Industry Status
The cost-driven model drives the development of technology, and the LED industry cannot do without this model. LED downstream applications continue to evolve, introducing light sources and lamps with higher wattage, smaller heat dissipation structure, and lower cost. These products have brought great difficulties in heat treatment, and also put more stringent reliability requirements on LED lamp beads, especially in anti-vulcanization, anti-oxidation and anti-bromination.
It is well known that LED brightness decay is caused by the blackening of the silver plating layer.
Blackening, which may be a vulcanization phenomenon, refers to a process in which a sulfur-(S) element in the environment is chemically reacted with a +1 valence silver to form a black Ag2 S under a certain temperature and humidity condition;
It may also be an oxidation phenomenon, which refers to a process in which oxygen (O) element in the environment is chemically reacted with +1 valence of silver to form black Ag 2 O under certain temperature and humidity conditions;
It may also be a bromination phenomenon, which refers to a process in which a bromine (Br) element in the environment is chemically reacted to form a light black AgBr under a certain temperature and humidity condition, wherein the -1 valence bromine reacts with the +1 valent silver.
Of course, other elements of Groups 6A and 7A are also likely to enter the interior of the LED lamp bead package to cause discoloration of the silver plating layer and reduce the brightness of the LED lamp bead.
How to solve the blackening problem?
Then, where the sulfur, oxygen, bromine and other substances enter the interior of the LED lamp bead package and react with the silver plating layer, understanding this entry channel is of decisive significance for us to solve the blackening problem.
Whether the various channels can effectively block is the key to our problem solving.
figure 1
Silicone and silicone resins (collectively referred to herein as silica gel) are commonly used as encapsulants for LED lamp beads, which have a certain moisture permeability and oxygen permeability, especially in high temperature environments, such as sulfur, oxygen, bromine and the like. Pass through the silica gel and enter the inside of the LED lamp bead package.
1. Method 1 adopted by the industry: hard silicone package
At present, most LED packaging plants use higher hardness silica gel as the packaging material of LED lamp beads to delay the blackening time, but the stress problem caused by the higher hardness silica gel increases the reliability of the internal structure of the LED lamp bead package. Sexual risk. In the case of thermal expansion and contraction, the bonding wires inside the LED lamp bead are easily broken to cause functional failure. However, even with a silica gel of higher hardness, the glass transition temperature of silica gel is only 50-70 ° C. At high temperatures, the molecular structure of the silica gel becomes larger, and sulfur, oxygen, bromine and the like are also easily accessible to the LED. The inside of the package reacts with the silver plating layer.
figure 2
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