Adhesion tester and method of operating adhesion tester

Abstract

An adhesion tester for testing characteristics of an adhesion between a substrate and an element adhered to the substrate, the adhesion tester comprising: a tool configured to contact the element during a test cycle, the tool being movable toward and away from the element to be tested; the positioning camera is used for observing the substrate through a lens of the positioning camera; and a processor arranged to communicate with the positioning camera for receiving an image captured by the camera, the processor configured for determining a position of the tool relative to the component based on the image, where the camera effectively observes the substrate at an angle with respect to a normal direction of the substrate, thus, when the tool is in a position close to or in contact with the element, the camera is allowed to observe the element to be tested and the tool.

Description

Technical Field

[0001] The present invention relates to an adhesion tester for testing the adhesion characteristics between a substrate and an element adhered to the substrate, and a method for determining the relative position of a tool of the adhesion tester with respect to an element to be tested. Background Art

[0002] An adhesion tester is a device for testing the characteristics (e.g., adhesion strength) of an element (such as a contact) mounted on a substrate. As the elements to be tested and the tools used become smaller and smaller, it becomes increasingly important to determine the position of the tool with high precision. Although previously an accuracy in the sub-millimeter range was considered sufficient, now the operator of an adhesion tester may require an accuracy of less than 1 μm.

[0003] Today, an adhesion tester typically includes a positioning camera and a tool for testing the element. Assuming that the distance between the tool and the positioning camera remains constant over time, the distance is calibrated at regular intervals. The calibration of the distance from the tool to the camera is performed by the operator, who uses a microscope to visually check whether the tool is positioned above a reference element. In another step, the positioning camera is positioned above the reference element. By obtaining the position difference of the positioning camera between the two steps, the distance from the camera to the tool can be obtained. Calibration may be required each time a different tool is selected and / or according to the needs of the operator. With the distance from the tool to the camera known, the test can be performed as follows: the camera is positioned above the element to be tested, and then the tool is moved to the distance from the camera to the tool so that the tool is positioned above the element to be tested, and then the test is performed. By this method, the test can be effectively performed "in the dark" because there is no visual confirmation whether the tool is positioned above the element. However, since the distance from the tool to the camera is known, it is currently considered not to be a problem, and adhesion testers are widely used and generally accepted with relatively low accuracy. As an alternative to testing "in the dark", the operator can observe the element to be tested and the tool through a microscope each time the test is performed. Obviously, this is very time-consuming work.

[0004] In addition to being time-consuming, requiring an experienced operator and possibly being inaccurate, the assumption that the distance from the tool to the camera remains constant over time has proven to be invalid. Although the variation may be at the micron level, when test accuracy in the micron range is required, this variation is too large.

[0005] To minimize the drift of the tool-to-camera distance, the solution provided is to use materials with a very low coefficient of thermal expansion to manufacture the base frame of the bonding tester. Examples of such materials are ceramic materials. The drawback of these solutions is that these materials are very expensive and difficult to process, thus significantly increasing the price of the bonding tester. In addition, these solutions do not alleviate the problem of manual calibration. Moreover, they generally cannot reduce the required precision to below 1 micron. Summary of the Invention

[0006] Accordingly, an object of the present invention is to at least partially overcome at least one of the above drawbacks. In particular, an object of the present invention is to take into account the change in the tool-to-camera distance after calibration.

[0007] Accordingly, a first aspect of the present invention relates to a bonding tester for testing the bonding characteristics between a substrate and an element bonded to the substrate, the bonding tester comprising: - a tool configured to contact the element during a test cycle, the tool being movable towards and away from the element to be tested; - a positioning camera configured to observe the substrate through the lens of the camera, and - a processor arranged to communicate with the positioning camera for receiving an image captured by the positioning camera, the processor being configured to determine the position of the tool relative to the element based on the image, wherein the camera effectively observes the substrate at an angle with respect to the normal direction of the substrate, so as to allow the camera to observe at least a part of the element to be tested and the tool when the tool is in a position close to or in contact with the element.

