A novel ultrasonic transducer comprises a machined solid metal unibody having a rectangular aperture in the center between a tool mounting end and a balanced end. The end portions are connected by two axial side members which connect to two transverse sides of the rectangular aperture. A stack of piezo electric crystals are mounted in said rectangular aperture between the transverse sides and spaced apart from the axial sides of the aperture. A bonding tool is mounted in a cylindrical aperture in the mounting end of the transducer and tightly mechanically coupled to the mounting end so that the stack of piezo electric crystals are acoustically coupled through the unibody to the bonding tool in a cylindrical aperture by a tightly coupled mounting surfaces.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to ultrasonic transducers of the type 
employed to bond two metallic elements together. More specifically, the 
present invention relates to a more efficient transducer of the type used 
on automatic wire bonders and ultrasonic machines employed in the 
semiconductor and other industries. 
2. Description of the Prior Art 
Heretofore, it was known that dissimilar metals could be joined at 
relatively low temperatures by the simultaneous application of pressure 
and ultrasonic energy applied through means of bonding tools mounted on or 
in ultrasonic transducers. At least since the introduction of integrated 
circuits in the 1960s, semiconductors have been bonded to a substrate or 
carrier using ultrasonic energy and fine wires have been interconnected 
from lead out pads on the semiconductor die to leads on carriers, 
substrates and lead frames using bonding tools mounted in ultrasonic 
transducers. 
Heretofore, ultrasonic transducers that were designed for use on flip chip 
die and wire bonders have remained substantially unchanged for years. Such 
prior art ultrasonic transducers comprise a large number of individual 
parts that are difficult to assembly. Once the prior art transducers were 
assembled, they had to be tested, sorted, tuned and reworked. It was 
common practice to trim metal from the transducer driver in an attempt to 
adjust the transducer to a desired frequency and/or to save the transducer 
as an operative device. Such transducers are known as having high "Q" 
systems. 
It would be highly desirable to provide a radically new ultrasonic 
transducer that eliminates most of the problems associated with prior art 
ultrasonic transducers. 
SUMMARY OF THE INVENTION 
It is a primary object of the present invention to provide a novel unibody 
ultrasonic transducer that is better, cheaper and more reliable than prior 
art transducers. 
It is a primary object of the present invention to provide a novel unibody 
ultrasonic transducer that has fewer parts, and transfers ultrasonic 
energy more efficiently and is more stable over a wide range of 
frequencies than prior art transducers. 
It is a primary object of the present invention to provide a novel 
ultrasonic driver for a novel unibody transducer that is easy to assemble 
and produces predictable and uniform results. 
It is a primary object of the present invention to provide a novel 
ultrasonic driver for a novel unibody transducer that seldom, if ever, 
requires frequency adjustment and when required is easily and simply 
performed. 
It is a primary object of the present invention to provide a novel unibody 
transducer that comprises an integral mounting flange located at the zero 
node of the ultrasonic driver mounted in the unibody that is substantially 
insensitive to the supporting structure on which it is mounted. 
It is another primary object of the present invention to provide a novel 
unibody transducer that comprises an integral mounting flange on a unibody 
that is not subject to radial expansion and contraction. 
It is a general object of the present invention to provide a novel 
capillary to mounting and clamping structure in an ultrasonic transducer. 
It is a general object of the present invention to provide a novel unibody 
ultrasonic transducer that may be built to exact frequency requirements by 
scaling. 
According to these and other objects of the present invention, there is 
provided a novel ultrasonic transducer comprising a machined solid metal 
unibody having a rectangular aperture in the center between two end 
portions connected by two axial side members which form transverse sides 
of the rectangular aperture. A stack of piezo electric crystals are 
mounted in said rectangular aperture between the axial sides of the 
aperture. The stack of piezo electric crystals are acoustically coupled to 
the bonding tool by a plurality of tapered shaped self-locking wedges 
which mount the piezo electric crystals in compression in the rectangular 
aperture. A bonding tool is mounted in a cylindrical aperture in one of 
the end portions.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Refer now to FIG. 1 showing an isometric drawing of a typical prior art 
ultrasonic transducer 10. The transducer 10 comprises numerous parts which 
are bolted together. The transducer horn 11 has mounted thereon a mounting 
flange 12 which can be tightly mounted or an integral part of the horn 11. 
The rear portion of the transducer horn 11R is provided with a threaded 
hole 13 which is aligned with a hole through front bell 14 of the driver 
20 shown having two flats 16 and a threaded through hole 17. A threaded 
screw 15 is mounted in the threaded holes 13 and 17 and connects the rear 
of the horn 11R to the front bell 14. A plurality of piezo electric 
crystals 19 are shown mounted between the front end bell 14 and a rear end 
bell 18. 
