JP3203854B2 - Inspection device for mounted printed circuit boards - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention inspects a mounted printed circuit board with a finely focused minute beam light and detects the reflected light, thereby inspecting for misalignment of a mounted component, missing parts, defective solder, and the like. In particular, the present invention has a feature in an electric circuit for arithmetically processing height information and luminance information of a board obtained from reflected light.

[0002]

2. Description of the Related Art In recent years, in order to inspect for misalignment, missing parts, defective soldering, etc. of components of a mounted printed circuit board, a narrowly focused light beam is applied to the mounted printed circuit board by using the principle of triangulation. A non-contact method for detecting reflected light is used.

In a conventional inspection apparatus for a mounted printed circuit board, a reflected light of a minute beam light irradiated on the board is received by a photoelectric conversion element, and the height and brightness of the board are calculated from the electrical output thereof. There is one that inspects the surface shape.

[0004]

SUMMARY OF THE INVENTION According to the present invention, a reflected light of a minute light beam that scans a substrate is received by a photoelectric conversion element in accordance with the scanning of the minute light beam, and luminance information and high luminance are obtained from the electrical output. It is an object of the present invention to provide an electric circuit that does not generate an electric error or is not affected by an optical error of a measurement portion in an electric circuit that performs arithmetic processing of information.

[0005]

In order to achieve this object, a mounted printed circuit board inspection apparatus according to the present invention receives reflected light of a beam light radiated on the mounted printed circuit board, and responds to the light receiving position. Photoelectric conversion means for outputting an electrical analog signal, analog-to-digital conversion means for converting the electrical analog signal from the photoelectric conversion means to a digital signal, and using the digital signal, the mounted printed circuit board What is claimed is: 1. An apparatus for inspecting a mounted printed board, comprising: height / brightness calculating means for calculating height data and brightness data, wherein an output value of the photoelectric conversion means when the light beam is not scanning on the printed board. Is converted by the analog / digital conversion means.
Multiple offset data and calculate the average of the offset data.
With obtaining the average value, when the scanning of the substrate, after the average value from the measurement digital signal output from the analog-to-digital converting means and subtraction, and outputs the in height and intensity computing means Things.

[0006]

According to the above arrangement, an electric circuit for converting the electrical analog output of the photoelectric conversion element, which is output in accordance with the position of receiving the reflected light from the substrate, into a digital signal to obtain height and luminance data of the substrate. In particular, when the photoelectric conversion element does not receive the reflected light from the mounted printed circuit board to be inspected, that is, among the outputs output from the photoelectric conversion element, the output not due to the reception of the reflected light Errors due to the above can be eliminated.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of an optical measuring unit of a device for inspecting a mounted printed circuit board effective for applying the present invention.

[0008]

According to the above arrangement, an electric circuit for converting the electrical analog output of the photoelectric conversion element, which is output in accordance with the position of receiving the reflected light from the substrate, into a digital signal to obtain height and luminance data of the substrate. In particular, when the photoelectric conversion element does not receive the reflected light from the mounted printed circuit board to be inspected, that is, among the outputs output from the photoelectric conversion element, the output not due to the reception of the reflected light Errors due to the above can be eliminated. Also, in particular,
For example, measure multiple offset data and calculate the average value
And subtract it from the actual board measurement result.
Since there is no variation in offset data,
More accurate inspection can be performed.

7, 8, 9 and 10 receive reflected light from the small beam light irradiation position on the mounted printed circuit board 6 from four directions, and receive the reflected light, respectively, using the light receiving fθ lens 11,
An optical path correction optical system that corrects the optical path of the reflected light to guide the light to 12, 13, and 14. Receiving fθ lenses 11, 12,
Reference numerals 13 and 14 are for guiding the reflected light that has passed through the optical path correction optical systems 7, 8, 9 and 10 to the polygon mirror 3. 15, 16, 17, and 18 are light receiving fθ lenses 11,
This is a PSD (semiconductor position detecting element) lens for condensing the reflected light passing through 12, 13, and 14 and deflected by the polygon mirror 3. 19, 20, 21, and 22 are PS
It is a PSD that receives the reflected light condensed by the D lenses 15, 16, 17, and 18, and generates an electrical output corresponding to the light receiving position.

