JPH04291108A - Height measuring instrument - Google Patents

Abstract

PURPOSE:To enable a height measuring instrument used for visual inspecting devices for printed wiring patterns, etc., to perform high-speed processing with a simple constitution by preventing the bit count of an A/D converter from becoming larger even when the variation of the reflectivity of an object to be measured is very large. CONSTITUTION:A selection control circuit 5 outputs a select signal which discriminates the object of a light radiating point based on the sum of a pair of outputs of an optical position detector 4. An amplifier circuit 6 has amplification factors corresponding to the sum and amplifies the difference between the pair of outputs. A selection circuit 8 selects one amplification factor based on the select signal and supplies the output of the circuit 6 to an A/D converter 7 as a height measured value.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a height measuring device used in a visual inspection device for printed wiring patterns and the like.

0002

2. Description of the Related Art FIG. 6 shows a conventional height measuring device used in a printed wiring pattern visual inspection device.

Sample 10 is a printed wiring board, and substrate 1
Printed wiring pattern 10b with a thickness of about 5 μm on 0a
is formed. This sample 10 is
It is placed on the stage 12.

A light source 14 and a light scanning optical system 16 are arranged above the sample 10, and the light beam emitted from the light source 14 is vertically irradiated onto the sample 10 by the light scanning optical system 16, and is directed in a direction perpendicular to the plane of the paper. is scanned. For each scan, the stage control circuit 18 steps the XY stage 12 by one line in a direction perpendicular to the optical scanning direction. Also,
A PS is installed obliquely above the sample 10 via an imaging lens 20.
D22 is arranged, and the scattered light from the light irradiation point passes through the imaging lens 20 and is imaged onto the PSD 22.

A pair of outputs a and b of the PSD 22 are supplied to an adder 24 and a subtracter 26, and (a+b) and (a-
b) is obtained. Each of these is an A/D converter 28A
, 28B, and then supplied to a divider 30 to calculate the height (a-b)/(a+b) of the light irradiation point.

As the substrate 10a for high-density mounting, a transparent or semi-transparent substrate made of polyimide or the like is used, and its reflectance is considerably smaller than that of the printed wiring pattern 10b. Therefore, in order to obtain a height of 8 significant digits, the A/D converters 28A and 28B must be made of 12 bits or more.

[0007]

[Problem to be solved by the invention] However, A/D
The converters 28A, 28B and the divider 30 internally perform repeated processing according to the number of bits, so if 12 bits or more are used, the processing speed is limited to a maximum of about 10 MHz and the circuit configuration becomes complicated. Become. This limits the optical scanning speed of the optical scanning optical system 16, making it difficult to shorten the visual inspection time.

SUMMARY OF THE INVENTION In view of these problems, it is an object of the present invention to provide a height measuring device that has a simple configuration and is capable of high-speed processing.

[0009]

[Means for Solving the Problems and Their Effects] FIG. 1 shows the principle configuration of a height measuring device according to the present invention. This height measuring device scans a light beam emitted from a light source 1 onto a sample 3 using an optical scanning means 2, focuses the light from a light irradiation point on the sample 3, and detects it with an optical position detector 4. Then, the height of the light irradiation point is measured based on a pair of outputs from the optical position detector 4. The sum of the pair of outputs represents the brightness of the light irradiation point, and the ratio of the difference between the pair of outputs and the sum represents the height of the light irradiation point. The feature of this height measuring device is that it includes the following components.

A selection control circuit 5 outputs a selection signal based on the sum.

Reference numeral 6 denotes an amplifier circuit, which has a plurality of amplification factors for amplifying the difference.

7 is an A/D that digitizes analog signals.
It is a converter.

Reference numeral 8 denotes a selection circuit which selects the amplification factor based on the selection signal and sends the output of the amplifier to the A/D converter 7.
supply to

The height measuring device configured as described above outputs the ratio of the difference to the sum or a value equivalent thereto as the height of the light irradiation point. In the present invention, since the output of the amplifier 6 with an amplification factor based on the brightness of the light irradiation point is converted into a digital value by the A/D converter 7, the fluctuation range of the input value of the A/D converter 7 is narrowed. be able to. This allows the use of an A/D converter with a small number of bits, and therefore enables high-speed processing with a simple configuration.

[0015] The invention with the above-mentioned basic configuration includes various types of height measuring devices as described below.

In the first aspect of the present invention, the selection control circuit 5 is a discrimination circuit 38 that discriminates the object of the light irradiation point based on the above-mentioned sum, and the amplification circuit 6 is a discrimination circuit 38 that discriminates the object of the light irradiation point based on the above-mentioned sum. A plurality of amplifier circuits 6 having amplification factors corresponding to
The output of the amplifier circuit 6 corresponding to the ratio of the difference and the sum is selected and supplied to the A/D converter 7, and the output of the A/D converter 7 is output as a height measurement value.

