6. Silver plating 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.
8. Silver plating layer oxidation
The discovery of sulfur / chlorine / bromine is harder and harder to find in the initial diagnosis of contact with LED black. However, there are obvious signs of blackness in the silver screen of the LED light source, which may be related to the oxidation of silver. But the EDS spectrum analysis and other pure element analysis and detection methods are not easy to determine oxidation, because exists in the air environment, sample surface adsorption and encapsulation of organic matter such as oxygen elements will interfere with the determination of the test results, so the conclusion of the decision to use oxidative black SEM, EDS, micro-infrared spectroscopy, XPS and other professional testing and optical, electrical, chemical, environmental aging and a series of reliability comparison experiments, combined with professional knowledge and electroplating knowledge of a comprehensive analysis.
9. Excellent plating quality
The quality of the coating depends on the quality of the metal deposition layer of the crystal structure, in general, the smaller the crystal structure, the coating is also more dense, smooth, protective performance is also higher. This fine crystal coating is called a "microcrystalline layer". Jin Jian pointed out that a good coating should be fine crystal coating, smooth, uniform, continuous, do not allow contaminants, chemical residues, spots, black spots, charred, rough, pinhole, pitting, crack, Blistering, skin wrinkling, coating peeling, yellow, crystalline coating, local no plating and other defects.
In the practice of electroplating, the thickness of the metal coating and the uniformity and integrity of the coating are one of the important indexes to check the quality of the coating because the protective properties and porosity of the coating are directly related to the thickness of the coating. The special change is the cathodic coating, with the thickness increases, the protective performance of the coating also increases. If the thickness of the coating is not uniform, often the thinnest place is first destroyed, the rest of the coating and then thick will lose the protective effect.
Coating porosity more oxygen and other corrosive gases through the pores into the corrosion of copper matrix.
10. Organic pollution
Jin Kam also pointed out that because the electroplating process will use a variety of organic matter containing syrup, silver-plated layer if the cleaning is not clean or the use of poor quality and deterioration of the syrup, the residual organic matter once in the light source in the environment, Light, heat and electricity under the action of organic matter may occur redox and other chemical reactions lead to silver-plated layer surface discoloration.
11. Outlet material
Plastic material is the key to LED package brackets, gold inspection found that if the PPA stent is the nozzle material, will reduce the plastic properties of PPA, resulting in the following problems: high temperature tolerance is poor, easy to deformation, yellowing, low reflectivity ; High water absorption, the stent will be due to changes in size caused by water and mechanical strength decreased; and metal and silica gel poor adhesion, compared to glue, and a lot of silicone does not match. These potential problems make the lamp beads difficult to use in the slightly larger power, once beyond the use of power range, the initial brightness is high, but the attenuation is very fast, useless a few months on the dark.
12. Phosphor hydrolysis
Nitride phosphor is easy to hydrolyze and fail.
13. The mechanism of phosphor self-heating
The mechanism of phosphor self-heating, making the phosphor layer temperature is often higher than the LED chip p-n junction. The reason for this is that the conversion efficiency of the phosphor can not reach 100%, so that part of the blue light absorbed by the phosphor is converted into yellow light, and the other part of the light energy absorbed by the phosphor in the high light energy density LED package becomes heat. Since the phosphor is usually mixed with silica gel and the thermal conductivity of the silica gel is very low, only 0.16 W / mK, so the heat generated by the phosphor will accumulate in the smaller local area, resulting in local high temperature, LED optical density The greater the heat, the greater the calorific value of the phosphor. When the temperature of the phosphor reaches 450 ° C or more, the silica gel near the phosphor particles will be carbonized. Once there is a place where the silica gel carbon black, its light conversion efficiency is lower, the region will absorb more LED light emitted and convert more heat, the temperature continues to increase, making the area of carbonization is growing.