Method For Producing Wire Bond Connection And Arrangement For Implementing The Method

Abstract

Method for producing wire bond connections between an electronic component or a module and a substrate with energy input into a bonding wire by an ultrasonic transducer, wherein during the energy input for forming a first wire bond connection, at least one bonding parameter characterizing the instantaneous state of the bonding wire is measured in dependence on time, the curve shape of the time dependence is differentiated by means of predetermined comparative criteria or curves into three curve sections and hereby the temporal course of the method into three phases, to be specific, a cleaning, a fusion and a tempering phase, and the energy fed into the ultrasonic transducer and/or the bonding force exerted on the bonding wire and/or the duration of the energy input into at least one partial section of at least the cleaning and the fusion phase, in particular each of the cleaning, fusion and tempering phases is/are controlled independent of the measurement result in quasi real time during the formation of the first wire bond connection or during the subsequent formation of a second wire bond connection of the same type in dependence on the curve shape in the associated curve section in a phase-specific manner.

Claims

1. Method for producing wire bond connections between an electronic component or a module and a substrate with energy input into a bonding wire by an ultrasonic during the energy input for forming a first wire bond connection, at least one bonding parameter characterizing the instantaneous state of the bonding wire is measured in dependence on time, the curve shape of the time dependence is differentiated by means of predetermined comparative criteria or curves into three curve sections and hereby the temporal course of the method into three phases, to be specific, a cleaning, a fusion and a tempering phase, and the energy fed into the ultrasonic transducer and/or the bonding force exerted on the bonding wire and/or the duration of the energy input into at least one partial section of at least the cleaning and the fusion phase, in particular each of the cleaning, fusion and tempering phases is/are controlled independent of the measurement result in quasi real time during the formation of the first wire bond connection or during the subsequent formation of a second wire bond connection of the same type in dependence on the curve shape in the associated curve section in a phase-specific manner.

2. Method according to claim 1, wherein the duration of the energy input in the cleaning phase and thus the point of transition to the fusion phase is variably controlled in dependence on the curve shape of the at least one bonding parameter.

3. Method according to claim 1, wherein the or each of the controlled bonding parameters is/are set to one of a plurality of prestored values, to each of which a comparative curve shape is allocated in the associated curve section, wherein that value of the controlled bonding parameter is set whose allocated comparative curve shape is closest to the instantaneously detected curve shape in the curve section.

4. Method according to claim 1, wherein the or each of the controlled bonding parameters is/are controlled in the subsequent formation of a second wire bond connection of the same type in the entire activating, fusion and tempering phases thereof in each case in dependence on at least one partial section of the associated curve section of the time dependence detected in the formation of the first wire bond connection.

5. Method according to anyone of claim 1, wherein during the formation of the first wire bond connection, the curve shape is detected and evaluated in an initial partial section of at least one, in particular each of the cleaning and fusion phases, and the evaluation result is utilized immediately in quasi real time to define the or each of the controlled bonding parameters during a subsequent partial section of the respective phase of the formation of the first wire bond connection.

6. Method according to claim 1, wherein the evaluation of the curve shape of the overall time dependence for differentiating into the three curve sections and/or the evaluation for defining the value of the or each of the controlled bonding parameters comprises the comparison to at least one stored overall reference curve, in particular to an array of overall reference curves.

7. Method according to claim 1, wherein the impedance and optionally the frequency of the ultrasonic transducer and/or a deformation of the bonding wire are measured as the bonding parameter characterizing the state of the bonding wire.

8. Method according to 1, wherein in at least one of the three phases of the process sequence (exclusively or in any case primarily) a selection of bonding parameters characterizing the state of the bonding wire is detected other than in at least another phase and is taken as a basis for the control, wherein in particular in the cleaning phase, the deformation of the bonding wire and the impedance and frequency of the ultrasonic transducer are detected while in the fusion phase the deformation of the bonding wire is detected.

9. Method according to claim 8, wherein the duration of the cleaning phase and thus the point of transition to the fusion phase is determined based on the evaluation of the wire deformation curve shape, in particular on a comparison thereof to a corresponding reference curve.