[0017] With this configuration, a divider is not required. Further, for example, when the sample is a printed wiring board, there are two objects, the board and the wiring pattern, and it is sufficient to provide two amplifier circuits. The construction is therefore particularly simple.

[0018] In a second aspect of the present invention, in addition to the above basic configuration invention, a second amplification circuit having a plurality of amplification factors that amplifies the sum of the pair of outputs, a second A/D converter, and a second A/D converter; A second selection circuit selects the amplification factor of the second amplifier circuit based on the selection signal and supplies the output of the second amplifier circuit to the second A/D converter; 2A/D
It is equipped with a division means, such as a divider or a division table ROM, which outputs the value divided by the output of the converter as a height measurement value, and has a configuration in which the same amplification factor is selected for the amplifier circuit 6 and the second amplifier circuit. do.

In this configuration, since the sum of the pair of outputs of the optical position detector 4 is accurately taken into account, height measurement becomes more accurate.

In a third aspect of the present invention, in the second aspect, the selection control circuit 5 is a discrimination circuit that discriminates the object of the light irradiation point based on the above sum, and the amplification circuit 6 and the second amplification circuit are , a plurality of amplifier circuits each having an amplification factor corresponding to the brightness of the light irradiation point of the object, the input terminals of which are commonly connected to each other.

In the case of this configuration, for example, when the sample is a printed wiring board, there are two objects: the board and the wiring pattern,
Two amplifier circuits may be provided. The construction is therefore particularly simple.

[0022]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings.

(1) First Embodiment FIG. 2 is a block diagram of a height measuring device according to a first embodiment of the present invention. Components that are the same as those in FIG. 6 are given the same reference numerals and their explanations will be omitted.

The output (a-b) of the subtracter 26 is sent to the amplifier 3.
2A and 32B, and are multiplied by A and B, respectively. The amplification factors A and B are determined as follows.

When the entire surface or a portion of the sample 10 is optically scanned to create a frequency distribution graph of brightness (a+b), which is the output of the adder 24, results such as those shown in FIG. 3 are obtained, for example. Of the two peaks in the figure, the one with lower brightness corresponds to the substrate 10a, and the one with higher brightness corresponds to the printed wiring pattern 10b. The maximum frequency brightness of both peaks corresponding to the printed wiring pattern 10b and the substrate 10a are assumed to be K/A and K/B, respectively. These A and B are amplifiers 32A and 32B shown in FIG.
is the amplification factor of For example, K is 1.

If the amplification factors A and B are determined in this manner, the output of the amplifier 32A represents the height of the light irradiation point on the printed wiring pattern 10b, and the output of the amplifier 32B represents the height of the light irradiation point on the printed wiring pattern 10a. Represents the height of the irradiation point. Amplifier 32A
Output A (a-b) of amplifier 32B, output B (a-b) of amplifier 32B
and the fixed value 0 are supplied to the analog selector 34, and one of them is selected and supplied to the A/D converter 36, where it is converted into a digital value.

The analog selector 34 is switched and controlled by a discrimination circuit 38. This discrimination circuit 38 determines whether the light irradiation point is on the substrate 10 based on the brightness (a+b) of the light irradiation point.
It discriminates whether it is on the printed wiring pattern 10b or on the printed wiring pattern 10b, and is configured as follows.

The output of the adder 24 is sent to a comparator 40A.
and 40C, and to the inverting input terminals of comparators 40B and 40D. The inverting input terminals of comparators 40A and 40C are supplied with adjustable reference voltages E1 and E3 from a reference voltage generator 42, and the non-inverting input terminals of comparators 40B and 40D are supplied with adjustable reference voltages E3 and E4. It is supplied from a reference voltage generator 42.

These reference voltages E1 to E4 are determined as shown in FIG. That is, E1 and E2 are set to values near the left and right ends of the hem of the peak corresponding to the printed wiring pattern 10b, and E3 and E4 are set to values near the left and right ends of the hem of the peak of the board 10a. .

The outputs of comparators 40A and 40B are:
The outputs of comparators 40C and 40D are supplied to AND gate 44B. Therefore, the output of the AND gate 44A is E1<a+
When b<E2, the level becomes high, and the AND gate 44B
The output becomes high level when E3<a+b<E4. The outputs of the AND gates 44A and 44B are supplied to a NOR gate 46, and the output of the NOR gate 46 is at a high level when the outputs of the AND gates 44A and 44B are both at a low level.

The outputs of the AND gates 44A, 44B and the NOR gate 46 are supplied to the control terminal of the analog selector 34 as the output of the discrimination circuit 38. When the output of the AND gate 44A is at a high level, the analog selector 34 selects and outputs input A (a-b). This output represents the height of the light irradiation point on the printed wiring pattern 10b. When the output of the AND gate 44B is at a high level, the analog selector 34 selects and outputs input B (a-b). This output represents the height of the light irradiation point on the substrate 10a.

