How to improve wire bonding operations

Abstract

A method for determining a new search height for a wire bonding operation is provided, the method including providing a search height, performing a plurality of wire bonding operations using the search height, monitoring a wire bonding metric during each of the plurality of wire bonding operations, and determining a new search height using the monitored wire bonding metric.

Description

[Technical field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Provisional Application No. 63 / 336,227, filed April 28, 2022, the contents of which are incorporated herein by reference.

[0002] The present invention relates to wire bonding operations, and more particularly to techniques for improving wire bonding operations, for example in terms of time efficiency. [Background technology]

[0003] In semiconductor device processing and packaging, wire bonding remains the primary method of electrically connecting two locations in a package (e.g., between a die pad of a semiconductor die and a lead of a lead frame). More specifically, a wire bonder (also called a wire bonding machine) is used to form a wire loop between the respective locations to be electrically connected. The primary methods of forming the wire loop are ball bonding and wedge bonding. Various types of bonding energy can be used in forming the bond between (a) the end of the wire loop and (b) the bond site (e.g., die pad, lead, etc.), e.g., ultrasonic energy, thermo-sonic energy, thermo-compression energy, etc. Wire bonding machines (e.g., stud bumping machines) are also used to form conductive bumps from portions of the wire.

[0004] In certain applications, the process of forming the wire loop involves positioning a wire bonding tool at an elevation above a workpiece and then moving the wire bonding tool into contact with the workpiece associated with the wire bonding operation. The time elapsed between (i) the elevation above the workpiece and (ii) the contact with the workpiece is important to the efficiency of the wire bonding operation. Summary of the Invention [Problem to be solved by the invention]

[0005] It would therefore be desirable to provide improved wire bonding operations, including those related to the timing and efficiency of such operations. [Means for solving the problem]

[0006] According to an exemplary embodiment of the present invention, a method for determining a new search height for a wire bonding operation is provided, the method comprising the steps of: (a) providing a search height, (b) performing a plurality of wire bonding operations using the search height, (c) monitoring a wire bonding metric during each of the plurality of wire bonding operations of step (b), and (d) determining a new search height using the wire bonding metric monitored during step (c).

[0007] According to another exemplary embodiment of the present invention, there is provided a method for determining a new blockout time for a wire bonding operation, the method comprising the steps of: (a) providing a blockout time, the blockout time being a time after a wire bonding tool reaches a seek height in a wire bonding operation but before the wire bonding tool enters a seek mode, (b) performing a plurality of wire bonding operations using the blockout time, (c) monitoring a wire bonding metric during step (b) in each of the plurality of wire bonding operations, and (d) determining a new blockout time using the wire bonding metric monitored during step (c).

[0008] 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 including a wire bonding program for use in association with a wire bonding machine). [Brief description of the drawings]

[0009] The invention is best understood from the following detailed description when read in conjunction with the accompanying drawings, in which: It is emphasized that, according to common practice, the various features of the drawings are not to scale. Conversely, dimensions of the various features have been arbitrarily expanded or reduced for clarity. The drawings include the following figures: [Figure 1] FIG. 1 is a timing diagram illustrating key points for carrying out methods in accordance with various exemplary embodiments of the present invention. [Diagram 2] 2-4 are flow diagrams for implementing various methods for determining a new search height for a wire bonding process according to various exemplary embodiments of the present invention. [Diagram 3] 2-4 are flow diagrams for implementing various methods for determining a new search height for a wire bonding process according to various exemplary embodiments of the present invention. [Figure 4] 2-4 are flow diagrams for implementing various methods for determining a new search height for a wire bonding process according to various exemplary embodiments of the present invention. [Diagram 5] 5-7 are flow diagrams for implementing various methods for determining a new blockout time for a wire bonding process according to various exemplary embodiments of the present invention. [Figure 6] 5-7 are flow diagrams for implementing various methods for determining a new blockout time for a wire bonding process according to various exemplary embodiments of the present invention. [Figure 7]5-7 are flow diagrams for implementing various methods for determining a new blockout time for a wire bonding process according to various exemplary embodiments of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] An exemplary aspect of the present invention relates to monitoring signals (e.g., seek time signals, seek distance signals, impact force signals, impact crush signals, etc.) on a wire bonding system as feedback to automatically adjust (and improve, possibly optimize) the height of a wire bonding tool. Adjusting the height (e.g., search height) of the wire bonding tool can improve the performance and efficiency (e.g., UPH, units per hour) of the wire bonding operation. Additionally, if the height (e.g., search height) of the wire bonding tool is not optimal or deviates, a communication (e.g., a warning message) can be sent to an operator. Additionally, the monitored seek time (or seek distance) and / or impact force (or impact crush) can be used in connection with a closed loop adjustment of the height (e.g., search height) of the wire bonding tool. Such closed loop adjustment may be an automated process (e.g., performed using software on the wire bonding system without operator intervention).

