JPH11296657A - Image pickup optical system for image processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately pick up the image of a work in a distorted mirror surface shape. SOLUTION: The diffusion surface of a diffusion hemisphere 4 is irradiated with light emitted from a halogen lamp from the tips of optical fibers 3a and 3b and the inner wall of the diffusion hemisphere 4 is turned to a hemispherical reflection type diffusion surface. In such a manner, diffused indirect light is generated by the diffusion hemisphere 4 and the work 6 is irradiated with the diffused indirect light. Reflected light from the work 6 is passed through an observation window 14 provided on the hemisphere 4 and made incident on a camera 1. Since the diffused indirect light by the diffusion hemisphere 4 is made incident on the work 6 from various directions, the variously distorted surface of the work 6 is uniformly irradiated and the image of the work 6 is correctly picked up.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image processing apparatus such as a pattern inspection apparatus, and more particularly to an image pickup optical system for picking up an image of a work to be subjected to image processing.

[0002]

2. Description of the Related Art Conventionally, TCP (Tape Carrier Packa) has been used as a mounting technique suitable for a demand for increasing the number of pins of an IC or LSI.
ge) is known. TCP is TAB (Tape Automat
This is a film carrier type package that uses the technology of ed bonding). A copper foil pattern formed by etching on a polyimide film carrier (TAB tape) is bonded to the electrodes of the IC chip to form external leads. . FIG. 7 is a sectional view of the TCP. TCP is a film carrier 21, a copper foil pattern 22 formed on the film carrier 21, an IC chip 23, a bump 24 made of Au or the like formed on a pad of the chip 23, and a portion serving as an inner lead of the copper foil pattern 22. 25 for protecting the chip and the chip 23 from external force, moisture, contaminants, etc.
It is composed of

In TCP, defects such as short-circuit or chipping of the copper foil pattern 22 may occur during manufacturing. Conventionally, the presence or absence of these defects has been visually inspected manually. However, due to the increase in production volume and fine patterning due to high density, visual inspection has required a lot of human labor, and in recent years the demand for automation has been rapidly increasing, and the copper foil pattern of a film carrier has been imaged with a TV camera. Inspection technology has been proposed (see, for example,
341960).

[0004] Apart from such an inspection relating to the front surface of the TCP, as an inspection relating to the back surface of the TCP (the lower surface in FIG. 7), the shortage or protrusion of the resin 25 and the film carrier 21
Alternatively, it is necessary to inspect the adhesion of the resin 25 to the IC chip 23 (in FIG. 7, this means the adhesion to the film carrier 21 or the lower surface of the IC chip 23), the non-mounting of the IC chip 23, and the like. Therefore, it is desired to automate the inspection of the TCP back surface as well as the front surface, but this has the following problems.

FIG. 8 shows a back surface of the TCP. The white part at the center of the TCP is the IC chip 23, the black part around it is the resin 25, and the other gray parts are the film carrier 21. The back surface of the film carrier 21 has a smooth texture and very strong gloss. Furthermore, the film carrier 21 has distortion and undulation due to the effects of mounting the IC chip 23, applying the resin 25, and curing the resin 25. On the other hand, the resin 25 is semi-glossy when dried after passing through a baking oven, and the back surface of the IC chip 23 is not resin-coated and has a metallic luster.

As described above, the back surface of TCP must be considered as a kind of mirror surface due to its high gloss. Since mirror-like objects reflect the emitted visible light with high efficiency,
The observer is observing an image (visible light specularly reflected from the object) reflected on a mirror-like object. Therefore, the observation of a mirror-like object is based on the premise that an object that satisfies the observation conditions is projected on the object surface. When direct light is used for illumination in observing the TCP back surface, the specularly reflected direct light itself is observed depending on the observation position. When observation is performed while avoiding direct reflection of direct light, the amount of light applied to the TCP surface is extremely small, and satisfactory observation results cannot be obtained. For these reasons, an illumination method of directly irradiating light to the TCP back surface that causes specular reflection is not advisable.

