JPH03259703A - Inspecting method for wiring pattern of printed wiring board - Google Patents

Abstract

PURPOSE:To inspect the printed wiring board at a fast processing speed with high reliability by irradiating the printed wiring board with fluorescent light which has long wavelength enough to attenuate reflected light from a writing pattern on the reverse surface of the wiring board almost completely in the insulating base material of the wiring board so that the reflected light does not reach a photodetection part. CONSTITUTION:An internal layer plate 9 which has wiring patterns 8 formed on both surfaces of the translucent insulating base material 7 is placed on an XY table 10 which is movable in an X and a Y direction. Then the white fluorescent light from a fluorescent light generation part 11 which is arranged above is passed through a filter 12 to obtain light 13 close to red light, which moves and irradiates the entire top surface of the internal layer plate 9 continuously. Its reflected light 14 is detected by the photodetection part 16, whose output electric signal is processed by an image processing unit 17 to recognize and evaluate an image. Consequently only the reflected light from the wiring pattern on the top surface can be extracted purely, so the need for the reflected light removing process for the reverse surface pattern is eliminated. Further, virtual information is reduced.

Description

Detailed Description of the Invention [Purpose of the Invention (Industrial Application Field) The present invention is an optical inspection method for wiring patterns on printed wiring boards that does not require complicated algorithms during image processing and has a high processing speed. Regarding the method.

(Prior art) Generally, when optically inspecting a copper foil pattern on the surface of an inner layer printed wiring board (inner layer board), as shown in FIG. A method is adopted in which the reflected light 3 (3a, 3b) that is irradiated and received is optically processed (image processing), and the result is compared with the original pattern to extract pattern defects.

However, when the reflected light 3 is subjected to image processing as it is by this method, the insulating base 4 constituting the inner layer board 1 is semi-transparent, and the reflected light 3a from the copper foil pattern 5 on the front surface is reflected from the copper foil pattern 6 on the back surface. Since the reflected light (light reflected at the interface between the copper foil pattern 6 on the back side and the insulating base material 4) 3b is received in a state of interference, there is a risk that pattern recognition and evaluation by image processing may be inaccurate. there were.

By the way, in the image processing, the processing results are compared with the pig designed by the computer and output, but since the reflected light 3b from the back surface pattern 6 that has interfered and mixed is also output, it is possible to distinguish between genuine defects and false defects. The problem was that it was difficult to distinguish between the two.

Therefore, conventionally, the light received by the light receiving section, for example, the fifth
By differentially binarizing the amount of reflected light A having the waveform shown in the figure, the reflected light ff1A1 from the back pattern 6 is divided and the remainder is extracted as the reflected light m A 2 from the front pattern, and based on this, Performing image processing.

(Problem to be Solved by the Invention) However, in such a method, not only does image processing take time, but also the reflected light amount A1 value of the back pattern 6 must be set in advance in order to perform the correction based on the division. I needed to keep it.

The present invention was made to solve these problems, and it eliminates the need for setting a correction light amount value and removing light interference during image processing, and the processing speed is fast by either image processing or image processing. The purpose of the present invention is to provide a highly reliable method for inspecting the wiring pattern of a printed wiring board with less false information.

[Structure of the Invention (Means for Solving the Problem) The wiring pattern inspection method for a printed wiring board of the present invention irradiates one main surface of the printed wiring board with a fluorescent beam such that the incident position continuously moves. a step of receiving the reflected light of the fluorescent rays by a light receiving section; and a step of inputting the output signal from the light receiving section, performing image processing, and recognizing and evaluating the obtained image. In the wiring pattern inspection method for a printed wiring board, the reflected light from the wiring pattern formed on the other main surface of the printed wiring board is almost completely attenuated inside the insulating part of the printed wiring board so that it does not reach the light receiving section. It is characterized by irradiating fluorescent rays with a sufficiently long wavelength.

(Function) According to the inspection method of the present invention, fluorescent light with a sufficiently long wavelength is irradiated depending on the material and thickness of the insulating parts constituting the printed wiring board. The light reflected by the wiring pattern formed on the insulating layer gradually attenuates as it travels inside the insulating shell, and does not reach the light receiving section. The amount of light reflected by the wiring pattern on the surface in this way,
Since the light is received by the light receiving section and subjected to image processing, the incorporation of false alarms is completely avoided or prevented, and the reliability of the inspection is increased.

Furthermore, processing to remove reflected light from the wiring pattern on the back side is no longer necessary, and image processing speed is improved.

(Example) The present invention will be described in detail below with reference to FIGS. 1 to 3.

First, as shown in FIG. 1, wiring patterns 8a, 8 are formed on both sides of a translucent insulating piece 7, such as a glass epoxy base, by etching copper foil.
The inner layer plates 9 each having a thickness of 0.4 to 0.8 +++ m and each having a thickness of 35 to 70 μm are placed on an XY table 10 that can be moved at any speed in the XY directions.

Next, after removing dust etc. from the surface of the inner layer plate 9,
Move the Y table IO in any XY force direction at any speed. Then, the white fluorescent rays (including fluorescent rays with a frequency of 4800 Hz or more) generated from the fluorescent ray generator 11 disposed above are transmitted through the filter 12 and are converted into red-ish light 13 (with a sufficiently long wavelength). The frequency is changed to 2,500 Hz or less), and the entire surface of the inner layer plate 9 is continuously irradiated with this moving beam.

Next, the reflected light J4 of the long wavelength fluorescent rays 13 irradiated in this manner is detected by the light receiving section 1G, which is disposed opposite to the fluorescent ray generating section 11 with the normal 15 erected on the inner layer plate 9 interposed therebetween.

