Introduction to SMT mounting technology] 2.2.1: SMT assembly process types: single / double-sided surface mounting, single-sided mixed mounting and double-sided mixed mounting.
2.2.2: classification of welding methods: wave soldering – Welding of inserts (DIP) and welding of partial patches (SMC / SMD). Reflow welding – heating methods include infrared, infrared heating wind combination, full hot air heating, etc.
2.2.3: printed circuit board: substrate material – glass fiber, ceramic and metal plate. Circuit board design – graphic design, wiring, gap setting, composition, SDM pad design and layout, 2.2: SMT mounting equipment: screen printing machine, dispensing machine, chip mounter, reflow soldering, wave soldering, detection system and maintenance system
2.2.4 introduction to SMT process flow basic process elements of SMT: silk screen printing (or dispensing) → mounting → (curing) → reflow welding → cleaning → detection → repair silk screen printing: its function is to leak solder paste or patch adhesive onto PCB pad to prepare for component welding. The equipment used is screen printing machine (screen printing machine), which is located at the front end of SMT production line.
Dispensing: it drips glue to the fixed position of PCB. Its main function is to fix components to PCB. The equipment used is a dispensing machine, which is located at the front end of the SMT production line.
Mounting: its function is to accurately install the surface assembled components to the fixed position of PCB. The equipment used is the mounter, which is located behind the screen printing machine in the SMT production line. Curing: its function is to melt the patch adhesive, so as to firmly bond the surface assembled components with the PCB board. The equipment used is a curing furnace, which is located behind the mounter in the SMT production line.
Reflow soldering: its function is to melt the solder paste and firmly bond the surface assembled components with the PCB board. The equipment used is the reflow furnace, which is located behind the mounter in the SMT production line.
Cleaning: its function is to remove the welding residues harmful to human body, such as flux, on the assembled PCB. The equipment used is a cleaning machine, and the position can be fixed, online or offline. The cleaning agent can be HCFC-141b or NPB. Inspection: its function is to inspect the welding quality and assembly quality of the assembled PCB. The equipment used include magnifying glass, microscope, on-line tester (ICT), flying needle tester, automatic optical inspection (AOI), X-ray inspection system, function tester, etc. The position can be configured in the appropriate place of the production line according to the needs of detection.
Repair: its function is to rework the PCB board that is detected to be faulty. The tools used are soldering iron, repair workstation, etc. Configure anywhere in the production line.
II. Characteristics and current development trends of SMT