JPH02132311A - Circuit pattern inspection instrument for printed wiring board - Google Patents

Abstract

PURPOSE:To remove the influence of unnecessary reflected light to be given upon a pattern detection signal by detecting retroreflected light through a spatial filter which has an annular light transmission area arranged at the periphery of a minute light shield area arranged in the center of an optical axis and a light shield area arranged at its periphery. CONSTITUTION:On the circuit pattern surface of the printed wiring board 13 which is formed by forming a circuit pattern having no light diffusibility on a surface having light diffusibility, a laser beam is scanned through a polygon 16, a scanning lens 17, and a mirror 18 and its retroreflected light is detected through the annular transmission type spatial filter 27. A direct reflected component contained in the retroreflected light is cut off by the minute light shield part 100 arranged in the center of the optical axis of the spatial filter 27 and unnecessary retroreflected light is cut off by the outside light shield area 102. Only a diffused light component is transmitted through the annular transmission area 101 to reach a photomultiplier 22, and the influence of the unnecessary retroreflected light to be given upon the pattern detection signal is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for inspecting circuit patterns of printed circuit boards and wiring boards.

As LSIs and other devices become faster and more highly integrated, printed wiring boards, which serve as motherboards on which electronic components are mounted, also become denser.
(even if there is a demand for smaller and thinner products).

Under such circumstances, circuits on printed wiring boards tend to become more complex. In order to improve the quality and reliability of printed wiring boards, it is necessary to inspect the circuit boards. The printed wiring board circuit pattern inspection apparatus according to the present invention is used for such purpose.

[Conventional technology]

FIG. 4 shows an example of a circuit pattern inspection device for a printed wiring board using a conventional laser beam scanning method.

In FIG. 4, a laser beam from a laser light source 14 has its beam diameter expanded by a beam expander 15, passes through a beam splitter 19, is scanned by a polygon (rotating polygon mirror) 16, and is scanned by a scanning lens 17 and a mirror. 1
The circuit pattern surface on the printed wiring board 13 placed on the mounting table 11 is irradiated via the beam 8 . This laser beam is focused into a spot 1 by a scanning lens 17,
It is reflected by the mirror 18 and scanned over the circuit pattern in the direction of the arrow shown.

The light reflected by the circuit pattern is returned to the beam splitter 9 by following the path of the mirror 18, the scanning lens 17, and the polygon 16, contrary to the path during scanning. A beam splitter 19 separates the reflected light components. This separated light is hereinafter referred to as retroreflected light R. The retroreflected light R is imaged by the reimaging lens 20. A spatial filter 21 is arranged on this re-imaging plane. This spatial filter 21 is for removing noise components included in the retroreflected light R, improving the S/N ratio, and improving inspection accuracy, and details will be described later. The retroreflected light R from which noise components have been removed is sent to the photomultiplier (photomultiplier tube) 2.
2, and its light intensity is detected.

Here, the function of the spatial filter 21 will be explained. FIG. 5 shows the intensity distribution of retroreflected light on the pattern surface and re-imaging surface of the print 1/wiring board 13.

In addition, in FIG. 5, for convenience of explanation, the polygon 16
Although a vibrating mirror 26 is used instead, its function is the same.

The retroreflected light R includes retroreflected light RA from the base member A on the printed wiring board 13, retroreflected light RB from the conductor side surface B constituting the circuit nozzle, retroreflected light from the upper surface C of the conductor, and light R. There are 03. Each of these retroreflected lights R - R
The light intensity A distribution on the reimaging surface of o is as follows: i, IB, Io. That is, the light intensity distribution IA of the retroreflected light RA has a broad mountain shape. This is because polyimide or epoxy resin is generally used as the base portion A of the printed wiring board 13, and these resins have high light diffusing properties. On the other hand, retroreflected light R.

■ Light intensity minute. becomes a narrow mountain shape centered on the leather spot 1 position.

This is because the upper surface C of the conductor is made of metal (copper foil), so the light diffusivity on the upper surface C of the conductor is extremely small, and the specular reflection component is the majority. Light intensity distribution I of retroreflected light R. Due to the deviation of the reflection direction, etc. B, the light intensity distribution ■4 and the light intensity distribution I. It has intermediate characteristics.

