Introduction To Basic Knowledge Of Patch Adhesive And Drop Adhesive Used In Led Explosion-Proof Lamp
Writer：Jane Time：2021-07-20 Browse：197 1. LED explosion-proof lamp inside the patch adhesive:
Surface Adhesives (SMA, Surface Mount Adhesives) are used for wave soldering and reflow soldering, mainly to fix components to the printed board, usually dispensing or steel screen printing method to distribute, to maintain the position of the components on the printed circuit board (PCB), to ensure that the components will not be lost during transmission on the assembly line. After affixing the components, put them into the oven or the reflow welding machine to heat and harden. It is called solder paste is not the same, once heated after hardening, reheating will not melt, that is to say, the thermal hardening process of the patch glue is irreversible. The application effect of SMT patch adhesive will vary according to the thermal curing conditions, the connected material, the equipment used and the operating environment. Use according to the production process to choose the patch adhesive.
2. LED explosion-proof lamp inside the adhesive composition:
Most SMAs used in PCB assembly are epoxy resins, although polypropylene is also used for specific purposes. After the introduction of high-speed drip systems and the electronics industry's grasp of how to deal with products with relatively short shelf life, epoxy resins have become a 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 components are: base material (that is, the main polymer material), filler, curing agent, other additives, etc.
3. LED explosion-proof lamp in the use of adhesive:
(1) Prevent components from falling off during wave soldering (wave soldering process)
(2) prevent the other side components from falling off during reflow welding
(3) Prevent component displacement and vertical position (reflow welding process, pre-coating process)
(4) When the most marks, printed boards and components batch change, use the patch adhesive to mark.
4. The use of LED explosion-proof lamp patch adhesive classification:
A. Dispensing type: by dispensing equipment on the printed circuit board sizing.
B. Scraping type: by steel mesh or copper mesh printing and scraping for sizing.
SMA can be applied to PCB using syringe drop method, needle transfer method or template printing method. Needle transfer, which is used in less than 10% of all applications, uses an array of needles dipped in a tray of glue. The hanging glue drops are then transferred to the board as a whole. These systems require a glue with a low viscosity and good resistance to moisture absorption because it is exposed to indoor conditions. Key factors controlling needle transfer drop include needle diameter and style, glue temperature, needle immersion depth, and drip cycle length (including delay time before and during needle contact with PCB). The tank temperature should be between 25 °C and 30°C, which controls the stickiness of the glue and the number and form of glue points.
Template printing is widely used for solder paste and also for dispensing adhesives. Although less than 2% of SMAs are currently printed in templates, interest in this method has increased and new devices are overcoming some of the limitations of earlier models. Correct template parameters are the key to achieve good results. For example, contact printing (zero plate height) may require a delay period to allow good glue spot formation. In addition, non-contact printing of polymer samples (approximately 1mm clearance) requires optimal scraper speed and pressure. The thickness of the metal plate is generally 0.15~2.00mm, which should be slightly larger than the gap between the component and the PCB (+0.05mm).
The final temperature will affect the viscosity and the shape of the glue point. Most modern glue drip machines rely on the nozzle or chamber temperature control device to keep the glue temperature above room temperature. However, if the PCB temperature is increased from the previous process, the glue spot profile may be damaged.