É normal que displays de LED-coloridos tenham luzes mortas. O que é anormal é que o número de luzes mortas excede um determinado intervalo. O padrão atual da indústria para luzes mortas em displays de LED é de três em dez mil. Este padrão era o padrão há vários anos. A Huarong Optoelectronics controlou a -taxa de luz morta da maioria dos expositores de LED em uma em 300,000, excedendo em muito muitos pares, e também foi reconhecida pelos clientes.
So what is the reason for the dead light on the led display? What are the factors that cause the dead light of the led display?
As we all know, the LED display dead light situation restricts the development of various companies specializing in the development and production of LED products, and also restricts the development of the LED industry. What are the factors that cause LED dead lights? In view of the status quo of this industry, Huarong Optoelectronics used a media interview with industry experts to analyze the specific factors in LED RD, production, sales and application from a professional perspective that would cause LED dead lights.
De acordo com big data, pode haver mais de cem razões para luzes mortas de LED. O tempo é limitado. Hoje tomamos apenas como exemplo as fontes de luz LED. Das cinco principais matérias-primas das fontes de luz LED (fio de ouro, chip, suporte, fósforo, cola de cristal sólido e embalagem) Comece com cola), introduza alguns dos motivos que podem causar luzes mortas.
Exibição led colorida
Linha Dourada
1. Liga de cobre, fio de liga de prata revestido de ouro-, fio de liga de prata em vez de fio de ouro
O fio de ouro tem as vantagens de alta condutividade elétrica, boa condutividade térmica, resistência à corrosão, boa tenacidade e excelente estabilidade química. No entanto, o preço do fio de ouro é caro, o que leva a altos custos de embalagem. Na tabela periódica dos elementos, os quatro elementos metálicos dos elementos de metais de transição, ouro, prata, cobre e alumínio, possuem alta condutividade elétrica. Muitos fabricantes de LED tentam desenvolver materiais como liga de cobre, fio de liga de prata revestido de ouro-e fio de liga de prata para substituir os caros fios de ouro. Embora essas alternativas sejam superiores aos fios de ouro em algumas propriedades, elas são muito piores em termos de estabilidade química. Por exemplo, fios de prata e fios de liga de prata revestidos de ouro-são suscetíveis à corrosão por enxofre/cloro/bromação, e fios de cobre são propensos à oxidação. No caso da sílica gel encapsulada semelhante à esponja-absorvente e respirável, essas alternativas tornam o fio de ligação suscetível à corrosão química, reduzem a confiabilidade da fonte de luz e a utilizam por muito tempo, e o LED contas de lâmpada são fáceis de quebrar e morrer.
2. Desvio de diâmetro
One gram of gold can draw a gold wire with a length of 26.37m and a diameter of 50μm (2 mil), or a gold wire with a length of 105.49m and a diameter of 25μm (1 mil). If the length of the gold wire is fixed, if the diameter of the incoming gold wire is half of the original, then the resistance measured on the gold wire is one-fourth of the normal.
Para os fornecedores, quanto menor o diâmetro do fio de ouro, menor o custo e maior o lucro quando o preço permanece inalterado. Para clientes de LED que usam fios de ouro, a compra de fios de ouro que cortam cantos no diâmetro aumentará a resistência dos fios de ouro e reduzirá o risco de corrente de fusão, o que reduzirá bastante a vida útil da fonte de luz LED. Por exemplo, a vida útil do fio de ouro de 1,0 mil deve ser menor que o fio de ouro de 1,2 mil.
3. Defeitos de superfície
(1) The surface of the wire should be free of nicks, pits, scratches, cracks, bumps, discounts and other defects that reduce the service life of the device that exceed 5 percent of the wire diameter. During the drawing process of the gold wire, the surface defects on the wire surface will increase the current density and make the damaged part easily burned. At the same time, the resistance to mechanical stress is reduced and the damaged part of the inner lead is broken.
(2) The surface of the gold wire should be free of oil, rust, dust, and other adherents, which will reduce the bonding strength between the gold wire and the LED chip, and between the gold wire and the bracket.