[0008] According to the first aspect of the present invention, compared with the existing known solutions, due to the tilted orientation of the camera, the camera can directly observe the element to be tested and the tool at or near the tool test position. Therefore, it can be verified by an operator or using image processing techniques whether the tool is indeed correctly aligned with the element to be tested at the required position. If it turns out that the element to be tested is not aligned with the tool at the required position, the tool can be moved until it is aligned with the element to be tested at the required position. This verification and / or repositioning of the tool relative to the element to be tested ensures that the correct test is always carried out, even if the distance from the tool to the camera has changed since the last calibration.

[0009] Accordingly, the present invention adopts a completely different approach compared with the previous efforts to change the material of the base frame and other efforts to minimize the change in the tool-to-camera distance, and provides a solution to compensate for the change in the tool-to-camera distance while allowing the distance change to occur.

[0010] Advantageously further, when recording an image of the tool above the component to be tested, this can verify the correctness of the test performed. This becomes particularly important when the test is performed automatically rather than manually, which is also the standard today.

[0011] Another advantage of the tilted orientation of the camera is that a clear image of the tool / component to be tested can be obtained even if the physical distance between the camera and the component changes. The position of the component in the image may change depending on the exact distance, but within a relatively wide range of distances, a clear image can still be advantageously obtained.

[0012] According to the present invention, the tool can be moved towards and away from the component to be tested. In particular, the tool can be moved up and down relative to the component to be tested to approach the component and perform a test on it. After the test is completed, the tool can be lifted again. During the up and down movement, the lateral and longitudinal positions of the tool remain unchanged. When the tool is lifted relative to the component to be tested, the tool can be moved with the camera towards the position of another component to be tested.

[0013] According to the present invention, the camera observes the substrate through a lens. As will be explained below, in principle any lens can be used. However, the best results can be obtained when the lens is a telecentric lens.

[0014] According to the present invention, the camera effectively observes the substrate at an angle with respect to the normal direction of the substrate. This "effective observation" can be achieved in at least three different ways. In one possible embodiment, the camera can be arranged at an angle with respect to the normal direction of the substrate. In another possible embodiment, a mirror can reflect the light received by the camera while the camera itself is arranged parallel to the normal direction of the substrate. In yet another embodiment, the lens can be arranged at an angle with respect to the camera.

[0015] In one embodiment, the bonding tester includes a base frame, a tool, and a positioning camera, both the tool and the positioning camera being mounted on the base frame such that when the base frame moves towards and away from the component to be tested, the tool and the positioning camera move together. It should be noted that even when the tool and the positioning camera are mounted on the same base frame, the distance between the tool and the camera may not be constant because temperature changes in the bonding tester environment may cause the base frame to become longer or shorter. Therefore, the principle of the proposed camera for observing the tool and the component to be tested still applies to such a bonding tester. Additionally, in such an embodiment, the base frame can be made of substantially any material, regardless of the coefficient of thermal expansion.

[0016] In one embodiment, the direction of movement of the tool is substantially perpendicular to the substrate, and the lens of the camera is mounted at an angle relative to the tool, with the angle between the lens and the direction of movement of the tool being between 10 degrees and 60 degrees, preferably between 20 degrees and 40 degrees. Those skilled in the art will recognize that the exact angle at which the camera is mounted depends on the horizontal and vertical distances between the camera and the tool. Preferably, when both the element to be tested and the tool are close to the midpoint of the image, and when the tool is just above / at the element to be tested, the image is clearest at the midpoint when the camera is tilted.

[0017] In one embodiment, the body of the camera is arranged at an angle relative to the lens of the camera, with the angle between the body and the lens of the camera being between 10 degrees and 80 degrees, preferably between 20 degrees and 50 degrees. The inventors have found that tilting the body of the camera relative to the lens can increase the area of the image that is in focus, thereby obtaining more accurate results when the tool is not placed correctly. The tilting of the camera body relative to the lens can be achieved in two different ways.

