Patent ID: 12235302

DETAILED DESCRIPTION

In accordance with certain exemplary embodiments of the invention, a “health check” for robustness of wire bonding tool gripping (i.e., connection) with an ultrasonic transducer is provided.

More specifically, in accordance with certain exemplary embodiments of the invention, new methods of using (i) an electrical characteristic of an ultrasonic transducer (e.g., impedance of the transducer) versus (ii) an electrical power signal applied to the transducer (e.g., electrical current) are provided to check the clamping robustness between (a) a wire bonding tool and (b) the ultrasonic transducer. Such methods may be used, for example, to detect subtle abnormalities such as improper screw torque, a worn wire bonding tool screw, worn transducer clamp hole, worn transducer clamp thread, wire bonding tool (e.g., capillary) non-conformances, or the use of unauthorized third-party wire bonding tool screws, which all manifest as a reduced (or undesirable) gripping force on the wire bonding tool (e.g., capillary). Such methods may be implemented, for example, each time a wire bonding tool is replaced (or at some predetermined interval) since this is when a variation in gripping force often occurs.

Aspects of the invention may reduce yield loss of bonded semiconductor packages which may result, for example, after a wire bonding tool (e.g., capillary) change that may cause a degradation of the wire bonding tool gripping force. According to aspects of the invention, such a loss of gripping force may manifest itself as a change in process parameters (e.g., higher μm/mA gain) resulting in de-centering of process windows.

Exemplary aspects of the invention aggregate impedance data (or other electrical characteristic data) of the ultrasonic transducer at many different electrical current operating points (e.g., from the lowest to the highest specification range of the ultrasonic transducer) to measure the instantaneous change in impedance (or other electrical characteristics). For example, when the clamping force is overcome by high capillary accelerations at an ultrasonic drive frequency, a loss of gripping may occur—and may result in an incrementally higher impedance with increasing current (in other words, a “parabolic response” that is more obvious to detect).

In a specific exemplary embodiment of the invention, ultrasonic transducer impedance versus electrical current applied to the transducer is used for the detection of clamping force degradation (i.e., degradation of the clamping force of the wire bonding tool secured within the aperture of the transducer).

Referring now toFIGS.1A-1D,FIG.1Aillustrates a worn wire bonding tool102a(e.g., a capillary tool) engaged in an aperture100aof an ultrasonic transducer100, where worn wire bonding tool102aneeds to be replaced. Aperture100a(e.g., a clamp hole) is defined by ultrasonic transducer100and is tightened by an engagement mechanism108(e.g., a screw or other engagement mechanism).FIG.1Aillustrates loosening of engagement mechanism108(i.e., through counterclockwise rotation), and lowering of wire bonding tool102a.FIG.1Billustrates the worn wire bonding tool102ahaving been removed from aperture100a.FIG.1Cillustrates a new wire bonding tool102bhaving been installed in aperture100aof ultrasonic transducer100. More specifically,FIG.1Cillustrates engagement of new wire bonding tool102bwith aperture100a, and tightening of engagement mechanism108(i.e., through clockwise rotation). With this installation of new wire bonding tool102b, one of the inventive methods of detecting potential issues in connection with the engagement between new wire bonding tool102band ultrasonic transducer100may be utilized.FIG.1Dillustrates an electrical signal104(e.g., electrical power, electrical current, etc.) being applied by a variable electrical power source106to detect potential connection issues (e.g., to determine the current response of ultrasonic transducer100at resonance for the calculation of impedance, to determine an electrical/impedance characteristic at each of a plurality of levels of electrical power/current, etc.).

FIG.2is an exemplary plot of (i) electrical current applied to a transducer versus (ii) the impedance of the transducer, used to detect potential issues in connection with the engagement between various wire bonding tools (i.e., engagement mechanisms1-8) and the ultrasonic transducer. In this illustration, one of the inventive methods has been applied to investigate the performance of various engagement mechanisms. For example, an “engagement mechanism” may be: a brand new screw installed for the first time; an existing screw that has been used for some time in the past; a screw designed for the transducer by the OEM; a third party screw (e.g., a screw produced by an unauthorized third party not associated with the OEM); etc. For each of these various engagement mechanisms, there is an indication of whether the associated coupling between transducer and the wire bonding tool is acceptable (e.g., determined by considering if an electrical characteristic, such as impedance of the transducer, is acceptable at each of a plurality of levels of electrical power/current).

