How to solve the black problem of LED lamp beads?

- Jan 29, 2020-

Industry Status


The cost-driven model drives the development of technology, and the LED industry cannot do without this model. LED downstream applications are constantly being introduced, and light sources and lamps with higher wattage, smaller heat dissipation structure and lower cost are introduced. These products have brought great difficulties in heat treatment, and at the same time, they have imposed more stringent reliability requirements on LED lamp beads, especially in anti-sulfurization, anti-oxidation, and anti-bromination.


As we all know, the brightness attenuation of LED is caused by the blackening of the silver-plated layer.


Blackening can be a sulfuration phenomenon, which refers to the process in which sulfur (S) in the environment under certain temperature and humidity conditions, where -2 sulfur and +1 silver chemically react to form black Ag2 S;


It can also be an oxidation phenomenon, which refers to the process in which oxygen (O) in the environment under certain temperature and humidity conditions, where -2 valent oxygen and +1 valent silver chemically react to form black Ag2 O;


It can also be the bromination phenomenon, which refers to the process of bromine (Br) element in the environment under a certain temperature and humidity conditions, where -1 valent bromine and +1 valent silver chemical reaction to produce light black AgBr.


Of course, other 6A and 7A group elements may also enter the interior of the LED lamp bead package, causing the silver plating layer to change color and reducing the brightness of the LED lamp bead.


How to solve the black problem?


So, where do these 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 problem of blackening.


Whether all kinds of channels can be effectively blocked becomes the key to solving our problems.


Organic silicon and silicone resin (collectively referred to herein as silicone) are commonly used as encapsulants for LED lamp beads. They have a certain moisture and oxygen permeability, especially in high temperature environments, sulfur, oxygen, bromine and other elements are easily Penetrate the silicone into the LED lamp bead package.


1. Method adopted by the industry 1: hard silicone package


At present, most LED packaging factories use silica gel with higher hardness as the sealing material for LED lamp beads, which can delay the blackening time, but the stress caused by the silica gel with higher hardness 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 beads are easily broken to cause functional failure. However, even with higher hardness silica gel, the glass transition temperature of silica gel is only 50-70 ° C. At high temperatures, the gap between the molecular structure of silica gel becomes larger, and sulfur, oxygen, bromine and other substances can easily enter the LED The inside of the package reacts with the silver plating layer.


2. Method used in the industry 2: Organic gas barrier material is coated on the surface of silica gel


Therefore, many LED packaging plants still use softer silicone, coating a layer of organic gas barrier material on the surface of the LED lamp bead package, while delaying the darkening time, avoiding the stress of the silicone with high hardness.


It is not difficult to see that the two methods of solving the problem of blackening by using a higher hardness encapsulant or surface coating of organic gas barrier materials are only improved in the front channel of the colloid (1), the other channels are still not blocked, sulfur , Oxygen, bromine and other substances easily enter the LED lamp bead package, these two methods have very poor results. What's more, when coated on the surface of LED lamp beads, the organic gas barrier layer is easily worn in the later processing. At the same time, organic gas barrier materials are prone to degradation and cracking due to molecular fission under high-temperature environments for a long time, and ultimately do not provide effective protection.


3. Method used in the industry 3: silver-plated layer coated with organic gas barrier material


Because of the structure of the patch LED, the barriers of (2) and (3) channels are quite difficult, which is also the technical bottleneck of the current LED packaging industry. It is more difficult to block the channel. To effectively solve the problem of blackening, only the surface of the silver plating can be completely protected. Some LED packaging plants apply organic gas barrier materials on the surface of the silver-plated layer. Even if the channels are not blocked, sulfur, oxygen, bromine and other substances entering the LED package cannot react with the silver-plated layer.


However, the thickness and consistency of this organic gas barrier material are difficult to control. The important thing is that organic materials are easily degraded under high temperature for a long time, molecular fission occurs, and the organic gas barrier layer cracks. In the end, it does not provide good protection .


Solutions from SMART Semiconductor


Hongli Zhihui Group's wholly-owned subsidiary Smart Semiconductor Co., Ltd. uses advanced, cutting-edge, unique PPL technology to solve the problem of blackening, and deposits an inorganic substance on the surface of the silver-plated layer. The inorganic substance has excellent compactness. , Effectively block the reaction of sulfur, oxygen, bromine and other substances with the silver coating. At the same time, it has long-lasting and stable chemical properties, has outstanding performance in corrosion resistance and high temperature resistance, and completely solves the problem of blackening caused by sulfurization, oxidation, and bromination. The vulcanization test of products produced by our company's PPL technology at a high temperature of 110 ° C is 40% higher than that of ordinary products.


PPL technology has re-improved the long life of LED lamp beads. The LED lamp beads packaged with PPA and PCT injection molded bracket carriers can achieve a lifetime (L70) of more than 50,000 hours in most applications. PPL technology Will shine in more demanding applications.


In January 2017, SMART Semiconductor's PPL non-sulfur product solution achieved the first mass production in China. The launched PPL non-vulcanization process solution can cover a full range of SMD, SMC, and EMC products, and can completely solve the vulcanization problem. Up to now, it has applied for 3 invention patents.


In addition, EMC3030 / 5050/7070 products are more widely used. In outdoor lighting, especially EMC5050 products, light efficiency of 240LM / W can be achieved at 1W. Combined with PPL anti-sulfur technology, SMC packaging, higher reliability, SMC5050 / 7070 products will have a rapid growth in outdoor product applications. . At the same time, it will also be widely used in high-power products, automotive lighting and other fields.