[0011] According to certain exemplary aspects of the present invention, a desirable (possibly optimal) search height may be achieved when a minimum seek time (or seek distance) meets a threshold. If the seek time (or seek distance) is too long, it may adversely affect the UPH of the wire bonding system. If the seek time (or seek distance) is too short, it may degrade the bond quality of the wire bonding system.

[0012] According to certain exemplary aspects of the present invention, a desirable (and perhaps optimal) impact force (and / or impact crush) can be achieved. If the impact force (or impact crush) is too high, which usually means that the search height is too low, the bond quality may be reduced.

[0013] In accordance with certain exemplary aspects of the present invention, changes in seek time (or seek distance) and impact force (or impact crush) can also be analyzed to monitor the health of the wire bonding system for optimization of the wire bonding tool height.

[0014] As used herein, the term "search height" refers to the height of the wire bonding tool above the bonding location when transitioning from high speed to low speed. Examples of search heights include the transition point between (i) the high speed drop and (ii) the transition to a slower constant speed (i.e., CV) mode.

[0015] As used herein, the term "seek time" refers to the time interval between (i) the start of a seek for contact between the wire bonding tool and the bonding location and (ii) until contact between the wire bonding tool and the bonding location is declared. As used herein, the term "seek distance" refers to the distance between (i) the start of a seek for contact between the wire bonding tool and the bonding location and (ii) until contact between the wire bonding tool and the bonding location is declared.

[0016] As used herein, the term "seek mode" refers to the initiation of seeking contact between the wire bonding tool and the bonding location.

[0017] As used herein, the term "seek mode" refers to the initiation of seek contact between the wire bonding tool and the bonding location. As used herein, the term "blockout time" refers to the time before the wire bonding tool enters a seek mode after the wire bonding tool reaches a search height in a wire bonding operation. In certain applications, the blockout time may be referred to as the "seek delay."

[0018] Referring now to the drawings, FIG. 1 is a timing diagram illustrating key points for carrying out various methods in accordance with the present invention (including the embodiments shown in FIGS. 2-7). The vertical axis indicates the Z-axis position of the wire bonding tool 100. The horizontal axis indicates the time of the wire bonding tool 100 descent in relation to a wire bonding operation. FIG. 1 shows the wire bonding tool 100 in an initial position above a workpiece (workpiece not shown). This initial position refers to a position during the rapid descent of the wire bonding tool 100. At time T1, the wire bonding tool 100 reaches a search height. At this search height, there is a transition from a high speed to a low speed (e.g., a lower constant speed). The wire bonding tool 100 continues to descend between time T1 and time T2. The period between time T1 and time T2 is sometimes referred to as the "blockout time". This is the time after the search height is reached and before entering a seek mode.

[0019] At time T2, a seek mode is initiated. Seek mode refers to a mode of operation in which the system is monitoring for contact between the wire bonding tool 100 and the bonding location. Contact between the wire bonding tool 100 and the bonding location is declared at time T3. Thus, the time between time T2 (when the seek mode begins) and time T3 (when contact is declared) is referred to as the "seek time" (or "seek distance" if distance is monitored).

[0020] Figures 2-4 are flow diagrams illustrating an exemplary method for determining a new search height for a wire bonding process in accordance with the present invention. Figures 5-7 are flow diagrams illustrating an exemplary method for determining a new blockout time for a wire bonding process in accordance with the present invention. As will be appreciated 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 steps may be changed from the order shown, all within the scope of the present invention.

