JPS6150381B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in wire bonding in which electrodes on a semiconductor chip and a lead frame are electrically connected using ultrafine metal wires, and in particular to protection of capillaries during automatic wire bonding processes. This is what we are trying to achieve.

In recent years, attempts have been made frequently to automate the manufacturing of semiconductor devices, and in particular, fully automated equipment has been developed for the process of bonding wires to electrodes on semiconductor chips.

When wires are bonded to semiconductor chip electrodes, the wires used are extremely thin and therefore have an unstable shape, and there is a risk of deformation or disconnection even when a slight external force is applied. Conventionally, therefore, in this type of device, a wire is led out from a capillary having a wire guide hole bored in the center and supplied to a bonding section. During bonding work, the wire and electrode are connected by pressing a capillary with a protruding wire tip onto a desired bonding position such as a semiconductor chip electrode. However, in such a bonding process, in order for the wire to be firmly bonded at the desired position, the tip of the capillary that is pressed against the bonding part must always be maintained in an appropriate state without damage or foreign matter. It is more important than anything else.

The following situations can cause damage to the capillary tip during bonding work.

(a) When the wire end is pressed against the semiconductor chip electrode by the capillary, the adhesive force that binds the semiconductor chip to the lead frame is insufficient, so the chip is attached to the lead frame during the process of lifting and moving the capillary. peels off,
The capillary is adjusted to the next bonding position with the chip still attached.

(b) When pressing the capillary against the semiconductor chip electrode and bonding the wire end, part of the chip or electrode peels off and adheres to the wire end, and the capillary is adjusted to the next bonding position in that state. Ru.

If there is an abnormality at the tip of the capillary as in a and b above, it is necessary to stop the work and remove the obstruction.

On the other hand, a state in which wire bonding is not performed normally may be due to so-called wire breakage. In the case of this wire breakage, there is no particular abnormality at the tip of the capillary, and therefore it does not pose a particular problem even if the bonding work is continued, and it would be extremely uneconomical to interrupt the work each time, so automation The meaning of what was done is significantly diminished.

The present invention has been made in view of the problems in the conventional wire bonding method described above, and is intended to determine a situation in which an abnormality occurs at the tip of a capillary and to control the continuation of the bonding operation thereafter.

Next, the present invention will be explained in detail with reference to Examples.

First, the principle of the present invention will be explained.

If there is a risk of damaging the tip of the capillary as in a and b above, after the capillary is pressed against the electrode, move the capillary to the next bonding position, and in case a, return to the original lead frame. There is no semiconductor chip, and in case b, the chip surface after capillary pressing has changed significantly from the semiconductor chip surface image before bonding, and in any case can be clearly distinguished from the semiconductor chip surface before bonding. For example, as is well known, a semiconductor chip is broken down into small rectangles of several tens of micrometers, and the reflected light from above in each section is captured by an ITV camera, etc., and a video signal of a certain level or higher is transmitted to the semiconductor chip. Count as existing. At this time, if the semiconductor chip peels off or a significant change occurs on the chip surface, the light irradiated from above will be diffusely reflected and will not return to the camera, resulting in a decrease in the number of counts. Therefore, in the present invention, an image of the semiconductor chip that has been previously imaged is used to recognize the electrode position before bonding, and after bonding, the same area is imaged again and the two images are compared, and based on the comparison result. Controls the bonding operation of the next capillary.

In Figure 1, 1 is a semiconductor chip 2 on the top of the tip.
The lead frame 1 is formed by punching a metal plate, and a plurality of lead pairs are integrally provided in a repeating pattern on the same metal plate. A semiconductor chip 2 is fixed to the tip of one of the lead wires of the lead pair using a conductive paste or the like, and wire bonding is performed between the electrode on the semiconductor chip and the other lead wire of the lead pair using a bonding device. The lead frame 1 to which the semiconductor chip 2 is die-bonded is mounted on a lead frame transport mechanism of a bonding apparatus, and is transported at a constant pitch in synchronization with the bonding operation, and is sequentially transported to a bonding work position. An ITV camera 3 is installed at the bonding work position to capture images of the mounted lead frame and the surface of the semiconductor chip 2. The optical system attached to the ITV camera 3 is further provided with a light source that illuminates the imaging area during imaging. Also connected to the ITV camera 3 is a video processing circuit 4 and a memory device 5 for storing signals processed by the video processing circuit. A comparison circuit 6 is connected to the video processing circuit 4 and the memory device 5 to compare the video signals outputted from both, and the comparison result is transferred to the control device 7 to form a command signal for controlling the bonding operation. be done. The control device 7 outputs various control signals for controlling the operation of the bonding device, and controls the video processing circuit 4, the memory device 5, and the capillary 8 described later.
control the behavior of The capillary 8 sequentially feeds out the wire 9 and press-bonds the tip of the wire 9 to the electrode of the semi-moving chip, and then moves and press-bonds the other end of the wire 9 to the other lead in the vicinity, thereby forming a lead wire. A semiconductor device in which semiconductor chips are electrically connected is obtained.

