fig2 through 6 , discussed below , and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention . those skilled in the art will understand that the principles of the present invention may be implemented in any suitably arranged chemical mechanical polishing ( cmp ) system . fig2 illustrates a side view of selected portions of multiple disk break - in head 200 according to an exemplary embodiment of the present invention . when cmp system 100 is taken off line , polishing head 150 is removed and break - in head 200 is installed in cmp system 100 in place of polishing head 150 . the exemplary embodiment of break - in head 200 holds four pad conditioning disks 115 , namely disk 115 a , disk 115 b , disk 115 c and disk 115 d ( not visible in fig1 ). in alternate embodiments of the present invention , break - in head 200 may hold more than four disks 115 or less than four disks 115 . multiple disk break - in head 200 comprises coupling 205 , circular housing 210 , drive shaft 215 , and drive mechanism 250 ( shown by dotted outline ). coupling 205 is used to attach break - in head to drive shaft 165 in cmp system 100 . drive shaft 215 transfers the rotation of drive shaft 165 to drive mechanism 250 . break - in head 200 further comprises four spindles 120 , namely spindle 120 a , spindle 120 b , spindle 120 c and spindle 120 d ( not visible in fig2 ). disk 115 a is removably coupled to spindle 120 a , disk 115 b is removably coupled to spindle 120 b , disk 115 c is removably coupled to spindle 120 c , and disk 115 d is removably coupled to spindle 120 d . break - in head 200 also comprises four drive shafts 220 , including drive shaft 220 a , drive shaft 220 b , drive shaft 220 c , and drive shaft 220 d ( not visible in fig2 ). spindles 120 are coupled to drive shafts 220 by retaining rings 225 , springs 230 , and retaining rings 235 . for example , retaining ring 235 a is rigidly attached to spindle 120 a and to drive shaft 220 a . retaining ring 225 a is rigidly attached to the body of housing 210 and is slidably coupled to drive shaft 220 . drive shaft 220 is slidably attached to a drive gear in drive mechanism 250 . when break - in head 200 is pressed down on pad 110 , spindle 120 a and retaining ring 235 a press upward on spring 230 a . drive shaft 220 a also is pressed upward by retaining ring 230 a . the upward movement of drive shaft 220 a is accommodated by the slidable coupling to the gears in drive mechanism 250 . retaining ring 225 a is rigidly attached to housing 210 and resists the upward movement of spring 230 a . thus , the pressure of disk 115 a against the surface of pad 110 is determined by the characteristics of spring 230 a . disks 115 b , 115 c and 115 d are connected to drive shafts 220 b , 220 c and 220 d by similar assemblies of retaining rings , spindles , and springs . the operation of these other assemblies are similar to the operation of ring 225 a , ring 235 a , and spring 230 a and need not be explained separately . to avoid redundancy , such separate explanations are omitted . fig3 illustrates a top view of selected portions of multiple disk break - in head 200 according to an exemplary embodiment of the present invention . exemplary drive mechanism 250 is enclosed by a dotted line . exemplary drive mechanism 250 comprises central gear 310 , transfer gears 311 – 314 and drive gears 321 – 324 . disks 115 a – 115 d are positioned below break - in head 200 and are shown in partial dotted outlines . central gear 310 is coupled to , and rotated by , drive shaft 215 . transfer gear 311 transfers the rotation of central gear 310 to drive gear 321 , which in turn causes the rotation of disk 115 a . transfer gear 312 transfers the rotation of central gear 310 to drive gear 322 , which in turn causes the rotation of disk 115 b . transfer gear 313 transfers the rotation of central gear 310 to drive gear 323 , which in turn causes the rotation of disk 115 c . transfer gear 314 transfers the rotation of central gear 310 to drive gear 324 , which in turn causes the rotation of disk 115 d . in this manner , the rotation of drive shaft 165 in cmp system 100 causes the individual rotations of each of disks 115 a , 115 b , 115 c and 115 d . the relative sizes of central gear 310 , transfer gears 311 – 314 , and drive gears 321 – 324 determine the speed of rotation of disks 115 a – 115 d . the exemplary arrangement of the gears in drive mechanism 250 is by way of example only and should not be construed to limit the scope of the present invention . those skilled in the art will readily understand that many other types of mechanical drive systems may be used to rotate pad conditioning disks 115 a – 115 d . for example , in an alternate embodiment , a single large central gear 310 may directly couple to drive gears 321 – 324 without the use of intermediate transfer gears . in still other embodiments , belts or chains may be used to rotate disks 115 a – 115 d . fig4 illustrates a top view of selected portions of multiple disk break - in head 200 according to an alternate exemplary embodiment of the present invention . in fig4 , drive mechanism 250 has been removed entirely , so that disks 115 a – 115 d are not driven by drive shafts 165 and 215 . nonetheless , pad conditioning disks 115 a – 115 d rotate when pressed down upon pad 110 due to the speed differences between different points on the surface of pad 110 . surface points near the outer diameter of pad 110 must move at a faster speed than surface points near the center of rotation of pad 110 in order to complete one rotation in the same time period . thus , a first point on the bottom surface of disk 115 that is closer to the center of pad 110 contacts a slower moving portion of the surface of pad 110 than a second point on the bottom surface of disk 115 that is further from the center of pad 110 . thus , there is a greater amount of friction at the second point . spindle 120 is at the center of rotation of disk 115 . collectively , the combined friction of all of the points on the bottom surface of disk 115 that are located to