Patent Publication Number: US-9425163-B2

Title: Systems and methods for determining and adjusting a level of parallelism related to bonding of semiconductor elements

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of application Ser. No. 14/553,782 filed Nov. 25, 2014, which claims the benefit of U.S. Provisional Patent Application No. 61/911,011 filed Dec. 3, 2013, and U.S. Provisional Patent Application No. 61/916,930 filed Dec. 17, 2013, the content of all of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the formation of semiconductor packages, and more particularly, to improved systems and methods for bonding semiconductor elements together. 
     BACKGROUND OF THE INVENTION 
     In certain aspects of the semiconductor packaging industry, semiconductor elements are bonded to bonding locations. For example, in conventional die attach (also known as die bonding) applications, a semiconductor die is bonded to a bonding location (e.g., a leadframe, another die in stacked die applications, a spacer, etc.). In advanced packaging applications, semiconductor elements (e.g., bare semiconductor die, packaged semiconductor die, etc.) are bonded to bonding locations of a substrate (e.g., a leadframe, a PCB, a carrier, a semiconductor wafer, a BGA substrate, etc.), with conductive structures (e.g., conductive bumps, contact pads, solder bumps, conductive pillars, copper pillars, etc.) providing electrical interconnection between the semiconductor element and the bonding location. 
     In many applications (e.g., thermocompression bonding of semiconductor elements including solder bumps, etc.) it is particularly desirable to have a significant level of parallelism between the bonding tool and respective portions of a support structure of the bonding machine. For example, there may be many interconnections between (1) the semiconductor element being bonded by the bonding tool, and (2) the substrate supported by the support structure. These interconnections may include solder or the like, and as such, it is particularly desirable that there be substantial parallelism between the contact portion of the bonding tool and respective portions of the support structure. 
     Thus, it would be desirable to provide improved systems for, and methods of, determining and adjusting the parallelism between elements of bonding machine. 
     SUMMARY OF THE INVENTION 
     According to an exemplary embodiment of the present invention, a bonding machine for bonding semiconductor elements is provided. The bonding machine includes: a support structure configured to support a substrate; a bond head assembly including a bonding tool configured to bond a plurality of semiconductor elements to the substrate; and a calibration tool including a contact portion configured to be positioned between the bonding tool and the support structure, the contact portion configured to be contacted by each of the bonding tool and the support structure simultaneously during a calibration operation. 
     According to another exemplary embodiment of the present invention, a method of determining a level of parallelism between a bonding tool and a support structure of a bonding machine is provided. The method includes the steps of: (a) positioning a contact portion of a calibration tool between the bonding tool and the support structure; (b) lowering the bonding tool to drive the contact portion of the calibration tool to a contact position within a bonding location of the support structure where the contact portion of the calibration tool contacts the bonding tool and the contact position simultaneously; and (c) determining a z-axis height value for the contact position when each of the bonding tool and the support structure is in contact with the contact portion of the calibration tool. 