Specifically referring now toFIG.2: engagement mechanism #1is an example of a brand new screw designed for the transducer by the OEM, with acceptable coupling; engagement mechanism #2is an example of a used screw (e.g., a screw after ten wire bonding tool changes) designed for the transducer by the OEM, with acceptable coupling; engagement mechanism #3is an example of a used screw (e.g., a screw after twenty wire bonding tool changes) designed for the transducer by the OEM, with acceptable coupling; engagement mechanism #4is an example of a used screw (e.g., a screw after fifty wire bonding tool changes) designed for the transducer by the OEM, with acceptable coupling; engagement mechanism #5is an example of a used screw (e.g., a screw after one hundred wire bonding tool changes) designed for the transducer by the OEM, with acceptable coupling; engagement mechanism #6is an example of a used screw (e.g., a screw after ten wire bonding tool changes) provided by an unauthorized third party (not by the OEM), with unacceptable coupling; engagement mechanism #7is an example of a used screw (e.g., a screw after twenty wire bonding tool changes) provided by an unauthorized third party (not by the OEM), with unacceptable coupling; and engagement mechanism #8is an example of a used screw (e.g., a screw after fifty wire bonding tool changes) provided by an unauthorized third party (not by the OEM), with unacceptable coupling.

The resultant plot ofFIG.2shows that, for the acceptable engagement mechanisms (e.g., OEM screws indicated by the solid lines on the plot), all impedances fall within an acceptable range (e.g., less than a 5 ohm impedance change across the various current levels). In other words, engagement mechanisms #1-5are considered “acceptable”.

However, for the “not acceptable” engagement mechanisms (e.g., unauthorized third-party screws indicated by the dotted lines on the plot), after a small number of inserts (e.g., ten uses, etc.), the impedance values do not fall within an acceptable range. Thus, an indication (e.g., alarm) may be provided indicating that the electrical characteristic of the ultrasonic transducer (e.g., the transducer impedance) is considered “not acceptable” (e.g., not within an acceptable range for at least one of the plurality of levels of electrical power). In other words, engagement mechanisms #6-8are considered “not acceptable”.

FIGS.3-6are flow diagrams illustrating methods of detecting potential issues in connection with engagement between a wire bonding tool and an ultrasonic transducer of a wire bonding machine. As is understood by those skilled in the art, certain steps included in the flow diagrams may be omitted; certain additional steps may be added; and the order of the steps may be altered from the order illustrated—all within the scope of the invention.

Referring now toFIG.3, at Step300, electrical power is provided to an ultrasonic transducer at each of a plurality of levels of electrical power (e.g., at a plurality of different levels of electrical current). At Step302, an electrical characteristic of the ultrasonic transducer is detected at each of the plurality of levels of electrical power (e.g., the electrical characteristic of the ultrasonic transducer is related to an impedance of the ultrasonic transducer). At Step304, a determination is made as to whether the electrical characteristic of the ultrasonic transducer at each of the plurality of levels of electrical power is acceptable (e.g., by comparing the detected characteristic, such as impedance, to some acceptable criteria). At optional Step306, an indication is provided if the electrical characteristic of the ultrasonic transducer is not acceptable for at least one of the plurality of levels of electrical power. Each of Steps300,302, and304may be performed each time a wire bonding tool on a wire bonding machine is changed, or at a predetermined interval. The indication provided in Step306may be an alarm on a wire bonding machine and/or information provided to an operator of the wire bonding machine. The indication provided in Step306may provide instructions for checking at least one of: (i) screw torque of a screw holding a wire bonding tool in place in connection with the ultrasonic transducer; (ii) screw wear or other damage of the screw; (iii) wear related to a clamp hole of the ultrasonic transducer; (iv) wear related to a clamp thread of the ultrasonic transducer; (v) a non-conformity of the wire bonding tool; and (vi) use of an unauthorized screw holding the wire bonding tool in place in connection with the ultrasonic transducer.

