Patent Publication Number: US-6340112-B1

Title: Stepwise autorotation of wire bonding capilliary

Description:
This application is a Divisional Application of Ser. No. 08/992,270 filed Dec. 17, 1997 now U.S. Pat. No. 5,996,877, which claims priority under 35 USC 119(e)(1) of provisional application 60/033,483, filed Dec. 19, 1996. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present invention generally relates to a wire bonding process and capillaries used in the wire bonding process during the manufacture of electronic integrated circuit chip packages and, more particularly, to stepwise autorotation of wire bonding capillaries. 
     BACKGROUND OF THE INVENTION 
     Integrated circuit chip packages are typically formed by mounting an integrated circuit chip on a lead frame and coupling these two elements to form a package. The integrated circuit chip and lead frame may be encapsulated. Typically, the chip includes a number of bond pads which may be positioned about a perimeter of the chip according to a predetermined spacing between the bond pads. The lead frame typically includes a number of leads about a perimeter thereof. One type of lead frame, for example, has a generally rectangular shape with each side of the rectangle having a number of leads. The leads may each have a relatively narrow elongated shape. 
     A lead frame may be said to have an X direction and a Y direction. The X direction is perpendicular to one pair of opposing sides and the Y direction is perpendicular to the other pair of opposing sides. Typically, each lead has a relatively narrow elongated shape defining a lead axis. The lead axis for any given lead frame may extend in the X or Y direction, or be offset by an angle from either the X or Y direction. The angle of offset may vary from lead to lead. Moving from the center of a given side of the lead frame toward the corner leads, the lead axes may be angularly offset from perpendicular by increasing amounts. Also, a bonding path is defined by the direction from a bond pad to a corresponding lead. The bonding wire may extend along the bonding path. For any given set of corresponding bond pads and leads, the bonding path may extend in the X or Y direction, or be offset by an angle from either the X or Y direction. 
     In order to electrically couple the integrated circuit chip to the leads of the lead frame, a wire bonding technique is often used. A wire bonding machine may have a spool of bonding wire mounted on the machine. The bonding wire may be threaded through a capillary which is mounted to a horn of the wire bonding machine. The horn may be manipulated to move the capillary both vertically and horizontally. Typically, the wire bonding machine includes a device for heating or applying a spark to an end of the bonding wire which protrudes from an exit end of the capillary. The molten wire may form the shape of a ball which is placed on a target bond pad by manipulating the horn to move the capillary. 
     After this bond pad bond is created, a sufficient amount of bonding wire is released to allow the capillary to be moved to a location near an inner end of a target lead of the lead frame. The capillary is manipulated to connect the bonding wire to the inner end of the target lead and cut off the bonding wire so that the bonding wire protruding from the exit end of the capillary is now free to form a new wire bond between a new target bond pad and target lead. Any type of suitable bond may be made at either the bond pad or the lead, including ball bonds, stitch bonds and wedge bonds. A ball bond may be used, for example, at the bond pad. A stitch bond may be used, for example, at the lead. To complement the bonding process the package may be heated. Also, ultrasonic energy may be applied. 
     Problems in wire bonding techniques arise in part from the desire to increase the number of leads in a given package and to make integrated circuit chip packages smaller and smaller. This may require that the bonding pads located on the chip be made smaller and be spaced closer together. The same can be said for the leads on a lead frame. 
     The exit end of a wire bonding capillary is often referred to as the capillary face. Previous capillaries have had a circular face. A disadvantage of having a capillary with a circular face is that the spacing between bonds is limited. After a bond is made at a particular bond pad, for example, if the adjacent bond pad is too close then the capillary face may strike the ball bond which has been made at the first bond pad during the process of making a bond on the adjacent bond pad. One method for solving this shortcoming is to use a wire bonding capillary with a non-circular face. This type of approach is shown, for example, in U.S. Pat. No. 5,544,804 issued to Test et al., which is hereby incorporated by reference for all purposes. The Test et al. patent shows a BowTI™ capillary having a non-circular face. The face of a BowTI™ capillary may have a shape which includes a pair of opposed convex sides joining a pair of opposed concave sides. The BowTI™ capillary may be generally described as having a longitudinal axis extending across the midpoints of the convex sides and through the center of the BowTI™. The BowTI™ capillary allows ball bonds, for example, to be made closer to one another than with a circular capillary face. This can be accomplished because the concave sides avoid striking adjacent bonds. The BowTI™ capillary can also make other types of bonds including stitch bonds. 