     According to another exemplary embodiment of the present invention, a method of determining a level of parallelism between a contact portion of a bonding tool and a contact region of a flux station of a bonding machine is provided. The method includes the steps of: (a) positioning a contact portion of a calibration tool between the bonding tool and the contact region of the flux station; (b) lowering the bonding tool to drive the contact portion of the calibration tool to a contact position within the contact region of the flux station where the contact portion of the calibration tool contacts the contact portion of the bonding tool and the contact position within the contact region of the flux station simultaneously; and determining a z-axis height value for the contact position within the contact region of the flux station when each of the contact portion of the bonding tool and the contact region of the flux station is in contact with the contact portion of the calibration tool. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is best understood from the following detailed description when read in connection with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawings are the following figures: 
         FIG. 1A  is a block diagram side view illustrating a semiconductor element carried by a bonding tool prior to bonding to a substrate; 
         FIG. 1B  illustrates the semiconductor element of  FIG. 1A  after bonding to the substrate; 
         FIG. 2  is a block diagram perspective view of elements of a bonding machine in accordance with an exemplary embodiment of the present invention; 
         FIG. 3  is a block diagram perspective view of elements of another bonding machine in accordance with another exemplary embodiment of the present invention; 
         FIG. 4A  is an detailed block diagram perspective view of a bonding location of a substrate of  FIG. 3  in accordance with an exemplary embodiment of the present invention; 
         FIGS. 4B-4D  are block diagram side views illustrating motion of a bonding tool and a calibration tool in connection with a calibration process in accordance with various exemplary embodiments of the present invention; 
         FIG. 5  is a flow diagram illustrating a method of determining a level of parallelism between a bonding tool and a support structure of a bonding machine in accordance with an exemplary embodiment of the present invention; 
         FIG. 6  is a block diagram perspective view of elements of yet another bonding machine in accordance with yet another exemplary embodiment of the present invention; and 
         FIG. 7  is a flow diagram illustrating a method of determining a level of parallelism between a contact portion of a bonding tool and a contact region of a flux station of a bonding machine in accordance with an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As used herein, the term “semiconductor element” is intended to refer to any structure including (or configured to include at a later step) a semiconductor chip or die. Exemplary semiconductor elements include a bare semiconductor die, a semiconductor die on a substrate (e.g., a leadframe, a PCB, a carrier, a semiconductor wafer, a BGA substrate, etc.), a packaged semiconductor device, a flip chip semiconductor device, a die embedded in a substrate, a stack of semiconductor die, amongst others. Further, the semiconductor element may include an element configured to be bonded or otherwise included in a semiconductor package (e.g., a spacer to be bonded in a stacked die configuration, a substrate, etc.). 
     As used herein, the term “substrate” is intended to refer to any structure to which a semiconductor element may be bonded (e.g., thermocompressively bonded, ultrasonically bonded, thermosonically bonded, die bonded, etc.). Exemplary substrates include, for example, a leadframe, a PCB, a carrier, a semicondcutor wafer, a BGA substrate, a semiconductor element, etc. 
     In accordance with certain exemplary embodiments of the present invention, a thermocompression flip chip bonding machine includes a bond head assembly carrying a bonding tool. The bonding tool places and bonds a semiconductor element (e.g., a semiconductor die, an interposer, etc.) to a substrate by melting and re-solidifying solder bumps on the semiconductor element being placed to create solder bonds. Controlling the height of the finished solder bonds is a desirable process control objective. In this embodiment, because all of the solder bumps on the semiconductor element are bonded at one time, the variation in the resulting solder bond height across the semiconductor element depends directly on the parallelism of the semiconductor element being bonded and the target substrate. In terms of the bonding machine, it is desirable to control the paralellism between the bonding tool (e.g., a contact portion/contact surface of the bonding tool) and the support structure (which may also be referred to as the bonding stage) of the bonding machine. The desired window for parallelism (or coplanarity) across the substrate may be very narrow (e.g., a variation of 2-3 microns across the substrate). Therefore, very accurate alignment of the bonding tool and the support structure is desired. 
     According to certain exemplary embodiments, the present invention relates to a method of determining (e.g., measuring) a level of parallelism between the bonding tool and the support structure, for example, in order to verify that the calibration has been successful, so that bonding can proceed with confidence in achieving the desired bond height control. Further, the determination of the level of parallelism may be used to generate a desired correction motion/adjustment for the bonding tool (e.g., using an active/passive tilt control mechanism in the bonding tool) and/or the support structure. 
