JPS62284246A - Inspecting device for printed board - Google Patents

Abstract

PURPOSE:To detect all peaks and bottoms of an output signal waveform by varying a threshold value according to variation in signal waveform when converting a fluorescence signal from a printed board into a binary signal. CONSTITUTION:The output signal S of a CCD detector 11 is converted by a signal binary-coding circuit 16 into a binary signal. The signal binary-coding circuit 16 consists of a delay circuit 17, a threshold value setting circuit 18, and a comparator 19. The threshold value setting circuit 18 inputs the output signal S of the detector 11, averages waveform values of specific ranges, and sets the threshold value Tv which varies according to variation in the waveform of the output signal S, and this setting circuit 18 consists of an amplifier 20, an averaging circuit 21, an adder 22, and an offset circuit 23. This threshold value setting circuit 18 sets the threshold value Tv which varies automatically according to the variation of the waveform of the output signal S shown by a solid line. A threshold value shown by a broken line crosses all peaks (a)-(f), and bottom (g) of the waveform of the output signal S, so all the peaks and bottoms of the waveform of the output signal S are detected in the binary-coded signal B.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention Industrial Application Field The present invention is a method for improving wiring by irradiating light onto the wiring surface of a printed circuit board, exciting the base material, and detecting the emitted fluorescence. The present invention relates to a printed circuit board inspection device that inspects patterns, and particularly to a printed circuit board inspection device that can more accurately measure the shape of a wiring pattern.

2. Description of the Related Art As shown in FIG. 6, a conventional fluorescence detection type printed circuit board inspection apparatus includes a light source 5 that irradiates a wiring surface 2 of a printed circuit board 1 with light 4, a collimator lens system 6, and a An excitation light transmission filter 7 that selects light with a wavelength that has a large fluorescence excitation ability from the emitted light 4, a dichroic mirror 8, and a dichroic mirror 8 that cuts reflected light from the wiring surface 2 of the printed circuit board 1 and A fluorescence transmission filter 9 that transmits only the fluorescence generated from the base material 3; and an imaging lens 10 that forms an image of the light transmitted through the fluorescence transmission filter 9;
A light receiver 11 such as a charge-coupled device (CCD) that detects the light imaged by the imaging lens 10 and a signal binarization circuit 12 that binarizes the output signal from the light receiver 11 are connected. was. and.

The excitation light 13 from the light source 5 is applied to the printed circuit board 1 from above.
When the fluorescent light 14 generated by being absorbed by the base material 3 is detected by the light receiver 11 and photoelectrically converted, the fluorescent light 1
4, an output signal S having a voltage waveform whose amplitude is not constant as shown in FIG. 7 is obtained. This output signal S is input to the signal binarization circuit 12, where it is binarized using a preset threshold value, and the wiring pattern on the wiring surface 2 is inspected by identifying brightness and darkness using this binarized signal. Was.

Problems to be Solved by the Invention However, in such a conventional printed circuit board inspection device, the threshold value T set in the signal binarization circuit 12 is
As shown in FIG. 7, is a constant value fixed at a certain voltage level, and when the voltage of the output signal S is greater than this threshold T, it is converted to II 1 +1. , when it was small, it was converted to II O71 and a binary signal as shown in FIG. 8 was output. Here, as shown in FIG. 7, the waveform of the output signal S of the light receiver 11 in the fluorescence detection method includes small valleys g within large peaks a and b, and between large peaks and d. small mountain C
The amplitude is generally not constant. Therefore, when binary conversion is performed using only one fixed threshold value T as described above, only the output signal S having a voltage level higher than the threshold value T is shown as a shaded area in FIG. As shown in FIG. 8, the above-mentioned valleys g and peaks C were not detected in the obtained binarized signal. That is, the binarized signal output from the signal binarization circuit 12 did not correspond accurately to the waveform of the output signal S of the fluorescence 14 detected by the light receiver 11. This thing.

