JPS6333094B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a printed board pattern inspection method that can accurately inspect the height, width, etc. of a pattern.

2. Description of the Related Art Conventionally, a method shown in FIG. 1 has been known for inspecting patterns of printed circuit boards for electronic computers and the like. That is, a copper lead wire 2- with a width of several hundred microns and a thickness of several tens of microns is placed on a plastic plate 1.
1, 2-2... are placed parallel to each other using printed wiring technology, and a flat light beam 3
The pattern width of the copper lead was measured by irradiating the copper lead approximately vertically and observing the reflected light visually or with a TV camera in the direction {arrow 4} of approximately 45 degrees, and defects in the pattern were discovered. Since this method detects only the reflected intensity from the pattern, the reflected light output intensity varies depending on the condition on the pattern surface, and even if there is a defect in the edge condition of the pattern, that is, the height or width of the copper lead, it can be clearly detected. could not be detected. The height of the copper lead has also been detected using a microscope, but the operation is complicated and the inspection requires a long time.

An object of the present invention is to provide a relatively simple method of inspecting the height, width, etc. of a pattern using a laser beam.

Figure 2 is a diagram for explaining the principle of the present invention, where 5 is a laser beam, 6 is a condensing lens for the reflected laser beam, and its focal length is F, which is 2F away from the pattern to be detected. be there. 7-1,
7-2 are photodetectors, which are placed vertically in contact with each other and are located 2F apart from the lens 6.
When the laser beam 5 is scanned perpendicularly to the longitudinal direction of the printed board pattern, laser reflected light can be detected by different photodetectors in areas where there is no pattern and areas where the pattern is present. That is, where there is no copper lead pattern, there is an output from the photodetector 7-2, and where there is a pattern, there is an output from the photodetector 7-2.
1, so if the outputs of each detector are separately applied to the positive and negative terminals of one operational amplifier, pulse outputs above and below the zero line are obtained from the outputs. Therefore, when the beam scanning speed is known, the width of the pattern can be determined from the difference in the times at which the beam crosses the zero line. In other words, the width of the pattern is converted into the time of output change. According to this method, the width of the pattern can be accurately determined by checking the time of positive output. Now that a certain position scanned perpendicular to the longitudinal direction of the pattern has been inspected, the entire printed board pattern can be inspected by so-called two-dimensional scanning by moving it a certain distance in the longitudinal direction and scanning again.

FIG. 3 shows a photodetector 7-3 whose number is approximately equal to the total number of times the scanning position is moved in the longitudinal direction of the pattern.
7-4...7-n is provided corresponding to the scanning pitch, and the outputs of adjacent photodetectors are used as input signals of different polarities to the differential amplifier (for example, by using an operational amplifier). This allows the height and width of the pattern to be clearly inspected no matter where the scanning position is. However, in practice, it is necessary to line up photodetectors with a width of about several tens of microns, so it is better to use a mask with a small window and a corresponding photodetector.

FIG. 4 shows a mask with holes of a size corresponding to the photodetector connected to the positive terminal, for example, with widths and spacings of about a few tens of microns. This mask can be easily created mechanically.

FIG. 5 shows an apparatus for inspecting a pattern obtained using this mask 8. Reference numeral 9 indicates a rotating mirror for obtaining a scanning light beam, and 10 indicates a lens for scanning light.
As a result of the beam scanning, the portion corresponding to the photodetector in FIG. 4 passes through the mask 8 and enters the photodetector 7-1. Further, the light is reflected from the mask 8 and enters the photodetector 7-2. Both photodetectors 7-
It is sufficient to compare the outputs of 1 and 7-2.

Here, calculate the size and number of mask windows.
As shown in FIG. 6, when the light beam observation angle is 45 degrees, the height H of the copper lead pattern is the difference h in the position of the reflected light, so h=Hsin=H/√2.

When the light beam moves by this difference h, the location where the output difference is maximum is obtained when the difference h and the window width (pitch) w are equal. Therefore, the window width and pitch are both h.

Note that when h is equal to the window width, it is possible that the light beam shifts from one window boundary to the next.
At this time, there is no difference in output between the detectors. In this case, if you shift the windows by 1/4 pitch and install another set as shown in Figure 7, the characteristics will be averaged. Figure 8 is a diagram showing a pattern inspection device when using the mask shown in Figure 7, with two condenser lenses 6-1 and 6-2 and detectors 7-11, 7-12, and 7-21. , 7-22 are used in total, and two lines after the differential amplifier are also used. 11 is a waveform shaping circuit 12 is a binarization circuit, 13
14 is a length measuring circuit, 14 is a reference value signal generating circuit, and 1 is a length measuring circuit.
5 is a comparison circuit, and 16 is a defect detection circuit.

In this manner, according to the present invention, the height, width, etc. of a printed board pattern can be clearly inspected. By using a mask, a photodetector can be practically equivalent to a small array, so it is easy to construct a practical measuring device.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a conventional method for inspecting printed board patterns, Fig. 2 is a diagram explaining the principle of the present invention, and Fig. 3 is a diagram showing the principle of the configuration of a photodetector used during overall scanning. FIG. 4 is a perspective view of a mask used when carrying out the present invention, FIG. 5 is a diagram showing a pattern inspection device, and FIG. 6 is an explanatory diagram of the operation shown in FIG.
FIG. 7 is a diagram showing another example of the mask, and FIG. 8 is a diagram showing another example of the mask.
It is a figure which shows the other example of a figure. 1... Plastic plate, 2-1, 2-2... Copper lead wire, 3... Luminous flux, 5... Laser beam, 6,
6-1, 6-2...Condensing lens, 7-1, 7-
2, 7-11, 7-12, 7-21, 7-22...
...Photodetector, 8...Mask, 9...Rotating mirror, 10
……lens.

Claims (1)

[Scope of Claims] 1. A printed board pattern inspection method in which a light beam is irradiated orthogonally to the longitudinal direction of the printed board pattern and the pattern condition is inspected by scanning the light beam in the longitudinal direction, comprising: a laser beam as the inspection light; A detector for receiving reflected light reflected from a printed board pattern and a detector for receiving reflected light reflected from a printed board without a pattern are provided as a pair of detectors in contact with each other, and the above-mentioned detection A printed board pattern inspection method characterized by detecting pattern conditions based on output fluctuations of a pair of devices.