Method of detecting connection problems between a wire bonding tool and an ultrasonic transducer of a wire bonder

Abstract

A method of detecting potential problems related to the engagement between a wire bonding tool and an ultrasonic transducer of a wire bonder is provided. The method includes the steps of: (a) providing electrical power to the ultrasonic transducer at each of a plurality of electrical power levels; (b) detecting an electrical characteristic of the ultrasonic transducer at each of the plurality of electrical power levels; and (c) determining whether the electrical characteristic of the ultrasonic transducer at each of the plurality of electrical power levels is acceptable.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 126,328, filed December 16, 2020, the contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to wire bonding systems, and more specifically, to an improved method for detecting connection problems between wire bonding tools and ultrasonic transducers on a wire bonding machine. Background Technology

[0004] In the assembly of semiconductor devices, wire bonding remains the primary method for providing electrical interconnects between two locations, such as between die pads on a semiconductor die and leads in a leadframe. Wire bonding tools are used to form wire loops to provide this interconnection.

[0005] In connection with the wire bonding process, wire bonding tools are attached to (or otherwise engaged with) the ultrasonic transducer of the wire bonding machine. For example, screws are used to secure (i.e., engage) the wire bonding tool (e.g., a capillary tube) in place within the bore of the ultrasonic transducer.

[0006] If the gripping force between the wire bonding tool and the ultrasonic transducer degrades or is otherwise altered, it can lead to undesirable wire bonding results (e.g., inconsistent wire bonding quality).

[0007] Therefore, it is desirable to provide an improved method for detecting connection problems between the wire bonding tool and the ultrasonic transducer on a wire bonding machine. Summary of the Invention

[0008] According to an exemplary embodiment of the present invention, a method is provided for detecting potential problems related to the bonding between a wire bonding tool of a wire bonding machine and an ultrasonic transducer. The method includes the steps of: (a) providing electrical power to the ultrasonic transducer at each of a plurality of electrical power levels; (b) detecting the electrical characteristics of the ultrasonic transducer at each of the plurality of electrical power levels; and (c) determining whether the electrical characteristics of the ultrasonic transducer at each of the plurality of electrical power levels are acceptable.

[0009] According to another exemplary embodiment of the present invention, a method is provided for detecting potential problems related to the bonding between a wire bonding tool of a wire bonding machine and an ultrasonic transducer. The method includes the steps of: (a) supplying current to the ultrasonic transducer at each of a plurality of current levels; (b) detecting the impedance characteristics of the ultrasonic transducer at each of the plurality of current levels; and (c) determining whether the impedance characteristics of the ultrasonic transducer at each of the plurality of current levels are acceptable.

[0010] According to yet another exemplary embodiment of the present invention, a method is provided for detecting potential problems related to the bonding between a wire bonding tool of a wire bonding machine and an ultrasonic transducer. The method includes the steps of: (a) determining acceptable criteria for the electrical characteristics of the ultrasonic transducer; (b) applying a current to the ultrasonic transducer; and (c) determining whether the electrical characteristics of the ultrasonic transducer are acceptable after step (b).

[0011] According to yet another exemplary embodiment of the present invention, a method is provided for detecting potential problems related to the bonding between a wire bonding tool of a wire bonding machine and an ultrasonic transducer. The method includes the steps of: (a) determining an acceptable standard for the impedance characteristics of the ultrasonic transducer; (b) applying a current to the ultrasonic transducer; and (c) determining whether the impedance characteristics of the ultrasonic transducer are acceptable after step (b). Attached Figure Description

[0012] The invention can be best understood from the following detailed description when read in conjunction with the accompanying drawings. It should be emphasized that, in accordance with common practice, the various features in the drawings are not drawn to scale. Instead, for clarity, the dimensions of the various features have been arbitrarily enlarged or reduced. The drawings include the following figures:

[0013] Figures 1A to 1D It is a series of block diagrams illustrating, according to an exemplary embodiment of the present invention, the removal of a wire bonding tool from an ultrasonic transducer, the installation of a new wire bonding tool with an ultrasonic transducer, and the detection of potential problems related to the bonding between the new wire bonding tool and the ultrasonic transducer.

[0014] Figure 2 This is a transducer current versus transducer impedance graph according to an exemplary embodiment of the present invention, which helps to detect potential problems related to the bonding between the wire bonding tool of a wire bonding machine and the ultrasonic transducer; and

[0015] Figures 3 to 6 This is a flowchart illustrating a method for detecting potential problems related to the bonding between the wire bonding tool and the ultrasonic transducer of a wire bonding machine, according to various exemplary embodiments of the present invention. Detailed Implementation

[0016] According to a specific exemplary embodiment of the present invention, a "health check" is provided for the robustness of a wire bonding tool that holds (i.e. connects to) an ultrasonic transducer.

