JP2555120B2 - Wire bonding method - Google Patents

Description

The present invention relates to a technique particularly effective when applied to a wire bonding apparatus used for manufacturing a semiconductor device.

[Conventional technology]

As an example that describes the wire bonding device, the Industrial Research Institute Co., Ltd., issued November 10, 1981,
"Electronic Materials Separate Volume, VLSI Manufacturing and Testing Equipment Guidebook" P
There are 156 to P162.

As a wire bonding method, as described in the above-mentioned document, a method in which an ultrasonic method is used in combination with a thermocompression bonding method is known.

[Problems to be Solved by the Invention]

In the thermocompression bonding method using the ultrasonic method as described above,
Since the mechanism of the apparatus itself is basically a thermocompression-dedicated machine, the present inventor has clarified that the following problems occur.

That is, the ultrasonic method is a method of applying ultrasonic vibration of about 60 KHz in a predetermined one direction to bond a wire to a bonded portion such as a lead, but in a wire bonding apparatus that is used in combination with thermocompression bonding, An object to be joined such as a lead frame is placed on a fixed stage, and a bonding tool is horizontally moved by controlling an XY table of a bonding head.

Therefore, particularly during the second bonding to the lead, the ultrasonic oscillation direction is often different from the lead axis direction depending on the position of the lead. At this time, there is no problem when ultrasonic vibration is applied in a direction parallel to the axial direction of the lead, but when ultrasonic vibration is applied in a direction perpendicular to the axial direction, that is, in the width direction of the lead, The lead may cause a resonance phenomenon.

In recent years, with the progress of higher integration of semiconductor devices, for example, the number of leads having a fine lead structure with a thickness of about 0.15 mm and a width of about 0.2 mm has been increasing. It has been found by the present inventors that, when ultrasonic vibration in the width direction is applied to the leads, the leads are particularly in a resonance state.

When the leads are in a resonance state as described above, it is not possible to sufficiently secure the bonding strength between the leads and the wires, and in the subsequent resin encapsulation process, wire peeling or contact failure due to disconnection may cause defective bonding. In many cases.

The present inventors have further clarified the conditions under which such a resonance phenomenon occurs, as described below.

That is, FIG. 7 is a conceptual diagram showing a state in which the lead is fixed by the lead retainer, and FIG. 8 is an explanatory diagram showing the relationship between the fixing position by the lead retainer and the resonance frequency of the lead.

Now, as shown in FIG. 7, when ultrasonic oscillation is applied in the width direction of the lead 72 with the outside of the lead 72 fixed by the lead retainer 71, the lead retainer 71 is pressed from the tip of the lead 72.
The relationship between the distance l and the resonance frequency fm is as shown in FIG. According to the figure, for example, when a lead frame 73 made of copper (Cu) with a width b = 0.15 mm is used, when the lead holder 71 is fixed at a position 1.2 mm from the tip of the lead 72, the normal 60 KHz It can be easily understood that the ultrasonic oscillation causes a resonance state and a bonding failure is likely to occur.

The present invention has been made in view of the above problems, and an object thereof is to provide a wire bonding technique with high bonding reliability by preventing resonance of leads when ultrasonic vibration is applied.

[Means for solving the problem]

The wire bonding method of the present invention detects a voltage and a current supplied from an ultrasonic oscillator to an ultrasonic vibrator that vibrates an ultrasonic horn, calculates a ratio between them, and calculates the calculated value and a preset resonance. It is characterized in that the oscillating frequency supplied from the ultrasonic oscillator to the ultrasonic transducer is controlled by comparing with the set value which becomes the state. In addition, the voltage and current supplied from the ultrasonic oscillator to the ultrasonic vibrator that vibrates the ultrasonic horn is detected to calculate the ratio of these, and this calculated value and the preset value that results in a resonance state In comparison, the oscillation output supplied from the ultrasonic oscillator to the ultrasonic transducer is controlled.

[Action]

According to the above-mentioned means, when the resonance position is within the resonance range due to the position condition of the leads, the resonance of the leads is prevented by changing the oscillation frequency or the output is increased, the bonding strength of the wire is increased, and the defective bonding is prevented. be able to.

