Displacement imaging system and method suitable for semiconductor IGBT power module detection

Abstract

The invention relates to a displacement imaging system suitable for semiconductor IGBT power module detection, which comprises a camera, a lens, a coaxial illumination module, an execution mechanism, an image processing module and a control module, and is characterized in that the execution mechanism drives the lens to reciprocate up and down in a direction vertical to an IGBT module; the control module controls the execution mechanism to drive the lens to move up and down and controls the camera to shoot images. And the image processing module is used for calculating the sharpness of different image areas of each image, performing height mapping according to the height of the sharpness of the image areas to obtain a height map, and using the gray value of the clearest image in the area as the gray value of the full-clear image in the same area to finally obtain the final full-clear image. According to the method, the height information of each point on the surface of the IGBT module can be accurately obtained to generate the height map, so that quantitative detection of three-dimensional shape parameters such as the height of the aluminum wire is realized, and the visibility and detectability of defects are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor IGBT power module testing, and more particularly to a displacement imaging system and method suitable for semiconductor IGBT power module testing. Background Technology

[0002] In new energy vehicles, IGBT (Insulated Gate Bipolar Transistor) power modules are high-speed semiconductor switching devices that determine the power output of the battery. Because they must withstand high current and high voltage, IGBT modules typically use aluminum wires with a diameter of approximately 300 μm, bonded together via wire-bonding to electrically connect the collector, emitter, and gate.

[0003] like Figure 1 The diagram shows the internal structure of an IGBT, including aluminum wire 101, chip one 102, chip two 103, substrate 105, and ceramic surface 104. In the manufacturing process, quality control includes, but is not limited to, the height, offset, poor soldering, and wire contact of aluminum wire 101; scratches, foreign objects, and damage to ceramic surface 104 and substrate 105; and damage, positional errors, and impacts to chip one 102 and chip two 103.

[0004] Current detection methods are mostly 2D detection, which involves taking a picture from above with a camera to obtain a 2D image, such as... Figure 1 As shown, local processing is performed on the image, such as at the chip location, image matching is added, using a defect-free image as a reference, and pixel matching is performed point by point. If there is a grayscale difference between the reference and the object being measured, or if the variance of the region is too large, it is determined that there is a defect in that region.

[0005] Currently, most IGBT testing is 2D testing, which involves taking a picture with a camera facing directly at the camera to obtain a 2D image, such as... Figure 1 As shown. This method can detect defects in chip 102, chip 2 103, ceramic surface 104, and substrate 105, but it is not applicable to the detection of defects in aluminum wires. 2D inspection has several main shortcomings: (1) The true height of the aluminum wire cannot be measured.

[0006] (2) The height of the aluminum wire generally exceeds the depth of field of the vision system, resulting in the inability to obtain a clear image.

[0007] (3) There are surfaces with large differences in elevation, for example Figure 1 The high surface 106 and the base 105 in the image cannot be focused simultaneously.

[0008] Therefore, there is an urgent need for a technology that can obtain aluminum wire height data to detect height-related anomalies. Summary of the Invention

[0009] The technical problem to be solved by this invention is to design a displacement imaging system and method suitable for the detection of semiconductor IGBT power modules, so as to solve the problems that existing 2D detection technology cannot measure the height of aluminum wires, the image is blurred due to insufficient depth of field, and the detection fails in weak texture areas.

[0010] To address the aforementioned technical problems, this invention provides a displacement imaging system suitable for detecting semiconductor IGBT power modules, comprising a camera, a lens, a coaxial illumination module, an actuator, an image processing module, and a control module. The actuator drives the lens to reciprocate up and down in a direction perpendicular to the IGBT module. The coaxial illumination module includes a beam splitter and a structured light illumination system. The structured light illumination system is used to add active texture information to the weak texture areas of the IGBT power module to create sharpness differences at different heights. The beam splitter is a beam splitting prism or a beam splitting plate. The control module controls the actuator to drive the lens to move up and down and controls the camera to capture images. The image processing module calculates the sharpness of different image regions in each image, performs height mapping based on the height of the image region's sharpness to obtain a height map, and uses the grayscale value of the sharpest image in that region as the grayscale value of the full-sharp image in the same region, ultimately obtaining the final full-sharp image.

[0011] Furthermore, in this invention, the actuator includes a stator and a mover, the mover being rigidly connected to the lens via a machining component, and the mover being driven by a driving device to reciprocate along the vertical direction.

