Ultrasonic transducer operable at multiple resonant frequencies

Abstract

An ultrasonic transducer configured to selectively operate at a first resonant frequency or a second resonant frequency during a wire bonding operation, comprising: an elongated transducer body having an aperture thereon for mounting a piezoelectric driver stack to drive the ultrasonic transducer to operate at the first or second resonant frequency; and a mounting flange connected to the transducer body at a first nodal vibration region of the transducer body when the ultrasonic transducer is operating at the first resonant frequency. The length of the elongated transducer body is substantially equal to two wavelengths of a first oscillatory wave transmitted along the length of the transducer body when the transducer is operating at the first resonant frequency, and substantially equal to one-half wavelength of a second oscillatory wave transmitted along the length of the transducer body when the transducer is operating at the second resonant frequency.

Description

Technical Field

[0001] This invention generally relates to a multi-resonant ultrasonic transducer for use with wire bonding tools, and more specifically, to an ultrasonic transducer capable of operating at multiple resonant frequencies, including ultra-high resonant frequencies up to 300 kHz. Background Technology

[0002] Cross-referencing of related patent applications.

[0003] This application is a continuation-in-part of U.S. Patent Application No. 17 / 963,489, filed October 11, 2022, the entire contents of which are incorporated herein by reference.

[0004] Ultrasonic transducers are widely used in wire bonding tools to provide wire bonding between semiconductor bonding pads and lead frames or carriers during wire bonding operations. Typically, conventional ultrasound is generated at a single operable resonant frequency to create reliable wire bonds. However, in practice, more than one resonant frequency may be required during wire bonding operations. Various solutions have been proposed in the prior art to provide ultrasonic transducers that can operate at multiple resonant frequencies in practice.

[0005] U.S. Patent 7,137,543B2 discloses an ultrasonic transducer 100A suitable for use at multiple ultrasonic frequencies. (Reference) Figure 1A The ultrasonic transducer includes integrated flexible mounting units 108a-108d for each mounting flange 105 to prevent vibration from being transmitted from the ultrasonic transducer 100A to the machine bonding head of the wire bonding machine on which the ultrasonic transducer 100A is mounted. However, because the flexible element is a structure intentionally weakened in one direction to eliminate stress, the integrated flexible mounting units 108a-108d have low stiffness in the weakening direction (i.e., the axial direction of the ultrasonic transducer). This will affect the stability of the ultrasonic transducer 100A, thereby reducing the quality of the wire bonding.

[0006] US Patent 5,578,888A discloses an ultrasonic transducer 100B with both low and high usable resonant frequencies. For example... Figure 1B The ultrasonic transducer 100B shown includes a single, integrated body with a rectangular aperture at its center of mass. A multi-frequency transducer driver stack 28 is mounted within the rectangular aperture 31, which has a compression wedge 29. The structure of the ultrasonic transducer 100B, particularly the fixed position of the rectangular aperture 31, limits the frequency interval between its higher and lower resonant frequencies. For the ultrasonic transducer 100B, the higher resonant frequency is only about twice the lower resonant frequency. Therefore, this prior art ultrasonic transducer 100B can only operate within a limited frequency range.

[0007] US Patent 5,595,328A discloses a self-isolating ultrasonic transducer 100C, which is as follows: Figure 1C The ultrasonic transducer 100C shown has low mounting impedance. The ultrasonic transducer 100C includes two modified mounting flanges 13 for mounting the ultrasonic transducer 100C onto a bonding machine through mounting holes 15. Each modified mounting flange 13 includes a hole 21, i.e., a stress-relieving groove, in the mounting flange 13 or the transducer body 14 to prevent transverse radial stress in the transducer body 14 from entering the mounting flange 13 and coupling to the bonding machine. Unless a common mounting node for multiple ultrasonic frequencies can be identified on the transducer body 14, the ultrasonic transducer 100C will not function well at multiple ultrasonic frequencies. Furthermore, the stress-relieving groove on the mounting flange 13 or the transducer body 14 will reduce the bending stiffness of the ultrasonic transducer 100C.

[0008] Therefore, it would be beneficial to provide a new design for an ultrasonic transducer that can operate at multiple resonant frequencies, which can overcome at least one of the disadvantages of the ultrasonic transducers in the prior art described above. Summary of the Invention

[0009] Therefore, the object of this invention is to provide an improved multi-resonant ultrasonic transducer that operates at a first (higher) resonant frequency and a second (lower) resonant frequency. The latter may be less than one-third of the first resonant frequency.

