JPS6034260B2 - wire bonding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic position compensation wire bonding method.

2. Description of the Related Art In the manufacture of semiconductor devices and the like, there is a wire bonding operation in which electrodes of silicon pieces (belets) forming circuit elements are connected to leads serving as external terminals using wires.

Since this wire bonding work is extremely time-consuming, automation is being attempted. One form of this automation is to measure (detect) the positional relationship between the pellet and the lead in the integrated state, calculate and determine the bonding layer from this measurement result, and automatically control the wire bonding machine iso section. A method of continuously performing wire bonding has been proposed. By the way, in this method, it is fine if wire bonding is performed at the same set position without moving the bullet and lead frame after measuring the positions of the bullet and IJ, but the measurement position (measuring station) and the wire bonding If the positions (wire bonding stations) are different, the positions of the pellets and leads are likely to be misaligned between the two. Furthermore, if the position measurement system or wire bonding system deviates from its initially set position due to thermal deformation or vibration of various parts of the device, the actual bonding position will deviate. Therefore, it is necessary to occasionally inspect the bonding state of the wire to the electrode of the pellet, and conventionally this work has been performed by visual observation by an operator.

However, such visual observation work is performed by the operator, resulting in low workability and disadvantages such as inconsistency in judgments of pass/fail and judgment of the amount of correction of the bonding mechanism.

Therefore, an object of the present invention is to perform wire bonding accurately and reliably. Another object of the present invention is to automatically recognize the bonding state after wire bonding, thereby realizing unmanned operation of an automatic wire bonding apparatus.

In order to achieve such an object, the present invention measures the relative positional relationship between the leads and the pellet when connecting each electrode of the pellet with each lead using a wire, and the information obtained from this measurement and the The actual bonding position is calculated using information about the wire rod and pellet that has been input in advance, and the bonding mechanism of the wire bonding device is driven and controlled based on the calculation results to perform a series of wire Z bondings. In the wire bonding method, after each electrode of the pellet and each lead are bonded with a wire at the bonding station, the connection state of the wire connection part against the bonding pad of the pellet is also detected, and the above-mentioned bonding position is corrected based on the detection result. It is characterized by

The present invention will be explained below with reference to Examples. FIG. 1 shows an embodiment of the automatic position correction type wire bonding method of the present invention.

The figure shows a flowchart of the bonding method. First, a board frame with a part of the pellet fixed is loaded onto a stage that serves as both an inspection device (measuring device) and a wire bonding device station, and is positioned and fixed.Then, the inspection device and stage are positioned (initial position settings). Thereafter, the position of the bullet pattern is inspected using an inspection device attached to the wire bonding machine, such as an industrial camera and an industrial television. Next, based on the information on this inspection (measurement) result and the information entered in advance such as the positional relationship between each electrode on the pellet and each lead on the lead frame, each bonding process is performed using a computing device such as a computer. Perform position calculations (operations). next,
The industrial camera is removed from the stage, the wire bonding mechanism of the wire bonding apparatus is exposed, and gold wires are sequentially connected by thermocompression bonding based on the information obtained from the calculation results, and wire bonding of unit pellets is automatically performed. The wired frames that have been sequentially wire-bonded in this manner are sequentially transported by a transport mechanism and unloaded to a predetermined storage box or to the next assembly line. At this time, an inspection position is provided in a part of the transport mechanism, and an inspection mechanism is installed to inspect the state of the joint (connection part) of the gold wire connected to the bonding pad of the bullet, that is, the state of the connection area. has been done. This inspection mechanism can detect the bonding part using an optical method, and determines and recognizes the bonding state based on the distribution of light intensity. This information is sequentially sent (feedback) to control systems such as computers,
Statistical processing is performed by the control system. Then, a certain tendency appears, and the deviation of the spherical part (crimped ball), which is the bonding part of the gold wire against the bonding pad of the bullet, approaches the limit of permissible accuracy, or there are cases where it deviates from the permissible accuracy. , the initial position is corrected (corrected), and the wire bonding position is calculated based on a new standard. Here, two examples of methods for recognizing the positional relationship of the spherical portion of the wire with respect to the bonding pad (electrode) of the bullet will be described.

first. In the method shown in FIGS. 2a and 2b, when the displacement of the crimp ball 1 is small, that is, when the center 0 of the crimp ball is within the bonding pad 2, the X, Y
If the misalignment in the direction is less than half the length of the bonding pad 2 in the x and y directions, the tangent to the crimp ball 1 in the x and y directions can be found by recognizing the bonding pad 2 covered by the bonded ball. I can do it. That is, the second
As shown in figure a, if the bonding ball 1 is shifted by 1 with respect to the center of the bonding pad 2, the recognition result of the bonding pad 2 is as shown in figure 2b, when the light is bright. A matrix consisting of the bonding pad part (the area marked 1 in the box) and a dark area made of the gold crimp ball (the area shown by hatching in the figure, and the area marked 0 in the box). Therefore, the point where the value changes from 0 to 1 in the X and Y directions is the contact point, so if you draw a perpendicular line in the X and Y directions through that point, you will find that the approximate center 0 of the crimp ball 1 is In this case, if the position changing from 0 to 1 is a line segment, the approximate center of the crimped ball can be found by drawing a perpendicular line at the center of the line segment. The more the matrix is subdivided, the smaller the difference ΔS between the stop of the press-bonded ball and the center peak of the matrix line tends to be.