[0018] In one embodiment, the angle between the camera body and the direction of movement of the tool is greater than the angle between the lens of the camera and the direction of movement of the tool. In such an embodiment, the camera body rotates away from the tool compared to the camera lens.

[0019] In an alternative embodiment, the angle between the camera body and the direction of movement of the tool is less than the angle between the lens of the camera and the direction of movement of the tool. In such an embodiment, the camera body rotates towards the tool (e.g., parallel to the direction of movement of the tool) compared to the camera lens.

[0020] One embodiment or the other may be preferred, depending mainly on the construction and orientation of the other components of the bonding tester.

[0021] In one embodiment, the camera includes a telecentric lens. This is beneficial for producing an image with the least amount of distortion and the most accurate view of the element to be tested, so that the tool can be moved to the desired position with a minimum number of iterations.

[0022] The second aspect of the present invention relates to a method for determining the relative position of a tool of a bonding tester relative to an element to be tested, the method comprising the following steps: - Moving the tool towards the element, - Simultaneously observing the tool and the element in the same image with a positioning camera of the bonding tester; and - Processing the image captured by the positioning camera with a processor to determine the position of the tool relative to the element to be tested.

[0023] Compared with the advantages obtained by the present invention according to the first aspect of the present disclosure, the method can also visually confirm whether the tool is located at the desired position of the component to be tested.

[0024] In particular, if it turns out that the tool is not correctly positioned, the method may include the following additional steps: providing feedback to the tool position controller of the bonding tester (the feedback being related to the determined distance between the tool and the component to be tested), and moving the tool until the tool is correctly aligned with or exactly above the component to be tested. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] These and other aspects of the present invention will now be described with reference to the accompanying drawings, in which like or identical elements are denoted by the same reference numerals. In these drawings: Figure 1 A first embodiment of a bonding tester according to the present invention is schematically shown in a side view; Figure 2 A second embodiment of a bonding tester according to the present invention is schematically shown in a side view; Figure 3 A third embodiment of a bonding tester according to the present invention is schematically shown in a side view; and Figure 4 Is schematically shown using a camera of a bonding tester as shown in one of Figures 1 to 3 The obtained image. DETAILED DESCRIPTION

[0026] Figure 1 A bonding tester 1 for testing the characteristics of the bond, in particular the bond strength, between a substrate 100 and a component 200 bonded to the substrate 100 is shown. For this purpose, a tool 11 is located above the component 200 and is moved downward in the movement direction M, contacts the component 200 and applies a load on the component 200 until the component is displaced. Based on the load required to move the component 200, the load cell 12 can derive the bond strength between the component 200 and the substrate 100. Thus, this test is generally a destructive test, in which the bond strength of one component 200 is tested, and in which it is assumed that the other components not tested have the same bond strength. After the bond between the component 200 and the substrate 100 is broken, the tool 11 can be moved upward again to move towards a different position and / or place a different substrate 100 with the component to be tested below the tool 11.

[0027] Figure 1Further shown therein is the positioning camera 21, here with a telecentric lens 22. Importantly, while the positioning cameras of previously known bonding testers look straight on in the normal direction N of the substrate and use a previously established distance from the tool to the camera to determine the position of the bonding tester relative to the element to be tested, the positioning camera 21 shown here has an angled orientation, so that it observes the substrate 100 at an angle α. The beneficial effect of this is that when the tool 11 is near or in contact with the element 200, the camera 21 can observe not only the element 200 to be tested but also the tool 11 in the same image. Based on this image, the processor 31 of the bonding tester 1 can determine the position of the tool 11 relative to the element 200 to be tested, the processor 31 being arranged to communicate with the camera 21 and being configured to receive the image obtained by the camera 21. Thus, the processor 31 can determine whether the tool 11 is accurately placed on the element 200, in particular in the middle of the element 200, or whether the tool should be moved to be accurately positioned on the element 200. This results in the bonding test being not only more accurate than previously available tests, but most importantly, it is now possible to confirm and record whether the test was carried out in an optimal manner.