4. A carga de ruptura e a taxa de alongamento são muito baixas
A good gold wire that can withstand the impact generated by resin encapsulation must have a specified breaking load and elongation. At the same time, the breaking force and elongation of the gold wire play a key role in the quality of wire bonding, and bonding wires with high breaking rate and elongation are more conducive to bonding. Gold wire that is too soft can cause the following disadvantages:
(1) O fio do arco cede;
(2) Instabilidade esférica;
(3) O pescoço da bola é fácil de encolher;
(4) O fio de ouro é fácil de quebrar.
O fio de ouro muito duro pode causar as seguintes desvantagens:
(1) Perfure os eletrodos do chip ou epitaxia;
(2) O gargalo da bola de ouro está quebrado;
(3) Dificuldades na formação de ligas;
(4) É difícil controlar o arco do arco.
lasca
1. Pouca capacidade antiestática do chip
The anti-static index of LED lamp beads depends on the LED light-emitting chip itself, and basically has nothing to do with the expected packaging process of the packaging material, or the influencing factors are very small and subtle; LED lights are more susceptible to electrostatic damage, which is related to the distance between the two pins. The relationship between the two electrodes of the LED chip die is very small, generally within 100 microns, while the LED pin is about two millimeters. When the electrostatic charge is to be transferred, the greater the distance, the easier it is to form a large potential difference. , That is, high voltage. Therefore, it is more prone to electrostatic damage accidents after being sealed into LED lights.
2. Defeitos epitaxiais do chip
During the high-temperature growth of LED epitaxial wafers, impurities are introduced into the substrate, residual deposits in the MOCVD reaction chamber, peripheral gases, and Mo sources. These impurities will penetrate into the epitaxial layer to prevent the nucleation of gallium nitride crystals and form a variety of Various epitaxial defects eventually form tiny pits on the surface of the epitaxial layer, which will also seriously affect the crystal quality and performance of the epitaxial film material.
3. Resíduos químicos de cavacos
Electrode processing is a key process for making LED chips, including cleaning, evaporation, yellowing, chemical etching, fusion, and grinding. Many chemical cleaning agents will be exposed. If the chips are not cleaned enough, harmful chemicals will remain. These harmful chemicals will electrochemically react with the electrode when the LED is energized, resulting in dead lights, light decay, dimming, and blackening. Therefore, the identification of chip chemical residues is very important for LED packaging factories.
4. Danos ao chip
The damage of the LED display chip will directly lead to the failure of the LED, so it is very important to improve the reliability of the LED chip. During the evaporation process, it is sometimes necessary to fix the chip with a spring clip, so clamping marks are generated. If the yellow light work is incomplete and the mask has holes, there will be excess metal 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. Therefore, scratches on the die electrode may occur.
The impact of chip electrodes on solder joints: the chip electrode itself is not reliably evaporated, causing the electrode to fall off or damage after the wire bonding; the chip electrode itself is poorly solderable, which will cause the solder ball to solder; improper chip storage will cause the electrode surface to be oxidized and the surface is stained And so on, slight contamination of the bonding surface may affect the diffusion of metal atoms between the two, resulting in failure or false welding.
5. Os chips do novo processo de estrutura são incompatíveis com os materiais da fonte de luz
The new structure of the LED chip electrode has a layer of aluminum, which functions to form a layer of reflector in the electrode to improve the light-emitting efficiency of the chip, and secondly, it can reduce the amount of gold used when evaporating the electrode to a certain extent, thereby reducing the cost. However, aluminum is a relatively active metal. Once the packaging factory does not strictly control the incoming materials and uses glue with excessive chlorine content, the aluminum reflective layer in the gold electrode will react with the chlorine in the glue, resulting in corrosion.