[Embodiment 1] FIG. 1 is a conceptual diagram showing an oscillation mechanism of a wire bonding apparatus according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing oscillation characteristics of a 60 kHz standard oscillator, and FIG. It is the schematic which shows the whole structure of the wire bonding apparatus of an Example.

As shown in FIG. 3, the wire bonding apparatus 1 of this embodiment has a bonding stage 2 on which a lead frame 73 is mounted and a bonding head 4 mounted on an XY table 3.

The lead frame 73 is obtained, for example, by etching or pressing a conductive plate material having a thickness of about 0.15 mm, which is mainly composed of copper (Cu), and a tab (silicon) is formed on the tab formed by the processing. A semiconductor pellet (hereinafter, simply referred to as “pellet”) 5 made of Si or the like is attached with the circuit formation surface facing upward. This pellet 5
A pad 5a made of a conductive material such as aluminum for performing the first bonding is provided on the surface of the pad, and the pad 5a is electrically connected to each circuit formed on the pellet 5. Therefore, in the circuit of the pellet 5, the pad 5a and the lead 72 extending around the pellet 5 are electrically connected by the conductive wire 17 made of gold (Au) or the like to supply the power supply voltage from the outside. And signals are input and output, and the operation is ready.

A heater 6 as a heating source is provided inside the bonding stage 2.
The structure is such that the upper lead frame 73 is heated to a predetermined temperature. By the heating, the pad 5a of the pellet 5 can also obtain a temperature condition suitable for wire bonding.

The bonding head 4 mounted on the XY stage 3 is attached with a voice coil type linear motor 7 which is an operation drive source in the Z-axis direction. The voice coil type linear motor 7 is provided with a bonding arm 8 which is rotatable about a shaft support 21 at a predetermined angle. The bonding arm 8 is linked with a position sensor 10 and a speed sensor 11 to perform bonding. The structure is such that the position and swing speed of the arm 8 are detected.

An ultrasonic horn 12 is formed at one end of the bonding arm 8. An ultrasonic transmitter 13 is attached to the mounting portion of the ultrasonic horn 12. In this embodiment, the ultrasonic oscillator 13 is composed of a pair of ultrasonic oscillators including a first ultrasonic oscillator 13a having an oscillation frequency of 60 kHz and a second ultrasonic oscillator 13b having an oscillation frequency of 100 kHz. Is configured to operate. Ultrasonic oscillator of any of the above
The ultrasonic oscillations from 13a and 13b are transmitted through the ultrasonic horn 12 to a capillary 14 attached to the tip of the ultrasonic horn 12. A capillary 14 as a bonding tool is attached in a vertical direction with respect to the ultrasonic horn 12, and a lower end thereof has a structure facing the stage surface of the bonding stage 2.

A wire 17 wound around a spool 16 from a position above the capillary 14 via a clamper 15 is inserted in a state of slightly protruding from the tip of the capillary 14.

Bonding head 4 and XY table 3 described above
The operation of the ultrasonic oscillator 13 and the like is controlled by the control unit 18.

Here, FIG. 1 conceptually shows the control of the ultrasonic oscillators 13a and 13b in the control unit 18. As is also clear from the figure, the pair of ultrasonic oscillators 13a and 13b has a structure that can be switched by a switch mechanism 20 surrounded by a broken line, and selects 60 kHz or 100 kHz ultrasonic oscillation for the capillary 14. Application is possible.

Here, when the landing of the capillary 14 on the pad 5a or the lead 72 is recognized, the control unit 18 switches the switch so that bonding to the pad 5a is performed at 60 kHz and bonding to the lead 72 is performed at 100 kHz. Has been The recognition of the landing of the capillary 14 on the pad 5a or the lead 72 can be performed by monitoring the impedance calculated by the current-voltage ratio in each ultrasonic oscillator 13a, 13b. The load of the linear motor 7 may be monitored.

