LED dead lights in the end how many?

Today we LED death light, for example, to analyze how many kinds of reasons:

To failure analysis of big data, LED dead lights may be hundreds of reasons, limited to time, today we only LED light source, for example, from the LED light source of the five raw materials (chips, stents, phosphors, solid crystal plastic, plastic packaging And gold line) to start, introduce some of the reasons may lead to dead lights.

chip

01, chip antistatic ability is poor

LED lamp beads antistatic index level depends on the LED light-emitting chip itself, and the packaging material is expected to have little or no impact on the packaging process, the impact is very small, very subtle; LED lamp is more susceptible to electrostatic damage, which with two pin spacing Relationship, LED chip nude two electrodes spacing is very small, usually less than one hundred microns, while 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, sealed LED lights are often more prone to electrostatic damage accident.

02, chip epitaxial defects

LED epitaxial wafers in the process of high temperature crystal growth, the substrate, MOCVD reaction chamber residual deposits, peripheral gases and Mo sources will introduce impurities, these impurities will penetrate the epitaxial layer to prevent gallium nitride crystal nucleation, the formation of various Various epitaxial defects finally form tiny pits on the surface of the epitaxial layer, which will also seriously affect the crystal quality and performance of the epitaxial wafer thin film material.

03, chip chemical residue

Electrode processing is the key process of LED chips, including cleaning, evaporation, yellow, chemical etching, fusion, grinding, will come into contact with many chemical cleaning agents, if the chip is not clean enough clean, harmful chemicals will remain. These harmful chemicals in the LED power, electrochemical reaction with the electrode, leading to dead lights, light fades, dark, dark and so on. Therefore, the identification of chip chemical residue LED packaging plant is crucial.

04, chip damage

LED chip damage will directly lead to LED failure, so to improve the reliability of LED chips is essential. Vapor deposition process sometimes need to use the spring clip to fix the chip, it will have a nick. Yellow work if the development is not complete and the mask has a hole in the light emitting area will have more residual metal. Grains in the first stage of the process, the process such as cleaning, evaporation, yellow, chemical etching, fusion, grinding and other operations must use tweezers and flower baskets, carriers, etc., there will be scratched the grain electrode occurs.

Chip electrode on the impact of solder joints: the chip electrode evaporation itself is not reliable, resulting in wire after the electrode off or damage; chip electrode itself solderability will lead to solder ball Weld; chip storage improper will lead to electrode surface oxidation, surface contamination Etc., slight contamination of the bonding surfaces may affect the diffusion of metal atoms between the two, resulting in failure or Weld.

05, the new structure of the chip and light source material is not compatible

The new structure of the LED chip electrode layer of aluminum, the role of the electrode in the formation of a layer of mirror to improve chip light efficiency, and secondly to a certain extent reduce the amount of gold deposited on the electrode to reduce costs. However, aluminum is a kind of more lively metal. Once the packaging factory is in charge of material control, the aluminum reflective layer in the gold electrode will react with the chlorine in the glue by using glue containing excessive chlorine to cause corrosion.

LED bracket

06, silver-plated layer is too thin

Existing LED light sources on the market choose copper as the lead frame substrate material. In order to prevent oxidation of copper, the general surface of the stent to be plated with a layer of silver. If the silver coating is too thin, under high temperature conditions, the stent easily yellowing. The yellowing of the silver coating is not caused by the silver plating itself but by the copper layer under the silver coating. At high temperatures, copper atoms can diffuse and penetrate into the surface of the silver layer, causing the silver layer to yellow. Copper oxidizability is the biggest drawback of copper itself. Once the oxidation state of copper appears, the thermal conductivity and thermal performance will be greatly reduced. So the thickness of the silver coating is crucial. At the same time, copper and silver are susceptible to various volatile air pollutants such as sulfides and halides, causing dark discoloration on their surfaces. Some studies have shown that discoloration increases the surface resistance of about 20 ~ 80%, power loss increases, so that the LED's stability, reliability greatly reduced, and even lead to serious accidents.

