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.Poor quality plating
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.
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.The 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 ° Cor 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.
14.Silver peeling off
Conductive silver plastic matrix is epoxy resin materials, thermal expansion coefficient than the chip and the bracket are much larger in the lamp beads of hot and cold impact of the use of the environment, because of heat problems stress, the temperature changes in the environment will be more intense To intensify, the colloid itself has tensile breaking strength and ductility, when the tension is over, then the colloid is cracked. Solid crystal glue at the interface of the peel, the heat drastically worse, the chip can not be derived from the heat, the junction temperature increased rapidly, greatly accelerated the process of light failure.
15, silver plastic layer
Silver powder particles dispersed in the suspension system in the slurry system, silver powder and the matrix due to the density difference, charge, cohesion, the force and the structure of the dispersion and many other factors, often appear silver deposition stratification phenomenon, if the sedimentation Fast will make the product in the hanging pulp when the sagging, coating thickness is not uniform, and even affect the physical and chemical properties of the coating, stratification will also affect the device heat, bonding strength and conductivity.
16, silver ion migration
A customer with silicone packaging, conductive silver glue bonded vertical flip light source leakage phenomenon, commissioned Jin Jian find the cause. According to the analysis of the bad lamp beads, abnormal silver elements were detected on the side of the chip, and it was observed that the silver particles gradually spread from the bottom positive silver colloidal area to the dendritic extension morphology to the vicinity of the P-N junction side of the upper part of the chip. It is very likely that the silver ions from the solid crystal silver glue are caused by ion transport on the side of the chip. The phenomenon of silver ion migration is gradually formed in the process of product use. With the increase of migration phenomenon, the final silver ion will turn on the chip P-N junction, resulting in the existence of low resistance path on the chip side, resulting in abnormal leakage current Even in the case of short circuit caused by the chip. The reason for the migration of silver is multifaceted, but the main reason is that the silver-based material is damp, and after the silver paste is damped, the intruding water molecules make the silver ionized and migrate along the chip side in the vertical direction. Therefore, the proposed inspection of customers with caution silicone packaging, silver glue bonded vertical flip chip beads, the use of gold and tin eutectic welding method will be fixed on the bracket in the chip, and to strengthen the waterproof characteristics of lamps and lanterns detection.