Wedge bonder and a method of cleaning a wedge bonder

Disclosed is a wedge bonder, comprising a wedge for bonding a wire to surfaces to form an electrical interconnection therebetween, a cleaning device for cleaning the wedge, and a positioning device to which the wedge is mounted. In particular, the positioning device is operative to move the wedge to the cleaning device for cleaning. A method of cleaning a wedge of a wedge bonder is also disclosed.

FIELD OF THE INVENTION

The present invention relates to a wedge bonder having a wedge for bonding a wire to surfaces to form an electrical interconnection therebetween. In particular, the wedge bonder further comprises a cleaning device for cleaning the wedge. The invention also relates to a method of cleaning a wedge of a wedge bonder.

BACKGROUND OF THE INVENTION

A wedge bonder utilizes ultrasonic energy to bond a wire to a semiconductor die and to a substrate to which the semiconductor die is mounted, so as to form an electrical interconnection between the semiconductor die and the substrate. Specifically, as the wedge presses the wire against a die pad of the semiconductor die or against the substrate, an ultrasonic transducer generates ultrasonic oscillations that are transmitted through a wedge of a bond tip of the wedge bonder and onward to the wire positioned beneath the wedge.

FIG. 1shows a bond tip100of a conventional wedge bonder, comprising: i) a wire guide102for guiding a wire104from a wire spool (not shown) through the bond tip100; ii) a wedge106having a bonding portion108for pressing a portion of the wire104against a bonding pad of a semiconductor die or against a substrate during bonding; and iii) a wire cutter110for cutting the wire104to detach the wire104from the wire spool after an electrical interconnection is formed between the semiconductor die and the substrate.

Repeated bonding operations of the wedge bonder will cause residue to build up at the bonding portion108of the wedge106. For instance, Aluminum (Al) residue will build up at the bonding portion108of the wedge106if Al wire is used for wedge bonding. Hence, it will be necessary to clean the wedge106. Conventionally, wedge cleaning involves removing the wedge106from the bond tip100, and immersing the removed wedge106in a cleaning solution (e.g. NaOH solution) for about 30 minutes to remove the residue from the wedge106. The wedge106is then reinstalled onto the bond tip100after cleaning, before the wedge bonder resumes its bonding operations.

However, reinstallation of the wedge106onto the bond tip100after cleaning requires set-up tasks such as recalibration of the ultrasonic transducer and fine component adjustment of the bond tip100. These tasks are not just time-consuming but also require skilled technicians to undertake.

Thus, it is an object of the present invention to at least ameliorate the problems associated with cleaning the wedge of a wedge bonder.

SUMMARY OF THE INVENTION

A first aspect of the invention is a wedge bonder comprising a wedge for bonding a wire to surfaces to form an electrical interconnection therebetween, a cleaning device operative to clean the wedge, and a positioning device to which the wedge is mounted. In particular, the positioning device is operative to move the wedge to the cleaning device for cleaning.

A second aspect of the invention is a method of cleaning a wedge of a wedge bonder, the wedge being for bonding a wire to surfaces to form an electrical interconnection therebetween, and the wedge bonder further comprising a cleaning device for cleaning the wedge. Specifically, the method comprises the steps of moving the wedge to the cleaning device, and cleaning the wedge by the cleaning device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2a-2care plan views of a wedge bonder200, showing a positioning device (illustrated by an XY-table202) and a bond tip204mounted to the XY-table202. Similarly to the bond tip shown inFIG. 1, the bond tip204may comprise: i) a wire guide for guiding a wire from a wire spool through the bond tip204; ii) a wedge having a bonding portion for pressing a portion of the wire against a bonding pad of a semiconductor die or against a substrate during bonding; and iii) a wire cutter for cutting the wire to detach the wire from the wire spool after an electrical interconnection is formed between the semiconductor die and the substrate.

In addition, the wedge bonder200comprises: i) a bonding zone206for supporting a substrate (e.g. a lead frame) when performing bonding operations; ii) an imaging zone208for inspecting the wedge; and iii) a cleaning zone210for cleaning the wedge.

Specifically, actuation of the XY-table202is controlled by a motion controller and a motor system comprising linear motors.FIG. 2aillustrates the bond tip204positioned by the XY-table202relative to and above the bonding zone206. In particular, the XY-table202actuates the bond tip204to move from an original start position at the left of the bonding zone206rightward along an X-direction to bond a row of semiconductor dies to the substrate. Thereafter, the substrate is then indexed upward along the V-direction while the XY-table202actuates the bond tip204leftward along the X-direction to reposition the bond tip204back to its original start position before bonding another row of semiconductor dies to the substrate.FIG. 2billustrates the bond tip204being actuated to move rightward along the X-direction by the XY-table202to a position relative to and above the imaging zone208, whileFIG. 2cillustrates the bond tip204being actuated to move downward along the Y-direction by the XY-table202to a position relative to and above the cleaning zone210.

