Control method for an automatic ultrasonic joining machine

Abstract

The invention relates to a control method for an automatic ultrasonic joining machine comprising a piezoelectric ultrasonic transducer which is electrically excited with a time-variable current i and a time-variable voltage u and mechanically oscillates at a high frequency as a result of the electrical excitation, wherein starting from a value |Y el| and a phase φel of an electrical admittance Y el determined from the current i and the voltage u a corrected admittance Y a with a value |Y a| and a phase φa is determined, and the value |Y a| of the corrected admittance Y a is used to control the piezoelectric ultrasonic transducer with respect to a first controlled variable. The invention further relates to the use of the control method to operate an automatic ultrasonic bonding machine and / or an automatic ultrasonic welding machine and / or a smart welder.

Description

[0001] Control procedure for an ultrasonic connection machine

[0002] The invention relates to a control method for an ultrasonic connection machine with a piezoelectric ultrasonic transducer, which is electrically excited with a time-variable current and a time-variable voltage and oscillates mechanically at a high frequency as a result of the electrical excitation.

[0003] Ultrasonic bonding machines include, in particular, ultrasonic wire bonders and ultrasonic welding machines. Furthermore, a so-called smart welder constitutes an ultrasonic bonding machine within the meaning of the invention. A smart welder combines elements of an ultrasonic wire bonder, namely its flexibility, precision, and speed, as well as advanced process control and quality monitoring, with elements of an ultrasonic welding machine, namely its power and ultrasonic performance.

[0004] In practice, the piezoelectric ultrasonic transducers of ultrasonic bonding machines have for many years been preferably operated in resonance and regulated to an electrical phase of 0°. This works particularly well in applications such as thin-wire bonding and classic aluminum thick-wire bonding, as the process-related damping is comparatively low. Even at high loads, a clear zero phase crossing of the electrical admittance is established in these applications, and stable control is possible.

[0005] Recently, the requirements for operating ultrasonic interconnectors have shifted towards higher power levels. For example, 500 µm copper wires, wires with a rectangular cross-section of 2000 µm x 300 µm (so-called ribbons), or load current connections with contact surfaces of 4 mm x 4 mm must be connected. In such applications, the load-side influence on the ultrasonic system is significantly greater, and consequently, the classic control approach no longer works, or at least no longer reliably, due to the lack of a phase zero crossing of the electrical phase. In these cases, it is known to control the ultrasonic transducer for a different electrical phase, for example, +30°. With ultrasonic transducers equipped with suitable sensors, the mechanical vibration and / or a proportional quantity can also be detected.Since mechanical oscillation exhibits no antiresonance, it always experiences a zero phase crossing. This property is exploited in control engineering by adjusting the mechanical phase to 0°.

[0006] The object of the present invention is to provide an improved control method for an ultrasonic connection machine with a piezoelectric ultrasonic transducer.

[0007] To solve this problem, the invention has the features of claim 1. Accordingly, a control method for an ultrasonic connection machine with a piezoelectric ultrasonic transducer, which is electrically excited with a time-variable current i and a time-variable voltage u and oscillates mechanically at a high frequency as a result of the electrical excitation, provides that, starting from a magnitude |Yei| and a phase <p ei an electrical admittance Y determined from the current i and the voltage u eia corrected admittance Y a with an amount |Y a | and a phase <p a determined and the amount |Y a | of the corrected admittance Y a is used for controlling the piezoelectric ultrasonic transducer with respect to a first controlled variable. To determine the corrected admittance Y a Here, the electrical admittance Y is preferably used. ei in relation to its imaginary part, it is corrected by the product of the angular frequency Q and the capacitance CP of the piezoelectric transducer, or the locus curve is shifted by -JQC.

[0008] The particular advantage of the invention is that a stable control algorithm is available that is independent of the load and is based on the amount |Y. a | of the corrected admittance Y aor whose amplitude is closely aligned with the actual mechanical vibration, and which, due to the absence of antiresonance in the mechanical vibration, allows for stable operation, especially in critical load cases where the vibration in the connection zone almost ceases. It is therefore unnecessary to include sensors to detect the mechanical vibration. Consequently, the design of the ultrasonic transducer or the ultrasonic connection system is simplified, and no additional costs for sensors are incurred.

