We know that the main purpose of SMT patch coating is to accurately apply glue or solder paste on the PCB so that the components mounted in the patch process can be glued to the PCB pads. According to the different coating methods, the surface coating process can be divided into the following types:

According to the different composition of SMT patch processing solder paste and patch adhesive, solder paste coating usually adopts stencil screen printing process, spraying process, and dot coating process; patch adhesive coating usually adopts injection dot coating process and needle transfer process. The preferred order of printing process, stencil screen printing process, solder paste and patch glue coating process are stencil screen printing process and injection dot coating process respectively. Here we mainly introduce the related content of patch glue coating.

SMD glue is also called adhesive. In hybrid assembly, surface mount components are temporarily fixed on the PCB land pattern to facilitate subsequent wave soldering and other processes to proceed smoothly. In the double-sided surface assembly process, the surface mount components are assisted to fix the surface mount components to prevent the surface mount components from falling due to vibrations during the flip and process operations. In the double-sided reflow soldering process, in order to prevent the large components that have been soldered on the PCB surface from falling due to the heat and melting of the soldering, they also need to be fixed with patch glue before mounting.

The application of the patch glue refers to the application of the patch glue to the designated area of the PCB. The application of the patch glue can use the dispenser dot coating process, the needle transfer process and the offset printing process. ①The dispensing process of the dispenser refers to applying the patch glue drop by drop on the PCB mounting surface where the components are mounted. The principle is to install the patch glue in the needle tube, attach the dispensing nozzle to the head of the needle tube, and then install the needle tube on the dispenser. The dispenser is controlled by a computer and is similar to the placement machine. It automatically dispenses the glue. Go to the designated position on the PCB.

②Needle transfer process refers to the simultaneous transfer of the patch adhesive to all parts of the PCB mounting surface mount components. The principle is to install several needles on the metal plate, each needle is aligned with the position where the patch glue is to be applied, and the needle bed is immersed in a groove containing the patch glue before coating, the depth of which is about 1.2~2mm, Then move the needle bed to the PCB and press it down gently. When the needle bed is lifted, the glue will be transferred to the PCB due to capillary action and surface tension effects. The amount of glue depends on the diameter of the needle and the size of the patch glue. Determined by viscosity.

③The offset printing process is similar to the solder paste printing process. The offset printing process is also called the screen/stencil printing process. The principle, process and equipment of applying SMT glue are similar to those of solder paste printing. It distributes the patch glue to the PCB through the screen/template of the leakage pattern. The coating process is controlled by the viscosity of the glue and the thickness of the template.

The above is the introduction of the SMT patch coating process, the following is a brief introduction to the use of the coating equipment. When applying solder paste or patch glue, SMT processing plants generally use large-scale automation equipment, such as printing machines, glue dispensers, and paste dispensers, for mass production. For small batches or manual coating, desktop dispensers or paste dispensers, desktop printers or even manual coating are usually used.

The above is some basic knowledge about SMT processing and coating technology and equipment shared by Sanjing. I hope that you can have a better understanding of SMT.