JP2559602B2 - Ultrasonic transducer for wire bonder - Google Patents

Description

TECHNICAL FIELD The present invention relates to an ultrasonic transducer used in an ultrasonic wire bonder for manufacturing a semiconductor integrated circuit.

[Prior Art] An ultrasonic wire bonder is provided with optimum bonding conditions depending on the bonding line, speed, pressure, time, dynamic friction coefficient, and the like.

Assuming that the speed of the bonding tool is V, the resonance frequency is f, the tip vibration amplitude is ξ, and the bonding time is t under a constant condition, the relationship of tV ^α = C (1) V = ωξ = 2πfξ (2) is experimentally obtained. Is obtained.

 However, C is a constant, 1 ≦ α ≦ 6.

Therefore, in order to shorten the bonding time t, the frequency f may be set to a high frequency but the vibration amplitude ξ may be set to a high amplitude.

However, if the vibration amplitude is set to a high amplitude, the amount of deformation of the bonding wire becomes excessive and, in addition, there is a risk of damaging the welded chip, so it is necessary to suppress the vibration amplitude to a certain level or less.

Therefore, the most effective means to shorten the bonding time is to set the bonding frequency f to a high frequency, but f is 60KH.
I cannot find an ultrasonic wire bonder that uses a lot of z and has a frequency of 100 KHz or more and high speed (bonding time is short) and high reliability.

An example of a conventional ultrasonic transducer for a wire bonder is shown in FIG.

As shown in the figure, the ultrasonic transducer for wire bonder is a bolted Langevin type ultrasonic transducer (hereinafter abbreviated as BLT) 1 having a resonance frequency of 60 KHz, a cone 2 and a horn 3. It is tightened by 7,8 to form an integral structure.

The material of each component is the back body 1a and front body 1c of BLT.
Is a high strength aluminum alloy, the hollow electrostrictive element 1b is lead zirconate titanate, the cone 2 is titanium, and the horn 3 is stainless steel.

A wire 10 is installed on the tip of a tool 9 through a hole 4 for supplying a wire in the horn 3, and a vibration mode 11 of the entire vibrator is a two-wavelength resonance type. As illustrated in FIG. 4, in the conventional ultrasonic transducer, in addition to heat loss due to ultrasonic elastic vibration caused by the horn material being stainless steel,
Heat loss in the boundary layer and in each connecting screw occurs due to the non-uniform acoustic properties between the components. This heat loss does not pose a practical problem up to a resonance frequency of about 60 KHz, but 1
It is not suitable for ultrasonic transducers for wire bonders of 00 KHz or higher.

Also, since the position of the electrostrictive element of the BLT is not installed near the maximum point of the BLT, the dynamic admittances of even number of electrostrictive elements constituting the BLT become uneven, and each is proportional to the dynamic admittance. The vibration speed of the electrostrictive element is also non-uniform.

While the most effective BLT is realized when the force that each electrostrictive element can have is uniformly concentrated, the BLT is vibrated with a driving force that does not damage the electrostrictive element that has the largest dynamic admittance in the past. Therefore, there is a drawback that it is practically required to be used with low efficiency.

As illustrated in FIG. 4, the conventional cone 2 has a support structure by the flange 5 on the node surface of vibration.

However, since the wire feeding hole 4 of the horn 3 is asymmetric with respect to the central axis of the BLT, the nodal surface of the cone is also not axisymmetric.

Nevertheless, since the flange 5 has a virtually axisymmetric structure, ultrasonic vibration leaks to the same flange, and when the flange is tightened on the support, the leakage vibration energy differs depending on the tightening condition, and the tool that interlocks with it. 9 had a drawback that the vibration speed fluctuated.

Further, the set length l ₃ of the tool 9 is uniquely determined by the angle formed by the position of the wire feeding hole 4 and the central axis. Therefore, it is impossible to cope with different tool set lengths with the same horn. was.

[Problems to be solved by the invention]

The prior art, when applied to an ultrasonic bonder utilizing a high frequency of 100 KHz or more, a hollow electrostrictive element and BLT,
There is heat generation at the boundary between the cone and the horn screw connection, and heat generation due to internal loss of the horn, which is practically impossible.

