(1) There are two types of LED patch glue
1. Dispensing type: glue is applied on the printed circuit board through dispensing equipment.
2. Scraping type: glue is applied through steel mesh or copper mesh printing and scraping.
(2) LED patch glue surface adhesive (SMA, surface mount adhesives) is used for wave soldering and reflow soldering. It is mainly used to fix components on the printed circuit board. It is generally distributed by dispensing or steel mesh printing to maintain the position of components on the printed circuit board (PCB) to ensure that components will not be lost during the transmission process on the assembly line. After the components are attached, they are placed in an oven or reflow soldering machine for heating and hardening. It is different from the so-called solder paste. Once heated and hardened, it will not melt again. In other words, the thermal hardening process of the patch glue is irreversible. The effect of SMT patch glue will vary depending on the thermal curing conditions, the objects to be connected, the equipment used, and the operating environment. When using it, the patch glue should be selected according to the production process.
(3) LED SMD adhesive Most surface mount adhesives (SMA) are epoxies, although acrylics are used for special purposes. After the introduction of high-speed glue dispensing systems and the electronics industry mastered how to deal with products with relatively short shelf lives, epoxy resins have become the more mainstream adhesive technology worldwide. Epoxy resins generally provide good adhesion to a wide range of circuit boards and have very good electrical properties. The main ingredients are: base material (i.e. main polymer material), filler, curing agent, other additives, etc.
(4) LED SMD adhesive use purpose
1. Prevent components from falling off during wave soldering (wave soldering process)
2. Prevent components from falling off on the other side during reflow soldering (double-sided reflow soldering process)
3. Prevent components from shifting and standing (reflow soldering process, pre-coating process)
4. Marking (wave soldering, reflow soldering, pre-coating). When printed boards and components are changed in batches, SMD adhesive is used for marking.
(5) LED glue dispensing method SMA can be applied to the PCB using syringe glue dispensing, needle transfer or template printing. The needle transfer method is used in less than 10% of all applications. It uses an array of needles immersed in a tray of glue. The suspended glue droplets are then transferred to the board as a whole. These systems require a lower viscosity glue and good resistance to moisture absorption because it is exposed to the indoor environment. The key factors controlling needle transfer glue dispensing include needle diameter and style, glue temperature, needle immersion depth and glue dispensing cycle length (including delay time before and during needle contact with PCB). The tank temperature should be between 25~30°C, which controls the viscosity of the glue and the number and form of glue dots. Temperature will affect viscosity and glue dot shape. Most glue dispensers rely on temperature control devices on the needle nozzle or in the chamber to keep the glue temperature above room temperature. However, if the PCB temperature is increased from the previous process, the glue dot profile may be damaged.