Refer now to FIG. 2 and 2A showing a plan view of the transducer driver 20 
of FIG. 1 attached to a horn 11R. The horn 11R is shown having a threaded 
aperture 13 which receives the threaded screw 15 and connects the front 
bell 14 of the driver 20 to the horn 11. The mounting flange 12 is shown 
having a thin diaphragm 12D which is mounted at the zero node of the horn 
11. 
The rear or end bell 18 is provided with a through hole for receiving a cap 
screw 21 therethrough. The threaded end of the cap screw 21 is connected 
into the threaded through hole 17 in the front bell 14. Tightening the cap 
screw 21 places the crystals 19 in compression sufficient that during 
operation they stay in the compression mode. Each of the crystals has a 
positive and a negative side which is indicated opposite the terminals 22. 
In the enlarged view shown in the circle, there is shown an electrically 
conductive shim 23 which is provided with a thin epoxy layer 24 on either 
side to give a tight surface to surface connection between the crystals 
19. In the preferred way of assembling the shims, the epoxy layer 24 is 
wet and compressed to squeeze out any excess when the cap screw 21 is 
tightened to its predetermined force by a predetermined torque value,. 
It will be noted that the prior art transducer 10 comprises at least five 
separate parts which are bolted together by screws 15 and 21 and that the 
mounting flange 12 may be a separate part which would simplify its 
manufacture. 
Refer now to FIG. 3 showing an enlarged plan view in partial section of the 
prior art transducer horn 11 showing a capillary recess 25 having a relief 
recesses 26 at the front and rear. The front end of the transducer horn 11 
is provided with a through hole 27 for receiving a cap screw 28 which 
threads into a square nut 29. Tightening the cap screw 28 reduces the size 
of the capillary recess 25, thus tightening the capillary by flexing the 
relief recesses 26. The problem with this prior art recess 25, 26 is that 
after prolonged usage and changing of tools it causes the hole to become 
elliptical and it loses its grip on the capillary (not shown). Further, 
the diameter of commercially available capillaries are not uniform, thus 
causing a loose fit of any undersized new capillary which accelerates the 
wear in the recess 25. If the capillary is too large, it cannot be fitted 
into the recess 25 or fits so tight as to become jammed in the hole. 
Refer now to FIG. 4 showing a plan view of a typical preferred embodiment 
unibody portion of an ultrasonic transducer. The transducer unibody 31 is 
shown having a front end 32 and a rear end 33 which are substantially 
similar. The front end 32 is provided with a wire receiving cone 34 which 
connects to a tool receiving cylinder 35. A through hole or key hole 36 is 
shown in phantom lines transverse to the tool receiving hole 35. A 
rectangular aperture 37 is provided at the geometrical center line 38 of 
the transducer body 31. The rectangular aperture 37 has two axial sides 39 
and two transverse sides 41 for engaging the piezo electric crystals (not 
shown). In the preferred embodiment of the present invention, when the 
piezo electric crystals are mounted in the aperture 37, they abut the 
transverse sides 41 to place the piezo electric crystals in compression, 
but are spaced apart from the axial sides 39 as shown by the clearance 
line 42. Thus, it will be understood that the piezo electric crystals 
expand in the axial direction against the abutting transverse walls 41 but 
do not touch the axial sides 39. 
Refer now to FIG. 5 showing an elevation view of the present invention 
unibody transducer shown in FIG. 4. The elements explained with reference 
to FIG. 4 are numbered the same in FIG. 5 and do not require additional 
explanation. The mounting flanges 43 are shown having mounting holes 44. 
The recess 45 is provided for clearance of cap screws or bolts used for 
mounting the flange 43 onto a supporting structure. It will be noted that 
the flange 43 is centered on center line 38 at the center of the 
rectangular aperture 37 so it will be at the zero node of the driver to be 
explained in greater detail hereinafter. 
The through hole or key hole 36 is shown intercepting the tool receiving 
cylinder 35 which interconnects with the wire receiving cone 34. It will 
be noted that the front end 32 is provided with a taper 32T and that the 
symmetrical end 32 will have less mass than its symmetrical end 33. The 
amount of mass removed by the taper 32T is equal to the amount of mass 
added by the capillary bonding tool (not shown) and the locking mechanism 
to be explained hereinafter. 