     A need arising from the use of capillaries having non-circular faces is precise alignment of the longitudinal axis of the capillary face along either the X or Y direction of the lead frame, or along the longitudinal axis of a target lead, or along a given bonding path as necessary. Precise alignment of non-circular capillaries is especially difficult due to the relatively small size of a typical capillary face (e.g., 4-8 mils). Improper alignment of the capillary, particularly in view of the decreasing size of integrated circuit chip packages, can lead to defective wire bonds during the manufacturing process. This can result from many factors including improper positioning of the capillary face over the bond pad, the lead or both. Defective wire bonding can also occur when improper alignment causes the capillary to strike and/or damage an existing bond during the formation of a subsequent bond. Other problems, shortcomings and disadvantages of known capillaries and wire bonding techniques exist. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to address the needs associated with capillaries used in wire bonding. 
     It is a further object of the present invention to address the needs associated with wire bonding techniques. 
     It is a further object of the present invention to provide a capillary for a wire bonding machine which may be easily aligned during installation of the capillary into the wire bonding machine. 
     It is a further object of the present invention to provide a capillary for wire bonding which may be easily aligned and realigned during the wire bonding process. 
     It is a further object of the present invention to provide a capillary, the alignment of which may be easily established and/or checked during use of the capillary. 
     It is a further object of the present invention to provide automated, stepwise rotation of wire bonding capillaries. 
     To accomplish these and other objects of the present invention, a rotation device is provided for imparting stepwise rotation to a wire bonding capillary. In a first embodiment, the device includes a first part adapted to be coupled to the capillary and a second part engageable with the first part to impart stepwise rotation to the capillary. 
     According to one aspect the first part is a first rotation element and the second part is a second rotation element. The first and second rotation elements may form a click ring. The first and second rotation elements may form a cam-roller device. 
     According to another aspect, a wire bonding capillary includes a tubular body portion and a first rotation element coupled to the tubular body portion. The first rotation element is engageable with a second rotation element to impart stepwise rotation to the capillary. 
     According to another embodiment, a wire bonding machine includes a horn and a capillary rotatably mounted on the horn. A rotation device is at least partially coupled to the capillary and adapted to impart stepwise rotation to the capillary. 
     According to another embodiment a method of wire bonding is provided. A capillary face is aligned along a first direction. The capillary is used to make a first wire bond. The capillary face is realigned along a second direction. The capillary is used to make a second wire bond. Realignment may be accomplished by rotating the capillary in a stepwise manner. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention and for further features and advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is an elevation view of a wire bonding capillary; 
     FIG. 2 is a cross section of the wire bonding capillary of claim  1  taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is a horn of a wire bonding machine; 
     FIG. 4 is a cross section of the horn of FIG. 3 taken along line  4 — 4  of FIG. 3; 
     FIG. 5 is a rotation device in accordance with a first embodiment of the present invention; 
     FIG. 6 shows a first position of the rotation device of FIG. 5; 
     FIG. 7 shows a second position of the rotation device of FIGS. 5 and 6; 
     FIG. 8 shows a rotation device according to a second embodiment of the present invention and in a first position; 
     FIG. 9 is a top view of the rotation device of FIG. 8 viewed in the direction of arrows  9 — 9  in FIG. 8; 
     FIG. 10 shows a second position of the rotation device of FIGS. 8 and 9; 
     FIG. 11 is a top view of the rotation device of FIG. 10 viewed in the direction of arrows  11 — 11  in FIG. 10; and 
     FIG. 12 shows a rotation device and a wire bonding machine in accordance with a third embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Wire bonding machines are generally known. A typical wire bonding machine includes a spool of bonding wire which may comprise any suitable bonding material such as gold. The bonding wire is fed through a guide which is generally known as a capillary. This capillary also acts as the bonding tool. The capillary may be mounted on an arm of the wire bonding machine known as a horn. The present invention, among other things, contemplates rotatably mounting the capillary on the horn and providing a device which enables stepwise rotation of the capillary about its longitudinal axis. If the capillary is precisely aligned according to an initial alignment (e.g., upon installation of the capillary onto the horn), then the stepwise movement of the capillary ensures rotation of the capillary by precise angular amounts. 