Reference numeral 23 denotes a mounted printed board which has returned along the light projecting optical axis through the light projecting fθ lens 5 and the polygon mirror 3 among the reflected light from the small beam light irradiation position on the mounted printed circuit board 6. The tunnel mirror deflects reflected light in a direction perpendicular to the substrate 6. Reference numeral 24 denotes a lens for collecting the reflected light deflected by the tunnel mirror 23. Reference numeral 25 denotes an aperture that blocks reflected light from directions other than the vertical direction. Reference numeral 26 denotes a photodiode that receives the reflected light in the vertical direction and converts the amount of received light into an electrical output.

Reference numeral 27 denotes a table for fixing the mounted printed circuit board 6. Reference numeral 28 denotes a ball screw that moves the table 27 in the sub-scanning direction (the direction of the arrow y) by rotating. Reference numeral 29 denotes a ball screw motor for rotating the ball screw 28. Reference numeral 30 denotes a guide rail for guiding the table 27. The operation of the mounted printed circuit board inspection apparatus configured as described above will be described.

The minute light beam generated from the light source 1 is converted into a parallel light beam by the collimating lens system 2, passes through a hole in the tunnel mirror 23, is deflected by the polygon mirror 3, is condensed by the light projecting fθ lens 5, and The light beam is irradiated substantially perpendicularly onto the mounted printed circuit board 6 as a light beam irradiation optical axis. At this time, the minute beam light generated from the light source 1 scans the mounted printed circuit board 6 in the main scanning direction (the direction of the arrow x) in the figure as the polygon mirror 3 is rotated and driven by the polygon motor 4. . And
The reflected light diffused from the scanning position on the mounted printed circuit board 6 is guided to the light receiving fθ lenses 11, 12, 13, and 14 by the optical path correction optical systems 7, 8, 9, and 10.

The optical path correcting optical systems 7, 8, 9, and 10 are provided for irrespective of a change in the scanning position of the minute beam light among the reflected light diffused from the irradiation position on the mounted printed circuit board 6.
The scanning direction when the angle (hereinafter referred to as the tilt angle) between the optical axis of the microbeam light irradiation and the optical axis of the reflected light is substantially constant, and the reflected optical axis is projected on a plane perpendicular to the optical axis of the microbeam light irradiation Angle (hereinafter, the allocation angle) is substantially constant,
That is, reflected light having a substantially constant direction vector is received. Irrespective of the change in the scanning position, the light is made to enter the light receiving fθ lenses 11, 12, 13, and 14 substantially perpendicularly to the position in the main scanning direction (arrow x direction) at the same position as the optical axis of the microbeam light irradiation, Furthermore, even if the scanning position changes, the reception of reflected light f
The reflected light is guided so that the incident position of the θ lens in the sub-scanning direction (the direction of the arrow y) does not change.

Since the light receiving fθ lens 13 has the same shape as the light projecting fθ lens 5, the reflected light is guided to the polygon mirror 3 by following the same path as the minute light beam of the light projecting. Then, the reflected light is deflected by the polygon mirror 3 and an image of the reflected light is formed at a position on the PSD 21 according to the height of the irradiation position of the minute light beam on the printed circuit board 6 irrespective of a change in the scanning position of the minute light beam. Imaged. Other optical path correcting optical system 7,
8, 10 are the same, and the optical path correction optical system 7,
The reflected light received by 8, 10 is the received light fθ lens 11, 1
2 and 14 and the PSD lenses 15, 16 and 18, and are guided to the PSDs 19, 20 and 22.