Refer now to FIG. 6 showing an isometric view of the present invention 
ultrasonic transducer and also showing the transducer drivers and 
capillary clamping mechanism. The unibody and driver have been numbered 
the same as FIGS. 4 and 5 and do not require additional explanation. The 
key hole 36 is shown having a flat mounting surface 36F for receiving 
therein a pair of cylindrical clamping elements 47 and 48 also having a 
similar flat surface. The cylindrical clamping elements 47 and 48 are 
provided with inclined cam surfaces 49 which engage upon the capillary 46 
when the cap screw 51 is threaded into the threaded hole 53 of the 
cylindrical element 48. The cylindrical element 47 is provided with a 
through hole 52 which is not threaded. When the cap screw 51 is turned and 
threaded into the threaded hole 53, the two cylindrical elements 47 and 48 
are loose in the key hole 36 and are biased towards each other and against 
the side wall of the capillary 46 in line contact and are forced in 
surface contact with the flat 36F, thus providing an excellent mechanical 
coupling. 
The rectangular aperture 37 having axial side walls 39 and transverse side 
walls 41, are shown having mounted therein a plurality of piezo electric 
crystals 54 separated by a plurality of shims 55 each having an electrical 
connecting tab 56. 
Shown directly above the piezo electric crystals 54 is a preferred wedge 
mechanism 57 which comprises three elements. The center element is a 
double tapered wedge 58 having removing ears 59 fitted between a pair of 
single tapered wedges 61. The angle of the taper between the wedges 58 and 
61 is designed to be self-locking. The surface of the wedges 58 and 61 is 
relatively smooth but enhances self-locking when forced together under 
pressure. A predetermined amount of pressure in the vertical direction 
will result in a known amount of compressive force in the axial direction 
as is well known in the wedge and cam art. Thus, the piezo electric 
crystals and shims may be placed in the rectangular aperture 37 separated 
from the sides 39 and then compressed to a predetermined compression force 
by inserting the wedge 59 into the wedges 61. Testing after the fact, 
confirms that the resonant frequency and amount of compression was 
correct. 
In the preferred embodiment of the present invention, careful manufacture 
of the unibody 10 and assembly of the drivers usually results in obtaining 
the proper predetermined frequency. However, it is possible to remove 
material from the extreme ends 32 and 33 which will increase the 
frequency. Thus, the preferred method of manufacture is error on the low 
frequency side if the manufacturing process is not exact and precise. In 
the present invention, the shims 55 are made from an electrically 
conductive brass and do not require the aforementioned epoxy 24 to achieve 
excellent mechanical coupling. 
Refer now to FIG. 7 showing a top view of a 60 kilohertz unibody transducer 
10 which operates in a half wave (1/2 .lambda.) displacement mode as shown 
by wave form 62. The center of the wave form 62 at zero node 63 is on 
center line 38 of the drivers which comprise a plurality of piezo electric 
crystals 54 separated by electrically conductive shims 55. The stack of 
piezo electric crystals are shown engaged against the transverse walls 41 
and spaced apart from the axial sides 39. The stack piezo electric 
crystals are placed in a preferred amount of compression by the wedge 
mechanism system 57 as explained hereinbefore. The 60 kilohertz unibody 
transducer shown in FIG. 7 is divided into four 1/8.sup.th wave length 
(1/8 .lambda.) wave segments showing that the maximum displacement occurs 
at the end 40 of the unibody and not at the center 38 of the unibody. 
The horn or end 40 which holds the capillary incurs the maximum 
displacement while the mounting flange 43 incurs the minimum displacement. 
Should the horn 40 be extended a full half wave (1/2 .lambda.), a maximum 
displacement node 50 will again occur at the length of maximum 
displacement. Thus, the present unibody transducers may be lengthened by 
half wave (1/2 .lambda.) extensions E (shown in phantom lines) and still 
maintain the operational efficiency of the 60 kilohertz unibody transducer 
shown in FIG. 7. Stated differently, the 60 kilohertz transducer shown in 
FIG. 7 may be extended by one or more 1/2 wave lengths while maintaining 
the resonant frequency at 60 kilohertz. 
Refer now to FIG. 8 showing a top view of a 120 kilohertz unibody 
transducer 10 which has elements numbered identically as the elements in 
FIG. 7. It will be noted that the rectangular aperture 37 for receiving 
the piezo electric crystals is shorter in the axial direction and 
approximately the same width. However, the length of the unibody 10 is 
longer than the length of the unibody shown in FIG. 7 and has a 
displacement wave form 64 that is one and one-half wave lengths overall 
(11/2 .lambda.). It will be noted that the front end 32 which holds the 
capillary has the maximum displacement and that the center of the 
transducer is provided with a zero node 65 which also occurs at the center 
of the driver. 
While the overall length of the 120 kilohertz transducer is only slightly 
longer in physical length than the 60 kilohertz transducer, it is 11/2 
wavelengths (or three times as long) even though the frequency is doubled. 
