JP2768368B2 - Pattern inspection equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] A pattern inspection apparatus, in particular, a technique for inspecting the presence or absence of a defect in a wiring pattern on a printed circuit board, enables detection of a minute defect as large as the pixel to be inspected, and In order to increase the reliability of inspection, light is emitted to a printed circuit board to form an image of reflected light from the board at a predetermined position, and a pattern signal is output in accordance with the amount of light of the formed image. An image detection optical system, a means for digitizing the output pattern signal, and a predetermined number of pixels to be inspected for the digitized pattern signal. Means for encoding a signal intensity distribution indicating how the intensity is changing in accordance with a predetermined standard, and creating and registering the encoded signal intensity distribution for each pixel to be inspected in advance Means for performing binarization by comparing with a dictionary code which has been set, and inspecting the wiring pattern for the presence or absence of a defect based on the binarized pattern.

[Industrial applications]

The present invention relates to a pattern inspection apparatus, and in particular, to a defect (chip, protrusion, disconnection,
The present invention relates to a technique for inspecting the presence or absence of a short circuit or a dent.

As the speed and density of electronic computers have increased, the width and spacing of the wiring patterns on the printed circuit boards used for them have been reduced to 100 μm or less, and the outer shape has been reduced to 600 μm.
It is getting bigger with mm square. In this wiring pattern,
Since there is a possibility that a defect such as disconnection or short-circuit has occurred, it is necessary to inspect for such a defect. However, this inspection has become impossible with human eyes in view of the reliability of the inspection and the inspection speed. For this reason, development of a system for automatically inspecting a pattern is demanded.

[Conventional technology and problems to be solved by the invention]

In the conventional pattern inspection method, for example, a level of about 50% of the amplitude is set as a threshold (threshold level) for a detected pattern signal, and the threshold level is set as the level of the detected pattern signal. Then, binarization was performed, and the presence or absence of a pattern defect was inspected based on the result.

That is, since there is one reference level (threshold level) for performing binarization, as shown in FIGS. 6 (a) and 6 (b), a minute defect having the same size as the pixel to be inspected. For a short-circuit defect or a disconnection defect, as shown in FIGS. 3C and 3D, the intensity of the detected signal changes its threshold level Vth (from “H” level to “L” level, (Or vice versa) it may not change to the extent that it crosses. Therefore, there is a problem that the defect cannot be detected even though the defect is originally a defect. This is not preferable because it leads to a decrease in detection accuracy and, consequently, a decrease in the reliability of the pattern inspection.

As another technique, there is a method in which a plurality of threshold levels are set, each of which is used to detect a specific defect. However, with this method,
Since three types of binarized images can be obtained, the circuit scale required for inspection increases, and dust and scratches that are not originally defects are excessively (erroneously) detected as defects. is there. This form is not preferable from the viewpoint of the reliability of the inspection, similarly to the above-mentioned method.

The present invention has been made in view of the problems in the related art, and provides a pattern inspection apparatus capable of detecting a minute defect as large as a pixel to be inspected, thereby improving the reliability of the inspection. It is intended to be.

[Means for solving the problem]

In order to solve the above problems, according to the present invention, there is provided an apparatus for inspecting the presence or absence of a defect in a wiring pattern of a printed board, and irradiating the printed board with light and reflecting light from the board at a predetermined position. An image detection optical system that forms an image and outputs a pattern signal according to the amount of light of the formed image;
Means for digitizing the output pattern signal;
A signal intensity distribution indicating how the signal intensity of another pixel changes with respect to the signal intensity of a specific pixel in units of a predetermined number of inspection target pixels with respect to the digitized pattern signal according to a predetermined standard. Means for coding, and means for performing binarization by comparing the coded signal intensity distribution of the inspection target pixel unit with a dictionary code created and registered in advance, wherein the binarized There is provided a pattern inspection apparatus characterized by inspecting a wiring pattern for the presence or absence of a defect based on a pattern.

[Action]

According to the above-described configuration, the pattern signal detected by the image detection optical system is not immediately binarized, but is digitized once and then encoded as a signal representing a signal intensity distribution in a predetermined number of pixels. And binarized based on a check with a predetermined dictionary code. And based on this binarized pattern,
It is determined whether or not the wiring pattern has a defect.

That is, since the presence or absence of a defect is inspected after analyzing the distribution of the signal intensity for each pixel, even a minute defect having the same size as the pixel to be inspected can be detected with high accuracy. This contributes to improving the reliability of the inspection.

