Lens, optical system, imaging device, and inspection device

Abstract

This lens (43), which condenses light such that the light is incident on a target (14) on a first axis (21) at a prescribed incidence angle θ, comprises: an entry surface (61) through which light enters; a reflection surface (62) which reflects light that has entered; and an exit surface (63) which outputs light that has been reflected by the reflection surface (62). At least one of the entry surface (61), the reflection surface (62), and the exit surface (63) is provided with a shape that condenses light which spreads in the circumferential direction of a circle centered on the first axis (21). The reflection surface (62) is provided with a shape that condenses light which spreads in the radial direction of the circle.

Description

Lens, optical system, imaging device and inspection device

[0001] The present disclosure relates to lenses, optical systems, imaging devices, and inspection devices.

[0002] An illumination device disclosed in Patent Document 1 is an illumination device for dark-field observation for observing scattered light.

[0003] The illumination device shown in Patent Document 1, particularly in Figures 1 and 3, is disposed facing the illumination target and includes a substrate 16 with a central hole 16a. An illuminator is provided on the substrate 16, which includes light-emitting element arrays 15a-15c each consisting of a plurality of LED lamps 14aa-14ch arranged in a ring shape around the hole 16. Furthermore, the illumination device is also provided with illumination control means for selectively controlling each LED lamp to emit a desired light. This configuration is said to enable precise setting of the illumination conditions of the illuminator according to the target being observed.

[0004] Japanese Patent Application Publication No. 4-241476

[0005] Consider using the device described in Patent Document 1 to image a multilayer board having two types of reflective surfaces with different diffusion characteristics. To capture images with clear contrast for high-precision inspection, scattered light from the two different reflective surfaces is captured. The amount of scattered light depends on the diffusion characteristics of each reflective surface and the angle of incidence of the light. Therefore, when imaging a multilayer board, there is an angle of incidence at which contrast is maximized. Therefore, to capture images with high contrast, it is desirable for the LED lamp to irradiate the multilayer board with light at an optimal angle of incidence.

[0006] However, when the optimal incident angle is large, selecting only the LED lamp with the optimal illumination angle will reduce the amount of light irradiated onto the target, resulting in a darker image and poor visibility.

[0007] In addition, LED lamps generally have insufficient brightness, and the number that can be installed in a device is limited. As a result, in order to capture bright images, it is necessary to use LED lamps with illumination angles that are not optimal from the perspective of contrast, which reduces the contrast of the captured image.

[0008] As such, it is difficult to achieve both high contrast and brightness in a captured image.

[0009] The present disclosure provides a lens, an optical system, an imaging device, and an inspection device that achieve both high contrast and brightness when inspecting, imaging, or otherwise inspecting an object.

[0010] The lens of the present disclosure, which focuses light so that it is incident on an object on a first axis at a predetermined angle of incidence θ, includes an incident surface onto which the light is incident, a reflecting surface that reflects the incident light, and an exit surface that emits the light reflected by the reflecting surface. At least one of the incident surface, reflecting surface, and exit surface has a shape that focuses light that diffuses in the circumferential direction of a circle centered on the first axis. The reflecting surface has a shape that focuses light that diffuses in the radial direction of the circle.

[0011] The optical system of the present disclosure includes a lens of the present disclosure and a plurality of light emitting elements arranged around a first axis, the light emitting elements emitting light onto an entrance surface of the lens.

[0012] The imaging device according to the present disclosure includes the optical system according to the present disclosure, and an objective lens, an imaging lens, and an imaging element arranged on a first axis in this order from the object side. The lens causes light emitted from the light-emitting element to be incident on the object at an incident angle θ and collects the light. The objective lens, the imaging lens, and the imaging element are used to capture an image of the diffusely reflected light scattered by the object.

[0013] The inspection device of the present disclosure includes the imaging device of the present disclosure, a control device that controls the imaging device, and a display device that displays an image captured by the imaging device.

[0014] Another imaging device disclosed herein includes a plurality of light-emitting elements arranged around a first axis, a plurality of transmission lenses respectively arranged between the plurality of light-emitting elements and an object on the first axis, and an objective lens, an imaging lens, and an imaging element arranged on the first axis in this order from the object side. The light-emitting elements are arranged so that their optical axes form a predetermined angle of incidence θ with respect to the object. The transmission lens focuses light emitted from the light-emitting elements onto the object. The objective lens, the imaging lens, and the imaging element are used to capture an image of diffuse reflected light scattered by the object.

[0015] Another imaging device of the present disclosure includes a plurality of light-emitting elements arranged around a first axis, a mirror whose reflective surface is a surface shaped like a portion of an ellipse rotated around the first axis, and an objective lens, an imaging lens, and an imaging element arranged in this order from the target side on the first axis. The mirror reflects light emitted from the light-emitting elements, causing it to be incident on the target at a predetermined angle of incidence θ and focusing the light. The objective lens, the imaging lens, and the imaging element are used to capture an image of the diffuse reflected light scattered by the target.

[0016] The lens, optical system, imaging device, and inspection device of the present disclosure can achieve both high contrast and brightness when inspecting, imaging, etc. an object.

[0017] FIG. 1 is a front view schematically illustrating an exemplary imaging device according to a first embodiment of the present disclosure. FIG. 2 is a plan view schematically illustrating an LED and a lens in the imaging device of FIG. 1. FIG. 3 is a diagram schematically illustrating a cross section of a multilayer substrate as an object to be imaged and inspected, and the resulting reflection of light. FIG. 4 is a diagram illustrating the reflection characteristics of an electrode portion and a background portion of the multilayer substrate. FIG. 5 is a diagram illustrating the relationship between the angle of incidence and the amount of vertically diffused light in the electrode portion and the background portion of the multilayer substrate. FIG. 6 is a diagram illustrating the relationship between the angle of incidence and contrast in a multilayer substrate. FIG. 7 is a front view schematically illustrating an imaging device according to a modified example of the first embodiment. FIG. 8 is a front view schematically illustrating an exemplary imaging device according to a second embodiment of the present disclosure. FIG. 9 is a front view schematically illustrating an LED and a lens in the imaging device of FIG. 8. FIG. 10 is a plan view schematically illustrating the LED and a lens in the imaging device of FIG. 8. FIG. 11 is a cross-sectional view schematically illustrating the LED and a lens in the imaging device of FIG. 8. FIG. 12 is a diagram illustrating a simulation configuration of an illumination system in an imaging device of a comparative example. FIG. 13 is a plan view schematically showing a multilayer substrate to be imaged. FIG. 14 is a diagram showing the configuration of an inspection apparatus including the imaging device of the present disclosure. FIG. 15 is a flowchart showing the operation of the inspection apparatus of the present disclosure. FIG. 16 is a front view schematically showing an imaging device of Modified Example 1 of the second embodiment. FIG. 17 is a plan view schematically showing an LED and a mirror in the imaging device of FIG. 16. FIG. 18 is a plan view schematically showing an LED and a lens in Modified Example 2 of the second embodiment. FIG. 18 is a cross-sectional view schematically showing an LED and a lens in Modified Example 3 of the second embodiment. FIG. 20 is a front view schematically showing an imaging device of Modified Example 4 of the second embodiment. FIG. 21 is a front view schematically showing an LED and a lens in Modified Example 5 of the second embodiment. FIG. 21 is a cross-sectional view schematically showing an LED and a lens in Modified Example 5 of the second embodiment. FIG. 23 is a front view schematically showing an LED and a lens in Modified Example 6 of the second embodiment. FIG. 24 is a cross-sectional view schematically showing an LED and a lens according to the sixth modification of the second embodiment.

[0018] Hereinafter, embodiments will be described with reference to the drawings. In each drawing, the same components are denoted by the same reference numerals, and the description thereof may be omitted.

[0019] First Embodiment FIG. 1 is a front view schematically illustrating an exemplary imaging device 100 according to a first embodiment of the present disclosure. The imaging device 100 captures an image of a multilayer substrate 14, which is an image target, using an objective lens 15, an imaging lens 16, and an imaging element 17. The multilayer substrate 14, the objective lens 15, the imaging lens 16, and the imaging element 17 are arranged in this order on a first axis 21. Note that the X, Y, and Z directions (axes) that are orthogonal to each other are shown in the figure. In FIG. 1, the side parallel to the first axis 21 and facing the imaging element 17 from the multilayer substrate 14 (vertically upward in the figure) is the positive side of the Z axis. The right side of the X axis is the positive side in the figure, and the back side of the Z axis is the positive side perpendicular to the plane of the paper in the figure. The X, Y, and Z directions are also shown in FIG. 2 and subsequent figures.

[0020] In addition, a plurality of bullet-shaped LEDs 11 and a plurality of transmission lenses 13 are provided, each disposed between the bullet-shaped LEDs 11 and the multilayer substrate 14, and these are used to illuminate the multilayer substrate 14 when capturing an image.

[0021] High contrast and brightness can be achieved simultaneously when an object (e.g., the multilayer substrate 14) is imaged using the imaging device 100. To explain this, it will be explained with reference to Figures 3 to 6 that contrast is improved when light is incident at an appropriate angle of incidence when imaging the multilayer substrate 14.

[0022] 3 shows a cross-sectional view of the multilayer substrate 14. The multilayer substrate 14 has two or more reflective surfaces with different diffusion characteristics, and is assumed to have an electrode portion 31 and a background portion 32 in this example.

[0023] FIG. 4A schematically shows the reflection and diffusion characteristics of light when light 33 is incident on the electrode unit 31. In the electrode unit 31, light 33 tends to be diffused in various directions. Therefore, the amount of light 34a diffused in the vertical direction, as well as the reflected light 35a in the specular reflection direction, is relatively large. FIG. 5A shows the relationship between the incident angle θ and the vertically diffused light 34a in this case. In the case of the electrode unit 31, the amount of vertically diffused light 34a is proportional to the amount of incident light, so it decreases linearly as the incident angle θ increases.

[0024] In contrast, FIG. 4B schematically shows the reflection / diffusion characteristics of light when light 33 is incident on the background portion 32. In the background portion 32, light 33 tends to be strongly reflected in the specular reflection direction, and the reflected light 35b in the specular reflection direction is strong. However, diffusion occurs, so vertically diffused light 34b also exists. FIG. 5B shows the relationship between the incident angle θ and the vertically diffused light 34b in this case. In the case of the background portion 32, as the incident angle θ increases, the vertically diffused light 34b decreases more rapidly than in the case of the electrode portion 31, and then the decrease becomes more gradual.

[0025] As a result, when light is irradiated onto the electrode portion 31 and the background portion 32 at the same incident angle θ, the contrast varies depending on the incident angle θ. This is shown in FIG. 6 . The contrast can be calculated by dividing the amount of vertically diffused light 34a at the electrode portion 31 by the amount of vertically diffused light 34b at the background portion 32. The difference in the dependency of the amount of diffused light on the incident angle θ shown in FIGS. 5A and 5B results in a maximum value for the contrast. Therefore, the contrast can be maximized by selecting an optimal incident angle θ. A desirable incident angle θ is 40° or more and 80° or less, more preferably 50° or more and 65° or less. As a more specific example, when the incident angle θ is 57°, the contrast between the electrode portion 31 and the background portion 32 is maximized. However, since the optimal incident angle θ varies depending on the materials and surface conditions of the two portions to be imaged, such as the electrode portion 31 and the background portion 32, it is preferable to measure it in advance.

[0026] Based on the above, a method for obtaining an image with both high contrast and brightness using the imaging device 100 of this embodiment will be described.

[0027] As shown in the plan view of Figure 2, multiple bullet-shaped LEDs 11 are mounted on an illumination board 12 and arranged around a first axis 21. In this embodiment, the illumination board 12 is annular. Each bullet-shaped LED 11 emits light (emitted light 22) with a certain spread centered on an optical axis 24, where the light intensity is greatest. Each bullet-shaped LED 11 is mounted on the illumination board 12 so that the incident angle of the optical axis 24 is the optimal incident angle θ (e.g., 57°) at which the contrast is maximized, as described above.

[0028] The light 22 emitted from each bullet-shaped LED 11 is incident on the corresponding transmission lens 13. The light is collected by the transmission lens 13 and incident on the multilayer substrate 14 at or near the optimal angle of incidence θ. The incident light is diffused by the electrode portion 31 and the background portion 32, exhibiting different diffusion characteristics. The vertically diffused light 34a and 34b pass through the objective lens 15 and the imaging lens 16 and form an image on the image sensor 17. By setting the angle of incidence θ to an appropriate value, the contrast of the diffused light 34a and 34b is increased, allowing a high-contrast image to be captured.

[0029] The objective lens 15 is disposed at a position spaced apart from the objective lens 15, which is the object of image capture, by the focal length thereof. The image sensor 17 is disposed at a position spaced apart from the imaging lens 16 by the focal length thereof.

[0030] The transmission lens 13 is preferably made of optical glass or resin. One transmission lens 13 is disposed between each bullet-type LED 11 and the multilayer substrate 14. More specifically, the transmission lens 13 is disposed at a position where an image of the light-emitting chip surface of the bullet-type LED 11 is formed on the multilayer substrate 14. The focal length of the transmission lens 13 may be determined based on the imaging magnification of the imaging system formed by the objective lens 15 and the imaging lens 16 and the light-receiving range of the imaging element 17. For example, if the light-receiving range of the imaging element 17 is 10 mm square and the magnification of the imaging system is 20x, the focal length and position of the transmission lens 13 are set so that the chip surface of the bullet-type LED 11 is imaged to a size of 0.5 mm square.

[0031] Furthermore, it is desirable that the transmission lens 13 be positioned relative to the bullet-shaped LED 11 and the multilayer substrate 14 (image plane) at an angle such that the chip surface of the bullet-shaped LED, the multilayer substrate surface, and the main surface of the transmission lens 13 intersect on the same straight line, i.e., an angle that satisfies Scheimpflug's theorem. This allows light emitted from the bullet-shaped LED 11, even light that diffuses off the optical axis 24, which was previously unavailable, to be focused onto the multilayer substrate 14. As a result, the amount of light incident on the multilayer substrate 14 increases, improving image brightness. Note that when the light emitted on the optical axis from the bullet-shaped LED 11 is incident on the multilayer substrate 14 at an optimal incident angle θ, the light that diffuses off the optical axis is incident on the multilayer substrate 14 at an angle slightly different from the optimal incident angle θ.

[0032] As a result, it is possible to capture a high-contrast, bright image using as many bullet-shaped LEDs 11 as can be arranged in the device.

[0033] Although the above description has been given of a configuration in which the bullet-shaped LEDs 11 are arranged on the lighting board 12, other configurations are also possible. For example, a configuration may be used in which a housing with multiple holes is used, and the bullet-shaped LEDs 11 are inserted into the holes and wired.

[0034] There is no particular limitation on the wavelength of light emitted by the bullet-shaped LED 11. Furthermore, it is not necessary for all of the bullet-shaped LEDs 11 to have the same wavelength. In other words, it is also possible to use a plurality of bullet-shaped LEDs 11 with different wavelengths (emission colors).

[0035] Furthermore, an LED chip may be used instead of the bullet-shaped LED 11. In this case, a transmission lens 13 or a prism may be disposed on the entire surface of the LED chip.

[0036] 1 and 2 show an example in which a plurality of transmission lenses 13 are provided independently, but a lens having a combined structure including some or all of the adjacent transmission lenses 13 may also be used.

[0037] Although the above description has been given of an example in which only the combination of the bullet-shaped LED 11 and the transmission lens 13 is used as illumination, the present invention is not limited to this. For example, as in the modified imaging device 101 shown in FIG. 7, an epi-illumination control unit 42 and a half mirror 41 may be provided. The other configuration is the same as in FIG. 1. This allows the light from the epi-illumination control unit 42 to be reflected by the half mirror 41 and irradiated onto the multilayer substrate 14. By combining and controlling this light with the light from the bullet-shaped LED 11, an image that is easy to recognize can be obtained.

[0038] Furthermore, although the multilayer substrate 14 has been described as an example of an imaging target, this is not limiting. Other imaging targets may include bonding wires, IC leads, etc., and high-contrast, bright images can be captured in the same manner as above.

[0039] Second Embodiment Next, a second embodiment of the present disclosure will be described.

[0040] 8 is a schematic front view of an exemplary imaging device 102 according to this embodiment. The multilayer substrate 14, which is the imaging target, the objective lens 15, the imaging lens 16, and the imaging element 17 are the same as those in the imaging device 100 shown in FIG. 1. The imaging device 102 according to this embodiment includes a single lens 43 instead of the multiple transmissive lenses 13 shown in FIG. 1. Furthermore, the optical axis of the bullet-shaped LED 41 provided on the illumination substrate 42 is parallel to the first axis 21 (in the −Z direction).

[0041] Fig. 9 shows in more detail the lens 43, the bullet-shaped LED 41 provided on the lighting board 42, and the multilayer board 14. Fig. 10 is a plan view of Fig. 9 seen from the lighting board 42 side. Furthermore, Fig. 11 shows a cross section taken along line XI-XI in Fig. 10.

[0042] In this embodiment, the illumination board 42 is arranged around the first axis 21 and perpendicular to the first axis 21. The bullet-shaped LED 41 is provided on the illumination board 42 so that its optical axis is parallel to the first axis 21. Therefore, the bullet-shaped LED 41 emits light in the -Z direction. This arrangement is useful for stabilizing the light emission direction and improving optical stability.

[0043] The bullet-shaped LEDs 41 are arranged at equal intervals on a circle centered on the first axis 21. This is a desirable arrangement, but is not essential. Depending on design needs, bullet-shaped LEDs 41 may be arranged at intervals different from other locations or arranged off the same circle.

[0044] The illumination board 42 has a board center hole 67 in the center to capture light reflected in the vertical direction from the multilayer board 14, and also has a cutout portion to accommodate the focus sensor 44 required for aligning the objective lens 15 during imaging. In a plan view ( FIG. 10 ), the illumination board 42 has an overall shape resembling the letter C. The board center hole 67 penetrates the illumination board 42.

[0045] Light emitted from each bullet-shaped LED 41 enters the lens 43. The lens 43 includes an incident surface 61 through which the light enters, a reflecting surface 62 that reflects the incident light, and an exit surface 63 through which the reflected light exits. A holding edge 64 is provided at the outermost periphery of the lens 43. Furthermore, the lens 43 includes a lens center hole 68 for capturing light reflected vertically from the multilayer substrate 14 and a cutout portion for locating the focus sensor 44. In plan view ( FIG. 10 ), the lens 43 has an overall C-shaped configuration similar to that of the illumination board 42. Preferably, the cutout portion is formed by a plane parallel to the first axis 21. This minimizes the effect of the cutout portion on the function of the lens 43 when light enters in the -Z direction. The lens center hole 68 also penetrates the lens 43.

[0046] The incident surface 61 has identical cylindrical curved surfaces arranged circumferentially around the first axis 21, with adjacent cylindrical shapes connected at the intersection of the surfaces. The cylindrical shapes and the bullet-shaped LEDs 41 are arranged in a one-to-one correspondence. The cylindrical shape is desirable for concentrating the light 65 ( FIG. 9 ) diffused and emitted from the bullet-shaped LEDs 41, which diffuses in the circumferential direction of a circle centered on the first axis 21. However, a similar effect may be achieved by using curved surfaces of other shapes.

[0047] This improves the utilization efficiency of the light emitted by the bullet-shaped LED 41, making it possible to brighten the captured image. In other words, if the incident surface 61 does not have a cylindrical shape, the light emitted by the bullet-shaped LED 41 that diffuses off the optical axis is difficult to guide onto the multilayer substrate 14 and cannot be used efficiently for imaging. In contrast, the cylindrical shape of the incident surface 61 makes it possible to collect and utilize the radiant light 65 that diffuses in the circumferential direction of the circle.

[0048] In this embodiment, the cylindrical shapes are arranged on the same circumference, which is a preferred arrangement, but is not essential.

[0049] Next, the light incident from the incident surface 61 is reflected (total reflection) by the reflecting surface 62. As shown in Fig. 11, the reflecting surface 62 has a shape obtained by rotating a portion of an ellipse around the first axis 21. The ellipse referred to here has two foci: a virtual point light source position coordinate P1 (x1, z1) calculated from the spread angle of the light from the bullet-shaped LED 41, and a central coordinate P0 (x0, z0) of the multilayer substrate 14.

[0050] The shape of the reflecting surface 62 also improves the utilization efficiency of the light emitted by the bullet-shaped LED 41, making it possible to brighten the captured image. In other words, because the cross section of the reflecting surface 62 has the above-mentioned elliptical shape, on the cross section including the first axis 21 shown in Figure 11, the radiant light 66 emitted from the virtual point light source position coordinate P1 of the bullet-shaped LED 41 and diffused is concentrated at the center coordinate P0 by total reflection. This corresponds to concentrating the diffused light from the bullet-shaped LED 41 in the radial direction of a circle centered on the first axis 21.

[0051] As described above, the cylindrical shape of the incident surface 61 and the reflective surface 62 having a shape obtained by rotating a predetermined ellipse make it possible to collect and utilize the diffused light emitted from the bullet-shaped LED 41, which has not been used in the past.

[0052] The shape of the reflecting surface 62 is designed to set the angle of incidence θ of light onto the multilayer substrate 14 to a desired angle (e.g., 57°). Specifically, in FIG. 11 , the point where a line drawn from P1 in the −Z direction intersects with the elliptical curve of the reflecting surface 62 is designated as intersection point P2 (x2, z2). The elliptical curve is designed so that the angle between a straight line P2P0 drawn from intersection point P2 to the center coordinate P0 and a perpendicular line (first axis 21) from the center coordinate P0 in the Z direction is the desired angle θ. Furthermore, the lens 43 is designed to adjust the ratio between the major and minor axes of the ellipse to increase the amount of light incident on the multilayer substrate 14.

[0053] The light reflected by the reflecting surface 62 is emitted from the exit surface 63 to the outside of the lens 43. The exit surface 63 may have a shape formed by rotating an arc around the first axis 21. This makes it possible to adjust the angle of the light emitted from the lens 43, improve the uniformity of the illuminance within the imaging range on the multilayer substrate 14, and improve the contrast.

[0054] In this regard, let us consider the case where the light emitted from the bullet-shaped LED 41 is reflected by the reflective surface 62 and travels straight ahead. In this case, the light on the optical axis is incident on a point (center coordinate P0) on the multilayer substrate 14 at an incident angle θ, while the diffused light off the optical axis is incident on the same point at an angle different from the incident angle θ. In response to this, by designing the shape of the reflective surface 62, it is possible to mitigate the concentration of the diffused light, bring the incident angle closer to θ, and shift the incident position away from the center coordinate P0. This allows the light from the bullet-shaped LED 41 to be incident at an angle close to the desired incident angle θ and to spread within the imaging range. It is possible to design this so that the light on the optical axis is not affected.

[0055] The light emitted from the exit surface 63 enters the multilayer substrate 14 at a desired incident angle θ (e.g., 57°) or an angle close to it, and is diffused. Of the diffused light, the light that is diffused in the vertical direction (+Z direction) passes through the objective lens 15 and the imaging lens 16, and is imaged on the image sensor 17. This makes it possible to capture a high-contrast, bright image.

[0056] Table 1 shows the results of a simulation of the brightness and contrast of images captured by the imaging device 102 of this embodiment and an imaging device with a conventional structure as a comparative example. The configuration of the illumination system for the imaging device of the comparative example is shown in FIGS. 12A and 12B. In the imaging device of the comparative example, LED lamps 111a, 111b, and 111c are arranged in three concentric rows inside a spherical shell-shaped substrate 110. The three rows of LED lamps 111a, 111b, and 111c have optical axis incident angles of 33°, 41.25°, and 49.5°, respectively, with respect to the imaging target 112, and the number of lamps provided is 16, 16, and 9, respectively.

[0057] In the imaging device 102 of the second embodiment, the number of bullet-shaped LEDs 41 is 24.

[0058]

[0059] As shown in Table 1, the image capture device 102 of this embodiment has 1.7 times the contrast and twice the brightness of the comparative example. In other words, even though the image capture device 102 has fewer LEDs, it significantly exceeds the comparative example in both contrast and brightness.

[0060] Furthermore, although the bullet-shaped LEDs 41 and the lens 43 are partially missing in the circumferential direction in order to provide the focus sensor 44, no deviation in the illuminance distribution due to this was observed. This is because the illumination range of each bullet-shaped LED 41 is wide relative to the imaging range, so even if a portion is missing, the impact on the illuminance distribution is small. In addition, for the same reason, the reduction in light intensity due to positional deviation, rotational deviation, or tilt of the lens 43 is also small.

[0061] Furthermore, since the bullet-shaped LED 41 is arranged in the direction of the first axis 21 (Z-axis direction) and the lens 43 is used to both focus the light and adjust the angle of incidence, the device can be made smaller in both the X-axis and Y-axis directions.

[0062] As described above, light is emitted from the bullet-shaped LED 41, which is arranged with its optical axis perpendicular to the multilayer substrate 14, and the light is concentrated on the multilayer substrate 14 by the lens 43, which has the incident surface 61, the reflecting surface 62, and the exit surface 63. At this time, the light emitted from the bullet-shaped LED 41 reaches each surface in the order of the incident surface 61, the reflecting surface 62, and the exit surface 63. As a result, a large amount of light is irradiated onto the multilayer substrate 14 at an incident angle that increases the contrast, and a high-contrast, bright image can be captured.

[0063] The lens 43 of this embodiment is also preferably made of optical glass or resin. Furthermore, light is reflected at the reflecting surface 62 depending on the refractive index of the lens 43 and the angle of incidence of the light with respect to the reflecting surface 62. However, metal may be vapor-deposited on the outside of the reflecting surface 62. This can ensure more reliable reflection at the reflecting surface 62.

[0064] (Inspection Apparatus) Next, an inspection apparatus using the imaging device 102 of this embodiment will be described.

[0065] 13 is a schematic plan view of the multilayer substrate 14 to be imaged and inspected. The multilayer substrate 14 is provided with an electrode portion 71. A reference position O for image capturing and inspection is determined in the electrode portion 71.

[0066] 14 is a diagram schematically showing an inspection device that inspects a multilayer substrate 14. The inspection device includes an imaging system 73, an XY stage 74, a Z stage 75, an imaging element 17, a control device 76, and a display device 77. The imaging system 73 includes the lens 43, the illumination board 42, the bullet-shaped LED 41, the objective lens 15, the imaging lens 16, etc. shown in FIG.

[0067] The multilayer substrate 14 to be inspected is placed on an XY stage 74. The control device 76 moves the XY stage 74 in the X-axis direction and the Y-axis direction, thereby adjusting the positions of the multilayer substrate 14 and the imaging system 73. Similarly, the control device 76 moves the Z-stage 75 in the Z-axis direction, thereby adjusting the positions of the multilayer substrate 14 and the imaging system 73.

[0068] The control device 76 controls the on / off and light intensity of the bullet-shaped LED 41. Furthermore, the image pickup element 17 is also controlled by the control device 76. The display device displays information related to the inspection, including the image picked up by the image pickup element 17.

[0069] 15 shows a flowchart of the inspection of the multilayer substrate 14 by the inspection device of FIG. 14. Here, an example is shown of an indentation inspection on the multilayer substrate 14. The following operations are all performed through the control device 76.

[0070] First, it is checked whether the focus position of the image captured by the image sensor 17 is correct. If it is correct, the process proceeds to the next step, and if it is not correct, the Z stage 75 is moved in the Z direction and the process returns to checking the focus.

[0071] If the focus position is correct, the bullet-shaped LED 41 is turned on. Next, the image sensor 17 and the image pickup system 73 are used to capture an image of the multilayer substrate 14, and an inspection image is obtained. Next, the positions of the electrode portions 71 are recognized from the obtained inspection image, and a reference position O is obtained. Thereafter, the multilayer substrate 14 is moved by the XY stage 74 so that the reference position O becomes the reference position for the indentation inspection.

[0072] The inspection apparatus of this embodiment includes the imaging device 102 of this embodiment, and therefore can acquire and use high-contrast and bright inspection images, thereby improving the accuracy, efficiency, etc. of the inspection.

[0073] It should be noted that an inspection device can be configured in any manner using any imaging device disclosed herein, including the imaging device 100 of the first embodiment.

[0074] (Modifications of the Second Embodiment) Next, several modifications of the imaging device of the second embodiment will be described.

[0075] (Modification 1) Fig. 16 is a front view schematically showing an imaging device 103 of modification 1. Instead of the lens 43 in the imaging device 102 of Fig. 8, the imaging device 103 of Fig. 16 includes a mirror 81. The mirror 81 has an ellipsoidal reflective surface 82 that has a shape similar to the reflective surface 62 of the lens 43 and is reflectively coated. Fig. 17 shows a plan view of the mirror 81, the illumination board 42, and the bullet-shaped LED 41.

[0076] By using such a mirror 81, it is possible to condense the light emitted from the bullet-shaped LED 41 onto the multilayer substrate 14 at a predetermined incident angle θ.

[0077] 18 shows a second modification of the lens 43. In the second modification, for example, a stopper hole 84 provided parallel to the first axis 21 and / or a through-hole 83 provided in the edge portion 64 is provided. The use of such stopper hole 84 and through-hole 83 can suppress rotational misalignment of the lens and misalignment in the X and Y directions, which is useful for suppressing a decrease in the amount of light, etc.

[0078] (Variation 3) FIG. 19 also shows Variation 3 of the lens 43. Variation 3 differs from the lens 43 of FIG. 11 in the shape of the exit surface 63. Specifically, while the cross section of the exit surface 63 in FIG. 11 is arc-shaped, the cross section of the exit surface 63 in FIG. 19 is linear (segmented). Therefore, in Variation 3, the exit surface 63 has a shape formed by rotating a segment around the first axis 21. This results in a different angle of incidence and position of incidence of light emitted from the exit surface 63 with respect to the multilayer substrate 14 compared to the case of FIG. 11. This may be done to uniformly irradiate the imaging range on the multilayer substrate 14 with the light on the optical axis of the bullet-shaped LED 41 and the light off the optical axis at a desired angle of incidence.

[0079] Similarly, although the shape of the reflecting surface 62 has been described as having a predetermined elliptical cross section, the present invention is not limited to this. In particular, taking into consideration the shapes of the reflecting surface 62 and the exit surface 63 and the refractive index of the lens material, the reflecting surface 62 may have a shape obtained by rotating a free-form curve around the first axis 21. The shape of the exit surface 63 may also have a cross section other than an arc or a line segment.

[0080] 20 shows an image capturing device 104 of Modification 4, which further includes an epi-illumination control unit 42 and a half mirror 41 for illumination. The other configuration is the same as that of the image capturing device 102 of Fig. 8. By reflecting light from the epi-illumination control unit 42 off the half mirror 41 and irradiating it onto the multilayer substrate 14, it is possible to combine this with light from the bullet-shaped LED 11 to achieve illumination that is more desirable for imaging.

[0081] 21 and 22 show a fifth modification of the lens. Fig. 21 is a front view of a lens 43a of this modification, and Fig. 22 is a cross-sectional view taken along line XXII-XXII in Fig. 21. Comparing the lens 43a of this modification with the lens 43 of Figs. 9 and 10, the shapes of the incident surface 61a and the reflecting surface 62a are different.

[0082] 9 has a shape in which cylindrical curved surfaces are arranged, and focuses light in the circumferential direction of a circle centered on the first axis 21. In contrast, the incident surface 61a of the lens 43a of this modified example is flat, and does not have a function of focusing light.

[0083] The reflecting surface 62 of the lens 43 in FIG. 9 has a shape obtained by rotating a portion of an ellipse around the first axis 21. This allows light diffusing in the radial direction of a circle centered on the first axis 21 to be focused. In contrast, the reflecting surface 62a of the lens 43a in this modified example has a shape in which curved surfaces are arranged circumferentially around the first axis 21, with one curved surface corresponding to each bullet-shaped LED 41. This shape, on a cross section including the first axis 21, is similar to that of FIG. 11 and focuses light diffusing in the circumferential direction of a circle centered on the first axis 21. Furthermore, on a cross section perpendicular to the first axis 21 (FIG. 22), the shape also focuses light diffusing in the circumferential direction of a circle centered on the first axis 21.

[0084] In this manner, the lens 43a of this modification uses the reflecting surface 62a to focus light in both the circumferential and radial directions of a circle centered on the first axis 21. A lens 43a of this shape can be used to efficiently utilize the light (especially off-axis light) emitted by the bullet-shaped LED 41. Also, in the mirror 81 of the imaging device 103 of modification 1 (FIG. 16), the ellipsoidal reflecting surface 82 can be modified to focus light in both the circumferential and radial directions of a circle centered on the first axis 21.

[0085] 23 and 24 show a sixth modification of the lens. Fig. 23 is a front view of a lens 43b of this modification, and Fig. 24 is a cross-sectional view taken along line XXIV-XXIV in Fig. 23. Comparing the lens 43b of this modification with the lens 43 of Figs. 9 and 10, the shapes of the entrance surface 61a and the exit surface 63a are different.

[0086] In the lens 43b of this modified example, the incident surface 61a is flat (similar to the lens 43a in FIG. 21). The reflecting surface 62 is similar to the lens 43 in FIG. 9 and focuses light that diffuses in the radial direction of a circle centered on the first axis 21. In contrast, the exit surface 63a has a shape that focuses light that diffuses in the circumferential direction of a circle centered on the first axis 21. In other words, the exit surface 63a has a shape in which curved surfaces are arranged on the circumference so that one curved surface corresponds to one bullet-shaped LED 41.

[0087] In this way, the lens 43b of this modified example also focuses light by the reflecting surface 62a in both the circumferential direction and the radial direction of the circle centered on the first axis 21. In order to efficiently utilize the light (especially off-axis light) emitted from the bullet-shaped LED 41, the lens 43a having such a shape can also be used.

[0088] Furthermore, in the second embodiment and each of the modified examples, an LED chip may be used instead of the bullet-shaped LED 41. In this case, a transmission lens or prism may be placed in front of the LED chip. Furthermore, in the case of an LED chip, light is diffused over a wider area than in the case of a bullet-shaped LED. Therefore, it is desirable to place the LED chip closer to the lens 43 than when using a bullet-shaped LED.

[0089] There is no particular limitation on the wavelength of light emitted by the bullet-shaped LED 11. Furthermore, it is not necessary for all of the bullet-shaped LEDs 11 to have the same wavelength. In other words, it is also possible to use a plurality of bullet-shaped LEDs 11 with different wavelengths (emission colors).

[0090] Furthermore, in the imaging device and inspection device of this embodiment, the lens 43 may be changed depending on the imaging target. That is, by using a lens with a different shape for at least one of the entrance surface 61, the reflection surface 62, and the exit surface 63, it is possible to optimize the illumination conditions, including the angle of incidence, for different imaging targets. This makes it possible to obtain high-contrast, bright images of various targets.

[0091] In the above example, the bullet-shaped LEDs 41 are arranged on one circumference, but they may be arranged in two or more concentric circles. The bullet-shaped LEDs 41 may also be selectively controlled to emit light. Control is made according to the shape of the subject to be imaged, allowing for image capture with settings that allow for good image recognition.

[0092] In the above, the optical axis of the bullet-shaped LED 41 faces in the -Z direction and is perpendicular to the incident surface 61 of the lens 43. This is desirable for purposes such as stabilizing the direction of light emission. However, for other design reasons, it is possible to tilt the optical axis of the bullet-shaped LED 41 from the -Z axis direction.

[0093] Also in this embodiment, the object to be imaged is not limited to the multilayer substrate 14, but may be a bonding wire, an IC lead, or the like.

[0094] The above-described embodiments are merely examples and are not intended to be limiting. Furthermore, modifications, combinations, and substitutions of form and details are possible as long as they do not deviate from the spirit and scope of the claims and are effective.

[0095] According to the present disclosure, it is possible to achieve both high contrast and brightness in a captured image, and the present disclosure is useful as a lens, an optical system, an imaging device, and an inspection device.

[0096] REFERENCE SIGNS LIST 11 Bullet-shaped LED 12 Illumination board 13 Transmissive lens 14 Multilayer board 15 Objective lens 16 Imaging lens 17 Image sensor 21 First axis 22 Radiated light 24 Optical axis 31 Electrode section 32 Background section 33 Light 34a Diffused light (electrode section) 34b Diffused light (background section) 35a Reflected light (electrode section) 35b Reflected light (background section) 41 Half mirror 41 Bullet-shaped LED 42 Illumination board 42 Epi-illumination control section 43, 43a, 43b Lens 44 Focus sensor 61, 61a Incident surface 62, 62a Reflecting surface 63, 63a Exit surface 64 Edge section 65 Radiated light 66 Radiated light 67 Board center hole 68 Lens center hole 71 Electrode section 73 Imaging system 74 XY stage 75 Z stage 76 Control device 77 Display device 81 Mirror 82 Ellipsoidal reflecting surface 83 Through hole 84 Hole 100 to 104 Imaging device 110 Substrate 111a, 111b, 111c LED lamp 112 Image pickup object

Claims

1. A lens that focuses light so that it is incident on an object on a first axis at a predetermined angle of incidence θ, comprising: an incident surface onto which the light is incident; a reflecting surface that reflects the incident light; and an exit surface that emits the light reflected by the reflecting surface, wherein at least one of the incident surface, reflecting surface, and exit surface has a shape that focuses light that diffuses in the circumferential direction of a circle centered on the first axis, and the reflecting surface has a shape that focuses light that diffuses in the radial direction of the circle.

2. A lens according to claim 1, characterized in that the lens has a hole in a region including the first axis.

3. A lens according to claim 1, wherein the entrance surface has a shape in which a plurality of identical curved surfaces are arranged around the first axis, and the identical curved surfaces have a cylindrical shape.

4. A lens according to claim 1, characterized in that the reflecting surface has a surface shaped as a part of an elliptical curve or a part of a free curve rotated around the first axis.

5. A lens according to claim 1, wherein the incident angle θ is 40° or more and 80° or less.

6. A lens according to claim 1, wherein the light exit surface has a surface formed by rotating a portion of a curve or a line segment around the first axis, and diffuses light in the radial direction of a circle centered on the first axis.

7. A lens according to claim 1, characterized in that the lens has at least one of a stop hole and a through hole at a position different from the first axis.

8. A lens according to claim 1, characterized in that the lens has a defect cut by two planes parallel to the first axis.

9. An optical system comprising: a lens according to claim 1; and a plurality of light-emitting elements arranged around the first axis, the light-emitting elements emitting light onto the entrance surface of the lens.

10. An imaging device comprising the optical system of claim 9, an objective lens, an imaging lens and an imaging element arranged on the first axis in this order from the object side, wherein the lens causes light emitted from the light-emitting element to be incident on the object at the incident angle θ and collects the light, and wherein the objective lens, the imaging lens and the imaging element are used to image the diffuse reflected light scattered by the object.

11. An inspection device comprising: the imaging device of claim 10; a control device for controlling said imaging device; and a display device for displaying an image captured by said imaging device.

12. An imaging device comprising: a plurality of light-emitting elements arranged around a first axis; a plurality of transmission lenses respectively arranged between the plurality of light-emitting elements and an object on the first axis; an objective lens, an imaging lens, and an imaging element arranged on the first axis in this order from the object side; wherein the light-emitting elements are arranged so that their optical axes form a predetermined angle of incidence θ with respect to the object; the transmission lens focuses light emitted from the light-emitting elements onto the object; and wherein the objective lens, the imaging lens, and the imaging element are used to image the diffuse reflected light scattered by the object.

13. An imaging device according to claim 12, wherein the incident angle θ is equal to or greater than 40° and equal to or less than 80°.

14. An inspection device comprising: the imaging device of claim 12; a control device for controlling said imaging device; and a display device for displaying an image captured by said imaging device.

15. An imaging device comprising: a plurality of light-emitting elements arranged around a first axis; a mirror whose reflective surface is a surface shaped like a part of an ellipse rotated around the first axis; and an objective lens, an imaging lens, and an imaging element arranged on the first axis in this order from the object side; wherein the mirror reflects light emitted from the light-emitting elements, makes the light incident on the object at a predetermined angle of incidence θ, and focuses the light; and wherein the objective lens, the imaging lens, and the imaging element are used to image the diffuse reflected light scattered by the object.

16. An imaging device according to claim 15, wherein the incident angle θ is equal to or greater than 40° and equal to or less than 80°.

17. An inspection device comprising: the imaging device of claim 15; a control device for controlling said imaging device; and a display device for displaying an image captured by said imaging device.

Images