CN115165899A - LED chip welding quality detection method adopting optical means - Google Patents
LED chip welding quality detection method adopting optical means Download PDFInfo
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Abstract
The invention relates to the field of testing flaws and defects of an LED chip, in particular to an LED chip welding quality detection method adopting an optical means, which comprises the following steps: pushing the currently selected LED chip template to a welding quality detection station, irradiating the LED chip template to be detected by a red light source arranged on the welding quality detection station, controlling the pose of the LED chip template to be detected, adjusting the angle of the red light source, and irradiating the LED chip template by the red light source in a vertical mode; and acquiring an image of the LED chip to be analyzed, and determining the welding quality of the LED chip to be analyzed. The LED chip is tested for flaws and defects by means of an optical means, and the condition that the color of the welding part of the LED chip is close to red is considered, so that the welding position is brighter by using a red light source, the quality detection result of the chip can be accurately obtained, and the LED chip is not influenced by the position of the LED chip.
Description
Technical Field
The invention relates to the field of testing flaws and defects of an LED chip, in particular to an LED chip welding quality detection method adopting an optical means.
Background
The LED chip, also called LED light emitting chip, is a core component of an LED lamp, i.e. the P-N junction, and its main function is to convert electrical energy into light energy. The LED chip is mainly made of monocrystalline silicon and consists of two parts, wherein one part is a P-type semiconductor, holes are dominant in the P-type semiconductor, and the other part is an N-type semiconductor, and the electron concentration of the N-type semiconductor is far greater than that of the holes; when the two semiconductors are connected, a P-N junction is formed between the two semiconductors, and when current is applied to the LED chip through the wires, electrons are pushed to a P region where they recombine with holes, and then energy is emitted in the form of photons, which is the principle of LED chip light emission.
With the development of modernization, LED chips are widely used in various industries, and the most important factor affecting the performance of LED chips is the quality of soldering. The defects of offset welding, PN junction connection, ball wireless connection and the like can occur in the welding process of the LED chip, and the service life of the LED chip can be greatly influenced by the defects. Therefore, it is necessary to detect defects in the bonding result of the LED chip.
In the prior art, an AOI detection method is often adopted to detect defects of a welding result of an LED chip, but the method cannot ignore the requirement of the position, and the position of the LED chip is not fixed in an industrial scene, so the method is not high in accuracy when used for detection.
Disclosure of Invention
In order to solve the above technical problems, an object of the present invention is to provide a method for detecting the soldering quality of an LED chip by an optical means, wherein the method comprises the following steps:
pushing the currently selected LED chip template to a welding quality detection station, irradiating the LED chip template to be detected by a red light source arranged on the welding quality detection station, controlling the pose of the LED chip template to be detected, adjusting the angle of the red light source, and irradiating the LED chip template by the red light source in a vertical mode;
collecting an LED chip template image by a CCD industrial camera arranged on the welding quality detection station, wherein the CCD industrial camera is positioned right above the LED chip template, and transmitting the LED chip template image collected by the CCD industrial camera to an industrial computer by adopting the industrial computer as a main controller;
judging whether the collected LED chip template image meets a preset definition standard rule or not, if not, adjusting light emitting parameters of the red light source and then skipping to the step of collecting the LED chip template image until the definition standard rule is judged; if the collected LED chip template image meets the preset definition standard-reaching rule, processing the collected LED chip template image to obtain a texture characteristic value of the template texture image;
and acquiring an LED chip image to be analyzed, analyzing the LED chip image to be analyzed and the template texture image according to the texture characteristic value of the template texture image, and determining the welding quality of the LED chip to be analyzed.
The embodiment of the invention at least has the following beneficial effects:
the LED chip is tested for flaws and defects by means of an optical means, the color of the welding part of the LED chip is close to red, and the gray value change of pixel points on the circumferences with different sizes around the pixel points on the template gray image is considered, the red light source is used in the invention to enable the welding part to be brighter, and the gray difference between the welding part and other parts can be enlarged. After the light source is selected to be finished, the LED chip template is polished in a vertical irradiation mode, the vertical irradiation has the advantages that the irradiation area is large, the illumination uniformity is good, whether the collected LED chip template image meets the preset definition standard-reaching rule or not is judged, if the collected LED chip template image does not meet the preset definition standard-reaching rule, after the light emitting parameters of the red light source are adjusted, the step of collecting the LED chip template image is skipped to until the definition standard-reaching judgment is carried out to obtain the texture value of the pixel point, the influence of the position of the chip to be analyzed is avoided, the rotation invariability is realized, the matching result is accurate, and the quality detection result is accurate.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions and advantages of the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
Fig. 1 is a flow chart of a method for detecting the welding quality of an LED chip by optical means according to the present invention.
