JP2001298040A - Wire-bonding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wire-bonding method that can carry out grounding detection at a high speed without damaging balls. SOLUTION: This wire bonding method is carried out by using a capillary tool 42 where a wire 41 is inserted, a horn 3 7 that retains the capillary tool 42 at a tip and is supported while the horn 37 can be freely rocked in upper and lower directions, a motor 40 that rocks the horn 37 in the upper and lower directions, an encoder E that detects the position of the horn 37, and a pulse width comparison circuit 54 that compares the output of the encoder E with a set threshold and outputs the ground signal of the capillary tool 42 when the output of the encoder E meets grounding conditions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wire bonding method capable of detecting that a capillary tool is in contact with a bonding surface at high speed and without damaging a ball.

[0002]

2. Description of the Related Art In the field of manufacturing electronic components, a ball formed at the lower end of a wire is pressed against a substrate on which a chip is mounted, and a loop of a wire continuous with the ball is formed. A wire bonder that presses the tip to a substrate is widely used.

[0003] A wire bonder performs the above operation by moving up and down a capillary tool held by a horn. During the operation, it is necessary to detect that the capillary tool is grounded to a chip or a substrate. As the ground detecting means, there are a conventional one using a mechanical contact and a one using an impedance change with respect to ultrasonic vibration applied to the horn.

FIG. 15 is a side view of a ground detecting means using a mechanical contact. In FIG.
Is the capillary tool held at the tip of the horn 1, 3
Oscillator 3a, 3b is a pair of support arms protruding from the rear of the oscillating body 3, and 5 and 6 are a pair of support arms 3,
Reference numerals 7 and 8 denote cam followers which are pivotally supported at the rear ends of the oscillating body 3. Reference numeral 7 denotes an eccentric cam contacting the cam followers 5 and 6, reference numeral 8 denotes a motor for rotating the eccentric cam 7, and reference numeral S denotes a contact type sensor. Fixed at the top. The boss 1a, that is, the horn 1, is constantly urged in the direction of the arrow N1 by the coil spring 9, and as shown in FIG. Is in contact with

[0005] Next, as shown in FIG.
Is operated, the eccentric cam 7 rotates in the direction of the arrow N2, so that the rocking body 3 rocks in the direction of the arrow N1. Here, since the boss 1a is urged in the arrow N1 direction,
The horn 1 also swings integrally with the swinging body 3, and the capillary tool 1 is grounded to the substrate 10. Then, as shown in FIG. 15C, when the eccentric cam 7 is further rotated after the capillary tool 1 is grounded on the substrate 10, the boss 1 a urged in the direction of the arrow N <b> 1 moves the capillary tool 1 from the substrate 10. It slightly rotates in the direction of arrow N3, losing the received drag. As a result, the protruding piece 1b integral with the boss 1a does not come into contact with the sensor S, and this is detected by the sensor S and a ground signal is output.

However, in such a configuration, the driving force of the motor acts on the horn 1 secondary through the oscillating body 3 and is employed in a wire bonder of a system in which the horn 1 is directly oscillated by the motor. Can not. In addition, the detection time is as long as about 5 msec, which is not suitable for high-speed detection, and has a problem that phenomena such as chattering are liable to occur since mechanical contacts are used.

FIG. 16 is a front view showing the outline of the operation of the ground detecting means utilizing the change in impedance. 11
Is an ultrasonic transducer for applying ultrasonic vibration to the horn 1;
Is an impedance detection circuit that detects the impedance to vibration in the ultrasonic transducer 11, and 13 is an impedance value input from the impedance detection circuit 12,
This is a ground determination circuit that determines whether the capillary tool 2 is grounded.

Next, the operation of the ground detecting means will be described. First, as shown in FIG. 16A, before the capillary tool 2 is grounded to the substrate 10 or the electrode of the chip.
The ultrasonic vibrator 11 is operated, and while the ultrasonic vibration of a certain intensity is applied to the horn 1 in advance, the capillary tool 2
Is lowered. At the same time, the impedance detection circuit 12 detects the impedance of the ultrasonic vibration, and the ground determination circuit 13 inputs the impedance value. Here, since the capillary tool 2 and the horn 1 are in the air and there is almost no vibration suppression, the impedance value is low.