[0021]

[0023] Referring now to Figure 2, a method for determining a new search height for a wire bonding process is shown. In step 200, a search height is provided (e.g., the search height of Figure 1). In step 202, a number of wire bonding operations are performed using the search height provided in step 200. In step 204, wire bonding metrics are monitored during each of the number of wire bonding operations in step 202. For example, such wire bonding metrics may include signals monitored during step 204 related to at least one of the following: (i) wire bonding tool seek time, (ii) wire bonding tool seek distance, (iii) wire bonding tool impact force, (iv) wire bonding tool impact crush, (v) Z-axis deformation profile, (vi) bond force vibration profile, (vii) ultrasonic impedance characteristics, and (viii) servo performance of the xyz motion system of the wire bonding machine.

[0022] In step 206, a new search height is determined using the wire bond evaluation criteria monitored in step 204. For example, the criteria monitored in step 204 may indicate that the seek time (or seek distance) is too long. In that case, the new search height is lowered. In another example, the criteria monitored in step 204 may indicate that the seek time (or seek distance) is too short. In that case, the new search height is higher. In other examples, the search height can be adjusted in step 206 using various criteria monitored in step 204 (e.g., impact force, impact crush, etc.).

[0023] The new search height determined in step 206 may be the same as the previous search height (e.g., the search height provided in step 200) or may be a different search height. According to certain exemplary embodiments of the present invention, the new search height may be determined to be low enough to provide a time efficient wire bonding process while providing an acceptable level of wire bonding criteria monitored in step 204. In optional step 208, the blockout time for the subsequent wire bonding operation is determined using the new search height determined in step 206.

[0024] 3, a method for determining a new search height for a wire bonding operation is shown. In step 300, a search height (or a new search height for step 306) is provided (e.g., the search height of FIG. 1). In step 302, a number of wire bonding operations are performed using the search height of step 300 (or the new search height for step 306). In step 304, a wire bonding criterion (see the exemplary criterion discussed above in connection with step 204) is monitored during each of the multiple wire bonding operations of step 302. In step 306, a new search height is determined using the wire bonding criterion monitored during step 304 (see the discussion discussed above in connection with step 206).

[0025] In step 308, it is determined whether a predetermined criterion has been met. The predetermined criterion can be any criterion required for a particular application. For example, the predetermined criterion relates to the criterion monitored in step 304 (e.g., seek time, seek distance, impact force, impact crush, etc.). Alternatively, the predetermined criterion in step 308 can be a different criterion, such as a minimum or maximum number of iterations completed (or a maximum timeout). If the answer to the decision block in step 308 is "no," steps 300-306 are repeated with a new search height. If the answer to the decision block in step 308 is "yes," the determination of the new search height is completed in step 310. In optional step 312, the new search height determined in step 306 is used to determine the blockout time for the subsequent wire bonding operation.

[0026] 4, a method for determining a new search height for a wire bonding process is shown. According to this method, multiple search heights are checked to determine a desired (possibly optimal) search height. For example, multiple search heights are known prior to performing this method, and each of the multiple known search heights is checked.

[0027] In step 400, a search height (or another search height in step 408) is provided (e.g., the search height of FIG. 1). In step 402, a plurality of wirebonding operations are performed using the search height of step 400 (or another search height in step 408). In step 404, during each of the plurality of wirebonding operations in step 402, a wirebonding metric is monitored (see the exemplary metric described above in connection with step 204). In step 406, it is determined whether another search height needs to be checked (i.e., whether all known plurality of search heights have been checked). If the answer to the decision block in step 406 is "yes," another search height is provided in step 408, and steps 400-404 are repeated. If the answer to the decision block in step 406 is "no," the determination of a new search height is completed in step 410 (see above with respect to step 206, except that step 410 may also use the monitored metric for each of the plurality of search heights to determine a new search height). In optional step 412, the new search height determined in step 410 is used to determine the blockout time of the subsequent wire bonding operation.

[0028] 5, a method for determining a new blockout time for a wire bonding process is shown. In step 500, a blockout time (e.g., the blockout time of FIG. 1) is provided. In step 502, a number of wire bonding operations are performed using the blockout time provided from step 500. In step 504, wire bonding metrics are monitored during each of the multiple wire bonding operations of step 502 (see example metrics discussed above in connection with step 204). In step 506, a new blockout time is determined using the wire bonding metrics monitored during step 504. The new blockout time determined in step 506 may be the same as the previous blockout time (e.g., the blockout time provided in step 500) or may be a different blockout time. According to certain exemplary embodiments of the present invention, the new blockout time may be determined to be short enough to provide a time efficient wirebonding process while still providing an acceptable level of wirebonding metrics monitored in step 504.