Detailed Description
To further illustrate the technical means and effects of the present invention adopted to achieve the predetermined objects, the following detailed description of the LED chip soldering quality inspection method using optical means according to the present invention with reference to the accompanying drawings and preferred embodiments shows the following detailed descriptions. In the following description, different "one embodiment" or "another embodiment" refers to not necessarily the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
The following describes a specific scheme of the LED chip soldering quality detection method by optical means in detail with reference to the accompanying drawings.
Example (b):
referring to fig. 1, a flowchart of a method for detecting a bonding quality of an LED chip by an optical method according to an embodiment of the present invention is shown, where the method includes the following steps:
the method comprises the steps of firstly, acquiring a gray level image of an LED chip template by using a visible light means, segmenting the gray level image of the LED template by using an Otsu threshold method to obtain a welding pad area, and acquiring the longest side length of the welding pad area.
First, the inspection of the bonding quality of the LED chip is mainly determined based on the bonding area. The main judgment basis is whether the welding pad is in contact with the PN line or not, and the covering relation between the welding point and the welding pad. When the welding quality of the LED chip is excellent, the welding pad is not in contact with the PN line, the welding spot completely covers the welding pad, and the PN line is obvious. Therefore, in order to detect the welding quality of the LED chip, the image of the LED chip to be detected must be positioned on the welding portion for detection, and a template of a welding area needs to be obtained first, so that the welding area in the image to be analyzed can be accurately obtained.
Specifically, an LED chip with excellent soldering quality is obtained as a template, and since the color of the soldering portion of the LED chip is close to red, the use of a red light source in the present embodiment makes the soldering portion brighter, and can enlarge the grayscale difference between the soldering portion and other portions. After the light source is selected, the LED chip template is polished by the light source in a vertical irradiation mode, and the vertical irradiation has the advantages of large irradiation area and good illumination uniformity. And a CCD industrial camera is adopted to collect the LED chip template image, and the camera is positioned right above the chip. And carrying out graying processing on the collected LED chip template image to obtain the LED chip template grayscale image. Further concretely: pushing the currently selected LED chip template to a welding quality detection station, irradiating the LED chip template to be detected by a red light source arranged on the welding quality detection station, controlling the pose of the LED chip template to be detected, adjusting the angle of the red light source, and irradiating the LED chip template by the red light source in a vertical mode; collecting an LED chip template image by a CCD industrial camera arranged on the welding quality detection station, wherein the CCD industrial camera is positioned right above the LED chip template, and an industrial computer is used as a main controller to transmit the LED chip template image collected by the CCD industrial camera to the industrial computer; judging whether the collected LED chip template image meets a preset definition standard rule or not, if not, adjusting light emitting parameters of the red light source and then skipping to the step of collecting the LED chip template image until the definition standard rule is judged; if the collected LED chip template image meets the preset definition standard-reaching rule, processing the collected LED chip template image to obtain a texture characteristic value of the template texture image; and acquiring an LED chip image to be analyzed, analyzing the LED chip image to be analyzed and the template texture image according to the texture characteristic value of the template texture image, and determining the welding quality of the LED chip to be analyzed. The welding quality detection method is characterized in that an aluminum profile is used as an integral frame of a welding quality detection station, a CCD industrial camera is arranged on the camera frame with adjustable inclination, and an electric rotating platform is arranged on the welding quality detection station.
Meanwhile, in the embodiment, the LED chip that is determined manually or is detected to be qualified or excellent in soldering quality is used as the template for the related research, and the implementer may select an appropriate method to obtain the template according to the actual situation.
Then, the LED chip template gray level image is segmented by utilizing an Otsu threshold value method to obtain a welding spot area and other areas; processing the welding spot area by using morphological operation to obtain a quasi-circular area, and acquiring a central point of the quasi-circular area; performing circular expansion by taking the central point as a circular point, counting gray values of edge pixel points on each circle in the process of performing circular expansion, and constructing a gray histogram; and acquiring a circular area corresponding to a second mutation point on the gray level histogram, and performing threshold segmentation on the LED chip template gray level image according to the circular area to obtain a welding pad area.
Specifically, the LED chip template gray level image is segmented by using an Otsu threshold method to obtain a welding spot area and other areas. Because the gray difference between the welding spot area and other areas after graying is larger, the welding spot area can be directly obtained by utilizing an Otsu threshold method or other threshold segmentation methods. Meanwhile, the wiring part on the LED chip with excellent welding quality is basically superposed with the welding spot area, and the collected image may have the phenomenon that the wiring part is connected with a circuit to further damage the segmentation effect, so that the welding spot area is processed by adopting morphological operation, namely, the welding spot area is subjected to open operation to obtain a quasi-circular area. The morphological opening operation is a well-known technique and will not be described herein.
