Abstract:
An improved pitch and roll mechanism is disclosed herein which provides for increased flexibility, stability, and accuracy of motion in positioning a miniaturized electronic component in a flip chip bonding system. The pitch and roll mechanism generally includes a pitch axis assembly comprising a plurality of bearing surfaces, each possessing a circular curvature, and at least one roller bearing in operative contact with at least one of the aforementioned pitch axis bearing surfaces. In addition, a roll axis assembly, mounted at a right angle, or perpendicularly, to the pitch axis assembly, is provided. The roll axis assembly typically includes a plurality of bearing surfaces, each possessing a circular curvature, and at least one roller bearing in operative contact with at least one of the aforementioned roll axis bearing surfaces. The curvatures of the pitch and roll axis bearing surfaces are such that a single, coincident center of rotation for both the pitch and roll axis assemblies is created.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application derives priority from U.S. Provisional Patent Application No. 60/201,998 for “PITCH AND ROLL ASSEMBLY FOR A FLIP CHIP BONDING MACHINE” filed May 4, 2000. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to flip chip bonding systems for automatically positioning and bonding miniaturized electronic components (i.e. multi-chip modules, flip chips, optoelectronic components, and other bonded assemblies), and in particular, to an improved pitch and roll mechanism used to position the workpieces in the bonding head assembly.  
           [0004]    2. Description of the Background  
           [0005]    A “flip chip” bonding system is a computer-controlled system for automatically positioning and bonding a variety of miniaturized electronic components, and in particular, flip chips. Flip chip bonding systems typically utilize articulated bonding heads to position the workpieces. Stability, accuracy, and flexibility are paramount considerations in the design of such bonding heads. Most bonding heads are designed for movement along X- and Y-axes in accordance with a linear coordinate table (i.e. axial motion). An example of prior art utilizing linear coordinate table movement is U.S. Pat. No. 6,182,355 to Zach. However, designs based solely on axial motion sacrifice flexibility of motion. Others have improved on this basic concept by introducing arcuate motion. U.S. Pat. No. 5,556,022 to Orcutt et al. discloses a polar motion bonding head, for use in positioning and bonding semiconductor devices, that replaces the axial motion of a typical X/Y-axis coordinate table with that of a polar coordinate table. This particular design, however, sacrifices stability. Still others have added some degree of adjustment for the angle of inclination of the workpiece. U.S. Pat. No. 4,899,921 to Bendat et al. discloses an apparatus that provides for angular workpiece adjustment in addition to motion along the X-, Y-, and Z-axes.  
           [0006]    While the means to create the required axial motion are well known in the art, the present inventors are unaware of any apparatus that uses roller bearings to provide the precise angular adjustment required to establish absolute parallelism between the miniaturized electronic components that are to be bonded. Additionally, as discussed above, this must be accomplished without sacrificing stability, accuracy, and flexibility. Therefore, it would be greatly advantageous to provide a bonding head assembly that, in addition to the standard, multi-axis linear motion capabilities, possesses the requisite degree of pitch and roll functionality (i.e. rotational motion centered on the X- and Y-axes, respectively). Once bonding head assemblies are equipped with improved pitch and roll capabilities, component assembly errors, and the resulting operational malfunctions, due to planar misalignment at the moment of bonding will be greatly reduced.  
         SUMMARY OF THE INVENTION  
         [0007]    It is, therefore, the primary object of the present invention to provide an improved pitch and roll mechanism for use in flip chip bonding systems that increases the range of motion of the workpiece contained therein without sacrificing stability, accuracy, and flexibility.  
           [0008]    It is another object to provide an improved pitch and roll mechanism that provides rotational workpiece motion around two, perpendicular axes (i.e. X- and Y-axes, or pitch and roll axes) of motion.  
           [0009]    It is a further object to provide an improved pitch and roll mechanism that provides two-axis, rotational workpiece motion utilizing a concept incorporating two primary sub-assemblies (i.e. the pitch axis assembly and the roll axis assembly), where the two sub-assemblies operate both independently of each other and in coordination with each other.  