[0029] In optional step 508, the search height used for the subsequent wire bonding operation is modified based on the new blockout time determined in step 506. For example, if the new blockout time is longer (e.g., longer than the previous blockout time), the search height is increased, and if the new blockout time is shorter (e.g., shorter than the previous blockout time), the search height is decreased.

[0030] 6, a method for determining a new blockout time for a wire bonding process is shown. In step 600, a blockout time (or a new blockout time for step 606) is provided (e.g., the blockout time of FIG. 1). In step 602, a number of wire bonding operations are performed using the blockout time of step 600 (or the new blockout time for step 606). In step 604, during each of the multiple wire bonding operations of step 602, a wire bonding metric is monitored (see example metrics discussed above in connection with step 204). In step 606, a new blockout time is determined using the wire bonding metric monitored during step 604.

[0031] In step 608, it is determined whether some predetermined criteria is met. The predetermined criteria may be any criteria required for a particular application. For example, the predetermined criteria may relate to the criteria monitored in step 604 (e.g., seek time, seek distance, shock force, shock crush, etc.). Alternatively, the predetermined criteria from step 608 may be a different criteria, such as a minimum or maximum number of iterations completed (or a maximum timeout). If the answer to the decision block of step 608 is "no," steps 600-606 are repeated with a new blockout time. If the answer to the decision block of step 608 is "yes," the determination of the new blockout time is completed in step 610. In optional step 612, the search height used for subsequent wire bonding operations is modified based on the new blockout time determined in step 606 (see description of step 508 above).

[0032] 7, a method for determining a new blockout time for a wire bonding process is shown. According to this method, a number of blockout times must be checked to determine a desired (possibly optimal) blockout time. For example, a number of blockout times are known before performing this method, and each of the number of known blockout times is checked.

[0033] In step 700, a blockout time (or another blockout time in step 708) is provided (e.g., the blockout time of FIG. 1). In step 702, a plurality of wirebonding operations are performed using the blockout time in step 700 (or another blockout time in step 708). In step 704, wirebonding metrics are monitored during each of the plurality of wirebonding operations in step 702 (see example metrics discussed above in connection with step 204). In step 706, it is determined whether another blockout time needs to be checked (i.e., have all of the known plurality of blockout times been checked). If the answer to the decision block in step 706 is "yes," another blockout time is provided in step 708, and steps 700-704 are repeated. If the answer to the decision block of step 706 is "no", then the determination of the new blockout time is completed in step 710 (see the discussion above regarding step 506, although step 710 may also use the monitored metrics for each of multiple blockout times to determine the new blockout time). In optional step 712, the search height used for the subsequent wire bonding operation is modified based on the new blockout time determined in step 710 (see discussion of step 508 above).

[0034] 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, but rather various changes in the details may be made within the scope and range of equivalents of the claims and without departing from the invention.

Claims

1. 1. A method for determining a new search height for a wire bonding process, comprising: (a) providing a search height; (b) performing a plurality of wire bonding operations using the search height; (c) monitoring wire bond metrics during each of the plurality of wire bonding operations of step (b); (d) determining a new search height using the wire bond metrics monitored during step (c); The method according to claim 1,

2. 2. The method of claim 1, wherein the new search height is the height of the wire bonding tool above the bond location before entering a constant speed mode.

3. 2. The method of claim 1 , wherein the wire bonding evaluation criteria comprises signals monitored during step (c) related to at least one of: (i) a wire bonding tool seek time, (ii) a seek distance of the wire bonding tool, (iii) an impact force of the wire bonding tool, (iv) an impact crush of the wire bonding tool, (v) a Z-axis deformation profile, (vi) a bond force vibration profile, (vii) an ultrasonic impedance characteristic, and (viii) a servo performance of an xyz motion system of a wire bonding machine.

4. 2. The method of claim 1, wherein during step (d), the new search height is determined to be the same as the search height.

5. 2. The method of claim 1, wherein during step (d), the new search height is determined to be different from the search height.