[0010] According to a first aspect of the invention, an ultrasonic transducer configured to selectively operate at a first resonant frequency or a second resonant frequency during wire bonding operations is provided. The ultrasonic transducer includes: an elongated transducer body having apertures for mounting a stack of piezoelectric actuators to drive the ultrasonic transducer to operate at the first or second resonant frequency, wherein the length of the transducer body is substantially equal to two wavelengths of a first oscillating wave propagating along the length of the transducer body when the transducer operates at the first resonant frequency, and substantially equal to half the wavelength of a second oscillating wave propagating along the length of the transducer body when the transducer operates at the second resonant frequency; and a mounting flange connected to the transducer body at a first node vibration region of the transducer body when the ultrasonic transducer operates at the first resonant frequency.

[0011] In some embodiments of the present invention, the first resonant frequency may be between 200 kHz and 300 kHz, and the second resonant frequency may be between 50 kHz and 100 kHz.

[0012] In some embodiments of the invention, it is not necessary to position the ultrasonic transducer so that its centroid is aligned with the center of the aperture used to mount the piezoelectric actuator. The transducer body of the ultrasonic transducer has a first end and a second end opposite to the first end. The aperture may be closer to the first end than the second end. In one embodiment, the second end may be the end of the transducer body to which a bonding tool is attached. With this arrangement, the aperture is relatively far from the bonding tool, allowing the ultrasonic transducer to be constructed with a more robust or durable structure, thereby ensuring better bonding quality.

[0013] To further reduce vibration and rotation of the transducer body during wire bonding operations, the ultrasonic transducer may also include at least one resilient preload element located within the aperture to provide a non-uniform thickness preload structure for generating preload on the piezoelectric actuator stack. This at least one resilient preload element may be positioned on the inner surface of the aperture.

[0014] In some embodiments, the ultrasonic transducer may further include a flexible connecting element extending between the mounting flange and the transducer body at a first node vibration region of the transducer body. In one embodiment, the flexible connecting element may include at least one flexible member extending between the mounting flange and the transducer body.

[0015] In some embodiments, the ultrasonic transducer may further include a rigid connecting member having a first end and a second end. When the ultrasonic transducer operates at a first resonant frequency, the first end is connected to a mounting flange, and the second end is connected to the transducer body at a second node vibration region of the transducer body. In one embodiment, the rigid connecting member may include: a first portion extending from the second node vibration region of the transducer body in an axial direction perpendicular to the transducer body; and a second portion extending from the first portion in an axial direction of the transducer body, the second portion being connected to the mounting flange.

[0016] Both the flexible connecting element and the rigid connecting member are attached to the nodal vibration regions of the transducer body. These regions have minimal vibration amplitude when the ultrasonic transducer operates at the first resonant frequency, so as to minimize the vibration transmitted to the mounting flange when the ultrasonic transducer operates at the first resonant frequency.

[0017] In one embodiment, when the ultrasonic transducer operates at a first resonant frequency, the minimum vibration amplitude can be a vibration amplitude not exceeding 10% of the maximum vibration amplitude of the transducer body.

[0018] In some embodiments, the first node vibration region is located closer to the bonding tool than the second node vibration region, and the second node vibration region is located near the rectangular aperture.

[0019] In some embodiments, the rigid connection member may include: a first portion extending from the second node vibration region of the transducer body in a direction perpendicular to the axial direction of the transducer body; and a second portion (long support arm) extending from the first portion along the axial direction of the transducer body until the second portion is connected to the mounting flange. This rigid connection member is designed to increase the stiffness of the mounting flange and mitigate radial stress caused by transducer body vibration during wire bonding. Preferably, the length of the second portion of the rigid connection member is approximately half the wavelength of the sinusoidal ultrasonic signal used to drive the ultrasonic transducer at the first resonant frequency.

[0020] To increase the bending stiffness of the ultrasonic transducer, the ratio Rh of the height of the first part in a first direction perpendicular to the axial direction of the transducer body (e.g., the z-axis direction) to the thickness of the second part in a second direction perpendicular to the axial direction of the transducer body (e.g., the x-axis direction) is selected such that: Rh 2 >Rb, where Rb refers to a predetermined ratio of the bending stiffness about the second direction to the bending stiffness about the first direction. In one embodiment, the predetermined ratio Rb is 10, so the height of the first portion in the second direction is not less than 3.2 times the thickness of the second portion in the first direction.

