LED chip manufacturing process and inspection project analysis

- Aug 07, 2019-

The chip is the most important raw material of LED, and its quality directly determines the performance of LED. Especially for high-end LEDs used in automotive or solid-state lighting, defects are never allowed, which means that the reliability of such devices must be very high. However, due to the lack of experience and equipment for chip inspection, LED packaging factories usually do not perform incoming inspection on chips. After purchasing unqualified chips, they often only suffer from dumb losses. Based on the accumulation of a large number of LED failure analysis cases, Jinjian Testing introduced the LED chip incoming inspection business and identified the pros and cons of the chip by using high-end analytical instruments. This testing service can be used as a supplement to the incoming inspection of the LED packaging factory/chip agent to prevent defective chips from being placed in the warehouse and avoid the overall loss of the lamp beads due to chip quality problems.


  Test items:


First, the chip performance parameter test


Optical performance test of chips such as Wd (primary wavelength), Iv (brightness), Vf (forward voltage), Ir (leakage), ESD (antistatic capability), etc. As a third-party testing organization, Jinjian can identify products provided by suppliers. Whether the data is up to standard.


Second, chip defect search


  Test content:


1. Chip size measurement, chip size and electrode size meet the requirements, and the electrode pattern is complete.


2. Whether the chip has defects such as solder joint contamination, solder joint damage, crystal grain damage, grain cutting size, and grain cutting inclination.


Damage to the LED chip directly leads to LED failure, so it is important to improve the reliability of the LED chip. In the evaporation process, it is sometimes necessary to fix the chip with a spring clip, so that a pinch is generated. If the yellow light operation is incomplete and the mask has holes, there will be residual metal in the light-emitting area. In the pre-stage process, various processes such as cleaning, evaporation, yellow light, chemical etching, fusion, grinding, etc. must use tweezers and flower baskets, carriers, etc., so there will be scratches of the die electrodes.


The effect of the chip electrode on the solder joint: the evaporation of the chip electrode itself is not reliable, resulting in the electrode being peeled off or damaged after the wire; the poor solderability of the chip electrode itself will lead to solder ball soldering; improper storage of the chip will result in oxidation of the electrode surface and surface contamination. Etc., slight contamination of the bonding surface can affect the diffusion of metal atoms between the two, causing failure or solder joints.


3. Defect search in the epitaxial region of the chip


In the high-temperature crystal growth process of the LED epitaxial wafer, the substrate, the residual deposits in the MOCVD reaction chamber, the peripheral gas and the Mo source all introduce impurities, which will penetrate into the epitaxial layer and prevent the GaN crystal from nucleating and forming various kinds. Various epitaxial defects eventually form tiny pits on the surface of the epitaxial layer, which also seriously affect the crystal quality and performance of the epitaxial film material. Jinjian detection has developed a detection method for quickly identifying defects in the epitaxial region of the chip, which can detect 80% epitaxial defects of the epitaxial layer of the chip at low cost and quickly, and help LED customers to select high-quality epitaxial wafers and chips.


4. Chip process and cleanliness observation


Electrode processing is the key process for making LED chips, including cleaning, evaporation, yellowing, chemical etching, fusion, and grinding. It will come into contact with many chemical cleaning agents. If the chip cleaning is not clean enough, it will cause harmful chemicals to remain. These harmful chemicals react electrochemically with the electrodes when the LEDs are energized, resulting in dead lights, light decay, darkness, blackening, and the like. Therefore, identifying chip chemical residues is critical to LED packaging plants.