JPS609664B2 - sonic wire bonder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic wire bonder, and more particularly to an ultrasonic wire bonder that detects wire feeding defects.

One of the assembly processes for semiconductor devices, integrated circuits (IC), etc.
There is a wire bonding process in which electrodes of a semiconductor element and terminals of external leads are connected with wires, and an ultrasonic wire bonder as shown in FIG. 1 is used for this wire bonding operation. This ultrasonic wireponder includes a rotatable stage 1, a wedge 2 located directly above the stage 1, and a horn 3 that holds the wedge 2 at its tip and has a built-in oscillator that vibrates the wedge 2 ultrasonically. , an elevating mechanism section 4 that moves the wedge 2 up and down while supporting the other end of the horn 3, and an XY table 5 that supports the elevating mechanism section 4 and is controlled to move in the XY direction of the plane. Further, a clamper 6 that moves together with the wedge 2 is disposed on the side of the wedge 2, and is adapted to clamp the wire 8 unwound from the spool 7 above the horn 3. Further, although not shown, back tension is generally applied to the wire 8. In wire bonding using such an ultrasonic wire bonder, a workpiece is first positioned and fixed on a stage.

For example, when manufacturing a semiconductor device, the semiconductor element 9 is fixed on the dub 10, the lead frame 12 having the lead 11 is positioned and fixed on the stage 1, and the wedge 2 is placed on the semiconductor element at the first bonding position. 9 onto an electrode (not shown). At this time, since the tip of the wire 8 is projected below the wedge 2 by the clamper 6, the tip of the wire 8 is pressed against the electrode surface by the wedge 2. Thereafter, since the horn vibrates ultrasonically, the wedge 2 also vibrates, and the wire 8 is lacquered and bonded to the electrode surface by the wedge 2. Next, after opening the clamper 6 to release the wire 8, the wedge 2 is raised, moved in a plane, and lowered to fall onto the inner end of the lead 11, which is the second bonding position. Since the wire 8 has one end fixed to the electrode and is in a released state, it is unwound from the spool 7 as the wedge 2 moves. Also, during this unraveling, back tension (generated by directional force that causes the wire to enter the guide hole of the wedge 2) is generated in the wire 8, so the rigidity of the wire 8, back tension, etc. The unraveled length of the wire is adjusted, and the other end is connected to the lead 11 and the wedge 2 while forming a mountain-like loop.
caught in between. Thereupon, the wedge 2 undergoes ultrasonic vibration again, and the other end of the wire 8 is joined to the lead 11. Thereafter, when the clamper 6 closes and holds the wire 8, the wedge 2 rises. At this time, the clamper 6 also holds the wire 8 and rises, so a large force is applied to the wire, causing it to break from the base of the joint where the strength is the weakest. Then, the clamper moves forward slightly toward the wedge to position the tip of the wire 8 below the wedge 2 in preparation for the next wire bonding. By the way, in such wire bonding, if the wire is not bonded to the first bonding butt, the clamper then opens and back tension is applied to the wire, so the wire is rewound onto the spool and the wedge There are no wires below. As a result, wire bonding is no longer possible. Conventionally, such automatic detection technology for wire supply defects has been applied to other wire bonding technologies such as nail head wire bonding, but no practical technology has been developed for ultrasonic wire bonders.

On the other hand, in ultrasonic wire bonding, Fig. 2a
As shown in FIG.
As shown in , the cross-sectional shape of the wire after ultrasonic vibration of the wedge 2 is different.

In other words, the cross-sectional shape of the wire during the pressing operation is circular, keeping almost the original shape of the wire, but after vibration (or during vibration after a certain period of time has passed from the start of vibration), the cross-sectional shape of the wire is crushed by about half of its original shape, and the top and bottom are flat. This results in an elliptical shape. Therefore, after the wire compression, the roundness before and after the vibration of the wedge 2 is slightly reduced due to the deformation of the wire 8. For example, in the case of an AI wire with a diameter of about 30 tangles, the height of the wire is about half that, about 15 tangles, and the wedge 2 also drops by about 15 tangles before and after vibration. The relationship between the height displacement of the wedge and time is shown in FIG. That is, as shown by the solid line, the wedge descends toward the surface to be joined, and when the lower surface of the wire comes into contact with the surface to be joined, and the lower end pressing surface of the wedge comes into contact with the upper surface of the wire, the wedge stops descending (
P point). Thereafter, after t seconds have elapsed, the wedge begins to vibrate, the wire is crushed, and the wedge reaches point Q. Next, when t2 seconds have elapsed, the wedge rises. By the way, the above-mentioned t, and the ultrasonic wireponders currently on the market, exist in the range of 30 to 50 seconds. In addition, when the surface to be welded is high, the initial stopping position of the wedge is high, as shown by the sharp line in the same graph, but the subsequent movement is the same as above.On the other hand, there is no wire below the wedge. When the wedge directly contacts the surface to be joined, the surface to be joined does not become depressed much, so the height displacement before and after vibration of the wedge is extremely small.