     A wire bonding system may include a wire bonding machine which has a horn. A capillary is mounted into the horn and guides bonding wire from a source to various bonding points on the integrated circuit chip package. The capillary may have one or more indicators located thereon which provide one or more signals to be received by one or more detectors spaced from the capillary. The signals indicate the rotational alignment of the capillary. Therefore, the signal also indicates the direction of an axis of the face of the capillary. Each signal may have a relative signal strength which indicates an angular offset of the capillary face compared to a predetermined, desired alignment. 
     During operation, the capillary may be rotated to a first rotational alignment at which the capillary face axis extends in a first direction. A first signal received by the detector indicates when the first rotational alignment has been achieved. A first bond may then be made at a first bond point (e.g., at a bond pad on the integrated circuit chip) by guiding the capillary to the first bond point. 
     The capillary may then be realigned by rotating the capillary to a second rotational alignment so that the capillary face axis extends in a second direction different from the first direction. A second bond may then be made at a second bond point (e.g., at a lead on the lead frame) by guiding the capillary to the second bond point. 
     The capillary may then be rotated back to the first direction or to a third direction for a subsequent bond (e.g., at a second bond pad on the integrated circuit chip). Rotation of the capillary is achieved by the cooperation of the indicators and detectors and the production of signals which indicate rotational alignment and realignment. The ability to precisely rotate the capillary is especially beneficial for capillaries with non-circular faces. An axis of a non-circular face is ideally aligned in the direction of bonding when a bond is made. For example, it may be desirable to align the capillary face axis along the lead axis. Furthermore, as wire bonds are made around an integrated circuit chip package, the direction of bonding may change. The present invention is adapted to changing bonding directions. Further aspects of an overall capillary alignment system are disclosed in U.S. patent application Ser. No. 08/993,638 (Attorney Docket No. TI-24970) which is assigned to Texas Instruments Incorporated. This application was filed on Dec. 19, 1996 and is hereby incorporated by reference for all purposes. 
     The present invention provides stepwise rotation of the capillary. This may either supplement or replace the use of indicators and detectors. As shown in greater detail in FIG. 1, capillary  10  has a tubular body comprising a shaft portion  20  which is integral with a tip portion  30 . The capillary has a longitudinal bore extending through its interior along the general direction of longitudinal axis AA. The longitudinal bore of capillary  10  has an entry end  40  and an exit end  50 . Bonding wire may be inserted into entry end  40  to extend through the interior of capillary  10  and exit from capillary  10  through exit end  50 . 
     Preferably, shaft portion  20  is cylindrical in shape and has a circular cross section as shown more clearly in FIG.  2 . However, other shapes may be used so long as the bonding wire may be threaded through the interior of capillary  10 . For example, the capillary may have a rectangular or elliptical cross section. Preferably, the shaft portion  20  of capillary  10  is defined by a longitudinal bore of diameter D i  and an outer surface having a cross-sectional diameter of D o . Preferably, inner diameter D i  is constant throughout an entire length of the bore of capillary  10 . However, if capillary  10  has a constant wall thickness, then D i  will vary according to changes in D o . 
     Preferably, tip portion  30  is tapered downwardly and inwardly from a first point  31 , where tip portion  30  meets shaft portion  20 , to a second point  32  located at the exit end of capillary  10 . Preferably, the outer diameter of tip portion  30  at first point  31  is equal to D o  of shaft portion  20 . Preferably, the outer diameter of tip portion  30  at second point  32  is a predetermined value which is less than the outer diameter at first point  31 . 