As an effective illumination method for the TCP back side,
A method using diffuse indirect light is conceivable. FIG. 9 shows a block diagram of an imaging optical system of a conventional pattern inspection apparatus using a half mirror and a diffusion plate. In this inspection device, the light source 31
Is diffused by the diffusion plate 32 and the TCP 34 is irradiated with the diffused light by the half mirror 33. Then, the reflected light from the TCP 34 passes through the half mirror 33 and enters the camera 35. According to the illumination method as shown in FIG. 9, a pseudo-uniform surface light source can be created and illuminated as complete epi-illumination. Further, since diffused light is generated by the diffuser plate 32, the mirror-like object TC
This is very effective as illumination for the back surface of P34. This is because the diffused light obtained by the half mirror 33 is light having a single directivity, so that a flat mirror surface can be evenly irradiated with a light beam.

However, the rear surface of the TCP 34 is far from a flat mirror surface due to distortion and undulation, and has tilt components in various directions. Since the camera 35 has no direct relationship with the reflection component of the irradiation light on the inclined surface of the TCP 34, it is impossible to obtain a uniform illumination effect on the inclined portion by the half mirror 33. In this case, the camera 35 observes an object other than the illumination reflected on the inclined surface of the TCP 34. If the reflected object is black, the captured image also has a low luminance level in the reflected portion, which may cause erroneous detection. In order to avoid such a state, the light source for the TCP must be able to irradiate the inclined surface of the TCP evenly,
The conventional imaging method using a half mirror has no ability to respond to the inclination of TCP.

[0009]

As described above, the imaging optical system of the conventional inspection apparatus has a problem that a distorted mirror-like object such as TCP cannot be properly imaged and inspected. SUMMARY An advantage of some aspects of the invention is to provide an imaging optical system capable of correctly imaging a workpiece having a mirror surface and having a distortion.

[0010]

According to a first aspect of the present invention, there is provided a hemispherical diffusing surface disposed at a position facing the work so that reflected light is incident on the work. Diffusion hemisphere, annular illumination means for illuminating the diffusion surface of the diffusion hemisphere, and imaging of the work, which is arranged such that reflected light from the work enters through a window provided in the diffusion hemisphere. Camera. in this way,
When diffused indirect light is generated using a diffuse hemisphere and the work is illuminated with this diffuse indirect light, the diffused indirect light obtained by the diffuse hemisphere enters the work from various directions, causing distortion in the mirror-like work. Even if present, the variously distorted surfaces of the work can be evenly illuminated. Further, as described in claim 2, the annular illuminating means comprises a plurality of optical fibers arranged to receive light from the light source at one end and to have an end face on the emission side surrounding the ring.

According to a third aspect of the present invention, the camera is a line sensor camera disposed at a predetermined angle with respect to the workpiece, and the window of the diffuse hemisphere is provided at an angle of the camera. It is a slit-shaped window provided at a position off the vertex of the diffusion hemisphere accordingly. As described above, the camera is disposed at a predetermined angle with respect to the workpiece, and the window of the diffusion hemisphere is provided at a position deviated from the vertex of the diffusion hemisphere in accordance with the inclination of the camera. Can be prevented from being reflected in the image.

[0012]

FIG. 1 is a block diagram of an image pickup optical system of a pattern inspection apparatus according to a first embodiment of the present invention, and FIG. 2 is a plan view of the image pickup optical system of FIG. However, in FIG. 2, the line sensor camera is omitted. 1 is a line sensor camera, 2a is a light guide bundling a plurality of optical fibers 3a, 2b is a light guide bundling a plurality of optical fibers 3b, 4 is a diffusion hemisphere whose inner wall is a hemispherical diffusion surface,
Reference numeral 5 denotes a bracket that holds the light guides 2a and 2b, optical fibers 3a and 3b, and the diffusion hemisphere 4, and reference numeral 6 denotes a work (TCP in the present embodiment) whose observation surface is a mirror surface.