Further, when the frequency is 100 KHz or higher, the fluctuation of the tool vibration due to the flange mounting condition due to the axial asymmetry of the vibration nodal surface increases, and the flange structure of FIG. 4 becomes unsuitable for practical use.

In the prior art, it was not possible to realize an ultrasonic bonder that can handle different tool setting lengths with a single horn, but in the case of a high frequency bonder, fine adjustment of the tool setting length is required, so this problem is more than conventional. Cannot be overlooked.

An object of the present invention is to solve the above problems and provide an ultrasonic vibrator for a wire bonder that can be used at a resonance frequency of 100 KHz or higher.

[Means for solving problems]

In order to solve the above-mentioned problems, the back body of the ultrasonic transducer is viewed from the unloaded end of the back body by the dynamic admittance of the BLT.
The length that becomes the maximum value at the distance of mm or more first, the front body has an integrated structure including the cone and the horn, the material of both is titanium alloy, and the harmonic resonance frequency of the synthetic BLT is set to 100 KHz or more. A slit for wire supply is installed on the body,
Adjacent two nodal surfaces of the front body are supported by a plurality of set screws.

[Work]

In this structure, the BLT, cone, and horn are integrated with one connecting screw, so the boundary layer that causes vibration loss is very small, and the internal friction due to vibration is low. A high-frequency bonder oscillator is realized.

Since even number of electrostrictive elements are driven at constant speed, the usage conditions of the electrostrictive elements are increased, and drive energy is concentrated on a single electrostrictive element as in the past, and problems such as damage eventually occur. Is wiped out.

Further, by providing a wire supply slit on the front body, a variable tool setting length is possible, and in addition, the vibration nodal surface of the front body is substantially perpendicular to the axis. Therefore, by holding the adjacent vibration node surfaces with the set screw, it is possible to provide a structure in which the tool vibration amplitude is not affected by the holding conditions of the vibrator.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of an ultrasonic vibrator for a wire bonder of the present invention.

In this figure, the tool 9 and the wire 10 are the same as in FIG. 12 is a back body, 13 is an even number of hollow electrostrictive elements, 14 is a front body, 15 is a connection screw, 16 is a wire supply slit, 19 is a vibrator holder, 20 is a set screw for supporting the front body 14, 21 Is the vibration mode of the ultrasonic transducer. In FIG. 1, the rear body 12 and the front body 14 are made of titanium alloy, and the rear body 12 is the BLT1 shown in FIG.
In a, the front body 14 corresponds to the integrated structure of FIG. 1c, connecting screw 7, cone 2, connecting screw 8 and horn 3.

In Fig. ₁ , assuming that the length of the back body 12 is l ₁ and the total length of the electrostrictive element 13 is 2 l ₂ , the influence of the connecting screw 15 is ignored and the dynamic admittance exhibited by the hollow electrode plates 17 and 18 of the BLT. Ym Becomes

However, K = constant n = 1,2,3 βi = ω / Ci wavelength constant of element i ω = 2πf f = fundamental wave frequency Ci = sound speed of element i k = S ₂ ρ ₂ C ₂ / S ₁ ρ ₁ C ₁ Let Si = cross-sectional area of element i ρi = density of element i.

FIG. 2 shows a dynamic admittance characteristic diagram in which the relationship of equation (3) is applied to the ultrasonic transducer of FIG.

This figure is for explaining the effect of the present invention, and the harmonic frequency is 120 KHz.
The relationship between the installation position (back body length l ₁ ) of the hollow electrostrictive element at (f = 20KHzn = 6) and Ym / K ² is that 22,23,24 are 5 mm in total length 2l ₂ of the electrostrictive element, respectively. For 2.5 mm and 1 mm.

From the figure, when the total length 2l ₂ of the electrostrictive element is 5 mm, the dynamic admittance has a maximum value when the length l ₁ of the back body is 6.6 mm.

The maximum value of dynamic admittance is calculated from equation (3). Given in.

 However, m is a positive integer given by 0 ≦ m <n.

In formula (4), when m = 0 and l ₁ a <6 mm, the back body
The 12 threads are not long enough for the mating threads 15 to mate. In this case in the same manner sought l ₁ a (4) determine the l ₁ a as m = 1 in formula, but when the time of l ₁ a <6 of m = 2, the first l ₁ a ≧ 6 Let l ₁ a when m such that is the length of the back body.

