WO2009002345A1

WO2009002345A1 - Method of determining a height profile of a wire loop on a wire bonding machine

Info

Publication number: WO2009002345A1
Application number: PCT/US2007/072378
Authority: WO
Inventors: Gary S. Gillotti; Wei Qin; Jon W. Brunner; John Foley
Original assignee: Kulicke And Soffa Industries, Inc.
Priority date: 2007-06-28
Filing date: 2007-06-28
Publication date: 2008-12-31

Abstract

A method of determining a height profile of a wire loop is provided. The method includes: (1) moving a bonding tool towards a portion of the wire loop; (2) detecting when a portion of a conductive wire engaged with the bonding tool contacts the portion of the wire loop; (3) determining the height of the portion of the wire loop based on the position of the bonding tool when the portion of the conductive wire contacts the portion of the wire loop; and (4) repeating steps (1), (2), and (3) for a plurality of portions of the wire loop such that a height profile of at least a portion of the wire loop is determined.

Description

METHOD OF DETERMINING A HEIGHT PROFILE OF A WIRE LOOP ON A WIRE

BONDING MACHINE

FIELD OF THE INVENTION

[0001] The present invention relates to the formation of wire loops, and more particularly, to improved methods of making height measurements of wire loops.

BACKGROUND OF THE INVENTION

[0002] In the processing and packaging of semiconductor devices, wire bonding continues to be the primary method of providing electrical interconnection between two locations within a package (e.g., between a die pad of a semiconductor die and a lead of a leadframe). More specifically, using a wire bonder (also known as a wire bonding machine) wire loops are formed between respective locations to be electrically interconnected.

[0003] An exemplary conventional wire bonding sequence includes: (1) forming a free air ball on an end of a wire extending from a bonding tool; (2) forming a first bond on a die pad of a semiconductor die using the free air ball; (3) extending a length of wire in a desired shape between the die pad and a lead of a leadframe; (4) stitch bonding the wire to the lead of the leadframe; and (5) severing the wire. In forming the bonds between (a) the ends of the wire loop and (b) the bond site (e.g., a die pad, a lead, etc.) varying types of bonding energy may be used including, for example, ultrasonic energy, thermosonic energy, thermocompressive energy, amongst others.

[0004] It is desirable to know the height of portions of wire loops. For example, in order that a wire loop fit within a particular package, or in order that a wire loop provide a certain amount of clearance below said wire loop, such height data is desirable. Conventional systems for determining the height of a wire loop include optical systems such as those described in U.S. Patent Nos. 7,145,162 ("Wire Loop Height Measurement Apparatus and Method"); 5,621,218 ("Method and Apparatus Inspecting Bonding-Wire Status Using a Plurality of Light Sources"); 5,576,828 ("Bonding Wire Detection Method"); 5,347,362 ("Bonding Wire Inspection Method"); 4,942,618 ("Method and Apparatus for Determining the Shape of Wire or Like Article"); and 5,583,641 ("Bonding Wire Height Detection Method"). However, using such optical systems results in additional expense because of the components used, time delay issues, amongst other problems. [0005] Thus, it would be desirable to provide improved methods of determining the height profile of at least a portion of a wire loop.

SUMMARY OF THE INVENTION

[0006] According to an exemplary embodiment of the present invention, a method of determining a height profile of a wire loop is provided. The method includes: (1) moving a bonding tool towards a portion of the wire loop; (2) detecting when a portion of a conductive wire engaged with the bonding tool contacts the portion of the wire loop; (3) determining the height of the portion of the wire loop based on the position of the bonding tool when the portion of the conductive wire contacts the portion of the wire loop; and (4) repeating steps (1), (2), and (3) for a plurality of portions of the wire loop such that a height profile of the wire loop is determined.

[0007] The methods of the present invention may also be embodied as an apparatus (e.g., as part of the intelligence of a wire bonding machine), or as computer program instructions on a computer readable carrier (e.g., a computer readable carrier used in connection with a wire bonding machine).

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The invention is best understood from the following detailed description when read in connection with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawing are the following figures:

Fig. IA is a side sectional view of a wire loop and a bonding tool, the wire loop providing interconnection between two bonding locations of a semiconductor device, in accordance with an exemplary embodiment of the present invention;

Fig. IB is a view of the bonding tool of Fig. IA in contact with a portion of the wire loop of Fig. IA in accordance with an exemplary embodiment of the present invention; Fig. 1C is a view of the bonding tool of Fig. IA in contact with another portion of the wire loop of Fig. IA in accordance with an exemplary embodiment of the present invention;

Fig. ID is a view of the bonding tool of Fig. IA in contact with yet another portion of the wire loop of Fig. IA in accordance with an exemplary embodiment of the present invention;

Fig. IE is a view of the bonding tool of Fig. IA in contact with yet another portion of the wire loop of Fig. IA in accordance with an exemplary embodiment of the present invention;

Fig. 2 is a detailed view of a portion of the semiconductor device and a portion of the wire loop of Fig. IA in accordance with an exemplary embodiment of the present invention;

Fig. 3A is a top view of a portion of a semiconductor die, a portion of a leadframe, and a wire loop providing interconnection between a die pad of the semiconductor die and a lead of the leadframe, in accordance with an exemplary embodiment of the present invention;

Fig. 3B is a detailed view of the wire loop of Fig. 3A where the wire loop has been labeled with various contact points for making height measurements of the wire loop; and

Fig. 4 is a flow diagram illustrating a method of determining a height profile of a wire loop in accordance with an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0009] According to certain exemplary embodiments of the present invention, methods of measuring/determining a height profile of at least a portion of a wire loop on a wire bonding machine is provided. For example, the methods may use existing detection circuitry (e.g., a BITS system, that is, a bond integrity test system) that is conventionally used to detect if first bonds and second bonds of a wire loop are properly attached to their respective bonding locations (e.g., bond pads, leads, contacts, traces, etc.). [0010] According to such exemplary embodiments, after a wire loop is formed

[e.g., where the wire loop provides electrical interconnection between two bonding locations such as (1) a die pad of a semiconductor die and (2) a lead of a leadframe], a free air ball is formed at the end of bonding tool (e.g., a capillary). The bonding tool travels (e.g., with the wire clamp cycled open then closed) down toward the wire loop seating the free air ball at the tip of the bonding tool. The bonding tool moves downward toward a location (e.g., a predetermined or programmed location) along the wire loop. For example, the location may be determined by (1) manually targeting a location along the wire loop, or (2) automatically calculating a location along the wire loop. As the bonding tool travels down toward the selected portion of the wire loop, a detection circuit is activated (or already has been activated) to detect contact between the ball seated in the bonding tool and the wire loop.

[0011] For example, the detection circuit can detect a predetermined amount

(e.g., a very small amount) of current. Such a detection circuit may be particularly desirable when the detection circuit is a DC (i.e., direct current) based system. According to another example, the detection circuit can detect a predetermined change in capacitance that would occur when there is contact between the free air ball seated in the bonding tool and the wire loop. Such a detection circuit may be particularly desirable when the detection circuit is an AC (i.e., alternating current) based system. The detection circuit/system may be configured to be very sensitive to the electrical changed detected (e.g., a small amount of current flow, a small change in capacitance, etc), and as such, the wire loop will tend to be undeformed by the gentle contact of the free air ball.

[0012] After contact is detected between the free air ball and the selected portion of the wire loop, the height at the the selected portion of the wire loop is determined (e.g., is reported and stored in memory of the wire bonding machine). For example, the height of the wire loop at the selected portion can be determined using the z-encoder which is a conventional component of a wire bonding system for determining a z-height of the bonding tool (i.e., the height along the z-axis or vertical axis of the wire bonding operation).

[0013] In order to provide a height profile of the wire loop (or a portion of the wire loop) the operation described above is repeated at different locations along the wire loop. Thus, using data provided by the z-encoder at the various selected locations (in conjunction with the first and second bond locations) a height profile of the wire loop may be provided. [0014] Using the various methods of the present invention, real-time feedback regarding the height profile of a wire loop may be provided to the wire bonding machine (and/or an operator of the wire bonding machine). This height profile serves many uses. For example, this height profile may be used to optimize looping parameters to achieve a desired height profile. That is, looping parameters may be adjusted based on the measured height profile as part of an iterative process in order to achieve the desired loop height profile. Such adjustments to looping parameters may be made in any of a number of ways. For example, such adjustments may be made manually (e.g., by an operator of a wire bonding machine) in connection with an iterative process to obtain a desired height profile. Alternatievly, such adjustments may be made automatically in connection with a closed loop iterative process (e.g., the algorithm controlling the iterative process may adjust one or more looping parameters by a predetermined increment based on the height measurement at one or more locations along the height profile).

[0015] As another example, this height profile may be used to adjust portability between different wire bonding machines. That is, the same parameters may not achieve the same loop height profile in different wire bonding machines, and as such, the present invention may be used to determine the height profile on different wire bonding machines, and also may be used to achieve the substantially the same loop height profile on different wire bonding machines by adjusting parameters as part of the aforementioned iterative process.

[0016] These and other aspects of the present invention may be particularly useful in connection with complex loops/packages such as stacked and multi-tiered die packages. The present invention may be used to provide a three-dimensional analysis of wire loop shapes (in contrast to conventional two dimensional analyses).

[0017] Referring now to Fig. IA, a side view of wire loop 104 is provided. Wire loop 104 provides electrical interconnection between a first bonding location (i.e., bond pad 102b of semiconductor die 102) and a second bonding location (i.e., lead 100a of leadframe 100, where leadframe 100 supports semiconductor die 102). Wire loop 104 includes first bond 104a (e.g., ball bond 104a), wire span 104b, and second bond 104c (e.g., stitch bond 104c). First bond 104a is bonded to bond pad 102b of semiconductor die 102 (adjacent die pad 102a is also shown in Fig. IA). Second bond 104c is bonded to lead 100a of leadframe 100. [0018] Also shown in Fig. IA is detection system 106, bonding tool 108, conductive wire 110, free air ball 110a, wire clamp 112, and conductive path 114. More specifically, conductive wire 110 is engaged in bonding tool 108 to form wire bonds and the like. Wire clamp 112 is operated between closed and open positions in conjunction with a wire bonding operation. Free air ball 110a is formed on the end of conductive wire 110 (e.g., using a electronic flame-off wand or the like) and has been seated at the tip portion of bonding tool 108. Conductive path 114 (in the illustrated embodiment wire clamp 112 may be considered part of the conductive path) provides an electrical connection between conductive wire 110 and detection system 106.

[0019] Thus, in Fig. IA, exemplary system components are provided in connection with certain exemplary embodiments of the present invention just prior to approaching the wire loop (e.g., wire loop 104) with a portion of a conductive wire (e.g., free air ball 110 of conductive wire 110) engaged in a bonding tool (e.g., bonding tool 108). In order to determine the height profile of wire loop 104, bonding tool 108 repeatedly approaches (and contacts with free air ball 110a) different portions of wire loop 104 as shown in Figs. IB-IE.

[0020] Fig. IB illustrates bonding tool 108 having been lowered towards a portion of wire loop 104 until free air ball 110a is in contact with the portion of wire loop 104. Detection system 106 detects the contact between free air ball 110a and the portion of wire loop 104. A height position of the portion of the wire loop contacted by free air ball 110a is then determined using the position of bonding tool 108 (that is, the position of bonding tool 108 during the contact between free air ball 110a and the portion of wire loop 104). As is known to those skilled in the art, wire bonding machines often include encoder systems, vision systems, and the like for monitoring the position of the bonding tool.

[0021] In order to provide a "height profile" of a targeted portion of wire loop

104, or a height profile of the entire length of wire loop 104, this process described above is repeated for different portions of the wire loop.

[0022] Figs. IB-IE illustrate bonding tool 108 having been repeatedly raised and lowered such that free air ball 110a has contacted a number of portions of wire loop 104. More specifically, Fig. IB illustrates free air ball 110a in contact with a portion of wire loop 104 adjacent first bond 104a; Fig. 1C illustrates free air ball 110a in contact with a portion of wire loop 104 close to the end of the straight (e.g., horizontal) length of wire just before the downward kink; Fig. ID illustrates free air ball 110a in contact with a portion of wire loop 104 just after the kink; and Fig. IE illustrates free air ball 110a in contact with a portion of wire loop 104 farther down the sloped length extending toward second bond 104c. Of course, these illustrated points of contact are exemplary in nature. Different (and additional) points of contact with the wire loop may be selected as is desired to provide a height profile of a wire loop.

[0023] The actual determination of the loop height at each of the selected portions of the wire loop (where the height at each of the selected portions are used to provide a height profile of the wire loop) may be accomplished in any of a number of ways depending upon, for example, the wire bonding machine provided, the desired algorithm, etc. One approach to this determination is to establish a reference height such that the height of the portion of the wire loop can be determined by comparing (a) the position of the bonding tool when the portion of the conductive wire contacts the portion of the wire loop to (b) the reference height. Fig. 2 is a detailed view of a portion of the components shown in Fig. IA useful for explaining an exemplary approach to determining the height of a selected portion of a wire loop. As in Fig. IA, Fig. 2 illustrates bond pads 102a and 102b of semiconductor die 102, where semiconductor die 102 is supported by leadframe 100. Also illustrated in Fig. 2 are two "phantom" bonding tools 108 with corresponding free air balls 110a.

[0024] The left hand free air ball 110a is shown in contact with die pad 102a of semiconductor die 102. Thus, after this contact is established by detection system 106, a reference height is established at 0.5 (0.5 and the other measurements are unitless numbers provided for explanatory purposes only). The right hand free air ball 110a is shown in contact with a portion of wire loop 104. After this contact is established by detection system 106, a measured height of the contacted portion of wire loop 104 is determined to be 4.3. Thus, in relative terms, the actual height of the selected portion of wire loop 104 is 3.8 (that is, the measured height of 4.3 minus the reference height of 0.5 is 3.8).

[0025] Thus, in the example provided in Fig. 2, the reference height is selected to be the height of a bond pad (i.e., bond pad 102a) of a semiconductor device (e.g., semiconductor die 102) to which the wire loop has been bonded. Of course, other reference heights may be selected including, but not limited to, (a) a height corresponding to the first bond of the wire loop, (b) a height corresponding to the second bond of the wire loop, (c) a height corresponding to the leadframe surface or (d) a height corresponding to a surface of the semiconductor die. [0026] It is also noteworthy that in the exemplary scheme illustrated in Fig. 2, free air ball 110a is used to contact both (a) the reference height (i.e., bond pad 102a) and (b) wire loop 104. Thus, the height of free air ball 110a is not taken into account to determine the actual height because the free air ball is present at both contacts (i.e., the contact at bond pad 102a and the contact of the wire loop); however, in certain embodiments of the present invention, the height of free air ball 110a may be considered in the determination of the actual height of the wire loop. For example, if the reference height is established independent of free air ball 110a (e.g., independent of the position of bonding tool 108 with which free air ball 110a is engaged), then the height of the free air ball may be relevant when using the position of bonding tool 108 (with free air ball 110a engaged therewith) to determine the relative height of wire loop 104 (e.g., the height of free air ball 110a, or a partial/deformed height of free air ball 110a, may be substracted from the calculated wire loop height).