[0012] Furthermore, in this invention, the stroke of the actuator is greater than the height difference between the lowest and highest surfaces of the IGBT power module.

[0013] Furthermore, in this invention, the size of the beam splitter is greater than or equal to the size of the lens.

[0014] Furthermore, in this invention, the structured light illumination system uses a DLP system, an LCOS system, or an LCD system, or a pattern is photolithographically etched on a glass substrate and then imaged onto the IGBT module via a critical illumination system.

[0015] This method also provides a displacement imaging method suitable for the detection of semiconductor IGBT power modules, which uses the displacement imaging system for the detection of semiconductor IGBT power modules as described above, and includes the following steps: Step S1: Project the pattern onto the IGBT module using a coaxial illumination system; Step S2: Drive the lens downwards until the focal plane of the lens is focused on the lowest surface of the IGBT module, denoted as height H1; Step S3: Slowly move the lens upwards until its focal plane is focused on the highest surface of the IGBT module, denoted as height H2. During the movement of the lens from the lowest to the highest surface of the IGBT module, take one image at intervals of distance G, obtaining a total of N images. Number the N images, where G = k * D. N = (H2 - H1) / G, where D is the depth of field of the lens; Step S4: Calculate the sharpness of different image regions for each image; Step S5: Traverse the resolution of all regions in the IGBT module, perform height mapping based on the height of the resolution of the image region, and obtain a height map; Step S6: Based on the height map, map the grayscale of the corresponding image to the full-resolution image.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention, through vertical scanning and sharpness analysis, can accurately acquire the height information of various points on the surface of an IGBT module, generating a height map, thereby achieving quantitative detection of three-dimensional morphological parameters such as aluminum wire height. This invention fuses the clearest parts at different heights into a single image, obtaining a clear two-dimensional image from the substrate to the aluminum wire apex, greatly improving the visibility and detectability of defects. By introducing structured light illumination, this invention actively adds artificial textures to weakly textured areas such as chips and ceramic surfaces, causing significant differences in sharpness at different heights in these areas, thus making sharpness-based height measurement methods equally effective for such areas. This invention can simultaneously detect the height, shape, and positional defects of aluminum wires, as well as various surface defects of chips and substrates, providing an integrated, high-precision solution. Attached Figure Description

[0017] The specific embodiments of the present invention will be further explained below with reference to the accompanying drawings.

[0018] Figure 1 This describes the internal structure of the IGBT module.

[0019] Figure 2 This is a schematic diagram of the displacement imaging system for detecting semiconductor IGBT power modules according to the present invention.

[0020] Figure 3 This is a flowchart of the displacement imaging method for detecting semiconductor IGBT power modules according to the present invention.

[0021] Figure 4 This is a schematic diagram of height mapping in this invention.

[0022] Figure 5 This refers to the height data of the IGBT module in this invention.

[0023] Figure 6 This is the image obtained from the current 2D detection.

[0024] Figure 7 This is a clear global image obtained by the displacement imaging system of the present invention, which is applicable to the detection of semiconductor IGBT power modules. Detailed Implementation Example 1

[0025] Combination Figure 2 As shown, the displacement imaging system for semiconductor IGBT power module detection in this embodiment includes a camera 201, a lens 202, a coaxial illumination module, an actuator 207, an image processing module, and a control module. The actuator 207 drives the lens 202 to reciprocate up and down in the direction perpendicular to the IGBT module. The coaxial illumination module includes a beam splitter 203 and a structured light illumination system 204. The structured light illumination system 204 is used to add active texture information to the weak texture area of ​​the IGBT power module to form a sharpness difference at different heights. The beam splitter 203 is a beam splitter prism or a beam splitter plate. The control module controls the actuator 207 to drive the lens 202 to move up and down and controls the camera 201 to capture images. The image processing module is used to calculate the sharpness of different image regions in each image, and to perform height mapping based on the height of the image region's sharpness to obtain a height map. The grayscale value of the sharpest image in that region is used as the grayscale value of the full-sharp image in the same region, finally obtaining the final full-sharp image.

