With the development trend of miniaturization and thinness of electronic products, many circuit boards in electronic products now adopt SMT manufacturing technology, that is, surface mount technology, that is, all electronic components are attached to the surface of circuit boards. There is no need to insert it through the reserved via hole on the circuit board and then solder it from the back as before.
SMT technology can make the production process of circuit board more automatic and rapid, and reduce human intervention. Moreover, compared with the previous plug-in, the components used in this technology have the advantages of smaller volume, lighter weight and stronger reliability.
An SMT production line includes the following main parts: printing press, mounter, reflow oven, cooling equipment and some auxiliary optical inspection equipment, cleaning equipment, drying equipment and material storage equipment.
Let’s take a look at how a circuit board with SMT technology is produced.
Firstly, according to the electronic material list of the circuit board to be produced, prepare the electronic components to be used and install them on the mounter. The installation method is to install the materials on the feeder, and then insert the feeder into the corresponding area of the mounter. It is fixed where the materials of what material number are placed, which was set by the technicians when writing the program before production. The prepared materials are waiting for the boards flowing down the assembly line.
The circuit board that comes out is called PCB board, which has no parts. The PCB needs to be manually attached to a supporting board one by one by an employee, and several PCB boards are placed on each supporting board, which needs to be decided according to the size of the board.
The pallet for loading PCB is made of a high-temperature resistant material. This pallet will load the PCB through the whole production process, and then the employees at the end of the assembly line will take down the PCB with installed parts, and the empty pallet will return to the thread end.
The first battle of the production line is to solder these PCB boards, that is, to cover the top of these boards with steel mesh, which has holes. These holes face the place where components need to be installed on the PCB board, and this place is the solder pad. The solder joints between components and PCB are evenly brushed through the whole steel mesh by a scraper controlled by a machine. At this time, the solder paste with the thickness of the steel mesh will cover the solder pad on the PCB.
The whole pallet will be loaded with PCB printed with tin and flow into the next station through the conveying track, followed by the chip mounter station that has been waiting here for a long time. The components have already been installed in the machine. At this time, the machine will install the components on the designated position of the PCB board according to the program written in advance by technicians. The installation process is actually like holding a feeder, sucking electronic materials one by one from the feeder and putting them on the PCB. Of course, this absorption speed is countless times that of human beings, and the error will not exceed one twentieth of the component size.
PCB with electronic components installed is waiting to flow into the next station.
When the mounter has installed all the electronic components, the pallet will carry the PCB loaded with these components and flow into the last station in the manufacturing process, the high-temperature reflow furnace. The temperature in this furnace is enough to melt the solder paste, and the melted tin will firmly weld the components and PCB together.
Back to the entrance of the soldering furnace, the PCB with components attached will be sent into the furnace through the track.
The board flowing out of the reflow oven has a high temperature, and it needs to be cooled by a cooling device before it can flow to the final optical inspection station. After the end of this station, the manufacturing process of the electronic circuit board is basically completed, and then the manufactured circuit board is inspected.
After cooling, the manufactured PCB board on the pallet flows into the optical inspection equipment, and optical inspection is carried out to confirm whether the welding between components and PCB is good and whether there are defects.
After the inspection of the optical equipment, the final visual inspection will be carried out, and the electronic magnifying glass will be used to make the final confirmation of the welding status of the circuit board.
Finally, the staff at the end of the line will take the inspected circuit board off the pallet and put it into a special plastic tray. The whole production process is over.