           [0010]    It is another object to provide an improved pitch and roll mechanism that provides a single, coincident center of rotation for both the pitch axis assembly and the roll axis assembly.  
           [0011]    It is still another object to provide an improved pitch and roll mechanism that provides for the linking of a variety of drive means to either the pitch axis assembly or the roll axis assembly.  
           [0012]    It is a further object of the present invention to provide an economical design for an improved pitch and roll mechanism that utilizes existing, commercially available components and established machining practices to the extent possible.  
           [0013]    In accordance with the above-described and other objects, an improved pitch and roll mechanism is disclosed which provides for increased flexibility, stability, and accuracy of motion in positioning a workpiece in a flip chip bonding system. The pitch and roll mechanism generally includes a pitch axis assembly including a first pitch axis sub-assembly in operative engagement with a second pitch axis sub-assembly, the two sub-assemblies being adapted for relative translational movement such that rotational movement only of the component/workpiece is generated. In addition, the pitch and roll mechanism includes a roll axis assembly having a first roll axis sub-assembly in operative engagement with a second roll axis sub-assembly, these two sub-assemblies being adapted for relative translational movement such that rotational movement only of the component/workpiece is generated, wherein the axis of rotation is orthogonal to that of the pitch axis assembly.  
           [0014]    In one embodiment, the pitch axis assembly includes one pitch axis sub-assembly comprising a plurality of bearing surfaces, each possessing a circular curvature, and a second cooperating sub-assembly having at least one roller bearing in operative contact with at least one of the aforementioned pitch axis bearing surfaces. The opposing pitch axis sub-assemblies are adapted for translational movement relative to each other such that rotational movement only of a component/workpiece is generated. In addition, the roll axis assembly is mounted at a right angle, or perpendicularly, to the pitch axis assembly. The roll axis assembly likewise includes a first sub-assembly having a plurality of bearing surfaces, each possessing a circular curvature, and a cooperating second sub-assembly having at least one roller bearing in operative contact with at least one of the aforementioned roll axis bearing surfaces. Again, the opposing roll axis sub-assemblies are adapted for translational movement relative to each other such that rotational movement only of a component/workpiece is generated. The curvatures of the respective pitch and roll axis bearing surfaces are such that the pitch axis defines an axis of rotation, the roll axis defines an orthogonal axis of rotation, and the respective pitch and roll axes of rotation intersect at a single coincident point which is defined as a single, coincident center of rotation for both the pitch and roll axis assemblies is created.  
           [0015]    An alternative embodiment is shown in which a plurality of radial slide assemblies are used instead of discrete roller bearings and bearing surfaces.  
           [0016]    In either case, the pitch and roll assemblies may each be equipped with an independent drive mechanism (i.e. the combination of a lead screw assembly and a lead screw pivot assembly) that provides a connecting means for any one of a variety of drive devices incorporated within a flip chip bonding system. The improved pitch and roll mechanism is economical as it can be reduced to practice using many commercially available components (e.g. roller bearings, springs), conventional raw materials (e.g. aluminum, brass, stainless steel), and by established machining practices (i.e. to convert the raw materials into finished parts). 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    Other objects, features, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiment and certain modifications thereof when taken together with the accompanying drawings in which:  
         [0018]    [0018]FIG. 1 is a perspective view of the improved pitch and roll mechanism  100  according to a first embodiment of the present invention.  
         [0019]    [0019]FIG. 2 is a partially exploded perspective view of the improved pitch and roll mechanism  100  according to a first embodiment of the present invention where the pitch axis assembly  12  is shown separated from the roll axis assembly  15 .  
         [0020]    [0020]FIG. 3 is a bottom perspective view of the pitch axis carriage assembly  40  of the improved pitch and roll mechanism according to a first embodiment of the present invention.  
         [0021]    [0021]FIG. 4 is a partially exploded bottom perspective view of the roll axis assembly  15  of the improved pitch and roll mechanism according to a first embodiment of the present invention.  
         [0022]    [0022]FIG. 5 is a bottom perspective view of the roll axis carriage assembly  80  of the improved pitch and roll mechanism according to a first embodiment of the present invention.  
