less than the target , but the uniformity of the polished layer and the average surface roughness were sufficient . copper layers of substrates were polished by the polishing machine shown in fig1 and 2 . only the polishing slurry was changed as follows : 10 samples were polished , the uniformity of the polished layer was appraised as well as experiment 1 , and the results were as follows : the stock removal rate was slightly less than the target , but the uniformity of the polished layer and the average surface roughness were sufficient as well as experiment 1 . these were measured as well as experiment 1 . copper layers of substrates were polished by the polishing machine shown in fig1 and 2 under following conditions : note that , the uniformity of polished layer is standard deviation ( 1σ ) of thickness of the copper layer evenly measured at 25 points . the average surface roughness was measured by the noncontacting measuring instrument as well as experiment 1 and 2 . the stock removal rate was slightly greater than the target and the uniformity of the polished layer and the average surface roughness were sufficient . copper layers of substrates were polished by the polishing machine shown in fig1 and 2 as well as experiment 3 . only the polishing slurry was changed as follows : the stock removal rate , the uniformity of the polished layer and the average surface roughness were highly sufficient . these were measured as well as experiment 1 . copper bumps of substrates were polished by the polishing machine shown in fig1 and 2 under following conditions : note that , in each substrate , nine copper bumps were formed at a center and at mid portions and outermost portions of four virtual lines radically extended from the center with regular angular separations . height of the nine copper bumps of each substrate was measured . a difference between the highest bump and the lowest bump was calculated for each substrate . thus , in the present experiment , a scattering range of said differences of 10 samples is considered as the uniformity of height of the polished copper bumps . the stock removal rate and the uniformity of height were highly sufficient . note that , in experiments 1 - 5 , no scratches were observed in the polished surfaces of any copper layers and bumps . copper layers of substrates were polished by the polishing machine shown in fig1 under following conditions : the uniformity of polished layer and the average surface roughness were measured as well as experiment 1 . copper bumps of substrates were polished by the polishing machine shown in fig1 under following conditions : 5 . rotational speed of polishing plate : 7 rpm 10 samples were polished , the uniformity of height was appraised as well as experiment 5 , and the results were as follows : the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof . the present embodiments are therefore to be considered in all respects as illustrative and not restrictive , the scope of the invention being indicated by the appended claims rather than by he foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein .