BACKGROUND

In the semiconductor industry, wire bonding is commonly performed to electrically interconnect an integrated circuit (IC), such as a semiconductor die or chip, to various structures, such as a metal leadframe. Wedge bonding, for example, is a conventional method used to bond thin wires, such as thin aluminum or gold wire, between a bonding point on the semiconductor die to another point, such as a lead finger of the leadframe. Conventionally, in order to initiate a bond, the wire is pressed against the IC and/or leadframe with a tip of a bonding tool. The bonding tool is ultrasonically vibrated for a period of tens of milliseconds, wherein a plane of motion of the tip of the bonding tool is generally parallel to the surface of the semiconductor chip to which the bond is to be formed. The combination of a static load of the bonding tool normal to the chip's surface against the wire and chip coupled with the vibration at the tip of the tool causes the wire to plastically deform, thus simultaneously joining the bond wire with atoms of the material composing the chip's or leadframe' s surface, and accordingly, providing a cold weld between the wire and the chip or leadframe.

One problem associated with wire bonding is the handling of the wire throughout the bonding process, and the breaking or severing of the wire after the bond has been made. To perform these functions, most conventional fine wire wedge bonding tools break the wire by clamping and/or pulling the wire away from the bonded substrate. Typically, with small diameter wires (circular cross-section wires having diameters of less than 0.025 inches), such a pulling action is sufficient, and does not cause significant damage to the substrate. However, with the ever-increasing demands for speed and performance of ICs, larger sized wires, such as gold, aluminum, copper metal or metal alloy ribbon wires, have been introduced, wherein a cross-sectional area of the wires (for example, a flat rectangular cross- section of a ribbon wire) is significantly greater than previously-used round cross-section

wires, thus providing greater electrical current-carrying capabilities for the wire. Accordingly, when the conventional bonding tools are used with the thicker ribbon wires, the pulling force required to break the ribbon wire tends to deleteriously deform the chip and/or leadframe. As a consequence, various configurations for bonding tools have been formulated, such as one wherein a blade is pressed against the chip and/or leadframe in order to deform or cut the ribbon wire prior to pulling the bonding tool away from the substrate.

FIGS. 1A-1C illustrate one such conventional bonding device 10 during various operations, wherein a ribbon wire 15 is bonded to a substrate 20, such as a leadframe finger or semiconductor chip by an ultrasonic bonding tool 25. As illustrated in FIG. IA, the bonding tool 25 is pressed against the ribbon wire 15, thus compressing the ribbon wire between the bonding tool and the substrate 20. At this point, the bonding tool 25 ultrasonically vibrates, thus cold- welding the ribbon wire 15 to the substrate 20. FIG. IB illustrates a cutter 30 that is pressed against the ribbon wire 15, wherein the cutter significantly thins or cuts through the ribbon wire by the force F exerted by the cutter. FIG. 1C illustrates the bonding tool 25 being pulled away from the substrate 20, wherein a clamp 35 further pulls the ribbon wire 15 from the substrate, thus fully severing the ribbon wire generally at a tip 40 of the cutter 30.

One problem with the conventional bonding of ribbon wires, however, is that the force F of the cutter 30 against the ribbon wire 15 illustrated in FIG. IB typically translates into a force on the substrate 20, wherein the substrate is potentially permanently deforming and/or damaged by the cutting operation. For example, as in the case of the ribbon wire 15 being bonded to a thin leadframe finger, the force F significantly deforms the leadframe finger (as illustrated by arrow 45), wherein the deformation remains after the cutter is pulled away from the substrate 20. Furthermore, if the ribbon wire 15 is not completely severed, the pulling force may further bend the leadframe finger in a direction opposite of the arrow 45 when the clamp 35 pulls the ribbon wire away. Alternatively, as in the case of the ribbon wire 15 being bonded to a chip, the cutting force F can deleteriously impact the chip, such as potentially damaging metallization layers or other layers of the IC.