The reflected light from the printed circuit board 6 thus mounted has a PSD corresponding to the height of the minute beam light irradiation position.
Since the image is formed at the upper position, the PSD 19, 2
The height of the minute beam light irradiation position is determined using the electrical outputs from 0, 21, and 22. The data obtained by measuring the electrical output of the reflected light at a plurality of positions on the scanning line in the x direction is subjected to processing such as selection described later, so that the correct height is obtained regardless of the surface condition of the measurement object. Can be measured.

The reflected light reflected from the minute beam light irradiation position in the direction of the minute beam light irradiation optical axis (substantially perpendicular direction) passes through the light projecting fθ lens 5, polygon mirror 3, tunnel mirror 23, lens 24, and aperture 25. Through the photodiode 26. At this time, the reflected light in the vertical direction is
5 and lens 24, and the collected reflected light is received by photodiode 26. Further, light other than the reflected light in the optical axis direction of the microbeam light irradiation is blocked by a diaphragm 25 provided between the lens 24 and the photodiode 26. Therefore, only the amount of reflected light reflected from the minute beam light irradiation position in the direction of the minute beam light irradiation optical axis can be correctly measured.

Next, from the outputs of the PSDs 19, 20, 21, 22 and the photodiode 26, the height and luminance information are used to calculate
An electric circuit in the inspection device of the mounted printed board of the present invention for inspecting the surface shape will be described. FIG. 2 shows an electric circuit and its operation in one embodiment of the present invention.

In FIG. 2, 52, 53, 54, 55
Is a PSD 19 for measuring height and brightness data,
A height / luminance calculation circuit for obtaining flagged luminance data and flagged height data from the outputs of 20, 21 and 22. The height / luminance calculation circuits 52, 53, 54 and 55 have the same configuration, respectively, I / V conversion circuits 40 and 41 for converting the current from each PSD into a voltage, and convert an analog voltage into a digital value. A / D conversion circuit 4 for performing
2, 43, comparator circuits 44, 45, 50 for comparing a certain threshold value with an input value, an adding circuit 46 for adding digital values, and a dividing circuit 47 for dividing digital values. , Correction ROMs 48 and 49 for correcting digital values, and comparator circuits 44 and 4
And a flag calculation circuit 51 for calculating a flag from the outputs of the counters 5 and 50. A / D conversion circuit 4
2, 43, an adding circuit 46, and a dividing circuit 47, between which an offset average value calculating / holding circuit 90, 91 and a subtracting circuit 9
2, 93 are arranged.

Reference numeral 58 denotes the output of the photodiode 26,
This is a luminance calculation circuit for obtaining luminance data. The luminance calculation circuit 58 includes an I / V conversion circuit 56 for converting a current from the photodiode 26 into a voltage, and an A / D conversion circuit 57 for converting an analog voltage into a digital value.

The luminance data with a flag and the height data with a flag are sent to a luminance information selection processing circuit 59 and a height information selection processing circuit 60, respectively. Outputs from these circuits are output to the RAM 6 together with the luminance data of the luminance calculation circuit 58.
1. Guided to CPU 62.

The operation of the electric circuit configured as described above will be described. The height luminance calculation circuits for the PSDs 19, 20, 21, 22 are 52, 53, 54, 55, respectively.
The two current outputs from the PSD are converted into I / V conversion circuits 40, 4
1 for current / voltage conversion, and then A / D conversion circuit 4
Analog / digital conversion is performed by 2 and 43. On this occasion,
The digital output value is compared with a certain threshold value (limit value that can guarantee the calculation accuracy) by the comparator circuits 44 and 45, and the comparison result is sent to the flag calculation circuit 51.

