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LED SMD Epoxy glue and basics

1, The role of surface mount adhesive glue adhesive (SMA, surface mount adhesives) for wave soldering and reflow soldering, mainly used for the components mounted on the printed circuit board, usually with dispensing or stencil printing method to allocate , to maintain the position of the component on the printed circuit board (PCB) on, to ensure that transfer element in an assembly line process is not lost. After the paste components into the oven or reflow welding heat-curing. It is the so-called paste is not the same, after a heated hardening, reheating does not melt, that is, plastic patch thermosetting process is irreversible. SMT plastic patch effect due to the thermal curing conditions, the linker, the equipment used, different operating environment differ. To be selected patch of plastic production process according to use.
2, Most of the surface mount adhesive (SMA) components PCB assembly of glue used are epoxy resin (epoxies), although there are polypropylene (acrylics) are used for special purposes. The introduction of high-speed dispensing system and electronics industries to learn how to deal with a relatively short shelf life of the product after the epoxy glue has become more mainstream technology worldwide. Epoxy resins generally wide boards provide good adhesion, and has very good electrical properties. The main ingredients are: base material (ie, high body material elements), fillers, curing agent and other additives.
3, Plastic patch intended use of a. In wave soldering components to prevent falling (wave soldering) b. Reflow soldering components off to prevent the other side of the (double-sided reflow process) c. Prevent displacement and vertical components when at (reflow process, the pre-coating process) d. mark (wave soldering, reflow, the pre-coat), PCB and components batch change, marked with a plastic patch.
4, The use of glue dispensing a classification type: By dispensing device on the printed wiring board sizing. b Squeegee type: sizing by stencil or screen printing copper Scraping way.
5. The method of SMA Epoxy Epoxy can be used syringe method, the needle transfer method or template printing method applied to the PCB. Transfer method using a needle less than 10% of all applications, it is the use of needles arranged array immersed in a plastic tray. Then hanging drops of glue transferred to the board as a whole. The system requires a low viscosity adhesive, but also a good moisture absorption resistance, because of its exposure in the indoor environment. Control the needle transfer Epoxy key factors including needle diameter and style of glue temperature, cycle length and depth of the needle immersed Epoxy (including time delay before the needle PCB exposure and periods). Pool bath temperature should be between 25 ~ 30 ° C, which controls the amount and form of plastic viscosity and gel point.
Templates are widely used in solder paste printing, and distribution of glue can also be used. SMA Although less than 2% of the model is printed, but the interest in this method has increased, the new device is to overcome some of the limitations of earlier. Correct template parameter is the key to achieving good results. For example, contact printing (zero off-board height) may require a delay cycle allows good dot formation. In addition, the polymer template non-contact printing (approximately 1mm gap) requires optimum blade speed and pressure. Thickness of the metal template is generally 0.15 ~ 2.00mm, should be slightly larger than (+ 0.05mm) gap between the component and the PCB.
Finally, viscosity and temperature will affect the shape of the gel-point temperature of most modern dispensing machines rely on the needle mouth or chamber capacity control device to keep the glue temperature above room temperature. However, if the temperature of the PCB is improved from the previous procedure, then the outline of the gel-point may be damaged.