Therefore, the inventor of the present invention found that when the wire is not supplied below the wedge, there is no significant difference in the height of the wedge before and after the vibration, but when the wire is pressed against the wedge, The fact that the height of the wedge changes before and after, and the time required to measure the height of the wedge before and after vibration of the wedge after pressing the wire against the supported surface with the wedge (for example, the time t2 mentioned above) is Measure the height of the wedge within this time and
The present invention allows the wire supply state to be determined based on whether or not there is a height displacement of the wedge between the two.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an ultrasonic wire bonder having a detection mechanism that can reliably detect whether the wire is constantly being fed below the wedge or not.

In order to achieve such an object, the present invention aims to reduce the height difference between the before and after vibrations of the wedge after the wedge presses the wire against the surface to be welded. (displacement) is larger than the preset value, the wire is being supplied below the wedge (YE
S), and if it is less than the set value, it is determined that the wire is not supplied below the wedge (NO),
In the case of NO, the movement of the wire bonder is automatically stopped and a warning is issued to the operator using a buzzer, a lamp, etc. The present invention will be explained below with reference to Examples.

FIG. 4 is a schematic diagram of an embodiment of the ultrasonic wire bonder of the present invention.

As shown in the figure, a wedge 16 that presses and vibrates a wire 15 is attached to the tip of a horn 14 that incorporates an oscillator that oscillates ultrasonic vibrations. Also, horn 14
The other end of the horn 14 is supported by a support shaft 17, and the tip (wedge portion) of the horn 14 is controlled to move up and down by a swinging mechanism (not shown). Further, the other end of the horn 14 is mounted on an XY table (not shown). Furthermore, a sample stage 18 whose rotation is controlled is arranged below the wedge 16 . A capacitive displacement meter 19 is attached to the support shaft 17 of the horn 14 to detect the rotational displacement of the horn 14, that is, the vertical displacement of the wedge 16. Further, the capacitive displacement meter 19 has a determination circuit and is connected to a determination control mechanism that controls the entire mechanical section. In the judgment circuit, the information from the capacitive displacement meter 19, in particular, the wedge 16 descends toward the surface to be joined (sample stage surface), comes into contact with the surface to be joined directly or via a wire, and stops, and the wedge 16 vibrates. Wedge 16 detected within a short period of time (or at the start of vibration)
The difference (displacement) between the height of the wedge 16 (horn inclination) and the height of the wedge 16 (horn inclination) at the time when the wedge 16 finishes vibrating and the wedge 16 rises (or at a point in time) receives the information (electrical signal), determines whether the information is above a certain set value or not, and transmits the output to the control system,
If the signal is YES and the signal is greater than the set value, wire bonding is continued; if NO, wire bonding is stopped and an alarm (buzzer, lamp, etc.) is activated to notify the operator. For example, the setting value (
The dark value) is set as an electrical signal corresponding to a wedge height displacement of 10 degrees. As a result, the height displacement of the wedge is 10
If the height is above the mountain surface, a YES signal is issued to continue wire bonding, and if the height displacement is less than 10 mm, a NO signal is issued to continue wire bonding since there is no wire below the wedge. That is, when the wedge is lowered with no wire below the wedge, the lower surface of the wedge directly contacts the surface to be joined. Even if the wedge vibrates, the surface to be joined will not be affected much.For example,
The AI electrode is extremely thin, about 1 to 2 inches thick, so it hardly sinks. According to such an embodiment, it is possible to accurately detect whether or not there is a wire under the wedge, and to automatically stop the operation of the device if the wire supply is insufficient. , inform the operator.

Therefore, the yield of wire bonding is improved. Note that the present invention is not limited to the above embodiments.

That is, a generally used displacement meter other than a capacitive displacement meter may be used to detect the displacement of the wedge.
For example, a photoelectric displacement meter, an air micrometer, etc. may be used. However, when these measuring instruments are used, the mounting state, mounting mechanism, etc. will naturally differ from the above embodiments depending on the features of each measuring instrument. As described above, according to the ultrasonic wire bonder of the present invention, it is possible to accurately detect whether or not the wire is always being properly supplied below the wedge, thereby improving the yield of wire bonding. This makes it possible to reduce wire bonding costs.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the state of wire bonding using a conventional ultrasonic wire bonder, Figures 2 a and b are explanatory diagrams showing the state of the wire during wire bonding, and Figure 3 is the height displacement of the wedge during wire bonding. FIG. 4 is an explanatory diagram of an ultrasonic wire bonder according to an embodiment of the present invention. 1... Stage, 2... Wedge, 3... Horn, 4.
...Lifting mechanism section, 5...XY table,
6... Clamper, 7... Spool, 8... Wire, 9.
...Semiconductor element, 10...Tab, 11...
...Lead, 12...Lead frame, 13...
... object to be joined, 14... horn, 15... wire, 16
... Wedge, 17 ... Support shaft, 18 ... Sample stage, 19.
...Capacitive displacement meter. Tsutomu, Leopard, 2 *3, Chrysanthemum, 4

Claims (1)

[Claims] 1. In an ultrasonic wire bonder that connects the wire to the surface to be bonded by applying ultrasonic vibration to the wedge while pressing the wire to the surface to be bonded with the wedge, the height displacement before and after vibration of the wedge after the wire pressure welding operation of the wedge is detected. 1. An ultrasonic wire bonder comprising: a displacement detection mechanism that detects the displacement; and a determination control mechanism that compares the displacement with a preset value to determine whether or not there is a wire below the wedge.