Light-emitting chip screening method and device

Abstract

The invention relates to the technical field of semiconductor electronics, in particular to a light-emitting chip screening method and device. The invention provides a light-emitting chip screening method, which comprises the following steps of: injecting a first current into a chip to be detected, and acquiring first brightness and first wavelength of the chip to be detected under the driving of the first current; second current is injected into the to-be-tested chip, second brightness and second wavelength of the to-be-tested chip driven by the second current are obtained, and the current value of the first current is different from that of the second current; and according to the first brightness, the first wavelength, the second brightness and the second wavelength, judging the qualification condition of the chip to be tested. According to the technical scheme, the two direct optical parameters of the brightness ratio and the wavelength difference are combined for comprehensive judgment, the chips with low brightness under the low current can be efficiently screened out, the chips which are prone to the dark brightness phenomenon under the low current can be removed, and then the quality of final LED products is improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor electronics technology, and in particular to a method and apparatus for screening light-emitting chips. Background Technology

[0002] In the current lighting and display technology field, LED products, with their high brightness and excellent color rendering, have become the core light source for products such as light strips and displays. To ensure visual display effects, the industry generally pursues performance characteristics such as uniform and stable luminous brightness.

[0003] However, in practical applications, when LED strips or displays are driven by low current, some LED chips exhibit significantly lower brightness, resulting in "dark and bright" defects in certain areas of the screen. This uneven brightness severely disrupts the consistency of the display effect, directly reducing the overall quality and market competitiveness of the product.

[0004] The fundamental reason for the aforementioned brightness differences lies in the inherent dispersion of luminous brightness within LED chips themselves (i.e., inconsistency in individual chip performance). Currently, the industry's common solution mainly relies on screening based on the voltage-current thyristor characteristics of the chips, attempting to eliminate defective products through this physical characteristic in order to obtain chips with higher luminous consistency. However, this existing method has low screening accuracy. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for screening light-emitting chips, thereby improving the accuracy of screening LED chips for consistent light emission.

[0006] A method for screening light-emitting chips, the method comprising: A first current is injected into the chip under test, and the first brightness and first wavelength of the chip under test are obtained under the drive of the first current. A second current is injected into the chip under test, and the second brightness and second wavelength of the chip under test are obtained under the drive of the second current, wherein the current value of the first current is different from the current value of the second current. The pass / fail status of the chip under test is determined based on the first brightness, the first wavelength, the second brightness, and the second wavelength.

[0007] The beneficial effects of this invention are as follows: This invention injects different values ​​of first and second currents into the chip under test, and obtains the first brightness, first wavelength, second brightness, and second wavelength under each driving current. The pass / fail status of the chip is determined based on these obtained values. Since the wavelength of the chip differs under different driving currents, and chips with different wavelengths exhibit differences in brightness and color (the greater the wavelength difference, the more pronounced the difference in brightness and color), directly measuring and comparing the brightness and wavelength parameters of the chip under two different driving currents allows for more accurate identification of chips with low brightness in specific current ranges. Compared to related technologies that primarily rely on the thyristor characteristics between voltage and current for indirect screening, this invention combines two direct optical parameters—brightness ratio and wavelength difference—for comprehensive judgment. This efficiently filters out chips with low brightness under low current, helping to eliminate chips prone to dimming under low current, thereby improving the quality of the final LED product. Attached Figure Description

[0008] Figure 1 A flowchart illustrating the steps of a light-emitting chip screening method provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of a light-emitting chip screening and testing device provided in an embodiment of the present invention; Label Explanation: 900. A light-emitting chip screening and testing device; 901, Integrating Ball; 902. Photoelectric conversion device. Detailed Implementation

[0009] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0010] The following describes in detail a method for screening light-emitting chips according to the present invention, with reference to the appendix. Figure 1 ,include: Step 110: Inject a first current into the chip under test (DUT) and obtain the first brightness and first wavelength of the DUT under the first current drive; the DUT includes a light-emitting diode (LED) chip. In this invention, brightness is specifically characterized and measured by "Luminous Optical Power (LOP)," typically measured in milliwatts (mW) or watts (W). Alternatively, "illuminance" or "light intensity" values ​​related to light intensity can also be used. Wavelength specifically refers to the "Peak Wavelength (WLD)" of the chip's emission spectrum, typically measured in nanometers (nm). "Dominant Wavelength" can also be used when determining color consistency.