Next, as shown in FIG. 16 (b), when the capillary tool 2 is grounded to the chip or the substrate 10, the capillary tool 2 and the horn 1 integrated therewith are
The vibration is suppressed by 0, and the impedance value rises rapidly. Thereby, the ground determination circuit 13 outputs a ground signal.

However, in such a configuration, when the capillary tool 2 is grounded, the ultrasonic vibration has already been applied, and especially when the wire bonding is performed on the electrode of the chip, it is formed at the lower end of the wire. There has been a problem that excessive damage may be given to the ball, and the ball may be excessively crushed, thereby deteriorating the bonding quality.

[0011]

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a wire bonding method capable of detecting a ground contact at a high speed without damaging a ball.

[0012]

SUMMARY OF THE INVENTION A wire bonding method according to the present invention is a wire bonding method for crimping a wire inserted through a capillary tool held at the tip of a horn to a chip. The capillary tool is lowered toward the chip by driving and swinging the horn, and the period of the pulse signal output from the encoder that detects the rotational position of the shaft that pivotally supports the horn is predetermined. When the time is longer than the time, a ground detection signal is output, the position control method is switched to the torque control method in response to the ground detection signal, and a predetermined torque is generated in the motor to crimp the wire to the chip.

Preferably, in the position control method, a deviation between a pulse signal based on an operation pattern and a pulse signal output from the encoder is counted as a droop pulse, and a current corresponding to the droop pulse is output to the motor. Control method, when the ground detection signal is output,
Clear the droop pulse and switch to torque control.

[0014]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a perspective view of a wire bonder according to an embodiment of the present invention, where 31 is a base member, and 32 is a Y motor 33 provided on the base member 31.
Table 34 is driven by a support block 35 slidably mounted on the Y table 32 in the X direction.
Is an X motor provided on the Y table 32 to slide the support block 34 in the X direction. Support block 34
A shaft 36 facing in the X direction is rotatably supported at the front of the box, and the shaft 36 is mounted on a box 38 to which a horn 37 is fixed. E is an encoder for detecting the rotational position of the shaft 36, 39 is an ultrasonic vibrator attached to the rear of the horn 37, 40 is the box 38 that swings up and down to directly swing the horn 37 in the direction of arrow N. Motor. Reference numeral 41 denotes a wire inserted through a capillary tool 42 held at the tip of the horn 37.
3 is a tension clamper of the wire 41, 44 is a cut clamper fixed to the box 38 by a support arm 45, 46 is a ball 41a (FIG. 7) at the lower end of the wire 41 by applying a high voltage to generate an electric spark.
) To form a torch electrode. 47 is a lead frame as a substrate positioned below the capillary tool 42, 47a is an inner lead of the lead frame 47, 48 is a chip mounted on the lead frame 47, and 49 is a plate for holding the lead frame 47.

FIG. 2 is a block diagram showing a control device of the wire bonder of FIG. In FIG. 2, reference numeral 50 denotes an input of the A-phase signal and the B-phase signal of the encoder E, and it is determined in which direction the horn 37 is swinging up or down. If it is falling, a direction discriminating circuit that outputs a falling detection pulse signal to the reversible counter 51 alternatively. The counting circuit 51 counts the rising detection pulse signal, increases the count value, counts the falling detection pulse signal, and counts. , And outputs the current count value as a current position signal to the interface unit 52. Also, 53
Is a reference pulse signal generating circuit that generates a reference pulse signal composed of a square wave having a sufficiently high constant frequency and outputs the reference pulse signal to a pulse width comparison circuit 54. At the same time as inputting the signal, the threshold value N previously input from the interface unit 52 is compared with a value obtained by reducing the pulse width of the falling detection pulse signal by the pulse width of the reference pulse signal.
Is exceeded, the pulse width comparison circuit outputs an active ground signal to the ground detection switch 55. The ground detection switch 55 outputs the ground signal to the interface unit 52 only when the permission signal is obtained from the interface unit 52.
Is output to

