JPH0980335A - Laser scanning optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser scanning optical system which can widen an inspection range by increasing angle of incidence and also shorten WD(working distance). SOLUTION: The laser beam emitted by a laser light source 1 is made to scan in two dimensions by galvanomirrors 2a and 2b, and imaged as a spot through a lens 3 to make a scan on a scanning surface 6. Wedge prisms 10a-10d which transmit and deflect the laser beam are arranged behind the lens 3. The galvanomirrors 2a and 2b are arranged nearby the front focus position of the lens 3 so as to form a telecentric optical system, so that a laser beam having a scanning angle at which the laser beam passes through the wedge prisms 10a-10d is made incident obliquely on the scanning surface and a laser beam having a scanning angle at which it does not pass through the wedge prisms 10a-10d is made incident perpendicularly on the scanning surface. The angle of refraction of the wedge prisms 10a-10d is large, so the inspection range can be widened by making the angle of incidence large and the WD(working distance) can be shortened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser scanning optical system, and more particularly to a laser scanning optical system capable of causing a laser beam from a laser light source to enter a scanning surface vertically or obliquely.

[0002]

2. Description of the Related Art Conventionally, such a laser scanning optical system has a structure as shown in FIG. 1, and a laser beam 1a emitted from a laser light source 1 has an axis extending in the vertical direction in FIG. The light is incident on the scanning unit 2 which is composed of a galvanometer mirror 2a that can swing about the center and a galvanometer mirror 2b that can swing about an axis perpendicular to the axis. The laser beam 1a is
The galvano mirrors 2a and 2b are swung to two-dimensionally scan, and the imaging lens 3 forms an image as a minute spot, and the object surface 6 is scanned. Behind the lens 3, a plane mirror 5 for reflecting and deflecting only a laser beam at a specific scanning angle is arranged, and the scanning means 2 (galvano mirrors 2a, 2b) forms a lens so as to form a telecentric optical system. Since it is placed near the front focus position of 3,
The laser beam having a scanning angle which does not reflect on the plane mirror 5 after passing through the lens 3 is incident on the surface 6 to be inspected, that is, the scanning plane from a vertical direction, passes through the lens 3, and is reflected on the plane mirror 5 after scanning. The laser beam in the position is reflected by the plane mirror 5 and is incident on the scanning surface at an angle θ from an oblique direction.

[0003]

Such a laser scanning optical system is used, for example, as an optical system of a soldering visual inspection apparatus. As shown in FIGS. 2A and 2B, the lead portions 7a and 8a of the chips 7 and 8 such as semiconductors are soldered onto the substrate which is the surface 6 to be inspected. Generally, the soldering parts 7b and 8b as shown in FIG.
Is in a good soldering state, while the soldering portions 7b and 8b in FIG. 2B are in a bad soldering state.

When this soldered portion is irradiated with a laser spot obtained by the above laser scanning optical system and scanned, the change in the direction of the reflected light is as shown by the arrows shown in FIGS. 3 (A) and 3 (B). . The reflected light from the defective soldering part as shown in FIG. 3 (B) has a different distribution as compared with the reflected light in the case of FIG. 3 (A). Therefore, a plurality of light receiving elements are arranged in the peripheral portion. The shape of the soldered appearance can be determined by detecting the change in the signal current from each light receiving element.

Generally, a lead portion 8a of a chip 8 such as a semiconductor, which is soldered on a substrate, extends vertically to the substrate and is soldered as shown in FIG. ), It may be bent and soldered inside the chip body. Particularly in the latter case, when the laser spot obtained by the laser scanning optical system is vertically incident, it becomes impossible to irradiate the solder spot 8b with the laser spot. There is a need to inspect by obliquely entering at an incident angle of 10 degrees.

In such a laser scanning optical system, since the incident angle at the time of scanning must be kept substantially constant, the object side is required to have telecentricity. Therefore, the scanning means (galvano mirror) is located in front of the lens 3. It is arranged near the focal position.