In the above-mentioned wire bonding apparatus, the lead frame 1 is transported to the bonding position, and the two sides of the semiconductor chip are first photographed by the camera 3 and transferred to the image processing circuit 4, where they are subjected to processing such as amplification as appropriate. The amplified video signal is transferred to the memory device 5 and becomes one signal for comparison, which will be described later, and is also provided to the control device 7 to determine the electrode position by comparison with a preset slice level, etc. Information is formed, the amount of displacement of the capillary 8 is calculated from the electrode position information, and the capillary drive mechanism is driven to cause the wire feeding tip of the capillary 8 to face the tip electrode position. The capillary 8 is pressed against the chip electrode while facing a predetermined position, and one end of the wire 9 is first bonded to the electrode. Next, in response to a command from the control device 7, the capillary 8 is moved linearly or in a detour by a distance l to a position opposite to the other of the pair of lead wires, and the second bonding The position will be adjusted accordingly.

In the present invention, after the first bonding is performed, the position of the capillary 8 for the second bonding is adjusted, so that the image of the lead frame, especially the second side of the semiconductor chip, after the first bonding is captured by the camera. 3 and subjected to processing such as amplification in the same manner as in the first bonding process. The output of the video signal processing circuit 4 obtained by re-imaging is sent to the comparison circuit 6, and at the same time, the video signal before bonding stored in the memory device 5 is given to the comparison circuit 6 and both signals are compared. Ru. For example, if a video signal is to be binarized with a logic value of "1" when it is above a certain level,
The part where semiconductor chip 2 exists has a logical value of “1”
In addition, the logic value is set to "0" in a portion where the semiconductor chip 2 does not exist or a chipped portion.
Therefore, the number of sections that have such a logical value of "1" or "0" is counted, and the difference between the count number of the chip part taken in advance before bonding and the count number of the chip part after the first bonding is calculated. When removed, it becomes possible to detect peeling or partial loss of the chip.

When the first bonding is properly performed, even after bonding, only a wire image is added and there is no significant difference between the two signals.
However, if the entire semiconductor chip is detached from the lead frame or a part of the electrode is peeled off, a difference will occur between the two signals, and the comparison circuit 6 will output that there is a difference between the two signals. , recognizes the abnormal state and issues a command to stop the bonding work from the control device 7, as well as notifying the abnormal state.

When it is recognized that there is no abnormality in the first bonding, the capillary 8 whose position has already been adjusted for the second bonding is pressed against the other lead wire, and the other end of the wire 9 is bonded to the lead wire. Thus, a structure in which the semiconductor chip 2 and the lead frame are wire bonded is obtained.

As described above, according to the present invention, in order to recognize the bonding position, the video signal of the semiconductor chip captured before bodying is stored in advance, and after bonding, the same area is photographed again by the imaging device and stored. The chip image is compared with the image after bonding to form an output, and if it is recognized from the comparison result that an abnormality has occurred during the first bonding operation, the bonding operation is stopped and the comparison result shows an abnormality. By performing the operation assuming that the bonding has been carried out properly, it is possible to prevent the capillary of automated bonding equipment from being damaged and protect the equipment, as well as to improve the reliability of wire bonding in semiconductor devices. .

[Brief explanation of the drawing]

The figure is a block diagram of an embodiment according to the invention. 1: Lead frame, 2: Semiconductor chip, 3:
ITV camera, 4: video signal processing circuit, 5: memory, 6: comparison circuit, 7: control device.

Claims (1)

[Claims] 1 In a method in which wire bonding is performed by supplying wires from a capillary to electrodes on a semiconductor chip mounted on a lead frame, the image signal of the semiconductor chip on the lead frame sent to the bonding work position by an imaging device is captured and the image signal is transferred to the chip. The video signal is stored, the electrode position is recognized by the chip video signal, the capillary is positioned based on the recognized content, one end of the wire is first bonded to the electrode position, and the capillary and the lead frame are relatively displaced. Then, the capillary is positioned at a position where the other end of the wire is to be subjected to second bonding, and at the same time during the capillary positioning period, the semiconductor chip video signal at the bonding work position is captured again by the imaging device, and the chip video signal and the semiconductor chip video signal are By comparing the chip video signal captured and stored in advance before the first bonding, peeling of the chip after the first bonding or partial peeling of the chip or electrode is detected, and when such peeling is detected, the above-mentioned An automatic wire bonding method for semiconductors characterized by stopping step 2 of bonding.