10. Method according to claim 1, wherein a phase-specific definition of the energy fed into the ultrasonic transducer and of the bonding force is performed for each of the cleaning, fusion and tempering phases, in particular as a calculation process executed in quasi real time, or a selection from one of a plurality of prestored sets of control parameters in dependence on the curve shape.

11. Method according to claim 1, wherein the control of the fed energy and/or the bonding force and/or the duration of the energy input includes at least one regulation component.

12. An arrangement for producing wire bond connections between an electronic component or a module and a substrate with energy input into a bonding wire by an ultrasonic transducer, comprising at least one measuring device for a bonding parameter characterizing an instantaneous state of the bonding wire, a registering device connected to an output of the least one measuring device for registering a time dependence of an output signal of the at least one measuring device during a duration of the energy input, an evaluating device for evaluating a curve shape of the time dependence of the bonding parameter, wherein the evaluating device includes a curve shape differentiating device for differentiating an overall time dependence into three curve sections that are different due to a respective characteristic course, and a bonding parameter control unit connected to an output of the evaluating device, wherein in the bonding parameter control unit, in particular differentiated sets of control parameters each are stored for the cleaning, fusion and tempering phases of the bonding process for the selection by phases in dependence on initial data of the evaluating device for a phase-specific control of the fed energy and/or the bonding force and/or the duration of the energy input.

13. Arrangement according to claim 12, wherein the evaluating device includes a reference curve memory for storing reference curves differentiated into three curve sections and a comparator unit for comparing the curve shape of the current time dependence of the or each of the detected bonding parameters to the reference curves and for outputting data defining the three periods of time.

14. Arrangement according to claim 12, wherein the bonding parameter control device comprises a feedback member for realizing a regulation component in the control of at least one bonding parameter.

15. Arrangement according to claim 12 further comprising a wire bonder.

Description

[0030] Advantages and utilities of the invention incidentally will arise from the following description of preferred exemplary embodiments and aspects by means of the Figures. Shown are in:

[0031] FIG. 1 a schematic representation of a first arrangement for implementing the method according to the invention, in a kind of a functional block diagram,

[0032] FIG. 2 a schematic representation of a second arrangement for implementing the method according to the invention, in a kind of a functional block diagram, and

[0033] FIG. 3 a schematic graphic representation of the time sequence of a bonding process by means of the relevant measuring and control parameters, respectively.

[0034] In the production sequence of a wire bond connection on a contact surface of an electronic component or module, three phases are usually distinguished: (a) a cleaning or activating phase, in which an activation of the boundary surface occurs due to the vibration of the bonding wire generated by means of the ultrasonic transducer on the substrate surface; (b) a phase of the material mixing between bonding wire and material of the contact surface, thus the actual welding (called welding or deformation phase here), and finally (c) a tempering phase, in which the generated weld connection is thermally stabilized. A finer subdivision of the bonding process is possible and even reasonable for certain purposes, however, is not made in the context of the present invention.

[0035] While usually each of the three phases is executed with a predefined set of bonding parameters, it is proposed here to control not only in the welding phase but at least also in the preceding activating phase at least a part of the bonding parameters (thus in particular the energy fed into the ultrasonic transducer and/or the bonding force exerted on the bonding wire and/or the duration of the energy input into the bonding wire) in dependence on a state detection of the connection partners or the connection being formed in a manner depending on the measured values, and namely in particular while following the detected time dependence of at least one measurement parameter.

[0036] As is generally known, the quality of a wire bond connection depends decisively on the adequate setting of the bonding parameters, and this not only in the welding or deformation phase but also in the activating and tempering phases (in dependence on the condition of the connection partners). Suboptimal surface conditions (oxide coating, contaminations, roughness, local hardening occurrences, etc.) may in particular be compensated within certain limits by appropriately setting the bonding parameters such that a high-quality bond connection may be produced.

[0037] In a realization of the invention, a rubbing, scrubbing relative motion of wire and contact surface is desired in the cleaning or activating phase; so, a high movement amplitude of the wire is set for logical reasons (via a corresponding energy supply to the transducer) and a low bonding force. Hereby, a welding or fusion is initially prevented until an at least locally sufficiently activated boundary surface has formed so that first bonding islands or local welding spots develop. This becomes evident in an increasing damping of the vibration of the bonding wire, metrologically therefore in an increasing impedance (or a decreasing measured current) at the transducer and a rising transducer frequency. At the same time, an initial deformation of the bonding wire takes place which can likewise be detected metrologically. In a manner of proceeding that is advantageous from the current point of view, the ultrasonic power will in this phase be kept at a low to medium value, and the bonding force at a low value.