As a result of this light reception detection, an electrical signal is output from the light receiving section 16, and the image processing unit 1 receives this output signal.
7 processes the signal and performs image recognition and evaluation.

Note that, in the image processing unit j7, as shown in FIG. 2, necessary processing is performed according to a processing flow that is roughly divided into nine processing blocks, including processing in the light receiving section 16.

That is, the reflected light 14 that first enters the light receiving section I6 having an arbitrary light receiving element is subjected to color separation input, analog/digital (A/D) conversion, and output as a waveform of the amount of reflected light.

Next, the waveform output obtained above is subjected to preprocessing such as prefiltering, normalization, smoothing, and thinning, and after second-order differential binarization, raster/vector conversion, gradation processing, feature extraction, and matching. Pattern recognition - feature synthesis -> image synthesis - vector/raster conversion - decoding - view conversion -> post filter -> pseudo color -> analog/digital conversion -> image output, and output processing of the defective part of the wiring button is performed in real time.

In the process, information regarding the defective portion is obtained from the inner layer plate 9.
The data are stored in the storage buffer of the central processing unit until the inspection of the entire surface of the area is completed, and after the inspection is completed, they are sequentially output in the form of position data and defect images.

As described above, in the inspection method according to the present invention, the light reflected by the surface wiring pattern 8a of the inner layer board 9 enters the light receiving section 16 and is processed by the image processing unit 17. That is, the wiring pattern 8a is provided on both the front and back surfaces.
, 8b are formed on the surface of the inner layer plate 9.
When the normal white fluorescent light generated in step 1 is directly irradiated, it travels straight through the nonwoven fabric of the insulating base material 7, such as glass epoxy, without being diffusely reflected or attenuated. To Penetrate. Then, after being reflected by the wiring pattern on the back surface (at its interface with the insulating base H7), it passes through the inside of the insulating base material 7 again and reaches the light receiving section 16.

On the other hand, in the case of the method according to the present invention, a normal white fluorescent beam is passed through a filter 12 whose transmittance is set for each wavelength according to the thickness of the insulating material 7, etc. After changing to a long wavelength fluorescent beam, the surface of the inner layer plate 9 is irradiated with this. However,
When the long-wavelength fluorescent light 13 hits the surface wiring pattern 8a, the copper foil surface reflects it almost completely because of its high reflectance.
The reflected light 14 reaches the light receiving section 16. In addition, the light incident on the inside of the insulating base material 7 travels through the nonwoven fabric constituting the profiteering material while being diffusely reflected at the interface, and is attenuated.
Some of it is absorbed as heat. Therefore, the light receiving part 1
This means that the light received at 6 contains almost no reflected light from the back wiring button 81).

As described above, the image processing unit 17 uses the waveform output of only the reflected light 14 from the surface wiring pattern 8a to
Since pattern defect areas are inspected, it is possible to eliminate the waveform subtraction process that was performed in the conventional image processing process.This simplifies the image processing process, and enables feature extraction and defective areas from image input. The speed of processing up to output is greatly improved.

Also, corresponding to the reflected light from the back wiring pattern 8b,
There is no need to set a light amount value for correction, and the setup time when inspecting a wide variety of small-volume models can be shortened.

Furthermore, since image processing is performed by taking in only the information from the pure surface wiring pattern 8a, the probability that false information will be mixed into the display of the defective area is reduced, which makes searching for the defective area after inspection smooth and time-consuming. It has the effect of shortening the

Note that by selecting the most appropriate filter 12 according to the thickness of the insulating base material 7 and the transparency of the nonwoven fabric, the inspection method of the present invention can be effectively implemented on a wide range of inner layer plates 9. .

[Effects of the Invention] As explained above, according to the wiring pattern inspection method of a printed wiring board according to the present invention, it is possible to purely extract the amount of light reflected from the wiring pattern on the surface, and based on this light, By performing image processing, defective portions of a pattern can be extracted efficiently and accurately. Therefore, according to the present invention, it is possible to increase the image processing speed, which does not require a processing step to remove light reflected by the backside wiring pattern. Furthermore, it is no longer necessary to set a light quantity value for correcting and removing the reflected light, and the number of false alarms is further reduced, greatly improving the reliability of inspection.

[Brief explanation of drawings]

FIG. 1 is a side view schematically showing an embodiment of the wiring pattern of a printed wiring board according to the present invention;
The figure is a flowchart showing the image processing procedure in the wiring pattern inspection method for a printed wiring board according to the present invention, and FIG. 4 is a side view schematically showing an embodiment of the conventional optical inspection method for wiring patterns, and FIG. 5 is a schematic diagram showing the waveform of the amount of reflected light received in the conventional optical inspection method for wiring patterns. FIG. 7... Insulating base material 8a... Front wiring pattern 8b... Back wiring pattern 9... Inner layer board (printed wiring board to be inspected) 1...
... Fluorescent ray generating section 2 ... Filter 3 ... Long wavelength fluorescent ray 4 ... - Reflected light 6 ... Light receiving section 7 ... Image processing unit] 1

Claims (1)

[Scope of Claims] A step of irradiating one main surface of a printed wiring board with a fluorescent beam so that the incident position moves continuously, a step of receiving reflected light of the fluorescent beam by a light receiving section, and the light receiving section. A wiring pattern inspection method for a printed wiring board, comprising a step of inputting an output signal from received light from the printed wiring board, performing image processing, and recognizing and evaluating the obtained image. The printed wiring board is characterized in that the printed wiring board irradiates fluorescent light with a sufficiently long wavelength such that the light reflected by the printed wiring pattern is almost completely attenuated inside the insulating base material of the printed wiring board and does not reach the light receiving part. Wiring pattern inspection method.