FIG. 3illustrates the bond tip204having the wire guide302, the wedge304, and the wire cutter306, together with a cleaning device307of the cleaning zone210of the wedge bonder200that cleans the wedge304using a dry approach. This cleaning device307of the cleaning zone210comprises: i) a motor308; and ii) a rotary cleaning wheel (shown as a rotatable grinding wheel310) coupled to the motor308. The motor308is controlled by a motion controller to drive the grinding wheel310at a controlled speed against a bonding portion312of the wedge304, to remove residue (e.g. Al residue) mechanically therefrom.

Optionally, the geometry of the grinding wheel310may vary based on the corresponding geometry of the bonding portion312of the wedge304.

For instance,FIG. 4aillustrates a configuration of a wedge400having a flat-end bonding portion402for pushing a ribbon wire against a semiconductor die or a substrate during bonding. For such a configuration of the wedge400, the corresponding geometry of the grinding wheel310may comprise corresponding flat ends when viewed in a direction perpendicular to its rotational axis or to its major surface. On the other hand,FIG. 4billustrates a configuration of a wedge404having a bonding tip that includes a V-shaped groove406for at least partially housing and pushing a round wire against a semiconductor die or a substrate during bonding. In this embodiment of the wedge404, the corresponding geometry of the grinding wheel310may comprise tapered ends when viewed in a direction perpendicular to its rotational axis or to its major surface.

Of course, it should be appreciated that other geometries of the grinding wheel310may also be possible to match corresponding geometries of the wedge404for the purpose of cleaning. For instance, the grinding wheel310may comprises trapezoidal ends when viewed in a direction perpendicular to its rotational axis or to its major surface for cleaning a corresponding U-shaped groove of a wedge-bonding tip.

Besides the dry approach for cleaning the wedge304as described above, the wedge304may instead be cleaned at the cleaning zone210of the wedge bonder200using a wet approach.

FIG. 5illustrates a configuration500of the cleaning zone210based on the wet approach. Such a configuration500comprises three chambers502,504,506—i) a first chamber502for storing a cleaning solution503(e.g. NaOH solution) for removing residue (e.g. Al residue); ii) a second chamber504for storing a rinsing solution505(e.g. H2O); and iii) a third chamber506for housing a dryer508for drying. Specifically, the XY-table202of the wedge bonder200first positions the bond tip204relative to and above the first chamber502of the cleaning zone210, before immersing the bonding portion312of the wedge304into the cleaning solution503to remove residue from the wedge304. After the bonding portion312of the wedge304has been immersed in the cleaning solution503for a sufficient period of time, the XY-table202of the wedge bonder200withdraws the wedge304from the cleaning solution503, before immersing the same into the rinsing solution505to remove the cleaning solution503from the wedge304for another period of time as required. The XY-table202of the wedge bonder200then withdraws the wedge304from the rinsing solution505, before moving the wedge304into the third chamber506for drying the same. This completes the wedge-cleaning process based on the wet approach.

Preferably, the first and second chambers502,504are deep enough to store the respective cleaning and rinsing solutions503,505to avoid spillage within the wedge bonder200during operation.

FIG. 6aandFIG. 6billustrate the imaging zone208of the wedge bonder200, comprising an imaging device for capturing an image of the bonding portion312of the wedge304. Specifically, the imaging device comprises a beam-splitter602and a camera600positioned with respect to the beam-splitter602for capturing different images of the wedge304. When the wedge304is arranged perpendicularly to a line-of-view604of the camera600above the beam-splitter602as shown inFIG. 6a, the beam-splitter602allows the camera600to capture an image of a base of the bonding portion312. When the wedge304is aligned along the line-of-view604of the camera600such that the beam-splitter602is positioned between the camera600and the bonding portion312as shown inFIG. 6b, the beam-splitter602allows the camera600to capture an image of a side of the bonding portion312.

FIG. 7aandFIG. 7brespectively illustrate a sample side image and a sample bottom image of the bonding portion312of the wedge304as captured by the imaging device before cleaning. It can be seen that the residue701(e.g. Al residue) accumulates at the inner walls of the wedge-bonding portion312after repeated bonding operations (e.g. 3000 bonding cycles).FIG. 7candFIG. 7drespectively illustrate a sample side image and a sample bottom image of the bonding portion312of the wedge304after cleaning. It can be seen that the residue (e.g. Al residue) that previously accumulated at the inner walls of the wedge-bonding portion312has been removed.