Referring now toFIG.4, at Step400, electrical current is provided to an ultrasonic transducer at each of a plurality of levels of electrical current. At Step402, an impedance characteristic of the ultrasonic transducer is detected at each of the plurality of levels of electrical current. At Step404, a determination is made as to whether the impedance characteristic of the ultrasonic transducer at each of the plurality of levels of electrical current is acceptable. At optional Step406, an indication is provided if the impedance characteristic of the ultrasonic transducer is not acceptable for at least one of the plurality of levels of electrical current. Each of Steps400,402, and404may be performed each time a wire bonding tool on a wire bonding machine is changed, or at a predetermined interval. The indication provided in Step406may be an alarm on a wire bonding machine and/or information provided to an operator of the wire bonding machine. The indication provided in Step406may provide instructions for checking at least one of: (i) screw torque of a screw holding a wire bonding tool in place in connection with the ultrasonic transducer; (ii) screw wear or other damage of the screw; (iii) wear related to a clamp hole of the ultrasonic transducer; (iv) wear related to a clamp thread of the ultrasonic transducer; (v) a non-conformity of the wire bonding tool; and (vi) use of an unauthorized screw holding the wire bonding tool in place in connection with the ultrasonic transducer.

Referring now toFIG.5, at Step500, acceptable criteria are determined for an electrical characteristic of an ultrasonic transducer (e.g., an electrical characteristic of the ultrasonic transducer that is related to an impedance of the ultrasonic transducer). At Step502, an electrical current is applied to the ultrasonic transducer. At Step504, a determination is made as to whether the electrical characteristic of the ultrasonic transducer is acceptable after Step502. At optional Step506, an indication is provided if the electrical characteristic of the ultrasonic transducer is not acceptable. Each of Steps500,502, and504may be performed each time a wire bonding tool on a wire bonding machine is changed, or at a predetermined interval. The indication provided in Step506may be an alarm on a wire bonding machine and/or information provided to an operator of the wire bonding machine. The indication provided in Step506may provide instructions for checking at least one of: (i) screw torque of a screw holding a wire bonding tool in place in connection with the ultrasonic transducer; (ii) screw wear or other damage of the screw; (iii) wear related to a clamp hole of the ultrasonic transducer; (iv) wear related to a clamp thread of the ultrasonic transducer; (v) a non-conformity of the wire bonding tool; and (vi) use of an unauthorized screw holding the wire bonding tool in place in connection with the ultrasonic transducer.

Referring now toFIG.6, at Step600, acceptable criteria are determined for an impedance characteristic of an ultrasonic transducer. At Step602, an electrical current is applied to an ultrasonic transducer. At Step604, a determination is made as to whether the impedance characteristic of the ultrasonic transducer is acceptable after Step602. At optional Step606, an indication is provided if the impedance characteristic of the ultrasonic transducer is not acceptable. Each of Steps600,602, and604may be performed each time a wire bonding tool on a wire bonding machine is changed, or at a predetermined interval. The indication provided in Step606may be an alarm on a wire bonding machine and/or information provided to an operator of the wire bonding machine. The indication provided in Step606may provide instructions for checking at least one of: (i) screw torque of a screw holding a wire bonding tool in place in connection with the ultrasonic transducer; (ii) screw wear or other damage of the screw; (iii) wear related to a clamp hole of the ultrasonic transducer; (iv) wear related to a clamp thread of the ultrasonic transducer; (v) a non-conformity of the wire bonding tool; and (vi) use of an unauthorized screw holding the wire bonding tool in place in connection with the ultrasonic transducer.

The inventive methods recited herein may be performed at any time, and in connection with any application, as desired. For example, the methods may be performed each time a wire bonding tool is changed. In other examples, the methods may be performed at a predetermined interval (e.g., after a predetermined time, a predetermined number of machine operations, etc.). In related examples, the methods may be performed at various times along the life of a specific engagement mechanism (e.g., screw), for example, when the screw is new (a baseline performance), after 10 wire bonding tool changes, after 20 wire bonding tool changes, etc. Thus, the performance of the engagement mechanism (and its effect on coupling between the ultrasonic transducer and the wire bonding tool) may be considered over the life of the screw.

Although the invention has been described primarily with respect to methods implemented in connection with a wire bonding tool change (e.g., replacing an old tool with a new tool), the invention is not limited thereto. For example, the inventive detection methods may also be utilized at a predetermined interval during a wire bonding operation.

Although the invention is illustrated and described with respect to ball bonding tools (e.g., capillaries), the teachings of the invention may also be applied to other types of wire bonding tools such as wedge bonding tools, ribbon bonding tools, etc.

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.