[0021] In some embodiments, the ultrasonic transducer may be configured to operate at a second resonant frequency lower than the first resonant frequency. To further prevent vibration of the transducer body from being transmitted to the wire bonding machine when the ultrasonic transducer operates at the second resonant frequency, a first vibration point located in the first node vibration region of the transducer body and a second vibration point located in the second node vibration region have substantially equal vibration amplitudes and opposite vibration directions when the ultrasonic transducer operates at the second resonant frequency. In other words, when the ultrasonic transducer operates at the second resonant frequency, a rigid connecting member and a flexible connecting element are respectively attached to the first and second node vibration regions having substantially equal vibration amplitudes and opposite vibration directions. With this novel arrangement of the ultrasonic transducer, the second resonant frequency may be less than one-third of the first resonant frequency.

[0022] In some embodiments of the present invention, the mounting flange may include two components symmetrically arranged on two opposite sides of the transducer body, and thus the rigid connecting member and the flexible connecting element each include two independent components symmetrically arranged on two opposite sides of the transducer body.

[0023] According to a second aspect of the invention, an ultrasonic wire bonding apparatus is provided, comprising an ultrasonic transducer according to various embodiments of the invention.

[0024] These and other features, aspects, and advantages will become more readily understood from the detailed description section, the appended claims, and the accompanying drawings. Attached Figure Description

[0025] Embodiments of the invention will now be described by way of example with reference only to the accompanying drawings, wherein:

[0026] Figure 1A A perspective view and a front view of a first prior art ultrasonic transducer are shown.

[0027] Figure 1B A top view of a second prior art ultrasonic transducer is shown.

[0028] Figure 1C A top view of a third prior art ultrasonic transducer is shown.

[0029] Figure 2A and Figure 2B A perspective view and a top view of an ultrasonic transducer according to a preferred embodiment of the present invention are shown respectively.

[0030] Figure 2C This is a top view of an ultrasonic transducer according to an alternative embodiment of the present invention.

[0031] Figure 3 Is it like this? Figure 2A An enlarged perspective view of the rigid connection component of the ultrasonic transducer shown.

[0032] Figure 4 Is it like this? Figure 2A An enlarged perspective view of the pre-compression structure with uneven thickness in the pores of the ultrasonic transducer shown.

[0033] Figure 5A and Figure 5B The diagrams show the displacement waveforms relative to the transducer body length when the ultrasonic transducer operates at the first (higher) and second (lower) resonant frequencies, respectively. Figure 5C A top view of an ultrasonic transducer is shown, including, for example... Figure 5A and Figure 5B The waveform diagram shown represents the vibration amplitude of the ultrasonic transducer when it operates at lower and higher resonant frequencies.

[0034] Figure 6A Simulation results of the vibration shape of an ultrasonic transducer with a pre-compression structure of uniform thickness are shown.

[0035] Figure 6B Simulation results of the vibration shape of an ultrasonic transducer with a pre-compression structure of non-uniform thickness are shown.

[0036] In the accompanying drawings, similar reference numerals indicate similar parts. Detailed Implementation

[0037] Figure 2A and Figure 2BPerspective and top views of an ultrasonic transducer 200 according to a preferred embodiment of the present invention are shown respectively. The ultrasonic transducer 200 can operate at multiple frequencies. The multiple frequencies include a first (higher) resonant frequency and a second (lower) resonant frequency. The first resonant frequency may be between 200 kHz and 300 kHz, while the second resonant frequency may be between 50 kHz and 100 kHz.

[0038] like Figure 2A and Figure 2B As shown, the ultrasonic transducer 200 includes: an elongated transducer body 210 having a rectangular aperture 220, a mounting flange including a first flange element 230a and a second flange element 230b, a rigid connecting member including a first rigid connecting element 240a and a second rigid connecting element 240b, and a flexible connecting element including a first flexible connecting element 250a and a second flexible connecting element 250b.

[0039] The elongated transducer body 210 has an end on which a bonding tool 201, fitted with a wire bonding machine, is mounted. One advantage of this is that ultrasonic scrubbing assistance can also apply pressure and heat during the bonding process to form a thermoacoustic bond with the bonding tool 201. For example... Figure 2B As shown, the transducer body 210 typically comprises three parts: a front part, a middle part, and a rear part. The rectangular aperture 220 is located approximately between the middle and rear parts of the transducer body 210. Figure 2B The image shows the centroid M of the ultrasonic transducer 200, which is not located at the center of the rectangular aperture 220. The rectangular aperture 220 is adapted to mount a piezoelectric driver stack 260 for driving the ultrasonic transducer 200 to operate at multiple frequencies.