     As will be appreciated by those skilled in the art, bonding machines have differing motion system architectures. In the present application, much of the description relates to a specific architecture (with certain elements having certain motion axes); however, it is understood that the present invention is not limited to such an architecture. As will be explained in greater detail below with respect to the drawings, the exemplary architecture includes: (1) a support structure that is moveable along an x-axis direction; (2) a bond head assembly (carrying a bonding tool) that is moveable along a y-axis direction, a z-axis direction, and about a theta axis; and a secondary motion system (e.g., an optical assembly motion system) that is moveable along an x-axis direction, a y-axis direction, and a z-axis direction. The secondary motion system is configured to carry a calibration tool (e.g., including a beam portion compliant in the z-axis direction, and a contact portion having 2 spherically shaped contact surfaces/portions), and can position the contact portion of the calibration tool between the bonding tool and the support structure. The bonding tool is lowered along the z-axis until it makes contact with the calibration tool, and continues until the calibration tool contacts the support structure. After contact is made between the calibration tool and the support structure, the position of a z-axis position encoder (e.g., on the bond head assembly or another portion of the bonding machine) is recorded. This position measurement may be repeated at several x, y locations within a bonding location of the support structure (e.g., through motion of the secondary motion system). The set of measurements allows the creation of a data set of z-axis data at a plurality of x, y coordinate locations within the bonding location, which provides an indication of the parallelism/planarity error between the bonding tool and the bonding location of the support structure. The position measurement may also be repeated for each of the bonding locations on the support structure by moving the support structure and/or the bond head assembly along the x, y axes, respectively, to the various bonding locations. Further, such methods may also be used to measure the parallelism between the bonding tool and an optional fluxing station. Further still, such methods may also be used to measure the flatness of the support structure. 
     The techniques described above may also be used in connection with adjustment/calibration processes. For example, z-axis position data provided for a plurality of bonding locations of a support structure (where the z-axis position data for each bonding location may include z-axis height values for a plurality of positions within each bonding location) may be used to adjust at least one of the bonding tool and the support structure to improve the relative parallelism therebetween. Likewise, z-axis position data provided for a plurality of x-axis and y-axis locations within a contact region of a flux station may be used to adjust the flux station to improve the parallelism between the flux station and the bonding tool. 
     As will be appreciated by those skilled in the art, bonding machines (such as machines  100 ,  200 ,  300 , and  300   a  illustrated and described herein) may include many elements not shown in the drawings herein for simplicity. Exemplary elements include, for example: input elements for providing input substrates/workpieces to be bonded with semiconductor elements; output elements for receiving processed substrates/workpieces that now include additional semiconductor elements; transport systems for moving substrates; semiconductor element supply structures (e.g., semiconductor wafers) including a plurality of semiconductor elements to be bonded to one or more substrates; a computer system including software for operating the machine; amongst other elements. 
     Referring now to the drawings,  FIG. 1A  illustrates portions of bonding machine  100  (e.g., a thermocompressive flip chip bonding machine) including bond stage  104  (e.g., a shuttle, a heated shuttle, a heat block, an anvil, etc.), and support structure  108  supported by bond stage  104  (where support structure  108  and bond stage  104  may be integrated into a single element). As will be appreciated by those skilled in the art, support structure  108  (e.g., an application specific part, sometimes referred to in the industry as a p-part) includes a plurality of bonding locations  106 . Substrate  130  is supported by support structure  108 , and includes a plurality of bonding areas (corresponding to bonding locations  106  of support structure  108 ). Lower conductive structures  144   a ,  144   b  (e.g., conductive traces, conductive pads, etc.) are provided on substrate  130 . Bonding machine  100  also includes bonding tool  110  (e.g., carried by a bond head assembly, not shown) carrying semiconductor element  132 . Upper conductive structures  138   a ,  138   b  (e.g., conductive pillars such as copper pillars, shown including solder contact portions  136  or solder bumps  136 ) are provided on semiconductor element  132 . Bonding tool  110  is lowered such that upper conductive structures  138   a ,  138   b  contact lower conductive structures  144   a ,  144   b  (e.g., see  FIG. 1B ). As illustrated in  FIG. 1B , through a bonding process (e.g., a thermocompressive bonding process) solder contact portions  136  are melted, and then re-solidified as solder interfaces  138 , providing a permanent conductive coupling between ones of upper conductive structures  138   a ,  138   b  and lower conductive structures  144   a ,  144   b . Although  FIGS. 1A-1B  illustrate only two pairs of conductive structures (pair  138   a ,  144   a  and pair  138   b ,  144   b ), this is of course a simple example for ease of explanation. In practice, any number of pairs of conductive structures may be provided (e.g., tens of conductive structure pairs, hundreds of conductive structure pairs, etc.). 