Those skilled in the art of designing transducers understand that the 
higher frequency transducer shown in FIG. 8 may be constructed by scaling 
from the model of the lower frequency transducer shown in FIG. 7. 
The horn or end 40' which holds the capillary incurs the maximum 
displacement and may also be extended by one-half wave lengths E' shown in 
phantom lines as explained hereinbefore. 
Refer now to FIG. 9 showing a wave form of frequency versus impedance (1/R) 
to illustrate the low Q and broad resonant frequency of the present 
invention 60 kilohertz transducer shown in FIG. 7. Q is a dimensionless 
factor that shows the mechanical efficiency of the resonant system. In 
this case, the center frequency F.sub.c is equal to 60.213 kilohertz. The 
frequency band width (.DELTA.F) at 0.707 times the peak height H, is shown 
as 740 hertz, thus Q is equal to 60,213 divided by .DELTA.F which is equal 
to 81. Stated differently the resonant frequency of the transducer can be 
varied over a range of 740 hertz without diminishing the displacement by 
approximately 30%. While not shown on FIG. 9, it is known that the Q of 
the prior art transducer shown in FIG. 1 is approximately 1200, and at a 
resonant frequency of 60 kilohertz, the same amount of displacement 
reduction will occur over a range of frequency of only 60 hertz. It will 
be appreciated that the broader .DELTA.F frequency or lower Q of the 
present invention transducer provides a wider range of operations under 
loads which changes the resonant frequency of the transducer. 
Refer now to FIG. 10 showing a wave form of frequency versus phase in 
degrees between current and the voltage. The wave form 66 is shown having 
a portion 67 where the displacement of the tip of the transducer leads the 
voltage. Then wave form 66 passes through a node 60 where the voltage and 
current are in phase, then passes into a portion 68 where the displacement 
lags the voltage and again rises to a portion 69 where the displacement of 
the end of the transducer leads the voltage. The wave form 66 is another 
representation of the insensitivity of the transducer to frequency 
variations. If the Q was larger than 81 as shown in FIG. 9, the portion of 
the curve on either side of the node 60 would be sharply inclined. 
Refer now to FIG. 11 showing an enlarged plan view in section of a 
preferred capillary clamping mechanism of the type shown in FIG. 6. The 
capillary 46 is shown engaged in line contact with the cam surfaces 49 on 
the cylindrical clamping elements 47 and 48. The line contact wears in to 
provide a concave mating surface and superior coupling. The cylindrical 
clamping element 47 is provided with a smooth through hole 52, whereas the 
cylindrical clamping element 48 is provided with a threaded through hole 
53. The rear surface of the cylindrical clamping elements 47 and 48 is 
flat so as to provide a tight mechanical coupling with the flat surface 
36F of the through hole 36. To prevent the clamping mechanism from sliding 
completely through the through hole 36, a protrusion or chamfer 71 
provided at the lower end and prevents the cylindrical element 48 from 
passing therethrough when the capillary 46 is not in place. The cap screw 
51 when tightened acts as a Dutch key to force the cylindrical surface of 
the capillary 46 into surface contact with the wall 72 of the receiving 
cylinder 35 and at the same time, causes a forcing action which engages 
the flat surface on the cylindrical elements 47, 48 against surface 36F. 
It is has been found that the clamping structure shown in FIG. 11 is 
insensitive to the size of the capillary 46 and in fact tends to wear so 
as to make a tight mating surface between the cylinder wall 35 and the 
cylinder wall 35 and the capillary 46. Further, another feature of the 
present invention is that end holder for the transducer 46 is more massive 
than a tapered horn transducer of the type shown in FIG. 1 and is less 
sensitive to breaking and fractures. 
Having explained a preferred embodiment of the present invention, it will 
be understood that the novel unibody 31 can be constructed in frequency 
harmonics of each other. The resonant frequency can cover a wide range 
selected at ranges between 20 to 200 kilohertz and still operate as an 
efficient bonding tool. 
It will be appreciated that the unibody of the present invention is much 
easier to manufacture, thus incurs less acoustic energy losses, less labor 
cost and lasts longer than prior art type transducers. Another feature of 
the present invention is that the unibody may be easily and cheaply 
constructed so uniformly so that the resonant frequency is very accurately 
predicted and repeatable. Further, the impedance of different transducers 
is within a very small range and requires less testing and tuning and 
adjusting than the prior art type transducers. Removal of an end portion 
of the balance end of approximately several millimeters will increase the 
frequency by 10 hertz in the preferred embodiment transducer shown. 
It has been found that the unibody transducer incurs less acoustic energy 
loss, thus delivers higher energy.