METHOD FOR OPERATING AN ULTRASONIC CONNECTING DEVICE

Abstract

A method for operating an ultrasonic bonding apparatus, the ultrasonic bonding apparatus providing an ultrasonic transducer with a carrier, displaceable in a z direction, including an ultrasound generating device which is movable relative to the carrier and is held thereon, and including an ultrasonic tool which is excitable to ultrasonic vibrations by the ultrasound generating device.

Claims

1. A method for operating an ultrasonic bonding apparatus, the ultrasonic bonding apparatus comprising an ultrasonic transducer with a carrier displaceable in a z direction, an ultrasound generating device held on the carrier and movable relative thereto, and an ultrasonic tool adapted to be excited to ultrasonic vibrations by the ultrasound generating device, the method comprising: positioning an electrically conductive connection conductor above an electrically conductive bonding region provided on a bonding component such that a gap having a determined clearance in the z direction is formed between the connection conductor and a connecting surface of the bonding region facing the connection conductor; positioning the ultrasonic transducer relative to the connection conductor and the bonding component such that a contact surface of the ultrasonic tool, designed for contact with the connection conductor, faces the connection conductor; a bonding force active in the z direction is applied to the ultrasound generating device, which is pressed against the carrier; lowering the ultrasonic transducer in the z direction, and a displacement position of the ultrasonic transducer in the z direction as well as a determined relative position of the ultrasound generating device to the carrier in the z direction is ascertained; and ascertaining a contact point in time, taking into account the displacement position and the relative position, at which contact point in time, the connection conductor is lowered by the ultrasonic tool until it touches the bonding region of the bonding component.

2. The method according to claim 1, wherein the contact point in time is determined in that a difference between a temporal change in the displacement position and the relative position is ascertained, and a zero value for the difference is detected.

3. The method according to claim 1, wherein the bonding force is determined as a function of the relative position of the ultrasound generating device to the carrier and comprises a bond path force component dependent on the relative position of the ultrasound generating device to the carrier.

4. The method according to claim 3, wherein the bonding force is additively derived from a bonding base force component applied to the ultrasonic transducer and the bond path force component.

5. The method according to claim 1, wherein a known and linear dependency is present between the bonding force and/or the bond path force component, on the one hand, and the relative position of the ultrasound generating device to the carrier, on the other hand.

6. The method according to claim 3, wherein the bond path force component is applied and/or settable by an actuator.

7. The method according to claim 1, wherein a supporting force is determined for the contact point in time, with the aid of which the ultrasound generating device is pressed against the carrier.

8. The method according to claim 7, wherein the supporting force is measured in any case at the contact point in time and/or continuously.

9. The method according to claim 1, wherein a closing force is determined for the contact point in time, which is applied to close the gap between the connection conductor and the bonding component.

10. The method according to claim 9, wherein the closing force is determined as a sum of the bonding basic force component and the bond path force component at the contact point in time.

11. The method according to claim 7, wherein a process force active between the connection conductor and the bonding component during the establishment of the ultrasonic bond is determined from the bonding force and the supporting force and/or closing force determined for the contact point in time.

12. The method according to claim 11, wherein the process force is ascertained as a difference between the bonding force and the closing force.

13. The method according to claim 1, wherein the relative position and/or the displacement position is/are captured metrologically.

14. The method according to claim 1, wherein the ultrasound generating device is activated after the contact point in time and the ultrasonic tool is excited to ultrasonic vibrations.

15. The method according to claim 1, wherein the ultrasonic bonding apparatus is provided to electrically conductively bond a load current connection conductor to a bonding region of a power electronic assembly as a bonding component.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

[0015] FIG. 1 shows a schematic diagram of an ultrasonic transducer of an ultrasonic bonding apparatus prior to establishing an ultrasonic bond;

[0016] FIG. 2 shows the ultrasonic transducer of the ultrasonic bonding apparatus according to FIG. 1 during the manufacturing of the ultrasonic bonding apparatus;

[0017] FIG. 3 shows various velocity/time curves during the establishment of the ultrasonic bond for a first bonding case;

[0018] FIG. 4 shows various force/time curves for the first bonding case; and

[0019] FIG. 5 shows various velocity/time curves during the manufacturing of the bonding system for a second bonding case.

DETAILED DESCRIPTION

[0020] An ultrasonic bonding apparatus suitable for carrying out the method according to the invention comprises an ultrasonic transducer 1, which is displaceable in a z direction. Ultrasonic transducer 1 provides a carrier 2 as well as an ultrasound generating device 3, which is movable relative to carrier 2 and is held thereon. An ultrasonic tool 4, which, in the present case, extends longitudinally in the z direction and tapers in a wedge-shaped manner on a free end facing away from ultrasound generating device 3, is fixed to ultrasound generating device 3. Ultrasound generating device 3 comprises, for example, piezoceramic elements or converters, which excite ultrasonic tool 4 to mechanical vibrations in the ultrasonic range as a result of electrical input signals.

