In the process of production and use of LEDs, product vulcanization often leads to product failure, causing significant losses to customers and manufacturers. In particular, SMD LEDs and high-power LEDs are used in a large number of polymer materials such as silica gel and silicone modified materials, which have become the hardest hit areas for product vulcanization.
In the process of production and use of LEDs, product vulcanization often leads to product failure, causing significant losses to customers and manufacturers. In particular, SMD LEDs and high-power LEDs are used in a large number of polymer materials such as silica gel and silicone modified materials, which have become the hardest hit areas for product vulcanization. How to prevent LED vulcanization during manufacture and use has become a common problem faced by various LED manufacturers.
LED sulfuration refers to the process of generating black silver sulfide due to the chemical reaction between sulfur (S), or sulfur-containing substances under certain temperature and humidity conditions, in which -2 valent sulfur and +1 valent silver react. Due to the highly moisture-permeable and oxygen-permeable nature of LED products encapsulated in silicone materials, LED vulcanization causes product failure to be particularly severe in such products.
The vulcanization of LED products mainly occurs in the following steps: First, LED production process. Raw materials and finished products are vulcanized, which are preventable and have a low occurrence rate. Second, the SMT process. The finished product is vulcanized, which can be prevented and has a high probability of occurrence. Third, the use process. Finished products are vulcanized, preventable and have a high probability of occurrence.
1. Prevention of vulcanization during production
The first link to prevent LED vulcanization is in the manufacturing process. The following SMD packaged in silicon illustrates the material that may be vulcanized during production:
1 The silver-plated stent was vulcanized, the stent became yellow and black and lost its luster. The process of crystal fixation decreased the reliability.
2 Silver glue is vulcanized, silver paste is black, dull, solid crystal process, reliability is reduced or invalid;
3 silicon properties The solid crystal glue is vulcanized, resulting in solidification hindrance, incomplete solidification, and in the solidification process, the adhesive strength is reduced or failed;
4 Silicon nature point powder glue is vulcanized, resulting in curing hindrance, unable to completely cure, dispensing, powder, packaging process, product failure;
5 phosphor sulfur, resulting in curing obstacles, point powder process, product failure.
The vulcanization in the production process mainly occurs in the process of die bonding and dispensing. Most of the sulfidation occurs with silver-containing materials and silicon-based film materials. In the production process, we must pay great attention to the vulcanization prevention of these two links.
The main possible sources of sulphide pollution are:
Sulfur-containing gloves, finger cots, sulphur masks, sulphur-containing PCBs, sulphur-containing cleaners, vulcanized ovens, vulcanized cartridges, and clamps.
The prevention method is to use:
Desulfurization gloves, finger sleeves, non-sulfur masks, cleaning, desulfurization before use, non-sulfur cleaning agent, independent baking, set up a special non-sulfur oven, separate use, distinguish between non-sulfur materials, folder fixtures.
From the above analysis, we can see that in the LED manufacturing process, the main prevention is mainly to prevent raw materials (silver material, silicon material) that are easily vulcanized from being sulphur-containing tools, fixtures, and gloves during the production process. Sulfur-containing materials such as masks lead to vulcanization.
The best preventive measure is to minimize the use of sulfur-containing materials and fixtures and other sulfur-containing auxiliary tools and materials during the production process. The production environment of LED is basically a dust-free workshop, and the isolation of sulfur in the environment is very high. As long as the isolation measures for sulfur-containing materials, fixtures, and auxiliary materials in the production are well prepared, they will not be easily vulcanized in production.
2. Prevention of vulcanization during SMT
Sulfurization in the SMT process is the most serious link in the curing of LED products. The main reason is that during the SMT process, a large amount of sulfur-containing materials are encountered. During the inspection process, PCBs, solder pastes, plate washers, and other irrigations are found. There is a record of sulphur in fillings. These materials will enter the reflow oven along with the LEDs during the SMT operation. After being left for a period of time after reflow, blackening of the silver-plated parts of the stent will occur, mainly sulfur-containing substances in the reflow process. Penetration into the LED causes the silver to be vulcanized and the product fails.