Here, the operation of the ground detecting means in the present embodiment will be described with reference to FIGS. First, the pulse width comparison circuit 54 has a threshold N
Is set, a falling detection pulse signal is input from the direction discrimination circuit 50, and a high-frequency reference pulse signal is input from the reference pulse generation circuit 53. FIG. 9 is a time chart showing an example when the threshold value N = 4.
(A) is a reference pulse signal having a constant high frequency period A, FIG.
FIG. 9B shows a lowering detection pulse signal in a state where the lowering speed of the horn 37 gradually decreases and the capillary tool 42 is going to ground on the bonding surface. FIG. 9C shows a grounding signal output by the pulse width comparing circuit 54. FIG. 10 is a characteristic diagram showing grounding conditions under which the pulse width comparison circuit 54 outputs a ground signal. In this embodiment, the threshold value N = 4, and the pulse width comparison circuit 54 determines that the value obtained by reducing the period B of the falling detection pulse signal by the constant period A of the reference pulse signal is equal to the threshold value N.
And outputs a ground signal when the voltage exceeds the threshold value N. Of course, the ground condition may be such that a ground signal is output when the above-mentioned reduced value exceeds the threshold value N.

Now, in the falling detection pulse signal of FIG. 9B, in the periods B1 to B3, the period A of the reference pulse signal multiplied by the threshold value N is smaller than the predetermined time 4A and is substantially constant. Indicates that it is descending at a substantially constant speed. The cycle B4 is longer than before the cycle B3, indicating that the lowering operation of the horn 37 is decelerating. The period B5 is longer than the predetermined time 4A, and the horn 37 is almost stopped during the period B5 (that is, the capillary tool 42 is grounded on the bonding surface). The pulse width comparison circuit 54 outputs a ground detection signal at the time when the predetermined time 4A has elapsed.

In FIG. 2, reference numeral 56 denotes a bonder control circuit such as a CPU, and 57, a ROM. The ROM 57 stores a control program in accordance with the flowcharts of FIGS. As shown, the operation pattern storage unit 57a storing the operation patterns of FIGS. 11 and 13 and the torque command value storage unit 57 storing the torque command value corresponding to the bonding load F under torque control.
b are provided. 58 is a RAM, and this R
As shown in FIG. 4A, the AM 58 (see also FIG. 8)
A search level L1 (normally 200 to
An area is provided for storing a control switching level L2 which is a height at which the control method is switched from the position control to the torque control, and a correction level ΔL (constant value) which determines the next control switching level L2. . Also, in FIG.
L3 is the height when bonding is completed, and L2 = L3 +
There is a relationship ΔL. In FIG. 4, the numeral “()” in “” indicates “1”, the height at the time of the first bonding operation for pressing the ball 41 a to the chip 48, and “2” indicates the tip of the loop of the wire 41. Shows the height at the time of the second bonding operation of pressing the inner lead 47a to the inner lead 47a. In FIG. 2, reference numeral 60 denotes an ultrasonic oscillation circuit for controlling the ultrasonic vibrator 39 in accordance with a command from the bonder control circuit 56;
Reference numeral 9 denotes a digital servo driver that supplies a drive current I to the motor 40 in accordance with a command from the bonder control circuit 56. The bonder control circuit 56 outputs a pulse signal based on the operation pattern stored in the operation pattern storage unit 57a to the digital servo driver 40 as a command pulse signal.

As shown in FIG. 3, the digital servo driver 59 includes a drive circuit 59a for outputting a drive current I to the motor 40, and an arithmetic unit 5 provided at a stage preceding the drive circuit 59a.
9b. The arithmetic unit 59b receives the command pulse signal transmitted from the bonder control circuit 56 and the encoder E
The deviation of the feedback pulse signal transmitted from is counted as accumulated pulses. The drive circuit 59a
It has both a position control function and a torque control function. In the position control function, the drive circuit 59a provides the motor 40 with a torque in a direction in which a deviation (expressed by a pool pulse) between the current position of the capillary tool 42 and a target position (command pulse signal) is zero. Is output. Of course, if the absolute value of the deviation increases, the drive current I also increases. On the other hand, in the torque control function, the drive circuit 59a applies a drive current I according to the torque command value to the motor 40, and the motor 40 generates a constant torque corresponding to the torque command value.