         [0023]    [0023]FIG. 6 a  is a bottom perspective view of the pitch and roll axis drive mechanisms  120 ,  130 , respectively, of the improved pitch and roll mechanism according to a first embodiment of the present invention.  
         [0024]    [0024]FIG. 6 b  is an exploded side perspective view of the lead screw assembly  140  of the improved pitch and roll mechanism according to a first embodiment of the present invention.  
         [0025]    [0025]FIG. 6 c  is an exploded top perspective view of the lead screw pivot assembly  160  of the improved pitch and roll mechanism according to a first embodiment of the present invention.  
         [0026]    [0026]FIGS. 7 a - d  are side perspective views of the improved pitch and roll mechanism  100  according to a first embodiment of the present invention.  
         [0027]    [0027]FIG. 8 is a side perspective view of the tension spring assembly  24  of the improved pitch and roll mechanism according to a first embodiment of the present invention.  
         [0028]    [0028]FIG. 9 is a perspective view of the pitch and roll mechanism  101  according to an alternative embodiment of the present invention.  
         [0029]    [0029]FIG. 10 is an exploded perspective view of the pitch and roll mechanism  101  of FIG. 9 wherein the mechanism  101  has been rotated 90° counterclockwise (as viewed from above). 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    [0030]FIG. 1 is a perspective view of the improved pitch and roll mechanism  100  according to a first embodiment of the present invention. The pitch and roll mechanism  100  adjusts the angular orientation of two discrete workpieces prior to assembly and bonding (for example two layers of a multi-layer chip). More specifically, it adjusts the angular position of the mating surface of the integrated circuit wafer or chip so that it is parallel along two horizontal axes with the mating surface of the patterned substrate. In other words, the pitch and roll mechanism  100  allows adjustment of the angular position such that the planes of the two mating surfaces are parallel.  
         [0031]    The pitch and roll mechanism  100  includes two distinct major assemblies that are labeled in FIG. 1: a pitch axis assembly  12 ; and roll axis assembly  15 . These two assemblies work together in the flip chip bonding system to adjust the angular position of the workpiece along the two horizontal axes.  
         [0032]    Generally, the pitch axis assembly  12  includes a first pitch axis sub-assembly in operative engagement with a second pitch axis sub-assembly, the two sub-assemblies being adapted for relative translational-rotational movement as described above. Likewise, the roll axis assembly  15  includes a first roll axis sub-assembly in operative engagement with a second roll axis sub-assembly, these two sub-assemblies being adapted for relative translational-rotational movement, the rotation being orthogonal to that of the pitch axis assembly  12 .  
         [0033]    With specific regard to the embodiment shown in FIG. 1, the pitch axis assembly  12  further comprises two sub-assemblies including a pitch axis base plate  20  and pitch carriage assembly  40 .  
         [0034]    The roll axis assembly  15  further comprises two sub-assemblies including a roll axis base plate  60  and the roll axis carriage assembly  80 .  
         [0035]    [0035]FIG. 2 is partially exploded perspective view of the pitch and roll mechanism  100  according to the present invention which shows separation of the pitch axis assembly  12  (inclusive of the pitch axis base plate  20  and the pitch carriage assembly  40 ) and the roll axis assembly  15  (inclusive of the roll axis base plate  60  and the roll axis carriage assembly  80 ).  
         [0036]    [0036]FIG. 3 is a bottom perspective view of the pitch axis carriage assembly  40  as seen in FIG. 2. The pitch axis carriage assembly  40  further includes a pitch block  42  fabricated of aluminum, tool steel or the like, a plurality of commercially available pitch axis roller bearings  44 , a front roller bearing shaft  46  for rotational mounting of all forward pitch axis roller bearings  44 , a rear roller bearing shaft  48  for rotational mounting of all rearward pitch axis roller bearings  44 , and a pitch axis drive mechanism  120 . The two roller bearing shafts  46 ,  48  are preferably cylindrical rods of precision ground stainless steel which extend through the roller bearings  44  to hold them in the proper position relative to the pitch block  42 . The rear shaft  48  also extends through the lead screw pivot assembly  160  (see FIG. 6 a ), thereby creating a connection between the pitch axis drive mechanism  120  and the pitch block  42  that permits a degree of relative rotational motion between the pitch axis drive mechanism  120  and the block  42  while preventing any linear relative motion.  