Next, the structure of the imaging optical system of such a pattern inspection apparatus will be described. Light emitted from a halogen lamp (not shown) serving as a light source is guided by a plurality of optical fibers 3a bundled by a light guide 2a. Similarly,
Light emitted from another halogen lamp (not shown) is guided by a plurality of optical fibers 3b bundled by a light guide 2b.

The emission sides of the light guides 2a and 2b are fixed by brackets 5. To form a space through which the illumination light to the work 6 and the reflected light from the work 6 pass, the bracket 5 is provided with a through hole penetrating the bracket 5 in the vertical direction. The diffusion hemisphere 4 has a reflection-type diffusion surface having a hemispherical inner wall. This diffusion surface is white non-glare (matte) in order to prevent generation of a regular reflection component of illumination.
Processing has been applied. Then, the diffusion hemisphere 4 is mounted in a through hole of the bracket 5 as shown in FIG.

Each of the optical fibers 3a fixed by the bracket 5 is arranged at random so that the end face on the emission side is exposed at a predetermined upward angle from the wall surface of the through hole and the end face surrounds the through hole. . The same applies to the optical fiber 3b. At this time, the optical fiber 3a and the optical fiber 3
b are arranged at a predetermined interval in the vertical direction, as shown in FIG.

Thus, the light emitted from the halogen lamp irradiates the diffusion surface of the diffusion hemisphere 4 from the tips of the optical fibers 3a and 3b. The oblique irradiation from a plurality of directions using the optical fibers 3a and 3b is performed so that the diffusion surface of the diffusion hemisphere 4 cannot be shaded. As described above, since the diffusion hemisphere 4 is illuminated from a plurality of directions and the spread angle of the light beam emitted from each optical fiber is large, the diffusion hemisphere 4
Is uniformly illuminated. By uniformly irradiating the light on the diffusion surface of the diffusion hemisphere 4, the light reflected from the diffusion surface becomes diffuse indirect light.

The indirect light generated by the diffusing hemisphere 4 is
In principle, from a plane parallel to the diffusion hemisphere 4 (parallel here means perpendicular to the center axis of the hemisphere 4 passing through the vertex and center of the diffusion hemisphere 4), It is possible to uniformly irradiate light on all surfaces inclined immediately before (parallel to the central axis). Therefore, it is possible to effectively irradiate light even to a distorted portion that cannot be illuminated by illumination using a conventional half mirror.

Although one set of the halogen lamp and the light guide may be provided, two sets are provided as in the present embodiment in order to secure a sufficient amount of light. At this time, even if there is a difference between the light amounts of the two halogen lamps,
Since each of a and 3b is randomly arranged so as to surround the ring (the through hole of the bracket 5), the diffusion surface of the diffusion hemisphere 4 can be uniformly illuminated.

On the other hand, in order to image the work 6 with the line sensor camera 1, it is necessary to obtain the reflected light from the work 6. However, since the diffuse hemisphere 4 itself is colored and opaque, the work 6 It is indispensable to provide a window 14 (hereinafter referred to as an observation window) for observing. Thereby, the reflected light from the work 6 enters the line sensor camera 1 through the observation window 14. The observation window 14 has a slit shape because the camera 1 is a line sensor camera.

At this time, if the observation window 14 is provided at the apex of the diffusion hemisphere 4, the observation window 14 is reflected on the work 6 because the observation surface of the work 6 is mirror-like, and there is a problem in performing an inspection. Become. Therefore, in order to exclude the observation window 14 from the observation field of view, the window 14 is shifted from the vertex of the diffusion hemisphere 4 to a position not to be reflected, and the capturing axis of the camera 1 is set at a position perpendicular to the workpiece 6. And an image of the work 6 is taken in at an appropriate angle. With this method, the phenomenon that the observation window 14 is reflected on the work 6 can be prevented.