A showing such a light intensity distribution 1 , I , I
When the BC retroreflection light Rp, -Rc is detected by the photomultiplier 22, the detection signal level corresponding to the conductor upper surface C output from the photomultiplier 22 is high, and the detection signal level corresponding to the base material part A is high. (not shown). This is converted to 2 by the binarization circuit 23 (Fig. 4).
The light intensity distribution IA, 1, I
If signal processing is performed using BC as is, the following problems will occur.

That is, since the upper surface C of the conductor is made of copper foil, the surface may be oxidized. This oxidized portion becomes close to black, even if only partially, and the intensity level of the reflected light decreases, resulting in cases where it cannot be distinguished from the light intensity distribution IA.

This means a decrease in detection accuracy.

Therefore, in order to prevent such problems, on the re-imaging surface,
It is known to use a spatial filter 21 as shown in FIG. This spatial filter 21 is constructed by disposing a minute light shielding part 28 having a diameter d in a portion located at the center of the optical axis of the retroreflected light R in a transparent plate. Such a light shielding part 2
8, the retroreflected light R is blocked by an area corresponding to the diameter d. That is, as shown in FIG. 7(a), in the case of the retroreflected light RA, the light corresponding to the diameter d (shaded area) is blocked, but the retroreflected light RA itself is essentially a diffused light component. On the other hand, retroreflected light R. In this case, as shown in FIG. 7(b), most of the direct reflection components (shaded peak portion) included in the retroreflection light Rc are blocked. Therefore, the detection signal corresponding to the retroreflected light RA becomes a high level S, as shown in FIG.

The detection signal corresponding to is at a low level N. As a result, all the detection signals obtained are treated as diffused light only, so retroreflected light R. is no longer affected by direct reflection components. Therefore, even if there is an oxidized part on the upper surface C of the conductor and it turns black, there will be no detection error, and the S/N will be reduced.
ratio can be improved.

[Problem to be solved by the invention]

However, as described above, even if the spatial filter 21 having the minute light shielding part 28 at the center is used, the following problem still exists.

That is, as shown in FIG. 9, unnecessary reflected light RN is included as disturbance noise in retroreflected light R consisting of a diffused light component, and this unnecessary reflected light RN is used as retroreflected light RA, which should originally be used as a detection signal. It is superimposed on Ro and accurate detection is no longer possible.

This unnecessary reflected light RN is transmitted to the mirror 18, the scanning lens 17,
The optical system of the polygon 16, the beam splitter 19, and the re-imaging lens 20 (occurs due to multiple reflections in the mirror and surface reflection of the lens. These unnecessary reflected lights RN are generally retroreflected lights R, A is re-imaged at a position relatively far from the re-image-forming position of Ro. Therefore, the unnecessary reflected light RN is also
It passes through the spatial filter 21 and has an adverse effect on the pattern detection signal.

FIG. 10 shows an example where unnecessary reflected light RN is superimposed. If unnecessary reflected light RN is not mixed in, Fig. 8(a)
As shown in Figure 8(b), both the high level and the low level are at a constant level, but if unnecessary reflected light RN is mixed in, as shown in Figure 8(b).
The signal level increases as shown by the broken line, resulting in false detection.

Therefore, the present invention provides a printer I having a spatial filter that eliminates the influence of such unnecessary reflected light on the slam detection signal.
- The purpose is to provide a circuit pattern inspection device for wiring boards.

[Means to solve the problem]

In order to solve the above problems, the present invention provides a circuit pattern (C) having a non-light diffusing property on a substrate (A) having a light diffusing property.
) is formed on the circuit pattern surface of the printed wiring board (B) and detects the retroreflected light (R) through a spatial filter. In (27), a minute light-shielding region (100) is arranged at the center of the optical axis, a ring-shaped light-transmitting region (1.0 1 ) is arranged around it, and a light-shielding region (102) is arranged around it. Configure.

[Effect]

According to the present invention, the minute light shielding part (
100), the direct reflection component included in the retroreflection light (R) is blocked, and unnecessary retroreflection light (RN) is blocked by the outer light-shielding region (1.02). Therefore, only the diffused light component passes through the annular transmission region (1 0 1) and reaches the foI multiplier (22), which reduces the influence of unnecessary retroreflection light (RN) on the pattern detection signal. It can be prevented.