[0009] According to a preferred embodiment of the invention, the corrected admittance Y is obtained a and the voltage u a kinetic current i m determined. The flow of motion i m is used for controlling the piezoelectric ultrasound transducer with respect to the first controlled variable. In particular, an amount |i mThe current flow is used as the first controlled variable for the control of the piezoelectric ultrasonic transducer. Advantageously, the magnitude |i describes the current flow. m | of the flow of motion i m The electrical quantity approximates the mechanical vibration amplitude very well, thus allowing stable, load-independent control of the ultrasonic transducer. A setpoint value for the magnitude |i m | of the flow of motion i m can be constant in terms of time, or the amount |i can be m | of the flow of motion i m The system is controlled based on a time-varying or -variable target value profile, which, for example, serves to map a specific current amplitude-time profile.

[0010] Following a further development of the invention, the corrected admittance Y is used as the basis for calculations. a and / or the flow of motion i m a mechanical admittance Y mof the piezoelectric ultrasonic transducer and / or a mechanical vibration parameter of the piezoelectric ultrasonic transducer is determined. Preferably, a movement velocity v of the piezoelectric ultrasonic transducer is used as the mechanical vibration parameter. Advantageously, this allows stable, load-independent control based on a mechanical vibration parameter, for example, the actual mechanical amplitude. The mechanical admittance Y m is approximately proportional to the corrected admittance Ya.

[0011] After further development of the invention, the phase <p a the corrected admittance Y a It is used as a second control variable for the control of the piezoelectric ultrasonic transducer. The phase is preferred. <p aThe system is controlled to a constant setpoint value or to a time-varying setpoint profile. The operation of the ultrasonic transducer is advantageously improved by further phase control. <p a the corrected admittance Y a For example, the phase <p a the corrected admittance Y a be regulated to 0°.

[0012] Further advantages, features, and details of the invention can be found in the dependent claims and the following description. The features mentioned therein can be essential to the invention, either individually or in any combination. The drawings serve only as examples to clarify the invention and are not intended to be limiting.

[0013] They show:

[0014] Fig. 1 shows an electrical equivalent circuit of a piezoelectric ultrasonic transducer of an ultrasonic junction box,

[0015] Fig. 2 shows a comparison of the frequency response of an electrical admittance and a corrected admittance in magnitude and phase.

[0016] Fig. 3 shows the locus curves for the quantities according to Fig. 2,

[0017] Fig. 4 shows a mechanical admittance extended in magnitude and phase.

[0018] Representation according to Fig. 2 and

[0019] Fig. 5 shows the locus curves for the quantities according to Fig. 4. In practice, a piezoelectric ultrasonic transducer is used, among other things, to excite a tool of an ultrasonic joining machine to high-frequency mechanical vibrations in the ultrasonic range. Typically, the frequencies are at 20 kHz or above. The excitation of the piezoelectric ultrasonic transducer is electrical, and its operation is controlled. The mechanical vibrations arise depending on the electrical excitation, the specific implementation of the ultrasonic transducer, and the load. Typically, for energy reasons, the electrical excitation is chosen such that the piezoelectric ultrasonic transducer operates in resonance, and a vibration mode corresponding to the resonance frequency is formed, depending on the load.

[0020] Fig. 1 shows an electromechanical equivalent circuit of a piezoelectric ultrasonic transducer for a specific vibration mode. The left, electrical part of the equivalent circuit interacts with the middle, mechanical part of the equivalent circuit via a coupler represented as a coil pair or transformer. The mechanical part is in turn coupled to a load part, which represents the application side or the connection process via a load damping di and a load stiffness CL. The connecting quantity between the mechanical part and the load part is the force F provided by the piezoelectric ultrasonic transducer. The equivalent model now uses the electromechanical analogies according to which the mechanical force F provided by the ultrasonic transducer corresponds to an electrical voltage and the vibration or movement velocity v to an electrical current.

[0021] The analogy can be extended to the substitute parameters. Following this analogy, the mass m corresponds to an inductance. The damping d corresponds to an electrical resistance, and the stiffness c or compliance 1 / c to a capacitance. Since the substitute model is parameterized and valid only for a specific vibration mode or resonance frequency, the mass m, the stiffness c, and the damping d are referenced to the respective vibration mode and subsequently referred to as the modal mass m, modal stiffness c, and modal damping d of the piezoelectric ultrasonic transducer. The coupling of the mechanical and electrical parts of the substitute model is achieved via a coupling factor n, which has dimensions or units. The unit of n is amperes per meter per second or, equivalently, newtons per volt.

[0022] The operating parameters current i, voltage u, velocity v, and force F are considered as complex quantities. These complex quantities are each defined by their magnitude and phase, always referring to the phase difference with respect to the voltage u.