[0026] In this embodiment, preferably, the camera 201 is a 21-megapixel camera with a pixel size of 4.5 μm and a frame rate of 230 FPS using the GSPRINT4521 chip from Changguang Chenxin Technology Co., Ltd., and the lens 202 is an object-side telecentric or double telecentric lens with a magnification of 0.45x. Since the IGBT module is for macroscopic detection, and the width of the aluminum wire is typically 300 μm, the pixel resolution achieved by the actual combination of camera 201 and lens 202 only needs to be 10 μm.

[0027] In this embodiment, preferably, the actuator 207 includes a stator 2072 and a mover 2071. The mover 2071 is rigidly connected to the lens 202 through a machining part. The mover 2071 is driven by a driving device to reciprocate along the vertical direction.

[0028] Preferably, in this embodiment, the stroke of the actuator 207 is greater than the height difference between the lowest and highest surfaces of the IGBT power module. Since the height difference between the lowest and highest surfaces of the IGBT is typically 3 mm, in this embodiment, an actuator 207 with a stroke of 5 mm is specifically selected.

[0029] Preferably, in this embodiment, the size of the beam splitter 203 is greater than or equal to the size of the lens 202, thereby ensuring the light transmission effect. Specifically, in this embodiment, the outer diameter of the lens used in conjunction with a 21-megapixel camera (0.45 times the lens diameter) is typically 90mm, and the beam splitter 203 uses a beam splitter prism with a size of 100mm.

[0030] In this embodiment, preferably, the structured light illumination system 204 uses a DLP system, an LCOS system, or an LCD system, or it photolithographically patterns a pattern on a glass substrate and then images the pattern onto the IGBT module through a critical illumination system. Specifically, in this embodiment, the structured light illumination system 204 uses a 0.67-inch target surface of a DLP system manufactured by Texas Instruments, providing 4K resolution; the higher the resolution, the better the effect. Example 2

[0031] Combination Figure 3 As shown, the displacement imaging method for detecting semiconductor IGBT power modules in this embodiment adopts the displacement imaging system for detecting semiconductor IGBT power modules as described in Embodiment 1, and specifically includes the following steps: Step S1: Project the pattern onto the IGBT module using a coaxial illumination system.

[0032] In the application scenarios of IGBT modules, there are Figure 1 For example, the textures of the chip 102 surface, substrate 105, and ceramic surface 104 are very weak, lacking sharpness. This results in consistently low sharpness across all scanning heights, from H1 to H2, rendering the method of determining sharpness by height ineffective. Adding a coaxial illumination system below the lens 202 can effectively solve this problem. The structured light illumination system can actively add texture information to areas with weak textures, thus ensuring that these areas exhibit sharpness differences at different heights.

[0033] Step S2: Drive the lens downwards until the focal plane of the lens is focused on the lowest surface 2061 of the IGBT module, denoted as height H1. The lowest surface 2061 is usually the base 105.

[0034] Step S3: Slowly move the lens upwards until its focal plane is focused on the highest surface 2062 of the IGBT module, denoted as height H2. The highest surface 2062 is typically the vertex of aluminum wire 101. During the movement of the lens from the lowest surface to the highest surface of the IGBT module, take one image at intervals of G, obtaining a total of N images. Number the N images, where G = k * D. Specifically, in this embodiment, D represents the depth of field of the lens. To obtain the height of the aluminum wire, the captured images need to be height-mapped, and the N images are numbered from 1 to N.

[0035] Step S4: Calculate the sharpness of different image regions for each image.

[0036] Step S5: Traverse the resolution of all regions in the IGBT module, perform height mapping based on the resolution of the image region, and obtain a height map.

[0037] Combination Figure 4 As shown in the figure, A and B are regions within the IGBT module. If regions A and B have the best sharpness in the nth and mth images respectively, then the height of region A can be calculated as HA = H1 + n*G, and the height of region B as HB = H1 + m*G.

[0038] By iterating through the resolution of all regions in the IGBT module, the final result can be obtained. Figure 1 Height data of the IGBT module, such as Figure 5 As shown. Figure 5 The shades of color in the diagram indicate altitude; the whiter the color, the higher the altitude, and the darker the color, the lower the altitude.

[0039] Step S6: Based on the height map, map the grayscale of the corresponding image to the full-resolution image.

[0040] by Figure 4 Taking regions A and B as examples, their images are clearest in the nth and mth images, respectively. Therefore, we can set the grayscale values ​​of regions A and B to the grayscale values ​​of the nth and mth images, respectively. That is, let In represent the grayscale value of region A and Im represent the grayscale value of region B. Then, we create a new image ID, which is overlaid in both regions A and B using In and Im. Similarly, by traversing all IGBT module regions, we can obtain a globally clear image ID.