       FIG. 2  illustrates elements of bonding machine  200  including bond stage  204  carrying support structure  208  (where support structure  208  includes a plurality of bonding locations  206 ), where bond stage  204  (along with support structure  208 ) is configured to travel along an x-axis range of motion. Bonding machine  200  also includes bond head assembly  202  carrying bonding tool  210 . Bond head assembly  202  (along with bonding tool  210 ) is configured to travel along a y-axis range of motion, along a z-axis range of motion, and about a theta (θ) axis. Motion system  212  is also provided, and is configured to travel along an x-axis range of motion and a y-axis range of motion (independent of the x-axis range of motion of bond stage  204 , and independent of the y-axis range of motion of bond head assembly  202 ). In  FIG. 2 , motion system  212  is a motion system of an optical assembly of bonding machine  200  carrying look-up camera  216  and look-down camera  214 . In an exemplary bonding operation, a pick tool (not shown) removes a semiconductor element (e.g., a bare die) from a wafer (or other semiconductor element source). The pick tool, with the semiconductor element, moves (e.g., along an x-axis range of motion) to a transfer position (not shown). Bond head assembly  202  also moves to the transfer position, where the semiconductor element is transferred from the pick tool to bonding tool  210 . Support structure  208  is aligned in a given position along its x-axis range of motion. Bond head assembly  202  moves along its y-axis range of motion to a position above a bonding location of a substrate (not shown) supported by support structure  208 . Bond head assembly  202  is lowered along its z-axis range of motion such that bonding tool  210  is able to bond the semiconductor element to the bonding location of the substrate. This process may be repeated such that a number of semiconductor elements from semiconductor element source (not shown) may be bonded to respective bonding locations on the substrate. In connection with this bonding process, an imaging system (e.g., including cameras  214  and  216 ) is configured for use in determining proper placement and alignment of the semiconductor elements to respective bonding locations on the substrate. For example, look-up camera  216  may be used to image a semiconductor element carried by bonding tool  210 , and look-down camera  214  may be used to image a bonding location of the substrate. 
     Unless provided otherwise, elements in drawings other than  FIG. 2 , but having similar reference numerals as those shown and described above with respect to  FIG. 2  (e.g., numerals that are the same except the first numeral, such as bonding tool  210  and bonding tool  310 ), are substantially the same element. Likewise, the exemplary bonding operation described above with respect to  FIG. 2  also applies to the subsequent drawings and embodiments of the present invention. 
       FIG. 3  illustrates elements of bonding machine  300  including bond stage  304  carrying support structure  308  (including bonding locations  306 ), where bond stage  304  (along with support structure  308 ) is configured to travel along an x-axis range of motion. Bonding machine  300  also includes bond head assembly  302  carrying bonding tool  310 . Bond head assembly  302  (along with bonding tool  310 ) is configured to travel along a y-axis range of motion, along a z-axis range of motion, and about a theta (θ) axis. Motion system  312  is also provided, and is configured to travel along an x-axis range of motion and a y-axis range of motion. Motion system  312  is a motion system of an optical assembly of bonding machine  300  carrying look-up camera  316  and look-down camera  314 . Bonding machine  300  also includes calibration tool  318  carried by motion system  312  (and coupled to motion system  312  through tool attachment bracket  320 ). Calibration tool  318  includes arm portion  328  that supports contact portion  322 . Arm portion  328  may be, for example, a compliant beam portion configured to be compliant in a z-axis direction, and configured to support contact portion  322  of calibration tool  318 . Contact portion  322  includes upper contact portion  324  and lower contact portion  326 . Upper contact portion  324  and lower contact portion  326  are opposing contact portions each of which defines respective spherical surfaces, where such contact portions may be formed of a hard material (e.g., a hard metallic material). That is, each of contact portions  324 ,  326  has a spherical contact surface—where the spherical contact surface may be a portion of a spherically shaped contact portion (as shown in  FIG. 3 ), or may be a full sphere ball-shaped contact portion. As will be explained in greater detail below—when calibration tool  318  is in a desired position between bonding tool  310  and support structure  308 , bonding tool  310  is lowered along the z-axis until it contacts upper contact portion  324  and then continues downward, driving lower contact portion  326  into contact with a contact region of one of bonding locations  306  of support structure  308 . While driving lower contact portion  326  downward, arm portion  328  is flexed and as such, arm portion  328  is desirably compliant in the z-axis direction. After contact is established between lower contact portion  326  and the contact region of bonding location  306 , a z-axis height measurement is made, for example, using a z-axis encoder. Thus, a z-axis height value is established. 