The two digital output values are added by an adder circuit 46 to become luminance information of the minute beam light irradiation position, and are further divided by a divider circuit 47.
It becomes height information of the minute beam light irradiation position. Adder circuit 46
And output data of the dividing circuit 47 (luminance information, height information)
Includes the measurement error due to the scanning position (error of each optical system element,
Error due to the rotation of the polygon mirror). In order to correct this error, a configuration is adopted in which the correction amount based on the scanning position is measured in advance and recorded in the correction ROMs 48 and 49, and the output data of the addition circuit 46 and the division circuit 47 are corrected by referring to the correction amount. Has become. At this time, the correction RO
The luminance data after passing through M48 is compared with a certain threshold value (limit value at which PSD can be correctly measured) by the comparator circuit 50, and the comparison result is sent to the flag calculation circuit 51.
The information of the comparator circuits 44, 45, and 50 is flagged by the flag calculation circuit 51. The flag is added to the luminance data and the height data, and the resulting data is flagged luminance data and flagged height data, respectively.

According to this configuration, these data are supplied to four height / luminance calculation circuits 5 from four directions for one measurement point.
With 2, 53, 54, and 55, four flagged luminance data and flagged luminance data can be obtained. Reference numeral 59 denotes a luminance information selection processing circuit that performs a selection process on the four flagged luminance data. As a selection processing method, there is a method of obtaining the maximum value of four data. Reference numeral 60 denotes a height information selection processing circuit that performs a selection process on four pieces of height data with flags.

As a selection processing method, for example, data whose measurement accuracy cannot be guaranteed based on information from a flag is removed.
There are a method of averaging the remaining data, and a method of removing the maximum level data and the minimum level data and averaging the remaining data when the number of remaining data is large.
The luminance information selection processing circuit 59 and the height information selection processing circuit 60 are provided to save the RAM 61 and reduce the load on the CPU 62.
The outputs of 9 and 60 are sent to the RAM 61 and sent to the CPU 62.

The luminance calculation circuit 58 for the photodiode 26 outputs the current output from the photodiode to I
A / V conversion circuit 56 performs current / voltage conversion.
Analog / digital conversion by the D conversion circuit 57 and RA
Send to M61. Since the photodiode 26 receives the reflected light in the vertical direction from the mounted printed circuit board 6,
When the inclination of the solder surface is gentle or no solder is attached, the output increases because the reflected light in the vertical direction increases, and conversely, when the inclination of the solder surface is steep, the reflected light in the vertical direction decreases. Therefore, the output becomes smaller. For this reason, P
When the output of the SD is small and the height of the solder surface cannot be measured correctly, the luminance information of the photodiode 26 can be referred to.

Then, the CPU 62 compares the height and luminance information of the RAM 61 with the height and luminance information obtained and stored in advance from the reference mounted printed circuit board to determine the mounting state of the mounted printed circuit board. Inspect for pass / fail.

By the way, in the above configuration, the PSD 1
In the electric circuits between 9, 20, 21, and 22 and the A / D conversion circuits 42 and 43, an electric error occurs, and the influence cannot be eliminated. As a result, the height luminance operation circuit 52, Outputs from 53, 54 and 55 include errors. Therefore, in the electric circuit configuration of the present embodiment, in particular, the offset average value calculation / hold circuits 90 and 9 are provided between the A / D conversion circuits 42 and 43 and the addition circuit 46 and the division circuit 47.
1 and subtraction circuits 92 and 93 are added so that these electrical error components can be removed.

This operation will be described with reference to FIG.
Electrical error data is PS when reflected light is not received
D output, that is, P due to light other than light reflected from the substrate
This is the output of SD, and the measurement of the electrical error data is
This is performed using the output of the PSD in a state where there is no reflected light from the mounted printed board, that is, in a state where the light source 1 is turned off.

First, with the light source 1 turned off before the start of the inspection, the current signals of two electrical errors from the PSD 19 are
/ V conversion circuits 42 and 43 convert the signals into voltage signals. next,
The A / D conversion circuits 42 and 43 convert the voltage signal into a digital signal. This signal becomes the first offset data. The above measurement is repeated n times to create n offset data. From these n pieces of offset data, an offset average value calculation / holding circuit calculates an offset average value,
Store as average offset data.