As shown in FIG. 2, the accumulator pulse clear signal and command pulse signal from the bonder control circuit 56 and the feedback pulse signal from the encoder E can be input to the arithmetic unit 59b of the digital servo driver 59, respectively. The drive circuit 59a can receive a control switching signal and a torque command value from the bonder control circuit 56. The control switching signal switches the position control function and the torque control function of the drive circuit 59a, and the command pulse signal sets the target position under the position control.
The feedback pulse signal indicates the current position of the capillary tool 42, and the calculator 59b calculates the command pulse signal and the feedback pulse signal, and outputs the deviation to the drive circuit 59a. The accumulation pulse clear signal is a signal for forcibly setting this deviation to zero.

Next, the principle of braking under position control will be described with reference to FIG. H is the level at which the capillary tool 42 is to be braked. Here, FIG.
As shown in (a), when the capillary tool 42 descends and reaches this level H (of course, the position of the capillary tool 42 is monitored by the encoder E), it is assumed that it has a downward velocity V. . Here, under position control, having a downward velocity V at level H means that
This means that the target position is set below the level H, and the deviation in the state shown in FIG. 5A is not zero. Then, at the moment when the capillary tool 42 reaches the level H, when the accumulated pulse clear signal rises to make this deviation zero and stop transmitting the command pulse signal, the level H becomes a new target position. However, since the capillary tool 42 has the above-described velocity V, it goes too far from the level H by a small distance δ as shown in FIG. Here, since the target position is at the level H, the upward small distance δ
Is newly accumulated. Then, since the position control applies the drive current I to the motor 40 so as to make the deviation zero, a torque that makes this small distance δ zero is generated in the motor 40, and this torque is applied to the capillary. It acts so as to cancel the inertial motion of the movable parts such as the tool 42 and the horn 37. The above is a phenomenon that occurs in a very short time.In summary, under position control,
By raising the pulse clear signal and stopping the transmission of the command pulse signal at a certain level at which braking is to be applied, braking can be applied to the lowering of the capillary tool 42 at that level. As will be described later, in the present embodiment, in the bonding operation for detecting the ground (FIG. 11), the accumulated pulse clear signal rises when the ground is detected, and in the searchless bonding operation (FIG. 13), the control switching level is set. , And the pulse clear signal is started.

Next, an outline of the operation of the wire bonder of the present embodiment will be described with reference to FIGS. First, an initialization process is performed as shown in FIG. 6 (step 1). That is, the bonder control circuit 56 initializes the count value of the reversible counter 51, and outputs the threshold value N to the pulse width comparison circuit 54.
Set. Next, a high voltage is applied to the torch electrode 46 and the lower end of the wire 41 to generate a spark.
A ball 41a is formed at the lower end of the chip 1 (step 2), and a first bonding operation of pressing the ball 41a against the electrode of the chip 48 is performed. Next, the bonder control circuit 56
X motor 3 while driving horn 37
5. The Y motor 33 is driven to move the capillary tool 42 in the horizontal direction to form a loop (step 4), and the second bonding operation is performed by pressing the tip of the loop against the inner lead 47a (step 5). Then, the wire 41 is clamped by the cut clamper 44, the capillary tool 42 is raised, and the wire 41 is cut from the portion joined by the second bonding operation (step 6) until the bonding is completed (step 7). Steps 6 to 6 are repeated.

