1, the effect of surface adhesive glue (SMA surface, Mount Adhesives) for wave soldering and reflow soldering, mainly used to affix the components on a printed circuit board, generally with the stencil printing or dispensing method to distribute, to keep the components on the printed circuit board (PCB) on the position, ensure that components are not transmitted in in the process of assembly line loss. Paste components into the oven or reflow soldering machine heating hardening. It is not the same as the so-called solder paste. Once heated, it will not melt when heated. That is to say, the thermal curing process of the adhesive is irreversible. The effect of SMT adhesive is different due to the different curing conditions, the connection, the equipment and the operating environment. When using, according to the production process to select the patch glue.
2, the composition of the adhesive patch PCB assembly used in most of the surface mount adhesive (SMA) are epoxy resin (epoxies), although there are polypropylene (acrylics) for special purposes. After the introduction of high speed glue system and electronic industry master how to deal with a relatively short shelf life products, epoxy resin has become more mainstream glue technology in the world. Epoxy resins generally provide good adhesion to a wide range of circuit boards and have excellent electrical properties. The main components are: base material (i.e., the main body of high molecular material), fillers, curing agents, other additives, etc..
The use of A. to prevent the components off the 3 wave soldering, the adhesive (wave soldering process) B. reflow prevent the other side off the welding components (double reflow soldering) C. to prevent displacement and vertical components (at the reflow process, pre coating process (D.) marking, wave soldering, reflow soldering pre coated), printed circuit board and component volume change, marked by adhesive.
4, the use of patch glue classification A. dispensing type: through the dispensing equipment on the printed circuit board sizing. B. type: frictioning through steel mesh or copper mesh printing scraping of sizing.
5, another method SMA can use syringe needle glue method, transfer method or template printing method applied to PCB. Needle transfer method is less than 10% of all applications, it is the use of needle array dipped in the glue tray. Then the suspension of the glue drops is transferred to the board as a whole. These systems require a lower viscosity of the glue, but also a good resistance to moisture absorption, because it exposed in the indoor environment. Control the key factors including the glue needle transfer needle diameter and style, glue temperature, immersion depth and needle glue cycle length (including before and during needle contact PCB delay time). The bath temperature should be between 25~30 and C, which controls the viscosity and the number and form of the glue.
Stencil printing is widely used in solder paste and also can be used with dispensing adhesives. Although less than 2% of SMA is currently in print, the interest in this approach has increased, and new devices are overcoming some of the limitations of the earlier ones. The correct template parameters is the key to achieve good results. For example, contact printing (off board height) may require a delay period that allows for good glue point formation. On the other hand, it is necessary to optimize the squeegee speed and pressure for the non contact printing (about 1mm gap) of the polymer template. The thickness of the metal template is generally 0.15~2.00mm, should be slightly larger than (+0.05mm) the gap between the element and PCB.
The temperature will affect the viscosity and gel point shape, temperature control device of most modern machines depend on the glue needle mouth or chamber to keep the adhesive temperature higher than room temperature. However, if the PCB temperature is improved from the previous process, the gel profile may be impaired.