As described with reference to FIG. 4B, even if the lead portion 8a of the chip wraps inside and is soldered, it is necessary to increase the incident angle in order to perform a good inspection. is there. However, in the conventional laser scanning optical system shown in FIG. 1, since the plane mirror 5 is used,
If you try to widen the inspection range by increasing the incident angle, W
D (working distance) becomes long, and further, the plane mirror 5 becomes very large, and when WD becomes long, a lens 3 having a long focal length is required, and the entire apparatus becomes large and the cost becomes high. , There is a problem.

Therefore, an object of the present invention is to provide a laser scanning optical system capable of increasing the incident angle and widening the inspection range and shortening the WD (working distance) as compared with the conventional method. is there.

[0009]

In order to solve this problem, the present invention provides a laser light source, a lens for focusing a laser beam emitted from the laser light source on a minute laser spot, and the laser beam. Scanning means for two-dimensionally scanning at a predetermined scanning angle to scan a laser spot on a scanning surface perpendicular to the optical axis; and a wedge prism arranged behind the lens for transmitting and deflecting the laser beam passing through the lens. The scanning means is arranged in the vicinity of the front focal position of the lens so as to form a telecentric optical system, and the laser beam passing through the wedge prism at a scanning angle is oblique to the scanning surface, and the wedge prism is formed. A laser beam having a scanning angle that does not pass through is incident on the scanning surface perpendicularly.

In such a structure, since the deflection angle of the wedge prism is large, the incident angle can be increased to widen the inspection range and the WD (working distance) can be shortened. Further, since the wedge prism can be downsized and the WD is short, a lens having a long focal length is unnecessary, and the entire apparatus can be downsized.

A plurality of wedge prisms are arranged around the optical axis of the lens, for example, four wedge prisms are arranged at equal intervals. An optical element for compensating the optical path length, for example, an optical path length correcting glass is arranged between the wedge prism and the lens.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in the drawings. FIG. 5 shows an embodiment of the present invention, and the same parts as those shown in FIG. 1 are designated by the same reference numerals.

The parallel laser beam 1a emitted from the laser light source 1 oscillates around a galvano-mirror 2a which can swing about an axis extending in the vertical direction in FIG. 5A and an axis perpendicular to the axis. It is incident on the scanning means 2 which is composed of a movable galvanometer mirror 2b. The laser beam 1a is two-dimensionally scanned by the swing of the Galvano mirrors 2a and 2b, is imaged as a minute spot by the imaging lens 3, and scans the object surface 6. Behind the lens 3, wedge prisms 10a to 10d which transmit and deflect only a laser beam at a specific scanning angle are arranged.

Scanning means 2 (galvano mirrors 2a, 2b)
Is arranged near the front focus position of the lens 3 so as to form a telecentric optical system, whereby the laser beam emitted from the lens 3 is always parallel to the optical axis, and telecentricity is realized. The laser beam at a scanning angle that does not enter the wedge prisms 10a to 10d after passing through the lens 3 is incident on the object surface 6 placed perpendicular to the optical axis, that is, the scanning surface from the vertical direction. On the other hand, the laser beam at the scanning angle that has passed through the lens 3 and then enters the wedge prisms 10a to 10d is refracted and deflected by each wedge prism and obliquely enters the scanning surface at a predetermined angle.

When the scanning means 2 scans the central area defined by X'and Y'on the image plane (in this area, the laser beam is scanned at a scanning angle which does not enter the wedge prisms 10a to 10d), the surface of the object to be examined is scanned. 6 is two-dimensionally scanned by a laser beam which is incident perpendicularly on the surface of the object to be inspected and which is parallel to the optical axis. As shown in FIG. 4A, the lead portion 8a
In the case of the test object which is not bent inside the chip body 8, the soldering portion 8b is scanned and inspected by this scanning.

On the other hand, when the periphery of the central area is scanned by the scanning means 2 and the laser beam reaches the position where it is refracted and deflected by the wedge prism 4 after passing through the lens 3.
The laser beam is deflected by the wedge prisms 10a to 10d and is incident at a constant angle with respect to the optical axis, as shown in FIG.
The cross portion indicated by X and Y is scanned. When this portion is scanned, it is the scanning of obliquely incident light.
As shown in (B), the lead portion 8a is used to inspect the quality of the soldered portion 8b of the test object, which is bent inside the chip body.

