SMT Process of PCB

What is SMT?

SMT is a surface mount technology (surface mount technology), which is currently the most popular technology and process in the electronics assembly industry.

It is a kind of surface assembly component with no leads or short leads (SMC/SMD for short, chip components in Chinese) mounted on the surface of a printed circuit board (Printed Circuit Board, PCB) or the surface of other substrates. Circuit assembly technology in which reflow soldering or dip soldering is used for soldering and assembly.

Process composition

Printing (red glue/solder paste) --> inspection (optional AOI automatic or visual inspection) --> placement (first paste small devices and then paste large devices: divided into high-speed placement and integrated circuit placement) - >Inspection (optional AOI optical/visual inspection)-->Welding (using hot air reflow soldering for soldering)-->Inspection (can be divided into AOI optical inspection appearance and functional test inspection)--> Maintenance (use tool: welding Table and hot-air desoldering station, etc.)--> board splitting (cutting the board manually or by a splitting machine)

The process flow is simplified as: printing-------patch-------welding-------overhaul (testing links can be added to each process to control quality)

• Solder paste printing

Its function is to print the solder paste on the pads of the PCB with a scraper at a 45-degree angle to prepare for the soldering of the components. The equipment used is a printing machine (a solder paste printing machine), located at the forefront of the SMT production line.

• Folding parts placement

Its function is to accurately install the surface mount components to the fixed position of the PCB. The equipment used is a placement machine, which is located behind the printing machine in the SMT production line. Generally, high-speed machines and general-purpose machines are used in combination according to production requirements.

• Folding reflow soldering

Its function is to melt the solder paste, so that the surface mount components and the PCB are firmly welded together. The equipment used is a reflow oven, which is located behind the placement machine in the SMT production line. The temperature requirements are quite strict and need to be measured in real time. The measured temperature is reflected in the form of a profile.

• Folding AOI optical inspection

Its function is to inspect the welding quality of the welded PCB. The equipment used is an automatic optical inspection machine (AOI), and the position can be configured in a suitable place on the production line according to the needs of inspection. Some are before reflow soldering, and some are after reflow soldering.

• Folding repair

Its function is to repair the PCB that is faulty. The tools used are soldering irons, rework stations, etc. Configured after AOI optical inspection.

• Folding sub-board

Its function is to cut the multi-connected PCBA into individual individuals, generally using V-cut and machine cutting methods.