JPH0474860B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for detecting the contact position between a bonding tool and a bonding surface in wire bonding of semiconductor devices.

[Conventional technology]

In wire bonding, which performs bonding between the pad and leads of an IC chip, a bonding tool (for example, a capillary for ball bonding of gold wire, or a stitch bonding tool for aluminum wire) is installed at the tip of the bonding arm. Hold the wire with a wedge and bring it into contact with the bonding surface of the target pad or lead, and use a bonding tool to crush the ball or part of the wire formed at the tip of the wire, and then press the wire using thermocompression bonding. Welded using ultrasonic waves.

A conventional example of this type of bonding apparatus is shown in FIG. Reference numeral 10 denotes an ultrasonic transducer, which is swingably supported on a frame 11 by pins 12. 13 is a horn, with capillary 1 at the tip.
is provided and also functions as a bonding arm. A lever 14 is provided at the other end of the vibrator 10, and a roller 15 provided at the end is connected to a cam 16.
A counterclockwise moment is applied by the spring 17 so as to make contact with. 18 is a reel for the wire 2; 19 is a clamp for gripping and cutting the wire 2; 20 is a half clamp for pulling up the ball at the tip of the wire and bringing it into contact with the lower end 7 of the capillary 1; 21 is a clamp for holding and cutting the wire 2; It is a torch for forming a ball at the tip of the vertical axis 22
It is designed to be able to rotate around the 23 is a position detection device, which detects the pellet 4 and each pad 5;
Detects the deviation from the standard position. Depending on the detected value of this deviation, the frame 11 or pellet 4 is moved horizontally in the X or Y direction, and the capillary 1
The relative position between the pellet 4 and the pad 5 is adjusted and aligned.

In such conventional devices, the vertical movement of the capillary 1 is determined by the shape of the cam 16, and cams must be prepared and replaced for different vertical patterns corresponding to different types of pellets 4. Furthermore, there is a drawback that it is not possible to accommodate errors in dimensions such as the thickness of the pellet 4, the diameter of the ball, and the diameter of the wire 2, so that appropriate pressing force and contact area cannot be obtained.

By the way, in wire bonding, the pressing force exerted by the bonding tool after the wire comes into contact with the bonding surface has a great effect on the quality of the bonding. The pressing force is set to an optimum value as a standard. In this case, a method for detecting that the bonding tool has come into contact with the bonding surface is as shown in Japanese Patent Laid-Open No. 55-24403, by providing a contact on each of the lifting frame and the bonding arm, and attaching a contact to both contacts. It was determined whether the bonding tool came into contact with the bonding surface by applying voltage and turning the contactor on and off.

[Problem to be solved by the invention]

However, in the method disclosed in Japanese Patent Application Laid-Open No. 55-24403, the contact maintains the positional relationship between the lifting frame and the bonding arm, and applying a voltage between them causes electrolytic corrosion of the contact, causing a pressure change. There was a problem in that the contact could no longer be energized, making accurate detection impossible.

The present invention solves the above problems, accurately detects the contact position between the bonding tool and the bonding surface over a long period of time, is less affected by dimensional errors such as wire diameter and ball diameter, and is able to accurately detect the contact position between the bonding tool and the bonding surface over a long period of time. It is an object of the present invention to provide a bonding surface contact detection device that is easy to adjust even if the types are different and can reliably perform bonding with high reliability.

[Means to solve the problem]

The present invention provides an elevating frame with a swinging frame rotatably supported around a horizontal axis, a bonding arm having a bonding tool at the tip on one side of the swinging frame, and a bonding arm having a bonding tool at the tip, and A magnetic chip is provided on the side, and a magnetic sensor is provided on the lifting frame opposite to the magnetic chip, and the position where the bonding tool contacts the bonding surface is detected by a non-contact displacement detection sensor comprising the magnetic chip and the magnetic sensor. This is a bonding surface contact detection device characterized by:

〔Example〕

An embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, the elevating frame 24 is held movably up and down along the elevating guide 25 of the frame 11, and a female threaded portion 26 integrally formed on the elevating frame 24 is screwed into a threaded shaft 27. , and is driven up and down by a pulse motor 28 or a motor using an encoder. An ultrasonic transducer 10 is fixed to a swinging frame 30 which is rotatably supported by a pin 29 which is a horizontal axis in the lifting frame 24, and a capillary which is a bonding tool is attached to the tip of a horn 13 which acts as a bonding arm. 1 is provided. 31
is a leaf spring fixed to the lifting frame 24,
A counterclockwise moment is constantly applied to the swing frame 30 via the eccentric pin 32, and a downward pressing force is applied to the capillary 1 as a pressing force applying mechanism. By adjusting the eccentricity of the eccentric pin 32, the force of the leaf spring 31 can be adjusted. 33
is a stopper composed of an electromagnet, which determines the lowest position of the capillary 1 relative to the lifting frame 24.

34 is a magnet sensor, and the swing frame 30
The distance between the permanent magnet chip 36 provided on the lever 35 attached to the lever 35, that is, the amount of deviation of the center of the chip 36 from the center of the magnet sensor
An output signal corresponding to l ₀ is sent to the control mechanism 37. That is, an output signal corresponding to the displacement of the capillary 1 in the vertical direction is sent to the control mechanism 37,
It acts as a displacement detection mechanism that detects vertical displacement of the capillary 1 relative to the elevating frame 24.

Therefore, at the position where the swing frame 30 is in contact with the stopper 33, that is, when the capillary 1 is at the lowest position with respect to the lifting frame 24, the amount of deviation is
Set l ₀ to some positive value instead of zero. That is,
A positive output signal is made to be output at that position.

Cams 38 and 39 operate the clamper 19 and half clamp 20, respectively, and are driven by pulse motors.

FIG. 2 is a model explanatory diagram of the operation, and the size of the ball 3 is shown exaggerated. First, assume that the capillary 1 is initially located at a height h above the pellet 4 directly above the pad 5 to be bonded, as shown in FIG. 2a.

Next, the pulse motor 28 is driven to lower the elevating frame 24. Initially, the capillary 1 descends at high speed, and during that time, the horn 13 swings and the stopper 33 is excited and attracted to prevent the capillary 1 from vibrating unnecessarily. The bottom end of ball 3 is padded 5
When the ball 3 approaches the top (for example, about 0.2 mm), the speed is switched to low speed, and the ball 3 lowers further until the bottom end of the ball 3 reaches the position shown in Figure 2b.
It comes into contact with the pad 5 as shown in the figure. If the downward displacement at this time is Z ₀ , then Z ₀ =h−t ₀ . However, t ₀ is the height of the ball 3 protruding from the lower end of the capillary 1.

If it continues to descend further, as shown in FIG. 2c, since the ball 3 is already in contact with the pad 5, the capillary 1 does not descend and remains at the same height, but the elevating frame 24 continues to descend. Then, the amount of deviation l ₀ of the chip 36 gradually increases, and the output signal increases accordingly. The contact point is detected at the start of this increase, and in the scrub type thermocompression bonding method, scrubbing is started, and in the ultrasonic bonding method, the application of ultrasonic waves is started, and the number of pulses of the pulse motor 28 is started to be counted. The number determines the amount of downward displacement after the point of contact.

Next, it is determined that the displacement amount Z ₂ (i.e. Z ₂ = Z ₀ + Z ₁ ) has been reached by a predetermined downward distance Z ₁ from the point of contact.
This is detected by counting the set pulse number corresponding to this, and the lowering of the elevating frame 24 is stopped.

That is, a stop distance setting mechanism is formed by a displacement detection mechanism that detects the counting start time (time of contact), a pulse count and stop pulse number setting mechanism control mechanism 37, and the like.

At this point of stop, the leaf spring 31 has a maximum deflection S ₂
However, the apparent deflection is S ₂ −S ₀ . Also,
The amount of descent Z ₁ after the point of contact is determined by the set number of pulses of the corresponding counter, but it also takes into consideration the material of the wire 2, the size of the ball 3, the set amount of crushing amount, the preferred value of the pressing force, etc. selected. The amount of deviation is _l2 .

At this point, the elevating frame 24 stops, but the ball 3 is crushed by the restoring force of the leaf spring 31. Also, as the ball 3 is crushed, the amount of displacement l ₂ decreases again, but the amount of return displacement, which is the decrease value from the maximum value of the amount of displacement l ₂ , is proportional to the amount of crushing, so the amount of return displacement is output. If detected based on the signal, the amount of crushing can be known. The deflection of the leaf spring 31 decreases again.

As shown in Fig. 2d, it is detected by the return displacement amount _L1 that the crushing amount _t1 has reached a predetermined crushing amount, and in order to stop the crushing operation, the scrubbing or the application of ultrasonic waves is stopped. Alternatively, the elevating frame 24 is raised at high speed. The amount of deviation at this time is l ₁ (i.e. l ₁ = l ₂ - L ₁ ), and the amount of deflection of the leaf spring 31 is S ₁
(The apparent deflection is S ₁ −S ₀ ).

Thus, the amount of pressing reaches the predetermined set value _t1 , and bonding is completed with appropriate pressing force and contact area.

In this way, the displacement detection mechanism, return deviation amount setting mechanism, control mechanism 37, and the like form a crushing amount setting mechanism.

This preferable set value t ₁ of the amount of squeezing is selected depending on the material of the wire 2, the size of the ball 3, the preferable value of the pressing force, the preferable value of the contact area, etc.

Next, the stopper 33 is energized at the start of high-speed ascent to prevent vibration of the capillary 1, and during the ascent, the lower end 7 of the capillary 1 leaves the upper end of the ball 3 (flat part 8), and the amount of displacement returns to l ₀ and the plate spring 31
The amount of deflection S returns to ₀ . It continued to rise at high speed, and at an appropriate point it started moving horizontally, reaching the state shown in Figure 2e.