[0038] Once the cleaned and thereby activated opposite surfaces of bonding wire and contact surface begin to join, the relative movement of the contacting surfaces is impeded and a shearing action produced within the bonding wire. This results in a softening of the wire structure; the material flows below the bonding tool. This may be detected metrologically as a significant deformation which can be tracked dependent on time as a descent of the wedge. The curve shape of the time dependence of the deformation may be used as a correcting variable. In an advantageous configuration of this phase under normal conditions, the bonding force is increased in a first partial section and the ultrasonic power regulated in such a manner that a predetermined deformation rate is satisfied. In case it is observed that this desirable deformation rate is fallen below or exceeded, the ultrasonic power will be increased or decreased (for example, upward and downward at a determined regulating speed, minimum/maximum regulating amplitude, etc.) in a determined appropriate manner.

[0039] With an increasing deformation, a solidification of the wire can occur so that the desired deformation rate might also change. If need be, a switchover to another set of control parameters takes place in a second partial section of the welding phase, wherein a previously defined amount of the wire deformation may be used for this purposes as a switching threshold. Hence, it is also possible to utilize a single absolute or relative value for triggering a control process apart from the curve shape of the temporal course of the deformation (or another measured or set variable). The reaching of a previously defined deformation amount of the bond wire may also be utilized as a trigger for ending the welding phase (by switching to another set of control parameters).

[0040] In the tempering phase, a continuous shearing action is exerted on the bonding zone (welding zone) by the ultrasonic vibration, whereby the healing of lattice dislocations and flaws is enabled. For this purpose and in an advantageous way from the current point of view, a lower level of ultrasonic vibration is set and kept constant for a defined time (or else until a defined total bonding process time is reached). The impedance and frequency may be monitored here so as to identify a possible slipping of the wedge over the bonding wire surface, which would generate over-bonds or so-called burnt bonds, and preferably to suppress it by changing the bonding force and, where appropriate, the ultrasonic amplitude as well. Although basically a fixed predefined set of control parameters could be used in the tempering phase, here as well, a bonding process control depending on measured values could therefore be advantageous.

[0041] In realizations of the proposed process sequence, the time dependence of the relevant measurement parameters may be used by means of observation windows in a manner that is sufficient for the process control and is reducing the demands on the processing of measured data. These observation windows may correspond widely to partial sections of the single phases or even may be considerably shorter, and are in particular variably selectable in their position on the time axis. If appropriate, the position may be preselected already at the start of the process based on product data of the bonding wire and/or the condition of the contact surface of the electronic component; however, the position may even be varied in other realizations in dependence on measurement results gained initially in the process.

[0042] FIG. 1 schematically illustrates an arrangement 1 for implementing a bonding process which is controlled in dependence on a deformation-time curve and an impedance-time curve, which arrangement is typically integrated in a wire bonder (not shown as a whole). Among the usual components of a wire bonder, a wedge 2 and a horn 4 of an ultrasonic transducer 6 are illustrated, which horn is mounted to the wedge. The wedge serves to produce a bond connection on a substrate 10 by means of a bonding wire 8.

[0043] The horn 4 of the ultrasonic transducer 6 has a deformation sensor 12 allocatedthat is known per se. In a power supply 14 of the transducer 6, an amperage measuring device 16 and a voltage measuring device 18 are integrated, which, on the output side, are connected to an impedance determining device 20 for calculating instantaneous impedance values. The transducer 6 has a bonding head drive unit 22 allocated which generates a predetermined pressing force (bonding force) the bonding tool 2 exerts on the bonding wire 8. To the output of the impedance determining device 20, an impedance registering device 24 is connected for registering the time dependence of the impedance, which is connected to a timer 26 via a further input. The deformation sensor 12 is connected to the input of a deformation registering device 28 for registering the time dependence of the bonding wire deformation, which likewise receives a time signal from the timer 26.

