JP3203852B2 - 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 relates to an apparatus for inspecting a mounted printed circuit board, and particularly to an apparatus for scanning a board by deflecting a minute beam light by a polygon mirror and having a configuration for correcting jitter of the polygon mirror.

[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 printed circuit board inspection device, a minute light beam generated from a light source is deflected by a polygon mirror to scan the substrate, and the reflected light from the irradiation position of the minute light beam on the substrate is transmitted to a photoelectric conversion element. And inspects the surface shape.

[0003]

In the inspection apparatus using the above-mentioned conventional polygon mirror, the output of the photoelectric conversion element is sampled at a plurality of positions in accordance with the scanning of the minute light beam to obtain the substrate shape. ing. However, if there is jitter in the polygon mirror, it is necessary to correct the jitter so that the actual scanning position of the light beam does not differ from the interval at which the output of the photoelectric conversion element is sampled.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a device for inspecting a mounted printed circuit board using a polygon mirror, which comprises a jitter correction section which is not affected by uneven rotation of the polygon mirror.

[0005]

In order to solve the above-mentioned problems, an apparatus for inspecting a mounted printed circuit board according to the present invention comprises:
Of the light beam deflected with a polygon mirror, while scanning the loaded printed on the substrate to be inspected, said port
Obtained for each scan corresponding to each surface of the rigon mirror,
From each irradiation position of the first beam light on the substrate
In the inspection apparatus for a mounted printed circuit board that samples the reflected light of the above and obtains the surface shape of the board, the polygon mirror is irradiated with a second light beam and the second light beam is condensed. A photoelectric conversion unit that is disposed on a scanning line on which the second light beam from the light projecting unit deflected by the polygon mirror is condensed and obtains an electrical output for each surface of the polygon mirror; by detecting the rotation time required between each surface of the polygon mirror from the output of the photoelectric conversion unit, a polygon mirror for each respective surfaces
The rotation speed of each surface is detected, and the rotation speed of each
Next, from the information indicating the sampling position,
Circuit means for generating a signal indicating the timing of sampling at a position to be ringed .

[0006]

According to the configuration of the jitter correcting section, even if the polygon mirror causes jitter, it is possible to generate a sample clock at a time interval corresponding to the rotation speed of the polygon mirror. Without receiving it, it is possible to always obtain accurate height data of the scanning position coordinates.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an apparatus for inspecting a mounted printed circuit board to which the present invention is applied. In FIG. 1, reference numeral 1 denotes a light source for generating a minute light beam to irradiate the mounted printed circuit board 6. Reference numeral 2 denotes a collimating lens system for condensing the minute beam light from the light source 1 to make it a parallel light beam. 3 deflects the parallel light beam, and
This is a polygon mirror for deflecting light reflected from the mounted printed circuit board 6. Reference numeral 4 denotes a polygon motor that drives the polygon mirror 3 to rotate. Reference numeral 5 denotes a light projecting fθ lens that condenses the parallel light beam deflected by the polygon mirror 3 and irradiates the mounted printed circuit board 6 substantially perpendicularly. Reference numeral 6 denotes a mounted printed board to be inspected.

[0008]

According to the configuration of the jitter correcting section, even if the polygon mirror causes jitter, a sample clock can be generated at a time interval corresponding to the rotation speed of the polygon mirror, and the influence of uneven rotation of the polygon mirror can be reduced. Without receiving it, it is possible to always obtain accurate height data of the scanning position coordinates. In particular, according to the present invention, each surface of the polygon mirror is
The rotation speed and the information of the position to be sampled from now on
Sample at the next sampling position based on
The timing to be decided is decided. In this configuration
Scanning of optical components between each sampling position
Scan position errors due to performance can be corrected.

Reference numeral 23 denotes a mounted printed board which has returned along the light projecting optical axis along the light projecting fθ lens 5 and the polygon mirror 3 among reflected light from the minute 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 the hole of 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, out of the reflected light diffused from the irradiation position on the mounted printed circuit board 6, regardless of the change in the scanning position of the minute light beam.
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 light beam of the projected light. 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 measured by the PSDs 19, 20, 21, and 22 arranged in these four directions is subjected to processing such as selection described later, and the correct height is measured regardless of the surface condition of the measurement object. Can be.

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.

Thus, the four PSDs 19, 20, 2
At 1 and 22, four luminance data and height data can be acquired from four directions for one measurement point. As a method of selecting four luminance data, there is a method of obtaining the maximum value of the four data. As a method of selecting height data, for example, a method of removing data for which measurement accuracy cannot be guaranteed and taking an average of the remaining data, or when the number of remaining data is large, the maximum level data and the minimum level data are used. There is a method of removing and averaging the remaining data.