〔Example〕

Next, embodiments of the present invention will be described based on the drawings.

FIG. 2 shows an embodiment of the invention. 4 in Figure 2
The same reference numerals are given to parts that overlap with those in the figures, and detailed explanation thereof will be omitted.

In Fig. 2, the difference from Fig. 4 is that the spatial filter 2
7 configurations.

That is, the details of the spatial filter 27 are shown in FIG. As shown in FIG. 1, the spatial filter 27 has a minute light blocking region 100 with a diameter D1 arranged on the substrate at the center of the optical axis of the retroreflected light R, and an annular transmission region 101 with a diameter D2 arranged around it. Furthermore, an outer light shielding area 102 is formed around the outer periphery. In other words, an annular transparent portion is provided within a region that has a light-shielding property as a whole.

The minute light-shielding region 100 has a diameter D1 and has the same function as the light-shielding portion 28 shown in FIG. 6, and shields directly reflected components as shown in FIG. 7. On the other hand, the outer light shielding area 102 is exposed to unnecessary reflected light RN.
The unnecessary reflected light RN having a beam diameter larger than its inner diameter, that is, the outer diameter D of the annular transmission region 101, is removed. Therefore, the annular transmission region 101 allows only diffused light to pass through, and it is possible to improve the accuracy of circuit pattern inspection on the printed wiring board 13 using the diffused light detection method.

The size of the diameter D2 depends on the beam diameter of the unnecessary reflected light RN generated in the inspection device, and is a value that can be determined empirically or experimentally.

When manufacturing the spatial filter 27, as shown in FIG.
In the manner shown in the figure, a minute light-shielding region 100 and an outer light-shielding region 102 are formed by vapor deposition of a metal film or the like. As a second method, as shown in FIG. 3(b), a method such as hollowing out a metal foil to a predetermined size may be considered. Reference numeral 29 in FIG. 3(b) is a bridge that connects the minute light shielding area 100 and the outer light shielding area 102, and is for supporting the minute light shielding area 100.

〔Effect of the invention〕

As described above, according to the present invention, in a circuit pattern inspection apparatus for print 1 and wiring boards using a diffused light detection method, pattern detection is performed using unnecessary reflected light generated due to multiple reflections in the optical system, surface reflection, etc. 1 ] ] 2 The influence on the signal can be removed, and highly accurate inspection can be performed.

[Brief Description of the Drawings] Fig. 1 is a diagram explaining the principle of the present invention, Fig. 2 is a professional diagram of an embodiment of the present invention, Fig. 3 is a perspective view showing an example of a spatial filter, and Fig. 4 is a diagram illustrating the principle of the present invention. Figure 5 is an explanatory diagram of the intensity distribution of retroreflected light on the re-imaging surface, Figure 6 is a configuration diagram of the re-imaging system, and Figure 7 is a diagram of the conventional inspection device. Optical output characteristic diagram of the spatial filter for the retroreflected light from the material part and the retroreflected light from the upper surface of the conductor, Fig. 8 is an explanatory diagram of the pattern detection signal, Fig. 9 is a perspective view showing the problems of the conventional technology, Fig. 10 FIG. 2 is an explanatory diagram showing the influence of unnecessary reflected light on a pattern detection signal. 13... Printed wiring board A... Base part C... Conductor top surface R, R, R, Ro... Retroreflected light AB 22... Photo multiplier 27, 27a, 27b... Space Filter 100...Small light shielding area 101...Annular transmission area 102...Outer light shielding area

Claims (1)

[Claims] A printed wiring board (B) in which a circuit pattern (C) having non-light diffusing properties is formed on a substrate (A) having light diffusing properties.
In a circuit pattern inspection device for a printed wiring board that scans a laser beam on a circuit pattern surface and detects the retroreflected light (R) through a spatial filter, the spatial filter (27) has a slight light shield at the center of the optical axis. A region (100) is arranged, and an annular light transmitting region (100) is placed around it.
01) and a light shielding area (102) around it.
A circuit pattern inspection device for a printed wiring board, characterized in that it is configured by arranging the following.