     Capillary  10  may be formed from any suitable material. However, it is preferable that capillary  10  be formed from a high-strength material. For example, capillary  10  may be formed from a high-strength ceramic material. 
     A horn of a wire bonding machine is depicted in FIGS. 3 and 4. Horn  60  has a capillary mounting receptacle  61  for mounting capillary  10  as shown. Horn  60  also preferably includes a locking mechanism  62  for selectively locking capillary  10  into capillary mounting receptacle  61 . Preferably, capillary  10  is freely rotatable about its longitudinal axis within mounting receptacle  61  when locking mechanism  62  is in the unlocked position. 
     Once capillary  10  is aligned according to a precise, predetermined initial alignment (e.g., so that the axis of the capillary face is aligned for X-direction bonding) it may be necessary to rotate capillary  10  about longitudinal axis AA by a precise angular amount. This may be necessary, for example, to align the axis of the capillary face along the Y-axis or in some other direction offset from either the X-axis or the Y-axis. For instance, a target lead might be oriented fifteen degrees offset counterclockwise from the X-axis. If the face of capillary  10  is initially aligned along the axis, then capillary  10  should be rotated precisely fifteen degrees counterclockwise (or 345 degrees clockwise) to ensure optimal bonding on the angularly offset target lead. 
     In accordance with the present invention, a device is provided to enable controlled stepwise rotation of the capillary in discrete incremental steps. A first part of the device is coupled to the capillary. A second part of the device is engageable with the first part to impart stepwise rotation to the capillary. 
     According to a first embodiment of the present invention, a device  100  for enabling precise, stepwise rotation of capillary  10  is depicted in FIGS. 5-7. As shown in FIG. 5, device  100  includes a first rotation element  110  and a second rotation element  120 . Preferably, first and second rotation elements  110  and  120  cooperate with one another to impart stepwise rotation to capillary  10 . 
     Preferably, first and second rotation elements  110  and  120  jointly form a click ring ratchet drive. It should be noted that other click ring configurations may be incorporated into the present invention. It should also be noted that stepwise multi-stable switches other than click rings may be incorporated into the present invention. 
     In accordance with the first embodiment, first rotation element  110  comprises a first ring  111  and second rotation element  120  comprises a second ring  122 . First ring  111  has at least one projection  113  formed thereon. Preferably, first ring  111  has a plurality of projections  113  formed on-an outer circumferential surface thereof and extending radially outward from the outer surface of first ring  111 . Each projection  113  preferably comprises a tooth having two longitudinal sides  115  and  116  and two sloped transverse sides  117  and  118 . First and second sloped transverse sides  117  and  118  join opposite ends of the longitudinal sides. Thus, first and second sloped transverse sides  117  and  118  have both a longitudinal component and a lateral component. Preferably, the sloped transverse sides  117  and  118  are sloped opposite one another. More preferably, the sloped transverse sides are sloped away from each other as they extend from first longitudinal side  115  toward second longitudinal side  116 . 
     As shown in FIGS. 6 and 7, first rotation element  110  is mechanically coupled to an exterior surface of capillary  10 . These two elements may be coupled together using any suitable bonding technique, such as adhesive bonding with consideration given to minimizing any interference with acoustical damping of the horn. Preferably, any bonding technique used will withstand the environmental conditions under which the capillary  10  will operate during the wire bonding process. Alternatively, first rotation element  110  may be integrally formed as a part of capillary  10 . As described in greater detail below, the device  100  should be positioned along the longitudinal axis of capillary  10  such that when device  100  is in a release position, capillary  10  is in the correct position along its longitudinal axis to perform the wire bonding function. 