07, silver-plated layer curing

LED light source is afraid of sulfur, which is because the sulfur-containing gas will vulcanize with the silvered layer of light source through the porous structure of silica gel or bracket gap. After the curing reaction of the LED light source, the functional area of ​​the product will be blackened, the luminous flux will be gradually decreased, and the color temperature will obviously drift. After vulcanized silver sulfide increases in conductivity with increasing temperature, leakage phenomenon will occur easily during use; more serious The condition is that the silver layer is completely eroded and the copper layer is exposed. As the gold wire two solder joints attached to the surface of the silver layer, when the silver layer is fully cured sulfide corrosion, the ball appears off, resulting in dead lights.

08, silver plating oxidation

Gold Kam Detection In contact with the LED black diagnosis of the initial business found sulfur / chlorine / bromine more difficult to find the more difficult, but LED light silver signs of obvious signs of silver, which may be related to the oxidation of silver. However, pure elemental analysis such as EDS is not easy to determine the oxidation of the determination of oxidation, because the existence of the air environment, the sample surface adsorption and encapsulation of organic matter such as oxygen will interfere with the determination of test results, so determine the conclusion of oxidation black need to use SEM, EDS, FTIR, XPS and other professional testing as well as light, electricity, chemistry, environmental aging and a series of reliability comparison experiments, combined with professional testing knowledge and knowledge of electroplating comprehensive analysis.

09, poor quality plating

The quality of the coating is mainly determined by the quality of the metal deposited layer of the crystalline structure, in general, the smaller the crystalline structure, the more dense coating, smooth, protective performance is also higher. This small crystalline coating is called "micro-crystal deposition layer." Golden Kam pointed out that good plating should be plated crystal fine, smooth, uniform, continuous, do not allow pollutants, chemical residues, spots, black spots, charred, rough, pinholes, pitting, cracks, Blistering, wrinkling, peeling, yellowing, crystalline coating, partial uncoated defects.

In the electroplating production practice, the thickness of the metal coating and coating uniformity and integrity of the coating quality is an important indicator of inspection, because the coating's protective properties, porosity and coating thickness are directly related. Special change is the cathode coating, with the increase of the thickness, the protection of the coating also increases. If the thickness of the coating is not uniform, it is often the thinnest area first destroyed, then the rest of the coating and then thick will lose protection.

Coating porosity, oxygen and other corrosive gases through the pores into the corrosive copper matrix.

10, organic pollution

Jinjian also pointed out that because the plating process will use a variety of organic-containing potion, silver-plated layer if the cleaning is not clean or use poor quality and deterioration of the potion, the residual organic matter once the light source in the light environment, Light, heat and electricity, the organic matter may occur redox chemical reactions lead to discoloration of the surface of the silver coating.

11, outlet material

The material of the plastic is the key to the heat conduction of the LED package bracket. If the PPA bracket is the material of the water outlet, the plastic performance of the PPA will be reduced, resulting in the following problems: high temperature tolerance, easy deformation, yellowing and low reflectivity ; High water absorption, scaffold due to water absorption caused by the dimensional changes and mechanical strength; poor adhesion with metal and silica gel, pick plastic, and a lot of silicone do not match. These potential problems make the lamp beads difficult to use at slightly larger power. Once out of range, the initial brightness is high, but the attenuation is very fast, leaving the lamp a few months dark.

Phosphor

12, phosphor hydrolysis

Nitride phosphor easy hydrolysis, failure.

13, phosphor self-heating mechanism

Phosphor self-heating mechanism, making the phosphor layer temperature is often higher than the LED chip p-n junction. The reason is that the conversion efficiency of the phosphor does not reach 100%, so a portion of the blue light that the phosphor absorbs converts into yellow light, and another part of the light energy absorbed by the phosphor in the high light energy density LED package becomes the heat. Because phosphors are usually blended with silica gel and silica gel has a very low thermal conductivity of 0.16 W / mK, the heat generated by the phosphor accumulates in smaller localized areas, causing localized high temperatures, LED optical density The larger the phosphor the greater the heat. When the temperature of the phosphor is above 450 degrees Celsius, the silica gel near the phosphor particles will be carbonized. Once there is a certain place of silica gel carbonized black, its light conversion efficiency is lower, the region will absorb more light emitted by the LED and convert more heat, the temperature continues to increase, making the area of ​​carbonation more and more.