[0011] Step 120: Inject a second current into the chip under test and obtain the second brightness and second wavelength of the chip under test under the second current drive. The current value of the first current is different from the current value of the second current. Step 130: Determine the pass / fail status of the chip under test based on the first brightness, the first wavelength, the second brightness, and the second wavelength; This embodiment injects different values ​​of a first current and a second current into the chip under test, and obtains the first brightness, first wavelength, second brightness, and second wavelength under their respective driving conditions. The pass / fail status of the chip is determined based on the obtained first brightness, first wavelength, second brightness, and second wavelength. Since the wavelength of the chip differs under different driving currents, and chips with different wavelengths exhibit differences in brightness and color, with larger wavelength differences resulting in more pronounced differences in brightness and color, directly measuring and comparing the brightness and wavelength parameters of the chip under two different driving currents allows for more accurate identification of chips with low brightness within a specific current range. Compared to related technologies that primarily rely on the thyristor characteristics between voltage and current for indirect screening, this invention combines two direct optical parameters—brightness ratio and wavelength difference—for comprehensive judgment. This efficiently filters out chips with low brightness under low current, helping to eliminate chips prone to dimming under low current, thereby improving the quality of the final LED product.

[0012] In one embodiment of this application, step 130, determining the pass / fail status of the chip under test based on the first brightness, the first wavelength, the second brightness, and the second wavelength, includes: Step 210: Calculate the ratio of the second brightness to the first brightness; the first and second brightness can be the light output power (LOP). The second brightness is less than or equal to the first brightness. The brightness of the LED chip (the chip under test) has a non-linear relationship with the current; before reaching saturation current, the higher the current, the higher the brightness. Therefore, the brightness ratio is used as the judgment criterion.

[0013] Step 220: Determine whether the brightness ratio is greater than or equal to the predetermined first threshold. If so, the chip under test is deemed qualified. Set the qualified value of the brightness ratio of the two current channels to value A. When the brightness ratio of LOP2 / LOP1 of a chip is ≥ value A under the two current conditions, it is determined to be a qualified chip; otherwise, it is a non-qualified chip.

[0014] For example, if the acceptable value for the brightness ratio between two current channels is set to value A, then a chip is considered acceptable if, under two current conditions, the brightness ratio of LOP2 / LOP1 is greater than or equal to value A. A larger ratio of low-current brightness to high-current brightness indicates a smaller difference between the low-current and high-current brightness. Otherwise, it is considered unacceptable and cannot be used in LED strips or display products.

[0015] As described above, this embodiment effectively identifies chips with uneven performance by setting a brightness ratio threshold as a pass / fail criterion. Compared to related technologies that only check whether the brightness meets the standard under a single current, this embodiment is less prone to issues like localized dimming due to low brightness under low current, which would affect the overall display effect, because the light-emitting chip is used in a display screen and requires different driving currents. This embodiment, by evaluating the brightness ratio, can more sensitively detect defects in the light-emitting chip under different current levels, thereby improving the accuracy of screening light-emitting chips with dimming issues.

[0016] In one embodiment of this application, it further includes: Step 310: Set a first threshold based on the brightness consistency requirements of the chip under test under low current drive. As described above, this embodiment makes the brightness ratio test standard more practical and flexible in engineering by associating the threshold setting with the low current operating conditions of actual applications. It can more accurately screen out chips that meet the brightness uniformity requirements under specific low current operating conditions, thereby improving the adaptability of the test solution to different product specifications.

[0017] In one embodiment of this application, step 130, determining the pass / fail status of the chip under test based on the first brightness, the first wavelength, the second brightness, and the second wavelength, includes: Step 410: Calculate the wavelength difference between the second wavelength and the first wavelength. The wavelength of the LED chip (the chip under test) is determined by its material and structure. Under different current driving conditions, the chip's internal temperature varies, causing a certain shift in the emitted wavelength, commonly known as red shift or blue shift. Therefore, the wavelength difference is used as the judgment criterion.