When the light source 1 is turned on and the inspection of the mounted printed circuit board is started, the measurement data sampled at a plurality of positions on the scanning line is obtained by converting a current output including an electric error component from the PSD 19 into an I / V conversion circuit. The signals are converted into voltage signals at 42 and 43, and the voltage signals are converted into digital signals at A / D conversion circuits 42 and 43. Then, the subtraction circuits 92 and 93 subtract the average offset data held in the offset average value calculation / holding circuits 90 and 91 from this digital signal to remove the electrical error signal. The digital signal from which the electrical error signal has been removed is input to the adding circuit 46 and the dividing circuit 47. Subsequent steps are the same as those of the electric circuit of the first embodiment.

In this embodiment, the method of turning off the light source 1 is described as an example in a state where there is no reflected light from the mounted printed circuit board. The electrical error data may be measured by a method in which the substrate is retracted from the irradiation position so that there is no reflective object.

FIG. 3 shows another embodiment of an electric circuit according to another embodiment of the present invention. FIG. 3A is an electric circuit block diagram, and FIG. 3B is an operation timing chart.

In the electric circuit configuration shown in FIG.
It is possible to eliminate the influence of electrical errors occurring in electrical circuits between 0, 21, and 22 and the A / D conversion circuits 42 and 43. Fθ lens 5
It is not possible to eliminate an optical error caused by reflection on the surface and the polygon mirror surface and the diffuse reflection light being incident on the PSDs 19, 20, 21, and 22.

In the electric circuit configuration shown in FIG. 3, an offset average value calculation / hold circuit 94 for each scanning position is provided between the A / D conversion circuits 42 and 43, the addition circuit 46, and the division circuit 47.
95 and subtraction circuits 92 and 93 are added to remove the electrical error component and the optical error component for each scanning position.

The operation of the electric circuit block diagram of FIG. 3A will be described with reference to FIG. Before actually scanning the mounted printed circuit board, electrical error data generated in an electric circuit and optical error data for each scanning position are measured. First, a state in which there is no reflected light from the mounted printed board, for example, a state in which the mounted printed board is retracted from the irradiation position, and the light source 1 is kept on. Then, in the first scan, each scan position (scan positions 1 to 5)
For each scanning position x), the current output of the electrical error and optical error of the PSD 19 is converted into a voltage signal by the I / V conversion circuits 42 and 43, and is converted into a digital signal by the A / D conversion circuits 42 and 43. , Offset data. This is scanned n times, and n pieces of offset data are created for each scanning position. Next, offset average value calculation / hold circuits 94 and 95
, An average value of n pieces of offset data is obtained for each scanning position to create average offset data, and this value is held.

When the mounted printed board is moved to the scanning position and the inspection is started, the measurement data sampled at a plurality of positions on the scanning line is a current output including an electrical error component and an optical error component from the PSD 19. I / V conversion circuit 42,
The signal is converted into a voltage signal at 43, and the voltage signal is converted into a digital signal at A / D conversion circuits 42 and 43 to obtain. And
For each scanning position, the subtraction circuits 92 and 93 convert the digital signal into an offset average value calculation and holding circuit.
The average offset data corresponding to the scanning position held at 4, 95 is subtracted to remove electrical errors and optical errors. The digital signal from which the electrical error and the optical error have been removed is input to the adding circuit 46 and the dividing circuit 47. Subsequent steps are the same as those of the above embodiment.

In this embodiment, a method is described in which the mounted printed board is retracted from the irradiation position on the assumption that there is no reflected light from the mounted printed board. By changing the optical path with a mirror, or by blocking the optical path with a light absorbing material,
The reflected light may not be incident on the light receiving fθ lenses 11, 12, 13, and 14.