[0017] More specifically, according to a particular exemplary embodiment of the invention, a novel method is provided to check the clamping robustness between (a) a wire bonding tool and (b) an ultrasonic transducer, the novel method using (i) the electrical characteristics of the ultrasonic transducer (e.g., the impedance of the transducer) compared to (ii) an electrical power signal (e.g., current) applied to the transducer. Such a method can be used, for example, to detect subtle anomalies such as inappropriate screw torque, worn wire bonding tool screws, worn transducer clamping holes, worn transducer clamping threads, non-compliant wire bonding tools (e.g., capillaries), or the use of unauthorized third-party wire bonding tool screws, all of which manifest as a decrease (or suboptimal) gripping force of the wire bonding tool (e.g., capillary). For example, such a method can be implemented each time the wire bonding tool is changed (or at some predetermined time intervals), as changes in gripping force tend to occur at these times.

[0018] Various aspects of the present invention can reduce yield losses in bonding semiconductor packages that may occur after wire bonding tool replacement, for example, after the replacement of wire bonding tools (e.g., capillaries) that could lead to degradation of the gripping force. According to various aspects of the invention, such loss of gripping force may itself manifest as a change in process parameters (e.g., a higher μm / mA gain) that results in a decentralization of the process window.

[0019] An exemplary aspect of the invention aggregates impedance data (or other electrical characteristic data) of an ultrasonic transducer at many different current operating points (e.g., from the lowest to the highest specification range of the ultrasonic transducer) to measure instantaneous changes in impedance (or other electrical characteristics). For example, when the clamping force is overcome by high capillary acceleration at the ultrasonic drive frequency, a loss of gripping force may occur, potentially leading to a gradually increasing impedance with increasing current (in other words, a more noticeable "parabolic response").

[0020] In a specific exemplary embodiment of the present invention, the comparison between the ultrasonic transducer impedance and the current applied to the transducer is used to detect clamping force degradation (i.e., degradation of the clamping force of the wire bonding tool fixed in the transducer hole).

[0021] Now for reference Figures 1A to 1D , Figure 1AThe illustration shows a worn wire bonding tool 102a (e.g., a capillary tool) engaged in a hole 100a of an ultrasonic transducer 100, wherein the worn wire bonding tool 102a needs to be replaced. The hole 100a (e.g., a clamping hole) is defined by the ultrasonic transducer 100 and tightened by a engagement mechanism 108 (e.g., a screw or other engagement mechanism). Figure 1A The illustration shows the loosening of the bonding mechanism 108 (i.e., by counterclockwise rotation) and the descent of the wire bonding tool 102a. Figure 1B The illustration shows the worn wire bonding tool 102a removed from the hole 100a. Figure 1C The illustration shows a new wire bonding tool 102b installed in the hole 100a of the ultrasonic transducer 100. More specifically, Figure 1C The illustration shows the engagement of the new wire bonding tool 102b with the hole 100a, and the tightening of the engagement mechanism 108 (i.e., by clockwise rotation). This installation of the new wire bonding tool 102b provides one of the ingenious methods for detecting potential problems related to the engagement between the new wire bonding tool 102b and the ultrasonic transducer 100. Figure 1D The illustration shows an electrical signal 104 (e.g., power, current, etc.) applied by a variable power source 106 to detect potential connectivity problems (e.g., determining the current response of the ultrasonic transducer 100 at resonance to calculate impedance, determining electrical / impedance characteristics at each of a plurality of power / current levels, etc.).

[0022] Figure 2 This is an exemplary graph comparing (i) the current applied to the transducer with (ii) the impedance of the transducer, used to detect potential problems related to the bonding between various wire bonding tools (i.e., bonding mechanisms 1 to 8) and the ultrasonic transducer. In this illustration, one inventive approach has been applied to investigate the performance of various bonding mechanisms. For example, a “bonding mechanism” can be: a brand-new screw being installed for the first time; an existing screw that has been used for some time; a screw designed for the transducer by the OEM (Original Equipment Manufacturer); a third-party screw (e.g., a screw manufactured by an unauthorized third party unrelated to the OEM); and so on. For each of these various bonding mechanisms, there is an indication of whether the associated bonding between the transducer and the wire bonding tool is acceptable (e.g., determined by considering whether electrical characteristics such as transducer impedance are acceptable at each of a plurality of power / current levels).

