JPS6223457B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to automation of wire bonding position measurement in the assembly process of semiconductor integrated circuits such as ICs and LSIs.

Conventionally, in the pellet die bonding process in the assembly process of semiconductor products such as ICs and LSIs, the pellets are quite large in size.
When thermocompression bonding pellets onto a jig called a lead frame, the positioning accuracy is ±100μ or more, so the amount of positional deviation is measured visually by the operator, but this visual work requires that the patterns are extremely concentrated. This caused mental pain to the workers. In addition, in such precision work, a slight measurement error can lead to a decrease in product yield, so a highly reliable automatic position measuring device has been required.

For such automatic position measurement, it is necessary to capture the target pattern with a camera, binarize it, and then process the pattern. In this case, if the threshold value for binarization is determined for the entire screen, the reflectance around the pellet may be unstable due to the fact that the field of view is generally not square. There is a risk that a stable threshold value may not be obtained.

The purpose of the present invention is to automate such visual inspection work for wire bonding, perform automatic position measurement with high reliability, high precision, and high speed, obtain stable threshold values, and improve the accuracy of binary patterns. An object of the present invention is to provide an automatic position detection device with improved accuracy.

Therefore, in the present invention, an object to be detected consisting of a first region having a brightness in a predetermined range and a second region having a brightness different from the brightness in the predetermined range and a region other than the target object can be separated. an imaging means for photoelectrically converting the included image; a means for calculating a threshold value for binarization from a signal obtained by the photoelectric conversion means; and a means for calculating a threshold value for binarization from a signal obtained by the photoelectric conversion means; In a signal processing device comprising a binarizing means, the threshold value calculating means calculates a threshold value from a video signal belonging to a predetermined specific region within the object, out of the signals obtained by the photoelectric conversion means. , is characterized by having means for calculating an intermediate level between the signal level of the first region and the signal level of the second region as a threshold value.

FIG. 1 shows a semiconductor component, such as an LSI pellet, before wire bonding. In the figure, 1 is an LSI pellet (hereinafter abbreviated as pellet), 2 is a pedestal part of the pellet called a tab, and 3-0, 3-1, ... (some not shown) are inside pellet 1. Bonding pads (hereinafter abbreviated as pads), 4-0, 4-1, etc. are external electrodes that are part of the lead frame, and pads 3-0, 3-1 are not shown in the figure for simplicity. 3-0,3
-1, only two are listed, but external electrode 4-
The same number of pads as 0 and 4-1, in fact about 20 to 40, are provided, and the corresponding pads and external electrodes are connected to each other by wire bonding with gold wires or aluminum wires.

The problems here are variations in the pellet position, that is, the coordinates (X, Y) when expressed in rectangular coordinates, and the pellet direction, that is, the angle (θ). In this case, the magnitude of the dispersion, that is, ΔX
and ΔY is ±100 to 150μ, Δθ is about 30′, and in order to perform wire bonding automatically,
It is necessary to detect the position of each pad within ±10μ.

In the present invention, for example, as shown in FIG. is a “specific pattern recognition method” that has already been filed by the same applicant as the present invention.
(Patent Application No. 51-14031). Although a plurality of visual field images are required in order to detect the rotational deviation Δθ of the pellet, in order to simplify the explanation, the number of visual field images is set to two for convenience. The size of the visual field image is approximately 600 μ so as to cover the pellet positional deviations ΔX, ΔY, rotational deviation Δθ, etc. In addition, the position of the visual field image is variable,
In order to perform pad detection on pellets of various sizes, the apparatus of the present invention allows the position of each visual field image to be specified arbitrarily.

FIG. 3 shows the basic configuration of a position detection device according to the present invention. In the figure, reference numeral 6 denotes a metal plate called a lead frame, and as shown in FIG. 1, the pellets 1 are crimped onto the tabs 2 at a constant pitch. Reference numeral 7 denotes a frame feeding mechanism that intermittently feeds the lead frame 6 in the direction of the dashed arrow shown in the figure, and feeds the pellets 1 one by one directly below the optical system. Further, 8 is a light source for illuminating the pellet, 9 is a semitransparent mirror, 10 is an objective lens for obtaining an enlarged image of the pellet 1, and 1
Reference numeral 1 denotes a reflecting mirror for image division, which divides the enlarged image from the pellet 1 into at least two partial images. The figure shows the case of dividing into two partial images, whereby an enlarged real image of a part of the pellet 1 is obtained at the positions 12-0 and 12-1 shown in the figure.

13-0, 13-1 are relay lenses, 14-
0, 14-1 is a photoelectric conversion device for scanning an optical image and converting it into a temporal analog video signal, and for example, a TV camera such as a vidicon is used.
Reference numerals 15-0 and 15-1 are mounting stands for moving the TV camera, and pellets 1 are moved by moving the photoelectric conversion devices within a plane parallel to the light receiving surfaces of the photoelectric conversion devices 14-0 and 14-1. This is to adjust the position of the field of view depending on the pellet when changing the type of pellet.