Since the photodiode 26 receives the reflected light in the vertical direction from the mounted printed circuit board 6, the reflected light in the vertical direction is generated when the inclination of the solder surface is gentle or when there is no solder. The output increases as the number increases, and conversely, when the inclination of the solder surface is steep, the reflected light in the vertical direction decreases and the output decreases. For this reason,
When the output of the PSD 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 height and luminance information subjected to the selection processing is compared with the height and luminance information obtained and stored in advance from the mounted printed circuit board as a reference, and the mounting state of the mounted printed circuit board is determined. The quality can be checked.

As described above, the minute beam light emitted from the light source is deflected by using the polygon mirror to scan the mounted printed board, and the light reflected from the board is taken out and deflected by the polygon mirror. It is necessary to correct the jitter of the polygon mirror in the inspection device that guides the light to the light receiving unit. Hereinafter, as an embodiment of the present invention, the configuration of the jitter correction unit applied to the inspection device of the mounted printed circuit board will be described.

FIG. 2 shows a configuration of the jitter correcting section in one embodiment of the present invention. In FIG. 2, reference numeral 37 denotes a light source for generating a minute light beam.
Is different from Reference numeral 38 denotes a collimating lens system for converting the minute light beam from the light source 37 into a parallel light beam. Reference numeral 39 denotes a converging lens system for converging a parallel light beam into minute spot light. Reference numeral 3 denotes a polygon mirror shown in FIG. 1 for deflecting the minute beam light after passing through the condenser lens system 39, and scans the focusing position of the minute beam light along an arc-shaped scanning line 40. Reference numeral 4 denotes the polygon motor shown in FIG.

Reference numeral 41 denotes a slit provided at a position on the scanning line 40 where the minute light beam from the light source 37 is incident before the light source 1 in FIG. 1 starts scanning the mounted printed circuit board 6. Reference numeral 42 denotes an inter-plane time measuring photoelectric conversion element for detecting a minute light beam after passing through the slit 41 and measuring the rotation time of one surface of the polygon mirror. For example, a photodiode plays this role. Reference numeral 46 denotes a slit provided on the scanning line 40 so that the minute light beam in FIG. 1 corresponds to the measurement start position of the mounted printed circuit board 6. Reference numeral 47 denotes a scanning start position detecting photoelectric conversion element for detecting the minute beam light after passing through the slit 46 and detecting the scan start position of the mounted printed circuit board. For example, a photodiode plays this role. 43 and 48 are I for converting current signals from the photoelectric conversion elements 42 and 47 into voltage signals.
/ V conversion circuit. 44 and 49 are comparators for comparing the voltage signals obtained from 43 and 48 with the reference voltages 45 and 50 and converting them into digital signals of 0 or 1. 5
Reference numeral 1 denotes a measuring unit described in the first embodiment.

The operation of the jitter correction unit of the polygon mirror in the printed circuit board inspection apparatus having the above-described structure will be described. The minute beam light generated from the light source 37 is converted into a parallel light beam by the collimating lens system 38 and becomes a minute spot light focused on the scanning line 40 by the focusing lens system 39. The polygon mirror 3 is rotationally driven by a polygon motor 4, deflects while rotating the minute light beam that has passed through the condenser lens system 39, and scans the scanning line 40 in the direction of the arrow x.

With the rotation of the polygon mirror 3, first, the minute spot light is incident on the photoelectric conversion element 42 for measuring the time between surfaces. The current signal output from the photoelectric conversion element 42 for measuring an inter-plane time is subjected to current-voltage conversion by the I / V conversion circuit 43 to become a voltage signal.
Is compared with the reference voltage 45. If the voltage is lower than the reference voltage 45, it is output as a digital signal of 0, and if it is higher, it is output as a digital signal of 1, and becomes a surface time measurement signal b for measuring the time between the surfaces of the polygon mirror 3.

Next, the minute spot light is incident on the photoelectric conversion element 47 for detecting the scanning start position. The current signal output from the scanning start position detecting photoelectric conversion element 47 is I
/ V conversion circuit 48 converts the current and voltage into a voltage signal,
The comparator 49 compares the voltage with the reference voltage 50. If the voltage is lower than the reference voltage 50, the signal is output as a digital signal of 0;

The polygon motor 4 outputs a z-phase signal a indicating the origin of the rotation angle every rotation.