Next, detailed calculations of the above-described imaging optical system will be described. First, a distance (hereinafter, referred to as a work distance) d between the work 6 and the line sensor camera 1 (more precisely, an image sensor of the camera 1) is determined by a focal length and resolution of a lens of the camera 1. Also,
The distance Wd between the edge of the diffusion hemisphere 4 and the work 6 and the radius r of the diffusion hemisphere 4 are determined by factors such as the resolution, the size of the observation area (inspection range) on the work 6, the distortion of the work 6, and the like.

The resolution and the observation area size are determined by the specifications, but the distortion of the work 6 is an uncertain factor.
Therefore, the distance Wd and the radius r are determined by limiting the distortion or the like of the work 6 to a realistic range and conducting an experiment to determine conditions for realizing an ideal illumination state as experimental values.

Subsequently, as shown in FIG. 3, the length of the imaging device 11 (for example, a CCD device) of the camera 1 in the x direction is represented by Wx
ccd, the length in the y direction is Wyccd, the length of the observation window 14 in the x direction is Wx, the length in the y direction is Wy, and the length of the observation area 15 on the workpiece 6 in the x direction is Wx.
Assuming that the length in the work and y directions is Wywork, the positional relationship among the image sensor 11, the observation window 14, and the observation area 15 is set as shown in FIG.

The y-direction and the z-direction are as shown in FIG. 1, but the x-direction means a direction perpendicular to the plane of FIG. Then, from the positional relationship of FIG. 4, the sizes Wx and W of the observation window 14 provided in the diffusion hemisphere 4 are shown.
y can be determined by the following equation.

Wx = Wxwork − {(Wxwork−Wxccd) × (Wd + r) / d} (1) Wy = Wywork − {(Wywork−Wyccd) × (Wd + r) / d} (2)

When the line sensor camera 1 is tilted as described above, it is unavoidable that a slight distortion occurs in the captured image, and therefore it is necessary to minimize the tilt of the camera 1. In addition, the direction in which the camera 1 is tilted is set to the short y direction in order to minimize distortion. Next, the position of the observation window 14 and the inclination angle θ of the line sensor camera 1
The calculation of No. 3 will be described. FIG. 5 is a diagram for explaining this calculation method.

In FIG. 5, an angle θ1 between a straight line connecting the edge E of the observation area 15 projected onto the diffusion hemisphere 4 and the center O of the diffusion hemisphere 4 and a perpendicular to the work 6 can be obtained by the following equation. . θ1 = arcsin {Wywork / (2 × r)} (3) When an observation window 14 is provided at the vertex P of the diffusion hemisphere 4 and an image is taken in from a position perpendicular to the work 6, The observation window 14 is reflected at the position of K1.

On the other hand, the observation area 1 on the work 6
In the case where the observation window 14 is set at a position not reflected in 5, the circumferential distance ds1 from the vertex P of the diffusion hemisphere 4 to the center Q of the observation window 14 can be obtained by the following equation. ds1 = (θ1 / 180) × π × r + (1/2) × Wy (4)

Therefore, the observation window 14 has a size of Wx in the x direction and Wy in the y direction, centered on the position Q shifted from the vertex P of the diffusion hemisphere 4 by the circumferential distance ds1. Further, an angle θ2 between a straight line connecting the center O of the diffusion hemisphere 4 and the center Q of the observation window 14 and the perpendicular line of the workpiece 6 is obtained by the following equation using the distance ds1. θ2 = {180 / (π × r)} × ds1 (5)

Therefore, the angle between the straight line connecting the center of the observation area 15 and the center Q of the observation window 14 and the perpendicular of the work 6, that is, the inclination angle θ3 of the line sensor camera 1
Can be calculated by the following equation. θ3 = arctan {r × sin θ2 / (r × cos θ2 + Wd)} (6)

By the above calculation, the position on the work 6 where the observation window 14 is reflected can be moved to K2,
The image of the observation area 15 where the observation window 14 is not reflected can be captured by the line sensor camera 1. Next, when the camera 1 is simply tilted by only the angle θ3 and moved to a position where the observation area 15 is taken in, the distance between the work 6 and the image sensor 11 becomes longer than the work distance d. Since the work distance d is a value determined by the resolution, it must be constant regardless of the tilt of the camera 1.