[0018] In LED chip testing, the first wavelength is the wavelength value obtained by photoelectric conversion after the first current is injected into the LED chip under test, and is denoted as WLD1. The second wavelength is the wavelength value obtained by photoelectric conversion after the second current is injected into the LED chip under test, and is denoted as WLD2. The wavelength difference can be the absolute value of the difference between the second wavelength and the first wavelength, and the calculation formula is |WLD2-WLD1|.

[0019] Step 420: Determine whether the wavelength difference is less than or equal to a predetermined second threshold. If so, the chip under test is deemed qualified. Specifically, the LED chip under test passes the wavelength stability test, meaning the wavelength difference (|WLD2-WLD1|) is less than or equal to the predetermined second threshold. This indicates that the chip's wavelength output variation under continuous current injection is within the allowable range, and its performance meets the requirements. Otherwise, it is a substandard chip and cannot be used in LED strips or display products.

[0020] As described above, this embodiment effectively identifies chips with excessive blue shifts in their emission wavelengths by introducing wavelength difference judgment. Compared to related technologies that may only focus on the absolute wavelength value under a single current, this embodiment evaluates the amount of wavelength change. Due to differences in the epitaxial structure of different chips, the blue shift values ​​differ under two different currents. Chips with different wavelengths exhibit differences in brightness and color, and the greater the wavelength difference, the more pronounced the difference in brightness and color. This allows for more effective detection of wavelength instability caused by material or process defects, further improving the screening accuracy.

[0021] In one embodiment of this application, it further includes: Step 510: Set a second threshold based on the wavelength stability requirements of the chip under test; the second threshold refers to the maximum allowable wavelength difference limit value, which is determined based on the LED chip's product specifications, testing standards, or tolerance requirements. The threshold is usually expressed in wavelength units (e.g., nanometers, nm).

[0022] As described above, this embodiment binds the wavelength difference threshold to the product wavelength stability requirements, enabling the testing standard to directly serve the color uniformity target of the final product, thereby enhancing the practical application value and relevance of the testing scheme.

[0023] In one embodiment of this application, step 130, determining the pass / fail status of the chip under test based on the first brightness, the first wavelength, the second brightness, and the second wavelength, includes: Step 610: Determine the brightness ratio of the first brightness and the second brightness, and obtain the first determination result; Step 620: Determine the wavelength difference between the first wavelength and the second wavelength, and obtain a second determination result; Step 630: When both the first judgment result and the second judgment result indicate that the chip under test is qualified, the chip under test is determined to be qualified. As described above, this embodiment combines two key parameters—brightness linearity and wavelength stability—for comprehensive evaluation, enabling a more complete assessment of the chip's overall performance and reliability. Compared to related technologies that may perform single-parameter testing, this embodiment significantly reduces the rate of missed detections of defective chips with hidden defects through multi-condition joint judgment, thereby improving the overall quality of LEDs.

[0024] In one embodiment of this application, the current value of the first current is greater than the current value of the second current.

[0025] As described above, this embodiment can simulate the current change scenarios that the chip may encounter in actual applications by adopting a test process from high current to low current. Because different chips have different epitaxial structures, the wavelength blue shift values ​​are different under the two currents of large and small. The brightness and color of the light emitted by chips of different wavelengths are different, which makes it possible to simulate the dim and bright chips.

[0026] In one embodiment of this application, it further includes: Step 710: After injecting the first current, wait for a preset time interval and then inject the second current; As described above, this embodiment avoids measurement errors caused by transient chip response or unstable thermal effects by setting a waiting time, thereby improving the accuracy and reliability of the acquired first brightness, first wavelength, second brightness, and second wavelength data, making subsequent qualification judgments based on these data more accurate.

[0027] In one embodiment of this application, step 110, injecting a first current into the chip under test, includes: Step 810: Inject a first current with a current value of 20mA to 500mA into the chip under test; In step 120, injecting a second current into the chip under test includes injecting a second current with a value of 0 to 10 mA into the chip under test. In one alternative implementation, the first current is 0mA, 5mA, or 10mA, and the second current is 20mA, 260mA, or 500mA; the small current and the large current can be combined with each other.