         [0037]    Referring back to FIG. 2, the pitch axis base plate  20  is fabricated of aluminum, tool steel or the like, and is attached to the drive mechanism  120  via a threaded lead screw nut  28  fixedly mounted in a support block  26  (also preferably fabricated of aluminum). A plurality of pitch axis bearing surfaces  22  are also fixedly attached to the base plate  20 . The pitch axis bearing surfaces  22  are preferably fabricated as blocks (bronze, cast iron or steel, or other suitable bearing materials) that direct identical concave curved surfaces toward the plurality of pitch axis roller bearings  44 , thereby providing individual bearing surfaces for each pitch axis roller bearing  44  when the drive mechanism  120  is rotated. Proper contact between the pitch axis roller bearings  44  and the pitch axis bearing surfaces  22  is maintained by tension spring assemblies  24  (described in detail below with respect to FIG. 8) positioned on both sides of the pitch axis assembly  12 . As the pitch axis roller bearings  44  move along the pitch axis bearing surfaces  22 , the pitch axis carriage assembly  40  moves through an arc (described in more detail below with respect to FIGS. 7 a - b ). The center of that arc is herein referred to as the center of rotation of the pitch axis carriage assembly  40 .  
         [0038]    [0038]FIG. 4 is a partially exploded bottom perspective view of the roll axis assembly  15  as in FIGS. 1 and 2 (inclusive of the roll axis base plate  60  and the roll axis carriage assembly  80 ).  
         [0039]    The roll axis base plate  60  is preferably fabricated of aluminum, tool steel or the like, and is attached to the roll axis drive mechanism  130  via a threaded lead screw nut  68  fixedly mounted in a support block  66  (support block  66  may also be fabricated of aluminum). A plurality of roll axis bearing surfaces  62  are also fixedly attached to the base plate  60 . The roll axis bearing surfaces  62  are, like those of the pitch axis bearing surfaces  22  (see FIG. 2), preferably fabricated of brass or the like and possess identical circular curvatures which are traversed by the plurality of roll axis roller bearings  84  when the drive mechanism  130  is rotated. Proper contact between the roll axis roller bearings  84  and the roll axis bearing surfaces  62  is maintained by tension spring assemblies  24  positioned on both sides of the roll axis assembly  15 . As the roll axis roller bearings  84  move along the roll axis bearing surfaces  62 , the roll axis carriage assembly  80  moves through an arc (described in more detail below with respect to FIGS.  117   c - d ). The center of that arc is herein defined as the center of rotation of the roll axis carriage assembly  80 , and it is directly orthogonal to the aforesaid pitch axis of rotation.  
         [0040]    [0040]FIG. 5 is a bottom perspective view of roll axis carriage assembly  80 . The roll axis carriage assembly  80  includes the roll block  82  preferably fabricated of aluminum or the like, a plurality of commercially available roll axis roller bearings  84 , a front roller bearing shaft  86 , a rear roller bearing shaft  88 , and a roll axis drive mechanism  130 . The shafts  86 ,  88  are preferably formed as precision ground cylindrical stainless steel shafts that extend through the roller bearings  84  to hold them in the proper position relative to the roll block  82 . The rear shaft  88  also extends through the lead screw pivot assembly  160  (see FIG. 6 a ) creating a connection between the roll axis drive mechanism  130  and the roll block  82  that permits a degree of relative rotational motion between the mechanism  130  and the block  82  while preventing any linear relative motion.  