[0040] The mounting flange is used to mount the transducer body 210 onto the wire bonding machine. In this embodiment, the mounting flange includes a first flange element 230a and a second flange element 230b. The first flange element 230a and the second flange elements 230b are symmetrically arranged on two opposite sides of the transducer body 210. Each flange element 230a, 230b includes mounting holes 231a, 231b for receiving screws to mount the transducer body 210 onto the wire bonding machine.

[0041] The rigid connection member is provided to create a rigid connection between the transducer body 210 and the mounting flange, thereby increasing the rigidity of the ultrasonic transducer 200. In this embodiment, the rigid connection member includes a first rigid connection element 240a and a second rigid connection element 240b. (See reference...) Figure 2A and Figure 2BThe first rigid connecting element 240a has a first end and a second end. When the ultrasonic transducer 200 operates at a higher resonant frequency, the first end is connected to the transducer body 210 at a first point H1 in the first nodal vibration region of the transducer body 210; the second end is connected to the first flange element 230a. The second rigid connecting element 240a also has a first end and a second end. When the ultrasonic transducer 200 operates at the first resonant frequency, the first end is connected to the transducer body 210 at a second point H2 in the first nodal vibration region of the transducer body 210. The first point H1 and the second point H2 are located on opposite sides of the transducer body 210. The nodal vibration region refers to the region of the transducer body 210 that has a lower vibration amplitude compared to other (non-nodal) regions of the transducer body 210, for example, a region where the vibration amplitude is no higher than 10% of the maximum vibration amplitude of the transducer body 210 when the ultrasonic transducer 200 operates at the first resonant frequency. A method for determining the first nodal vibration region of the transducer body 210 will be explained below.

[0042] Reference Figure 2A and Figure 2B The first rigid connecting element 240a includes a first portion 240a-1 and a second portion 240a-2. The first portion 240a-1 extends from a first point H1 on the transducer body 210 along an X-axis direction perpendicular to the axial direction (or Y-axis direction) of the transducer body 210, and the second portion 240a-2 extends from one end of the first portion 240a-1 along a direction parallel to the axial direction (i.e., along the Y-axis direction) of the transducer body 210. The second portion 240a-2 is then connected to a first flange element 230a from the transducer body 210. Similarly, the second rigid connecting element 240b includes a first portion 240b-1 and a second portion 240b-2. The first portion 240b-1 extends from a second point H2 on the transducer body 210 along an X-axis direction, and the second portion 240b-2 extends from one end of the first portion 240b-1 along a Y-axis direction. The second part 240b-2 is connected to the second flange element 230b of the transducer body 210.

[0043] When the ultrasonic transducer 200 is driven to vibrate axially along the transducer body 210, the radial stress generated by the compression and extension of the horn of the transducer body 210 is transmitted to the mounting flange through the rigid connecting members 240a, 240b. Since the second portions 240a-2, 240b-2 of the rigid connecting members 240a, 240b are designed to provide bending freedom, the radial stress caused by the vibration of the transducer body 210 is configured to be reduced by the deformation of the second portions 240a-2, 240b-2 during bending. When the second portions 240a-2, 240b-2 have sufficient length, the radial stress at the mounting flange can be drastically reduced. In this embodiment, the lengths L1, L2 of the second portions 240a-2, 240b-2 are approximately half the wavelength of the sinusoidal ultrasonic signal used to drive the ultrasonic transducer 200 at the first resonant frequency. Preferably, the length L1 of the second portion 240a-2 is substantially equal to the length L2 of the second portion 240b-2.

[0044] Figure 3 Is it like this? Figure 2A The image shows an enlarged perspective view of the rigid connection member of the ultrasonic transducer. To improve the stiffness of the ultrasonic transducer 200, the rigid connection member is designed to enhance the bending stiffness Bx in the X-axis direction of the ultrasonic transducer 200, but weaken the bending stiffness Bz in the Z-axis direction to eliminate stress. Therefore, the ratio Rh of the height H of the first part 240b-1 in the Z-axis direction to the thickness T of the second part 240b-2 in the X-axis direction can be determined based on a predetermined ratio Rb between Bx and Bz. Specifically, Bx is related to TH3, and Bz is related to HT3, so the corresponding ratio Rh can be determined according to the formula Rh2>Rb. In one example, the predetermined ratio Rb is 10, and the ratio Rh of H to T can be calculated according to the following formula:

[0045] Rb=Bx / Bz=TH 3 / HT 3 =(H / T) 2

[0046] Rh=H / T=Rb 1 / 2 >10 1 / 2 =3.16≈3.2.