Even if the above-mentioned binary signal is processed to identify brightness and darkness, the result does not correspond accurately to the wiring pattern of the printed circuit board 1, and the shape of the above-mentioned wiring pattern cannot be accurately determined in total by 81g at low resolution. It was something.

To deal with this and increase the resolution, the imaging lens 1
If the light source 5 is made large and bright, or if the light source 5 is made large, the overall size of the device increases and the cost increases. Therefore, an object of the present invention is to solve such problems.

Means for Solving the Problems The means of the present invention for solving the above problems is to selectively irradiate the wiring surface of a printed circuit board with light having a wavelength that has a large fluorescence excitation ability from among the light emitted from a light source. A printed circuit board that inspects the wiring pattern on the wiring surface by transmitting only the fluorescence generated from the base material of the printed circuit board and detecting it with a light receiver, and by binarizing the output signal from the light receiver and distinguishing between brightness and darkness. In the inspection device, a threshold value is set on the output side of the photoreceiver by averaging the waveform values of each predetermined range of the output signal, and changes in accordance with fluctuations in the waveform of the output signal. This is done by a printed circuit board inspection device equipped with a signal binarization circuit that generates a binarization signal for the output signal.

Embodiments One embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a side view showing an embodiment of a printed circuit board inspection apparatus according to the present invention. In the figure, a light source 5 irradiates the wiring surface 2 of the printed circuit board 1 with light 4, and is composed of, for example, an ultra-high pressure mercury lamp having a large spectral intensity in the ultraviolet to near ultraviolet regions. The light 4 emitted from this light source 5
enters the collimator lens system 6 and becomes a parallel light beam.

An excitation light transmission filter 7 is provided behind the collimator lens system 6. This excitation light transmission filter 7 is for selecting light having a wavelength that has a high fluorescence excitation ability from the light 4 emitted from the light source 5, and is a filter that only transmits, for example, violet or ultraviolet light having a wavelength of 400 nm or less. Therefore, of the light 4 emitted from the light source 5, only the excitation light 13 having the ability to excite fluorescence is transmitted through the excitation light transmission filter, and light of other wavelengths is cut off.

A dichroic mirror 8 is provided behind the excitation light transmission filter. This dichroic mirror 8 reflects the excitation light 13 and changes its optical path downward by 90 degrees to irradiate the excitation light 13 onto the wiring surface 2 of the printed circuit board 1. It is inclined at a 45 degree angle. The excitation light 13 whose optical path is changed downward by 90 degrees by the dichroic mirror 8 is directly irradiated onto the wiring surface 2 of the printed circuit board 1. This excitation light 13 is reflected at the wiring pattern portion of the wiring surface 2, and transmitted or absorbed into the base material 3, and locally excites the base material 3 during this period. As a result, fluorescence having a wavelength of around 600 nm is emitted, for example.

Light 15, which is a combination of the fluorescence generated from the base material 3 of the printed circuit board 1 and the excitation light reflected by the wiring pattern on the wiring surface 2, enters the dichroic mirror 8 again. This dichroic ink mirror 8.

Only the fluorescence generated from the base material 3 is transmitted, and all the reflected components of the excitation light 13 are reflected.

Dichroic mirror 8 above the printed circuit board 1
A fluorescence transmission filter 9 is provided behind the. This fluorescence transmission filter 9 includes the dichroic mirror 8
This device completely removes the reflected component of the excitation light 13 that has slightly passed through the excitation light 13 and the background noise light, and allows only the fluorescence 14 generated from the base material 3 of the printed circuit board 1 to pass through.
This is a filter that only transmits yellow or red light with a wavelength of 0 nm or more. Therefore, this fluorescence transmission filter 9 cuts out light with a wavelength of less than 600 nm, and only the fluorescence 14 is transmitted.

An imaging lens 10 is provided behind the fluorescence transmission filter 9. This imaging lens 1o is configured to form a wiring pattern image by entering the fluorescence 14 that has passed through the fluorescence transmission filter 9. And this imaging lens 1o
A light receiver 11 is provided behind the. The light receiver 11 receives and photoelectrically converts the light imaged by the imaging lens 10, and outputs an output signal S in the form of a voltage waveform whose amplitude changes depending on the strength of the light, as shown in FIG. One example of the output device is a detector in which charge-coupled devices (COD) are arranged in a linear manner.