suporte de LED
1. A camada de revestimento de prata é muito fina
The existing LED light sources on the market choose copper as the base material of the lead frame. In order to prevent the oxidation of copper, a layer of silver is generally plated on the surface of the stent. If the silver plating layer is too thin, the stent is easy to yellow under high temperature conditions. The yellowing of the silver-plated layer is not caused by the silver-plated layer itself, but is affected by the copper layer under the silver layer. At high temperatures, copper atoms will diffuse and penetrate to the surface of the silver layer, making the silver layer yellow. The oxidizability of copper is the biggest drawback of copper itself. Once the copper appears in an oxidized state, the thermal conductivity and heat dissipation performance will be greatly reduced. Therefore, the thickness of the silver plating layer is very important. At the same time, both copper and silver are easily corroded by various volatile sulfides and halides in the air, causing their surfaces to become dark and discolored. Studies have shown that the discoloration increases the surface resistance by about 20-80 percent , and the power loss increases, which greatly reduces the stability and reliability of the LED, and even leads to serious accidents.
Exibição led colorida
2. Vulcanização da camada de revestimento de prata
LED light sources are afraid of sulfur. This is because sulfur-containing gas will pass through the porous structure of the silica gel or the gap between the brackets and cause a vulcanization reaction with the silver-plated layer of the light source. After the vulcanization reaction of the LED light source occurs, the functional area of the product will blacken, the luminous flux will gradually decrease, and the color temperature will drift significantly; the conductivity of the vulcanized silver sulfide increases with the increase in temperature, and leakage is very likely to occur during use; more serious The situation is that the silver layer is completely corroded and the copper layer is exposed. Since the second solder joint of the gold wire is attached to the surface of the silver layer, when the silver layer in the functional area of the stent is completely vulcanized and corroded, the gold ball appears to fall off, resulting in a dead light.
3. Oxidação da camada de revestimento de prata
In the preliminary diagnosis of LED blackening, it is found that the more difficult the sulfur/chlorine/bromine elements are, the more difficult it is to find. However, the signs of blackening of the silver plating layer of the LED light source are obvious, which may be related to silver oxidation. However, pure element analysis and detection methods such as EDS energy spectrum analysis are not easy to determine oxidation, because oxygen elements existing in the air environment, sample surface adsorption, and organic matter such as encapsulating glue will interfere with the determination of the detection result, so the conclusion of determining oxidation blackening needs to be used SEM, EDS, micro-infrared spectroscopy, XPS and other professional inspections and a series of reliability comparison experiments such as light, electricity, chemistry, environmental aging, etc., combined with professional inspection knowledge and electroplating knowledge for comprehensive analysis.
4. Baixa qualidade de galvanoplastia
The quality of the coating is mainly determined by the crystalline structure of the metal deposition layer. Generally speaking, the finer the crystalline structure, the denser and smoother the coating, and the higher the protective performance. This kind of fine crystalline coating is called "microcrystalline deposited layer". A good electroplating layer should crystallize finely, smoothly, uniformly, and continuously, and no contaminants, chemical residues, spots, black spots, scorching, roughness, pinholes, pitting, cracks, delamination, blistering, and bubbles are allowed. Skin wrinkles, coating peeling, yellowing, crystalline coating, partial no coating and other defects.
In the practice of electroplating production, the thickness of the metal coating and the uniformity and integrity of the coating are one of the important indicators for checking the quality of the coating, because the protective performance and porosity of the coating are directly related to the thickness of the coating. The special change is the cathode coating. As the thickness increases, the protective performance of the coating also improves. If the thickness of the coating is not uniform, the thinnest part is often destroyed first, and the other parts will lose the protective effect no matter how thick the coating is.
The coating has more porosity, and corrosive gases such as oxygen will enter and corrode the copper matrix through the pores
5. Poluição orgânica
Because various organic-containing potions are used in the electroplating process, if the silver plating layer is not cleaned or if poor quality and deteriorating potions are used, these residual organic matter will be affected by light, heat and electricity in the environment where the light source is lit. Under the action of, the organic matter may undergo chemical reactions such as redox and cause discoloration of the surface of the silver plating layer.