         [0041]    [0041]FIG. 6 a  is a bottom perspective view of an exemplary drive mechanism which serves as both pitch and roll axis drive mechanisms  120 ,  130 , respectively. Both pitch and roll axis drive mechanisms  120 ,  130 , respectively, are comprised of a lead screw assembly  140  and a lead screw pivot assembly  160  held together by connecting pin  168 . The connection established by pin  168  permits a degree of rotational relative motion between the two assemblies  140 ,  160  while preventing any linear relative motion.  
         [0042]    [0042]FIG. 6 b  is an exploded side perspective view of the lead screw assembly  140  of FIG. 6 a . The lead screw assembly  140  is comprised of a lead screw  142 , a lead screw actuator knob  144 , a lead screw clearance adjusting nut  146 , a lead screw locking nut  147 , a lead screw nut  28 ,  68 , lead screw support bearings  148 , a lead screw pivot assembly coupling  150 , a bearing block  152 , and a plurality of attachment screws  154 . The bearing block  152  is a square bearing preferably fabricated of aluminum and adapted to pass lead screw  142 . Commercially available support bearings  148  are slipped onto the appropriate end of the hardened steel lead screw  142 , and the assemblage of bearing block  152 , bearings  148 , and lead screw  142  is fixedly attached to the pivot assembly coupling  150  as shown. Pivot assembly coupling  150  is a yoke and may be fabricated of aluminum. Pivot assembly coupling  150  is threaded from the rear to facilitate attachment to bearing block  152  using a plurality of attachment screws  154 .  
         [0043]    Knob  144  may be fabricated of molded plastic, aluminum or any other commercially available material suitable for an external connection and turning thereby. Knob  144  is mounted on the distal end of lead screw  142  adjacent an adjusting nut  146 , commercially available locking nut  147 , and hardened steel lead screw nut  28 ,  68  (all of which are assembled onto the end of the lead screw  142 ).  
         [0044]    [0044]FIG. 6 c  is an exploded top perspective view of the lead screw pivot assembly  160  of FIGS. 6 a  and  6   b . The lead screw pivot assembly  160  is comprised of a connecting link  162 , two bearing blocks  164 , two bearings  166 , a plurality of attachment screws  167 , and a connecting pin  168 . The link  162 , preferably fabricated of aluminum, and the commercially available bearings  166  are held between, and rigidly fastened together with the two bearing blocks  164 , also preferably fabricated of aluminum, by the attachment screws  167 . The pin  168 , preferably fabricated of precision ground stainless steel, is used to connect the pivot assembly  160  with the lead screw pivot assembly coupling  150 .  
         [0045]    The entire assemblage of pitch and roll axis drive mechanisms  120 ,  130  (inclusive of knob  144 , adjusting nut  146 , locking nut  147 , and lead screw nut  28 ,  68 ) is then mounted in the respective support blocks  26 ,  66  (as shown in FIGS. 2 and 4), with lead screw nut  28 ,  68  held captive therein.  
         [0046]    [0046]FIGS. 7 a - d  are side perspective views of the improved pitch and roll mechanism according to a first embodiment of the present invention. Specifically, FIG. 7 a  shows the pitch axis assembly  12  rotated 3° from its center, or neutral, position. FIG. 7 b  is a close up view of the pitch axis base plate  20  and the pitch axis carriage assembly  40  of FIG. 7 a  showing the same degree of rotation. FIG. 7 c  shows the roll axis assembly  15  rotated 3° from its center position. FIG. 7 d  is a close up view of the roll axis base plate  60  and the roll axis carriage assembly  80  of FIG. 7 c  showing the same degree of rotation.  
         [0047]    Operation of either the pitch axis assembly  12  or the roll axis assembly  15  is generated by turning the respective lead screw actuator knob  144 . It is through an external connection to this knob  144 , or some variant design thereof, that the ability to link a variety of drive means to either the pitch axis assembly  12  or the roll axis assembly  15  is provided. The rigid connection between the knob  144  and the lead screw  142  (see FIG. 6 b ) causes the screw  142  to rotate. Rotation of the screw  142  within the lead screw nut  28 ,  68  (see FIGS. 2 and 4), fixedly mounted in the support block  26 ,  66 , respectively, causes the screw  142  to move slightly along the line of direction arrow  180 . Due to a series of direct connections, this causes corresponding movement of the lead screw pivot assembly coupling  150 , the lead screw pivot assembly  160 , and the pitch or roll block  42 ,  82 , respectively. Any movement by the block  42 ,  82  causes the pitch or roll axis roller bearings  44 ,  84  (see FIGS. 3 and 5), respectively, to traverse the corresponding bearing surfaces  22 ,  62 . Operation of the pitch axis assembly  12  and the roll axis assembly  15  can occur independently or simultaneously.  