[0047] In this embodiment, to ensure that the ultrasonic transducer 200 has sufficient rigidity, the height H of the first part 240b-1 in the Z-axis direction can be at least 3.2 times the thickness T of the second part 240b-2 in the X-axis direction.

[0048] Reference Figure 2BThe flexible connecting elements include a first flexible connecting element 250a and a second flexible connecting element 250b. The first flexible connecting element 250a extends between the first flange element 230a and the transducer body 210, and the second flexible connecting element 250b extends between the second flange element 230b and the transducer body 210. When the ultrasonic transducer 200 operates at a first resonant frequency, the first and second flexible connecting elements 250a and 250b are located at the first and second points, respectively, in the second node vibration region of the transducer body 210.

[0049] Figure 2C This is a top view of an ultrasonic transducer 200' according to an alternative embodiment of the present invention. It is related to... Figure 2B The difference in the ultrasonic transducer 200 shown is that each flexible connection element 250'a, 250'b includes two flexible elements extending between each mounting flange and the transducer body 210, instead of one flexible element.

[0050] The ultrasonic transducer 200 may further include at least one flexible or elastic preload element located on the inner surface of the aperture 220 to form a preload structure with non-uniform thickness within the aperture 220 for preloading the piezoelectric actuator stack 260. In this embodiment, reference is made to... Figure 2B and Figure 4 The flexible preload component includes a first preload element 260a extending or protruding from the center of the inner surface 220a of the aperture 220, and a second preload element 260b extending or protruding from the inner surface 220b of the aperture 220. The flexible preload components located on the inner surfaces 220a and 220b of the rectangular aperture 220 form a non-uniform preload structure or flexible element in the rectangular aperture 220 to further reduce undesirable bending of the transducer body 210 when the ultrasonic transducer 200 operates at a higher resonant frequency.

[0051] like Figure 2BAs shown, the non-uniform preload structure in this embodiment includes a cross-section with a first thickness t1 and other cross-sections with a second thickness t2. Specifically, the first and second preload elements 260a and 260b have a first thickness t1, which is greater than the second thickness t2 of the other cross-sections of the preload structure. The non-uniform preload structure provides greater freedom in selecting the attachment points of the flexible connecting elements 250a and 250b to minimize the vibration and rotation of the transducer body 210, thereby significantly eliminating undesirable bending of the transducer body 210 when the ultrasonic transducer 200 operates at the first resonant frequency. In other words, the non-uniform preload structure can minimize the number of local bending modes that affect the shape of the ultrasonic transducer 200 during operation. The design of the non-uniform preload structure allows the flexible elements 250a and 250b to be attached to the transducer body 210 at locations with minimal bending vibration. Therefore, arranging the non-uniform preload structure on the inner surface of the aperture 220 can minimize the mounting impedance of the ultrasonic transducer 200 when operating at the first resonant frequency.

[0052] The method for determining the first and second node vibration regions of the transducer body 210 will now be explained. When the ultrasonic transducer 200 operates at a first resonant frequency, the first and second node vibration regions are selected based on a predetermined vibration amplitude of the transducer body 210. In this embodiment, when the ultrasonic transducer 200 operates at a first (higher) resonant frequency, the vibration amplitude of the selected first and second node vibration regions does not exceed 10% of the maximum vibration amplitude of the transducer body 210.

[0053] Furthermore, when the ultrasonic transducer 200 operates at the first and second resonant frequencies, the first node vibration region and the second node vibration region can also be determined based on the displacement waveform relative to the length of the ultrasonic transducer 200. Figures 5A-5B The diagrams show the displacement waveforms relative to the length of the transducer body 210 when the ultrasonic transducer 200 operates at the first and second resonant frequencies, respectively. Figure 5C A top view of an ultrasonic transducer is shown, including, for example... Figure 5A and Figure 5B The waveform diagram shown illustrates the vibration level or amplitude of the ultrasonic transducer 200 in each region when it operates at the first and second resonant frequencies. See also... Figure 5AThe first node vibration points H1 and H2 are determined based on the first node Z1, and the second node vibration region is determined based on the second node Z2. The first node vibration region is the area surrounding the first node Z1, and the vibration amplitude in this region is less than a predetermined vibration amplitude. For example, when the ultrasonic transducer 200 operates at a first resonant frequency, the vibration amplitude in this region is less than 0.1 times the maximum vibration amplitude of the transducer body 210. The second node vibration region is the area surrounding the second node Z2, and this region also has a vibration amplitude less than the predetermined vibration amplitude. (Reference) Figure 2B and Figure 5C Compared to the second node vibration region, the first node vibration region is located closer to the end coupled with the bonding tool 201, and the second node vibration region is located near the rectangular aperture 220.