[0028] As Figure 1 shown, both the tool 11 and the camera 21 are mounted on the same base frame 41. When this base frame 41 moves, for example up or down away from / towards the element 200 to be tested, the camera 21 and the tool 11 move with it. However, importantly, this does not mean that the distance between the tool 11 and the camera 21 is constant. When the ambient temperature rises or falls, the base frame 41, regardless of the material it is made of, will elongate or shorten. This effect will be greater for one material than for another, but this effect is always present to some extent. As the element 200 to be tested becomes smaller and smaller, this relative movement between the camera 21 and the tool 11 becomes increasingly problematic. The angled camera 21 arrangement disclosed here solves this problem, because typically the relative movement may be large enough to displace the tool 11 relative to the element 200 to be tested, but it will not be large enough to cause the tool 11 and / or the element 200 to disappear from the image captured by the camera 21.

[0029] As Figure 1 shown, the angled view towards the substrate 100 can be achieved, for example, by orienting the lens 22 and the body 23 of the camera 21 at the same angle α relative to the normal direction N of the substrate 100. As those skilled in the art will recognize, the exact value of the angle α may vary in different setups, and in particular may depend on the total height of the tool 11 and the horizontal distance between the tool 11 and the camera 21. In the shown embodiment, the angle α is approximately 25 degrees.

[0030] Next, turn to Figure 2 and Figure 3 , where variations of the technical principle explained based on Figure 1 are shown. In particular, in Figure 2 and Figure 3 , the body 23 of the camera 21 is arranged at an angle β with respect to the telecentric lens 22 of the camera 21. Compared with the setting in Figure 1 , where the body 23 and the lens 22 are aligned with each other, this setting ensures that the obtained image is clear over a wider width, which will result in a faster convergence to the optimal position of the tool 11 for the test element 200. For example, the body can be rotated by an angle of up to 80 degrees compared with the orientation of the lens 22.

[0031] In particular, in the embodiment shown in Figure 2 , compared with the normal direction N of the substrate 100, the body 23 rotates away from the lens 22 such that the angle γ between the body 23 and the normal N is greater than the angle α between the lens 22 and the normal N.

[0032] On the other hand, in the embodiment shown in Figure 3 , compared with the normal direction N of the substrate 100, the body 23 rotates towards the tool 11 such that the angle γ between the body 23 and the normal N is less than the angle α between the lens 22 and the normal N.

[0033] Next, turn to Figure 4 , which schematically shows the images that can be obtained by the bonding tester 1 using Figure 1 , Figure 2 and / or Figure 3 . Figure 4 The substrate 100, two components (one of which is to be tested), and the tool 11 are visible in

[0034] . As shown, the center of the tool 11 is not precisely aligned with the center of the component 200 to be tested, and the lateral distance dy and the longitudinal distance dx need to be compensated. If the test is performed with the tool 11 in the position shown here, basically useless results will be obtained. Figure 4 Figure 4 Referring to the bonding tester 1 shown previously, determining the relative position of the tool 11 of the bonding tester with respect to the component 200 to be tested can be done by moving the tool 11 towards the component 200 (as shown in Figure 4 ), and using the positioning camera 21 of the bonding tester to simultaneously capture the same image ( Figure 4Observe the tool 11 and the component 200 in the example image shown, and process the image captured by the positioning camera 21 with the processor 31 to determine the position of the tool 11 relative to the component 200 to be tested (obtain the values of dx and dy). If it is subsequently determined that the tool 11 is arranged at a distance of dx, dy from the component to be tested, and this distance is greater than the acceptable threshold, inaccurate positioning can be compensated by providing feedback on the positioning inaccuracy to the tool position controller 51 of the bonding tester and repeatedly moving the tool until the positioning inaccuracy is overcome and the tool 11 contacts the component 200 at the desired position in the middle.