     The z-axis height value measurement may be made for a plurality of the bonding locations  306  of support structure  308 . Further, the z-axis height value may be made for a plurality of positions within each bonding location  306 . A detail of the portion of  FIG. 3  is shown in  FIG. 4A . Specifically,  FIG. 4A  illustrates a plurality of positions (i.e., positions  306   a ,  306   b ,  306   c ,  306   d ,  306   e , and  306   f —each marked with a cross-shaped marking) within one of the plurality of bonding locations  306 . Thus,  FIG. 4A  illustrates an exemplary progression for determining z-axis height values for a plurality of positions within bonding location  306 . That is, a z-axis height value is obtained at position  306   a  using contact portion  322  of calibration tool  318 . Then, calibration tool  318  is moved and another z-axis height value is obtained at position  306   b  using contact portion  322 . This process is repeated to obtain z-axis height values at positions  306   c ,  306   d ,  306   e , and  306   f . While  FIG. 4A  illustrates 6 positions within bonding location  306 , it is understood that any number of positions (e.g., 10 positions, 50 positions, etc.) for obtaining z-axis height values may be utilized in each bonding location  306 . 
       FIGS. 4B-4D  illustrate an exemplary process of using bonding tool  310  to bring contact portion  322  (of calibration tool  318 ) into contact with bonding location  306  of support structure  308 . More specifically,  FIG. 4B  illustrates contact portion  322  of calibration tool  318  after it has been positioned (e.g., moved along its x and/or y motion axes using motion system  312 ) between bonding tool  310  and support structure  308 .  FIG. 4C  illustrates bonding tool  310  having been lowered to a position where its contacts upper contact portion  324  of contact portion  322 . Bonding tool  310  continues to be lowered until, as shown in  FIG. 4D , bonding tool  310  drives lower contact portion  326  of contact portion  322  to be in contact with bonding location  306  of support structure  308  (i.e., at a contact position, while contact portion  322  remains in contact with bonding tool  310 . At this position, a z-axis height value is determined (e.g., using a z-axis encoder) for the contact position. 
       FIGS. 5 and 7  are flow diagrams in accordance with exemplary embodiments of the present invention. As is understood by those skilled in the art, certain steps included in the flow diagrams may be omitted; certain additional steps may be added; and the order of the steps may be altered from the order illustrated. 
