JPH01210853A - Pattern height detector - Google Patents

Abstract

PURPOSE:To execute a correct height detection even if surface deflection exists on the surface of rotary multi-surface mirrors by providing a means for generating a slice level corresponding to the fluctuation quantity of a height signal corresponding to a surface inclination angle and a means for subtracting the slice level from the height signal at every reflecting surface of the rotary multi-surface mirrors of a detector. CONSTITUTION:Rotary multi-surface mirrors 2 have plural reflecting surfaces and form repeatedly an optical scanning lie on the surface of an inspection object 1 by a reflected light from each reflecting surface in accordance with its rotation. An image splitter 3 distributes a reflected light from this optical scanning line into two directions in accordance with height from the substrate surface of its reflecting position and outputs it. A height signal generating means 4 converts the intensity difference of this distributed light to an electric signal and outputs it as a signal for showing the height of a pattern. Subsequently, a slice level generating means 5 generates a slice level corresponding to the fluctuation quantity of the height signal corresponding to its surface inclination angle at every reflecting surface, and a subtracting means 6 subtracts this slice level from the height signal. In such a way, a height signal which has corrected an error based on the surface waving of the multi-surface mirrors 2 can be generated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an apparatus for inspecting wiring patterns, etc. of printed wiring boards, and particularly when there is a dent defect that lowers the height of the wiring pattern. The present invention relates to a pattern height detection device that can automatically detect defects.

When manufacturing printed wiring boards, it is necessary to inspect the wiring patterns for abnormalities. In particular, even if the width of the wiring pattern is normal, if there is a dent defect whose height is lower than the specified value,
The reliability of the entire system may deteriorate due to reasons such as an increase in the resistance value of the wiring, so it is necessary to perform an inspection.

It is desirable that an inspection device that targets such concave defects in wiring patterns be capable of correctly detecting the pattern height even if there is surface wobbling in the rotating polygon mirror that forms the structure of the device. .

[Conventional technology]

FIG. 6 shows an outline of a conventional detection optical system and a detection optical system to which the present invention is applied.

The light generated by the laser 1) is converted into parallel light through a beam expander 12, reflected on the surface of a rotating polygon mirror 13, converged through a scanning lens 14, reflected by a mirror 15, and set on a mounting table 16. A light scanning cotton 17A is formed on the inspection object 17, which reciprocates in a fixed direction for each reflecting surface in accordance with the rotation of the rotating polygon mirror 13. The reflected light from the optical scanning line 17A on the inspection object 17 passes through the pre-scanning line imaging lens 18, is converged from an oblique direction, and forms an image on the image splitter 19. The image splitter 19 has two reflective surfaces arranged with a triangular cross section, and the light reflected from each reflective surface is applied to the photomultipliers 20 and 21, respectively, and converted into an electrical signal to produce an output.

FIG. 7 explains the operation of the wiring pattern height detection optical system, and the same parts as in FIG. 6 are indicated by the same numbers.

In FIG. 7, when the beam spot is on the substrate surface of the inspection object 17, the reflected light in the oblique direction is reflected by the imaging lens 18.
When the image is formed on the image splitter 19 via the image splitter 19, it is divided equally by the two reflective surfaces of the image splitter 19 and input to the photomultiplier 20.21, and electrical signal outputs a and b of equal magnitude proportional to the optical input level are generated. occurs.

If there is a wiring pattern 22 at the position of the optical scanning line on the inspection target 17, the optical path of the reflected light in the diagonal direction changes based on the height difference from the substrate surface, and the light is divided by the image splitter 19. The ratio changes, so in the case shown, the output signal a of the photomultiplex 20 increases, but the output signal a of the photomultiplex 21 decreases, so by extracting the difference between the two outputs using, for example, a differential amplifier, An output signal proportional to the height of the wiring pattern 22 can be extracted.

The apparatus shown in FIG. 6 is configured so that the entire surface of the inspection object 17 can be inspected by moving the mounting table 16 in a direction perpendicular to the optical scanning line while performing such optical scanning.

[Problem to be solved by the invention]

In the conventional pattern height detection device shown in FIGS. 6 and 7, a rotating polygon mirror 13 is used to
An optical scanning line is formed above.

The rotating polygon mirror 13 has a large number of plane mirrors arranged on its surface to form a regular polygonal prism, and as the plane mirror rotates, each plane mirror sequentially moves in the same rotation, so that the reflected light forms an optical scanning line with the same trajectory. is configured to occur repeatedly.