Therefore, a need currently exists for a reliable process and apparatus for bonding ribbon wires to substrates, wherein damage to the substrate is substantially minimized.

SUMMARY

The invention overcomes the limitations of the prior art by providing improved apparatus and methods for bonding wires, especially larger sized or ribbon wires, to various substrates.

According to one illustrative aspect of the invention, the apparatus comprises an ultrasonic bond capillary having a body region and a bonding region, wherein the body region comprises a passageway defined therein. A wire, such as a ribbon wire, is generally extended through the passageway and along a bonding surface associated with the bonding region, and a clamping jaw is operably coupled to the ultrasonic bond capillary in the vicinity of the passageway. Accordingly, the clamping jaw is operable to selectively grip the wire between an engagement surface of the passageway and a clamping surface of the clamping jaw. A cutting tool is further operably coupled to the ultrasonic bond capillary and generally positioned between the bonding surface and the engagement surface of the bond capillary. The cutting tool, for example, is operable to selectively extend and retract with respect to the ultrasonic bond capillary, wherein the cutting tool can at least partially penetrate through the ribbon wire positioned between the bonding surface and engagement surface of the ultrasonic bond capillary. Such a penetration of the ribbon wire between the bonding surface and the engagement surface while the ribbon wire is substantially clamped with respect to the bond capillary is highly advantageous over the prior art, since the cutting action of the cutting tool does not press on the workpiece, but rather, cuts the ribbon wire between two generally fixed and/or clamped regions. In accordance with another illustrative aspect of the invention, one or more of the clamping jaw and cutting tool are operably coupled to the bond capillary by one or more actuators, such as electro-mechanical actuators. The electro-mechanical actuators may comprise one or more of a servo motor, linear motor, spring actuator, pneumatic, and hydraulic actuators operable to selectively extend and retract the respective clamping jaw and cutting tool with respect to the ultrasonic bond capillary. The cutting actuator, for example,

may comprise a spring operable to extend the cutting tool with respect to the ultrasonic bond capillary, while a magnetic or electro-magnetic actuator retracts the cutting tool, or vice- versa.

According to another example, the cutting tool comprises an elongate member having a cutter blade generally defined at a distal end thereof. The cutting tool may further comprise a ring cutter having an inner region defined at the distal end of the elongate member, wherein the ribbon wire generally passes through the inner region of the ring, and wherein the cutting blade is generally defined by a cutting surface about an inner diameter of the ring. The ring cutter is then operable to selectively penetrate or sever the ribbon wire upon retraction of the cutter ring toward the bond capillary.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 A-IC (Prior Art) illustrate a conventional wire bonding apparatus in various positions during a bonding process.

FIG. 2 is a cross-sectional view of an example bonding apparatus according to one aspect of the invention.

FIG. 3 illustrates a plan view of a ring cutter according to another illustrative aspect of the invention.

FIG. 4 is a flow diagram of an example method for bonding a wire to a semiconductor device in accordance with the invention. FIGS. 5A-5F are cross-sectional views of an example bonding apparatus in various positions during a bonding process in accordance with the invention. DETAILED DESCRIPTION OF THE INVENTION

The invention is directed towards an apparatus and method for bonding a wire to a substrate or workpiece, such as an integrated circuit (IC) and/or leadframe assembly. More particularly, the invention provides a robust and reliable device and process for bonding a rectangular cross-section ribbon wire to the substrate, wherein damages or deformations to the substrate seen in conventional bonding apparatuses and processes are substantially mitigated. Accordingly, the invention will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout.