       FIG. 5  illustrates a method of determining a level of parallelism between a bonding tool (e.g., a contact portion of the bonding tool configured to contact a semiconductor element during bonding of the element to a substrate) and a support structure (supporting that substrate) of a bonding machine. At step  500 , a contact portion of a calibration tool is positioned between the bonding tool and a bonding location of the support structure. For example, in  FIG. 3 , contact portion  322  has been positioned (using motion system  312 , which travels along the x and y-axes, independent of bond head assembly) between bonding tool  310  and one bonding location  306  of support structure  308  (e.g., also see  FIG. 4B ). At step  502 , the bonding tool is lowered to drive the contact portion of the calibration tool to a contact position within the bonding location. For example, see  FIG. 4C-4D , where bonding tool  310  has driven contact portion  322  into contact with bonding location  306 . At step  504 , a z-axis height value is determined for the contact position when each of the bonding tool and the support structure is in contact with the contact portion of the calibration tool. At step  506 , each of steps  500 ,  502 , and  504  are repeated for each of a plurality of contact positions within the bonding location, thereby determining z-axis position data including the z-axis height values for each of the plurality of contact positions. For example, referring to  FIG. 4A , each of steps  500 ,  502 , and  504  may be repeated for each of positions  306   a ,  306   b ,  306   c ,  306   d ,  306   e , and  306   f  within bonding location  306 . After the z-axis height values have been determined for each of the positions (a “Yes” at step  506 ) then the process moves to step  508 —if not (a “No” at step  506 ), the process is repeated (steps  500 ,  502 , and  504 ). 
     At step  508 , each of steps  500 ,  502 ,  504 , and  506  are repeated for each of a plurality of bonding locations, thereby determining z-axis position data for each of the plurality of bonding locations. For example, referring to  FIG. 3 , each of steps  500 ,  502 ,  504 , and  506  may be repeated for each of the plurality of bonding locations  306 . After the z-axis position data has been determined for each of the bonding locations (a “Yes” at step  508 ) then the process moves to step  510 —if not (a “No” at step  508 ), the process is repeated (steps  500 ,  502 ,  504 , and  506 ). 
     The z-axis position data for each of the bonding locations may then be analyzed. That is, the z-axis position data may be processed to determine a level of parallelism for each of the bonding locations, and if that level of parallelism meets predetermined criteria through analysis of the z-axis position data. At step  510 , a determination is made as to whether the z-axis position data for each of the bonding location meets predetermined criteria (e.g., using a computer system of the bonding machine). If the predetermined criteria is met, the process may be considered complete. 
     Of course this determination (of step  510 ) may be made using various different techniques. In one example, a computer system may accomplish step  510  by determining if each of the z-axis height values (included in the z-axis position data for a given bonding location) is within a predetermined tolerance of each other. An exemplary acceptable tolerance range is 2 microns. In a second example, a computer system may accomplish step  510  using software to generate a best fit plane for the bonding location using the z-axis position data for the bonding location. Then, a determination is made as to whether the best fit plane for each bonding location falls within an acceptable range of criteria. An exemplary acceptable range of criteria may be defined by one or more slope values (e.g., a slope per unit length along the best fit place, etc.). Of course, other techniques for making the determination of step  510  are contemplated. 
     In accordance with certain exemplary embodiments of the present invention, in the event that the z-axis position data does not meet the predetermined criteria (e.g., as described above in connection with step  510 ) a closed loop process may be used to make a system adjustment. Such an adjustment may be manual (i.e., requiring operator intervention) or automatic (i.e., an adjustment made automatically without operator intervention). At step  512 , at least one of the bonding tool and the support structure is adjusted if the z-axis position data for at least one bonding location does not meet the predetermined criteria. An exemplary adjustment at step  512  may be a change to an orientation of a contact portion of the bonding tool. For example, the orientation of the contact portion of the bonding tool may be changed by unlocking an adjust mechanism of the bonding tool (e.g., an active or passive tilt adjust mechanism, such as an air bearing system), changing the bonding tool contact portion orientation (e.g., by changing the height or angle at a corner of the bonding tool contact portion based on an error as determined by the computer system of the bonding machine), and then relocking the adjust mechanism. Another exemplary adjustment at step  512  may be a change in the support structure mounting (e.g., a change in one corner of the support structure). Of course, other adjustments are contemplated. After step  512 , the process may optionally repeat (returning back to step  500 ) in order to determine if the z-axis position data for each of the bonding locations meet the predetermined criteria—that is, to determine if the adjustment had the intended result. The process may repeat (with multiple adjustments) until the predetermined criteria are met. 