FIG. 7 is a flowchart showing each bonding operation. Here, since the flow of the first bonding operation and the flow of the second bonding operation viewed from the bonder control circuit 56 are basically the same, only the first bonding operation will be described. First, the bonder control circuit 56
Sets the control method to position control (step 11), and drives the X motor 35, the Y motor 33, and the motor 40 to move the horn 37 to the lowering start position O (step 12).
Next, it is determined whether or not grounding detection is necessary for the bonding operation to be performed this time (step 13). Here, in the present embodiment, when performing bonding for the first time on a new chip 48, a bonding operation for detecting grounding is performed (FIG. 11, Steps 14 to 20, Steps 26 to 28), and grounding detection is performed for the second and subsequent times. It is assumed that there is no searchless bonding operation (FIG. 13, steps 21 to 28).
However, the setting condition of the bonding operation for detecting the grounding or the searchless bonding operation is determined by comparing the distance (known) between the electrode to be bonded this time and the electrode to be bonded next with a predetermined value, and determining the distance. May be changed variously, for example, only when the value exceeds a predetermined value.

Next, the bonding operation for detecting the grounding shown in FIG. 11 (steps 14 to 20 and steps 26 to 2 in FIG. 7)
8) will be described. In FIG. 11, the horizontal axis indicates time. First, at time T1, the capillary tool 42 is rapidly lowered from the descent start position O to a preset search level L1 under position control (steps 14 and 15). When the search level L1 is reached at time T2, the bonder control circuit 56 outputs a permission signal to the ground detection switch 55 via the interface unit 52, and monitors the rising of the ground signal (step 16). Is reduced, and the lowering speed of the capillary tool 42 is reduced (V2) (step 17). At time T3, the lower end of the ball 41a is grounded to the chip 48 (FIG. 12 (a)), and at time T4 after a short time ΔT has elapsed from time T3, a ground signal is issued from the pulse width comparison circuit 54 ( Step 18),
The above-described braking process is performed by raising the accumulation pulse clear signal (step 19, FIG. 12B), and the time T
In step 5, the control method is switched to torque control (step 2).
0), the ball 41a is pressed against the chip 48 as a bonding surface by a preset torque. In addition, an ultrasonic oscillation signal is started to apply ultrasonic vibration (step 2).
6). Then, at time T6, the control switching level L2
Is updated (step 27), and the control method is returned to the position control (step 28).
2 is raised at a high speed (step 28). Here, at step 27, the control switching level L2 is updated.
As shown in (5), the sum of the height L3 (measured by the encoder E) at the time when the bonding operation is completed (time T6) and the correction level ΔL (constant value) is used as the control switching level L2 for the next bonding operation. For example, even when the chip 48 is inclined with respect to the horizontal plane, the height L3 at the time of completion of the immediately preceding bonding operation is reflected in the control switching level L2 of the next bonding operation, and the control switching level L2 is always made appropriate. Can be. At the time of contact detection (time T4), the accumulated pulse clear signal rises to generate an upward torque on the movable portion having the speed V2 as shown in FIG. 41a can be prevented from being excessively crushed and damage to the chip 48 can be suppressed.

On the other hand, when it is determined in step 13 that the ground detection is unnecessary, the searchless bonding operation shown in FIG. 13 is performed (steps 21 to 25). First, at time t1, the capillary tool 42 located at the lowering start position O moves down at a high speed when a large command pulse signal is given from the position control lower bonder control circuit 56 to the calculator 59b (step 21). Then, the bonder control circuit 56 monitors the current position signal of the reversible counter 51, and when detecting that the capillary tool 42 has reached the control switching level L2 at time t2 (step 22), raises the accumulated pulse clear signal. The above-described braking process is performed (FIG. 1
4 (a)), the inertial force of the movable part such as the horn 37 is canceled (step 23). Then, at time t3, the bonder control circuit 56 outputs a control switching signal to the drive circuit 59a, reads a torque command value corresponding to the bonding load F from the torque command value storage unit 57b, and outputs it to the drive circuit 59a ( Step 24, FIG. 14 (b)). Then, the bonder control circuit 56 holds this state for a predetermined time until time t6 (step 25). Further, after the predetermined time, the ultrasonic oscillation circuit 60 is instructed to operate the ultrasonic oscillator (step 26). Then, at time t6, the bonder control circuit 56 modifies the control switching level L2 to reflect the height L3 at the time of completion of bonding in the same manner as in the bonding operation of FIG. 11 (step 27), and returns the control method to position control again. To raise the capillary tool 42 at high speed. As described above, even when the ground detection is not performed,
Each time a bonding operation is performed, the control switching level L2 is given a margin of the correction level ΔL from the height L2 at the time of completion of bonding, and the control switching level L2 is modified. Therefore, in the searchless bonding operation, even when the chip 48 is tilted, it is possible to omit the ground detection and prevent the chip 48 from receiving an excessive impact.