     Second ring  122  preferably interengages with first ring  111 . Second ring  122  includes at least one notch to cooperate with the at least one projection  113  of first ring  111 . Preferably the at least one notch is defined by a portion of a cavity  121  formed in the inner surface of second ring  122 . Projections  113  extend radially outward from first ring  111  into cavity  121 . Preferably, second ring  122  includes a plurality of first notches  123  and a plurality of second notches  124 . First notches  123  are longitudinally spaced from second notches  124 . Preferably, notches  123  and  124  are formed in an inner surface of second ring  122 . The inner diameter of second ring  122  is formed to be slightly larger than the outer diameter of first ring  111 . This allows second ring  122  to be fitted onto the exterior of first ring  111  as shown in FIGS. 6 and 7. Also first and second rings should be movable longitudinally with respect to each other. 
     Preferably, each notch  123  has a first edge  131  and a second edge  132 . First edge  131  extends longitudinally. Second edge  132  is sloped and extends transversely. Thus, second edge  132  has both a longitudinal and a transverse component. First and second edges  131  and  132  meet at one end to form a limit of the respective notch  123 . At the other ends thereof, first and second edges  131  and  132  form a notch opening. Preferably, the longitudinal component of second edge  132  is equal to the length of first edge  131 . Also, the longitudinal component of second edge  132  is preferably equal to the longitudinal component of first sloped edge  117  of a projection  113 . Further, the transverse component of second edge  132  is preferably equal in both length and direction to the transverse component of first sloped edge  117  of a projection  113 . Thus, a first tip of a projection  113  fits snugly into a first notch  123 . 
     Preferably, each second notch  124  has a first edge  141  and a second edge  142 . First edge  141  extends longitudinally. Second edge  142  is sloped and extends transversely. Thus, second edge  142  has both a longitudinal and a transverse component. First and second edges  141  and  142  meet at one end to form a limit of the respective notch  124 . At the other ends thereof, first and second edges  141  and  142  form a notch opening. Preferably, the longitudinal component of second edge  142  is equal to the length of first edge  141 . Also, the longitudinal component of second edge  142  is preferably equal to the longitudinal component of second sloped edge  118  of a projection  113 . Further, the transverse component of second edge  142  is preferably equal in both length and direction to the transverse component of second sloped edge  118  of a projection  113 . Thus, a second tip of a projection  113  fits snugly into a second notch  124 . 
     Preferably, first notches  123  are formed at predetermined intervals about the longitudinal axis of capillary  10 . This will allow precise stepwise rotation of capillary  10 . For example, first notches  123  may be positioned at every five, ten, forty-five or ninety degrees. When the interval is relatively small, there are more rotational positions available for rotation of capillary  10 . In contrast, when the interval is relatively large, there are fewer rotational positions available. The intervals may be of any angular amount. Also, each interval can be the same or one interval can be of a different angular amount than another interval. The bonding process, the desired resolution/precision and the orientation of the lead frames and the leads will determine the angular intervals between first notches  123 . 
     Preferably, second notches  124  are offset angularly offset from first notches  123 . Otherwise, each second notch  124  should have dimensions corresponding to a respective, angularly adjacent first notch  123 . The relative offset between first and second notches  123  and  124  provides a partial angular rotation during a click function as described further below. This allows the first tip of a projection  113  to be moved past an opening before a release function described below. Preferably, the length of second longitudinal side  116  of each projection  113  is small enough to allow rotational movement of projections  113  within cavity  121 . 
     It should be noted that the first and second rotation elements described are merely an example of the click ring-type devices which may be used in accordance with the present invention. Other devices which provide detentes at stepwise intervals may be incorporated into the present invention. Also, it is not necessary, in all cases, that a first rotation element and a second rotation element be provided or, if provided, that the first rotation element be coupled to the capillary and the second rotation element be coupled to the horn. The specific components and their orientation will depend upon the stepwise rotation device selected. 
     Returning to the example provided in FIGS. 5-7, a first biasing mechanism  151  is provided to bias capillary  10  in a first longitudinal direction. Preferably, first biasing mechanism  151  comprises a spring which surrounds first and second rotation elements  110  and  120 . One end of spring  151  abuts a surface horn  60 . The other end of spring  151  abuts a click pad  160 . Click pad  160  is preferably integral with first ring  111  and extends beyond the radial limits of first and second rings  111  and  122 . Spring  151  tends to bias click pad  160  toward a release position. Thus, spring  151  biases projections  113  into first grooves  123 . Preferably, first biasing mechanism  151 , provides a continuous bias. That is, first biasing mechanism  151  continuously urges capillary  10  along the first longitudinal direction. 