Here, in the present invention, on the output side of the light receiver 11, the waveform values of each predetermined range of the output signal S (see FIG. 3) are averaged, and the waveform values are changed in accordance with the fluctuation of the waveform of the output signal S. Signal binarization circuit 16 that can set the threshold value Tv
is provided.

This signal binarization circuit 16 has the above-mentioned changing threshold value T.
It generates a binarized signal B for the output signal S from the light receiver 11 using V, and as shown in FIG. The delay circuit 17 takes a certain amount of time for the threshold setting circuit 18 to input and average the output signal S from the light receiver 11 to set the threshold Tv, so in order to match this timing, This is to delay the output signal S from the light receiver 11 by a predetermined time.

The threshold setting circuit 18 inputs the output signal S from the light receiver 11, averages the waveform values in each predetermined range, and sets a threshold Tv that changes in accordance with fluctuations in the waveform of the output signal S. The amplifier 20 and the averaging circuit 21
, an adder 22, and an offset circuit 23. The above amplifier 20 is.

The averaging circuit 21 slightly compresses the original output signal S to reduce its value before averaging the waveform values, and a gain of 1, for example, 0.95 is set.

This is to prevent the desired threshold value Tv from sticking to the peak value even in a region where the peak value continues in the waveform of the original output signal S. The averaging circuit 21 inputs the output signal S' compressed by the amplifier 20 and averages the waveform values in each predetermined range.When the output signal S' is digitized by an A/D converter, For example, with 5 to 11 bits as a predetermined range, find the average value of the waveform values within that range, and then sequentially calculate the average value m for the entire compressed output signal S' while shifting the predetermined range 1 bit at a time. is now being sought. The offset circuit 23 is for adding a certain value n to the entire average value m obtained by the above-mentioned averaging circuit 21, and outputs, for example, a value obtained by multiplying the output signal S by 0.1. ing. This is to prevent the threshold value Tv required for the lowest value from becoming too high even in a region where the lowest value continues in the waveform of the output signal S. The average value m from the averaging circuit 21 and the value n from the offset circuit 23 are input to an adder 22, where the value n is added to the average value m, as shown in the broken line curve in FIG. A threshold value Tv as shown is set.

That is, as is clear from FIG. 3, this threshold setting circuit 18 produces an output signal S as shown by the solid curve.
Threshold value Tv that automatically changes according to fluctuations in the waveform of
is set, and this threshold value Tv is equal to the output signal S
It intersects with any of the peaks a''f and valleys g in the waveform.

The comparator 19 inputs the output signal S whose timing has been matched by the delay circuit 17, and also inputs the automatically changing threshold value TV set as described above, and compares the two. . In FIG. 3, when the voltage of the output signal S is larger than the threshold value Tv at that timing, rz 1 n is output, and when it is smaller, "OI+" is output, so that the voltage shown in FIG. Like 2
A valued signal B is generated. Here, as mentioned above, the threshold value Tv set by the threshold setting circuit 18 is:
Since it intersects with both peaks a = f and valleys g in the waveform of the output signal S, as is clear from Fig. 4,
In the binarized signal B, all the peaks a=f and valleys g in the waveform of the output signal S shown in FIG. 3 are detected.

Then, the value of the binary signal B obtained in this way is “1”.
By distinguishing the brightness and darkness of the fluorescent light 14 by the arrangement of I'Q I+, the wiring pattern on the wiring surface 2 of the printed circuit board 1 can be inspected with improved resolution.

FIG. 5 is a block diagram showing another embodiment of the signal binarization circuit 16 according to the present invention. In this embodiment, in addition to the averaging circuit 21, another averaging circuit 21' having a different range for calculating the average value is provided in parallel in the threshold setting circuit 18'.