However, if each reflective surface of the rotating polygon vi 13 is not parallel to its rotation axis and has surface wobbling, the position at which the light reflected by that surface forms an image on the image splitter 19 changes.

FIG. 8 shows detected light when there is surface wobbling on the rotating polygonal mirror surface 3. The same parts as in FIGS. 6 and 7 are designated by the same numbers, and 23 is a differential amplifier. Note that the objective lens 14 is omitted from the illustration.

In FIG. 8, if the optical path of the reflected light when there is no surface wobbling on the rotating polygon mirror 13 is represented by ■, the amount of light split by the image splitter 19 is equal, and therefore the photomultis 20 and 21 generate output signals of equal magnitude. . However, if there is surface wobbling in the rotating polygon mirror 13, the optical path of the reflected light changes, for example, as shown by ■, and the position of incidence on the inspection object 17 changes.

Therefore, the amount of light split by the image splitter I9 changes,
For example, as shown in FIG. 8, the number of light meters entering the photomulti 21 increases and its output signal increases, or conversely, the output signal of the photomulti 20 decreases and the output signal of the differential amplifier 23 becomes smaller. . Note that depending on the direction of the surface wobbling of the rotating polygon mirror 13, the output signal may increase.

If there is surface wobbling in the rotating polygon mirror 13 in this way, the magnitude of the output signal of the pattern height detection optical system changes, and therefore, in the apparatus shown in FIG. 6, the height of the wiring pattern existing on the board surface is Correct detection will not be possible.

The present invention aims to solve the problem of the conventional technology, and when detecting the height of a wiring pattern by forming an optical scanning line on the inspection target using a rotating polygon mirror,
It is an object of the present invention to provide a pattern height detection device capable of accurately detecting a required height even if there is surface wobbling on a rotating polygonal mirror surface.

[Means for Solving the Problems] FIG. 1 shows the basic configuration of the present invention, in which a rotating polygon mirror 2, an image splitter 3, and a height signal generating means 4 are provided for an inspection object 1. In the pattern height detection and sending system comprising: a slice level generating means 5; and a subtracting means 6; There is.

The rotating polygon mirror 2 has a plurality of reflective surfaces, and as the polygon mirror 2 rotates, optical scanning lines are repeatedly formed on the surface of the inspection object 1 using reflected light from each of the reflective surfaces.

The image splitter 3 divides the reflected light from this optical scanning line into two directions according to the height of the reflection position from the substrate surface and outputs the divided light.

The height signal generating means 4 converts the intensity difference of the distributed light into an electrical signal and outputs it as a signal indicating the height of the pattern.

The slice level generating means 5 generates a slice level corresponding to the variation amount of the height signal according to the inclination angle of each reflecting surface of the rotating polygon mirror 2.

The subtraction means 6 subtracts this slice level from the height signal.

[For production]

In the detection optical system shown in FIG. 6, the output of the differential amplifier 23 for determining the difference between the outputs of the two photomultipliers 20 and 21 is proportional to the angle of inclination of the surface of the rotating polygon mirror 13. Further, the wobbling angle of each reflecting surface in the rotating polygon mirror 13 is always constant.

Figure 2 illustrates the relationship between the tilt angle and the differential amplifier output, and shows that when there is no wiring pattern on the board, the differential amplifier output is proportional to the tilt angle of each reflective surface. ing.

FIG. 3 shows an example of surface wobbling in a rotating polygon mirror, and shows that the inclination of each reflecting surface corresponding to surface positions 1 to 10 changes sinusoidally as shown. Such a change in the tilt angle is likely to occur when the rotation axis is tilted at -1G with respect to the reflective surface.

Therefore, the differential amplifier output when there is no wiring pattern is determined for each surface of the rotating polygon mirror, corresponding to each surface tilt angle. When detecting the height of the wiring pattern, if you subtract the differential amplifier output corresponding to each reflection surface determined in advance from the output signal, the wiring pattern will be correct even if there is surface wobbling on the rotating polygon mirror. can perform height detection.

〔Example〕

FIG. 4 shows one embodiment of the present invention, and FIG.
The same parts as in FIGS. and FIG. 7 are designated by the same numbers,
24 is an encoder unit that indicates the surface position on the rotating polygon mirror 13; 25 is a sensor that reads the output of the encoder unit 24;
26 is a surface position detection section, 27 is a slice level generation section, 2
8 is a subtracter, and 2'9 is an analog-to-digital (A/D) converter that binarizes the output of the subtracter 28.