[0028] As described above, this embodiment effectively evaluates the chip's performance under normal operating conditions (first current) and low current conditions (second current) by setting two typical and significantly different current test points covering high and low currents. Compared to related technologies that may only test under a single conventional current, this solution, by expanding the dynamic range of the test current, especially by introducing extremely low current test points, can more sensitively detect defects such as uneven brightness, wavelength blue shift, or poor turn-on that are prone to occur in chips under low current drive, and can efficiently screen chips with low brightness.

[0029] Please refer to Figure 2 A light-emitting chip screening and testing device 900, the testing device comprising: The integrating sphere 901 is used to acquire the first brightness and first wavelength of the chip under test under a first current drive, and to acquire the second brightness and second wavelength of the chip under test under a second current drive, as described in claim 1; the current is provided by the LED chip tester. The LED chip emits visible light, and the visible light signal can be captured by the integrating sphere of the tester. Then, through a photoelectric conversion device, the light signal is converted into an electrical signal, thereby outputting the corresponding LOP value and WLD value under that current.

[0030] The photoelectric conversion device 902 is used to convert optical signals into electrical signals; The first brightness and the first wavelength are determined based on the electrical signal obtained when the first current is injected, and the second brightness and the second wavelength are determined based on the electrical signal obtained when the second current is injected. As described above, this embodiment uses an integrating sphere to uniformly collect the optical signal from the chip under test, and a photoelectric conversion device converts the optical signal into an electrical signal to determine the first brightness, first wavelength, second brightness, and second wavelength. This ensures the accuracy and consistency of the data used to determine the brightness ratio and wavelength difference, thereby improving the overall accuracy and reliability of the screening test.

[0031] The light-emitting chip screening method and apparatus of the present invention can be applied to LED chip screening, and will be described in detail below through specific embodiments.

[0032] LED chips are tested and screened, including steps A through E: Step A: Inject the first current into the chip (corresponding to the first current), and the brightness LOP1 and wavelength WLD1 corresponding to the first current can be obtained; corresponding to step 110 above.

[0033] Step B: Inject a second current (corresponding to the second current) into the chip, which has a different current value than the first current. This yields the brightness (LOP2) and wavelength (WLD2) corresponding to the second current. The first current is a large current, and the second current is a small current. Due to differences in chip size and input current requirements in different application scenarios, the large and small current conditions are only a subset of the conditions. The small current (x) ranges from 0 < x ≤ 10 (mA), and the large current (y) ranges from 20 ≤ x ≤ 500 (mA). This corresponds to step 120 above. In an optional implementation, the small current is 0mA, 5mA, or 10mA, and the large current is 20mA, 260mA, or 500mA; the small and large currents can be combined.

[0034] Step C: Filter the brightness ratio of the two current channels, LOP2 / LOP1. Set the acceptable value for the brightness ratio of the two current channels to value A (corresponding to the first threshold mentioned above). When a chip's brightness ratio of LOP2 / LOP1 is ≥ value A under the two current conditions, it is determined to be a qualified chip; otherwise, it is an unqualified chip and cannot be used in LED strips or display products. This corresponds to step 130 above.

[0035] Step D: Screen the wavelength difference between the two current channels, WLD2-WLD1. Due to differences in chip size and input current in different application scenarios, the large and small current conditions are only a subset of the conditions. The small current range is 0~10mA, and the large current range is 20mA~500mA. A qualified value for the wavelength difference between the two current channels is set as value B (corresponding to the second threshold mentioned above). When a chip's wavelength difference between WLD2 and WLD1 is ≤ value B under the two current conditions, it is considered a qualified chip; otherwise, it is an unqualified chip and cannot be used in LED strips or display products. This corresponds to step 130 above. In an optional implementation, the small current is 0mA, 5mA, or 10mA, and the large current is 20mA, 260mA, or 500mA; the small and large currents can be combined.

[0036] Step E: Further screening is performed by combining the brightness ratio of the two currents and the wavelength difference. Chips that exhibit uniform and consistent brightness under low current drive, without any dim or bright areas, are selected and can be used for subsequent fabrication of LED strips or displays with uniform and stable brightness. This corresponds to step 130 above.