FIG. 3 shows the relationship between the z-phase signal a, the inter-plane time measurement signal b, and the scanning start signal c output by the above-described apparatus.
Shown in First, one pulse of the z-phase signal a is output each time the polygon mirror makes one rotation. This signal is used as the origin of the rotation angle. Next, when the polygon mirror rotates, one pulse of the inter-surface time measurement signal b is output for each reflection surface, and thereafter a scanning start signal c is output. In this embodiment, since the number of surfaces of the polygon mirror is 6, when the polygon mirror makes one rotation, one pulse of the z-phase signal a and one pulse of the inter-plane time measurement signal b
Are output for six pulses and the scanning start signal is output for six pulses. Each surface is divided by a sample clock described later, and the interval between the sample clocks d is determined by the number of sample interval clocks of a reference clock e described later.

FIG. 4 shows a circuit for generating a sample clock for measurement using these signals. The measurement sample clock is a signal that generates a sample clock, advances scanning coordinates by one, and instructs height measurement.

First, the value of the surface number counter 52 representing the reflection surface of the polygon mirror is reset to 0 by the z-phase signal a. When the minute light beam enters the inter-plane time measuring photoelectric conversion element 42, the inter-plane time measurement signal b is obtained.
This inter-plane time measurement signal b is input to the plane number counter 52, and the value of the plane number counter 52 is incremented by one each time one pulse of the inter-plane time measurement signal b is input. Thus, the surface number counter 52 outputs the surface number of the polygon mirror currently used for scanning.

The inter-plane time measurement signal b resets the value of the inter-plane time counter 53 to zero. Thereafter, the inter-plane time counter 53 adds the value of the inter-plane time counter 53 one by one each time one pulse of the reference clock e from the reference clock oscillator 54 is input. Then, when the inter-plane time measurement signal b is newly input, the previous inter-plane time measurement signal b
The number of pulses of the reference clock oscillator 54 from the current time to the inter-plane time measurement signal b is held by the latch circuit 55 connected to the inter-plane time measurement counter 53. Thereby, the reference pulse number (inter-plane time pulse number) of the reference clock oscillator 54 between the previous inter-plane time measurement signal and the current inter-plane time measurement signal is obtained.

On the other hand, the inter-plane time measurement signal b resets the inter-plane time measurement counter 53 again, and repeats the same operation. Next, the value of the face-to-face time measurement counter 53 (the number of face-to-face time pulses) held by the latch circuit 55 and the value of the face number counter 52 are input to the decoder 56 as the address of the polygon mirror 3. The speed pattern corresponding to the surface number and the inter-surface time is previously written in the decoder 56, and the decoder 56 outputs the speed pattern from the sum of the surface number and the inter-surface time. For example, in plane number 1, the inter-plane time is 1001 pulses to 101 to reference oscillator.
The speed pattern is determined such that the speed pattern is A in the case of 0 pulse, and the speed pattern is B in the case of the surface number 1 and the inter-plane time is 1010 to 1020 reference pulses. By doing so, the number of output data (speed pattern) is smaller than the number of input data (the sum of the surface number and the inter-surface time) of the decoder 56, and the memory size of the sample interval storage ROM 58 described below can be reduced. . If the memory of the sample interval storage ROM 58 is not limited, the inter-plane time may be directly input to the sample interval storage ROM 58 without the decoder 56.

The inter-surface time measurement signal b resets the sample number counter 57, and every time a sample clock is input, the value of the sample number counter 57 is incremented by one. Thus, the sample number counter 57
Output the number of sample clocks (coordinates) in one scanning line. The time from measurement of one coordinate to measurement of the next coordinate is recorded in advance in the sample interval storage ROM 58 for each coordinate. When a coordinate number is input to the sample interval storage ROM 58, the time until the next coordinate is output. Here, the coordinate number is represented by the sum of the speed pattern number, the surface number, and the sample number, and the time until the next coordinate is measured is represented by the number of clocks of the reference clock (the number of sample interval clocks N). That is, when the speed pattern number, surface number, and sample number are input to the sample interval storage ROM 58 as addresses, the number of sample interval clocks up to the next sample clock is output. The number of sample interval clocks output from the sample interval storage ROM 58 is input to the next subtraction counter 59.