[0026]

According to the present invention, it is not necessary to apply ultrasonic vibration at the time of grounding, so that damage to the ball can be reduced, and high-speed accurate grounding detection can be performed without depending on mechanical contacts. .

[Brief description of the drawings]

FIG. 1 is a perspective view of a wire bonder according to an embodiment of the present invention.

FIG. 2 is a block diagram of a wire bonder according to one embodiment of the present invention.

FIG. 3 is a block diagram of a digital servo driver according to one embodiment of the present invention;

4A is a data configuration diagram of a RAM according to an embodiment of the present invention; FIG. 4B is a data configuration diagram of a ROM according to an embodiment of the present invention;

FIG. 5A is an explanatory diagram of a braking process according to an embodiment of the present invention. FIG. 5B is an explanatory diagram of a braking process according to an embodiment of the present invention.

FIG. 6 is a flowchart illustrating a wire bonding method according to an embodiment of the present invention.

FIG. 7 is a flowchart illustrating a wire bonding method according to an embodiment of the present invention.

FIG. 8 is an explanatory diagram of a level according to the embodiment of the present invention.

9A is a time chart illustrating a reference pulse signal according to an embodiment of the present invention; FIG. 9B is a time chart illustrating a falling detection pulse signal according to an embodiment of the present invention; Chart showing the ground signal in the form

FIG. 10 is an explanatory diagram of the operation of the ground detection means in one embodiment of the present invention.

FIG. 11 is a time chart of a bonding operation for detecting grounding according to the embodiment of the present invention;

12A is an explanatory diagram of a bonding operation for detecting a ground according to an embodiment of the present invention. FIG. 12B is an explanatory diagram of an operation of a bonding operation for detecting a ground according to an embodiment of the present invention. Operation explanatory diagram of a bonding operation for performing ground detection according to an embodiment of the present invention

FIG. 13 is a time chart of a searchless bonding operation in one embodiment of the present invention.

14A is an explanatory diagram of a searchless bonding operation according to an embodiment of the present invention. FIG. 14B is an explanatory diagram of an operation of a searchless bonding operation according to an embodiment of the present invention. Explanatory diagram of the searchless bonding operation in the embodiment

15A is a diagram illustrating the operation of a conventional wire bonder. FIG. 15B is a diagram illustrating the operation of a conventional wire bonder. FIG. 15C is a diagram illustrating the operation of a conventional wire bonder.

FIG. 16 is a block diagram of a conventional wire bonder.

[Explanation of symbols]

 37 Horn 40 Motor 41 Wire 42 Capillary tool 54 Pulse width comparison circuit E Encoder

Claims (2)

[Claims] 1. A wire bonding method for crimping a wire inserted into a capillary tool held at a tip of a horn to a chip, wherein the motor is driven by a position control system to swing the horn. The capillary tool is lowered toward the tip, and a ground detection signal is output when the period of the pulse signal output from the encoder that detects the rotational position of the shaft that pivotally supports the horn is longer than a predetermined time. Receiving the ground detection signal, switching from the position control method to the torque control method, generating a predetermined torque in the motor, and crimping a wire to a chip. 2. The control method according to claim 1, wherein a difference between a pulse signal based on an operation pattern and a pulse signal output from the encoder is counted as a droop pulse, and a current corresponding to the droop pulse is output to the motor. 2. The wire bonding method according to claim 1, wherein, when the ground detection signal is output, the droop pulse is cleared to switch to torque control.