FIGS. 8a-8dshow that the bond tip204of the wedge bonder200additionally comprises a wire-feeding mechanism800for removing a wire802from the bond tip204before the wedge-cleaning process begins, and for introducing a new wire804through the bond tip204after the wedge-cleaning process ends. The wire-feeding mechanism800may include a set of friction wheels or wire clamps for the wire-removal and wire-rethreading processes.

Specifically,FIGS. 8aand8bshow a kinked portion801of the wire802being pushed away from the bonding portion312by the wire-feeding mechanism800, in order to dislodge the wire802from a groove of the bonding portion312. Thereafter, the wire-feeding mechanism800retracts the wire802from the bond tip204to remove the wire802therefrom.

FIGS. 8cand8dshow the new wire804being re-threaded through the bond tip204until the wire804feeds out from the wire guide302. Thereafter, the bond tip204moves downwards and backwards (as shown by arrow806) during a dummy-bonding process, so that the wedge304pushes the new wire804against a dummy bond-off plate802. Following the dummy-bonding process, the new wire804is then firmly captured by the bonding portion312and thus, the wedge bonder200is able to continue its bonding operations.

FIG. 9is a flow chart900showing a wedge-cleaning process on the wedge bonder200.

The flow chart900first begins with the step902of wedge bonding followed by the step904of incrementing a bond counter by one. Iterations of the step902of wedge bonding and the step904of incrementing the bond counter continue until the bond counter registers a count number (e.g. 3000) to trigger the cleaning of the wedge304. The wedge bonder200then switches to a “pre-cleaning” mode.

During this pre-cleaning mode, the wedge bonder200performs the step906of removing the wire from the bond tip204. The wire-feeding mechanism800of the bond tip204actuates to remove the wire from the bond tip204. In particular, the kinked portion of the wire is pushed away from the bonding portion312of the wedge304, in order to dislodge the wire802from the groove of the bonding portion312. The wire-feeding mechanism800then retracts the wire from the bond tip204to remove the wire therefrom.

After the step906of removing the wire from the bond tip204, the wedge bonder200then performs the step908of inspecting the bonding portion312during which the wedge304is moved to the imaging zone208. Thereafter, the wedge bonder200performs the step910of cleaning the bonding portion312in which the wedge304is moved to the cleaning zone210. Subsequently, the wedge bonder200switches into a “post-cleaning” mode.

During this post-cleaning mode, the wedge bonder200again performs the step912of inspecting the bonding portion312in which the wedge is moved to the imaging zone208. Thereafter, the wedge bonder200performs the step914of re-threading a new wire through the bond tip204, before the wedge bonder200resumes its bonding operations.

This completes an iteration of the wedge-cleaning process on the wedge bonder200. Such an iteration of the wedge-cleaning process may be performed either automatically or manually. Indeed, any or all of the steps of the wedge-cleaning process may be performed either automatically or manually.

Optionally, the imaging device may provide feedback for the wedge-cleaning process. For instance, if no residue is detected from the sample images of the bonding portion312as captured by the imaging device during the pre-cleaning mode, the wedge bonder may bypass the wedge-cleaning process to resume its bonding operations. Likewise, if some residue is detected from the sample images of the bonding portion312as captured by the imaging device after the wedge-cleaning process, the wedge bonder may operate to reposition the wedge304relative to the cleaning zone210for another round of cleaning. If the sample images of the bonding portion312otherwise show that the wedge304has been sufficiently cleaned, the wedge bonder200then performs the step914of wire re-threading before resuming its bonding operations.

Since there is no need to dismantle the wedge304from the bond tip204for cleaning and to reinstall the dismantled wedge304back to the bond tip204after cleaning, the wedge-cleaning process advantageously reduces maintenance time and reliance on skilled technicians for set-up tasks such as recalibration of the ultrasonic transducer and fine component adjustment of the bond tip204. Furthermore, by automating the wedge-cleaning process, a reasonable wedge-cleaning quality could be expected without human intervention.

It should be appreciated that other embodiments of the present invention can be envisaged without departing from the scope of the invention. For instance, although it has been described that the imaging and cleaning zones208,210comprises the imaging and cleaning devices respectively, it can be envisaged that these devices do not have to be permanently positioned at their respective imaging and cleaning zones208,210. Instead, each of these devices could be moved by an actuator into its respective zone208,210to perform the necessary operations. Furthermore, the imaging zone208and the corresponding imaging device are optional and may thus be omitted.