The details of other structural features and operations of the present invention will be described with reference to the accompanying drawings and embodiments described below.

〔Example〕

FIG. 1 schematically shows a part of a configuration of a pattern inspection apparatus as one embodiment of the present invention.

In the figure, 1 is a printed circuit board including a wiring pattern, 2 is a table on which the printed circuit board is mounted, and a table which is moved and adjusted in an XY direction by a driving mechanism (described later) at the time of pattern inspection, and 3 is a light source (for example, a halogen lamp). 4) an optical fiber for guiding light from the light source to irradiate the printed circuit board 1 with light, 5 a lens for forming an image of reflected light from the printed circuit board 1 at a predetermined position, and 6 being disposed at the predetermined position. Figure 2 shows an image detector. The image detector 6 has, for example, a CCD (Charge Coupled Device), measures the amount of light of an image formed at the predetermined position, and outputs a pattern signal corresponding to the amount of light.

10 is an amplifier for amplifying the detected pattern signal, 11 is an analog / digital (A / D) converter for digitizing the amplified pattern signal, and 12 is a pattern signal digitized by the A / D converter. A frame memory 13 for temporarily storing the signal intensity distribution in a predetermined number of inspection target pixels (3 × 3 pixels in this embodiment) in units of a digitized pattern signal stored in the frame memory. 1 shows a coding circuit for coding according to a standard. This signal intensity distribution will be described in detail later,
It shows how the signal intensity of another pixel changes with respect to the signal intensity of a specific pixel in the inspection target pixel. Reference numeral 14 denotes a look-up table (LUT) storing dictionary codes created and registered in advance, and reference numeral 15 compares output of the encoding circuit 13 with the contents of the LUT 14 to determine whether to output 1 or 0. 3 shows a binarization circuit.

16 is a defect discriminating circuit for discriminating the presence or absence of a pattern defect based on a binarized pattern by, for example, radial matching logic or the like; 17 is a device (for example, a CRT) that outputs the result of the defect discrimination; A drive mechanism for moving in the XY direction, 19 is a drive mechanism for performing movement adjustment so that the position of the image detector 6 matches the focal position of the imaging lens 5, and 20 is a controller. The controller 20 controls the defect determination circuit 16 to determine the presence or absence of a pattern defect, controls the output device 17 to control the output of a defect instruction, and controls the drive mechanisms 18 and 19 in the form of a table 2. And a function of controlling the position adjustment of the image detector 6.

Next, the coding of the signal intensity distribution will be described with reference to FIGS. 2 and 3. FIG.

2 (a) to 2 (e) show various shapes of the signal intensity curved surface. In this embodiment, the characteristic of the signal intensity distribution is a curved surface characteristic around a specific pixel among the inspection target pixels (3 × 3 pixels). And signal strength. In the figure, (a) shows the top of a single protrusion, (b) shows a part of a continuous ridge, (c) shows a part of a continuous valley, and (d) and (e) show parts of a continuous slope.

The above-described binarization circuit 15 determines whether the pattern is normal or has a defect in accordance with the combination of the shape of the curved surface and the signal strength, and performs binarization.

At this time, the characteristics of the curved surface are represented as codes, and the signal intensity is also divided into a plurality of regions (three in this embodiment). To determine which combination is 1 or 0 among the combinations of the surface characteristic and the signal strength, as described above, the LUT 14
See

For example, when the strength is low in the form of a single projection as shown in FIG. 5 (a), 0 (no pattern) is output, and when the strength is the same, 1 in the form of a continuous projection as shown in FIG. 5 (b).
(With pattern) is output.

3 (a) to 3 (c) show an example of coding of the signal intensity distribution.

In the present embodiment, the inspection target pixels are 3 × 3 pixels (P _{1 to} P ₉ ), and therefore, first. Take four directions - as shown in FIG. 6 (a), whether the signal strength of each pixel (in the illustrated example P ₅₎ center pixel is changing how relative signal strength Determine. There are five modes of change: high at the center (peak), low at the center (valley), flat (flat), gradually rising (up), gradually falling (down).

As also shown in FIG. (B), as the signal intensity of the center pixel P _5, a relatively high (H) level of disconnection detection level (FIG. 6 see (d)) and a relatively low (L) The level is classified into three levels: a short detection level (see FIG. 6C) and an intermediate level (M) pattern width measurement level therebetween.