         [0048]    [0048]FIG. 8 is a side perspective view of an exemplary tension spring assembly  24  as in FIG. 2 which assemblies are positioned on both sides of the pitch axis assembly  12  as well as on both sides of the roll axis assembly  15 . The tension spring assembly is comprised of a tension spring  31 , a spring holder  32  which may be fabricated of stainless steel or the like, a spring tensioning block  33  which may be fabricated of aluminum, steel or the like, an adjustable tension screw  34 , a spring holder pivot bolt  35 , and two mounting screws  36 . The commercially available mounting screws  36  are used to fixedly attach the tensioning block  33  to the pitch block  42 , or the roll block  82  (see FIG. 2). The commercially available pivot bolt  35  is used to pivotally attach the spring holder  32  to the tensioning block  33 . One end of the tension spring  31  is fixedly attached to the spring holder  32 , while the other end is fixedly attached to the pitch axis base plate  20 , or the roll axis base plate  60  (see FIG. 2). The commercially available tension screw  34  extends through a threaded hole  37  in the tensioning block  33 . The spring holder  32  bears against the end of the tension screw  34 . Referring back to FIG. 2, an appropriate amount of spring tension must be maintained to keep the roller bearings  44 ,  84  in contact with the bearing surfaces  22 ,  62 . This is accomplished by spring tension afforded by assemblies  24 , and the tension may be increased by turning the tension screw  34  clockwise, or decreased by turning the screw  34  counterclockwise.  
         [0049]    Referring back to FIGS. 1, 2, and  4 , the roll axis assembly  15  is attached to the pitch axis assembly  12  at right angles and, therefore, operate along perpendicular axes. Thus, the axis representing the center of rotation of the pitch axis carriage assembly  40  can only intersect with the axis representing the center of rotation of the roll axis carriage assembly  80  at a single point. A single, coincident point exists because the curves defined by the plurality of pitch axis bearing surfaces  22  and the identical curves defined by the plurality of roll axis bearing surfaces  62  possess different radii. More specifically, the curve radius defined by the pitch axis bearing surfaces  22  is larger than that of the roll axis bearing surfaces  62  because the pitch axis bearing surfaces  22  are positioned a greater distance from the single, coincident point. The curve radius defined by the pitch axis bearing surfaces  22  and that of the roll axis bearing surfaces  62  must be different in order to compensate for the physical dimensions of the various assemblies (e.g. the thickness of the roll axis base plate  60 ). By definition, that single, coincident point is the center of rotation of the pitch and roll mechanism  100 . When positioned in the bonding head assembly, the center of the bonding surface of the workpiece (e.g. integrated circuit wafer/chip, substrate) is also located at the center of rotation of the pitch and roll mechanism  100 . The mechanism  100  provides a means to adjust the angular orientation of the planar surface of the workpiece around two axes of motion without causing any amount of workpiece translation (i.e. horizontal movement) that would affect its linear alignment.  
         [0050]    One skilled in the art would recognize that the same two axes of motion can be accomplished by alternate means without departing from the scope and spirit of the present invention. For example, FIG. 9 is a perspective view of a pitch and roll mechanism  101  according to an alternative embodiment of the present invention. FIG. 10 is an exploded perspective view of the mechanism  101  shown in FIG. 9 wherein the mechanism  101  has been rotated 90° counterclockwise (as viewed from above). This alternative embodiment  101  utilizes a plurality of commercially available, radial slide assemblies  200 ,  250  to achieve the same purpose. The radial slide assemblies  200 ,  250  take the place of the plurality of roller bearings  44 ,  84 , the plurality of bearing surfaces  22 ,  62 , the roller bearing shafts  46 ,  48 ,  86 ,  88 , and the plurality of tension spring assemblies  24  (all as shown in FIGS.  2 - 5 ). Each radial slide assembly  200 ,  250  includes a curved rail  202 ,  252  (i.e. bearing surface) and two roller bearing assemblies  204 ,  254  which hold the respective curved rails  202 ,  252  captive and ride there along.  