16-0, 16-1 are photoelectric conversion devices 15-0,
15-1 is an analog video signal, 17 is a video processing device, analog video signals 16-0, 16-1
Performs binarization, pad detection processing, etc. Reference numeral 21 denotes a control device such as a computer, which controls the data processing and video processing circuit necessary for pad detection processing by sending signals 18,
20 and interface 19. 22 is a frame feeding mechanism 7 and a stage 15-
Drive circuits 0 and 15-1, 23 are circuits for controlling the drive circuit 22, and are connected to the computer via a signal 24, an interface 19, and a signal 20.

25 is an automatic wire bonder, and an image processing device 17
Based on the positions of the pads determined in step 1, a computer 21 determines the positions of all pads, and an automatic wire bonder 25 automatically connects each pad to an external electrode using a metal wire. In this case, if the speed at which the pad position is detected and the speed at which automatic wire bonding is performed do not match, a buffer such as a cassette tape is added to the automatic wire bonder 25 to temporarily store the input signal, and the detection station 26 and the automatic wire bonder 25 A system that combines these offline is also conceivable.

Also, if the pad position detection speed is sufficiently faster than the frame feed speed, as shown in Figure 4,
A plurality of detection stations 26 can be controlled with one video processing device and computer. The present invention provides a system in which one video processing device and computer can serve at least four detection stations.

Next, an overview of video processing according to the present invention will be described. In FIG. 5, 30 is in the optical system of the present invention.
An analog video of a partially enlarged pellet image obtained from a photoelectric converter such as a TV camera is shown. In the figure, a square portion 31 is an aluminum pad, 32 is an extension of the above-mentioned 31 and is a lead-out portion to the internal wiring, and 33 is a scar from an inspection prober in the previous process.

There are pellets of various sizes depending on the variety, but the size of the square portion 31 of the pad is common to all pellets, and is approximately 120 μ□. in this case,
Depending on the type of LSI and the position of the field of view within the pellet, the pull-out portion 32 may extend to either the top, bottom, left or right. Furthermore, although the size of the prober scar 33 is approximately constant, its position within the pad is indeterminate. The peripheral part 34 of the pad 31 is a silicon oxide coating part, 35 is a silicon part at the edge of the pellet, and 36 is a gold-silicon eutectic part outside the pellet.

In the case of epi-illumination as shown in FIG. 3, the aluminum part like the pad is the brightest, followed by the silicon part 35 and the silicon oxide part 34 which become darker in that order. Since the gold-silicon eutectic region 36 is inclined in the optical axis direction of the optical system, it is darkest near the pellet as shown in the figure and gradually becomes brighter as it moves away from the pellet. Further, the prober scar 33 is dark because it is depressed.

FIG. 6 is a binarized image obtained by converting the analog image 30 of FIG. 5 into a binary image using a brightness intermediate between the brightness of the aluminum part and the brightness of the silicon oxide part as a threshold value. As shown, the pad 41, the drawer 42, the silicon part 45, and the part 46-1 of the gold-silicon eutectic part 46 that is far from the pellet is white, and the prober scar 43, the silicon oxide part 44, and the gold-silicon eutectic part 46 are white. Portion 46 of portion 46 near the pellet 46-
0 is black (hatched part). in this way,
If an analog video signal can be binarized, a relatively simple video processing device can be realized, so in the present invention, the processing target is a binarized video.

Further, in the present invention, in order to further facilitate the electrical processing of the image, the binarized image is sampled into 320 pixels in the X direction and 240 pixels in the Y direction, for example, as shown in FIG. In addition, 64 pixels in the X direction and 20 pixels in the Y direction in the same figure.
The picture element part is the return line section, and the X direction 32 in it
The picture element, a band-shaped part of 12 picture elements in the Y direction, is the part where the pulse of the external synchronization signal of the TV camera is output. In addition,
Hereinafter, it will be referred to as "mode 1", "mode 2", etc. that video is sampled every 1 pixel, every 2 pixel, etc. in both the X and Y directions of each divided grid point shown in the figure. I'll call you. In Figure 7,
The mark is mode 1 sampling, ○†g

Claims (1)

[Claims] 1. Photoelectrically converting an image including an object to be detected and an area other than the object, which is made up of a first region having a brightness in a predetermined range and a second region having a brightness different from the brightness in the predetermined range. an imaging means, a means for calculating a threshold value for binarization from the signal obtained by the photoelectric conversion means, and a means for binarizing the signal obtained by the photoelectric conversion means using the threshold value. In the signal processing device comprising: A signal processing device characterized by having means for calculating a threshold value using an intermediate level between the signal level and the signal level of the second region.