[0037] In summary, the present invention provides a method and apparatus for screening light-emitting chips. This involves injecting different values ​​of a first current and a second current into the chip under test, and obtaining the first brightness, first wavelength, second brightness, and second wavelength under each driving current. The pass / fail status of the chip is determined based on the obtained first brightness, first wavelength, second brightness, and second wavelength. Since the wavelength of the chip differs under different driving currents, and chips with different wavelengths exhibit differences in brightness and color, with larger wavelength differences resulting in more pronounced differences in brightness and color, directly measuring and comparing the brightness and wavelength parameters of the chip under two different driving currents allows for more accurate identification of chips with low brightness in a specific current range. Compared to related technologies that primarily rely on the thyristor characteristics between voltage and current for indirect screening, this invention combines two direct optical parameters—brightness ratio and wavelength difference—for comprehensive judgment. By screening the brightness ratio and wavelength difference under two different current conditions, chips with low brightness under low current can be efficiently screened out. The remaining qualified chips can be used for subsequent fabrication of LED strips or displays with uniform and stable brightness.

[0038] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for screening light-emitting chips, characterized in that, The method includes: A first current is injected into the chip under test, and the first brightness and first wavelength of the chip under test are obtained under the drive of the first current. A second current is injected into the chip under test, and the second brightness and second wavelength of the chip under test are obtained under the drive of the second current, wherein the current value of the first current is different from the current value of the second current. The pass / fail status of the chip under test is determined based on the first brightness, the first wavelength, the second brightness, and the second wavelength.

2. The method for screening light-emitting chips according to claim 1, characterized in that, The step of determining the pass / fail status of the chip under test based on the first brightness, the first wavelength, the second brightness, and the second wavelength includes: Calculate the brightness ratio of the second brightness to the first brightness; Determine whether the brightness ratio is greater than or equal to a predetermined first threshold. If so, the chip under test is deemed qualified.

3. The method for screening light-emitting chips according to claim 2, characterized in that, Also includes: The first threshold is set according to the brightness consistency requirements of the chip under test under low current drive.

4. The method for screening light-emitting chips according to claim 1, characterized in that, The step of determining the pass / fail status of the chip under test based on the first brightness, the first wavelength, the second brightness, and the second wavelength includes: Calculate the wavelength difference between the second wavelength and the first wavelength; Determine whether the wavelength difference is less than or equal to a predetermined second threshold. If so, the chip under test is deemed qualified.

5. The method for screening light-emitting chips according to claim 4, characterized in that, Also includes: The second threshold is set according to the wavelength stability requirements of the chip under test.

6. The method for screening light-emitting chips according to claim 1, characterized in that, The step of determining the pass / fail status of the chip under test based on the first brightness, the first wavelength, the second brightness, and the second wavelength includes: The brightness ratio of the first brightness and the second brightness is determined, and a first determination result is obtained; The wavelength difference between the first wavelength and the second wavelength is determined, and a second determination result is obtained; When both the first judgment result and the second judgment result indicate that the chip under test is qualified, the chip under test is determined to be qualified.

7. The method for screening light-emitting chips according to claim 1, characterized in that, The value of the first current is greater than the value of the second current.

8. The method for screening light-emitting chips according to claim 1, characterized in that, Also includes: After injecting the first current, wait for a preset time interval before injecting the second current.

9. The method for screening light-emitting chips according to claim 1, characterized in that, The injection of a first current into the chip under test includes: injecting a first current with a value of 20mA to 500mA into the chip under test; The injection of a second current into the chip under test includes injecting a second current with a value of 0 to 10 mA into the chip under test.

10. A light-emitting chip screening and testing device, characterized in that, The testing apparatus includes: An integrating sphere is used to obtain the first brightness and first wavelength of the chip under test under a first current drive as described in claim 1, and to obtain the second brightness and second wavelength of the chip under test under a second current drive. A photoelectric conversion device used to convert optical signals into electrical signals; The first brightness and the first wavelength are determined based on the electrical signal obtained when the first current is injected, and the second brightness and the second wavelength are determined based on the electrical signal obtained when the second current is injected.

Images