     A second biasing mechanism  152  is provided for biasing the capillary in a second longitudinal direction (opposite the first longitudinal direction). Thus, second biasing mechanism  152  urges projections  113  into second grooves  124  against the continuous bias of first biasing mechanism  151 . Preferably, second biasing mechanism provides a periodic bias. That is, second biasing mechanism only urges capillary  10  in the second longitudinal direction when second biasing mechanism is activated. This can occur at predetermined or selected time intervals or randomly. However, activation of second biasing mechanism  152  should only occur when rotation of capillary  10  is desired. 
     Cantilever  152  may be coupled to horn  60 . Alternatively cantilever  152  may be coupled to another part of the wire bonding machine (not shown) or to a base separate from the wire bonding machine. Also, second biasing mechanism need not be a cantilever. Any device may be used which can provide the desired biasing force. 
     The operation of the rotation device  100  will now be described. It may be assumed, for example, that first notches  123  are spaced at five degree intervals. Capillary  10  is initially aligned with respect to a given axis, for example, the X-axis of the bonding platform of the wire bonding machine. A first bond is made, for example, at a first bond pad. It is then necessary to rotate the capillary so that the capillary face axis is aligned with the lead axis for the lead corresponding to the first bond pad. Assuming that the lead axis is offset from the X-axis by five degrees, for example, the capillary would be rotated by one click step (e.g., for five degrees of rotation). Then a bond would be made on the lead. The capillary might then be rotated back to the X-direction for the second bond pad. This could be accomplished by a sufficient number of clicks to rotate the capillary another 355 degrees. Subsequent realignment and bonding continue until all wire bonds have been made. 
     Initially, capillary  10  is in a release position such that second biasing mechanism  152  is not activated. Thus, first biasing mechanism  151  is free to urge the projections  113  into the first notches  123  as shown in FIG.  7 . To rotate capillary  10  to the desired position, second biasing mechanism  152  is activated as shown in FIG.  6 . Cantilever  152  pushes against click pad  160  against the force of spring  151 . This moves projections  113  in the second longitudinal direction. A point along each second sloped edge  118  engages a respective opening end of a second edge  142  of a second notch  124 . Due to the relative slopes of edges  118  and second edges  142  of second notches  124 , rotation is imparted to projections  113  and, therefore, to capillary  10 . Projections  113  continue to be forced in the second longitudinal direction until they reach the longitudinal limit of notches  124 . At this point, the click function is complete and capillary  10  has only been rotated a portion of a five-degree interval. However, this partial rotation function is important because it sufficiently rotates each projection  113  past a respective notch  124 . This ensures that during the following release function, projection  113  will be urged into a notch  123  adjacent to the notch  123  from which projection  113  exited at the start of the click function. If partial rotation was not provided, projections  113  would simply return to the same first notches  123 . 
     During a following release step (FIG.  7 ), second biasing mechanism  152  is deactivated. Spring  151  is free to urge capillary  10  in the first longitudinal direction. First sloped edges  117  engage the opening ends of second edges  132  of first notches  123 . The relative slopes of edges  117  and second edges  132  of notches  123  impart further rotation in the same direction as the partial rotation provided during the click step. Rotation continues until spring  151  has completely biased projections  113  into first notches  123 . At this point, capillary  10  has been rotated a precise five degrees. 
     The click and release steps are repeated an additional seventeen times to complete the ninety-degree rotation. Then, horn  60  and/or the bonding platform may be manipulated to provide Y-direction bonding. It should be understood that the configuration and procedure described may be modified to provide any amount of desired stepwise rotation in either a clockwise or counterclockwise direction about the longitudinal axis of capillary  10 . Also, it will be seen that a complete predetermined interval of rotation consists of the total of a first amount of rotation provided during the click step and a second amount of rotation provided during the release step. Thus, back and forth longitudinal movement of the capillary is translated into stepwise rotation of the capillary and a longitudinal force is translated into a rotational force. 