And acquiring the central point of the circular-like region, performing circular expansion by taking the central point as a dot, counting the gray value of the edge pixel point on each circle in the process of performing circular expansion, and constructing a gray histogram. Because the gray scale change of the welding pad area and the background area is obvious, a gray scale abrupt change point exists at the critical position of the welding point area and the welding pad area, and an abrupt change point exists at the critical position between the welding pad area and the background area in the circular expansion process. Therefore, a circular area corresponding to the second break point on the gray level histogram can be obtained, and the circular area is segmented by utilizing an Otsu threshold method to obtain a welding pad area.
Finally, since the pad area is generally approximately a circular area, the maximum diameter of the pad area is obtained. If the pad area is not approximately circular, the length of the longest edge of the pad area can be obtained, and then the analysis of the subsequent steps can be performed.
Acquiring the mean value of the gray values of the pixel points in the neighborhood of each pixel point 8 on the gray image of the LED template; on the edge of a circle with the longest edge length as the diameter and each pixel point on the LED template gray image as the circle center, acquiring the gray value average value of the pixel points on the edge; calculating the difference value of the two gray value means to obtain the texture value of each pixel point on the gray image of the LED template; reassigning the pixel value of each pixel point on the LED template gray image to be the texture value of the pixel point to obtain a template texture image; and obtaining the texture characteristic value of the template texture image according to the difference between each pixel point on the template texture image and the pixel points in the 8 neighborhoods of the pixel points.
Specifically, calculating texture values of pixel points on the gray level image of the LED template, and expressing the texture values as follows by using a formula:
wherein the content of the first and second substances,
the texture value of the pixel point o is represented,
expressing the gray value of the ith pixel point on the edge of a circle with the pixel point o as the center r as the radius, and n expressing the gray value of the pixel pointThe point o is the total number of pixel points on the edge of a circle whose center r is the radius,
the gray value of the jth pixel point on the edge of the circle with the radius 1 of the center of the circle o is represented, and m represents the total number of the pixel points on the edge of the circle with the radius 1 of the center of the circle o. It should be noted that, in the following description,
or, the gray value of the jth pixel point in the 8-neighborhood of the pixel point o, then the value of m is 8 at this time.
On the LED template gray image, the gray value difference of the pixel points on the two selected circular edges is large at the welding part of the chip, and the gray value difference of the pixel points on the two selected circular edges is small at other parts, so that the texture value of each pixel point can be calculated, and the pixel value of each pixel point on the LED template gray image is assigned again to obtain the template texture image.
And then calculating the texture characteristic value of the template texture image, wherein the texture characteristic value is expressed by a formula as follows:
wherein the content of the first and second substances,
a value representing a texture feature of the template texture image,
the texture value of the pixel point o is represented,
and expressing the texture value of the a-th pixel point in the 8-neighborhood of the pixel point o, and expressing the total number of the pixel points on the template texture image by N.
It should be noted that, when calculating the texture features, the embodiment calculates the circle formed by taking the pixel point as the center of the circle, although the chip position may be slightly shifted in the industrial scene, if the chip position is similar to the template, the change of the pixel point around the chip position is not very large. Meanwhile, the pad area is approximately circular, and in order to accurately obtain the texture feature of the area, in this embodiment, two circles with different sizes are used to study the pixel values of the pixel points on the image. The radius of one circle is 1, 8 pixel points of one circle around the circle center are obtained, and namely all the pixel points in the 8 adjacent areas of the circle center are obtained. The radius of the other circle is the maximum radius of the welding pad area, and edge pixel points on the circle are obtained. This has the advantage that selecting the maximum radius of the pad area as the radius at which the texture is calculated ensures that the welded portion can be characterized.
Step three, obtaining an LED chip image to be analyzed, and performing template matching positioning on the LED chip image to be analyzed and the template texture image according to the texture characteristic value of the template texture image to obtain a chip welding area image; and performing threshold segmentation on the chip welding area image to obtain a welding area segmentation image, and determining the welding quality of the LED chip to be analyzed according to the welding area segmentation image.
Firstly, obtaining an image of an LED chip to be analyzed, specifically, polishing the LED chip to be analyzed in a red light source vertical irradiation mode, enlarging the gray difference between a welding part and other parts, collecting the image of the LED chip to be analyzed by using a CCD industrial camera, sending the LED chip to be analyzed to a conveyor belt after the welding of the LED chip to be analyzed is completed, stopping the transmission of the LED chip to a certain position, positioning the camera right above the LED chip to be analyzed, and continuing the movement of the conveyor belt after the image is collected. Meanwhile, the collected image is subjected to graying processing to obtain an LED chip image to be analyzed, so that the LED chip image is changed into a single-channel image, and subsequent operation is facilitated.