FIG. 2 is a cross-sectional view of an example bonding device 100, in accordance with aspects of the invention. The bonding device 100 comprises an ultrasonic bond capillary 102 for ultrasonically bonding a ribbon wire 104 to a substrate or workpiece 106, such as one or more of an IC chip or a leadframe. The ultrasonic bond capillary 102, for example, is operably coupled to an ultrasonic oscillator (not shown), as is known in the art for providing an ultrasonic vibration to the bond capillary. The ultrasonic bond capillary 102 comprises a body region 108 and a bonding region 110, wherein the ultrasonic bond capillary is operable to sandwich the ribbon wire 104 between a bonding surface 112 of the ultrasonic bond capillary and a surface 114 of the workpiece 106. The body region 108 of the bond capillary 102, for example, comprises a passageway 116 defined therein, wherein the ribbon wire 104 further generally extends through the passageway and along the bonding surface 114 associated with the bonding region 110. The passageway 116 may be comprised of a thru-hole, a channel, or various other surfaces (not shown) defined within or along the body region 108, wherein the ribbon wire 104 is operable to extend along the passageway. In one example, the ribbon wire 104 is generally rectangular in cross-section, wherein the passageway is also generally rectangular in cross-section.

FIG. 2 further illustrates a clamping jaw 118 operably coupled to the bond capillary 102 in the body region 110 thereof, wherein the clamping jaw is further associated with the passageway 116. The clamping jaw 118 is operable to selectively grip the ribbon wire 104 between an engagement surface 120 of the passageway 116 of the bond capillary 102 and a clamping surface 122 of the clamping jaw 118. In the present example, the engagement surface 120 of passageway 116 is generally planar, wherein the passageway is generally defined between the body region 110 of the bond capillary 102 and the clamping surface 122 of the clamping jaw 118. Alternatively, the passageway 116 may be defined by a channel (not shown) or other structure associated with the body region 110 of the bond capillary 102, wherein the clamping jaw 118 is operable to substantially grip or prevent movement of the ribbon wire 104 within the passageway.

The clamping jaw 118 of the invention may be operably coupled to an electromechanical actuator (not shown), wherein the electro-mechanical actuator is operable to retract and/or extend the clamping jaw, thus respectively gripping and/or releasing the ribbon

wire 104. For example, the clamping jaw 118 may be operably coupled to a motor (not shown), such as a servo motor, wherein the motor is operable to selectively extend and retract the clamping jaw with respect to the engagement surface 120. The clamping jaw 118 may be further coupled to one or more springs (not shown), wherein the one or more springs are further operable to substantially extend or retract the clamping jaw with respect to the engagement surface 120. Alternatively, the clamping jaw 118 may be operably coupled to a pneumatic or hydraulic actuator (not shown), wherein the pneumatic or hydraulic actuator is operable to extend and retract the clamping jaw with respect to the engagement surface 120. Accordingly, any actuator operable to extend and/or retract the clamping jaw 118 with respect to the engagement surface 120 of the bond capillary 102 is contemplated as falling within the scope of the invention. It should also be noted that the clamping jaw is generally integrated with the bond capillary 102, wherein the engagement surface 120 of the bond capillary 102 is generally near the bonding surface 114, as will be discussed hereafter. According to another illustrative aspect of the invention, the bonding device 100 further comprises a cutting tool 124, wherein the cutting tool is further operably coupled to the bond capillary 102. The cutting tool 124, for example, is generally positioned between the bonding surface 114 and the engagement surface 120 of the bond capillary 102, wherein the cutting tool is operable to selectively extend and retract with respect to the bond capillary. The cutting tool 124, for example, comprises an elongate member 126, wherein a cutting blade 128 is generally defined at a distal end 130 thereof. The cutting blade 128, for example, may be flattened, as illustrated in FIG. 2, or may alternatively converge to a point (not shown) at the distal end 130 of the cutting tool. According to the invention, the cutting tool 124 is operable to penetrate, at least partially, through the ribbon wire 104 between the bonding surface 114 and engagement surface 120 of the ultrasonic bond capillary 102 when the cutting blade 128 is extended past the clamping surface 122 of the clamping jaw 118 in a shear-like manner.