6. 2. The method of claim 1, wherein the wire bonding evaluation criteria includes a signal related to a seek time of a wire bonding tool, the seek time being the time interval between (i) a start of a seek for contact between the wire bonding tool and a bonding location and (ii) a point at which contact between the wire bonding tool and the bonding location is declared.

7. 2. The method of claim 1, wherein step (d) includes determining a new search height that is sufficiently low to provide a time efficient wire bonding process while providing an acceptable level of the wire bonding criteria monitored in step (c).

8. 2. The method of claim 1, wherein steps (a)-(d) are repeated for a number of iterations, and the new search height determined in step (d) is the search height used in a next iteration of the number of iterations.

9. 2. The method of claim 1, wherein steps (a)-(d) are repeated in a number of iterations until a predetermined criterion is met taking into account the wirebonding evaluation criteria monitored in step (c), and the new search height determined in step (d) is the search height used in a next iteration of the number of iterations.

10. 2. The method of claim 1, wherein steps (a)-(c) are repeated for a plurality of search heights, and step (d) includes, for each of the plurality of search heights, determining the new search height using the wire bonding evaluation criteria monitored during step (c).

11. 2. The method of claim 1, further comprising: (e) using the new search height determined in step (d) to determine a block-out time of a subsequent wire bonding operation, the block-out time being the time after a wire bonding tool reaches a search height in a wire bonding operation but before the wire bonding tool enters a seek mode.

12. 1. A method for determining a new blockout time for a wire bonding process, comprising: (a) providing a block out time, the block out time being a time after a wire bonding tool reaches a seek height in a wire bonding operation but before the wire bonding tool enters a seek mode; (b) performing a plurality of wire bonding operations using said blockout time; (c) monitoring wire bond metrics during each of the plurality of wire bonding operations during step (b); (d) determining a new blockout time using the wirebonding metrics monitored during step (c); The method according to claim 1,

13. 13. The method of claim 12, further comprising the step of determining a new search height to be used in a subsequent wire bonding operation based on the new blockout time determined in step (d).

14. 14. The method of claim 13, wherein determining the new search height comprises increasing the search height if the new blockout time is longer and decreasing the search height if the new blockout time is shorter.

15. 13. The method of claim 12, wherein the search height is the height of the wire bonding tool above the bonding location before entering a constant speed mode.

16. 13. The method of claim 12, wherein the wire bonding metrics include signals monitored during step (c) related to at least one of: (i) a seek time of the wire bonding tool, (ii) a seek distance of the wire bonding tool, (iii) an impact force of the wire bonding tool, (iv) an impact crush of the wire bonding tool, (v) a Z-axis deformation profile, (vi) a bond force vibration profile, (vii) an ultrasonic impedance characteristic, and (viii) a servo performance of an xyz motion system of a wire bonding machine.

17. 13. The method of claim 12, wherein the wirebonding metrics monitored during step (c) include signals related to servo performance of an xyz motion system of a wirebonding machine.

18. 13. The method of claim 12, wherein during step (d), the new blockout time is determined to be the same as the blockout time.

19. 13. The method of claim 12, wherein during step (d), the new blockout time is determined to be different from the blockout time.

20. 13. The method of claim 12, wherein step (d) includes determining the new blockout time to be sufficiently short to provide a time efficient wire bonding process while providing an acceptable level of the wire bonding criteria monitored in step (c).

21. 13. The method of claim 12, wherein steps (a)-(d) are repeated for a number of iterations, and the new blockout time determined in step (d) is the blockout time used in a next iteration of the number of iterations.

22. 13. The method of claim 12, wherein steps (a)-(d) are repeated in a number of iterations until a predetermined criterion is met taking into account the wirebonding criteria monitored in step (c), and the new blockout time determined in step (d) is the blockout time used in a next iteration of the number of iterations.

23. 13. The method of claim 12, wherein steps (a)-(c) are repeated for a plurality of blockout times, and step (d) includes, for each of the plurality of blockout times, determining the new blockout time using the wirebonding metrics monitored during step (c).

24. 13. The method of claim 12, wherein the blockout time is at least a portion of the time that elapses after the wire bonding tool reaches the search height in the wire bonding operation and before the wire bonding tool enters a seek mode.

25. 13. The method of claim 12, wherein the blockout time is the elapsed time between when the wire bonding tool enters a constant velocity mode and when the wire bonding tool enters the seek mode.

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