If the lens 3 is an fθ lens in which the laser spot position changes in proportion to the incident angle, the spot position can be easily controlled.

Since the laser beam emitted from the lens 3 is telecentric, the central area (wedge prism 10a ...
The laser beam parallel to the optical axis for scanning (the position not incident on 10d) and the laser beam for scanning the peripheral area (the position for incident on the wedge prisms 10a to 10d) are deflected by the wedge prisms 10a to 10d. The laser beam having a constant angle with respect to the optical axis has a different optical path length from the lens 3 to the object surface 6 and a different laser spot focus position. The laser beam deflected by the wedge prisms 10a to 10d and having a certain angle with respect to the optical axis has a longer optical path length than the laser beam parallel to the optical axis for scanning the central area, and as a result, the laser spot focus position in the peripheral area. Is closer to the lens 3 side than the object surface. Therefore, the optical path length correction glass 11a to
11d is arranged at the position shown in FIG. 5, for example, and the beam spot positions are set at the same position.

In the example described above, four wedge prisms are arranged at equal intervals around the optical axis, but the number of wedge prisms is not limited to this example, and may be one, for example. It may be an individual. In that case, it goes without saying that the optical path length correction glass is also increased or decreased accordingly.

[0020]

As described above, according to the present invention, since the wedge prism capable of enlarging the deflection angle is used for deflecting the laser beam after passing through the image forming lens, the incident angle of incidence is increased. The angle can be increased to widen the inspection range, and the WD (working distance) can be shortened. Further, since the wedge prism is small and has a short WD, a lens having a long focal length is unnecessary, and the entire device can be downsized.

[Brief description of drawings]

FIG. 1A is a plan view showing a configuration of a conventional laser scanning optical system, and FIG. 1B is a side view thereof.

FIG. 2A is an explanatory view showing a good soldering part of a chip such as a semiconductor to be inspected by a laser scanning optical system,
(B) is an explanatory view in the case where the soldering part is defective.

FIG. 3A is an explanatory diagram showing a laser beam reflection state in the case of a good soldering portion, and FIG. 3B is an explanatory diagram showing a laser beam reflection state in the case of a defective soldering portion. is there.

FIG. 4A is an explanatory view of a state in which a lead portion of a chip such as a semiconductor to be inspected by a laser scanning optical system extends vertically, and FIG. It is explanatory drawing which showed the attached state.

5A is a plan view showing a configuration of a laser scanning optical system according to the present invention, FIG. 5B is a side view thereof, and FIG. 5C shows a scanning range by oblique incident light obtained by a wedge prism. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 laser light source 2 scanning means 3 imaging lens 6 object surface 10a to 10d wedge prisms 11a to 11d optical path length correction glass

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masao Shinno 13-35 Miyanari-cho, Gamagori-shi, Aichi Prefecture Kowa Stock Company Electric Optics Division Gamagori Factory

Claims (3)

[Claims] 1. A laser light source, a lens for forming an image of a laser beam emitted from the laser light source on a minute laser spot, and a two-dimensional scanning of the laser beam at a predetermined scanning angle to form an optical axis of the laser spot. And a wedge prism disposed behind the lens for transmitting and deflecting the laser beam passing through the lens. The scanning unit forms a telecentric optical system. A laser beam, which is arranged near the front focal point of the lens and has a scanning angle that passes through the wedge prism, is oblique to the scanning surface, and a laser beam that has a scanning angle that does not pass through the wedge prism is perpendicular to the scanning surface. A laser scanning optical system characterized in that 2. The laser scanning optical system according to claim 1, wherein a plurality of the wedge prisms are arranged around the optical axis of the lens. 3. An optical element for compensating an optical path length is arranged between the wedge prism and the lens.
Alternatively, the laser scanning optical system according to item 2.