Solid crystal glue

14, silver peel off

Conductive silver plastic substrate is an epoxy resin material, thermal expansion coefficient than the chip and the stent are much larger, in the light of the impact of hot and cold use of the environment, the problem will be due to heat stress, temperature changes in the environment will be more dramatic effect To exacerbate, the colloid itself has tensile strength and elongation at break, when the tension exceeds, then the gel cracked. Solid crystal peel off at the interface, the heat rapidly worsened, the heat generated by the chip can not be exported, the junction temperature rapidly increased greatly accelerated the process of light failure.

15, silver plastic layering

Silver particles dispersed in slurry state in the suspension system, due to the silver powder and the matrix due to the density difference, charge, cohesion, force and the structure of the dispersion system and many other factors, often appear stratification of silver deposition, sedimentation Fast will make the product sag hanging when the coating thickness is uneven, and even affect the physical and chemical properties of the coating, delamination will also affect the device's heat dissipation, bonding strength and electrical conductivity.

16, silver ion migration

A customer with silicone encapsulation, conductive silver adhesive vertical flip light source leakage phenomenon, commissioned Kam Kam reason. Gold Kam through the poor lamp bead analysis, abnormal silver element was detected in the side of the chip, and silver particles can be observed from the bottom of the positive silver glue area dendritic extended morphology gradually spread to the chip near the top of the P-N junction side, so Golden Kam determine the poor lamp bead leakage failure is most likely caused by silver ions from the crystal silver plastic ion migration in the side of the chip. Silver ion migration phenomenon is gradually formed during the use of the product, with the migration of the phenomenon of aggravating, the final silver ions will lead the chip P-N junction, resulting in low resistance side of the chip path, leading to the chip leakage current abnormalities, serious The case even caused a chip short circuit. There are many reasons for the migration of silver, but the main reason is that the silver-based material is damp. After the silver glue is wetted, the invaded water molecules ionize the silver and migrate along the side of the chip under the vertical electric field from bottom to top. Therefore, the detection of gold Kam recommend customers with caution in silicone packaging, silver glue vertical flip chip beads, the choice of gold tin eutectic soldering the chip fixed on the bracket, and enhance the waterproof testing of lamps.

17, solid crystal glue quit

Silicon-based curing agents for LED packages contain platinum (platinum) complexes, which are extremely toxic and poisoning agents are any of nitrogen (N), phosphorus (P), and sulfur Compounds, once the curing agent poisoning, the silicone curing incomplete, it will result in high linear expansion coefficient, stress increases.

Plastic packaging

18, glue heat resistance is poor

According to our test shows that pure silica gel to 400 degrees began to crack, but the epoxy resin modified silicone heat resistance is pulled down to the level of epoxy resin, when the modified silica gel used to high-power LED Or high-temperature environment, there will be colloidal hair black hair cracking dead lights and other phenomena.

19, do not glue

Silicon-based curing agents for LED packages contain platinum (platinum) complexes, which are extremely toxic and poisoning agents are any of nitrogen (N), phosphorus (P), and sulfur Compounds, once the curing agent poisoning, the silicone curing incomplete, it will result in high linear expansion coefficient, stress increases.

Silicone prone to "poisoning" substances are: containing N, P, S and other organic compounds; Sn, Pb, Hg, Sb, Bi, As and other heavy metal ion compounds; containing ethinyl and other unsaturated groups of organic compounds. Pay attention to the following materials:

Organic Rubber: Sulfur Vulcanized rubber such as gloves

Epoxy resin, polyurethane resin: Amine, Isocyanate curing agent

Synthetic silicone RTV rubber: In particular, the use of Sn-based catalyst

Soft Polyethylene: plasticizers, stabilizers

Flux

Engineering Plastics: Flame Retardants, Heat Resistant Agents, UV Absorbers and more

Silver, gold-plated surface (the manufacture of the plating solution is the main reason)

Degassing caused by Solder register (caused by silicone heat curing)