The subtraction counter 59 decrements the value of the number of sample interval clocks by one each time one pulse of the reference clock is input from the reference clock oscillator 54. When the value becomes 0, the sample clock is output as a borrow signal. Instruct measurement. Then, the sample clock is input to the sample number counter 57. The operation of the subtraction counter 59 is controlled by a subtraction counter control circuit 60. When the scanning start signal c is input to the subtraction counter control circuit 60, the subtraction control counter 60 outputs an operation start signal to the subtraction counter 59 to instruct the operation to start. The end sample number storage circuit 61 stores the value of the last sample number of one scanning line, and the subtraction counter control circuit 60 compares the value of the sample number counter 57 with the value of the end sample number storage circuit 61. When the current sample number and the end sample number become equal, an operation end signal is output to the subtraction counter 59, and the operation of the subtraction counter 59 is stopped. That is, outside the scanning range, the operation of the subtraction counter 59 is stopped, and the generation of the sample clock is stopped.

As described above, the jitter correction unit is provided in the mounted printed circuit board inspection apparatus shown in FIG. 1 and the sample clock is generated at a time interval corresponding to the rotation speed of the polygon mirror, thereby reducing the influence of the rotation unevenness of the polygon mirror. Without receiving it, it is possible to always obtain accurate height data of the scanning position coordinates.

The scanning start position detecting photoelectric conversion element 4
At 7, both the scanning start position and the inter-plane time are measured, and the inter-plane time detecting photoelectric conversion element 42 may be removed.

[0035]

As described above, according to the present invention, a minute beam light is scanned on a mounted printed circuit board by using a polygon mirror, or reflected light irradiated on the mounted printed circuit board is deflected by a polygon mirror to receive light. In the inspection device of the mounted printed circuit board which is guided to the unit, the minute light beam emitted from the light source different from the light source is deflected by the polygon mirror, and the light receiving means arranged on the scanning line of the minute light beam is used. A jitter correction unit is configured to detect a rotation speed of the polygon mirror and generate a signal indicating a sample of the substrate surface shape according to the rotation speed.

As described above, by generating the sample clock at the time interval corresponding to the rotation speed of the polygon mirror, accurate height data of the scanning position coordinates is always obtained without being affected by the rotation unevenness of the polygon mirror. it can. Special
According to the present invention, the rotation speed of each surface of the polygon mirror
And information on the position to be sampled from now on.
Should be sampled at the next sampling position
The timing is decided. Therefore each coordinate
Can correct the scanning position error between
Inspection can be carried out.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a mounted printed circuit board inspection apparatus to which the present invention is applied.

FIG. 2 is a configuration diagram of a jitter correction unit in one embodiment of the inspection device for a mounted printed board according to the present invention;

FIG. 3 is a timing chart of the jitter correction unit.

FIG. 4 is a block diagram of the jitter correction unit.

[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 23 Tunnel mirror 24 Lens 25 Aperture 26 Photodiode 41, 46 Slit 42 Photoelectric conversion element (photodiode) 43, 48 I / V conversion circuit 44, 49 Comparator Lators 45 and 50 reference voltage 47 photoelectric conversion element (photodiode) 51 for detecting scanning start position 51 measuring unit

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuji Ono 2-2-110 Kotobukicho, Takamatsu-shi, Kagawa Prefecture Inside Matsushita Kotobuki Electronic Industry Co., Ltd. (72) Inventor Hidenori Nagata 2-2-2 Kotobukicho, Takamatsu-shi, Kagawa Prefecture No. 10 Matsushita Hisashi Electronics Co., Ltd. (56) References JP-A-4-352287 (JP, A) JP-A-1-200319 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB G01B 11/00-11/30 102 G01N 21/84-21/958 G02B 26/10 H05K 3/34 H05K 13/08

Claims (1)

(57) [Claims] A first light beam is deflected by using a polygon mirror to scan a printed circuit board to be inspected and to scan the first light beam according to each surface of the polygon mirror.
Obtained on the substrate by the first light beam
In the inspection apparatus for a mounted printed circuit board, which samples the reflected light from each irradiation position to obtain the surface shape of the board, the polygon mirror is irradiated with a second light beam, and the second light beam is irradiated onto the polygon mirror. A light projecting unit for condensing light, and a scanning line on which a second light beam from the light projecting unit deflected by the polygon mirror is condensed, and an electrical output is obtained for each surface of the polygon mirror. a photoelectric conversion means, by detecting the rotation time required between each surface of the polygon mirror from the output of the photoelectric conversion means, poly each surface
The rotational speed of the Gon mirror is detected, and the rotational speed of each surface
From the degree and the information indicating the next sampling position,
Timing of sampling at the position where sampling should be performed
Testing device loaded printed board, characterized in that a circuit means for generating a signal indicating the grayed.