Therefore, in order to maintain the work distance d, the shift amount dy in the y direction and the shift amount dz in the z direction of the camera 1 are calculated by the following equations. dy = d × sin θ3 (7) dz = d × (1-cos θ3) (8)

Thus, as shown in FIG.
1 (camera 1) is tilted by θ3, and dy and z are
By shifting by dz in the direction, it is possible to capture an image without reflection of the observation window 14 without changing the resolution.

When the camera 1 is tilted to capture an image, the captured image is distorted as described above. FIG. 6 is a diagram for explaining a method of correcting the distortion of the captured image. FIG.
As shown in the figure, when the camera 1 is tilted by θ3 with the work distance d unchanged, the observation area 1 on the work 6
Resolution PIXP of one pixel at edges P1 and P2 of 5
1, PIXP2 is calculated as follows.

PIXP1 = PIXorg × (d−δd) / d (9) PIXP2 = PIXorg × (d + δd) / d (10) In equations (9) and (10), PIXorg is a standard resolution. , Δd = (Wy × sin θ3) / 2. In this way, based on the equations (9) and (10), the resolution of the captured image is corrected and the actual inspection is performed.

In an actual inspection, a grayscale image of the work 6 captured by the line sensor camera 1 is not shown in A / A.
The work 6 can be inspected by digitizing with a D conversion circuit, binarizing the digital image data with a binarization circuit (not shown), and comparing the binarized pattern with, for example, a master pattern serving as a reference. If the entire inspection range of the work 6 cannot be imaged by one scan, the line sensor camera 1 and the bracket 5 (diffusion hemisphere 4) are moved, or the table (not shown) on which the work 6 is placed is moved. Needless to say, it should be done.

On the back surface of the TCP, there are a portion where strong reflection such as an IC chip and a film carrier occurs and a portion where weak reflection such as a resin occurs. However, such a TCP
When the back surface is taken in by a conventional imaging optical system, a sufficient difference in brightness (contrast) between the film carrier and the resin cannot be obtained. The reason why contrast cannot be obtained is that, due to the structure of the half mirror, the color of the indirect light diffused by the milky white acrylic plate slightly changes from white, so that when reflected on TCP, the brightness level of the film carrier can be sufficiently increased. It cannot be raised.

Further, since the TCP generates distortion under the influence of heat received in the baking furnace and has various angles on the film surface, the unidirectional light beam emitted from the half mirror cannot correspond to the angle of the film surface. As a result, shadows occur on the film carrier. Therefore, it is very difficult for the conventional imaging optical system to detect the shortage or protrusion of the resin and the adhesion of the resin on the film carrier.

On the other hand, when the back surface of the TCP is taken in by the image pickup optical system of the present invention, a sufficient difference in luminance between the film carrier and the resin is obtained, and no shadow is generated on the film carrier. This is due to the TC
This is because it has become possible to irradiate diffused light to the film surface inclined by the distortion of P.

As described above, according to the imaging optical system of the present invention,
Since the density can be appropriately captured, the value between the density of the IC chip or film carrier and the density of the resin is set as a threshold for binarization, and the captured image data is binarized. For example, a binary pattern in which the IC chip or the film carrier becomes “1” and the resin becomes “0” is obtained.

At this time, if the resin adheres to the IC chip or the film carrier, the portion of the chip or the film carrier which should be "1" becomes "0". Therefore, if the binarized pattern is compared with the master pattern, the adhesion of the resin can be easily detected. vice versa,
If the resin is insufficient, the portion that should originally be “0” becomes “1”. Thereby, shortage of resin can be easily detected.

