JPS58114277A - Pattern inspecting device - Google Patents

Abstract

PURPOSE:To minimize erroneous detection, by installing a slice level at a point where the slice level margin is maximum. CONSTITUTION:A light is converted into an electric signal by a photodetector 4, and the output is inputted into a binary coding circuit 6 through an amplifier circuit 5. The binary coding circuit 6 is composed of a comparator 7, a crystal oscillator 8, an AND circuit 9, a pulse counter 10, a computer 11, and a DA converting circuit 12, and has a function which finds the most suitable slice level by comparing and collating a binary coded value with an actual pattern width at its comparator 7. The output of a binary coding circuit 6 is inputted to a pattern inspecting circuit 13.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a device for inspecting defects in patterns of printed circuit boards, etc., and particularly relates to a device for inspecting defects in patterns of printed circuit boards, etc. Regarding inspection equipment.

(2) Background of the Technology In recent years, factories have been using automatic manufacturing equipment exclusively for printed boards that form electronic circuits. This automatic manufacturing device naturally includes a printed board pattern inspection device for inspecting printed boards.

This device is a device that checks the printed pattern formed on the printed board after the printed board is manufactured, and is necessary for detecting cracks in wiring due to overprinting, resist defects, etc.

(3) Prior Art and Problems Conventionally, the above-mentioned pattern inspection apparatus has a method of reading a printed board pattern using a laser, binarizing it, and then comparing it with, for example, pre-stored pattern data. However, this method has the disadvantage that it is not possible to fix the slice level during binarization due to the temporal output drop of the laser, the sensitivity drop of the photodetector, and the difference in reflectance of the substrate. Ta. Therefore, in the method described above, in order to determine the optimal slice level, the ratio between the laser power measured during calibration and the laser power measured during inspection is determined, and the slice level is changed according to this ratio.

However, the apparatus of the above-mentioned method requires optical parts such as a half mirror for monitoring power and a shutter for switching light, and is complicated and expensive. Furthermore, it was not possible to know the change margin of the slice level, and it was not possible to determine whether the slice level was within the range of the optimum slice level.

(5) Purpose of the Invention The purpose of the present invention is to provide a function to automatically determine the optimal slice level value that has the largest slice level fluctuation margin with a simple configuration. An object of the present invention is to provide a pattern inspection device having a value converting circuit.

(5) Structure of the Invention The features of the present invention include a means for converting a pattern into an electrical signal by raster scanning, a binarizing means for binarizing the electrical signal, and a It consists of a detection means for detecting defects in the pattern using data, and the binarization means binarizes a sample whose pattern width is known by changing the slice level, and compares the binarized value with the actual It has a function to compare and match the pattern width and find the optimum slice level.

(6) Examples of the invention Hereinafter, detailed explanation will be given using examples of the present invention.

The principle of the present invention is to arrange a linear pattern with a known pattern width perpendicular to the scanning direction of the laser beam, and when reading this pattern, the slice level of the binarization circuit is lowered in order from the highest value, and at each slice level, the binary The converted pattern signal is measured using a counter, etc., and the slice level at which this value crosses the upper and lower limits of the reading tolerance is determined.
The center value of these is set as the optimum slice level.

The figure shows an embodiment of the invention. The beam emitted from the laser 1 passes through the half mirror 2 and is reflected by the rotating mirror 3.
A calibration printed board PS with a known pattern width on the Y stage SxY is irradiated.

The beam irradiated onto the printed board PS is reflected and rotated by a rotating mirror 3. The light is reflected by the half mirror 2° and enters the photodetector 4. Rotating mirror 3 rotates around point A in the direction of arrow B. In other words, the beam is the calibration printed board PS
Scan the top in the direction of arrow C.

Light is converted into an electrical signal by the photodetector 4, and the output thereof is input to the binarization circuit 6 via the amplifier circuit 5. The binarization circuit 6 includes a comparator 7, a crystal oscillator 8. AND circuit 9
．． Pulse counter 10. Calculation 8111. It consists of a digital-to-analog conversion circuit 12. The signal input to the binarization circuit 6 is input to the first input of the comparator 7. Comparator 7
The output of the digital-to-analog conversion circuit is input to the second input, that is, the reference input terminal. The output of the comparator 7 enters the pattern detection circuit 13 as binarized pattern data, and also enters the first input of the AND circuit 9 in the binarization circuit 6. Further, the output of the crystal oscillator 8 is input to the second input of the AND circuit 9. The output of the AND circuit 9 is input to a pulse counter 10, and its output is input to a computer 11. The output of the computer 11 is input to the digital input of the digital-to-analog conversion circuit 12.

Before inspecting a printed pattern, it is necessary to optimally set the slice level for binarizing the pattern signal. The device of the present invention automatically does this. First, a calibration printed board with a known pattern width is placed on the inspection area at the end of the XY stage where the sample printed board is set, and a laser beam is scanned over this pattern. . In order to find the optimal value of the binarized data of the pattern, first generate the initial value of the binarized slice level from calculation @11, and then digitally
The signal is input to the analog conversion circuit 12. The digital-to-analog conversion circuit 12 converts the digital data into an analog value and outputs an initial slice level to the comparator 7. Then, the reflected light from the aforementioned calibration printed board PS is converted into an electrical signal by the optical inspection device 4, amplified by the amplifier circuit 5, and inputted to the comparator 7. The comparator binarizes the signal using the aforementioned slice level as a reference. This 2
The number of valued patterns becomes proportional to the value of 1 by an AND circuit. The clock at this time is the crystal oscillator 8
The output of is used. The number of pulses is counted by a pulse counter IO and stored in the computer 11. Further, the above operation is repeated sequentially with the digital data added by 1 from the computer 11. As a result, the computer 11 stores each digital value proportional to the value of 1 in the binary pattern when the slice level is changed. The computer 11 uses the data to determine the slice levels at which the upper and lower limits of the allowable reading error range are crossed, and outputs the center value of these slice levels to the digital-to-analog converter 112 as the optimum slice level.

By the above operation, the optimal slice level value is sent to the binarization circuit 6. Next, by scanning the printed circuit board PS to be inspected, a binarized pattern to be obtained is obtained, and its value is input to a pattern inspection circuit to inspect for chips and the like in the pattern.

In the above explanation, the pattern was read by laser scanning, but this can also be done by using a television camera or the like.

(7) Effects of the Invention According to the present invention, the slice level can be set at the point with the largest slice level margin, making it possible to obtain a pattern inspection device with fewer false detections.

[Brief explanation of drawings]

The drawing shows a circuit configuration showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Laser, 2... Half mirror 13... Rotating mirror, 4... Photodetector, 6... Binarization circuit, 7...
... Comparator, 8th - Crystal oscillator, 9... AND circuit, 1o... Pulse counter, 11... Calculator,
12... Digital-analog conversion circuit, 13... Pattern inspection circuit.

Claims (1)

[Claims] means for converting the pattern into electrical signals by raster scanning; binarization means for binarizing the electrical signals;
It has a detection means for detecting defects in the pattern using the data obtained by the digitization means, and the binarization means includes:
A sample with a known pattern width is binarized by changing the slice level, and the binarized value is compared and verified with the actual pattern width.