By the way, as described above, in the present embodiment, the first ultrasonic oscillator 13a has a frequency of 60 kHz which is generally used as the oscillation frequency in the conventional wire bonding apparatus, but the frequency of the second ultrasonic oscillator 13b is not. about,
Although it is set to 100 kHz as an example, it is not limited to this. Generally, as shown in FIG. 2, the easiness of oscillation Q of the ultrasonic horn 12 of 60 kHz standard has a characteristic that it rises about every 20 kHz.
The vicinity is a frequency band where oscillation is easy. Therefore, as the second ultrasonic oscillator 13b, for example, in addition to 100 kHz, 8
It is also possible to select an oscillation frequency of 0 kHz.

 Next, the operation of this embodiment will be described.

First, the lead frame 73 is mounted on the bonding stage 2.
When is mounted, the position of the lead frame 73 is recognized by the control unit 18 by a position recognition means such as a TV camera (not shown), and this is stored in the control unit 18 as position information of the pellet 5. Based on this position information, the XY table 3 is first actuated to position the capillary 14 above the predetermined pad 5a of the pellet 5 for the first bonding.

Next, the tip of the wire 17 protruding from the tip of the capillary 14 is heated by a heating means such as a discharge torch (not shown), and the tip is processed into a spherical shape. Next, when the voice coil type linear motor 7 is actuated and the bonding arm 8 is started to rotate counterclockwise around the shaft support portion 21, the tip of the capillary 14 is lowered to the predetermined pad 5a. When the tip of the capillary 14 lands on the predetermined pad 5a, the first ultrasonic oscillator 13a is started to operate, and ultrasonic oscillation of 60 kHz is transmitted to the capillary 14 through the ultrasonic horn 12. At this time, since the pad 5a is heated to a predetermined temperature by the heater 6 of the bonding stage 2, the spherical tip of the wire 17 is bonded to the pad 5a by the synergistic effect of thermocompression bonding and ultrasonic vibration. It becomes a state.

After the first bonding is completed in this way, the capillary 14 is activated by the operation of the voice coil type linear motor 7.
Moves upward by a certain amount while pulling out the wire 17 from the tip thereof, and after back tension is applied by the operation of the XY table 3 at a predetermined position, it is moved horizontally and stopped immediately above the predetermined bonding position of the lead 72. It When the voice coil type linear motor 7 is actuated again at this position, the capillary 14 starts moving downward with respect to the predetermined bonding position of the lead 72. When the controller 18 detects that the capillary 14 has landed on the lead 72 by the change in impedance of the ultrasonic horn 12, the switch mechanism 20 is operated by the control of the controller 18, and the first
The ultrasonic oscillator 13a is switched to the second ultrasonic oscillator 13b. As a result, ultrasonic oscillation of 100 kHz is transmitted to the capillary 14 via the ultrasonic horn 12, and the other end of the wire 17 is bonded to a predetermined position of the lead 72 by the application of ultrasonic vibration of that frequency. To be done. In this way, the frequency of the ultrasonic vibration on the lead 72 side in the second bonding is set to a frequency avoiding the resonance frequency (100 kHz in this embodiment).
By selecting z) and performing the bonding, it is possible to effectively prevent defective bonding due to resonance of the lead 72.

The oscillation frequency at the time of the first bonding of the pellet 5 to the pad 5a does not necessarily have to be 60 kHz constantly, but it is not desirable to select a high frequency in order to prevent damage to the pellet 5.

The landing of the capillary 14 on the lead 72 is detected, for example, as follows. That is, after the completion of the first bonding, the ultrasonic oscillation state by the first ultrasonic oscillator 13a is continued from the back tension of the capillary 14 to the horizontal movement, and the current value I and the voltage value for this ultrasonic oscillator 13a are maintained. V and V are measured, and the voltage value V is divided by the current value I to calculate the impedance R, which is monitored by the control unit 18. Where the capillary
When the tip of 14 is landed on the lead 72, a load is applied to the ultrasonic oscillation, and the impedance R also changes. As a result, the landing of the capillary 14 is detected.

After the other end of the wire 17 is joined to the lead 72 as described above, the extra line portion of the wire 17 is supported by the clamper 15, and the clamper 15 and the capillary 14 operate the voice coil linear motor 7. Then, the extra force of the wire 17 is cut by the pulling force, and one cycle of the wire 17 bonding operation is completed.

As described above, according to this embodiment, the following effects can be obtained.