This method is the simplest and most practical since the center of the crimp ball rarely deviates from the area of the bonding pad 2 during actual wire bonding. Further, the hatched chain line area in 2a is, for example, an area where the center of the press-bonded ball 1 with respect to the bonding pad 2 is allowed to shift. Further, a large-diameter chain-line circle indicates a state in which the press-bonded ball is aligned with the center of the bonding pad. Other recognition methods are shown in FIGS. 3a and 3b.

In this method, when the displacement of the crimp ball is large, that is, in the method shown in FIGS. 2a and 2b, if the center of the crimp ball is deviated from the bonding pad, tangents in the X and Y directions cannot be determined. Therefore, if one arbitrary tangent line is found, the center of the crimp ball will be located on a line perpendicular to the tangent line, so if the variation in the diameter of the crimp ball is small, the average value of the radius of the crimp ball will be Even if the point is considered as the center of the crimped ball, the error is small, so it is safe to consider that point as the center of the crimped ball. How to find the tangent line is to find the bonding pad area that is covered by the crimp ball 1 (the area indicated as 0 in the box shown in figure b) and the bonding pad area that is not covered (the hatched area shown in figure b). An arbitrary point (contact point) P on the boundary of the area marked as 1 inside the desk is found.

{2) Next, draw a straight line passing through the contact point P, change the slope of the straight line, check the brightness (0 or 1) on the straight line, and find the slope of the tangent.

For example, in the straight line A shown in FIG. 3b, a 0 area appears as a lotus line on the left side of the contact point P of the straight line, and a 1 area appears on the right side. Therefore, we know that this is not a tangent line. Similarly, straight line B is also not a tangent. As shown by a straight line C, when both sides of the contact point P are in the same area, that is, in one area, it becomes a tangent line. Therefore, by drawing a perpendicular line to the contact point S of this straight line C and finding the average radius r of the crimp ball from the contact point P, the position of the center 0 of the crimp ball can be found. This method is less accurate than the previous method, so
Since it is easy to know whether the crimp ball is misaligned in the X or Y direction, it is practical to move the position in the direction that reduces the misalignment, perform wire bonding, and repeat the position correction. Conceivable. On the other hand, if the crimp ball does not touch the bonding pad at all, in this case the crimp ball will not adhere to areas other than the bonding pad, and the wire bonding device will stop due to wire breakage or the like.

Therefore, only in this case, the operator has to perform alignment. The amount of displacement of the crimp ball is automatically determined by a program input into the computer in advance.

According to such an embodiment, the state after wire bonding is constantly inspected to ensure accurate wire bonding, thereby improving the yield of wire bonding.

Furthermore, automatic wire bonding work can be unmanned. Note that the present invention is not limited to the above embodiments.

In other words, as shown in the flowchart of FIG. 4, when the bullet position measurement and bonding position calculation and wire bonding are performed separately, the connection state information after wire bonding is used to set the position of the wire bonding device. The correction may be made during bonding. As described above, according to the automatic position correction type wire bonding method of the present invention, wire bonding is performed while correcting it by feeding back the bonding results, so that wire bonding can be performed accurately and reliably, and the speed of the wire bonding can be improved. In addition, according to the present invention, changes in wire bonding due to vibrations and misalignment of various parts that occur during loading and unloading, as well as during equipment operation, are automatically detected and fed back, so there is almost no need for an operator in the series of operations. becomes.

Therefore, one worker can manage a large number of these devices at once, resulting in benefits such as reductions in personnel costs.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing an embodiment of the automatic position correction type wire bonding method of the present invention, FIGS. 2a and b are explanatory diagrams showing a method for recognizing the connection position of the wire with respect to the bonding pad of the bullet, and FIG. 4A and 4B are explanatory diagrams showing another method of recognizing the connection position of a wire to a bonding pad of a bullet, and FIG. 4 is a flowchart showing another embodiment of the present invention. 1... Crimp ball, 2... Bonding pad, 0... Center of crimped ball, P... Contact point of crimped ball, r...... Bonding pad of crimped ball. Average radius, q... Center of the crimped ball due to the matrix, △S... Displacement between the center of the crimped ball due to the matrix and the center of the crimped ball, A, B, C...
・Straight line. Younger brother’ diagram Younger brother’s diagram Younger brother’s diagram Figure 4

Claims (1)

[Claims] 1. When connecting each electrode of the pellet and its corresponding lead with a wire, the relative positional relationship of the lead to the pellet should be measured, and bonding should be performed based on the information obtained from this measurement and the information about the lead and pellet that has been entered in advance. In a wire bonding method in which the position is calculated, the bonding mechanism of the wire bonding device is driven and controlled based on the calculation result, and a series of wire bonding is performed, after wire bonding each electrode of the pellet and each corresponding lead. . A wire bonding method characterized by detecting the state of a wire connection part to an electrode of a pellet and correcting a position to be bonded based on the detection result.