[0054] Reference Figures 5A to 5C The length of the elongated transducer body 210 is substantially equal to two wavelengths of the first oscillation wave W1 transmitted along the length of the transducer body 210 when the ultrasonic transducer 200 operates at the first resonant frequency, and substantially equal to half the wavelength of the second oscillation wave W2 when the ultrasonic transducer 200 operates at the second resonant frequency. The length of the transducer body 210 includes the lengths of the front, middle, and rear portions of the ultrasonic transducer 200 as shown in FIG2.

[0055] Reference Figure 5A and Figure 5C When the ultrasonic transducer 200 operates at a first resonant frequency, rigid connecting members are attached to a first point H1 and a second point H2 of the transducer body 210, at which the transducer body 210 has the lowest vibration amplitude. To increase the stiffness of the ultrasonic transducer 200, radial stress is eliminated using long solid arms spaced apart from the mounting flange and the transducer body 210 (i.e., the second portions 240a-2, 240b-2 of each rigid connecting member 240a, 240b), a method different from that used in prior art transducers to eliminate radial stress via mounting flanges or stress-relieving grooves on the transducer body. To further increase the stiffness of the mounting flange, a flexible connecting element including at least one flexible member is used to connect the mounting flange and the transducer body 210. The rotational stiffness of the ultrasonic transducer 200 can be further improved by these two connection points spaced apart along the transducer body 210. Flexible connecting elements (i.e., flexible elements 250a and 250b) are attached to the vibration region of the second node to achieve minimal vibration, especially low bending moment around flexible elements 250a and 250b.

[0056] Refer to 5B and Figure 5C, when the ultrasonic transducer 200 operates at the second resonant frequency, the vibration level or vibration amplitude (e.g., the vibration amplitude at Z3, Z4) in the first and second nodal vibration regions of the transducer body 210 is higher than the vibration amplitude in the first and second nodal vibration regions of the transducer body 210 when the ultrasonic transducer 200 operates at a higher resonant frequency (e.g., the vibration amplitude at Z1, Z2). However, the vibrations in the first and second nodal vibration regions have substantially equal amplitudes and opposite vibration directions. That is, when the ultrasonic transducer 200 operates at the second resonant frequency, the connection points of the rigid connection member and the flexible connection element vibrate in opposite directions with the same vibration amplitude. Based on the opposite vibration directions, the minimum vibration region suitable for installing the flange can be determined. As the flexible connection elements, i.e., the flexible members 250a, 250b, extend between the mounting flange and the transducer body 210, the vibration of the transducer body 210 will be isolated from the adjacent regions, especially the rest of the bonding machine. The vibration at the mounting flange will be significantly reduced, thereby reducing the mounting impedance to reduce the resonant drive.

[0057] Figure 6A The simulation results of the vibration shapes of the ultrasonic transducer with a preloaded structure of uniform thickness are shown when the ultrasonic transducer operates at frequencies f in the ranges of 200 kHz < f < 210 kHz, 210 kHz < f < 300 kHz, and f > 300 kHz, respectively. The simulation results of the preloaded structures with uniform thicknesses T = 1 mm, 1.4 mm, or 1.7 mm are as Figure 6A shown. The number of vibration shapes that appear within this frequency range is used to indicate the vibration level of the transducer body when operating in different frequency ranges. Referring to Figure 6A , when the thickness T is 1 mm, there are four vibration shapes in the frequency range greater than 200 kHz; when the thickness T is 1.4 mm or 1.7 mm, there are five vibration shapes in the frequency range greater than 200 kHz. In particular, regardless of whether the thickness value of the preloaded structure is large or small, there is at least one vibration shape in the high-frequency range of 200 kHz to 300 kHz.