In FIG. 4, the light reflected by the reflective surface of the rotating polygon mirror 13 passes through the mirror 15 and forms an optical scanning line on the surface of the inspection object 17, and the reflected light is imaged on the image splitter 19 and split. and enters the photomultiplier 20°21. The differential amplifier 23 calculates the difference between the outputs of the photomultis 20 and 21 and generates an output signal indicating the height of the wiring pattern on the inspection object 17.

On the other hand, the rotating polygon mirror 13 is provided with an encoder section 24 for each surface, which generates a code indicating the position of each reflecting surface. The sensor 25 reads the output of the encoder section 24, and the surface position detection section 26 decodes the read code to detect the surface position. The slice level generator 27 has slice levels corresponding to each surface set in advance,
In response to a surface position signal from the surface position detection section 26, a slice level corresponding to that surface is generated.

FIG. 5 shows the relationship between the surface position and the slice level in the slice level generator 27, and the value of the slice level at each surface position is the relationship between the surface position and the inclination angle illustrated in FIG. The value is determined from the relationship between the tilt angle and the differential amplifier output shown in FIG.

The subtracter 28 subtracts the slice level value of the slice level generator 27 from the output value of the differential amplifier 23. The output of the production reducer 28 is an analog signal indicating the height of the wiring pattern, which compensates for output fluctuations due to surface runout of the rotating polygon mirror 13. The A/D converter 29 performs analog-to-digital conversion on this signal and generates a binary output indicating the height of the wiring pattern.

〔Effect of the invention〕

As explained above, according to the present invention, when detecting the height of a wiring pattern by forming an optical scanning line on an inspection target using a rotating polygon mirror, it is possible to accurately detect the height of a wiring pattern even if the rotating polygon mirror has surface wobbling. Height detection can be performed.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle configuration of the present invention, FIG. 2 is a diagram illustrating the relationship between the tilt angle and the differential amplifier output, FIG. 3 is a diagram illustrating surface wobbling in a rotating polygon mirror, FIG. 4 is a diagram showing an embodiment of the present invention. FIG. 5 is a diagram showing the relationship between surface position and slice level. FIG. 6 is a diagram showing an outline of a conventional detection optical system and a detection optical system to which the present invention is applied. , FIG. 7 is a diagram explaining the operation of the height detection optical system, and FIG. 8 is a diagram showing detection light when there is surface wobbling in the rotating polygon mirror. 1)...Laser 13...Rotating polygon mirror I5...Mirror 17...Inspection object 18...Previous scanning line imaging lens 19...Image splitter 20.21...Photomulti 23. ... Differential amplifier 26 ... Surface position detection section 27 ... Slice level generation section 28 ... Subtractor Patent applicant Fujitsu Co., Ltd. Agent Patent attorney Kugobe Tama (1 other person) Book Fig. 1 shows the principle structure of the invention. Fig. 1 shows the relationship between the rectangular angle and the output of the mirror. Fig. 3 shows an example of surface wobbling in a rotating polygon mirror. (l splitter 29・--Analog digital (AKE) KM; 20, 2+...-Photomultiple Figure 5 showing the relationship between the device surface position and the slice level showing an embodiment of the present invention.
Figure 18-- Inuzashi Sosho! 1lLr-nce° 20,2+
...Diagram showing an overview of the photomultiply detection optical system No. 6 Diagram showing the outline of the photomultiplier sensing optical system Figure 7 Figure 18 --- Yukiyi! fM imaging lens 19...
Figure 8 shows the detected light when there is redness and l on the rotating polygon mirror.

Claims (1)

[Claims] A rotating polygon mirror (2) that is provided with a plurality of reflective surfaces and repeatedly forms optical scanning lines on the surface of the inspection target (1) using reflected light from each reflective surface according to its rotation. and an image splitter (3) that distributes and outputs the reflected light from the optical scanning line in two directions according to the height of the reflection position from the substrate surface, and converts the intensity difference of the distributed light into an electrical signal. A pattern height detection device comprising: a height signal generating means (4) for converting and outputting as a signal indicating the height of the pattern; A slice level generating means (5) for generating a slice level corresponding to the variation amount of the height signal according to the angle; and a production reduction means (6) for subtracting the slice level from the height signal, A pattern height detection device characterized in that it generates a height signal corrected for errors due to surface wobbling of a rotating polygon mirror (2).