[0023] Now for specific reference Figure 2The following are examples of coupling mechanisms: #1 is an example of a brand-new screw designed by the OEM for the transducer, with an acceptable connection; #2 is an example of a used screw designed by the OEM for the transducer (e.g., a screw after 10 wire bonding tool replacements), with an acceptable connection; #3 is an example of a used screw designed by the OEM for the transducer (e.g., a screw after 20 wire bonding tool replacements), with an acceptable connection; #4 is an example of a used screw designed by the OEM for the transducer (e.g., a screw after 50 wire bonding tool replacements), with an acceptable connection; #5 is an example of a used screw designed by the OEM for the transducer (…). For example, the example of screw #6 (after 100 wire bonding tool replacements) has an acceptable connection; the example of joint mechanism #7 (after 20 wire bonding tool replacements) is a used screw supplied by an unauthorized third party (not by the OEM) with an unacceptable connection; and the example of joint mechanism #8 (after 50 wire bonding tool replacements) is a used screw supplied by an unauthorized third party (not by the OEM) with an unacceptable connection.

[0024] Figure 2 The results show that for acceptable engagement mechanisms (e.g., OEM screws represented by solid lines in the graph), all impedances fall within acceptable limits (e.g., impedance variation less than 5 ohms across various current levels). In other words, engagement mechanisms #1-5 are considered "acceptable".

[0025] However, for "unacceptable" connection mechanisms (e.g., unauthorized third-party screws indicated by the dashed lines in the diagram), the impedance value does not fall within the acceptable range after a small number of insertions (e.g., ten uses, etc.). Therefore, an indication (e.g., an alarm) can be provided to indicate that the electrical characteristics of the ultrasonic transducer (e.g., transducer impedance) are considered "unacceptable" (e.g., not within the acceptable range for at least one of multiple power levels). In other words, connection mechanisms #6-8 are considered "unacceptable".

[0026] Figures 3 to 6 This is a flowchart illustrating a method for detecting potential problems related to the bonding between the wire bonding tool and the ultrasonic transducer of a wire bonding machine. As those skilled in the art will understand, certain steps included in the flowchart may be omitted; specific additional steps may be added; and the order of the steps may be changed from the order shown in the diagram, all of which fall within the scope of this invention.

[0027] Now for reference Figure 3At step 300, electrical power is supplied to the ultrasonic transducer at each of a plurality of power levels (e.g., at a plurality of different current levels). At step 302, the electrical characteristics of the ultrasonic transducer are detected at each of the plurality of power levels (e.g., the electrical characteristics of the ultrasonic transducer are related to the impedance of the ultrasonic transducer). At step 304, it is determined whether the electrical characteristics of the ultrasonic transducer at each of the plurality of power levels are acceptable (e.g., by comparing the detected characteristics, such as impedance, with some acceptable criteria). In an optional step 306, an indication is provided if the electrical characteristics of the ultrasonic transducer are unacceptable for at least one of the plurality of power levels. Each of steps 300, 302, and 304 can be performed each time when changing the wire bonding tool on the wire bonder or at predetermined time intervals. The indication provided in step 306 can be an alarm on the wire bonder and / or information provided to the wire bonder operator. The instructions provided in step 306 may provide instructions to check at least one of the following: (i) the screw torque of the screw holding the wire bonding tool in place with the ultrasonic transducer; (ii) screw wear or other damage to the screw; (iii) wear associated with the clamping hole of the ultrasonic transducer; (iv) wear associated with the clamping threads of the ultrasonic transducer; (v) non-compliance of the wire bonding tool; and (vi) use of an unauthorized screw holding the wire bonding tool in place with the ultrasonic transducer.

[0028] Now for reference Figure 4 At step 400, current is supplied to the ultrasonic transducer at each of a plurality of current levels. At step 402, the impedance characteristics of the ultrasonic transducer are detected at each of the plurality of current levels. At step 404, it is determined whether the impedance characteristics of the ultrasonic transducer at each of the plurality of current levels are acceptable. In an optional step 406, an indication is provided if the impedance characteristics of the ultrasonic transducer are unacceptable for at least one of the plurality of current levels. Each of steps 400, 402, and 404 can be performed each time when changing the wire bonding tool on the wire bonder or at predetermined time intervals. The indication provided in step 406 may be an alarm on the wire bonder and / or information provided to the wire bonder operator. The instructions provided in step 406 may provide instructions to check at least one of the following: (i) the screw torque of the screw holding the wire bonding tool in place with the ultrasonic transducer; (ii) screw wear or other damage to the screw; (iii) wear associated with the clamping hole of the ultrasonic transducer; (iv) wear associated with the clamping threads of the ultrasonic transducer; (v) non-compliance of the wire bonding tool; and (vi) use of an unauthorized screw holding the wire bonding tool in place with the ultrasonic transducer.