Then, the first averaging circuit 21 takes, for example, 11 bits as a predetermined range and calculates the average value m of the waveform values within that range, and the second averaging circuit 21' takes, for example, 5 bits as a predetermined range and calculates the average value m of the waveform values within that range. The average value m' of the waveform values within is calculated, and the combined value is input to the adder 22. In this case, the averaging circuit 2 with a large number of bits
1, it is possible to cope with the overall tendency of the waveform fluctuation of the output signal S, and the averaging circuit 21' with a small number of bits can be used.
Therefore, the final threshold value Tv outputted from the adder 22 can be adjusted in detail to match the waveform fluctuations of the output signal S. You can get something that changes. Therefore, the wiring pattern on the wiring surface 2 of the printed circuit board 1 can be measured accurately with further improved resolution.

Although FIG. 5 shows two averaging circuits (21, 21') with different ranges for calculating the average value, the present invention is not limited to this, and three or more circuits may be connected in parallel. may be provided. In this case.

The resolution of wiring pattern inspection can be further improved.

Effects of the Invention Since the present invention is constructed as described above, the signal binarization circuit 16 averages the waveform values of each predetermined range of the output signal S from the light receiver 11, and eliminates fluctuations in the waveform of the output signal S. While setting a threshold value Tv that automatically changes according to the threshold value Tv, the binarized signal B for the output signal S can be generated using this threshold value Tv. Here, in this binarized signal B, as shown in FIG. 4, all peaks a=f and valleys g in the waveform of the output signal S shown in FIG. 3 are detected. Therefore, this binary signal B corresponds to the waveform of the output signal S of the fluorescence 14 detected by the light receiver 11. Therefore, when the binary signal B is processed to distinguish between brightness and darkness, the result corresponds to the wiring pattern of the printed circuit board 1, and the resolution can be improved and the shape of the wiring pattern can be accurately determined. It can be measured.

Furthermore, since the resolution can be improved as described above, the imaging lens 10 can be made relatively small, and the light source 5 can also be made small, making it possible to make the entire device smaller and to reduce costs.

[Brief explanation of the drawing]

Fig. 1 is a side view showing an embodiment of the printed circuit board inspection device according to the present invention, Fig. 2 is a block diagram showing its signal binarization circuit, and Fig. 3 shows the waveform of the output signal from the light receiver and its fluctuation. FIG. 4 is an explanatory diagram showing the binarized signal obtained by the present invention, and FIG. 5 is a graph showing the relationship with the threshold value that changes according to the present invention. 6 is a side view showing a conventional printed circuit board inspection device, and FIG. 7 is a relationship between the waveform of the output signal from the light receiver and the threshold value set in the signal binarization circuit in the conventional example. FIG. 8 is an explanatory diagram showing a binary signal obtained by the conventional example. 1... Printed circuit board 2... Wiring surface 3... Base material 5... Light source 7... Excitation light transmission filter 8... Dichroic mirror 9... Fluorescence transmission filter 10... Image formation Lens 11... Light receiver 13... Excitation light. 14...Fluorescence 16...Signal binarization circuit 17...Delay circuit 18.18'...Threshold setting circuit 19...Comparator 21.21'...Averaging circuit S ...Output signal Tv from the photoreceiver...Changing threshold value B...Binarized signal Applicant Hitachi Electronics Engineering Co., Ltd. Figure 1 Figure 2 Prisoner Figure 3

Claims (1)

[Claims] The wiring surface of the printed circuit board is selectively irradiated with light having a high fluorescence excitation ability among the light emitted from the light source, and only the fluorescence generated from the base material of the printed circuit board is transmitted and detected by a light receiver. In a printed circuit board inspection device that inspects the wiring pattern on the wiring surface by binarizing the output signal from the photoreceiver and distinguishing between brightness and darkness, the output side of the photoreceiver has a predetermined range of the output signal. A signal binarization circuit is provided that averages the waveform values and sets a threshold value that changes in accordance with fluctuations in the waveform of the output signal, and generates a binarized signal for the output signal based on this threshold value. A printed circuit board inspection device featuring: