Optical axis deviation evaluating method, optical axis adjusting method, optical axis deviation evaluating means, and mounting apparatus

Abstract

To provide an optical axis deviation detecting method capable of easily detecting the inclination of an optical axis with a relatively simple configuration, an optical axis adjusting method for correcting the inclination when the optical axis is inclined, an optical axis deviation evaluating means, and a mounting device using the same.SOLUTION: Imaging a mark pair a plurality of times and associating the mark pair with an angle of rotation while rotating a transparent plate with a normal direction in a plane as a rotation axis direction in a state in which the mark pair is within a field of view, the mark pair including a pair of marks provided on both surfaces of the transparent plate which is disposed parallel to the plane and of which a thickness and an optical refractive index are known; To provide an optical axis deviation detection method for specifying an inclination angle from a positional relationship between an imaging means and a pair of marks provided on a transparent plate when an apparent inter-mark distance becomes maximum or minimum, an optical axis adjustment method for correcting an inclination when there is an optical axis inclination, an optical axis deviation evaluation means, and a mounting device using the same.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a mounting apparatus for mounting chip components on a substrate and an imaging device used therein. [Background technology]

[0002] When mounting a chip component on a substrate, it is important to accurately obtain positional information of alignment marks on the chip component or substrate by imaging means, and the alignment marks are used to align the relative positions of the chip component and the substrate.

[0003] However, if the optical axis of the imaging means is tilted relative to the normal to the substrate surface, accurate position information cannot be obtained. Specifically, if the optical axis of the imaging means is tilted, the position information also changes depending on the distance between the imaging means and the substrate. For example, as shown in Figure 16, the position information of the alignment mark A on the substrate S varies depending on the height of the imaging means 5. When this phenomenon occurs, it becomes difficult to accurately determine the relative positions when observing the alignment marks of the substrate and chip components from one direction (for example, Patent Document 1). For this reason, it is necessary to check the status of the optical axis misalignment of the imaging means and adjust the optical axis as necessary. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-119966 Summary of the Invention [Problem to be solved by the invention]

[0005] As explained using Figure 16, changing the height of the imaging means 5 relative to the substrate S changes the positional information of the alignment mark A, and therefore it is possible to detect misalignment of the optical axis of the imaging means 5. For example, as shown in Figure 17, when the height of the imaging means 5 relative to the substrate S is changed in three stages as shown in Figures 17(a) to 17(c), it is possible to calculate the tilt angle of the optical axis from the change in the coordinate position of the alignment mark A in the field of view V5 (of the imaging means 5) (Figure 17(d)).

[0006] However, in order to calculate the tilt angle of the optical axis using this method, the lift axis of the imaging means 5 must be perpendicular (normal) to the substrate S when changing the height of the imaging means 5. For example, as shown in Figure 18, even if the optical axis of the imaging means 5 is not misaligned in the normal direction to the substrate S, if there is a tilt (lift axis misalignment) in the lift axis AXM of the imaging means 5, the coordinate position of the alignment mark A in the field of view V5 will change as the imaging means 5 is raised and lowered. In other words, in a state where it cannot be proven that the lift axis AXM of the imaging means 5 is perpendicular to the substrate S, it is impossible to distinguish between optical axis misalignment and lift axis misalignment (of the imaging means), and it is difficult to evaluate the optical axis misalignment by changing the height of the imaging means 5 as shown in Figure 17.

[0007] When an optical axis misalignment occurs, the optical axis AX5 is tilted relative to the normal (Z axis) of the substrate as shown in Figure 19(a), and the optical axis misalignment can be expressed by the tilt direction θw around the Z axis as shown in Figure 19(b) and the tilt angle θ relative to the Z direction in the same tilt direction.However, even if the lift axis AXM is vertical in the method shown in Figure 17, complex calculations are required to calculate the tilt direction θw and tilt angle θ.

[0008] The present invention has been made in consideration of the above problems, and provides an optical axis deviation detection method that can easily detect the tilt of the optical axis with a relatively simple configuration, an optical axis adjustment method that corrects the tilt when the optical axis is tilted, an optical axis deviation evaluation means, and a mounting device using the same. [Means for solving the problem]

[0009] In order to solve the above problem, the invention described in claim 1 is as follows: 1. A method for evaluating optical axis deviation, in an imaging means that images at least one of a substrate or a chip component arranged on a plane, for determining a tilt direction and a tilt angle of an optical axis of the imaging means with respect to a normal line of the plane, comprising: A mark pair is set as an imaging target, the mark pair being a pair of marks provided on both sides of a transparent plate having a known thickness and a known refractive index, which is arranged parallel to the plane, The optical axis deviation evaluation method includes an imaging process of imaging the mark pair multiple times while rotating the transparent plate with the normal direction in the plane as the rotation axis direction, with the mark pair within the field of view; a mark distance calculation process of calculating the apparent mark distance between the mark pair imaged multiple times in relation to the angle of rotation; a tilt direction identification process of determining the tilt direction from the positional relationship between the imaging means and the mark pair provided on the transparent plate when the apparent mark distance becomes maximum or minimum; and a tilt angle identification process of identifying the tilt angle using the apparent mark distance in the tilt direction.

[0010] The invention described in claim 2 is the optical axis deviation evaluation method described in claim 1, This is a method for evaluating optical axis deviation, in which both marks forming the mark pair are provided at positions where they do not overlap when viewed from the normal direction of the plane.

[0011] The invention described in claim 3 is the optical axis deviation evaluation method described in claim 1, In this optical axis deviation evaluation method, the transparent plate is rotated within the plane by an angle of 180 degrees or more.

[0012] The invention described in claim 4 is the optical axis deviation evaluation method described in claim 1, This is an optical axis deviation evaluation method in which a plurality of mark pairs are provided, the angle of rotation and the distance between marks are calculated for each mark pair in the mark distance calculation process, and the tilt direction is determined by selecting the mark pair that yields the maximum or minimum value of the mark distance in the tilt direction identification process.

[0013] The invention described in claim 5 is an optical axis correction method for correcting the tilt angle in the tilt direction based on the tilt direction and tilt angle of the imaging means obtained in any one of claims 1 to 4.

[0014] The invention described in claim 6 is An optical axis deviation evaluation means for determining a tilt direction and a tilt angle of an optical axis of an imaging means for imaging at least one of a substrate or a chip component arranged on a plane, with respect to a normal line of the plane, comprising: The optical axis deviation evaluation means comprises a transparent plate with marks on both sides and a known thickness and optical refractive index, a rotation means for rotating the transparent plate in a plane, and a control unit connected to the imaging means and having image processing and calculation functions.

[0015] The invention described in claim 7 is A mounting apparatus for mounting chip components on a substrate, The mounting device includes a substrate stage that holds the substrate, a mounting head that is used when mounting the chip component on the substrate, an imaging means that images at least one of the substrate or the chip component, and an optical axis deviation evaluation means as described in claim 6.

[0016] The invention described in claim 8 is the mounting device described in claim 7, The mounting device further comprises an optical axis adjustment means, and the optical axis adjustment means corrects the tilt angle in the tilt direction based on the tilt direction and tilt angle of the imaging means obtained by the optical axis deviation evaluation means. [Effects of the Invention]

[0017] According to the present invention, the tilt of the optical axis can be easily detected, and if there is tilt of the optical axis, the tilt can be corrected. Since accurate position information of the chip component or the board can be obtained, high-precision mounting becomes possible. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 2 is a diagram showing the configuration of an optical axis deviation evaluation unit for an imaging unit in an embodiment of the present invention. [Figure 2] 1A and 1B are diagrams illustrating the refraction phenomenon of light used in the present invention. [Figure 3] 1A is a diagram for explaining the tilt angle of the optical axis, and FIG. 1B is a diagram for explaining the tilt direction of the optical axis, relating to the evaluation target of the optical axis deviation evaluation means in the embodiment of the present invention. [Figure 4] Regarding the method by which the optical axis deviation evaluation means in an embodiment of the present invention determines the tilt direction of the optical axis, (a) the apparent inter-mark distance of a pair of marks provided on both sides of a transparent plate is explained, (b) the apparent inter-mark distance is measured by an imaging means while rotating the transparent plate in a plane, and (c) a diagram showing the rotation angle and the apparent inter-mark distance determined by the same measurement. [Figure 5] Regarding the method by which the optical axis deviation evaluation means in an embodiment of the present invention determines the tilt direction of the optical axis, (a) the apparent inter-mark distance of a pair of marks provided on both sides of a transparent plate is explained, (b) the apparent inter-mark distance is measured by an imaging means while rotating the transparent plate in a plane, and (c) a diagram showing the rotation angle and the apparent inter-mark distance determined by the same measurement. [Figure 6] 1A and 1B are diagrams showing the apparent mark positions and the relationship between the direction of the mark pair and the apparent mark distance in the optical axis deviation evaluation means according to an embodiment of the present invention, respectively. [Figure 7] FIG. 10 is a diagram illustrating an example of using a transparent plate having multiple mark pairs as a modified embodiment of the present invention, showing (a) step 1 in which the apparent inter-mark distance between each mark pair is measured, (b) step 2 in which the transparent plate is rotated a certain angle from the state of step 1 and then the apparent inter-mark distance between each mark pair is measured, and (c) step 3 in which the transparent plate is rotated a certain angle from the state of step 2 and then the apparent inter-mark distance between each mark pair is measured. [Figure 8]FIG. 8 is a diagram showing an example in which a transparent plate having three pairs of marks, each with an angle of 60°, is used to rotate the rotation angle at intervals of 30° in a modified example of the embodiment of the present invention shown in FIG. [Figure 9] FIG. 8 is a diagram showing an example in which a transparent plate having three pairs of marks, each with an angle of 60°, is used to rotate the rotation angle at intervals of 40° in a modified example of the embodiment of the present invention shown in FIG. [Figure 10] 10A and 10B are diagrams illustrating the principle of determining the tilt angle of the optical axis after determining the tilt direction of the optical axis in the optical axis deviation evaluation means according to the embodiment of the present invention. [Figure 11] 10A shows an example of determining the tilt angle of the optical axis in the optical axis deviation evaluation means in an embodiment of the present invention, where (a) shows a state in which the thickness and refractive index of the transparent plate are known, and (b) is a table showing the effect of the tilt angle of the optical axis on the apparent displacement of the mark. [Figure 12] 10 is a graph showing the relationship between the apparent displacement obtained from the apparent distance between marks and the tilt angle of the optical axis. [Figure 13] 1A and 1B are diagrams illustrating an optical axis deviation correcting means for correcting an optical axis deviation based on the results obtained by the optical axis deviation evaluating means in an embodiment of the present invention, in which (a) shows a state in which the optical axis deviation evaluating means is determining the tilt direction and tilt angle of the optical axis, and (b) shows a state in which the direction of the optical axis has been corrected based on the results obtained by the optical axis deviation evaluating means. [Figure 14] 10 is a flowchart showing a process of correcting an optical axis deviation using an optical axis deviation correcting means according to an embodiment of the present invention. [Figure 15] This explains the preferred thickness of the transparent plate that constitutes the optical axis deviation evaluation means in an embodiment of the present invention, and (a) shows the relationship between apparent displacement and the transparent plate, and (b) is a table calculating the effect of the thickness of the transparent plate on the apparent distance between marks. [Figure 16]This figure explains the influence of misalignment of the optical axis of the imaging means, and shows (a) a state in which an imaging means with a tilted optical axis is used to capture an image so that the mark is at the center of the field of view, (b) a state in which the vertical distance between the imaging means and the mark has changed from the same state, and (c) the position of the mark within the imaging field of view before and after the change in vertical distance. [Figure 17] This explains the relationship between the height of an imaging means with an optical axis deviation and the coordinates within the field of view of the object to be measured, and shows (a) a state in which imaging is performed so that the mark is at the center of the field of view, (b) a state in which imaging is performed so that the mark is at a higher position than in the same state, (c) a state in which the imaging means is lower than in the state in which imaging is performed so that the mark is at the center of the field of view, and (d) a diagram showing the height of the imaging means and the position of the mark within the imaging field of view. [Figure 18] This explains an imaging means in which there is no optical axis misalignment but the elevation axis is tilted, and (a) shows the state in which an image is captured so that the mark is at the center of the field of view, and (b) shows the state in which the image is lowered along the elevation axis from the same state. [Figure 19] 1A is a diagram illustrating the state of optical axis misalignment in the Z direction, with the substrate surface being the XY plane; FIG. 1B is a diagram illustrating the tilt direction of the optical axis misalignment; and FIG. 1C is a diagram illustrating the tilt angle in the tilt direction. DETAILED DESCRIPTION OF THE INVENTION

[0019] An embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a schematic diagram showing the configuration of an optical axis deviation evaluation means 1 according to an embodiment of the present invention.

[0020] The optical axis deviation evaluation means 1 in Figure 1 evaluates the deviation of the optical axis AX5 of the imaging means 5 that images an imaging target on a plane from the normal direction (Z direction), and calculates the tilt direction θw of the optical axis AX5 and the tilt angle θ1 of the optical axis shown in Figure 19(b). Note that the tilt angle θ1 of the optical axis shown in Figure 1(a) is the same as the tilt angle θ of the optical axis shown in Figure 19(c), but is referred to as θ1 to distinguish it from the tilt angle (θ2) of the optical axis (within the transparent plate) described later.

[0021] In FIG. 1, the optical axis deviation evaluation means 1 includes, as components, a mark plate 2, a rotation means 6, and a control unit 10 in addition to the imaging means 5 to be evaluated.

[0022] The mark plate 2 has marks on both sides of a transparent plate 20. In FIG. 1, a front mark 2A is provided on the side facing the imaging means 5, and a back mark 2B is provided on the opposite side. The transparent plate 20 is a transparent flat plate with a uniform thickness and optical refractive index, which are known. The transparent plate 20 is preferably made of glass or quartz, but is not limited to these. Any material that is clear, can be processed to a uniform thickness, and is resistant to deformation is acceptable. The front mark 2A and back mark 2B are provided on the surface of the transparent plate 20. At least the front mark 2A is preferably formed thinly; a thin film formed by vacuum deposition or the like is preferable, but the selection should take into account the adhesion to the transparent plate 20.

[0023] The rotation means 6 rotates the mark plate 2 (transparent plate 20) in the XY plane. The rotation means 6 in Fig. 1 is configured such that the rotation axis in the Z direction is set perpendicular to the transparent plate 20, but this is not limited to this, and the transparent plate 20 may be in a disk shape and rotated by an actuator provided on the outer periphery.

[0024] The control unit 10 essentially consists of a CPU and a storage device as its main components, with interfaces to each device as necessary. The control unit 10 also has a built-in program, which allows it to perform calculations using acquired data and output the results of the calculations. It is also desirable for the control unit 10 to have the ability to record acquired data and calculation results and use them as new calculation data.

[0025] The control unit 10 is connected to the imaging means 5 and controls the image acquisition operation by imaging, and also has a function of capturing imaging data and a function of processing the captured image data to calculate position information and the like.

[0026] Control unit 10 is connected to rotation means 6 and can control the rotation angle of mark plate 2 .

[0027] Below, we will explain a method for determining the tilt direction θw and tilt angle θ1 of the optical axis of the imaging means 5 using the optical axis shift evaluation means 1, but before that, we will explain the light refraction phenomenon used in the present invention using Figure 2.

[0028] 2 shows a state in which a back mark 2B provided on the lower surface of a transparent plate 20 is observed from a line of sight that is tilted at an angle θ1 with respect to the normal (Z direction) of the transparent plate 20. In the example of FIG. 2, because the refractive index of the transparent plate 20 is greater than that of the atmosphere, the back mark 2B is recognized within the transparent plate 20 by being refracted at an angle θ2 (smaller than the tilt angle θ1), but appears to be located at the position of an apparent back mark I2B that travels straight at the tilt angle θ1. In other words, the apparent back mark I2B appears to be located at a position away from the actual back mark 2B (depending on the difference between the angle θ1 and the tilt angle θ2) in the direction of the line of sight along the optical axis.

[0029] FIGS. 3 to 5 explain a method for determining the tilt direction θw of the optical axis of the imaging unit 5 using the optical axis deviation evaluation unit 1. First, FIG. 3 explains the mark plate 2 used to determine the tilt direction θw of the optical axis, which is the target of evaluation by the optical axis deviation evaluation unit 1. Here, the thickness (transparent plate thickness t) and optical refractive index n1 of the transparent plate 20 shown in FIG. 3(a) are known, and the optical refractive index n0 is also known because it is the optical refractive index of air. FIG. 3(b) shows an example of the arrangement of the front mark 2A and the back mark 2B within the plane of the transparent plate 20, as well as the tilt direction θw of the optical axis. In FIG. 3(b), the dotted line extending from the imaging unit 5 indicates the tilt direction of the optical axis of the imaging unit 5. This direction is expressed as an angle on the XY coordinate system. In FIG. 3(b), the tilt direction θw of the optical axis is a counterclockwise angle with the +X direction set to zero. The tilt angle θ1 of the optical axis in FIG. 3(a) is the tilt angle of the optical axis AX5 with respect to the Z direction in a cross section including the Z direction and the dotted line direction extending from the imaging means 5 shown in FIG. 3(b).

[0030] 4 and 5 show examples of determining the tilt direction θw of the optical axis. FIG. 4 shows an example in which the back mark 2B is located at the end of the tilt direction θw of the optical axis (the front mark 2A is located in front), and FIG. 5 shows an example in which the front mark 2A is located at the end of the tilt direction θw of the optical axis (the back mark 2B is located in front).

[0031] In Figure 4, since the back mark 2B is located at the end of the tilt direction θw of the optical axis, the apparent back mark I2B is observed to be located farther away than the actual back mark 2B, as shown in Figure 4(a). In contrast, the front mark 2A is observed without passing through the transparent plate 20, so accurate position information can be obtained. Therefore, the apparent inter-mark distance rn between the front mark 2A and the back mark 2B obtained from the position information of the image acquired by the imaging means 5 is longer than the actual inter-mark distance r0.

[0032] The direction and amount of displacement of the apparent back mark I2B relative to the actual position of the back mark 2B are determined by the transparent plate thickness t, refractive index n1, and the tilt direction θw and tilt angle θ1 of the optical axis, and are unrelated to the position of the back mark 2B. Therefore, when the mark plate 2 is rotated as shown in Figure 4(b), the apparent inter-mark distance rn is longest when the line connecting the front mark 2A and the back mark 2B coincides with the tilt direction θw of the optical axis, and decreases as the angle relative to the tilt direction θw of the optical axis increases. That is, Figure 4(b) shows the front mark 2An and the back mark 2Bn rotated so that n is 1, 2, or 3. However, the direction from the front mark 2A2 to the back mark 2B2 coincides with the tilt direction θw of the optical axis, and the apparent inter-mark distance rn (when n is 2) in this state reaches a maximum value, as shown in Figure 4(c).

[0033] 5, since the front mark 2A (back mark 2B) is located at the end of the tilt direction θw of the optical axis, the apparent back mark 12B is observed to be closer to the front mark 2A than the actual back mark 2B. In contrast, the front mark 2A is observed without passing through the transparent plate 20, so accurate position information can be obtained. For this reason, the apparent inter-mark distance rn between the front mark 2A and the back mark 2B obtained from the position information of the image acquired by the imaging means 5 is shorter than the actual inter-mark distance r.

[0034] Here, the apparent displacement direction and amount of the back mark I2B relative to the actual position of the back mark 2B are determined by the transparent plate thickness t, refractive index n1, and the tilt direction θw and tilt angle θ1 of the optical axis, and are unrelated to the position of the back mark 2B. Therefore, when the mark plate 2 is rotated as shown in Figure 4(b), the apparent inter-mark distance rn is shortest when the line connecting the back mark 2B and the front mark 2A coincides with the tilt direction θw of the optical axis, and becomes longer as the angle with respect to the tilt direction θw of the optical axis increases. That is, Figure 4(b) shows the front mark 2An and the back mark 2Bn rotated so that n is 1, 2, or 3. However, the direction from the back mark 2B2 to the front mark 2A2 coincides with the tilt direction θw of the optical axis, and rn (when n is 2) in this state is minimal, as shown in Figure 4(c).

[0035] FIG. 6 shows an example of the change in the apparent inter-mark distance rn in an example where the front mark 2A (back mark 2B) is located at the end of the tilt direction θW of the optical axis as shown in FIG. 5. In FIG. 6(a), the apparent inter-mark distance r2 is defined as the line connecting the back mark 2B and the front mark 2A when the line coincides with the tilt direction θW of the optical axis. The apparent inter-mark distance r1 is observed when the mark plate 2 is rotated 60° to the right from this state, and the apparent inter-mark distance r3 is observed when the mark plate 2 is rotated 60° to the left from the state of the apparent inter-mark distance r2. FIG. 6(b) also shows examples of the numerical values ​​of the inter-mark distance r0 and the apparent inter-mark distance rn (n = 1, 2, 3). In an example where the actual inter-mark distance r0 is 4.00 mm, FIG. 6(b) shows the values ​​of the apparent inter-mark distance r1 and the apparent inter-mark distance r3 when the apparent inter-mark distance r2 is 3.65 mm. Observing the numerical change in the apparent inter-mark distance rn shown in FIG. 6(b) can be said to be an effective method for finding the state in which the line connecting the back mark 2B and the front mark 2A coincides with the tilt direction θw of the optical axis.

[0036] FIG. 4 shows an example in which the back mark 2B (front mark 2A) is located at the end of the tilt direction θw of the optical axis, and FIG. 5 shows an example in which the front mark 2A (back mark 2B) is located at the end of the tilt direction θw of the optical axis. However, the direction of the optical axis θw relative to the relative positions of the front mark 2A and back mark 2B is unknown. Therefore, during the process of rotating the transparent plate 20, there may be cases in which the state in which the back mark 2B (front mark 2A) is located at the end of the tilt direction θw of the optical axis changes to the state in which the front mark 2A (back mark 2B) is located at the end of the tilt direction θw of the optical axis. In such cases, unless the rotation angle of the transparent plate 20 is 180° or more, the apparent inter-mark distance rn may not include both the maximum and minimum values. In other words, when using one mark pair, the transparent plate 20 must be rotated by 180° or more to determine the tilt direction θw of the optical axis XA5.

[0037] Furthermore, through an imaging process in which both marks are imaged multiple times while the transparent plate 20 is rotated, the apparent inter-mark distance rn obtained by imaging is correlated with the rotation angle and calculated in the mark distance calculation process. However, to accurately determine the angle at which the apparent inter-mark distance rn becomes maximum or minimum, it is desirable for the angle change between each imaging to be small. However, even if the angle change between each imaging is too small, the change in the apparent inter-mark distance rn for a certain angle near the angle at which the apparent inter-mark distance rn becomes maximum or minimum is small, so making the angle change too small is ineffective. From this perspective, it has been found that it is preferable to determine the apparent inter-mark distance rn at angles of 5 to 8 points in a range of just over 180°. Furthermore, since the apparent inter-mark distance rn is a function with the rotation angle as a variable, the angle at which the apparent inter-mark distance rn becomes maximum or minimum may be determined by approximating the actual measured value to the function.

[0038] Up to this point, we have described an example in which there is one mark pair. However, due to space constraints and the like, it may be difficult to rotate the transparent plate 20 by 180 degrees. In such cases, as a modified example of an embodiment of the present invention, a mark plate 2 having multiple mark pairs provided on the transparent plate 20 may be used. FIG. 7 shows a modified example of a mark plate 2 using three mark pairs, viewed from vertically above. As shown in FIG. 7(a), the line extending from the front mark 2Aα to the back mark 2Bα, the line extending from the front mark 2Aβ to the back mark 2Bβ, and the line extending from the front mark 2Aγ to the back mark 2Bγ are all in different directions. In FIG. 7(a), the direction of the line extending from the front mark 2Aα to the back mark 2Bα differs by 60° from the direction of the line extending from the front mark 2Aβ to the back mark 2Bβ, and the direction of the line extending from the front mark 2Aγ to the back mark 2Bγ differs by 60° from the direction of the line extending from the front mark 2Aβ to the back mark 2Bβ, but this is not limited to this. Furthermore, the number of mark pairs is not limited to three, and the number of mark pairs and the angle between the mark pairs may be determined according to the rotatable angle of the transparent plate 20 .

[0039] 7, the distance between the front mark and the back mark in each mark pair is shown as being equal, but this does not necessarily have to be the same, as long as the distance is large enough to allow the center positions of both the front mark and the back mark to be estimated. Also, the center positions of each mark pair and the center of rotation of mark plate 2 do not have to coincide.

[0040] Figure 7(b) shows mark plate 2 rotated 30° from the state shown in Figure 7(a) as viewed from above, and Figure 7(c) shows mark plate 2 rotated 30° from the state shown in Figure 7(b) as viewed from above.

[0041] FIG. 8 shows the angle changes of the straight line from the front mark 2Aα to the back mark 2Bα, the straight line from the front mark 2Aβ to the back mark 2Bβ, and the straight line from the front mark 2Aγ to the back mark 2Bγ when the mark plate 2 shown in FIG. 7 is rotated from FIG. 7(a) to FIG. 7(c) (the X direction is set to an angle of 0°).

[0042] 7(a) to 7(c) is a 60° change in angle, but by using three mark pairs, it can be seen that this is equivalent to an overall angle change of 180°. In other words, the tilt direction of optical axis AX5 can be determined simply by rotating mark plate 2 by 60°. As a result, the apparent inter-mark distance rn of any of the mark pairs will have a maximum or minimum value, and the tilt direction θw can be identified from the angle at which the maximum or maximum value is reached.

[0043] 9 shows the change in the rotation angle of mark plate 2 from Figure 7(a) to Figure 7(b) and from Figure 7(b) to Figure 7(c) when the change in the rotation angle of mark plate 2 is 40° instead of 30°. In the example of Figure 9, mark plate 2 needs to be rotated by 80°, but the overall angle change is also wider at 200°, and in addition, the situation at many rotation angles can be seen, which is advantageous for grasping the change in the apparent distance between the marks.

[0044] The above has described a method for determining the tilt direction θW of the optical axis AX5 of the imaging means 5, but if the tilt direction θw is known, the tilt angle θ1 can be determined. That is, in a cross section including the tilt direction θw as shown in Fig. 10, the optical refractive index n0 of the atmosphere, the optical refractive index n1 of the transparent plate 20, and the transparent plate thickness t are known, and the relationship between the tilt angle θ1 and the tilt angle θ2 (of the optical axis within the transparent plate) is known from the relationship sin θ1 / sin θ2 = n1 / n0, and distances A and B can be determined from the tilt angles θ1 and θ2, but there is a relationship in which the apparent displacement r determined by subtracting distance A from distance B is the difference between the actual mark-to-mark distance r0 and the apparent mark-to-mark distance rn, and the tilt angle θ1 can be determined from the known value and the apparent displacement r.

[0045] FIG. 11 illustrates an example of the tilt angle determination process for determining the tilt angle θ1. In FIG. 11(a), the optical refractive index n0 of the atmosphere is 1.0, the optical refractive index n1 of the transparent plate 20 is 1.5, and the thickness t of the transparent plate is 3.0 mm, all of which are known. FIG. 11(b) shows the change in apparent displacement r obtained by calculating the tilt angle θ2 of the optical axis within the transparent plate 20 with respect to the change in tilt angle θ1 of the optical axis AX5. In FIG. 11(b), the tolerance for the tilt angle θ1 of the optical axis AX5 of the imaging unit 5 is set to 0.5°, and the aim is to determine the relationship between the tilt angle θ1 and the apparent displacement r within the tolerance range. For example, if the measured apparent displacement value r' is 2.3 μm, FIG. 11(b) reveals that the tilt angle θ1 is between 0.10° and 0.15°.

[0046] The image sensor used in the imaging means 5 is composed of two-dimensionally arranged pixels, and the pixel resolution is determined by the number of pixels and the field of view. Therefore, when determining the tilt angle θ1 from the measured apparent displacement value r', it is necessary to consider the pixel resolution and imaging variability. For example, assuming a pixel resolution of 0.86 μm / pix and an imaging variability of ±0.1 pix, the variability of the measured apparent displacement value r' is approximately ±0.1 μm. Therefore, if the measured apparent displacement value r' is 2.3 μm, the apparent displacement r will be 2.2 to 2.4 μm, but as shown in Figure 11(b), it can be seen that the tilt angle θ1 is between 0.10° and 0.15°. In other words, if the tolerance θq of the tilt angle θ1 is 0.5°, the optical axis misalignment is within the allowable range, and no adjustment is required.

[0047] The relationship between the tilt angle θ1 and the apparent displacement r shown in Figure 11(b) is graphed and an approximate straight line is shown in Figure 12. As shown in Figure 12, the apparent displacement r can also be considered to be proportional to the tilt angle θ1. From this approximate formula, the tilt angle θ1 can be calculated to be 0.132° when the apparent displacement r is 2.3 μm.

[0048] On the other hand, if the measured apparent displacement r' is 9.5 μm, taking into account imaging variability, the apparent displacement r will be 9.4 μm to 9.6 μm. This result exceeds the apparent displacement r = 8.73 μm corresponding to a tilt angle θ1 of 0.5°, and it can be determined that the optical axis misalignment is outside the allowable range.

[0049] If the optical axis deviation exceeds a tolerance, the optical axis must be corrected. Fig. 13 shows an optical axis deviation correction means 101 in which an optical axis adjustment means 7 is added to the optical axis deviation evaluation means 1. In Fig. 13, the optical axis adjustment means 7 has the function of adjusting the optical axis AX5 of the imaging means 5 in a specified tilt direction θw by a specified tilt angle θ1. In addition, the control unit 10 is connected to the optical axis adjustment means 7 and has the function of specifying the tilt directions θw and θ1.

[0050] 1, in optical axis deviation correction means 101, a component corresponding to optical axis deviation evaluation means 1 shown in FIG. 1 identifies the tilt direction θw of optical axis AX5 of imaging means 5, and then identifies the tilt angle θ1. Also, FIG. 13(b) shows a state in which optical axis deviation correction means 101 has adjusted optical axis AX5 to face the normal direction of mark plate 2 based on the tilt direction θw and tilt angle θ1 obtained by the functioning of optical axis deviation evaluation means 1.

[0051] FIG. 14 is a flowchart showing the process of determining the tilt direction θw and tilt angle θ1 of the optical axis deviation by the optical axis deviation correcting means shown in FIG. 13, and then determining whether or not the optical axis deviation needs to be corrected, and bringing the optical axis deviation within the allowable range.

[0052] To accurately determine the value of the tilt angle θ1, it is desirable for the detection sensitivity to be as large as possible for a given change in the tilt angle θ1. Figure 15(b) shows the effect on detection sensitivity when the transparent plate thickness t, which is easily adjustable in Figure 15(a), is changed. Figure 15(b) shows the apparent displacement difference Δr calculated when the tilt angle θ1 is changed by 0.05° in increments of 0.05°, with the transparent plate thickness t set to 0.5 mm, 1.0 mm, and 2.0 mm.

[0053] Here, the change in tilt angle θ1 was set to 0.05° because the tolerance θq for tilt angle θ1 was set to 0.5°, and the aim was to detect a change of one-tenth of that. On the other hand, given that the pixel resolution of the imaging unit 5 is 0.86 μm / pix, the imaging variation is assumed to be ±0.1 pix. Therefore, a change of 0.43 μm, or 5 times that, or 0.5 pix, is considered valid for detection. Therefore, in Figure 15(b), it can be seen that the apparent displacement difference Δr when the tilt angle θ1 changes 0.05° is 0.43 μm or greater when the transparent plate thickness t is 2.0 mm. From this, it can be seen that in this embodiment of the present invention, a transparent plate thickness t of 2.0 mm or greater (for a transparent plate 20 with an optical refractive index n1 of 1.5) is sufficient to detect a change in tilt angle θ1 of 0.05°.

[0054] As described above, the present invention allows the tilt of the optical axis to be identified as the tilt direction and tilt angle without raising or lowering the imaging means, which makes it possible to correct any tilt in the optical axis and accurately obtain positional information for chip components or boards.

[0055] Therefore, by incorporating the optical axis deviation evaluation means or optical axis deviation correction means of the present invention into a mounting device that mounts chip components on a substrate, high-precision mounting becomes possible. That is, in a mounting device that includes a substrate stage that holds a substrate and a mounting head that is used to mount chip components on the substrate, by providing a mark plate parallel to the substrate surface, the optical axis of the imaging means that acquires positional information of the substrate or chip components can be adjusted in the normal direction to the surface of the object to be imaged, thereby enabling high-precision acquisition of positional information of the substrate or chip components, resulting in high-precision alignment and mounting. The application of the present invention is not limited to mounting devices, but can be applied to applications requiring highly accurate acquisition of positional information on a plane. This is particularly effective when it is necessary to adjust the vertical distance of the imaging means relative to the surface of the subject during imaging. Specifically, this invention is suitable for aligning the optical axis of the imaging means used to acquire positional information of marks to be detected in laminating devices, imprinting devices, exposure devices, etc. for sheet-fed substrates. [Explanation of symbols]

[0056] 1. Optical axis deviation evaluation method 2 Marking board 2A Surface Mark 2B Back Mark 5. Imaging Method 6 Rotation means 7 Optical axis adjustment means 10 Control Unit 20 Transparent plate 101 Optical axis deviation correction means AX5 Optical axis of imaging means I2B apparent backside mark position n0 Refractive index of the atmosphere n1 Refractive index of transparent plate r apparent displacement r' Apparent displacement measured value r0 distance between marks rn(n=1, 2, 3, . . .) Apparent distance between marks t Transparent plate thickness V5 Field of view of imaging device θw (optical axis of imaging means) tilt direction θ, θ1 (of the optical axis of the imaging means) tilt angle θ2 (of the optical axis within the transparent plate) tilt angle

Claims

1. 1. A method for evaluating optical axis deviation, in an imaging means that images at least one of a substrate or a chip component arranged on a plane, for determining a tilt direction and a tilt angle of an optical axis of the imaging means with respect to a normal line of the plane, comprising: A mark pair is set as an imaging target, the mark pair being a pair of marks provided on both sides of a transparent plate having a known thickness and a known refractive index, which is arranged parallel to the plane, an imaging process of imaging the mark pair multiple times while rotating the transparent plate with the normal direction in the plane as a rotation axis, with the mark pair within a field of view; a mark distance calculation step of calculating an apparent mark distance between the pair of marks imaged a plurality of times in relation to the angle of rotation; a tilt direction specifying step of determining the tilt direction from the positional relationship between the imaging means and the pair of marks provided on the transparent plate when the apparent distance between the marks becomes maximum or minimum; The optical axis deviation evaluation method includes a tilt angle specifying step of specifying the tilt angle using the apparent inter-mark distance in the tilt direction.

2. 2. The optical axis deviation evaluation method according to claim 1, The optical axis deviation evaluation method, wherein the marks forming the mark pair are provided at positions where they do not overlap when viewed from the normal direction of the plane.

3. 2. The optical axis deviation evaluation method according to claim 1, The method for evaluating optical axis deviation, wherein the transparent plate is rotated within the plane by an angle of 180 degrees or more.

4. 2. The optical axis deviation evaluation method according to claim 1, providing a plurality of the mark pairs, and calculating the angle of rotation and the mark distance for each mark pair in the mark distance calculation step; In the tilt direction specifying step, the tilt direction is determined by selecting a pair of marks that yields a maximum or minimum value for the distance between the marks.

5. From the tilt direction and the tilt angle of the imaging means obtained in any one of claims 1 to 4, An optical axis correction method for correcting an optical axis by the tilt angle in the tilt direction.

6. An optical axis deviation evaluation means for determining a tilt direction and a tilt angle of an optical axis of an imaging means for imaging at least one of a substrate or a chip component arranged on a plane, with respect to a normal line of the plane, comprising: a transparent plate with a known thickness and refractive index, with marks on both sides; a rotating means for rotating the transparent plate in a plane; An optical axis deviation evaluation means connected to the imaging means and equipped with a control unit having an image processing function and a calculation function.

7. A mounting apparatus for mounting chip components on a substrate, a substrate stage for holding the substrate; a mounting head used when mounting the chip component on the substrate; an imaging means for imaging at least one of the substrate and the chip component; A mounting device comprising the optical axis deviation evaluation means according to claim 6.

8. The mounting device according to claim 7, further comprising an optical axis adjusting means, From the tilt direction and the tilt angle of the imaging means obtained by the optical axis deviation evaluation means, The mounting device wherein the optical axis adjusting means corrects the tilt angle in the tilt direction.

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