It should be noted that, the texture feature value corresponding to the template is given according to the selected template, and because of an industrial scene, a situation such as position deviation may occur in industrial production, so that the texture feature value of the image is calculated according to the pixel values around the pixel points in this embodiment, and more differences between the pixel values of the pixel points and the pixel values around the pixel points are expressed, and even if the situation such as tilting or rotation occurs when the image of the LED chip to be analyzed is collected, the judgment of the result is not affected.
Obtaining windows with the same size as the template texture image, performing sliding window processing on the LED chip image to be analyzed, and respectively calculating texture characteristic values in the windows; obtaining the similarity between each window area and the template texture image according to the reciprocal of the difference value between the texture characteristic value of the template texture image and the texture characteristic value in each window; and acquiring a window area corresponding to the maximum similarity to obtain a welding area.
At this time, for the found region with the maximum similarity, the existence of the welding region in the region is confirmed, but due to the uncertain inclination angle in the industrial scene, only a part of the welding region may be in the region, and at this time, the confirmed region with the maximum similarity is translated and rotated to obtain the whole welding region.
And then, performing threshold segmentation on the chip welding area image to obtain a welding area segmentation image, wherein the welding area segmentation image comprises a welding spot area to be analyzed, a welding pad area to be analyzed, a PN line area to be analyzed and a background area to be analyzed. Wherein the area of the solder joint to be analyzed also comprises a wiring portion.
Specifically, since the solder joint area is bright, the image of the chip solder joint area can be segmented by using the Otsu threshold method to obtain the solder joint area to be analyzed and other areas to be analyzed.
Processing a welding spot area to be analyzed by using morphological operation to obtain a quasi-circular area to be analyzed, and acquiring a central point of the quasi-circular area to be analyzed; and performing circular expansion by taking the central point as a dot, counting the gray values of the edge pixel points on each circle in the circular expansion process, and constructing a gray histogram.
As the gray scale change of the welding pad area to be analyzed and the background area to be analyzed is obvious, in the process of circular expansion, a gray scale abrupt junction exists at the critical position of the welding pad area to be analyzed and the welding pad area to be analyzed, an abrupt junction exists at the critical position between the welding pad area to be analyzed and the PN line area to be analyzed, and an abrupt junction exists at the critical position between the PN line area to be analyzed and the background area to be analyzed.
Therefore, a circular area corresponding to a second mutation point on the gray level histogram can be obtained, and the threshold segmentation is carried out on the chip welding area image according to the circular area to obtain a welding pad area to be analyzed; and acquiring a circular area corresponding to a third mutation point on the gray level histogram, and performing threshold segmentation on the chip welding area image according to the circular area to obtain a PN line area to be analyzed.
And processing the image of the chip welding area by using an edge detection algorithm, and extracting the edge information of the chip welding area to be analyzed to obtain a background area to be analyzed. The algorithm for extracting the edge information is a Canny operator, which is a known technology and is not described in detail herein. And combining the welding spot area to be analyzed, the welding pad area to be analyzed, the PN line area to be analyzed and the background area to be analyzed to form a welding area segmentation image.
Finally, reassigning the pixel values of the pixel points in the welding spot area to be analyzed on the chip welding area image to be first numerical values; reassigning the pixel values of the pixel points in the welding pad area to be analyzed on the chip welding area image to be second numerical values; reassigning the pixel values of the pixel points in the PN line area to be analyzed on the chip welding area image to be third numerical values; and reassigning the pixel values of the pixels in the background area to be analyzed on the image of the chip welding area to be a fourth numerical value. In this embodiment, the values of the first, second, third and fourth values are 1, 2, 3 and 4, respectively.
Acquiring a pixel value of each edge pixel point on a circle which takes the center point of a welding spot area to be analyzed as a circle center and takes the longest edge length of the welding pad area to be analyzed as an enlarged step length as a diameter; when the number of the edge pixel points with the pixel values of the third numerical value is larger than a preset threshold value, the fact that the welding pad is in contact with the PN line is indicated, and the welding quality of the LED chip to be analyzed is unqualified; and when the number of the edge pixel points with the pixel value of the third value is smaller than a preset threshold value, the fact that the welding pad is not in contact with the PN line is indicated, and the welding quality of the LED chip to be analyzed is qualified.