[0021] In an initial configuration according to FIG. 1, ultrasonic transducer 1 is provided above an electrically conductive bonding region 8 formed on a bonding component 7. A connection conductor 6 is positioned between a contact surface 5 of ultrasonic tool 4, which faces bonding region 8, and bonding region 8. Connection conductor 6 is, for example, a load current connection conductor, which is connected in a materially bonded manner to bonding region 8 of bonding component 7 with the aid of the ultrasonic bonding apparatus. A connecting surface 9 of bonding region 8 faces connection conductor 6.

[0022] In the initial configuration, connection conductor 6 is positioned at a distance from bonding component 7 so that a gap 10 having a clearance s extending in the z direction is formed between bonding region 8 of bonding component 7 and connection conductor 6. Connection conductor 6 is furthermore provided at a distance from ultrasonic tool 4.

[0023] FIG. 2 shows the ultrasonic bonding apparatus during the establishment of the ultrasonic bond. It is such that connection conductor 6 is now pressed against connecting surface 9 of bonding region 8 by ultrasonic tool 4, which is placed with contact surface 5 on connection conductor 6. Ultrasonic tool 4 is excited to vibrations by ultrasound generating device 3, and a bonding force F.sub.B is applied thereto in the z direction. Ultrasonic transducer 1 is displaced or lowered in the z direction until ultrasound generating device 3 is provided at a distance from carrier 2.

[0024] The functioning of the operating method according to the invention is explained below for a first bonding case with reference to FIGS. 1 and 2, based on the velocity and force time curves in FIGS. 3 and 4.

[0025] Based on the configuration according to FIG. 1, ultrasonic transducer 1 is lowered in the z direction. Due to the lowering, a contact between contact surface 5 of ultrasonic tool 4 and connection conductor 6 is first formed at a transport point in time t.sub.0. Connection conductor 6, which is elastically deformable, is transported by ultrasonic tool 4 and descends in the direction of connecting surface 9 of bonding region 8. A touching between connection conductor 6 and bonding region 8 then forms for the first time at a contact point in time t.sub.1.

[0026] For bonding case 1, it is assumed that applied bonding force F.sub.B is greater than a closing force F.sub.G to be applied for closing gap 10. Bonding force F.sub.B is constant, while closing force F.sub.G increases linearly with a deflection z.sub.G of connection conductor 6 from the resting position illustrated in FIG. 1. Closing force F.sub.G is therefore variable over time. It is determined by the following formula:

F.sub.G(t)=c.sub.G.Math.z.sub.G(t)

[0027] c.sub.G may be understood as the unknown spring constant of connection conductor 6.

[0028] It is further assumed that ultrasonic transducer 1 is lowered slowly and at constant velocity v.sub.z in the z direction. Velocity v.sub.z is time derivation ż of a displacement position z of ultrasonic transducer 1 in the z direction. A quasi-stationary process is assumed for the explanation below. It is also assumed that the components of ultrasonic transducer 1, including ultrasonic tool 4 as well as the substrates are ideally rigid. The changes in velocity at transport point in time t.sub.0 and at contact point in time t.sub.1 may be seen as being abrupt.

[0029] If ultrasonic transducer 1 is lowered in the z direction, displacement position z of ultrasonic transducer 1 changes at assumed constant velocity v.sub.z=ż. Since it is assumed for the first bonding case that bonding force F.sub.B is greater than closing force F.sub.G, a velocity v.sub.w of ultrasonic tool 4 in the z direction corresponds to velocity v.sub.z of ultrasonic transducer 1. A relative movement between holder 2 and ultrasound generating device 3, on which ultrasonic tool 4 is held, does not result up until the closing of gap 10. Once gap 10 is closed at contact point in time t.sub.1, ultrasonic tool 4 stops.

[0030] If one alternatively considers the deformation of connection conductor 6, the latter remains stationary until transport point in time t.sub.0. Like deformation velocity v.sub.G, its deflection z.sub.G is zero up to transport point in time t.sub.0. Starting at transport point in time t.sub.0, gap 10 is closed at a velocity

v.sub.G=ż.sub.G=v.sub.z.

[0031] At contact point in time t.sub.1, connection conductor 6 abuts connecting surface 9 of bonding region 8. Starting at this point in time, its velocity v.sub.G is zero, just like velocity v.sub.w of ultrasonic tool 4.

[0032] Starting at contact point in time t.sub.1, ultrasound generating device 3 will detach from carrier 2, due to the further lowering of ultrasonic transducer 1 in the z direction. A relative position z.sub.NL between carrier 2 and ultrasound generating device 3 may thus be determined metrologically. Velocity v.sub.NL=ż.sub.NL, at which ultrasound generating device 3 moves away from carrier 2, corresponds to velocity v.sub.z, at which ultrasonic transducer 1 is lowered in the z direction. A difference Δv of zero therefore results starting at contact point in time t.sub.1. With the aid of the method according to the invention, it is therefore possible to determine contact point in time t.sub.1 from the velocity difference

Δv(t)=v.sub.z(t)−v.sub.NL(t).