[0038]

As described above, according to the present invention, the electrical analog output of the photoelectric conversion element, which is output according to the light receiving position of the reflected light from the substrate, is converted into a digital signal, and the height and the height of the substrate are reduced. An electric circuit for obtaining luminance data can be formed, particularly when the photoelectric conversion element does not receive the reflected light from the mounted printed circuit board to be inspected, that is, among the outputs output from the photoelectric conversion element, the reception of the reflected light It is possible to eliminate an error caused by an output that is not caused by performing the operation.

Further, by detecting the offset of the output of the PSD corresponding to a plurality of measurement positions on each scanning line on the board, an error caused by the optical measurement unit of the mounted printed board for each measurement position is detected. Can be constructed. Also in particular according to the invention
For example, measure multiple offset data and calculate the average value
And subtract it from the actual board measurement result.
Since there is no variation in offset data,
More accurate inspection can be performed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical measurement unit suitable for applying an inspection device for a mounted printed board according to the present invention.

FIG. 2 is a block diagram and an operation explanatory diagram of an electric circuit in one embodiment of the device.

FIG. 3 is a block diagram and operation explanatory diagram of an electric circuit in another embodiment of the device.

[Explanation of symbols]

Reference Signs List 1 light source 2 collimating lens system 3 polygon mirror 4 polygon motor 5 light emitting fθ lens 6 mounted printed circuit board 7, 8, 9, 10 optical path correction optical system 11, 12, 13, 14 light receiving fθ lens 15, 16, 17, 18 Lens for PSD 19, 20, 21, 22 PSD 26 Photodiode 40, 41 I / V conversion circuit 42, 43 A / D conversion circuit 44, 45 Comparator circuit 46 Addition circuit 47 Division circuit 48, 49 Correction ROM 50 Comparator circuit 51 Flag calculation circuit 52, 53, 54, 55 Height luminance operation circuit 56 I / V conversion circuit 57 A / D conversion circuit 58 Luminance operation circuit 59 Luminance information selection processing circuit 60 Height luminance selection processing circuit 61 RAM 62 CPU 90, 91, 94, 95 Offset data average value calculation / hold circuit 92, 9 Subtraction circuit

Continuation of the front page (72) Inventor Yuji Ono 2-2-1-10 Kotobukicho, Takamatsu-shi, Kagawa Prefecture Inside Matsushita Hisashi Electronics Co., Ltd. (72) Inventor Hidenori Nagata 2-2-110 Kotobukicho, Takamatsu-shi, Kagawa Matsushita (56) References JP-A-4-352287 (JP, A) JP-A-62-127604 (JP, A) JP-A-1-100409 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01B 11/00-11/30 102 G01N 21/84-21/958 G02B 26/10 H05K 3/34 H05K 13/08

Claims (2)

(57) [Claims] 1. A photoelectric conversion means for receiving reflected light of a light beam irradiated on a mounted printed circuit board and outputting an electrical analog signal corresponding to the light receiving position; and an electrical analog signal from the photoelectric conversion means. Analog-to-digital conversion means for converting a digital signal into a digital signal; and a height / brightness calculating means for calculating height data and brightness data of the mounted printed board using the digital signal. A plurality of offset data obtained by converting the output value of the photoelectric conversion unit when the light beam is not scanning on the printed board by the analog / digital conversion unit.
To calculate the average value of the multiple offset data
In addition, at the time of scanning the substrate, after subtracting the average value from the measurement digital signal output from the analog / digital conversion means, the result is output to the height / luminance calculation means. Inspection device for printed circuit boards. 2. A mounted print whose surface shape is to be inspected.
The analog-to-digital conversion means changes the electrical output value of the photoelectric conversion means when there is no reflected light of the light beam corresponding to a plurality of different measurement positions on the substrate.
A plurality of offset data that have been
The average value of multiple offset data is calculated for each inspection position.
In addition, at the time of scanning the substrate, a value calculated beforehand corresponding to the measurement position is obtained from an output digital signal of the analog / digital conversion means output according to each measurement position.
2. A printed circuit board inspection apparatus according to claim 1, wherein said average value is subtracted from each other, and then output to said height / luminance calculating means.