In another example, the cutting tool 124 comprises a ring cutter 132, as illustrated in FIG. 3. The ring cutter 132, for example, comprises a ring 134 positioned at the distal end 130 of the cutting tool 124 of FIG. 2, wherein the ribbon wire 104 generally passes through an inner region 136 of the ring. The ring cutter 132 of FIG. 3 is operable to selectively

extend and retract in a manner similar to the cutting blade 128 of FIG. 2, however, a cutting surface 138 of the ring cutter is operable to generally pass through the ribbon wire when being retracted towards the body region 110 of the bond capillary 102. Accordingly, the ring cutter of FIG. 3 is operable to be drawn against the engagement surface 120 of the bond capillary, thus penetrating, at least partially, through the ribbon wire 104.

In accordance with another illustrative aspect of the invention, the cutting tool 124 of FIG. 2 is operably coupled to a cutting actuator (not shown), such as an electro-mechanical actuator, servo motor, or other actuator, such as those described in reference to the clamping jaw 118. The cutting tool 124, for example, may be coupled to a magnetic actuator (not shown) and a spring (not shown), wherein the magnetic actuator is operable to retract the cutting tool (e.g., pull the distal end 130 of the cutting tool toward the body region 108 of the bond capillary 102), and wherein the spring is operable to provide a return force to the cutting tool, thus extending or returning the distal end of the cutting tool to its original position. FIGS. 4 and 5A-5F illustrate steps of a method 200 for bonding a ribbon wire to a substrate applied to the example bonding apparatus, in accordance with an implementation of the invention. It will be appreciated that the illustrated order of events may be varied as appropriate to suit particular needs. Method 200 begins with act 205, wherein a ribbon wire is fed through a bond capillary. As illustrated in FIG. 5 A, the ribbon wire 104 is fed through the passageway 116 of the bond capillary 102 when the clamping jaw 118 is generally extended, thus generally permitting the advancement of the ribbon wire through the passageway. In act 210 of FIG. 4, the ribbon wire is clamped against the bond capillary, and the result of act 210 is illustrated in FIG. 5B. For example, the clamping jaw 118 generally sandwiches the ribbon wire 104 between the clamping surface 122 of the clamping jaw and the engagement surface 120 of the bond capillary 102.

In act 215 of FIG. 4, the ribbon wire is bonded to the workpiece, such as by a cold welding the ribbon wire 104 of FIG. 5B to the workpiece 106 by ultrasonic vibration of the bond capillary 102. In one example, once the ribbon wire 104 is generally bonded to the workpiece 106, the ribbon wire can be cut by the cutting tool 124 in act 220 of FIG. 4. FIGS. 5C-5D illustrate the cutting tool 124 extending from the body region 108 of the bond

capillary 102, wherein in FIG. 5D, the cutting tool 124 completely severs the ribbon wire 104. It should be noted that the ring cutter 132 of FIG. 3 may be alternatively utilized, wherein the ring cutter is retracted toward the bond capillary to cut the ribbon wire 104 of FIGS. 5A-5F. Once the cutting tool 124 at least partially penetrates through the ribbon wire 104 (illustrated as severing the ribbon wire in FIG. 5D), the bonding tool 100 can be lifted from the workpiece 106, as illustrated in FIG. 5E, thus providing a secure bond 140 of the ribbon wire to the workpiece without damaging, bending, or otherwise deleteriously affecting the workpiece, as illustrated in FIG. 5F.

Thus, the invention provides apparatus and methods for bonding wire, such as ribbon wire, to a workpiece, wherein the cutting or severing of the wire is performed in a manner that does not significantly deform the workpiece. By providing a cutting tool and clamping jaw that are substantially integrated with the bond capillary, no additional clamping or holding of the ribbon wire or workpiece are required, and the bonding and cutting of the ribbon wire can be performed without bending leadframe fingers or damaging surfaces of the IC chips. Furthermore, the invention provides a bonding device that can be easily rotated between bonding positions, thus providing an efficient and reliable bonding of a ribbon wire between the bonding positions.

Those skilled in the art to which the invention relates will appreciate that various additions, deletions, substitutions and other modifications may be made to the described examples, without departing from the scope of the claimed invention.