Together foregoing, the type of the signal intensity distribution, direction four, shape five types, the signal intensity of the center pixel in three, the number of combinations is the 5 ⁴ × 3 = 1875 types.

FIG. 4 shows a flowchart of a pattern inspection process performed by the apparatus shown in FIG.

First, in step S1, a light amount is measured by the image detector 6, and a pattern signal is output according to the light amount. This pattern signal is temporarily stored in the frame memory 12 via the amplifier 10 and the A / D converter 11. In step S2, the signal intensity distribution is coded by the coding circuit 13 for each inspection target pixel (3 × 3 pixels).

In step S3, the coded signal intensity distribution is compared with the contents of the LUT 14 by the binarization circuit 15, and in step S4, the presence or absence (1 or 0) of the pattern is determined. That is, a binarization pattern is created. Step S5
Then, the presence / absence of a pattern defect is inspected by the defect determination circuit 16 based on the binarized pattern.

Finally, in step S6, it is determined whether the inspection has been completed for all the pixels (YES) or not (NO). If the determination is YES, this flow is "END". Returning to S1, the above processing is repeated.

As described above, according to the present embodiment, the pattern signal detected by the image detection system is once digitized and then coded as a signal representing a signal intensity distribution in a predetermined number of pixels, and the contents of the LUT 14 It is designed to be binarized based on matching with. Then, based on the binarized pattern, it is inspected whether or not the wiring pattern has a defect.

For example, as shown in FIG. 5 (a), even if the binarized pattern has a certain signal strength, if the pattern has the form of a single protrusion, Since the operation is not affected, it is determined that the operation is normal. That is, it is regarded as dust or a scratch which does not become a defect.

On the other hand, as shown in FIG. 5 (b), when the signal intensity is the same as that of the single projection in FIG. Is determined to have a short defect (see FIG. 6 (a)).

As described above, since the presence or absence of a defect is inspected after analyzing the distribution of the signal intensity for each pixel, the detection sensitivity and accuracy can be increased as compared with the conventional type. Therefore, it is possible to detect even a minute defect having the same size as the pixel to be inspected with high accuracy, and to improve the reliability of the inspection.

〔The invention's effect〕

As described above, according to the present invention, it is possible to detect only a practical defect such as a short circuit or a disconnection as a defect with high accuracy without making a pattern such as dust excessively defective. This leads to an improvement in the reliability of the inspection and is extremely useful.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically showing a part of the configuration of a pattern inspection apparatus as one embodiment of the present invention. FIGS. 2 (a) to 2 (e) are diagrams showing various shapes of a signal intensity curved surface. 3 (a) to 3 (c) are diagrams for explaining coding of signal intensity distribution, FIG. 4 is a flowchart showing a pattern inspection process performed by the apparatus of FIG. 1, and FIGS. 5 (a) and 5 (b) 6 is a signal intensity distribution diagram for explaining the operation of the apparatus in FIG. 1, and FIGS. 6 (a) to 6 (d) are diagrams for explaining problems in the conventional pattern inspection system. (Description of reference numerals) 1... Printed circuit board, 2... Table, 3.
... optical fiber, 5 ... imaging lens, 6 ... image detector, 10 ... amplifier, 11 ... A / D converter, 12 ... frame memory, 13 ... coding circuit, 14 ... lookup Table (LUT), 15: binarization circuit, 16: defect determination circuit, 17: output device, 18, 19: drive mechanism, 20: controller.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-2-123478 (JP, A) JP-A-1-301151 (JP, A) JP-A-59-108175 (JP, A) JP-A-62- 266406 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01B 11/00-11/30 G06F 15/70-15/70 465 G01N 21/84-21/91

Claims (1)

(57) [Claims] An apparatus for inspecting a printed circuit board (1) for a defect in a wiring pattern, wherein the apparatus irradiates light to the printed circuit board to form an image of reflected light from the substrate at a predetermined position. An image detection optical system (5, 6) for outputting a pattern signal in accordance with the amount of light of the formed image, and a means (1) for digitizing the output pattern signal
1) and a signal intensity distribution indicating how the signal intensity of another pixel changes with respect to the signal intensity of a specific pixel in a unit of a predetermined number of inspection target pixels with respect to the digitized pattern signal. Means (13) for coding according to a predetermined criterion; means for binarizing by comparing the coded signal intensity distribution for each inspection target pixel with a dictionary code (14) created and registered in advance ( 15) a pattern inspection apparatus characterized by inspecting a wiring pattern for the presence or absence of a defect based on the binarized pattern.