       FIG. 6  illustrates elements of bonding machine  300   a  (which is substantially similar to bonding machine  300  of  FIG. 3 , except as explained below). Bonding machine  300   a  includes flux station  640  configured to provide flux material (from a contact region of fluxing cavity  642 ) to solder contacts of semiconductor elements prior to bonding of a semiconductor element to a substrate. For example, referring to  FIG. 1A , solder contact portions  136  (of upper conductive structures  138   a ,  138   b ) on semiconductor element  132  may be “fluxed” by bringing them into contact with the flux material in fluxing cavity  642 . After this fluxing, upper conductive structures  138   a ,  138   b  are brought into contact with, and thermocompressively bonded to, lower conductive structures  144   a ,  144   b  (e.g., see  FIG. 1B ). In connection with such a fluxing operation (and the subsequent bonding operation)—it may be desirable to determine (and perhaps adjust) the level of parallelism between fluxing cavity  642  and bonding tool  310 . This may be accomplished using calibration tool  318 , in a manner substantially similar to the technique shown in  FIGS. 4B-4D . More specifically, a contact portion of bonding tool  310  is lowered into contact with contact portion  322 , and drives contact portion  322  into contact with a location within flux cavity  642 . A z-axis height value is obtained at this location (e.g., using a z-axis encoder). This process may be repeated for a plurality of x and y-axis locations within fluxing cavity  642 . As will be appreciated by those skilled in the art, depending upon the size of the semiconductor elements being bonded, only a portion of fluxing cavity  642  may be utilized during a fluxing operation. This portion of fluxing cavity  642  may be referred to as a “contact region”. 
       FIG. 7  illustrates a method of determining a level of parallelism between a contact portion of a bonding tool and a contact region of a flux station of a bonding machine. At step  700 , a contact portion of a calibration tool is positioned between a bonding tool and a contact region of the flux station (e.g., where an exemplary contact region is within fluxing cavity  642  shown in  FIG. 6 ). For example, in  FIG. 6 , contact portion  322  (not shown in  FIG. 6 ) has been positioned (using motion system  312 , which travels along the x-axis and y-axis, independent of bond head assembly) between bonding tool  310  and a contact region of fluxing cavity  642 . At step  702 , the bonding tool is lowered (in a manner similar to that shown in  FIGS. 4B-4D , but with respect to a flux station) to drive the contact portion of the calibration tool to a contact position within the contact region of the flux station. In this contact position, upper contact portion  324  of the calibration tool contacts the contact portion of the bonding tool, and lower contact portion  326  contacts the contact position within the contact region of fluxing cavity  642  simultaneously. At step  704 , a z-axis height value is determined for the contact position within the contact region of the fluxing cavity of the flux station. 
     At step  706 , each of steps  700 ,  702 , and  704  are repeated for each of a plurality of contact positions within the contact region of the flux station, thereby determining z-axis position data (including the z-axis height values) for the contact region of the flux station. After the z-axis position data has been determined (a “Yes” at step  706 ) then the process moves to step  708 —if not (a “No” at step  706 ), the process is repeated (steps  700 ,  702 , and  704 ). The z-axis position data for the contact region may then be analyzed. That is, the z-axis position data may be processed to determine a level of parallelism for the contact region, and if that level of parallelism meets predetermined criteria through analysis of the z-axis position data. At step  708 , a determination is made as to whether the z-axis position data for the contact region of the flux station meets predetermined criteria (e.g., using a computer system of the bonding machine). If the predetermined criteria is met, the process may be considered complete. 
     This determination (of step  708 ) may be made using various different techniques. In one example, a computer system may accomplish step  708  by determining if each of the z-axis height values (included in the z-axis position data for the contact region) is within a predetermined tolerance of each other. An exemplary acceptable tolerance range is 2 microns. In a second example, a computer system may accomplish step  708  using software to generate a best fit plane for the contact region of the flux station. Then, a determination is made as to whether the best fit plane for the flux station falls within an acceptable range of criteria. An exemplary acceptable range of criteria may be defined by one or more slope values (e.g., a slope per unit length along the best fit place, etc.). Of course, other techniques for making the determination of step  708  are contemplated. 