When the output of the NOR gate 46 is at a high level,
The analog selector 34 selects and outputs the input value 0. This output indicates that even if the height of the light irradiation point on the printed wiring pattern 10b is calculated as (a-b)/(a+b), the error is large and unreliable. For example, if the board 10a is a multilayer board, the reflected light from the lower layer printed wiring pattern and the reflected light on the board 10a are PSD.
This corresponds to the case where the light is incident on 22 (the peak corresponding to this is not shown in FIG. 3).

The value of A(a-b) when the light irradiation point is on the printed wiring pattern 10b and the value of A(a-b) when the light irradiation point is on the printed wiring pattern 10b.
The difference from the value of B(a-b) when the light is on the printed wiring pattern 10b is (a+b) when the light irradiation point is on the printed wiring pattern 10b.
and (a+b) when the light irradiation point is on the substrate 10a.
It is sufficiently small compared to the difference between the value of Therefore, about 8 bits is sufficient for the A/D converter 36.

Therefore, there is no need to use a 12-bit or more A/D converter as in the prior art, and there is no need for a divider, resulting in a simple configuration and high-speed processing.

(2) Second Embodiment FIG. 4 shows a circuit diagram of a height measuring device according to a second embodiment of the present invention. The optical system of this device is the same as that shown in FIG. 2, for example. Components that are the same as those in FIG. 2 are given the same reference numerals and their explanations will be omitted.

The output (a+b) of the adder 24 is sent to the amplifier 3
It is supplied to 2C and 32D and multiplied by C and D. The output (a-b) of the subtracter 26 is similarly supplied to amplifiers 32E and 32F and multiplied by C and D times. The values of C and D are such that the value of C(a+b) when the light irradiation point is on the printed wiring pattern 10b and the value of D(a+b) when the light irradiation point is on the board 10a are almost equal. It has been selected to be. For example, the values of C and D are respectively
Equal to K/B and K/A shown in FIG.

The output C(a+b) of the amplifier 32C, the output D(a+b) of the amplifier 32D, and the fixed value 0 are supplied to the analog selector 34A, and are outputted according to the control signal from the discrimination circuit 38 as in the first embodiment. One of them is selected and supplied to the A/D converter 36A. Amplifier 32E
Output C (a-b) of amplifier 32F, output D (a-b) of amplifier 32F
and the fixed value E0 are supplied to the analog selector 34B, and as in the first embodiment, one of them is selected according to the control signal from the discrimination circuit 38, and the A/D converter 36
B is supplied. The outputs of the A/D converters 36A and 36B are supplied to a divider 48, and the quotient of the two is calculated.

With this configuration, the outputs of the analog selectors 34A and 34B are such that the light irradiation point is on the substrate 1.
The difference between when it is on the printed wiring pattern 10b and when it is on the printed wiring pattern 10b becomes sufficiently smaller than when C=D, and 8 bits are sufficient for the A/D converters 36A and 36B.

[0039] Therefore, A/D converters 36A and 36
The configuration of not only B but also the divider 48 is simplified, and high-speed processing is possible.

In the first embodiment, the brightness (a+b) of the light irradiation point on the substrate 10a and the printed wiring pattern 10
The height of the light irradiation point was calculated assuming that the brightness (a + b) of the light irradiation point on b was constant, but this second embodiment does not use such an assumption, so the first The height of the light irradiation point can be measured more accurately than in the embodiment.

(3) Third Embodiment FIG. 5 is a circuit diagram of a main part of a height measuring device according to a third embodiment of the present invention.

This circuit is similar to that shown in FIG. 4 except that a division table ROM 50 is used instead of the divider 48 shown in FIG.
It has the same configuration as .

In FIG. 6, conventionally, when a division table ROM was used instead of the divider 30, it was necessary to use a 12-bit A/D converter, so the address of the division table ROM was 24 bits. Ta. On the other hand,
In the case of FIG. 5, since the A/D converters 36A and 36B are 8 bits, 16 bits are sufficient for the address of the division table ROM 50, and the storage capacity of the division table ROM 50 is only 1/256 of the conventional one.

Note that the present invention includes various other modifications. For example, the present invention is characterized by an arithmetic circuit, and in the optical position detector, the sum of a pair of outputs represents the brightness of the light irradiation point, and the ratio of the difference between the pair of outputs and the sum represents the height of the light irradiation point. Any type of device may be used, and various types other than PSD are applicable. Of course, it is also possible to use an addition amplifier circuit in which an adder and an amplifier (constant multiplier) are combined, and a subtraction amplifier circuit in which a subtracter and an amplifier are combined. Furthermore, the analog selector 34 may be placed on the input side of the amplifier 32A.