[0027] Fig. 3A is a top view of a portion of semiconductor die 302, a portion of leadframe 300, and wire loop 304 providing interconnection between die pad 302b of semiconductor die 302 and lead 300a of leadframe 300. More specifically, first bond 304a of wire loop 304 is ball bonded to die pad 302b, and second bond 304c of wire loop 304 is stitch bonded to lead 300a. Wire span 304b extends between first bond 304a and second bond 304c. Adjacent die pad 302a (which may be used as a reference point as described above with respect to die pad 102a in Figs. 1A-1E) is also shown.

[0028] Fig. 3B is a detailed view of wire loop 304. As is shown in Fig. 3B, wire loop 304 is broken into segments using points "A" through "R." For example, there are various ways of determining a height profile of a wire loop. For example, a plurality of points along the wire loop (i.e., portions of the wire loop) may be arbitrarily selected (e.g., automatically or manually) in order to determine the height profile. Alternatively, the plurality of points may be selected (e.g., in accordance with an algorithm or the like) at predetermined length increments along the wire loop. As shown in Fig. 3B, points "A" through "R" are at predetermined length increments along wire loop 304. Thus, in such an example, in order to determine a height profile of wire loop 304 a portion of a wire engaged in a bonding tool (e.g., a free air ball seated at the tip of a bonding tool) is brought into contact with wire loop 304 at each of points "A" through "R." By determining the height of wire loop 304 at each of the points, a height profile of wire loop 304 is provided. [0029] Of course, wire loops are formed in three dimensions, and often have bends and slopes in different planes. In Fig. 3B, a bend in a substantially horizontal plane (i.e., a plane parallel with the sheet of paper of Fig. 3B) is formed in wire loop at points "B", "C", "D", and "E." In recognition of the the fact that wire loops may be formed with different bends, slopes, etc, according to the present invention, a wire edge detection system may be used to detect the two outside edges of the wire loop. Thus, by knowing the 2 edges at a given point, the bonding tool may desirably target the approximate center of the wire loop at the desired location. For example, referring again to Fig. 3B, edges "Al" and "A2" have been detected (e.g., using a vision system or the like in connection with an edge detect algorithm) at point "A." By knowing the location of the edges, an approximate center of wire loop 304 at point A may be determined such that the bonding tool (with the free air ball seated at the tip) can approach the appropriate portion of wire loop 304 at point "A."

[0030] Of course, other techniques may be used to find the approximate center of wire loop 304 at point A (i.e., other than vision systems or the like). For example, the bonding tool (with a portion of a wire such as a free air ball engaged therewith) may be lowered to contact point A of wire loop 304 multiple times, where each time the bonding tool is moved laterally a very small amount. Through these repeated contacts, a determination of the approximate highest point at point A is enabled. More specifically, a wire used to form a wire loop typically has a round or circular cross section, where the portion of the wire exposed to contact by the bonding tool may be viewed as an "arc" of a circle. Thus, the bonding tool (e.g., with a free air ball engaged therewith) may contact multiple points along the "arc" of a circle, where the highest point of the "arc" is the actual center at point A (i.e., the midpoint between endpoints Al and A2). Such a technique may be particularly useful in devices with long wire spans, where the wire "sways" a small amount from its intended path.

[0031] However, any of a number of alternative methods may be utilized to find the desired point along the wire length for use in providing a height profile. For example, the locations may be manually targeted (e.g., by the operator) using the live video provided on the wire bonding machine. After selecting the desired points along the length of the wire span using the live video, the actual height measurements (using the bonding tool descending toward the selected points) may be conducted.

[0032] Yet another example relates to a relatively "straight" wire loop, where the wire loops are relatively straight lines in the X-Y plane extending between a first bonding location and a second bonding location. Knowing the positions of the first bonding location and the second bonding location, the present invention may utilize and algorithm or the like which specifies increments along the straight length at which to perform the height detection technique.

[0033] Fig. 4 is a flow diagram in accordance with certain exemplary embodiments of the present invention. As is understood by those skilled in the art, certain steps included in the flow diagram may be omitted; certain additional steps may be added; and the order of the steps may be altered from the order illustrated.

[0034] Fig. 4 is a flow diagram illustrating a method of determining a height profile of a wire loop in accordance with an exemplary embodiment of the present invention. At step 400, a bonding tool is moved towards a portion of the wire loop. At step 402, it is detected when a portion of a conductive wire engaged with the bonding tool (e.g., a free air ball seated at the tip of the bonding tool) contacts the portion of the wire loop. At step 404, a determination is made as to the height of the portion of the wire loop based on the position of the bonding tool when the portion of the conductive wire contacts the portion of the wire loop. At step 406, steps 400, 402, and 404 are repeated for a plurality of portions of the wire loop such that a height profile of the wire loop is determined. The portions of the wire loop included in the height profile could be any as desired in the particular application. For example, Figs. IB-IE illustrate free air ball 110a contacting exemplary portions of wire loop 104 in order to provide an exemplary height profile.

[0035] As provided above, the method illustrated in Fig. 4 may include additional or different steps. For example, the method may include a step of establishing a reference height such that the height of the portion of the wire loop can be determined at step 404 by comparing (a) the position of the bonding tool when the portion of the conductive wire contacts the portion of the wire loop to (b) the reference height. For example, the reference height may be established to be (a) a height of a bond pad of a semiconductor device to which the wire loop has been bonded; (b) a height corresponding to the first bond of the wire loop (e.g., a height at first bond after contact between a free air ball and the contact, a height at first bond prior to ultrasonic energy being applied, a height at first bond after ultrasonic energy is applied, etc.); (c) a height corresponding to the second bond of the wire loop (e.g., a height at second bond after contact between the end of the wire loop and the contact, a height at second bond prior to ultrasonic energy being applied, a height at second bond after ultraonic energy is applied, etc.); (d) a height corresponding to a surface of a substrate (e.g., a leadframe) to which a portion of the wire loop is bonded; or (e) a height corresponding to a surface of a semiconductor die to which a portion of the wire loop is bonded, amongst others.

[0036] Further, as described above, the steps of the method of Fig. 4 (or other methods within the scope of the present invention) may be repeated as part of an iterative process wherein a new wire loop is created in connection with each iteration. For example, the iterative process may be repeated until the height profile of the wire loop is within a predetermined height range (e.g., that the height profile meets predetermined height criteria). For example, such an iterative process may include changing one or more parameters of the wire bonding operation used to form the wire loop in connection with each iteration.

[0037] Step 402 described above may be accomplished using a variety of techniques. For example, step 402 may include detecting when a conductive path is established between (a) the portion of the wire loop, and (b) the portion of the conductive wire. For example, such a conductive path may be established by detecting at least one of (a) a predetermined current flow in the conductive path, (b) a predetermined change in capacitance between the conductive path and a ground connection of a wire bonding machine used to form the wire loop, and (c) a predetermined phase shift of current flowing in the conductive path.

[0038] In an exemplary embodiment of the present invention where step 402 includes detecting the establishment of such a conductive path, the conductive path may be established between (a) a detection system for detecting when the portion of the conductive wire engaged with the bonding tool contacts the portion of the wire loop, and (b) the wire loop. The conductive path may include components of a wire bonding system such as, for example, at least one of (a) a wire clamp for clamping the conductive wire engaged with the bonding tool (e.g., wire clamp 112 shown in Figs. 1A-1E), (b) a wire spool for supplying wire to the bonding tool (not shown), (c) a diverter element for assisting in the positioning of the conductive wire between the wire spool and the bonding tool (not shown), and (d) an air guide system for assisting in the positioning of the conductive wire between the wire spool and the bonding tool (not shown), amongst others.

[0039] As provided above, steps 400, 402, and 404 are repeated for a plurality of portions of the wire loop at step 406 of Fig. 4 in order to determine a height profile of the wire loop. For example, the plurality of portions of the wire loop may be spaced at predetermined increments between a first bonding point of the wire loop and a second bonding point of the wire loop (e.g., see Fig. 3B).

[0040] Although the present invention has been described primarily with respect to determining a height profile of a conductive wire loop, it is not limited thereto. For example, the techniques disclosed herein may be used to provide a height profile of a wire loop formed of a non-conductive wire (e.g., a conductive wire covered/coated with a non-conductive material). For example, detection of a capacitance change upon contact between (1) a free air ball engaged with a bonding tool and (2) the wire loop may be used to detect the contact therebetween, amongst other techniques.

[0041] 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.

Claims

What is Claimed:

1. A method of determining a height profile of a wire loop, the method comprising the steps of:

(1) moving a bonding tool towards a portion of the wire loop;

(2) detecting when a portion of a conductive wire engaged with the bonding tool contacts the portion of the wire loop;

(3) determining the height of the portion of the wire loop based on the position of the bonding tool when the portion of the conductive wire contacts the portion of the wire loop; and

(4) repeating steps (1), (2), and (3) for a plurality of portions of the wire loop such that a height profile of at least a portion of the wire loop is determined.

2. The method of claim 1 further comprising a step of establishing a reference height such that the height of the portion of the wire loop can be determined in step (3) by comparing (a) the position of the bonding tool when the portion of the conductive wire contacts the portion of the wire loop to (b) the reference height.

3. The method of claim 2 wherein the step of establishing a reference height includes at least one of (a) establishing the reference height to be a height of a bond pad of a semiconductor device to which the wire loop has been bonded; (b) establishing the reference height to be a height corresponding to a first bond of the wire loop; (c) establishing the reference height to be a height corresponding to a second bond of the wire loop; (d) establishing the reference height to be a height corresponding to a surface of a substrate to which a portion of the wire loop is bonded, or (e) establishing the reference height to be a height corresponding to a surface of a semiconductor die to which a portion of the wire loop is bonded.

4. The method of claim 1 wherein step (2) includes detecting when the portion of the conductive wire engaged with the bonding tool contacts the portion of the wire loop, wherein the portion of the conductive wire is a free air ball seated at the tip of the bonding tool.

5. The method of claim 1 wherein the plurality of portions of the wire loop are spaced at predetermined increments between a first bonding point of the wire loop and a second bonding point of the wire loop.

6. The method of claim 1 wherein steps (1), (2), (3), and (4) are repeated as part of an iterative process wherein a new wire loop is created in connection with each iteration, the iterative process continuing until the height profile of the wire loop meets predetermined height criteria.

7. The method of claim 6 wherein the iterative process includes changing one or more parameters of the wire bonding operation used to form the wire loop in connection with each iteration.

8. The method of claim 1 wherein step (2) includes detecting when a conductive path is established between (a) the portion of the wire loop, and (b) the portion of the conductive wire.

9. The method of claim 8 wherein step (2) includes detecting when the conductive path is established by detecting at least one of (a) a predetermined current flow in the conductive path, (b) a predetermined change in capacitance between the conductive path and a ground connection of a wire bonding machine used to form the wire loop, and (c) a predetermined phase shift of current flowing in the conductive path.

10. The method of claim 1 wherein step (2) includes detecting when the portion of the conductive wire engaged with the bonding tool contacts the portion of the wire loop using a conductive path established between (a) a detection system for detecting when the portion of the conductive wire engaged with the bonding tool contacts the portion of the wire loop, and (b) the wire loop.

11. The method of 10 wherein the conductive path includes at least one of (a) a wire clamp for clamping the conductive wire engaged with the bonding tool, (b) a wire spool for supplying wire to the bonding tool, (c) a diverter element for assisting in the positioning of the conductive wire between the wire spool and the bonding tool, and (d) an air guide system for assisting in the positioning of the conductive wire between the wire spool and the bonding tool.

12. The method of claim 1 wherein step (3) includes determining the height of the portion of the wire loop using an encoder system which is used to detect the position of the bonding tool.

13. A computer readable carrier including computer program instructions which cause a computer to implement a method of determining a height profile of a wire loop, the method comprising the steps of:

(1) moving a bonding tool towards a portion of the wire loop;