[0023] The next consideration will focus first on the electrical admittance Y ei It is based on the quotient of current i and voltage u. It is also called electrical input admittance Y. ei denoted by the electrical admittance Y. ei is together with a corrected admittance Y a Figures 2 to 5, which will be discussed in more detail below, are shown. Figures 4 and 5 also show a mechanical admittance Y. m . Mechanical admittance will also be considered later.

[0024] In Figures 2 and 4, the upper graphs show the magnitudes |Y e i|, |Y a |, |Y m| of the electrical, corrected and mechanical admittance Y e i, Y a , Y m in amperes per volt or meters per second per volt versus frequency f in kHz, and the lower graphs show the electrical, corrected, and mechanical phase. <p e i, <p a , <p m over the frequency f in kHz. Figures 3 and 5 show the locus curves of the admittances Y. e i, Y a , Y m , where the real part is plotted on the x-axis and the imaginary part on the y-axis.

[0025] The classical control of piezoelectric ultrasonic transducers, which relies on electrical admittance and the electrical phase q> eiWhen the system regulates to 0°, it considers a phase zero crossing for control purposes. This phase zero crossing is well-suited as a reference value for control when the damping caused by the bonding process is not too pronounced. This is the case, for example, with thin-wire bonding and classic thick-wire bonding. Even under full load, a clear zero crossing of the electrical phase is typically observed. <p ei The phase control is present and has a stable operating point. However, as applications with increasingly higher process loads have recently come into focus, classical phase control is reaching its limits. This can go so far that the phase characteristic of the electrical input admittance Y ei the zero line is no longer undercut and the classical approach to controlling the electrical phase <p eiwhich is no longer applicable to zero. Such behavior is therefore observed when bonding copper wires or in modern smart welder applications in the field of manufacturing power supply connections. This is where the invention comes in. Instead of the classic electrical admittance Y ei The corrected admittance Y is used for the regulation. a used, which has knowledge of the structure of the piezoelectric

[0026] utilizes an ultrasonic transducer. A distinction is made between a portion of the current attributable to the capacitance CP of the piezoelectric ultrasonic transducer on the one hand, and a motion current i on the other. m On the other hand, a distinction is made between the force that drives the mechanical vibration of the ultrasonic transducer (compare Fig. 1). The relationship between the corrected admittance Y a and the electrical admittance Y ei This results as follows:

[0027] Y a = Yei - j_QCp

[0028] The capacitance CP of the piezoelectric ultrasonic transducer is known from its design or can be measured. This is shown in the locus diagram of the admittances Y. e i, Y a , Y m According to Figs. 3 and 5, the corrected admittance Y is a opposite to electrical admittance Y ei The imaginary part of the admittance plotted on the Y-axis is shifted downwards by the product of the angular frequency Q and the CP of the piezoelectric ultrasonic transducer.

[0029] The corrected admittance Y a Regardless of the load, it always has a zero phase crossing. The reason for this is that the mechanical vibration exhibits no antiresonance, and consequently the phase characteristic of the corrected admittance Y shown in Figures 2 and 4 is not applicable. a always has a zero crossing.

[0030] The control method according to the invention now focuses on the amount of the corrected admittance Y.a or a derivable amount, in particular the amount |i m | of the flow of motion i m , off. The flow of movement i m is the part of the current i that flows through the electrical part of the coupler and excites the mechanical oscillation.

[0031] Instead of the corrected admittance Y a According to the invention, the mechanical admittance Y can be applied to the mechanical admittance Y. m be switched off. The mechanical admittance Y m As the locus diagram in Fig. 5 shows in particular, it is, to a first approximation, proportional to the corrected admittance Y. a , where the coupling factor n of the coupler forms the proportionality factor. For the mechanical admittance Y m A mechanical vibration parameter is preferably used for control. In particular, the control system uses the amplitude or magnitude of the motion velocity v, which, according to the analogy, corresponds to the motion flow i. mis proportional: v = n ■ in

[0032] Focusing on the corrected admittance Y a or the mechanical admittance Y m This control system offers more than just the stability advantage at high loads. Furthermore, the control system is based on the electrical admittance Y. aDuring operation, frequency shifts relative to the instantaneous resonant frequency increasingly deviate from the actual mechanical vibration. This is exemplified in Fig. 4: While the deviation Ai of the electrical admittance from the corrected admittance is comparatively small at a frequency f of 37 kHz, it increases significantly towards lower frequencies. The deviation A2 at a frequency f of 36 kHz and the deviation A3 at a frequency f of 35 kHz are shown as examples. The control method according to the invention is therefore considerably more robust, even with deviations in the frequency f of the ultrasonic vibration, and thus better represents the actual process.

