Cause analysis of LED dead light

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Cause analysis of LED dead light

According to the large data of failure analysis, there may be more than 100 causes of LED lamp death, limited to time, today we only take LED light source as an example, starting from the five raw materials of LED light source (chip, bracket, phosphor, solid crystal glue, packaging glue and gold wire), introduce some possible causes of LED lamp death.

Today we take the LED dead light as an example to analyze the reasons for this.

According to the large data of failure analysis, there may be more than 100 causes of LED lamp death, limited to time, today we only take LED light source as an example, starting from the five raw materials of LED light source (chip, bracket, phosphor, solid crystal glue, packaging glue and gold wire), introduce some possible causes of LED lamp death.

chip

01, chip anti-static ability is poor.

The anti-static index of LED beads depends on the LED light-emitting chip itself, and has little to do with the packaging material expected packaging process, or the influence factors are very small, very subtle; LED lights are more vulnerable to static damage, which is related to the distance between the two pins, LED chip bare crystal electrode spacing is very small, generally 100 microns Within it, the LED pins are about two millimeters, and when electrostatic charge is transferred, the greater the spacing, the easier it is to form a large potential difference, that is, a high voltage. Therefore, after sealing the LED lamp, it is more likely that there will be an electrostatic damage accident.

02, chip epitaxy defects

In the process of high-temperature epitaxial growth of LED wafers, impurities will be introduced into the substrate, the sediments left in the MOCVD reaction chamber, peripheral gases and Mo sources. These impurities will penetrate into the epitaxial layer, prevent the nucleation of GaN crystals, form various epitaxial defects, and eventually form tiny pits on the surface of epitaxial layer. These impurities will also seriously affect the epitaxial growth. Crystal quality and properties of the film.

03. Chip chemical residue

Electrode processing is the key process of making LED chips, including cleaning, evaporation, yellow light, chemical etching, fusion, grinding, will be exposed to many chemical cleaning agents, if the chip cleaning is not clean enough, will cause harmful chemical residues. These harmful chemicals will react electrochemically with the electrode when the LED is energized, resulting in dead lights, light fading, dark, blackening and other phenomena. Therefore, identification of chip chemical residues is essential for LED packaging plants.

04, chip damage

The damage of LED chip will directly lead to LED failure, so it is very important to improve the reliability of LED chip. Sometimes it is necessary to use the spring clamp to fix the chip in the evaporation process, so the clamp marks will be generated. If the yellow light operation is not fully developed and the mask has holes, there will be more metal left in the luminescent area. In the preceding stage of grain production, tweezers, flower baskets, carriers and so on must be used in various processes, such as cleaning, evaporation, yellow light, chemical etching, fusion, grinding and so on. Therefore, the scratch of grain electrode will occur.

The influence of chip electrode on solder joint: the chip electrode itself is not firmly evaporated, resulting in electrode shedding or damage after soldering; the chip electrode itself solderability is poor, will lead to virtual soldering; improper chip storage will lead to electrode surface oxidation, surface contamination and so on, bonding surface slight pollution may affect the metal between the two original. Sub diffusion causes failure or void welding.

05. The incompatibility between the chip of the new structural process and the material of the light source.

The new structure of LED chip electrode contains a layer of aluminum, which is used to form a mirror in the electrode to improve the chip luminous efficiency, and then to reduce the use of gold in the evaporation electrode to a certain extent to reduce the cost. However, aluminum is a relatively active metal, once the packaging plant incoming material control is not strict, the use of chlorine-containing glue, the gold electrode in the aluminum reflector will react with chlorine in the glue, resulting in corrosion.

LED stents

06. Silver plating is too thin.

The existing LED light source in the market selects copper as the matrix material of the lead frame. To prevent oxidation of copper, the surface of the scaffold must be plated with silver. If the silver plating layer is too thin, the stent will be yellowed at high temperature. The yellowing of silver plated layer is not caused by silver plating itself, but affected by the copper layer under the silver layer. At high temperatures, copper atoms diffuse and penetrate to the surface of the silver layer, causing the silver layer to yellowing. The oxidizability of copper is the biggest drawback of copper itself. Once copper is oxidized, the thermal conductivity and heat dissipation will be greatly reduced. So the thickness of silver plating is very important. At the same time, copper and silver are vulnerable to various volatile sulfides and halides in the air and other pollutants corrosion, making its surface darkening discoloration. Some studies have shown that the color change makes the surface resistance increase by about 20-80%, and the power loss increases, thus greatly reducing the stability and reliability of LED, even leading to serious accidents.

07. Silver plating vulcanization

LED light sources fear sulfur because sulfur-containing gases vulcanize silver-plated layers of light sources through porous silica gel or scaffolding gaps. After the curing reaction of LED light source, the functional area of the product will be blackened, the luminous flux will be gradually decreased, and the color temperature will be obviously drifted; the conductivity of the cured silver sulfide will increase with the temperature, and the leakage will easily occur in the course of using; the more serious situation is that the silver layer is completely corroded and the copper layer is exposed. Because the second solder joint of the gold wire adheres to the surface of the silver layer, when the silver layer in the functional area of the support is completely sulfurized and corroded, the gold ball falls off and a dead lamp appears.

08. Silver plating oxidation

The more difficult it is to find sulfur / chlorine / bromine in the primary diagnostic business of contact LED blackening, however, there are obvious signs of blackening in the silver plating layer of LED light source, which may be related to silver oxidation. However, the methods of elemental analysis such as EDS spectrum analysis are not easy to determine oxidation.