     A second embodiment of the present invention is depicted in FIGS. 8-11. A rotation device  200  includes a first rotation element and a second rotation element. The first rotation element is preferably a cam  211  and the second rotation element is preferably a roller  222 . Cam  211  and roller  222  cooperate to provide precise stepwise rotation of capillary  10 . 
     Cam  211  is coupled to capillary  10  by any suitable coupling technique such as adhesive bonding. Alternatively, cam  211  can be formed as an integral part of capillary  10 . Preferably, cam  211  is coupled to, and surrounds, a central portion of capillary  10 . As best seen in FIG. 9, cam  211  has a plurality of projections  212  interspersed between a plurality of grooves  213 . Preferably, projections  212  and grooves  213  are smoothly joined and rounded so as to provide a smooth transition for roller  222 . Preferably, roller  222  is rotatably mounted on a shaft  223 . Shaft  223  is preferably coupled to horn  60  and is only movable back and forth along a longitudinal axis of horn  60 . A biasing mechanism, such as a spring  230  is provided to bias roller  222  against cam  211 . 
     In an unstable position, as shown in FIGS. 8 and 9, cam  211  is oriented such that an outermost point on a projection  212  lies along a longitudinal axis of horn  60  and, therefore, contacts a respective point on roller  222 . In this situation, spring  230  is compressed. This position is unstable. Due to the biasing force of spring  230 , cam  211  will tend to rotate either clockwise or counterclockwise. Preferably, cam  211  is rotated, either automatically or by an operator, in a specific rotational direction depending upon the desired rotational alignment of capillary  10 . 
     In a stable position, as shown in FIGS. 10 and 11, roller  222  is biased into a groove  213 . In this situation, if no rotating force is applied to cam  211 , then cam  211  will not tend to rotate on its own. Further, due to the biasing force of spring  230 , and the fact that shaft  223  is only movable along the longitudinal axis of horn  60 , roller  222  tends to resist rotation of cam  211 . Thus, a certain amount of force is required to rotate cam  211  and cause roller  222  to move away from capillary  10 . The individual components can be designed such that a specific, predetermined force is necessary to rotate cam  211  against the resistance of roller  222 . 
     Preferably, grooves  213  are provided at predetermined intervals about the rotational axis of cam  211 . For example, grooves  213  may be provided at every five degrees. The spacing will depend upon the amount of rotational resolution required by the application using rotation device  200 . Preferably, at least one groove is aligned along an initial bonding axis and other grooves are aligned along other bonding axes of a lead frame undergoing the wire bonding process. 
     In operation, assuming five-degree spacing of grooves  213 , capillary  10  is aligned according to a precise initial alignment. Roller  222  is biased fully into a groove  213  at this point. If rotation of ninety degrees is required, for example, cam  211  is rotated such that roller  222  moves away from and toward capillary  10  in eighteen cycles. Roller  222  will then be biased fully into a groove  213  corresponding precisely to a ninety-degree rotational alignment of capillary  10 . 
     It should be noted that other types of cam arrangements may be used. For example, the cam and roller may be configured such that movement of roller  222  causes rotation of cam  211 . Also, the locations of cam  211  and roller  222  may be switched. Thus, any type of cam device is acceptable so long as it provides multiple stable positions of rotation for capillary  10 . 
     According to a third embodiment of the present invention, as depicted in FIG. 12, the rotation device of the present invention (e.g., device  100  or device  200 ) may be incorporated into a wire bonding machine. Machine  300  comprises a body  310  having a mounting platform  311 . Mounting platform  311  is adapted to receive a lead frame  312  for wire bonding. Machine  300  includes horn  360  attached thereto. Horn  360  has capillary  10  mounted in a mounting receptacle  361  thereof. Capillary  10  is rotatable with receptacle  361  as long as locking mechanism  362  is deactivated. Horn  360  may be manipulated to wire bond lead frame  312 . Machine  300  also includes a source (e.g., a spool) of bonding wire  320  mounted thereon. The bonding wire may be threaded through capillary  10  and used to complete wire bonds on the lead frame. 
