JPH0495859A - Optically inspecting apparatus for printed board - Google Patents

Abstract

PURPOSE:To enable inspection without being influenced by discoloration accompanied by a drop in intensity of regular reflection light even if a surface of a copper foil is blackened by measuring scattered light of a laser beam applied to a printed board and obtaining an intensity distribution in a direction of a radius. CONSTITUTION:A laser beam emitted from a laser source 1 is applied from a collimator lens 2 via a polygon mirror 3 and a collimator lens 4 to a printed board 5, and a part of the laser beam which has been reflected or scattered is returned to its approaching route. The applied light and the reflected/scattered light which is returning are separated from each other by using a half mirror 6 so that the reflected/scattered light forms an image of an intensity distribution by the laser beam applied on the board 5 on a diffraction light measuring photo multiplier 9 via an image forming lens 7. The photo multiplier 9 measures the light intensity of the scattered light which has passed through a small mask 8 and sends it to an arithmetic processor 10, which calculates an estimation value corresponding to an intensity distribution in a direction of a radius. By determining whether a fine pattern 51 is good or not from the characteristics of the above calculation, an inspection not influenced by discoloration of a copper foil is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a printed board optical inspection device, and more particularly to a printed board optical inspection device that inspects the quality of minute patterns arranged on a printed board by scanning a laser beam.

[Conventional technology]

Conventionally, this type of printed board optical inspection equipment receives a combination of reflected light and scattered light from a laser beam irradiated onto a printed board.
By measuring the light intensity, fine patterns were inspected based on the difference in reflection between the fine patterns and the printed circuit board.

There is also a method that uses only the scanning laser beam and specularly reflected light that returns in the reverse optical path. Note that these are detailed in, for example, [Needs and Seeds of Optical Measurement J, P301-305, Corona Publishing, etc.

[Problem to be solved by the invention]

The conventional printed board optical inspection apparatus described above captures both the reflected light and scattered light of the laser irradiated onto the printed board, and performs inspection based on the light intensity.

However, when a laser spot is irradiated onto a copper foil that forms a fine pattern, the reflected light intensity is strong but the scattered light intensity is weak; conversely, when the laser spot is irradiated onto a printed circuit board, the reflected light intensity is weak but scattered. The light intensity is strong. For this reason, when simply measuring without distinguishing between reflected light and scattered light, the difference between when the irradiated laser spot is irradiated on the copper foil and when it is irradiated on the substrate is small (measurement with a good S/N ratio). The disadvantage is that it is difficult to

Furthermore, the method of receiving only specularly reflected light has the drawback that when the surface becomes black, a sufficient amount of the reflected light returns and erroneous detection is unavoidable.

[Means to solve the problem]

The device of the present invention is a printed board optical inspection device that inspects the quality of minute patterns arranged on a printed board, and the device emits a laser beam that irradiates the printed board to be inspected and scans the printed board. a scanning means, and an image of the reflected light from the printed board obtained by the laser beam scanning means, and an evaluation value expressing the intensity distribution in the radial direction of this image, or a spatial differential value of this evaluation value, to form an image of the minute pattern. and a quality determination means for determining quality.

〔Example〕 Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention. The embodiment shown in FIG.
, a collimator lens 2, a polygon mirror 3, a collimator lens 4, and a half mirror 6 constituting a quality determining means.
, an imaging lens 7, a small mask 8, a diffracted light measurement 7 otomaru 9, and an arithmetic processing unit 10, and FIG.
A printed circuit board 5 and a micro pattern 51 disposed on the printed circuit board 5 are also shown.

Laser light emitted from a laser light source 1 is narrowed down by a collimator lens 2, vertically scanned by a polygon mirror 3, which is a rotating polygon mirror, and a collimator lens 4, and illuminates a printed circuit board 5.

The laser beam hitting the printed circuit board 5 is reflected or scattered, and part of it passes through the collimator lens 4 and the polygon mirror 3 and travels backward on the outgoing optical path. The irradiated light and the reflected/scattered light that travels in the opposite direction to the irradiated light are separated using a half mirror 6, and the reflected/scattered light is printed on the photomultiplier 9 for diffracted light measurement via the printed circuit board 5 and the imaging lens 7. An image of the intensity distribution of the laser beam irradiated onto the substrate 3 is formed. Also,
When the specularly reflected light intensity is strong, in order to protect the diffracted light measurement photomultiple 9, a small mask 8 configured to block only the specularly reflected light and allow only the scattered light to pass is used.

The photomultiplier 9 for diffracted light measurement has light receiving elements arranged concentrically, and the light intensity of the incident reflected and scattered light, or in the case of FIG. 1, the scattered light passing through the small mask 8, is distributed concentrically. The measurement is performed for each light-receiving element, and the combination is sent to the arithmetic processing section 10.

The arithmetic processing unit 10 generates the radial intensity distribution data of the scattered light obtained by the photomultiplier 9 for diffracted light measurement as an evaluation value.

The intensity of reflected and scattered light irradiated onto the photomultiplex 9 for diffracted light measurement is shown in FIGS. 2 and 3, centering on the position of specularly reflected light.

When the laser beam is irradiated onto the copper foil 51 on the printed board,
As shown in FIG. 2(a), the light intensity is concentrated at the specularly reflected light position in the center. In addition, when the specularly reflected light is blocked by the small mask 10, the intensity becomes weak and the distribution becomes a narrow signal as shown in FIG. 2(b).

Furthermore, when the printed circuit board 5 is irradiated with laser light, the third
As shown in Figure (a), the specularly reflected light is weak and the light is widely distributed as scattered light. This tendency is seen in Figure 3 (b) when wearing a mask.
) but the same is true.

The arithmetic processing unit 10 obtains evaluation values corresponding to the radial intensity distribution output from the photomultiplier 9 for diffracted light measurement, learns the state of the laser beam irradiated area from the features of these evaluation values, and determines the quality of the minute pattern. .

In the above embodiment, an evaluation value expressing the radial intensity distribution of the image formed by the imaging lens 7 was obtained, and the quality of the fine pattern was determined based on this evaluation value. However, this evaluation value may be used as is. Instead, it would be easy to take the spatial differential value of the evaluation value and use the difference in the degree of spatial change in the evaluation value, which expresses the strength distribution of the copper foil and the printed circuit board, as an evaluation measure. it is obvious.

〔Effect of the invention〕

As explained above, the present invention measures the scattered light of the laser beam irradiated onto the printed board and determines the radial intensity distribution, thereby detecting a decrease in the intensity of specularly reflected light when inspecting minute patterns on the printed board. This method has the advantage that it is not affected by the accompanying discoloration of the silver foil and can be inspected even if the surface of the copper foil turns black.

-n.

Claims (1)

[Claims] A printed board optical inspection device for inspecting the quality of minute patterns arranged on a printed board, the device comprising: a laser beam scanning means for emitting a laser beam to irradiate the printed board to be inspected and scanning the printed board; and the laser beam A pass/fail judgment for forming an image of the reflected light from the printed board obtained by the optical scanning means and judging whether the minute pattern is good or bad based on an evaluation value expressing the intensity distribution in the radial direction of this image or a spatial differential value of this evaluation value. A printed board optical inspection device comprising: means.