Similarly, when the IC chip is not mounted, the portion of the chip which should be "1" is "0". This makes it possible to easily detect that the IC chip is not mounted. As described above, whether or not the work 6 is normal can be inspected.

In the TCP, a hole is formed in the film carrier, and only the reflection illumination (illumination illuminated from the observation side) by the diffusion hemisphere 4 is taken in with the hole portion blackened out. As a result, the brightness level becomes the same as the resin,
This may cause erroneous detection. Such a problem can be prevented beforehand by setting the hole portion to the brightness level of the film.

Therefore, for the work 6 having a hole such as the back surface of the TCP, the observation surface is opposite (that is, FIG.
Illuminate the surface light source from below) and set the brightness level at the hole to the level of the film. By configuring such illumination, it is possible to obtain a stable image for performing an inspection. Further, in the present embodiment, the rear surface of the TCP is imaged, but it goes without saying that the present invention may be applied to other objects.

[0045]

According to the present invention, as described in claim 1, diffused indirect light is generated using a diffuse hemisphere, and the work is illuminated with the diffused indirect light. Even if there is distortion, the variously distorted surfaces of the work can be evenly illuminated, and the distorted work can be correctly imaged. As a result, if the captured image is used for an inspection device that inspects a work, the work can be correctly inspected.

Further, the light from the light source is received at one end, and the annular illuminating means is constituted by a plurality of optical fibers arranged so that the end face on the emission side surrounds the ring, thereby uniformly illuminating the diffusion hemisphere. it can.

According to a third aspect of the present invention, the camera is disposed at a predetermined angle with respect to the workpiece, and the window of the diffusion hemisphere is located at a position deviated from the vertex of the diffusion hemisphere in accordance with the inclination of the camera. With this arrangement, it is possible to prevent the window of the diffuse hemisphere from being reflected on the work in the observation area of the camera.

[Brief description of the drawings]

FIG. 1 is a block diagram of an imaging optical system of a pattern inspection apparatus according to a first embodiment of the present invention.

FIG. 2 is a plan view of the imaging optical system of FIG.

FIG. 3 is a diagram illustrating the size of an image sensor, an observation window, and an observation area of a line sensor camera.

FIG. 4 is a diagram illustrating a positional relationship among an image sensor, an observation window, and an observation area.

FIG. 5 is a diagram for explaining a method of calculating a position of an observation window and a tilt angle of a line sensor camera.

FIG. 6 is a diagram for explaining a method of correcting a distortion of a captured image.

FIG. 7 is a sectional view of a TCP.

FIG. 8 is a bottom view of the TCP.

FIG. 9 is a block diagram of an imaging optical system of a conventional pattern inspection apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Line sensor camera, 2a, 2b ... Light guide, 3
Reference numerals a, 3b: optical fiber, 4: diffusion hemisphere, 5: bracket, 6: work, 11: imaging element, 14: observation window, 15: observation area.

Claims (3)

[Claims] 1. A diffusion hemisphere having a hemispherical diffusion surface, which is disposed at a position facing the work so that reflected light is incident on the work, and an annular illumination for illuminating the diffusion surface of the diffusion hemisphere. And an imaging optical system for an image processing apparatus, comprising: a camera for imaging the work, the camera being arranged such that reflected light from the work enters through a window provided in the diffusion hemisphere. . 2. The imaging optical system according to claim 1, wherein the annular illuminating means receives a light from a light source at one end, and has a plurality of emission surfaces arranged so that an end surface on an emission side surrounds the ring. An imaging optical system for an image processing device, comprising an optical fiber. 3. The imaging optical system of the image processing apparatus according to claim 1, wherein the camera is a line sensor camera arranged at a predetermined angle with respect to a workpiece, and the window of the diffusion hemisphere is An imaging optical system for an image processing apparatus, comprising a slit-shaped window provided at a position deviated from a vertex of a diffusion hemisphere in accordance with an inclination of the camera.