[0041] by Figure 1 Taking the upper left corner as an example, existing 2D detection technology and the displacement imaging method suitable for semiconductor IGBT power module detection in Embodiment 1 are used for detection respectively. The images focused on the ceramic surface are as follows: Figure 6 and Figure 7 As shown: In the images obtained by existing methods, only the ceramic surface 5014 and the first aluminum wire solder joint 5013 are clear, while the middle part of the aluminum wire 5012, the second solder joint 5011, and the surface they occupy are very blurry. However, in the image obtained by the method of this embodiment, the first aluminum wire solder joint 5021 and the second solder joint 5023 are very clear, the middle part of the aluminum wire 5022 also has high sharpness, and particles can be seen on the ceramic surface 5024, resulting in a fully clear image with high sharpness at all heights.

[0042] Many specific details have been set forth in the foregoing description to provide a thorough understanding of the present invention. However, the above description is merely a preferred embodiment of the present invention, and the present invention can be implemented in many other ways different from those described herein. Therefore, the present invention is not limited to the specific embodiments disclosed above. Furthermore, any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, using the methods and techniques disclosed above, without departing from the scope of the present invention. Any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A displacement imaging system suitable for detecting semiconductor IGBT power modules, characterized in that: The system includes a camera (201), a lens (202), a coaxial illumination module, an actuator (207), an image processing module, and a control module. The actuator (207) drives the lens (202) to reciprocate up and down in the direction perpendicular to the IGBT module. The coaxial illumination module includes a beam splitter (203) and a structured light illumination system (204). The structured light illumination system (204) is used to add active texture information to the weak texture area of ​​the IGBT power module to form a difference in sharpness at different heights. The beam splitter (203) is a beam splitter prism or a beam splitter plate. The control module controls the actuator (207) to drive the lens (202) to move up and down and controls the camera (201) to capture images. The image processing module is used to calculate the sharpness of different image areas of each image, and to perform height mapping based on the height of the image area's sharpness to obtain a height map. The gray value of the sharpest image in that area is used as the gray value of the full-sharp image in the same area, and finally, the final full-sharp image is obtained.

2. The displacement imaging system for detecting semiconductor IGBT power modules according to claim 1, characterized in that: The actuator (207) includes a stator (2072) and a mover (2071). The mover (2071) is rigidly connected to the lens (202) through a machining part. The mover (2071) is driven by a driving device to reciprocate along the vertical direction.

3. The displacement imaging system for detecting semiconductor IGBT power modules according to claim 2, characterized in that: The stroke of the actuator (207) is greater than the height difference between the lowest and highest surfaces of the IGBT power module.

4. The displacement imaging system for detecting semiconductor IGBT power modules according to claim 1, characterized in that: The size of the beam splitter (203) is greater than or equal to the size of the lens (202).

5. The displacement imaging system for detecting semiconductor IGBT power modules according to claim 1, characterized in that: The structured light illumination system (204) uses a DLP system, an LCOS system, or an LCD system, or it photolithographically prints a pattern on a glass substrate and then images the pattern onto the IGBT module through a critical illumination system.

6. A displacement imaging method suitable for detecting semiconductor IGBT power modules, characterized in that: The displacement imaging system for detecting semiconductor IGBT power modules as described in any one of claims 1-5 includes the following steps: Step S1: Project the pattern onto the IGBT module using a coaxial illumination system; Step S2: Drive the lens downwards until the focal plane of the lens is focused on the lowest surface (2061) of the IGBT module, which is recorded as height H1; Step S3: Slowly move the lens upwards until its focal plane is focused on the highest surface (2062) of the IGBT module, denoted as height H2. During the movement of the lens from the lowest to the highest surface of the IGBT module, take one image at intervals of distance G, obtaining a total of N images. Number the N images, where G = k * D. N = (H2 - H1) / G, where D is the depth of field of the lens; Step S4: Calculate the sharpness of different image regions for each image; Step S5: Traverse the resolution of all regions in the IGBT module, perform height mapping based on the height of the resolution of the image region, and obtain a height map; Step S6: Based on the height map, map the grayscale of the corresponding image to the full-resolution image.

Images