[0044] The impedance registering device 24 is connected to an impedance evaluating device 30 on its output side, which is connected to a reference database 32 via a further input. The output of the deformation registering device 28 is connected to a deformation evaluating device 34. Both evaluating devices 30 and 34 are commonly connected to a bonding force control unit 36, on the one hand, and to a bonding energy control unit 38, on the other. The bonding force control unit 36 acts upon the bonding head drive unit 22 for the fast control of the bonding force, and the bonding energy control unit 38 acts upon the power supply 14 of the transducer 6 for the fast control of the bonding energy (ultrasonic vibration energy).

[0045] The functionality of the measuring and control arrangement 1 arises already from the above general explanations to the proposed method and will therefore not be described here again. It is pointed out that evaluating and control algorithms, respectively, are stored in the evaluating devices 30 and 34 and the control units 36 and 38, which are derived from measurement curves of the transducer impedance and wire bond deformation obtained in an experimental way on a plurality of substrates with different bonding wires and process parameter constellations and the associated usual quality analyses. The person skilled in bonding technology is familiar with such measurements and quality analyses so that he will be able to find specific control algorithms for specific components, substrates and bonding wires by himself.

[0046] FIG. 2 shows a partial representation of a further testing arrangement Y which is considerably simplified as compared to the measuring and control arrangement 1 according to FIG. 1. In this case, a wire bonder having the usual structurethe bonding tool 2, the horn 4, the transducer 6 and the bonding head drive unit 22 thereof being shown again in the Figurein addition has the amperage measuring device 16, the voltage measuring device 18 and the impedance determining device 20, as well as the impedance registering device 24 and the impedance evaluating device 30 including the associated database 32. However, the means illustrated in FIG. 1 for detecting and evaluation deformation are not present, and means for the online control of the bonding process are not shown.

[0047] Rather it is shown here that the impedance evaluating device 30, on its output side, is connected to a memory device 40 for storing the temporal course of the impedance. From the control unit (not shown here) of the bonding process, the time dependence of the set bonding parameters, and from the input control, the process-relevant data of the bonded component and the bonding wire are moreover supplied to the memory device 40f, which is symbolized in the Figure by arrows designated by the letters BP and PD. Thus, complete comparative data sets or total reference curves may be stored in the memory device as a basis for future bonding process controls.

[0048] The function of this embodiment arises also from the above explanations to the proposed method.

[0049] FIG. 3 schematically shows the time dependence of relevant measuring and control parameters of an exemplary bonding process for explaining the proposed method by way of example. The X axis is designated in arbitrary units; the dotted line represents the ultrasonic power, the dashed line the transducer current, (representative of the impedance), the dash-dotted line the ultrasonic frequency, and the solid line the bonding wire deformation. These are not real measurement or control signal curves, but curves smoothed for explanation purposes.

[0050] The bonding process starts with an activating and cleaning phase, respectively, wherein a relatively low ultrasonic force is applied to the bonding wire (and via the latter to the underlying substrate). At the point designated by A, deformation of the bonding wire starts, and thereupon, a switchover to the second phase of the bonding process takes place, the welding and fusion phase, respectively. Here, the ultrasonic power is increased, and also the measured current rises rapidly, whereas the deformation of the bonding wire increases essentially linearly. This phase is therefore also referred to as a deformation phase. The point designated by B is in this phase.

[0051] In the shown example, a slight reduction of the ultrasonic power takes place at a point C in response to the fact that the course of the deformation curve has deviated from that of the target curve in that the gradient of the actual deformation curve was greater than that of the target deformation curve. Hereby, the further progress of the bonding wire deformation is kept under control until a target deformation is reached at a point D (illustrated in the Figure as a horizontal dash-dotted line).

[0052] When this circumstance is identified, the ultrasonic power will de decreased significantly, and the measured current as well decreases accordingly. This represents the transition to the so-called tempering phase in which a thermal post-processing of the welding point or bond is performed at a constant input of ultrasonic energy until the expiration of a predefined maximum period of time.

[0053] Incidentally, the implementation of the invention is also possible in a plurality of modifications of the examples shown here and of the aspects of the invention highlighted further above.