The LED lamp bead is easy to blacken, and the plating of the LED bracket is silver plated (see the public information history message - LED bracket article). Because the sulfur-containing gas passes through the porous structure of the silica gel or the gap between the stent and the vulcanization reaction with the silver plating layer of the light source, the plastic used in the stent has many pore-like structures.

The cause of discoloration is one: the coating is vulcanized and discolored.

After the vulcanization reaction of the LED light source, the functional area of ​​the product will be blackened, the luminous flux will gradually decrease, and the color temperature will drift significantly. The vulcanized silver after vulcanization will increase in conductivity with increasing temperature, and it is prone to leakage during use; The condition is that the silver layer is completely corroded and the copper layer is exposed. Since the gold wire two solder joints are attached to the surface of the silver layer, when the silver layer of the bracket functional region is completely vulcanized and eroded, the golden ball appears to fall off, and a dead light appears. You can see that the silica gel and the silver layer are easily peeled off after vulcanization. The surface of the peeled silicone is covered with small black spots. These blacks are silver sulfide.

Ø Silver has a strong affinity for sulfur, oxygen and chlorine. The water molecules in the silver easily adsorbing air form a water film on the surface, and oxygen, sulfur and chlorine in the air enter the water film to form insoluble silver oxide, silver sulfide and silver chloride, which cause corrosion on the surface of the silver layer and cause discoloration.

Ø Rough silver-plated surface is more apt to condense moisture and enter corrosive media than smooth, causing discoloration.

Ø After silver plating, the surface cleaning is not clean. The residual plating solution contains silver ions, which will cause discoloration soon after contact with humid air.

The vulcanization of the silver-plated layer accounts for a large proportion of the discoloration of the lamp bead, and the general packaging factory corresponds to the reason that the color-changing customer always wants to pull the vulcanization. Once the sulfur content is analyzed by the elemental composition, the packaging factory does not recognize that the lamp is not ready. A lot of good cooperation between the two sides because a customer complained about the situation of the thin court.

Cause of discoloration 2, solid crystal glue discoloration.

The LED chip is bonded to the holder by glue (except for eutectic). We all know that the LED chip is a heat source, and all the heat needs to be emitted from here. And because the light emitted by the LED chip is not blue, the wavelength is short, the energy is high, and the molecular chain of the solid crystal glue is in a high energy state for a long time. The solid crystal glue is the hottest material outside the chip, and this reason will cause the solid crystal glue to change color.

Ø Epoxy high temperature is easy to carbonize, long-term blue light irradiation is easy to break the molecular bond and the quality changes yellow

Ø Silver halide in silver paste, vulcanization, oxidation, resulting in a decrease in thermal conductivity of the solid crystal adhesive and a decrease in bond strength.

Cause of discoloration 3. Encapsulation glue aging discoloration.

Since LED lamp beads need to be protected by transparent glue, the factors of high refractive index and high throwing rate are emphasized when selecting glue. Generally choose a base silicone or epoxy glue. These glues undergo molecular bond cleavage changes in the long-term exposure to light.

ØPhenyl silica gel due to the presence of benzene ring group, under the conditions of high temperature and ultraviolet light, it will produce discoloration group "醌", yellowing occurs.

Ø Epoxy materials are more prone to yellowing and cracking under high temperature and UV conditions.

The discoloration of LEDs is mainly due to these reasons, and of course, some LED discoloration caused by changes in halogenation and phosphors. For the LED lighting factory, in order to avoid the thin court, it is necessary to prevent it in advance. How to prevent it?

First, the inspection of LED incoming materials can not be less.

There are many companies that only test the parameters of light and voltage for LED incoming materials. Inspection of LED reflow soldering test, sulfurization resistance test and high temperature and high humidity environment storage. Due to the large number of parts and materials involved in LED lamps, the production environment is complex, and the environmental simulation test of LED lamp beads is carried out.

Second, the use of unknown ingredients chemicals with caution.

Some adhesives and cleaning agents should not be used casually. Be sure to confirm the ingredients and simulate the experiment before using them. In many cases, quality accidents have been caused by changing a little auxiliary material.

Third, batch sampling can not be less.

There are some suppliers who are forced by cost pressures to have quality differences in batch products. For the application plant, it is necessary to carry out batch sampling, and the materials that are initially confirmed after each spot check are compared, and many problems will be found in the long-term persistence.

Recommended packaging factory:

1, solid crystal glue must be used well, after all, the proportion of cost is very small.

2, the quality of the coating should be strictly controlled.

3. Communicate with customers and educate customers on how to use lights correctly.