[0035] Reference numeral 1 Bonding tester 11 Tool 12 Load cell 21 Positioning camera 22 Telecentric lens 23 Camera body 31 Processor 41 Base frame 51 Tool position controller 100 Substrate 200 Component to be tested d Distance between the tool and the component to be tested M Movement direction of the tool N Normal direction of the substrate α Angle between the lens and the movement direction of the tool β Angle between the lens and the camera body γ Angle between the camera body and the movement direction of the tool

Claims

1. An adhesion tester (1) for testing the characteristics of the adhesion between a substrate (100) and an element (200) adhered to the substrate (100), the adhesion tester (1) comprising: - A tool (11) configured to contact the element (200) during a test cycle, the tool (11) being movable towards and away from the element (200) to be tested, - A positioning camera (21) configured to observe the substrate (100) through a lens (22) of the camera (21), and - A processor (31) arranged to communicate with the positioning camera (21) for receiving images captured by the positioning camera (21), the processor (31) being configured to determine the position of the tool (11) relative to the element (200) based on the images, wherein the camera (21) effectively observes the substrate (100) at an angle with respect to the normal direction of the substrate (100), so that when the tool (11) is in a position close to or in contact with the element (200), the camera (21) is allowed to observe at least a part of the element (200) and the tool (11) to be tested.

2. The bonding tester according to claim 1, wherein, The adhesion tester (1) includes a base frame (41), and both the tool (11) and the positioning camera (21) are mounted on the base frame (41) such that when the base frame (41) moves towards and away from the element (200) to be tested, the tool (11) and the positioning camera (21) move together.

3. The bonding tester according to claim 1 or 2, wherein, The movement direction (M) of the tool (11) is substantially perpendicular to the substrate (100), and wherein the lens (22) of the camera (21) is mounted at an angle (α) with respect to the movement direction (M) of the tool (11), and the angle (α) between the lens (22) and the movement direction (M) of the tool (11) is between 10 degrees and 60 degrees, preferably between 20 degrees and 40 degrees.

4. The bonding tester according to any one of the preceding claims, wherein, The body (23) of the camera (21) is arranged at an angle (β) with respect to the lens (22) of the camera (21), and the angle (β) between the lens (22) and the body (23) of the camera (21) is between 10 degrees and 80 degrees, preferably between 20 degrees and 50 degrees.

5. The bonding tester according to claim 4, wherein, The angle (γ) between the body (23) of the camera (21) and the movement direction (M) of the tool (11) is greater than the angle (α) between the lens (22) of the camera (21) and the movement direction (M) of the tool (11).

6. The bonding tester according to claim 4, wherein The angle (γ) between the body (23) of the camera (21) and the movement direction (M) of the tool (11) is less than the angle (α) between the lens (22) of the camera (21) and the movement direction (M) of the tool (11).

7. The bonding tester according to any one of the preceding claims, wherein, The camera (21) includes a telecentric lens (22).

8. A method for determining the relative position of a tool (11) of an adhesion tester (1) with respect to an element (200) to be tested, the method comprising the following steps: - Moving the tool (11) towards the element (200); - Observing the tool (11) and the element (200) simultaneously in the same image with a positioning camera (21) of the adhesion tester (1); and - Processing the image captured by the positioning camera (21) with a processor (31) to determine the position of the tool (11) with respect to the element (200) to be tested.

9. The method according to claim 8, wherein If it is determined that the tool (11) is arranged at a certain distance (d) from the element (200) to be tested, the method further comprises the following steps: - Providing feedback to a tool position controller (51) of the adhesion tester (1), the feedback being related to the determined distance (d) between the tool (11) and the element (200) to be tested; and - Moving the tool (11) until at least a part of the tool (11) contacts the element (200) to be tested or is located directly above the element (200) to be tested.

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