Chip is the most critical raw material of LED, and its quality directly determines the performance of LED. Especially for high-end LEDs used in automobiles or solid-state lighting equipment, there is absolutely no room for defects, which means that the reliability of such equipment must be very high. However, due to the lack of experience and equipment for incoming chip inspection, LED packaging factories usually do not conduct incoming chip inspection. After purchasing unqualified chips, they often suffer losses. This inspection service can supplement the inspection of incoming materials from LED packaging factories/chip agents to prevent defective chips from being stored in the warehouse and avoid overall loss of lamp beads due to chip quality problems.
Test items:
1. Testing of various performance parameters of the chip
Wd (main wavelength), Iv (brightness), Vf (forward voltage), Ir (leakage), ESD (anti-static capability) and other chip photoelectric performance tests, Jinjian as a third-party testing agency can identify whether the product data provided by the supplier meets the standards.
2. Chip defect search
Test content:
1. Chip size measurement, whether the chip size and electrode size meet the requirements, and whether the electrode pattern is complete.
2. Whether the chip has defects such as solder joint contamination, solder joint damage, die damage, different die cutting sizes, and tilted die cutting.
Damage to the LED chip will directly lead to LED failure, so it is crucial to improve the reliability of the LED chip. During the evaporation process, spring clips are sometimes used to secure the chip, so clip marks may occur. If the development of the yellow light operation is incomplete and the photomask has holes, there will be excess metal remaining in the light-emitting area. In the front-end process of the die, various processes such as cleaning, evaporation, yellowing, chemical etching, fusion, grinding, etc. must use tweezers, flower baskets, carriers, etc., so the die electrodes may be scratched.
The impact of chip electrodes on solder joints: The evaporation of the chip electrode itself is not reliable, causing the electrode to fall off or be damaged after wire bonding; the chip electrode itself has poor solderability, which can lead to false soldering of the solder balls; improper storage of the chip can lead to oxidation of the electrode surface, surface contamination, etc. Slight contamination of the bonding surface may affect the diffusion of metal atoms between the two, causing failure or false soldering.
3. Defect search in the epitaxial area of the chip
During the high-temperature growth process of LED epitaxial wafers, impurities will be introduced into the substrate, residual sediments in the MOCVD reaction chamber, peripheral gases and Mo sources. These impurities will penetrate into the epitaxial layer, prevent the nucleation of gallium nitride crystals, form various epitaxial defects, and eventually form tiny holes on the surface of the epitaxial layer. These will also seriously affect the crystal quality and performance of the epitaxial wafer thin film material. Jinjian Inspection has developed a detection method to quickly identify defects in the epitaxial region of chips, which can quickly detect 80% of epitaxial defects in the epitaxial layer of chips at low cost and help LED customers choose high-quality epitaxial wafers and chips.
4. Observation of chip process and cleanliness
Electrode processing is a key process for making LED chips, including cleaning, evaporation, yellowing, chemical etching, fusion, and grinding. It will be exposed to many chemical cleaning agents. If the chip is not cleaned clean enough, harmful chemicals will remain. These harmful chemicals will react electrochemically with the electrodes when the LED is powered on, causing phenomena such as dead light, light failure, dimming, and blackening. Therefore, identifying chip chemical residues is crucial for LED packaging factories.
Case Analysis (1):
A customer found a dimming problem with red light beads, but could not find the cause. He commissioned Jinjian to analyze the cause of the failure. After Jinjian conducted a series of instrumental analyzes to rule out packaging reasons, it tested the bare chips provided by the supplier and found that the light-emitting area of each chip contained contaminants of varying sizes. The energy spectrum analysis results showed that the contaminants contained two elements, C and O, indicating that the contaminants were organic matter. We recommend that customers pay attention to the assessment of chip manufacturers' production process specifications and workshop environment, and strengthen the inspection of incoming chips.
Case Analysis (2):
A batch of lamp beads produced by a customer had leakage problems, and Jin Jian was entrusted to find the cause. Jin Jian used scanning electron microscopy to identify the cause of the leakage of this batch of lamp beads as electrostatic breakdown. He also tested the bare crystals provided by the supplier and found that there were a large number of black voids on the surface of the epitaxial layer of the chip. These defects indicate that the crystal quality of the epitaxial layer is poor and there are defects within the PN junction. Empty discovery helps customers identify the party responsible for the accident and recover losses for customers.
Note: LED chip manufacturing process flow chart
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LED chip manufacturing process flow chart
Epitaxial wafer → cleaning → transparent electrode layer plating → transparent electrode pattern photolithography → etching → glue removal → flattening Desk pattern photolithography → dry etching → stripping → annealing → SiO2 deposition → window pattern photolithography → SiO2 etching → stripping → N-pole pattern photolithography → pre-cleaning → coating → stripping → annealing → P-pole pattern photolithography → coating → stripping → grinding → cutting → chip → finished product testing.
After growing into an epitaxial wafer, the next step is to make electrodes (P pole, N pole) on the LED epitaxial wafer, and then start cutting the LED epitaxial wafer with a laser machine or a diamond knife. After manufacturing the chip, nine points are extracted at different positions on the wafer for parameter testing. This is mainly to test the voltage, wavelength, and brightness. Wafers that meet the normal shipping standard parameters will continue to the next step. Those that do not meet the requirements will be set aside for separate processing. After the wafer is cut into chips, 100% visual inspection (VI/VC) is required. The operator must conduct visual inspection under a microscope with a magnification of 30 times. Then a fully automatic sorting machine is used to fully automatically select, test and classify the chips based on different predicted parameters of voltage, wavelength and brightness. Finally, the LED chips are inspected (VC) and labeled. Chip type, lot number, quantity and photoelectric measurement statistics are recorded on the label, which is attached to the back of the glossy paper. The chips on the blue film will undergo a final visual inspection. The visual inspection standards are the same as the first time to ensure that the chips are arranged neatly and the quality is qualified. This is the manufacturing process of LED chips.
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