[0033] The ultrasonic bonding apparatus provides suitable measuring means for this purpose, for example position sensors.

[0034] Since spring constant c.sub.G of connection conductor 6 is unknown, closing force F.sub.G may not be determined from displacement position z of ultrasonic transducer 1 at contact point in time t.sub.1. Instead, supporting force F.sub.TD is measured, with which ultrasound generating device 3 is pressed against carrier 2. The ultrasound generating device may be provided with suitable measuring means for this purpose, for example force sensors. Process force F.sub.P after the positioning then corresponds to supporting force F.sub.TD at point in time t.sub.1—immediately prior to the positioning. Associated closing force F.sub.G at point in time t.sub.1, which may be calculated by

F.sub.G(t.sub.1)=F.sub.B−F.sub.TD(t.sub.1−)

[0035] may then be taken into account during the establishment of the electrically conductive, materially bonded connection between connection conductor 6 and bonding setup 7, since the following applies to process force F.sub.P

F.sub.P=F.sub.B−F.sub.G(t.sub.1).

[0036] For the second bonding case, it is assumed that closing force F.sub.G is greater than the force initially applied to ultrasonic transducer 1 in the z direction. The initially active force is to be understood below as bonding basic force component F.sub.B0.

[0037] If bonding basic force component F.sub.B0 is lower than closing force F.sub.G which must be applied to close gap 10, ultrasound generating device 3, which is movable relative to carrier 2 and is held thereon, detaches from carrier 2 even before gap 10 is completely closed. In addition to bonding basic force component F.sub.B0, a bond path force component is applied, which, together with bonding basic force component F.sub.B0, defines bonding force F.sub.B active in the z direction.

[0038] It is assumed that the bond path force component is described by a linear spring characteristic c.sub.B.Math.z.sub.NL(t). In this case, C.sub.B defines a known or experimentally determinable machine constant of the ultrasonic bonding apparatus. which is defined, for example, by the elasticity in the suspension of ultrasound generating device 3 on carrier 2.

[0039] If one now considers the bonding force predefined by the ultrasonic bonding apparatus,

F.sub.B(t)=F.sub.B0+C.sub.B.Math.z.sub.NL(t),

[0040] bonding force F.sub.B in the second bonding case increases linearly as a function of relative position z.sub.NL between carrier 2 and ultrasound generating device 3, gap 10 steadily reliably closing up to contact point in time t.sub.1.

[0041] At any point in time during the closing operation, the force equilibrium

F.sub.G(t)=F.sub.B(t)

or

C.sub.G.Math.z.sub.G(t)=F.sub.B0+C.sub.B.Math.z.sub.NL(t)

applies, and, by deriving the velocity ratio during the pressing down of connection conductor 6, the following also applies:

c.sub.G.Math.v.sub.G=c.sub.B.Math.v.sub.NL.

[0042] The sum of the velocities yields velocity v.sub.z, at which ultrasonic transducer 1 is lowered:

v.sub.z=v.sub.G+V.sub.NL,

[0043] so that the velocities are distributed to

v.sub.w=c.sub.B/(c.sub.G+c.sub.B).Math.v.sub.z and

v.sub.NL=C.sub.G/(C.sub.G+C.sub.B).Math.v.sub.z.

[0044] The velocity curves with the distribution of the velocity between points in time t.sub.0 and t.sub.1 are illustrated in FIG. 5. To simplify, it has been assumed here that F.sub.B0=0. The exact curve of velocities v.sub.w, v.sub.NL in the closing phase, which is constant in the present exemplary embodiment, is not important. Instead, the fact that contact point in time t.sub.1 may be detected again due to difference Δv between the temporal change in displacement position z and relative position z.sub.NL is relevant, which results in zero:

Δv(t)=v.sub.z(t)−v.sub.NL(t)=ż(t)−z.sub.NL(t)=0

[0045] In addition, closing force F.sub.G at contact point in time t.sub.1 may be determined as follows without additional force sensors:

F.sub.G=F.sub.B0+c.sub.B.Math.z.sub.NL(t.sub.1).

[0046] Process force F.sub.P, which is active between connection conductor 6 and bonding component 7 during the establishment of the ultrasonic bond, may therefore be ascertained from the difference between bonding force F.sub.B and closing force F.sub.G at contact point in time t.sub.1:

F.sub.P=F.sub.B−F.sub.G(t.sub.1).

[0047] In the present exemplary embodiment of the operating method according to the invention, it is assumed as an example that ultrasound generating device 3 is held on carrier 2 in a manner relatively movable thereto via elastic connecting elements. The force applied as a result of the deflection (relative position z.sub.NL) was derived by taking into account machine constant c.sub.B. It is also possible that the force active between carrier 2 and ultrasound generating device 3 does not depend linearly on relative position z.sub.NL and/or is determined as a function of time or velocity. Moreover, ultrasound generating device 3 may be fastened to carrier 2 via an actuator, so that the bond path force component may be set or determined in a variable manner.

[0048] Identical components and component functions are identified by the same reference numerals.

[0049] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.