What are the reasons for the yellowing of led lens lamp beads?

Led lens is a kind of lens, mainly used for lighting, chemical instruments, etc. What are the reasons for the yellowing of the LED lens lamp beads when in use?

1. LED lens lamp bead coating vulcanization discoloration

After the vulcanization reaction occurs in the light source of the LED lens, that is, the functional area of ​​the lamp will turn black, the luminous flux will gradually decrease, and the color temperature will drift significantly; the conductivity of the vulcanized silver sulfide increases with the increase of temperature, which is prone to leakage during use; In a more serious case, the silver layer is completely corroded and the copper layer is exposed. Silver has a strong affinity for sulfur, oxygen, and chlorine.

Silver easily adsorbs water molecules in the air to form a water film on its surface. Oxygen, sulfur, and chlorine in the air enter the water film to form insoluble silver oxide, silver sulfide, and silver chloride, which corrode and discolor on the surface of the silver layer.

The rough silver-plated surface is more likely to condense moisture than the smooth surface, enter the corrosive medium, and cause discoloration. After silver plating, the surface is not clean, and the residual plating solution contains silver ions, which changes color rapidly after contact with moist air.

2.led lens lamp beads solid crystal glue discoloration

The light-emitting diode chip is bonded to the support by the compound (except eutectic). The LED chip is the heat source and all the heat should start to dissipate from here. In addition, because the light emitted by the light-emitting diode chip is not blue, the wavelength is short, and the energy is high, the molecular chain of the die-bonding glue is in a high-energy state for a long time. The die-bonding glue is a hot substance outside the chip, and it is also the reason for the discoloration of the die-bonding glue.

Epoxy is easy to carbonize at high temperature, and it is easy to break molecular bonds and turn yellow when exposed to blue light for a long time. Silver halide, vulcanization and oxidation lead to the decrease of thermal conductivity and bond strength of die-bonding adhesive.

3. The encapsulant is aging and discolored

Because the LED lens lamp beads need to be protected with transparent glue, so when choosing glue, pay more attention to factors such as high refractive index and high projection rate. Usually use stupid silicone or epoxy glue.

These glues undergo changes in molecular bond cleavage when exposed to light for extended periods of time. Due to the existence of phenyl ring groups, phenyl silica gel will produce color-changing group quinone and yellowing under high temperature and ultraviolet conditions.

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