[0029] Now for reference Figure 5At step 500, an acceptable criterion is determined for the electrical characteristics of the ultrasonic transducer (e.g., the electrical characteristics of the ultrasonic transducer related to its impedance). At step 502, current is applied to the ultrasonic transducer. At step 504, it is determined whether the electrical characteristics of the ultrasonic transducer are acceptable after step 502. Optionally, at step 506, an indication is provided if the electrical characteristics of the ultrasonic transducer are unacceptable. Each of steps 500, 502, and 504 can be performed each time the wire bonding tool on the wire bonder is changed or at predetermined time intervals. The indication provided in step 506 can be an alarm on the wire bonder and / or information provided to the wire bonder operator. The instructions provided in step 506 may provide instructions to check at least one of the following: (i) the screw torque of the screw holding the wire bonding tool in place with the ultrasonic transducer; (ii) screw wear or other damage to the screw; (iii) wear associated with the clamping hole of the ultrasonic transducer; (iv) wear associated with the clamping threads of the ultrasonic transducer; (v) non-compliance of the wire bonding tool; and (vi) use of an unauthorized screw holding the wire bonding tool in place with the ultrasonic transducer.

[0030] Now for reference Figure 6 At step 600, an acceptable standard is determined for the impedance characteristics of the ultrasonic transducer. At step 602, current is applied to the ultrasonic transducer. At step 604, it is determined whether the impedance characteristics of the ultrasonic transducer are acceptable after step 602. Optionally, at step 606, an indication is provided if the impedance characteristics of the ultrasonic transducer are unacceptable. Each of steps 600, 602, and 604 can be performed each time when changing the wire bonding tool on the wire bonder or at predetermined time intervals. The indication provided in step 606 can be an alarm on the wire bonder and / or information provided to the wire bonder operator. The instructions provided in step 606 may provide instructions to check at least one of the following: (i) the screw torque of the screw holding the wire bonding tool in place with the ultrasonic transducer; (ii) screw wear or other damage to the screw; (iii) wear associated with the clamping hole of the ultrasonic transducer; (iv) wear associated with the clamping threads of the ultrasonic transducer; (v) non-compliance of the wire bonding tool; and (vi) use of an unauthorized screw holding the wire bonding tool in place with the ultrasonic transducer.

[0031] The inventive method described herein can be performed at any time and as needed, in any application context. For example, the method can be performed each time the wire bonding tool is replaced. In other examples, the method can be performed at predetermined time intervals (e.g., after a predetermined time, a predetermined number of machine operations, etc.). In relevant examples, the method can be performed at various times throughout the service life of a specific bonding mechanism (e.g., a screw), such as when the screw is new (baseline performance), after 10 wire bonding tool replacements, after 20 wire bonding tool replacements, etc. Therefore, the performance of the bonding mechanism (and its impact on the connection between the ultrasonic transducer and the wire bonding tool) can be considered throughout the service life of the screw.

[0032] Although the invention has been described primarily with respect to methods relating to wire bonding tool replacement (e.g., replacing an old tool with a new one), the invention is not limited thereto. For example, the detection method of the invention can also be employed at predetermined time intervals during the wire bonding operation.

[0033] Although the invention has been illustrated and described with respect to ball bonding tools (e.g., capillaries), the teachings of the invention can also be applied to other types of wire bonding tools, such as wedge bonding tools, ribbon bonding tools, etc.

[0034] Although the invention has been illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications to the details may be made within the scope and equivalents of the claims and without departing from the invention.

Claims

1. A method for detecting potential problems related to the bonding between a wire bonding tool and an ultrasonic transducer of a wire bonding machine, the method comprising the steps of: (a) Providing electrical power to the ultrasonic transducer at each of a plurality of electrical power levels; (b) Detect the electrical characteristics of the ultrasonic transducer at each of multiple power levels; as well as (c) By determining whether the electrical characteristics of the ultrasonic transducer are acceptable at each of the multiple power levels, examine the clamping between the wire bonding tool and the ultrasonic transducer to detect reduced gripping force on the wire bonding tool.

