Today, we LED die as an example, to analyze the number of reasons:
To failure analysis of large data show that LED dead light may be more than 100 reasons, limited to time, today we only LED light source, for example, from the five major sources of LED light source (chip, bracket, phosphor, solid crystal, And gold line) to start, introduce some of the reasons that may lead to dead lights.
1. Chip anti-static ability is poor
LED lamp beads of anti-static indicators depends on the LED light-emitting chip itself, and packaging materials are expected to package technology has nothing to do, or the impact of factors is very small, very subtle; LED lights are more susceptible to electrostatic damage, which is the distance between the two pins Relationship, LED chip die spacing of the two electrodes is very small, usually within a hundred microns, and the LED pin is about two millimeters, when the electrostatic charge to transfer, the greater the spacing, the more likely to form a large potential difference , That is, high voltage. Therefore, the closure of LED lights are often more prone to electrostatic damage accident.
2.Chip epitaxial defects
LED epitaxial wafers in the high temperature process, the substrate, MOCVD reaction chamber residual sediment, peripheral gas and Mo source will introduce impurities, these impurities will penetrate the epitaxial layer, to prevent gallium nitride crystal nucleation, the formation of various A variety of epitaxial defects, and ultimately in the epitaxial layer surface formation of small holes, which will seriously affect the epitaxial wafer film material quality and performance.
3.Chip chemical residues
Electrode processing is the key process for making LED chips, including cleaning, evaporation, yellowing, chemical etching, fusion, grinding, will come into contact with a lot of chemical cleaning agent, if the chip is not clean enough, will make harmful chemical residues. These harmful chemicals will be in the LED power, and electrochemical reaction with the electrode, resulting in dead lights, light failure, dark, black and so on. Therefore, the identification of chip chemical residues on the LED packaging plant is essential.
4.The chip is damaged
LED chip damage will lead directly to LED failure, so improve the reliability of LED chips is essential. During the evaporation process, it is sometimes necessary to fix the chip with a spring clip, thus creating a clip. Huangguang operation if the development is not complete and the mask has a hole will make the light area has more residual metal. Grain in the previous process, the process such as cleaning, evaporation, yellow, chemical etching, fusion, grinding and other operations must use tweezers and flower baskets, vehicles, etc., so there will be grain electrode scraping situation.
Chip electrode on the solder joint: chip electrode itself is not solid, resulting in solder wire after the electrode off or damage; chip electrode itself poor solderability, will lead to solder ball soldering; chip storage will lead to improper electrode surface oxidation, surface contamination And so on, the slight contamination of the bonding surface may affect the diffusion of metal atoms between the two, resulting in failure or Weld.
5.The new structure of the chip and the source material is not compatible
The new structure of the LED chip electrode with a layer of aluminum, the role of the electrode in the formation of a layer of mirrors to improve the efficiency of the chip, followed by a certain extent, reduce the amount of gold used in the deposition electrode to reduce costs. But aluminum is a relatively lively metal, once the packaging plant lax control, the use of chlorine exceeded the standard glue, gold electrode in the aluminum reflective layer will react with the chlorine in the glue, resulting in corrosion.
6. Silver layer is too thin
The existing LED light source on the market selects copper as the base material for the lead frame. In order to prevent oxidation of copper, the general surface of the bracket must be plated on a layer of silver. If the silver plating layer is too thin, under high temperature conditions, the stent is easy to yellow. The silver layer of the silver layer is not caused by the silver plating layer itself, but by the copper layer under the silver layer. At high temperatures, copper atoms diffuse and penetrate the surface of the silver layer, making the silver layer yellow. The oxidation of copper is the biggest drawback of copper itself. When the copper once the oxidation state, thermal conductivity and heat dissipation performance will be greatly reduced. So the thickness of the silver layer is essential. At the same time, copper and silver are susceptible to a variety of volatile sulfides and halides in the air and other pollutants corrosion, so that the surface dark color. Studies have shown that discoloration to increase the surface resistance of about 20 to 80%, power loss increases, so that the LED stability, reliability greatly reduced, and even lead to serious accidents.
7.Silver plating layer vulcanization
LED light source is afraid of sulfur, this is because the sulfur-containing gas through its porous structure of the silica gel or scaffold gap, with the light source silver layer vulcanization reaction. LED light source after the vulcanization reaction, the product function area will be black, the luminous flux will gradually decline, the color temperature appears drift; vulcanized silver sulfide with the temperature increase in conductivity, in the course of the phenomenon, prone to leakage; The situation is that the silver layer is completely corroded and the copper layer is exposed. As the gold wire two solder joints attached to the silver layer surface, when the stent function area silver layer is completely vulcanized corrosion, the golden ball fall off, resulting in dead lights.