[0058] Figure 6B The simulation results of the vibration shapes of the ultrasonic transducer with a non-uniform thickness preloaded structure are shown when the ultrasonic transducer operates at frequencies f in the ranges of 200 kHz < f < 210 kHz, 210 kHz < f < 300 kHz, and f > 300 kHz, respectively. As Figure 6BAs shown, the total number of vibration shapes that appear within the frequency range greater than 200 kHz is 3, and this number is less than the number of vibration shapes that appear within the frequency range greater than 200 kHz when the pre-tightening structure has a uniform thickness. Specifically, two vibration shapes appear within the resonant frequency range of 200 kHz < f < 210 kHz, one vibration shape appears within the range of f > 300 kHz, and no vibration shapes appear within the high resonant frequency range of 210 kHz < f < 300 kHz. Therefore, the simulation results show that the non-uniform preloading structure has a significant effect on eliminating the vibration of the transducer body, especially when the ultrasonic transducer operates at a high resonant frequency of up to 300 kHz.

[0059] As can be understood from the above description, an embodiment of the present invention provides an ultrasonic transducer that can operate at multiple resonant frequencies (including an ultra-high resonant frequency of up to 300 kHz). Compared with existing ultrasonic transducers, the ultrasonic transducer provided in the embodiment of the present invention includes an elongated transducer body, the length of which is determined by multiple operable resonant frequencies. Specifically, the length of the transducer body is substantially equal to the two wavelengths of the first oscillating wave transmitted along the length of the transducer body when the ultrasonic transducer operates at the first (higher) resonant frequency, and is substantially equal to half the wavelength of the second (lower) oscillating wave transmitted along the length of the transducer body when the ultrasonic transducer operates at the second resonant frequency.

[0060] In one embodiment, the ultrasonic transducer may include a rigid connection member that is used to connect the first node vibration region when the ultrasonic transducer operates with the mounting flange at a higher resonant frequency to increase the bending stiffness of the ultrasonic transducer. Moreover, the rigid connection member further includes a long support arm extending axially along the transducer body to relieve radial stress. In addition, when the ultrasonic transducer operates at a higher resonant frequency through a flexible connection element, the ultrasonic transducer may further include a mounting flange connected to the second node vibration region to further increase the bending stiffness of the mounting flange and isolate the vibration from the rest of the bonding machine through the mounting flange. The first and second node vibration regions are selected such that when the ultrasonic transducer operates at a lower resonant frequency, the vibration amplitudes of these two regions are substantially equal and the vibration directions are opposite. Therefore, when the ultrasonic transducer operates at a lower resonant frequency, the vibration transmitted from the transducer body to the mounting flange will be balanced and cancelled out. Therefore, the proposed ultrasonic transducer can maintain an effective installation while maintaining different vibration modes, regardless of whether its operating resonant frequency is large or small. In addition, a preloading structure with non-uniform thickness is provided in the pores of the ultrasonic transducer to control the local bending mode that affects the working stiffness of the ultrasonic transducer, thereby minimizing the installation impedance of the ultrasonic transducer when operating at a higher resonant frequency.

[0061] According to embodiments of the present invention, the mounting flange does not need to be attached to the common node displacement region of the higher and lower resonant frequencies. Furthermore, the piezoelectric actuator stack does not need to be located at the centroid of the ultrasonic transducer. In other words, it is not necessary to design the ultrasonic transducer so that its centroid coincides with the center of the transducer's aperture. Due to these arrangements, the selectable range of drive frequencies for both higher and lower resonant frequencies is greatly improved compared to prior art ultrasonic transducers. Specifically, in existing ultrasonic transducers, due to the transducer's structure and arrangement, in order to obtain pure axial drive with high bending stiffness, the higher resonant frequency must be less than three times the lower resonant frequency in the high resonant mode of 200kHz to 300kHz. However, using the ultrasonic transducer provided in the embodiments of the present invention, the higher resonant frequency can be more than three times the lower resonant frequency.

[0062] Although the invention has been described in considerable detail with reference to certain embodiments, other embodiments are also possible. Therefore, the spirit and scope of the appended claims should not be limited to the embodiments described herein.

Claims

1. An ultrasonic transducer configured to selectively operate at a first resonant frequency or a second resonant frequency during wire bonding operations, the ultrasonic transducer comprising: An elongated transducer body having apertures for mounting a stack of piezoelectric actuators to drive the ultrasonic transducer to operate at a first or second resonant frequency, wherein the length of the transducer body is substantially equal to two wavelengths of a first oscillating wave transmitted along the length of the transducer body when the transducer operates at the first resonant frequency, and substantially equal to half the wavelength of a second oscillating wave transmitted along the length of the transducer body when the transducer operates at the second resonant frequency. The mounting flange is connected to the first node vibration region of the transducer body. This first node vibration region is the node vibration region where the ultrasonic transducer operates at a first resonant frequency. A rigid connecting member having a first end and a second end, the first end being connected to the mounting flange, and the second end being connected to a second node vibration region of the transducer body, the second node vibration region being the node vibration region of the ultrasonic transducer when it operates at a first resonant frequency.

