From a professional perspective:
Drop molding: also known as micro-injection, it is a process where white or colored drops are dropped on the surface of knitted cotton and various chemical fiber fabrics and textiles. Glue jewelry is a product similar to PVC silicone. Most of the trademarks used on bags, backpacks, clothing... are of this type. The processing is relatively complex. The silicone trademarks, silicone plastic labels, silicone non-woven fabrics, silicone TC cloth, etc. we often say belong to this type of plastic. PVC plastic can also be made into plastic shoes, insoles, and supports. Shoe soles, sofa backrests, armrests, dining table tablecloths, mahjong tablecloths, car interior decoration and other products
Crystal glue: It is also a type of drop plastic, made of a combination of A and B glue. It is divided into elastic crystal glue and hard crystal glue. It is a processing technology that makes the surface of printed matter (or the surface of other plastic objects) obtain a crystal-like raised effect. People call it various names, such as: plastic trademark, Crystal drop plastic, drop plastic label, drop plastic sign, etc.
Uses: clothing accessories industry, shoe plastic industry, printing sign industry, gift industry. Many people use "drop plastic" and "crystal label" in these categories. These two words are confused. Many people equate crystal labels with plastic labels, and plastic labels with crystal labels. Now, Huilitong will give a simple description of these two concepts. If there are any mistakes, please correct them.
Dispensing method SMA can be applied to PCB using syringe dispensing method, needle transfer method or stencil printing method. The needle transfer method, used in less than 10% of all applications, uses an array of needles immersed in a tray of glue. The hanging glue drop is then transferred to the plate as a whole. These systems require a lower viscosity glue with good resistance to moisture absorption as it is exposed to the indoor environment. Key factors that control needle transfer dispensing include needle diameter and style, glue temperature, needle immersion depth, and dispensing cycle length (including delay time before and during needle contact with the PCB). The tank temperature should be between 25 and 30°C, which controls the viscosity of the glue and the number and form of glue dots. Stencil printing is widely used for solder paste and can also be used to dispense adhesives. Although less than 2 SMAs are currently printed using stencils, interest in this method has increased and new equipment is overcoming some of the earlier limitations. Correct template parameters are key to achieving good results. For example, contact printing (zero height from the plate) may require a delay period to allow good glue dot formation. In addition, non-contact printing (approximately 1mm gap) of polymer templates requires optimal squeegee speed and pressure. The thickness of the metal template is generally 0.15~2.00mm, which should be slightly larger (0.05mm) than the gap between the component and the PCB. More than 90% of SMT glue is currently dispensed through syringes, which can be further divided into two categories: pressure-time systems and volume control systems. Pressure-time syringe dispensing is the most common method and the remainder of this section describes this technique. The syringe can reach dispensing speeds of 50,000 points per hour and can be adjusted to meet changing production requirements.
Factors affecting drip plasticity Good drip molding does not solely rely on the quality of the glue. For the pressure-time syringe dispensing method, many machine-related factors affect dispensability and glue spot formation. The inner diameter of the needle tip is critical to the formation of glue dots and must be much smaller than the diameter of the glue dots on the board. As a principle, the ratio should be 2:1. Glue dots of 0.7~0.9mm require an ID of 0.4mm; glue dots of 0.5~0.6mm require an ID of 0.3mm. Equipment manufacturers typically provide technical specifications and operating guidelines for producing the desired dot size and shape. The distance between the PCB and the needle nozzle, or the height of the stopper, controls the height of the glue dot. It must be appropriate for the dispense volume and tip ID. For a given amount of glue, the ratio of glue dot height to width will increase with stop height. Typically, the maximum stop height is half the tip ID; beyond this point, discontinuous dispensing and wire pulling will occur. Today's high-speed equipment uses pressure that can time the dispensing cycle to begin before the needle is in place.
The needle tip retraction speed, retracement height and the delay between dispensing and needle tip retraction all affect the glue dot shape and wire pull. Finally, temperature will affect viscosity and dot shape. Most modern dispensing machines rely on temperature controls on the needle or chamber to keep the glue above room temperature. However, the glue dot profile may be damaged, which will affect the viscosity and glue dot shape if the PCB temperature is increased from the previous process.