     In accordance with certain exemplary embodiments of the present invention, in the event that the z-axis position data does not meet the predetermined criteria (e.g., as described above in connection with step  708 ) a closed loop process may be used to make a flux station adjustment. Such an adjustment may be manual (i.e., requiring operator intervention) or automatic (i.e., an adjustment made automatically without operator intervention). At step  710 , the contact region of the flux station is adjusted if the z-axis position data (for at least one location) does not meet the predetermined criteria. An exemplary adjustment at step  710  may be a change in the contact region mounting (e.g., a change in one corner of flux cavity  642  shown in  FIG. 6 ). Of course, other adjustments are contemplated. After step  710 , the process may optionally repeat (returning back to step  700 ) in order to determine if the z-axis position data for each of the bonding locations meet the predetermined criteria—that is, to determine if the adjustment had the intended result. The process may repeat (with multiple adjustments) until the predetermined criteria are met. 
     The various processes described herein (e.g., the processes described in connection with  FIGS. 5 and 7 ) may be performed at any desired interval. For example, such processes may be performed at machine set-up, any time a new application specific support structure (e.g., a p-part) is installed on the machine, at a predetermined interval (e.g., a predetermined time period, a predetermined number of bonds/operations), etc. 
     The exemplary machines and processes described herein (e.g., the processes described in connection with  FIGS. 5 and 7 ) may be used to measure and then store the parallelism data (e.g., z-axis height values, z-axis position data, etc.). For example, such parallelism data may be stored in the memory of the bonding machine, and may be used later as an input to an adjustable system element (e.g., an adjustable bonding tool such as a repositionable tilt adjust bonding tool contact surface), either automatically or manually. Such an adjustment may be made with, or without, re-checking the parallelism data to determine if the adjustment achieved the desired result. 
     The exemplary machines and processes described herein may also be applied to a bond stage planarity (flatness) determination and/or adjustment. That is, it may be desirable to detect a level of planarity (flatness) of the bond stage (independent of bonding locations on an application specific support structure. For example, using the calibration tool described herein, a plurality of z-axis height measurements may be made at different positions of the bond stage to determine its overall planarity (flatness). 
     As will be appreciated by those skilled in the art, z-axis height values for the various methods described herein may be measured with respect to any of a number of positions. That is, the absolute z-height is not as important as the relative z-height measured from position to position, and from bonding location to bonding location. Those skilled in the art will appreciate the use of z-axis encoders in semiconductor packaging equipment (such as wire bonders) to obtain such z-axis height values. 
     As will be appreciated by those skilled in the art, in connection with certain exemplary embodiments of the present invention, accurate and repeatable detection of contact between certain elements is desired. For example, it may be desired to obtain z-axis position data when each of the bonding tool and the support structure is in contact with the contact portion of the calibration tool (e.g., see  FIG. 4D ). The detection of this contact may be achieved using any of a number of techniques, as will be understood by those skilled in the art. Such exemplary techniques include monitoring at least one bond head assembly characteristic such as a bond head assembly velocity, a bond head assembly force, and a bond head assembly z-axis position, amongst others. Such characteristics may be monitored instantaneously, or may be monitored over a period of time, in order to recognize a signature by which contact may accurately be declared. More specifically, in an example where a bond head assembly z-axis position is monitored to declare contact—after the bond head assembly reaches a z-axis position (and remains at such position in spite of a force being applied to move further along the z-axis) contact may be declared. In such an example, after contact is declared the bonding machine may be operated in a constant force mode for the retrieval of the z-axis position data. The constant force in the constant force mode may be provided using a z-axis motor of the bond head assembly, which may optionally be regulated using a force sensor providing feedback of an actual sensed force value. 
     Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.