2. The ultrasonic transducer according to claim 1, wherein, The first resonant frequency is between 200 kHz and 300 kHz, and the second resonant frequency is between 50 kHz and 100 kHz.

3. The ultrasonic transducer according to claim 1, wherein, The transducer body has a first end and a second end opposite to the first end, and the aperture is closer to the first end than the second end.

4. The ultrasonic transducer according to claim 3, wherein, The bonding tool is attached to the second end of the transducer body.

5. The ultrasonic transducer of claim 1 further comprises at least one elastic preload element located in the pore to provide a preload structure with non-uniform thickness for generating preload on the piezoelectric actuator stack to minimize vibration and rotation of the transducer body.

6. The ultrasonic transducer according to claim 1 further includes a flexible connecting element extending between the mounting flange and the transducer body at the first node vibration region of the transducer body.

7. The ultrasonic transducer according to claim 6, wherein, The flexible connection element includes at least one flexible member extending between the mounting flange and the transducer body.

8. The ultrasonic transducer according to claim 1, wherein, The rigid connection member includes: a first portion extending from the second node vibration region of the transducer body in an axial direction perpendicular to the transducer body; and a second portion extending from the first portion in an axial direction of the transducer body, the second portion being connected to the mounting flange.

9. The ultrasonic transducer according to claim 8, wherein, The ratio Rh of the height of the first portion in a first direction perpendicular to the axial direction of the transducer body to the thickness of the second portion in a second direction perpendicular to the axial direction of the transducer body is selected such that: Rh 2 >Rb, where Rb refers to a predetermined ratio of the bending stiffness about the second direction to the bending stiffness about the first direction.

10. The ultrasonic transducer according to claim 9, wherein, The predetermined ratio is 10, and the height of the first part in the second direction is not less than 3.2 times the thickness of the second part in the first direction.

11. The ultrasonic transducer according to claim 1, wherein, The first node vibration region is located near the pore, and the distance between the second node vibration region and the bonding tool is less than the distance between the first node vibration region and the bonding tool.

12. The ultrasonic transducer according to claim 1, wherein, The first node vibration region and the second node vibration region of the transducer body are configured such that when the ultrasonic transducer operates at the first resonant frequency, the vibration amplitude of each of the first and second node vibration regions is not higher than 10% of its maximum vibration amplitude.

13. The ultrasonic transducer according to claim 1, wherein, The first node vibration region and the second node vibration region of the transducer body are configured such that when the ultrasonic transducer operates at the second resonant frequency, the first vibration point located at the first node vibration region of the transducer body and the second vibration point located at the second node vibration region oscillate with substantially equal and opposite vibration amplitudes.

14. The ultrasonic transducer according to claim 1, wherein, The second resonant frequency is less than one-third of the first resonant frequency.

15. The ultrasonic transducer according to claim 1, wherein, The mounting flange includes a first flange element and a second flange element symmetrically arranged on opposite sides of the transducer body.

16. The ultrasonic transducer of claim 15, further comprising a first flexible connecting element extending between the first flange element and the transducer body, and a second flexible connecting element extending between the second flange element and the transducer body.

17. The ultrasonic transducer according to claim 16, wherein, The first and second flexible connecting elements are respectively located at the first and second points of the second node vibration region on the transducer body, and the first and second points of the second node vibration region are symmetrically located on opposite sides of the transducer body.

18. The ultrasonic transducer according to claim 15, further comprising a first rigid connecting element and a second rigid connecting element symmetrically arranged on opposite sides of the transducer body, each rigid connecting element having a first end and a second end. in, The first end of the first rigid connecting element is connected to the transducer body at a first point in the first node vibration region, and the second end of the first rigid connecting element is connected to the first flange element; and The first end of the second rigid connecting element is connected to the second point of the vibration region of the first node, and the second end of the second rigid connecting element is connected to the second flange element; Furthermore, the first and second points of the first node vibration region are symmetrically located on opposite sides of the transducer body.

19. An ultrasonic wire bonding device, comprising the ultrasonic transducer according to claim 1.

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