Ultrasonic transducer operable at multiple resonant frequencies
An ultrasonic transducer that is configured to selectively operate at first or second resonant frequency during wire bonding operations includes an elongated transducer body an aperture for mounting a piezoelectric driver stack for driving 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 operated at the first resonant frequency. The elongated transducer has a length substantially equal to two wavelengths of a first oscillatory wave that is transmitted along the length of the transducer body when the transducer is operated at the first resonant frequency, and substantially equal to a half wavelength of a second oscillatory wave that is transmitted along the length of the transducer body when the transducer is operated at the second resonant frequency.
1 . An ultrasonic transducer configured to selectively operate at both a first resonant frequency in a first oscillatory mode where a first oscillatory wave is transmitted along a length of the transducer and a second resonant frequency in a second oscillatory mode where a second oscillatory wave is transmitted along the length of the transducer during wire bonding operations, the ultrasonic transducer comprising:
an elongated transducer body with an aperture for mounting a piezoelectric driver stack for driving the ultrasonic transducer to operate at the first or second resonant frequency, wherein the transducer body is dimensioned such that its length is substantially equal to two wavelengths of the first oscillatory mode, and substantially equal to a half wavelength of the second oscillatory mode,
a mounting flange connected to the transducer body at a first nodal vibration region of the transducer body associated with the first oscillatory mode, and
a first connecting member having a first end connected to the mounting flange and a second end connected to the transducer body at a second nodal vibration region associated with the first oscillatory mode.
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, the aperture being closer to the first end than the second end.
4 . The ultrasonic transducer according to claim 3 , wherein a bonding tool is attached to the second end of the transducer body.
5 . The ultrasonic transducer according to claim 1 , further comprising at least one preloading element located in the aperture to provide a preloading structure having a non-uniform thickness for generating a preload force against the piezoelectric driver stack to minimize vibration and rotation of the transducer body.
6 . The ultrasonic transducer according to claim 1 , wherein the mounting flange is connected to the transducer body through a second connecting member extending between the mounting flange and the transducer body at the first nodal vibration region of the transducer body.
7 . The ultrasonic transducer according to claim 6 , wherein the second connecting element includes at least one flexure extending between the mounting flange and the transducer body.
8 . The ultrasonic transducer according to claim 1 , wherein the rigid connecting member includes a first portion extending from the second nodal vibration region of the transducer body in a direction perpendicular to an axial direction of the transducer body, and a second portion extending from the first portion along the axial direction of the transducer body, the second portion being connected to the mounting flange.
9 . The ultrasonic transducer according to claim 8 , wherein a ratio Rh of a height of the first portion in a first direction perpendicular to the axial direction of the transducer body to a 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 a bending stiffness around the second direction to a 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 portion in the second direction is not less than 3.2 times the thickness of the second portion in the first direction.
11 . The ultrasonic transducer according to claim 1 , wherein the first nodal vibration region is located adjacent to the aperture, and a distance between the second nodal vibration region and a bonding tool is smaller than a distance between the first nodal vibration region and the bonding tool.
12 . The ultrasonic transducer according to claim 1 , wherein each of the first and the second nodal vibration regions has a vibration amplitude not higher than 10% of a maximum vibration amplitude thereof when the ultrasonic transducer is operated at the first resonant frequency.
13 . The ultrasonic transducer according to claim 1 , wherein when the ultrasonic transducer is operated at the second resonant frequency, a first vibration point at the first nodal vibration region of the transducer body and a second vibration point at the second nodal vibration region oscillate at 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 first and second flange elements that are disposed symmetrically on opposite sides of the transducer body.
16 . The ultrasonic transducer according to claim 15 , further comprising a second connecting element extending between the first flange element and the transducer body, and a third connecting element extending between the second flange element and the transducer body.
17 . The ultrasonic transducer according to claim 16 , wherein the second and the third connecting elements are respectively located at first and second points at the second nodal vibration region on the transducer body, the first and second points of the second nodal vibration region being symmetrically located on opposite sides of the transducer body.
18 . The ultrasonic transducer according to claim 15 , further comprising a fourth connecting element, wherein the first and the fourth connecting elements are arranged symmetrically on opposite sides of the transducer body, the fourth connecting element having first and second ends,
wherein the first end of the first connecting element is connected to the transducer body at a first point at the first nodal vibration region, and the second end of the first connecting element is connected to the first flange element, and
the first end of the fourth connecting element is connected to a second point at the first nodal vibration region, and the second end of the fourth connecting element is connected to the second flange element, and
wherein the first and second points of the first nodal vibration region are symmetrically located on opposite sides of the transducer body.
19 . An ultrasonic wire bonding device comprising an ultrasonic transducer according to claim 1 .