By installing the wire feeding slit 16 in the plane including the central axis, the vibrating nodal surface of the front body becomes almost orthogonal to the axis, so that by supporting the vibrating nodal surface adjacent to each other with the set screw 20, the synergistic effect is achieved. The tool tip width is not affected by the support condition of the holder 19.

Further, the wire feed slit can feed the wire even if the set length l ₃ of the tool in FIG. 1 changes like a solid line and a chain line.

FIG. 3 shows an ultrasonic oscillator free admittance diagram showing the effect of the present invention and a conventional ultrasonic oscillator free admittance diagram.

In the figure, reference numerals 25 and 26 are ultrasonic transducer free admittance diagrams of FIGS. 1 and 4, respectively.

From FIG. 3, f ₀ ≈ 118.9 KHz, Q ≈ of the ultrasonic transducer of the present invention
4663 The conventional ultrasonic transducer has f ₀ ≈ 60.4 KHz and Q ≈ 2237.

Q represents the mechanical sharpness of the ultrasonic oscillator and is a numerical value that is inversely proportional to the mechanical loss of the oscillator.

The ultrasonic oscillator of the present invention has a resonance frequency twice as high as that of the conventional oscillator, but the Q is almost doubled to enable low-loss drive, and there is no practical problem. If the vibrator having the conventional structure is applied to 120 KHz, the Q is reduced to about 10% of that of the vibrator of the present invention, and the mechanical loss becomes 10 times, which is not practical.

〔The invention's effect〕

According to the present invention, since bonding can be performed at a higher frequency than the conventional ultrasonic bonder, the bonding speed is high, the amount of wire deformation is small, and at the same time there is no damage to the welded tip, and a highly reliable ultrasonic bonder is provided. Can be provided. In addition, since the sample on the sample table is hard to jump, there is little variation in bonding strength.

Furthermore, even if the tool setting length is changed, the same vibrator can be used, so a bonder with high work efficiency can be realized.

[Brief description of drawings]

FIG. 1 is an embodiment of an ultrasonic vibrator for a wire bonder of the present invention, FIG. 2 is a rear body length and dynamic admittance characteristic diagram of the ultrasonic vibrator for explaining the effect of the present invention, and FIG. Ultrasonic transducer free admittance diagram showing the effect, and FIG. 4 is a sectional view of a conventional ultrasonic transducer for a wire bonder. 9 ... Tool, 10 ... Wire, 12 ... Rear body, 13 ... Hollow electrostrictive element 14 ... Front body, 15 ... Joining screw, 16 ... Wire supply slit, 19 ... Transducer holder, 20 …… Set screw.

Claims (4)

(57) [Claims] 1. A hollow electrostrictive element (13) and a hollow electrode plate (1)
Front body (14) and back body (1) that sandwich (7), (18)
2), the hollow electrostrictive element (13) and the hollow electrode plate (17),
In the bolted Langevin type ultrasonic transducer, which comprises a central bolt (15) which penetrates the hollow portion of (18) and is screwed into the central screw hole of the front body (1C) and the rear body (12), the front body (14 ) And the back body (12) are made of titanium alloy, and the front body (14) is an integral structure including the front body (14), the cone (2) and the horn (3) of the ultrasonic transducer for wire bonder, The harmonic resonance frequency of the ultrasonic transducer is 10
Ultrasonic transducer for wire bonder characterized by being configured to be 0 KHz or higher. 2. The position of the hollow electrostrictive element (13) is installed near the position where the dynamic admittance exhibited by the ultrasonic transducer first reaches a maximum value at a distance of 6 mm or more when viewed from the unloaded end of the back body (12). The ultrasonic transducer for a wire bonder according to claim 1, characterized in that 3. The ultrasonic wave for wire bonder according to claim 1, wherein the two nodal surfaces of vibration of the front body (14) adjacent to each other are supported by a plurality of set screws (20). Oscillator. 4. The ultrasonic vibrator for a wire bonder according to claim 1, wherein a slit (16) for supplying a wire is provided on the load side of the front body (14).