PCB products on the market all have different levels of sulfur, although PCB manufacturers will clean the plates during the manufacturing process to carry out desulfurization, but it is more difficult to remove them completely. Therefore, in the SMT operation, it is necessary to carry out quality control on the sulphur content of the PCB board. Generally, the maximum sulphur content above the PCB copper foil is not more than five thousandths.
In view of the fact that sulfur is active under high temperatures, during SMT operation, the PCB board can be pre-treated with a high-temperature reflow furnace to perform a surface cleaning process to reduce the sulfur content of the PCB board surface. If the process does not allow, PCB surface cleaning can be performed directly before SMT. After the reflow is completed, the surface of the product must be cleaned once again, and the possibility of curing the LED is reduced by cleaning the surface of the board and the soldering points. When cleaning, it is necessary to choose a non-sulfur and other acid-free cleaning agent.
During the SMT operation, it is necessary to prevent the use of sulfur-containing materials to cause vulcanization of the LED, and to prevent the use of vulcanized clip fixtures and machines. It is better to use them separately. It is better to establish a separate sulfur-free SMT production line or production workshop to ensure that the products are not subject to sulfidation during the process of making LED products SMT.
Let's study the composition of the glue. Generally, there are two types of LED potting glues. One is a low refractive index (usually around 1.43), and the methyl glue is relatively low in price, but the permeability of water is strong, so this Colloids have a high chance of vulcanization, while the second is phenyl glue, which has a higher refractive index (usually above 1.5) and is expensive because its molecular structure is complex and water and gas are difficult to get inside. The ability to prevent vulcanization is high.
If the LED sealed with methyl glue, the factory itself is equivalent to carrying the root cause, when the customer meets any of the conditions that can lead to LED curing, it will cause the disease to stimulate, resulting in LED sulfide. The LED encapsulated with phenyl-based glue will be strong when shipped from the factory and will not cause any cause of carry. Therefore, it will not cause vulcanization when it is applied.
3. Prevention of vulcanization during use
Sulfur is a very common odorless non-metal, pure sulfur is a yellow crystal, also known as sulfur. Sulfur has many different valences, common -2,0,+4,+6 and so on. In nature it often appears in the form of sulphide or sulphate, which is part of many amino acids and is therefore an integral part of most proteins.
It is mainly used in fertilizers and is also widely used in gunpowder, lubricants, insecticides and antifungals. It can be used to make sulfuric acid, sulfites, plastics, enamels, synthetic dyes, vulcanizates, bleaches, drugs, paints, and more.
In life and production, we are exposed to sulphur and sulphur-containing items everywhere, so we need to pay special attention when using LED products in our daily lives to prevent LED lamps or other products from being vulcanized. LED originals and LED application products should be kept in a uniform environment with sulfur-containing substances. Semi-finished products and finished products used in LED applications must be protected from exposure to natural environments if they are not sealed. In particular, exposure to acidic environments should be avoided.
Baby Water Mat
PD Toys plastic Co., Ltd is OEM & ODM manufacturer of inflatable products in the mainland of China with more 17 years of manufacturing experience. products ranges are Inflatable Toys, inflatable pools, inflatable Pool Floats, towable tubes, air furniture and Promotional Items etc. total have more than 1500 employees (4 factories) related to PVC inflatable products.
Operated under ISO 9001:2015 management system, We had passed factory Audit by Walmart, Taret, Disney ect, also passed all necessary certificates and testing such as ICTI, BSCI, SEMTA,Target FA, NBC Universal, FCCA, SGS, CVS Security, GSV, Disney FAMA ect. We have our own PVC raw materials manufacturing company, all the PVC we produced are compliance with European EN71, American ASTM standard and NON PHTHALATE (6P) standard.