[0045]

[Effects of the Invention] As explained above, according to the height measuring device according to the present invention, the output of the amplifier with the amplification factor based on the brightness of the light irradiation point is converted into a digital value by the A/D converter. , it is possible to narrow the fluctuation range of the input value of the A/D converter, which allows the use of an A/D converter with a small number of bits, and therefore enables high-speed processing with a simple configuration. It has excellent effects and greatly contributes to speeding up visual inspection and reducing the cost of visual inspection equipment.

In addition to the above effects, the first to third aspects of the present invention have the following effects.

In the first aspect of the present invention, there is no need for a divider and the configuration of the amplifier circuit is the simplest, so the configuration is particularly simple.

In the second aspect of the present invention, since the sum of a pair of outputs of the optical position detector is accurately taken into account, height measurement becomes more accurate.

In the third aspect of the present invention, the configuration of the amplifying circuit is the simplest among the second aspects, so the configuration is particularly simple.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle configuration of a height measuring device according to the present invention.

FIG. 2 is a configuration diagram of a height measuring device according to a first embodiment of the present invention.

FIG. 3 is a brightness frequency distribution graph when a printed wiring board is optically scanned.

FIG. 4 is a circuit diagram of a height measuring device according to a second embodiment of the present invention.

FIG. 5 is a circuit diagram of main parts of a height measuring device according to a third embodiment of the present invention.

FIG. 6 is a configuration diagram of a conventional height measuring device.

[Explanation of symbols]

10a Board 10b Printed wiring pattern 22 PSD 24 Adder 26 Subtractor 28A, 28B, 36, 36A A/D converter 30,
48 Divider 32A to 32F Amplifier 34, 34A, 34B Analog selector 38 Discrimination circuit 40A to 40D Comparator 50 Division table ROM

Claims (4)

[Claims] 1. A light beam emitted from a light source (1) is scanned onto a sample (3) by an optical scanning means (2), and light from a light irradiation point on the sample is focused to detect the optical position. (4) and measures the height of the light irradiation point based on a pair of outputs of the optical position detector, the sum of the pair of outputs being the height of the light irradiation point. a selection control circuit (5) that represents brightness, the ratio of the difference between the pair of outputs and the sum represents the height of the light irradiation point, and outputs a selection signal based on the sum; Amplification circuit (6) with multiple amplification factors that amplifies the difference
, an A/D converter (7), and a selection circuit (8) that selects the amplification factor based on the selection signal and supplies the output of the amplifier to the A/D converter; A height measuring device characterized by outputting a ratio between a difference and a sum or a value equivalent thereto as the height of the light irradiation point. 2. The selection control circuit (5) is a discrimination circuit (38) that discriminates the object of the light irradiation point based on the sum, and the amplification circuit (6) discriminates the object of the light irradiation point of the object. A plurality of amplifier circuits each having an amplification factor depending on the brightness, the input terminals of which are commonly connected to each other, and the selection circuit (
8) selects the output of the amplifier circuit corresponding to the ratio of the difference and the sum and supplies it to the A/D converter (7);
2. The height measuring device according to claim 1, wherein the output of the A/D converter is output as a height measurement value. 3. A light beam emitted from a light source (1) is scanned onto a sample (3) by a light scanning means (2), and light from a light irradiation point on the sample is focused to detect a light position. A height measuring device that measures the height of the light irradiation point based on a pair of outputs of the optical position detector, the sum representing the brightness of the light irradiation point. , a selection control circuit (5) where the ratio of the difference and the sum represents the height of the light irradiation point and outputs a selection signal based on the sum; and a plurality of amplifications that amplify the difference between the pair of outputs. a first amplifying circuit (32E, 32F) having a plurality of amplification factors, a second amplifying circuit (32C, 32D) having a plurality of amplification factors that amplifies the sum of the pair of outputs, and first and second A/Ds. a converter (36B, 36A), and a first selection circuit that selects the amplification factor of the first amplifier circuit based on the selection signal and supplies the output of the first amplifier circuit to the first A/D converter. (34B
), a second selection circuit (34A) that selects the amplification factor of the second amplifier circuit based on the selection signal and supplies the output of the second amplifier circuit to the second A/D converter; dividing means (48, 50) for outputting the output of the first A/D converter divided by the output of the second A/D converter as a height measurement value; A height measuring device characterized in that the circuits (32C to 32F) have the same amplification factor selected. 4. The selection control circuit (5) is a discrimination circuit (38) that discriminates the object of the light irradiation point based on the sum, and the selection control circuit (5) is a discrimination circuit (38) that discriminates the object of the light irradiation point based on the sum.
4. The height measuring device according to claim 3, wherein the height measuring device comprises a plurality of amplifier circuits each having an amplification factor depending on the brightness of the light irradiation point of the object, and whose input terminals are commonly connected to each other. .