Bonding head, wire bonder with such a bonding head and methods using the bonding head

Abstract

Bonding head of an ultrasonic wire bonder, wherein the bonding head comprises a bonding agent feed device for feeding a bonding wire as bonding agent, a bonding tool with an associated bonding tool drive for pressing the bonding agent onto a bonding surface with a predetermined contact force, and an ultrasonic transducer for imparting ultrasonic vibrations with a predetermined frequency or frequency spectrum and a predetermined direction of vibration to the bonding tool with the supplied bonding agent in order to produce a friction weld between the bonding agent and the bonding surface, wherein the bonding tool is designed as a bonding clamping holder with two clamping jaws configured such that the bonding agent can be held by the clamping jaws and pressed onto the bonding surface. the bond clamping holder has an actuator for actively bringing the clamping jaws together or pulling them apart in such a way that the bonding medium is held in the brought-together state, but is released in the pulled-out state, characterized by the fact that the bond clamp holder is designed in such a way that it essentially resonates with the ultrasonic transducer during operation, the ultrasonic transducer has frequency adjustment means for adjusting the vibration frequency and / or amplitude adjustment means for adjusting the vibration amplitude, in particular a resonance state with the bond clamp holder, and The actuator is only in mechanical contact with the clamping jaws during the process of bringing them together and pulling them apart, but not during the application of ultrasonic vibrations.

Description

[0001] The invention relates to a bonding head of a wire bonder, a method for producing a wire bond connection and a wire bonder.

[0002] Bond connections of various types are used en masse in an immense variety of electronic devices of all kinds and also for the realization of electronic components in many other industrial sectors, such as mechanical engineering, the automotive industry and the household appliance industry.

[0003] One of the most advanced and widely used bonding processes is ultrasonic wire bonding ("wedge bonding"), which is essentially a micro-friction welding technique. In this process—as described, for example, in US 4,619,397 A—an aluminum wire is placed in contact with the substrate surface to which it is to be bonded. It is subjected to rapid vibration by an ultrasonic transducer and simultaneously pressed against the surface. Under the influence of the pressure force (bonding force) and the vibrational energy (bonding energy), an oxide layer on the surface is broken up, and a metallurgical boundary layer bond is formed through significant deformation.

[0004] Other publications describing the bonding of a wire using ultrasound are US 7 216 794 B2, DE 102 07 498 A1 and DE 43 26 478 C2.

[0005] In this process, a bonding head is used, comprising a bonding agent feed device for feeding a bonding agent, in particular bonding wire, pin or tape, a bonding tool with associated bonding tool drive for pressing the bonding agent onto a bonding surface with predetermined pressure force, and an ultrasonic transducer for imparting ultrasonic vibrations to the bonding tool with the supplied bonding agent to create a friction weld connection between the bonding agent and the bonding surface.

[0006] The bonding tool is usually a so-called bonding wedge, which uses its end face to press the bonding agent onto the bonding surface and transmits the ultrasonic vibrations to the bonding agent.

[0007] In the past, wires with a circular cross-section, made primarily of gold or aluminum depending on the application, were used to create such connections. In recent years, the application range of these methods has expanded considerably, particularly into the fields of power electronics and battery technology. In these applications, significantly higher currents typically need to be transmitted via the conductor connections than with bond wires in the previously dominant applications of wiring logic and memory circuits and other signal electronics components. This requires considerably larger conductor cross-sections; more conductive materials such as copper are also increasingly being used.

[0008] When using bonding materials with a large cross-section or greater hardness (e.g., copper wire), a relatively high bonding force is required to press them together using a wedge. Experience has shown that such a high bonding force can lead to bond connections of insufficient quality or damage to the substrate on which the bond is applied.

[0009] The invention therefore aims to provide an improved bonding head with a bonding tool that can overcome these disadvantages. Furthermore, a corresponding bonding process and a corresponding wire bonder are to be provided.

[0010] This problem is solved in its apparatus aspect by a bonding head with the features of claim 1. In its method aspect, the problem is solved by a method with the features of claim 12. Advantageous embodiments are the subject of the dependent claims.

[0011] The invention incorporates the concept of using moderate bonding forces even with harder bonding materials or those with a larger cross-section. This necessitates, as a next step, a departure from the previous concept of holding the bonding material in place solely by pressing it onto the bonding surface using a pressure surface oriented essentially parallel to the bonding surface. Furthermore, this leads to the idea of ​​equipping the bonding head, instead of a simple wedge, with a bonding tool that at least partially encloses the bonding material and—in addition to providing a suitable pressure—also holds it in the correct position on the bonding surface through this enclosure.

[0012] Specifically, it is proposed to design the bonding tool as a bonding clamping holder with two clamping jaws configured in such a way that the bonding agent can be held by the clamping jaws and pressed onto the bonding surface, and to assign an actuator to the bonding tool for actively bringing the clamping jaws together or pulling them apart, so that the bonding agent is held in the brought-together state but released in the pulled-out state.

[0013] The process is carried out in resonance.

[0014] In an advantageous embodiment, the vibration generator, in conjunction with the clamping holder, is designed such that an alternating load, directed essentially parallel to the plane of the connection point on the component, is applied to the wire bond connection under test. Furthermore, the vibration generator is advantageously designed for operation in the frequency range between 20 kHz and 80 kHz.

[0015] According to the invention, the vibration generator has frequency adjusting means for adjusting the vibration frequency and / or amplitude adjusting means for adjusting the vibration amplitude, in particular a resonance state with the bond clamp holder.

[0016] A bonding head with such a bonding tool not only enables the handling of virtually endless bonding wires or tapes during conventional ultrasonic bonding without the application of excessively high pressure forces, but also allows for more flexible interaction with the bonding agent feeder. This is because the bonding clamp can simultaneously serve as the crucial means for positioning the bonding agent during the bonding process. Furthermore, the proposed bonding head (when used with a suitable bonding agent feeder) enables bonding with "discrete" bonding agents, particularly wire pins.

[0017] The proposed bonding head thus not only enables the bonding of bonding materials with a large cross-section and / or high material hardness while adhering to the highest quality standards, but also opens up new fields of application for the wire bonding techniques that are known in themselves.

[0018] In a preferred embodiment, the geometric configuration of the clamping jaws is adapted to the cross-sectional shape of the bonding agent such that, when the clamping jaws are brought together, a predetermined component of the contact force, in particular the entire bonding force generated by the bonding tool drive, is transferred towards the bonding surface. This enables precise control of the bonding force acting between the bonding agent and the bonding surface and thus precise control of the bonding process.

[0019] In one embodiment of this design, at least one clamping jaw of the bonding tool holder has a contact surface inclined at an angle between 45° and 90°, particularly 90°, relative to the direction of action of the bonding tool. In another embodiment, at least one of the clamping jaws of the bonding tool holder has a sawtooth profile or a roughened contact surface on an inner surface facing the bonding agent in the operating state. Furthermore, it is preferred that at least one clamping jaw of the bonding tool holder has a concavely curved inner surface facing the bonding agent. It is understood that both clamping jaws can also be designed in the manner described above.

[0020] In another embodiment, the bond clamp holder has an elongated basic shape in the direction of action of the bonding tool, essentially a "tweezer shape." This provides a largely unobstructed view of the bonding point and its surroundings, thus facilitating visual monitoring of the bonding process. However, a bonding head with a more compact bond clamp holder is also fundamentally within the scope of the invention.

[0021] In order to enable the bonding head to be used flexibly with different bonding agents in various application areas, further versions include cross-section adjusting devices for adapting to bonding agents with different dimensions and / or different cross-sectional shapes and / or clamping point adjusting devices for adjusting the clamping point on the bonding agent.

[0022] The actuator mentioned above can be a double-acting element, which causes both an active joining and an active pulling apart of the clamping jaws.

[0023] In an alternative embodiment, the actuator is designed as a single-acting element, but at least one of the clamping jaws of the bond clamp holder is designed by its material and shape to counteract the actuator. This clamping jaw (or both clamping jaws together) thus causes a passive pulling apart of the clamping jaws against the action of an actuator bringing them together, or a passive bringing together of the clamping jaws against the action of an actuator pulling them apart. A further alternative embodiment consists of the clamping jaws being assigned a return element, in particular a return spring, which counteracts the action of the actuator.

[0024] According to the invention, the bonding clamp is designed such that the actuator (the spreading or closing mechanism) only engages the tool during spreading or closing, but does not touch it during the ultrasonic exposure, i.e., during a bonding process. This makes maintaining the resonance condition during bonding much easier. This allows for a particularly simple and cost-effective manufacture of the actual clamp, which is subject to relatively high wear and tear and often needs to be replaced.

[0025] An electrostrictive or electromagnetic actuator with a control input, which can be connected to a control unit (especially one located externally from the bond head), is suitable as the actuator for the bond clamp holder. It is understood that the control unit can also be directly integrated into the bond head.

[0026] In a further embodiment, the actuator is equipped with clamping force adjustment devices for setting the clamping force of the clamping jaws. In addition to the adjustment devices mentioned above, these clamping force adjustment devices also allow adaptation to different types of bonding materials, particularly with regard to their stiffness, and also to specific requirements for the fine positioning of the bonding material relative to the bonding surface. If the clamping force adjustment devices are also located externally to the bonding head, the bonding head itself includes at least the control input of the electrostrictive or electromagnetic actuator.

[0027] The inventive method differs fundamentally from conventional wire bonding methods in that the bonding agent is not simply pressed onto the bonding surface by the bonding tool, but is instead gripped and guided, and must be released again after the bonding process. The method thus specifically comprises the following steps: supplying a bonding agent onto or over the bonding surface, clamping the bonding agent with the bonding clamp and pressing the bonding agent onto the bonding surface, activating the ultrasonic transducer to impart ultrasonic vibrations to the bonding tool with the supplied bonding agent to create a friction weld between the bonding agent and the bonding surface, and releasing the bonding agent from the bonding clamp.

[0028] According to the invention, it is provided that the bonding agent is positioned between the open clamping jaws of the bonding clamp after being supplied, and that these are brought together with the bonding agent in between, the bonding clamp with the brought-together clamping jaws is pressed towards the bonding surface by the associated drive, and after the friction weld connection has been created, the clamping jaws of the bonding clamp are pulled apart and the associated drive is deactivated.

[0029] The invention ultimately also encompasses ultrasonic wire bonders with the aforementioned design. This can be a stationary wire bonder with a generally known construction, to which the components to be bonded are fed. However, the proposed bonding head can also be used in a mobile, i.e., hand-held or robot-operated, bonding device. In this latter novel type of wire bonder, the bonding clamp, as the core element of the new concept, demonstrates its advantages with regard to the precise positioning of the bonding agent in a particularly striking manner.

[0030] The advantages and expediencies of the invention will become apparent from the dependent claims and the following description of exemplary embodiments with reference to the figures. These show: Fig. 1 a schematic representation of a bond head in the form of a block diagram; Fig. 2A and Fig. 2B two alternative embodiments of a bond clamp holder of a bond head according to the invention; Fig. 3 a schematic representation of a bond head according to the invention in the form of a block diagram.

[0031] Fig. Figure 1 schematically shows a bonding head 3 as an essential component of a wire bonder 1, in which a bonding tool 5 is movably held in operative connection with a bonding tool drive 7 and an ultrasonic transducer 9. The bonding head 3 further comprises a bonding agent feed device 11, from which a bonding agent (e.g., a bonding wire or ribbon) 13 is fed onto a bonding surface 15 below the bonding tool 5.

[0032] In practice, a bonding head includes other important components, such as a cutting device for the bonding agent after the bond has been formed, as well as sensor and control components. These have been omitted here, however, because they are not essential for explaining the invention.

[0033] To execute a bonding process, a predetermined length of bonding agent is usually fed from the bonding agent supply device 11 onto the bonding surface 15 and the bonding tool drive 7 is activated in such a way that it presses the bonding tool 5 with predetermined bonding force onto the top of the bonding agent 13 and thus simultaneously onto the bonding surface 15.

[0034] The ultrasonic transducer 9 is then activated and sets the bonding tool 5 into vibration at ultrasonic frequency, whereby, under the simultaneous influence of the bonding force provided by the drive 7, it creates a friction weld between the underside of the bonding agent 13 and the bonding surface 15.

[0035] Fig. Figure 2A schematically shows, as a first embodiment of a bonding tool according to the invention, a tweezer-like bonding clamp 50 with two clamping jaws 51, 53, which are connected to each other at an upper (proximal) end facing the bonding tool (not shown here). Depending on the specific design of the clamping jaws and their connection area, their free ends are pre-tensioned to a greater or lesser degree towards each other.

[0036] The clamping jaws 51, 53 either grip a bonding wire 13 tightly by means of their spring action and hold it firmly, or, in their resting state, they maintain a certain distance between themselves and also from the circumference of the bonding wire. Accordingly, an actuator 55 is positioned between the clamping jaws 51, 53, either to bring the clamping jaws together to grip the bonding wire 13 or to push the clamping jaws apart to release the bonding wire.

[0037] The lower ends 51a, 53a of the clamping jaws are thickened and each form a pressure surface 51b, 53b which, in the bond clamping holder 50 enclosing the bond wire 13, lie on the top of the bond wire and ensure the optimal introduction of the bond force provided by the bonding tool drive into the bond wire.

[0038] Fig. Figure 2B shows another embodiment of a bond clamping holder 50' according to the invention. This is formed by a fixed first part 51', which can also be referred to as the first clamping jaw in view of its function, and a part 53' pivotably connected to it via a rotary joint 52, which can be referred to as the second clamping jaw.

[0039] As an example, it is shown here that the distal end 51a' of the fixed part 51' has a pressure surface 51b' and a sawtooth profile 51c' in order to securely grip a ribbon 13' serving here as a bonding agent and to contribute to the transfer of the bonding force to the ribbon.

[0040] Similarly, the distal end 53a' of the pivoting part 53' also has a pressure surface 53b' and a sawtooth profile 53c', each of which has the same function as the corresponding sections of the fixed part 51'.

[0041] In this design, the fixed part and the pivotable part are not pre-tensioned against each other due to their shape or material elasticity, but by means of a tension spring 54'. This spring has such a spring force that the ribbon 13' is securely held between the sawtooth profiles 51a' and 53a' at the ends of the fixed and movable parts 51', 53'.

[0042] An actuator 55' provided between the two parts is designed here in such a way that it can push the movable part 53' away from the stationary part 51' in such a way that the ribbon 13' is released from the end 53a' of the movable part 53'.

[0043] To adjust the effective distance between the ends 51a' of the fixed part 51' and 53a' of the movable part 53' in the closed position, an adjusting screw 56' is provided. This thus acts as a cross-sectional adjustment means in accordance with the explanations given above.

[0044] Fig. Figure 3 shows, based on the representation explained above in Fig. 1 and using the same reference numerals for identical or functionally similar components, a bonding head 3' with a bonding clamping holder 5' as a novel embodiment of the bonding tool. The bonding clamping holder designated here by the numeral 5' can in particular be one of those described above with reference to Fig. 2A and Fig. 2B explained the following.

[0045] The bond clamping holder 5' is associated with an actuator 17, for example a piezoelectric or electromagnetic actuator 17, for adjusting its opening width to grip or release the bonding agent 13. The actuator 17 is connected via a control input 17a and a control line to a control unit 19, located, for example, outside the bonding head, which controls the opening and closing movements of the bond clamping holder. The force generated by the actuator, and thus the clamping force of the clamping jaws of the bond clamping holder, can also be adjusted via the control unit 19.

[0046] Furthermore, the bond clamping holder 5' is assigned cross-sectional adjustment means 21 for adapting the clamping holder opening width and, if necessary, the opening cross-sectional shape to bonding materials with different dimensions and / or different cross-sectional shapes. The cross-sectional adjustment means – like the clamping force adjustment means mentioned above – can be designed as purely mechanical adjustment means, but they can also include a motorized adjustment of the clamping jaws of the bond clamping holder, thus enabling adjustments of the bond clamping holder without manual handling.

[0047] The implementation of the invention is not limited to these examples and the aspects highlighted above, but is also possible in many different modifications and combinations within the scope of the attached claims.

Claims

[1] Bonding head of an ultrasonic wire bonder, wherein the bonding head comprises a bonding agent feed device for feeding a bonding wire as bonding agent, a bonding tool with an associated bonding tool drive for pressing the bonding agent onto a bonding surface with a predetermined pressure force, and an ultrasonic transducer for imparting ultrasonic vibrations with a predetermined frequency or frequency spectrum and a predetermined direction of vibration to the bonding tool with the supplied bonding agent in order to produce a friction weld between the bonding agent and the bonding surface, wherein the bonding tool is designed as a bonding clamping holder with two clamping jaws configured such that the bonding agent can be held by the clamping jaws and pressed onto the bonding surface. the bond clamping holder has an actuator for actively bringing the clamping jaws together or pulling them apart in such a way that the bonding medium is held in the brought-together state, but is released in the pulled-out state, characterized by , that the bond clamp holder is designed in such a way that it essentially resonates with the ultrasonic transducer during operation, the ultrasonic transducer has frequency adjustment means for adjusting the vibration frequency and / or amplitude adjustment means for adjusting the vibration amplitude, in particular a resonance state with the bond clamp holder, and The actuator is only in mechanical contact with the clamping jaws during the process of bringing them together and pulling them apart, but not during the application of ultrasonic vibrations. [2] Bond head according to claim 1, wherein the geometric configuration of the clamping jaws of the bond clamping holder is adapted to the cross-sectional shape of the bonding means such that, when the clamping jaws are brought together, a predetermined pressure force component, in particular the entire bonding force generated by the bonding tool drive, is transferred towards the bonding surface. [3] Bonding head according to claim 2, wherein at least one clamping jaw of the bonding clamping holder has a pressure surface with an inclination in the range between 45° and 90°, in particular of 90°, with respect to the direction of action of the bonding tool. [4] Bond head according to claim 1 or 2, wherein at least one of the clamping jaws of the bond clamp holder has a sawtooth profile or a roughened contact surface or a concave curved inner surface on an inner surface facing the bonding agent in the state of use. [5] Bond head according to one of the preceding claims, wherein the bond clamp holder has an elongated basic shape in the direction of action of the bond tool. [6] Bond head according to one of the preceding claims, wherein at least one of the clamping jaws of the bond clamp holder is designed by its material and shape to counteract the actuator, i.e. to passively pull the clamping jaws apart against the action of an actuator bringing them together or to passively bring the clamping jaws together against the action of an actuator pulling them apart. [7] Bond head according to one of claims 1 to 5, wherein the clamping jaws are associated with a return element, in particular a return spring, which counteracts the action of the actuator. [8] Bond head according to one of the preceding claims, wherein the bond clamping holder is associated with cross-sectional adjustment means for adapting to bond means with different dimensions and / or different cross-sectional shapes and / or clamping point adjustment means for adjusting the clamping point on the bond means. [9] Bond head according to one of the preceding claims, wherein the actuator is designed as an electrostrictive or electromagnetic actuator with a control input which can be connected to a control unit, in particular provided externally by the bond head. [10] Bonding head according to one of the preceding claims, wherein clamping force adjusting means for adjusting the clamping force of the clamping jaws are associated with the actuator. [11] Bond head according to claim 10, wherein the clamping force adjustment means comprise the control input of the electrostrictive or electromagnetic actuator. [12] Method for producing a wire bond connection using a bond head according to one of the preceding claims, comprising the steps: Applying a bonding agent to or over the bonding surface, Clamping of the bonding agent with the bonding clamp holder by actuating an actuator and pressing the bonding agent onto the bonding surface, Activation and frequency adjustment and / or amplitude adjustment of the ultrasonic transducer for imparting ultrasonic vibrations to the bonding tool with the supplied bonding agent to create a friction weld connection between the bonding agent and the bonding surface, such that the bonding tool essentially vibrates in resonance with the ultrasonic transducer. Releasing the bonding agent from the bonding clamp holder by releasing the actuator. [13] Method according to claim 12, wherein The bonding agent is positioned between the open clamping jaws of the bonding clamp after being fed in, and these are brought together with the bonding agent in between. The bond clamping holder with joined clamping jaws is pressed towards the bonding surface by the associated drive, and after the friction weld connection is created, the clamping jaws of the bond clamping holder are pulled apart and the associated drive is deactivated. [14] Ultrasonic wire bonder comprising a bonding head according to any one of claims 1 to 11.

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