6. Material do bocal
The plastic material is the key to the heat conduction of the LED package bracket. If the PPA bracket is a nozzle material, the plastic performance of the PPA will be reduced, resulting in the following problems: poor high temperature tolerance, easy deformation, yellowing, and low reflectivity; high water absorption , The stent will change its size and decrease its mechanical strength due to water absorption; it has poor bonding with metal and silica gel. It is relatively picky and does not match many silica gels. These potential problems make it difficult to use the lamp beads at a higher power. Once the power range is exceeded, the initial brightness is very high, but it decays quickly, and the lamp will be dimmed after a few months.
Fósforo
1. Hidrólise de fósforo
Nitride phosphors are easily hydrolyzed and become invalid.
2. O mecanismo de auto-aquecimento do fósforo
The self{{0}}heating mechanism of the phosphor makes the temperature of the phosphor layer often higher than the p-n junction of the LED chip. The reason is that the conversion efficiency of phosphors cannot reach 100 percent , so part of the blue light absorbed by the phosphors is converted into yellow light, and the other part of the light energy absorbed by the phosphors in the high light energy density LED package becomes heat. Since phosphor is usually mixed with silica gel, and the thermal conductivity of silica gel is very low, only 0.16 W/mK, the heat generated by the phosphor will accumulate in a small local area, causing local high temperature, and the greater the optical density of the LED The greater the calorific value of the phosphor. When the temperature of the phosphor exceeds 450 degrees Celsius, the silica gel near the phosphor particles will be carbonized. Once the silica gel in a certain place is carbonized and blacked, its light conversion efficiency is lower. This area will absorb more light energy emitted by the LED and convert more heat. The temperature continues to increase, making the carbonized area larger and larger.
Cola de cristal sólido
1. Decapagem de cola prateada
The matrix of conductive silver glue is epoxy resin material, and the coefficient of thermal expansion is much larger than that of chips and brackets. In the environment where the lamp bead is used under the impact of cold and heat, stress will be generated due to thermal problems, and the effect will be even greater in an environment with drastic temperature changes. In order to exacerbate it, the colloid itself has tensile breaking strength and elongation. When the tensile force exceeds, the colloid will crack. The die-bonding glue peels off at the interface, the heat dissipation deteriorates sharply, the heat generated by the chip cannot be discharged, and the junction temperature rises rapidly, which greatly accelerates the light decay process.
2. Camadas de cola prateada
The silver powder particles are dispersed in the slurry system in a suspended state. Due to the influence of density difference, charge, cohesion, force and the structure of the dispersion system between the silver powder and the matrix, the phenomenon of sedimentation and stratification of silver powder often occurs. Quickly will cause the product to sag during slurrying, and the thickness of the coating will be uneven, and even affect the physical and chemical properties of the coating film. Delamination will also affect the heat dissipation, bonding strength and conductivity of the device.
3. Migração de íons de prata
A customer used silica gel encapsulation and a vertical flip-chip light source bonded with conductive silver glue to leak electricity. Through the analysis of bad lamp beads. Abnormal silver elements are detected on the side of the chip, and it can be observed that the silver particles gradually spread from the bottom positive silver glue area to the side of the PN junction on the upper side of the chip. Therefore, it is determined that the leakage failure of the bad lamp is most likely to come from The silver ions of the solid crystal silver glue are caused by ion migration on the side of the chip. The silver ion migration phenomenon is gradually formed during the use of the product. With the increase of the migration phenomenon, the silver ion will eventually conduct the chip PN junction, resulting in a low resistance path on the side of the chip, resulting in abnormal leakage current of the chip. In severe cases It even causes a short circuit of the chip. 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 damp, the invading water molecules ionize the silver and migrate along the side of the chip under the action of the vertical electric field from bottom to top. Therefore, it is recommended that customers use silica gel encapsulation and silver glue to bond the vertical flip chip lamp beads, choose the gold-tin eutectic welding method to fix the chip on the bracket, and strengthen the waterproof characteristic test of the lamp.
4. A cola de cristal sólido não seca
The curing agent of silicone for LED encapsulation contains platinum (platinum) complex, and this platinum complex is very susceptible to poisoning. The poisoning agent is any kind of nitrogen (N), phosphorus (