[0033] The locus curves in Figures 3 and 5 show the influence of the capacitance CP of the piezoelectric transducer on the control based on the electrical admittance Y. ei on the one hand, and the corrected admittance Y aor the mechanical admittance Y m On the other hand. Since the electrical phase q> ei The shift of the locus curve by QCP is greater than the corrected phase. <p a or the mechanical phase q>m, a deviation also occurs with respect to the magnitude | Y. e i| of the electrical admittance Y ei on the one hand and the amount |Y a |, |Y m | of the corrected admittance Y a or the mechanical admittance Y m On the other hand, the regulation of the connection procedure based on the amount |Y a | of the corrected admittance Y a or the amount |Y m | of mechanical admittance Y m This is particularly accurate under high loads. If the phase is also controlled, the control is based on the corrected phase. <p a or the mechanical phase q> mmore stable, since the mechanical oscillation shows no anti-resonance and is corrected for the phase <p a or the mechanical phase q> m unlike for the electrical phase q> ei A phase zero crossing always exists.

[0034] List of formula symbols

[0035] Ai deviation at 37 kHz

[0036] A2 deviation at 36 kHz

[0037] A3 Deviation at 35 kHz c modal stiffness of the piezoelectric ultrasonic transducer

[0038] CL load stiffness

[0039] CP capacitance of the piezoelectric ultrasonic transducer d modal attenuation of the piezoelectric ultrasonic transducer di. load attenuation f frequency

[0040] Force in current in the flow of motion

[0041] |im| magnitude of the moving current j complex unit m modal mass of the piezoelectric ultrasonic transducer n coupling factor u voltage v velocity of movement

[0042] | v| Magnitude of the velocity of motion

[0043] Y a corrected admittance

[0044] | Y a | Amount of corrected admittance

[0045] Yei electrical admittance

[0046] | Yei| Amount of electrical admittance

[0047] Y m mechanical admittance

[0048] |Y m | Magnitude of mechanical admittance

[0049] <p a Phase of corrected admittance q>ei Phase of electrical admittance q>m Phase of mechanical admittance

[0050] Q angular frequency

Claims

Patent claims 1. Control method for an ultrasonic connection machine with a piezoelectric ultrasonic transducer, which is electrically excited with a time-variable current i and a time-variable voltage u and oscillates mechanically at a high frequency as a result of the electrical excitation, wherein starting from a magnitude | Y e i| and a phase q> ei an electrical admittance Y determined from the current i and the voltage u ei a corrected admittance Y a with an amount |Y a | and a phase <p a determined and the amount |Y a | of the corrected admittance Y a is used for controlling the piezoelectric ultrasound transducer with respect to a first controlled variable.

2. Control method according to claim 1, characterized in that the corrected admittance Y a and the voltage u a kinetic current i m is determined, whereby the flow of motion im is used for controlling the piezoelectric ultrasound transducer with respect to the first controlled variable.

3. Control method according to claim 1 or 2, characterized in that an amount |i m | of the flow of motion i m is used as the first controlled variable for the control of the piezoelectric ultrasound transducer.

4. Control method according to claim 3, characterized in that the amount |i m | of the control current i m is controlled either by a constant target value or by a time-varying target value profile.

5. Control method according to one of claims 1 to 4, characterized in that the corrected admittance Y a taking into account the capacitance CP of the piezoelectric ultrasound transducer.

6. Control method according to one of claims 1 to 5, characterized in that, based on the corrected admittance Y a and / or the flow of motion im a mechanical admittance Y m of the piezoelectric ultrasound transducer and / or a mechanical vibration parameter of the piezoelectric ultrasonic transducer is determined, preferably using a movement velocity v of the piezoelectric ultrasonic transducer as the mechanical vibration parameter.

7. Control method according to claim 6, characterized in that the mechanical admittance Y m and / or the mechanical vibration quantity is determined using a coupling factor n characteristic of the piezoelectric ultrasonic transducer.

8. Control method according to one of claims 1 to 7, characterized in that the mechanical vibration quantity and / or another vibration quantity proportional thereto are detected by sensors, wherein preferably either a sensor integrated into the piezoelectric ultrasonic transducer is used or the mechanical vibration quantity is detected without contact.

9. Control method according to one of claims 1 to 8, characterized in that the phase <p a the corrected admittance Y a is used as a second control variable for the control of the piezoelectric ultrasound transducer.

10. Control method according to claim 9, characterized in that the phase <p a is controlled either by a constant target value or by a time-varying target value profile.

11. Use of a control method according to one of claims 1 to 10 for operating an ultrasonic bonding machine and / or an ultrasonic welding machine and / or a smart welder.

Images