2. The method of claim 1, wherein each of steps (a), (b) and (c) is performed after at least one of (i) changing the wire bonding tool on the wire bonding machine and (ii) a predetermined time interval.

3. The method of claim 1, further comprising step (d), providing an indication if the electrical characteristics of the ultrasonic transducer are unacceptable for at least one of a plurality of electrical power levels.

4. The method of claim 3, wherein the indication is an alarm on the wire bonding machine.

5. The method of claim 3, wherein the instruction is information provided to the wire bonding machine operator.

6. The method of claim 3, wherein the instruction provides instructions to check at least one of the following: (i) the screw torque of the screw holding the wire bonding tool in place with the ultrasonic transducer; (ii) screw wear or other damage to the screw; (iii) wear associated with the clamping hole of the ultrasonic transducer; (iv) wear associated with the clamping threads of the ultrasonic transducer; (v) non-compliance of the wire bonding tool; and (vi) use of an unauthorized screw holding the wire bonding tool in place with the ultrasonic transducer.

7. The method of claim 1, wherein the electrical power supplied to the ultrasonic transducer is provided at multiple different current levels.

8. The method according to claim 1, wherein the electrical characteristics of the ultrasonic transducer are related to the impedance of the ultrasonic transducer.

9. A method for detecting potential problems related to the bonding between a wire bonding tool and an ultrasonic transducer of a wire bonding machine, the method comprising the steps of: (a) Providing current to the ultrasonic transducer at each of a plurality of current levels; (b) Detect the impedance characteristics of the ultrasonic transducer at each current level in multiple current levels; as well as (c) Degradation of the clamping force of the wire bonding tool fixed in the hole of the ultrasonic transducer is detected by determining whether the impedance characteristics of the ultrasonic transducer at each of the multiple current levels are acceptable.

10. The method of claim 9, wherein each of steps (a), (b) and (c) is performed after at least one of (i) changing the wire bonding tool on the wire bonding machine and (ii) a predetermined time interval.

11. The method of claim 9, further comprising step (d), providing an indication if the impedance characteristics of the ultrasonic transducer are unacceptable for at least one of a plurality of current levels.

12. The method of claim 11, wherein the indication is an alarm on the wire bonding machine.

13. The method of claim 11, wherein the instruction is information provided to the wire bonding machine operator.

14. The method of claim 11, wherein the instruction provides instructions to check at least one of the following: (i) the screw torque of the screw holding the wire bonding tool in place with the ultrasonic transducer; (ii) screw wear or damage; (iii) wear associated with the clamping hole of the ultrasonic transducer; (iv) wear associated with the clamping threads of the ultrasonic transducer; (v) non-compliance of the wire bonding tool; and (vi) use of an unauthorized screw holding the wire bonding tool in place with the ultrasonic transducer.

15. A method for detecting potential problems related to the bonding between a wire bonding tool and an ultrasonic transducer of a wire bonding machine, the method comprising the steps of: (a) Determine acceptable criteria for the electrical characteristics of the ultrasonic transducer for checking the clamping between the wire bonding tool and the ultrasonic transducer; (b) Applying current to the ultrasonic transducer; and (c) Determine whether the electrical characteristics of the ultrasonic transducer are acceptable after step (b) in order to detect the reduced gripping force on the wire bonding tool.

16. The method of claim 15, wherein each of steps (a), (b) and (c) is performed after at least one of (i) changing the wire bonding tool on the wire bonding machine and (ii) a predetermined time interval.

17. The method of claim 15, further comprising step (d), providing an indication if the electrical characteristics of the ultrasonic transducer are unacceptable.

18. The method of claim 15, wherein the electrical characteristics of the ultrasonic transducer are related to the impedance of the ultrasonic transducer.

19. A method for detecting potential problems related to the bonding between a wire bonding tool and an ultrasonic transducer of a wire bonding machine, the method comprising the steps of: (a) Determine acceptable criteria for the impedance characteristics of the ultrasonic transducer for checking the clamping between the wire bonding tool and the ultrasonic transducer; (b) Applying current to the ultrasonic transducer; and (c) Determine whether the impedance characteristics of the ultrasonic transducer are acceptable after step (b) to detect the degradation of the clamping force of the wire bonding tool fixed in the hole of the ultrasonic transducer.

20. The method of claim 19, wherein each of steps (a), (b) and (c) is performed after at least one of (i) changing the wire bonding tool on the wire bonding machine and (ii) a predetermined time interval.

21. The method of claim 19, further comprising step (d), providing an indication if the impedance characteristics of the ultrasonic transducer are unacceptable.

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