     The rotation device is at least partially coupled to capillary  10 . Preferably, a first part of rotation device  330  is coupled to capillary  10  and a second part of rotation device  330  is separate from capillary  10  but engageable with the first part. The second part of rotation device  330  may be coupled to, or engage, horn  360 . 
     The first part of rotation device  330  is engageable with the second part to impart stepwise rotation to the capillary. Preferably, longitudinal movement of the first and second parts toward each other causes the first part to rotate relative to the second part. 
     According to a feature of the present invention, capillary  10  may have one or more first indicators incorporated into the body thereof to provide one or more signals to one or more detectors. The indicators may be of any type including active, passive, mechanical, electrical, optical, magnetic, and others. Additionally, one or more second indicators may be provided to cooperate with the one or more first indicators on capillary  10 . For example, in the arrangement shown FIG. 12, a first indicator (e.g., indicator  380 ) may comprise, for example, reflective markings. The markings may be optically detected. Preferably, at least one marking is aligned with the axis of the face of capillary  10 . A detector (e.g., a transducer  390 ) may detect the indicator and produce a corresponding detection signal. Preferably, the indicator and transducer are positioned such that when transducer  390  detects the indicator, the axis of the face of capillary  10  is precisely aligned in the desired direction of bonding (e.g., along the X-axis or Y-axis, or offset by a precise amount). The electrical signal from transducer  390  may be passed to a display (not shown) to indicate that capillary  10  is properly aligned. 
     Thus, the indicators provide signals, which may be detected and used to determine the rotational position of capillary  10 . Alternatively, the indicators may provide a signal which is received by a detector. The signal may have a relative signal strength. For example, the signal may be stronger when the first indicator and a detector are in a closest proximity to one another. The signal may weaken as these two elements are separated by rotation of capillary  10 . The strength of the sensed signal would indicate an amount of angular offset from a predetermined rotational alignment of capillary  10 . 
     The indicators  380  and detector  390  are preferably used to establish precise initial alignment of the capillary  10  and the rotation device  100  with respect to horn  360  and/or the bonding platform or lead frames. After initial alignment, and during the wire bonding process, precise rotation is preferably provided by the stepwise rotation device (e.g., device  100  or  200 ) as described above. Indicators  380  and detector  390  may be used during wire bonding to confirm the proper desired rotational alignment of capillary  10 . 
     According to another feature of the present invention, rotation and alignment may be completely controlled by a computer, such as computer  350  shown in FIG.  12 . In the example shown, rotation device  330  is a click ring. However, any rotation device according to the present invention may be used. In the example of a click ring, computer  350  determines the desired rotational position of the capillary. This can be established based on a predetermined configuration of a lead frame. 
     Preferably, the computer sends a message which activates a power source  370  which activates a cantilever, causing the cantilever to engage a click pad of rotation device  330 . A counting device (not shown) may be included to count the number of click-and-release cycles of the click ring. Precise rotation is achieved when a number of cycles has been performed which corresponds to the rotational alignment needed to align an axis of the capillary face along the desired direction. This direction may change from one bonding point to another. Therefore, the computer would control the alignment and realignment accordingly. 
     Optionally, when the indicators provide a signal to a detector that indicate capillary  10  has reached the desired rotational position, the detectors provide input to the computer. The computer sends a deactivation message to the rotation device and the wire bonding machine may then proceed with bonding. 
     According to an aspect of this feature, other sensing devices are provided to sense the orientation of each respective lead directly. This may be accomplished, for example, by known scanning techniques. This information is transmitted to the computer, which may send a corresponding activation message to the rotation device. The rotation device rotates the capillary to an exact position based on the orientation of a particular lead, as opposed to a predetermined orientation of a lead frame stored in the computer memory. 
     The present invention has thus been described in connection with the preferred embodiments, which are intended as examples only. It will be appreciated by those having ordinary skill in the relevant art that modifications may be made to these embodiments without departing from the scope and spirit of the invention as defined by the appended claims.