the side of spindle 120 closer to the center of pad 110 is less than the combined friction of all of the points on the bottom surface of disk 115 that are located to the side of spindle 120 that is further from the center of pad 110 . the friction difference causes disk 115 to rotate about spindle 120 , even in the absence of drive mechanism 250 . the multiple disk break - in head described above overcomes the shortcomings of conventional chemical mechanical polishing ( cmp ) systems by greatly increasing the number of pad conditioning disks that may be broken in whenever a cmp system is taken off line . instead of mounting only one new disk 115 on spindle 120 in fig1 , multiple ( e . g ., 4 ) other new disks 115 are mounted on other spindles 120 on break - in head 200 ( which replaced polishing head 150 ) and are broken - in at the same time . however , the process of breaking - in new pad conditioning disks may be further improved by means of an off - line tool that completely eliminates the need to halt cmp system 100 in order to break in new disks . the new off - line tool uses one or more of the multiple disk break - in heads 200 described above to break in pad conditioning disks while cmp system continues to polish semiconductor wafers . fig5 illustrates a side view of selected portions of off - line break - in tool 500 , which uses multiple disk break - in heads 200 a and 200 b , according to an exemplary embodiment of the present invention . off - line break - in tool 500 comprises basin 501 , platen 505 , polishing pad 510 , head drive assembly 520 , support 530 , drive shaft 535 , motor 540 , drive shaft 545 , drive shaft 555 and drive shaft 565 . off - line break - in tool 500 further comprises gears 521 526 , drive chains ( or belts ) 527 – 529 , weight 560 , weight 570 , and a slurry dispenser 610 ( not visible in fig5 ). it is noted that the components of break - in tool 500 depicted in fig5 are not drawn to scale . the sizes and relative positions of the components of break - in tool 500 are selected for easy reference and explanation . basin 501 catches excess slurry that overflows polishing pad 510 and provides a support platform for the other components of break - in tool 500 . support 530 and drive shaft 535 support head drive assembly 520 in position above platen 505 . motor 540 rotates drive shaft 545 , which in turn rotates platen 505 and gear 525 . drive chain ( or belt ) 520 transfers the rotation of gear 525 to gear 526 , which is attached to drive shaft 535 . the rotation of gear 526 rotates drive shaft 535 , which in turn rotates gear 524 . drive chain ( or belt ) 528 transfers the rotation of gear 524 to gear 523 , which is attached to drive shaft 565 . the rotation of gear 523 rotates drive shaft 565 , which in turn rotates gear 522 . drive chain ( or belt ) 527 transfers the rotation of gear 522 to gear 521 , which is attached to drive shaft 555 . the rotation of gear 521 rotates drive shaft 555 . thus , the rotation of motor 540 rotates all of drive shafts 535 , 545 , 555 and 565 via gears 521 – 526 and drive chains 527 – 529 . moreover , the rotation of drive shaft 555 rotates the pad conditioning disks on the bottom surface of multiple disk break - in head 200 a in the manner described above in fig2 and 3 . similarly , the rotation of drive shaft 565 rotates the pad conditioning disks on the bottom surface of multiple disk break - in head 200 b in the manner described above in fig2 and 3 . thus , motor 540 powers the operation of all parts of off - line break - in tool 500 . drive shaft 555 is slidably attached to gear 521 , so that drive shaft 555 may slide vertically within gear 521 . a spring or a similar mechanism ( not shown ) pushes upward on drive shaft 555 , so that when multiple disk break - in head 200 a is attached to drive shaft 555 , multiple disk break - in head 200 a is held in a raised ( or up ) position in which the pad conditioning disks of multiple disk break - in head 200 a do not touch polishing pad 510 . however , when weight 560 is attached to drive shaft 555 , drive shaft 555 slides downward and multiple disk break - in head 200 a is pressed downward to a lowered ( or down ) position in which the pad conditioning disks of break - in head 200 a do make contact with polishing pad 510 . similarly , drive shaft 565 is slidably attached to gears 522 and 523 , so that drive shaft 565 may slide vertically within gears 522 and 523 . a spring or a similar mechanism ( not shown ) pushes upward on drive shaft 565 , so that when multiple disk break - in head 200 b is attached to drive shaft 565 , multiple disk break - in head 200 b is held in a raised ( or up ) position in which the pad conditioning disks of multiple disk break - in head 200 b do not touch polishing pad 510 . however , when weight 570 is attached to drive shaft 565 , drive shaft 565 slides downward and multiple disk break - in head 200 b is pressed downward to a lowered ( or down ) position in which the pad conditioning disks of break - in head 200 b do make contact with polishing pad 510 . fig6 illustrates a top view of selected portions of off - line break - in tool 500 according to an exemplary embodiment of the present invention . in fig6 , slurry dispenser 610 is visible , but weights 560 and 570 are not visible . support 530 , gear 521 , gear 522 , gear 524 , and belts 527 and 528 are visible within head drive assembly 520 . advantageously , the off - line break - in tool according to the principles of the present invention may also be used to break in , or condition , polishing head 150 prior to being used to polish semiconductor wafers . the lower surfaces of many conventional polishing heads , such as titan ™ polishing heads , must be smoothed prior to use to remove irregularities . although the present invention has been described with an exemplary embodiment , various changes and modifications may be suggested to one skilled in the art . it is intended that the present invention encompass such changes and modifications as fall within the scope of the appended claims .