         [0051]    The roll axis assembly  102  of FIGS. 9 and 10 is comprised of drive mechanism  130  (see FIG. 6 a ), two radial slide assemblies  200  (with curved rails  202  and roller bearing assemblies  204 ), two inner bearing mounting plates  206 , and two outer bearing mounting plates  208 . The mounting plates  206 ,  208  may be fabricated of aluminum or the like. The curved rails  202  are fixedly attached to the inner bearing mounting plates  206 . The roller bearing assemblies  204  are fixedly attached to the outer bearing mounting plates  208  and slidably interact with the curved rails  202 . Rotation of the drive mechanism  130  causes the roller bearing assemblies  204  to traverse the curved rails  202  due to the pivoting connection between the drive mechanism  130  and one of the inner bearing mounting plates  206 .  
         [0052]    The pitch axis assembly  104  of FIGS. 9 and 10 is comprised of a drive mechanism  120  (see FIG. 6 a ), two radial slide assemblies  250  (with curved rails  252  and roller bearing assemblies  254 ), two inner bearing mounting plates  256 , two outer bearing mounting plates  258 , and two center braces  260 . The mounting plates  256 ,  258  and center braces  260  may be fabricated of aluminum or the like. The curved rails  252  are fixedly attached to the inner bearing mounting plates  256 . The roller bearing assemblies  254  are fixedly attached to the outer bearing mounting plates  258  and slidably interact with the curved rails  252 . Rotation of the drive mechanism  120  causes the roller bearing assemblies  254  to traverse the curved rails  252  due to a pivoting connection between the drive mechanism  120  and one of the inner bearing mounting plates  256 . The pitch axis assembly  104  is attached to the roll axis assembly  102  via a fixed connection between the pitch axis inner bearing mounting plates  256  and the roll axis inner bearing mounting plates  206 .  
         [0053]    A workpiece (not shown) is held in a chuck (also not shown) that is fixedly attached to the two chuck mounting blocks  270 . The blocks  270  are fixedly attached to a plurality of connecting plates  262  and center braces  260  which are, in turn, each fixedly attached to the pitch axis outer bearing mounting plates  258 . The blocks  270  and connecting plates  262  may be fabricated of aluminum or the like.  
         [0054]    The right angle connection between the inner bearing mounting plates  206 ,  256  creates a configuration where the roll axis assembly and the pitch axis assembly operate along perpendicular axes. As before, the axis representing the center of rotation of the pitch axis assembly  104  can only intersect with the axis representing the center of rotation of the roll axis assembly  102  at a single point. A single, coincident point exists because the radial slide assemblies  200 ,  250  have curved rails  202 ,  252  possessing identical radii, and the rails  202 ,  252  are located equidistant from that coincident point. By definition, that single, coincident point is the center of rotation of the alternative pitch and roll mechanism  101 . When positioned in the aformentioned chuck, the center of the bonding surface of the workpiece is also located at the center of rotation of the alternative pitch and roll mechanism  101 . Consequently, the alternative pitch and roll mechanism  101  provides an equally effective means to adjust the angular orientation of the planar surface of the workpiece around two axes of motion without causing any amount of workpiece translation (i.e. horizontal movement) that would affect its linear alignment.  
         [0055]    Having now fully set forth the preferred embodiments and certain modifications of the concept underlying the present invention, various other embodiments as well as certain variations and modifications of the embodiments herein shown and described will obviously occur to those skilled in the art upon becoming familiar with said underlying concept. It is to be understood, therefore, that the invention may be practiced otherwise than as specifically set forth in the appended claims.