(1). First ultrasonic oscillator 13a and second ultrasonic oscillator 1
3b and a structure in which these are switched by the switch mechanism 20 controlled by the control unit 18, the first bonding to the pad 5a of the pellet 5 and the lead
It is possible to change the oscillation frequency by the second bonding with respect to 72, and it is possible to prevent defective bonding due to resonance of the lead 72.

(2). According to the above (1), since the oscillation frequency for the pad 5a of the pellet 5 can be applied to the conventional frequency (for example, 60 kHz), the pellet 5 generated by high-frequency ultrasonic oscillation
It can prevent damage.

(3). According to the above (1) and (2), it is possible to realize a wire bonding process with high bonding reliability in the manufacture of semiconductor devices.

[Embodiment 2] FIG. 4 is a conceptual diagram showing an oscillation mechanism of a wire bonding apparatus which is another embodiment of the present invention, and FIG. 5 is an explanatory diagram showing characteristics of an ultrasonic oscillator used in this Embodiment 2. Is.

In this embodiment, a single ultrasonic oscillator 43 is used, but the ultrasonic oscillator 43 has a frequency of 20 kHz centered at 60 kHz.
It has a structure in which the oscillation frequency is variable in the range of about Hz.
The ultrasonic oscillator 43 has the characteristics shown in FIG. 5, and the maximum value of the easiness of oscillation Q is relatively low, but the oscillatable range is 40% as described above. ~
It covers a wide band of 80kHz, and at the frequency in this range, almost uniform oscillation characteristics can be obtained. Further, the oscillation characteristic at such a relatively low value can be improved by increasing the output to the ultrasonic oscillator 43 to some extent.

Also in the second embodiment, similarly to the first embodiment, the voltage value V and the current value I output from the ultrasonic oscillator 43 are constantly measured, and the impedance (calculated impedance R1) is calculated from these, The structure is such that it is input to the comparator 22. In the comparator 22, the calculated impedance is calculated by comparing with the impedance (resonance impedance R2) in which the lead 72 is in a resonance state which is obtained in advance from experimental values and the like.
The oscillation frequency of the ultrasonic oscillator 43 is controlled so that R1 is always larger than the resonance impedance R2, that is, R1> R2. The resonance impedance R2 is preferably set for each of all the leads 72 in a single semiconductor device, but may be a constant value for all the leads 72.

In this embodiment, the calculated impedance R1 from the ultrasonic oscillator 43 is monitored by utilizing the characteristic that the impedance changes with the change of the oscillation frequency, and this value is preset by the resonance impedance R2 and the comparator 22. By comparison, the oscillation frequency is controlled to be changed so that R1> R2 always holds.

Therefore, according to the second embodiment, bonding can be performed at an oscillation frequency within an optimum range without causing resonance of the bonded portion such as the lead 72 and causing no damage to the bonded portion such as the pad 5a. Bonding reliability can be further improved.

[Embodiment 3] FIG. 6 is a conceptual diagram showing an oscillation mechanism of a wire bonding apparatus which is still another embodiment of the present invention.

In the third embodiment, the oscillation frequency of the ultrasonic oscillator 53 is 60 kHz.
The output P is variably controlled.

That is, in the present embodiment, the voltage value V and the current value I from the ultrasonic oscillator 53 are monitored as in the second embodiment, and the calculated impedance R1 calculated from these values,
The comparator 22 has a structure in which the resonance impedance R2 that is the oscillation frequency is compared. The third embodiment is different from the second embodiment in that the output of the ultrasonic oscillator, that is, the voltage value V and the current value I is based on the comparison result of the comparator 22.
The point is to control the output P multiplied by.

That is, when the calculated impedance R1 approaches the preset resonance impedance R2, the ultrasonic oscillator
The output from 53, in particular the current value I, is increased to give an output oscillation exceeding the resonance of the lead 72 to the capillary 14 to avoid a joint failure due to the resonance of the lead 72.

As described above, according to this embodiment, since the output from the ultrasonic oscillator 53 is controlled to be increased only during the second bonding on the lead 72 side, the bonding failure due to the resonance on the lead 72 side is prevented. At the same time, the output from the ultrasonic oscillator 53 becomes relatively small during the first bonding to the pad 5a, and the pellet 5 is not damaged.

The present invention has been specifically described above based on each embodiment,
The present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention.

For example, as the moving structure of the bonding arm 8 in the Z-axis direction, the swinging drive type using the voice coil type linear motor 7 has been described, but a ball screw type or a cam driving type may be used. .

〔The invention's effect〕

According to the present invention, the voltage and the current supplied from the ultrasonic oscillator to the ultrasonic transducer that vibrates the ultrasonic horn is detected, the ratio between them is calculated, and the calculated value and a preset resonance state are obtained. By changing the oscillation frequency or the oscillation output supplied from the ultrasonic oscillator to the ultrasonic transducer by comparing with the set value, the oscillation frequency is changed when the resonance range is reached due to the lead position conditions etc. Alternatively, it is possible to prevent the occurrence of a resonance state by increasing the oscillation output, increase the bonding strength of the wire, and prevent defective bonding.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing the oscillation mechanism of the wire bonding apparatus described in the first embodiment, FIG. 2 is an explanatory diagram showing the oscillation characteristics of the 60 kHz standard oscillator in the first embodiment, and FIG. 1 is a schematic diagram showing the overall structure of the wire bonding apparatus of FIG. 1, FIG. 4 is a conceptual diagram showing an oscillation mechanism of a wire bonding apparatus according to a second embodiment of the present invention, and FIG. 5 is an ultrasonic oscillator used in the second embodiment. 6 is a conceptual diagram showing the oscillation mechanism of the wire bonding apparatus according to the third embodiment, and FIG. 7 is a conceptual diagram showing a state in which the leads are fixed by the lead retainer for explaining the conventional technique, FIG. 8 is an explanatory view showing the relationship between the fixed position of the lead retainer and the resonance frequency of the lead shown in FIG. 1 ... Wire bonding device, 2 ... Bonding stage, 3 ... XY table, 4 ... Bonding head, 5 ... Pellet, 5a ... Pad, 6 ... Heater, 7
...... Voice coil type linear motor, 8 …… Bonding arm, 10 …… Position sensor, 11 …… Speed sensor, 12 ……
Ultrasonic horn, 13 ... Ultrasonic oscillator, 13a, 13b ... Ultrasonic oscillator, 14 ... Capillary, 15 ... Clamper, 16 ...
Spool, 17 ... Wire, 18 ... Control part, 20 ... Switch mechanism, 21 ... Shaft support part, 22 ... Comparator, 43,53 ... Ultrasonic oscillator, 71 ... Lead retainer, 72 ... Lead , 73 ... lead frame, I ... current value, P ... output, R ... impedance, R1 ... calculated impedance, R2 ... resonance impedance, V ... voltage value.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshio Oshima 1450, Kamimizumoto-cho, Kodaira-shi, Tokyo Inside Musashi Plant, Hitachi Ltd. (56) References JP-A-57-109348 (JP, A) JP-A-SHO 62-154748 (JP, A)

Claims (2)

(57) [Claims] 1. A wire bonding method, wherein when a pad of a semiconductor pellet and a lead of a lead frame on which the semiconductor pellet is mounted are connected by a conductive wire, ultrasonic vibration is applied to the wire by an ultrasonic horn. The voltage and current supplied from the ultrasonic oscillator to the ultrasonic transducer that vibrates the ultrasonic horn is detected to calculate the ratio of these, and the calculated value and a set value that results in a preset resonance state. And the oscillation frequency supplied from the ultrasonic oscillator to the ultrasonic oscillator is controlled. 2. A wire bonding method, wherein when a pad of a semiconductor pellet and a lead of a lead frame on which the semiconductor pellet is mounted are connected by a conductive wire, ultrasonic vibration is applied to the wire by an ultrasonic horn. The voltage and current supplied from the ultrasonic oscillator to the ultrasonic transducer that vibrates the ultrasonic horn is detected to calculate the ratio of these, and the calculated value and a set value that results in a preset resonance state. In comparison with the above, the wire bonding method is characterized in that the oscillation output supplied from the ultrasonic oscillator to the ultrasonic vibrator is controlled.