In the present embodiment, the determination is made only as to whether or not the bonding of the LED chip is acceptable, and the level of the bonding quality of the LED chip, that is, the bonding quality is excellent or good, is not considered. The important factor for analyzing whether the welding of the LED chip is qualified is whether the PN line is contacted with the welding pad. The implementer can also select the specific step length for expansion according to the actual situation, or select other more suitable methods to judge whether the PN line is in contact with the pad.
The above-mentioned embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; the modifications and the substitutions do not cause the essence of the corresponding technical solution to depart from the technical solution and scope of the embodiments of the present application, and are all included in the protective scope of the present application.
Claims (5)
1. A method for detecting the welding quality of an LED chip by adopting an optical means is characterized by comprising the following steps:
pushing the currently selected LED chip template to a welding quality detection station, irradiating the LED chip template to be detected by a red light source arranged on the welding quality detection station, controlling the pose of the LED chip template to be detected, adjusting the angle of the red light source, and irradiating the LED chip template by the red light source in a vertical mode;
collecting an LED chip template image by a CCD industrial camera arranged on the welding quality detection station, wherein the CCD industrial camera is positioned right above the LED chip template, and an industrial computer is used as a main controller to transmit the LED chip template image collected by the CCD industrial camera to the industrial computer;
judging whether the collected LED chip template image meets a preset definition standard-reaching rule or not, if the collected LED chip template image does not meet the preset definition standard-reaching rule, adjusting light-emitting parameters of the red light source, and then skipping to the step of collecting the LED chip template image until the definition standard-reaching judgment; if the collected LED chip template image meets the preset definition standard-reaching rule, processing the collected LED chip template image to obtain a texture characteristic value of the template texture image;
and acquiring an LED chip image to be analyzed, analyzing the LED chip image to be analyzed and the template texture image according to the texture characteristic value of the template texture image, and determining the welding quality of the LED chip to be analyzed.
2. The method of claim 1, wherein an aluminum profile is used as a frame of the welding quality detection station, the CCD industrial camera is mounted on the camera frame with adjustable inclination, and the welding quality detection station is provided with an electric rotary platform.
3. The method for detecting the welding quality of the LED chip by adopting the optical means as claimed in claim 1, wherein the method for acquiring the texture feature value of the template texture image specifically comprises the following steps:
wherein, the first and the second end of the pipe are connected with each other,
a value representing a texture feature of the template texture image,
the texture value of the pixel point o is represented,
expressing the texture value of the a-th pixel point in the 8-neighborhood of the pixel point o, and N expressing the template textureThe total number of pixel points on the image is counted.
4. The method for detecting the welding quality of the LED chip by adopting the optical means as claimed in claim 1, further comprising the step of acquiring an image of a chip welding area, wherein the method for acquiring the image of the chip welding area specifically comprises the following steps:
obtaining windows with the same size as the template texture image, performing sliding window processing on the LED chip image to be analyzed, and respectively calculating texture characteristic values in the windows; obtaining the similarity between each window area and the template texture image according to the reciprocal of the difference value between the texture characteristic value of the template texture image and the texture characteristic value in each window; and acquiring a window area corresponding to the maximum similarity to obtain a chip welding area image.
5. The method for detecting the welding quality of the LED chip by adopting the optical means as claimed in claim 1, wherein the determining the welding quality of the LED chip to be analyzed is specifically as follows:
reassigning the pixel values of the pixel points in the welding spot area to be analyzed on the chip welding area image to be first numerical values; reassigning the pixel values of the pixel points in the welding pad area to be analyzed on the chip welding area image to be second numerical values; reassigning the pixel values of the pixel points in the PN line area to be analyzed on the chip welding area image to be third numerical values; reassigning the pixel values of the pixel points in the background area to be analyzed on the chip welding area image to be fourth numerical values;
acquiring pixel values of pixel points at each edge on a circle which takes the center point of a welding spot area to be analyzed as the circle center and takes the length of the longest edge of the welding pad area to be analyzed to be enlarged by two step lengths as diameters;
when the number of the edge pixel points with the pixel values of the third numerical value is larger than a preset threshold value, the welding quality of the LED chip to be analyzed is unqualified; and when the number of the edge pixel points with the pixel values of the third numerical value is less than a preset threshold value, the welding quality of the LED chip to be analyzed is qualified.
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| CN115753015A (en) * | 2022-11-08 | 2023-03-07 | 广东艾斯谱光电科技有限公司 | MINI LED luminescence detection method and system |
| CN116626064A (en) * | 2023-06-02 | 2023-08-22 | 奈米科学仪器设备(上海)有限公司 | Chip appearance detection device and method based on multi-layer multicolor annular light source |
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