After that, while continuing to move horizontally, the elevating frame 24
The wire 2 is lowered again, and when it reaches the position directly above the bonding position of the lead 6, the lowering speed is changed to low speed. After that, bonding is performed while crushing a part of the wire 2 in the same process as the crushing process of the ball 3 described above. I do. In this case, the preferred amount of compression is determined by the diameter of the wire 2, the required pressing force, the required contact area, etc.

After the bonding is completed, the wire 2 is cut from the end of the bonding point by moving the clamp 19 upward, the capillary 1 is raised, and the clamp 19 is cut from the end of the bonding point.
With the wire 2 protruding a predetermined length from the lower end 7 of the capillary 1, the capillary 1 is positioned directly above the next pad, and the torch 21 is used to form the ball 3. The ball 3 may be formed before reaching directly above the pad.

Frame 1 is used to move capillary 1 directly above a predetermined pad and a predetermined lead.
1 or pellets 4 may be placed on an XY table to perform relative movement in the X or Y direction in a horizontal plane.

The control mechanism 37 includes the following abnormality detection mechanism. That is, a timer is provided that starts when the lower end of the ball 3 contacts the pad 5 when the lifting frame 24 is lowered, and is sufficient to provide an appropriate amount of compression for the stroke of the ball 3 and the lifting frame 24 in a normal state. A certain amount of squeezing time is set, and an abnormal signal is generated when the amount of wire squeezing detected by the displacement detection mechanism using the magnetic sensor 34 does not reach the predetermined amount of squeezing even after this predetermined squeezing time has elapsed. , the bonding operation is stopped by this abnormal signal.

Also, if the dimensions of the ball 3 are too small,
Since the crushing operation stops before reaching the predetermined crushing amount, the crushing amount detection value does not reach the predetermined crushing amount even if the timer reaches the predetermined setting point, but in this case, an abnormality in the abnormality detection mechanism The bonding operation is stopped by the signal.
Thereby, it is possible to detect that the ball 3 is too small in size, and to prevent conduction failure or peeling off due to insufficient contact area of the ball 3.

The above is an example of capillary bonding, but the same applies to wedge bonding.

The pressing force applying mechanism is not limited to the leaf spring 31.
Any mechanism that changes the pressing force depending on the displacement may be used. For example, a moving coil may be used to apply a pressing force depending on the displacement. In this case, the pressing force can be changed by changing the applied voltage. For example, if the applied voltage is strengthened when the lifting frame 24 is rapidly lowered, it will be pressed strongly against the stopper 33, so that vibration of the bonding arm such as the horn 13 can be prevented. Therefore, there is no need for the stopper 33 to be an electromagnet, and it may be a simple solid piece, resulting in a simple structure.

〔Effect of the invention〕

As described above, in the present invention, the contact position between the bonding tool and the target object is always detected by a non-contact displacement detection sensor consisting of a magnet chip fixed to the displacement side and a magnet sensor installed to the fixed side. Since the output voltage waveform is linear, it is possible to easily control the wire bonding work by controlling the contact position, the amount of crushing, and stopping the bonding operation based on abnormal signals.
Therefore, reliable and reliable bonding can always be performed with appropriate pressing force and contact area without being affected by errors in wire diameter, ball diameter, or variations in wire material. Optimum conditions can be easily set according to the type, wire material, dimensions, ball dimensions, etc., and since the displacement detection sensor is a non-contact type, errors will not occur even after long-term use. There is no risk of this happening, and it can be extremely effective in practice.

[Brief explanation of drawings]

Fig. 1 is a partially sectional front view of an apparatus showing an embodiment of the present invention, Fig. 2 a, b, c, d, and e are explanatory diagrams showing the order of its operating steps, and Fig. 3 is a conventional bonding apparatus. FIG. 1... Capillary, 2... Wire, 3... Ball,
4... Pellet, 5... Pad, 6... Lead, 8... Flat part, 10... Vibrator, 11... Frame, 12, 2
9...Pin, 13...Horn, 14,35...Lever,
15...roller, 16...cam, 17...spring, 18...
Reel, 19...Clamp, 20...Half clamp, 21...Torch, 22...Vertical axis, 23...Position detection device, 24...Elevating frame, 25...Elevating guide, 26...Female thread portion, 27...Screw shaft, 28...Pulse motor , 30... Swing frame, 31... Leaf spring,
32... Eccentric pin, 33... Stopper, 34... Magneto sensor, 36... Chip, 37... Control mechanism.

Claims (1)

[Claims] 1. A swing frame 30 rotatably supported around a horizontal axis 29 is provided on the lifting frame 24,
A bonding arm 13 having a bonding tool 1 at its tip is provided on one side of the swinging frame 30, and a magnet chip 36 is provided on the other side of the swinging frame 30.
In addition, a magnetic sensor 34 is provided on the lifting frame 24 facing the magnetic chip 36, and a non-contact displacement detection sensor consisting of the magnetic chip 36 and the magnetic sensor 34 detects the position where the bonding tool 1 contacts the bonding surface. A bonding surface contact detection device characterized by detecting contact with a bonding surface.