SMT production process

　　The basic elements of SMT process include: screen printing (or dispensing), mounting (curing), reflow soldering, cleaning, testing, and rework.

　　1. Silk screen printing: Its function is to print solder paste or patch glue onto the pads of PCB to prepare for the welding of components. The equipment used is a silk screen printer (screen printer), which is located at the forefront of the SMT production line.

　　2. Glue dispensing: It is to drip glue onto the fixed position of PCB. Its main function is to fix the components to the PCB. The equipment used is a glue dispensing machine, which is located at the front end of the SMT production line or behind the testing equipment.

　　3. Mounting: Its function is to accurately install surface mounted components on the fixed position of the PCB. The equipment used is a placement machine, which is located behind the screen printer in the SMT production line.

　　4. Curing: Its function is to melt the patch glue so that the surface mounted components and the PCB board are firmly bonded together. The equipment used is a curing oven, which is located behind the patch machine in the SMT production line.

　　5. Reflow soldering: Its function is to melt the solder paste so that the surface mounted components and the PCB board are firmly bonded together. The equipment used is a reflow oven, which is located behind the placement machine in the SMT production line.

　　6. Cleaning: Its function is to remove the soldering residues such as flux that are harmful to the human body on the assembled PCB board. The equipment used is a cleaning machine, which can be located in an unfixed position and can be online or offline.

　　7. Inspection: Its function is to inspect the welding quality and assembly quality of the assembled PCB board. The equipment used includes magnifying glass, microscope, online tester (ICT), flying probe tester, automatic optical inspection (AOI), X-RAY inspection system, functional tester, etc. The location can be configured at a suitable place on the production line according to the needs of the inspection.

　　8. Rework: Its function is to rework the PCB board that has been detected to be faulty. The tools used are soldering iron, rework workstation, etc. It can be configured at any position in the production line.

　　1. Single-sided assembly:

　　Incoming material inspection => Silk screen solder paste (applying SMD glue) => SMD => Drying (curing) => Reflow soldering => Cleaning => Inspection => Rework

　　2. Double-sided assembly:

　　A: Incoming material inspection => Silk screen solder paste (apply SMD glue) on PCB A side => SMD => Drying (curing) => Reflow soldering on A side => Cleaning => Flip board => Silk screen solder paste (apply SMD glue) on PCB B side => SMD => Drying => Reflow soldering (preferably only on B side => Cleaning => Inspection => Rework)

　　This process is suitable for mounting larger SMDs such as PLCC on both sides of the PCB.

　　B: Incoming material inspection => Silk screen solder paste on PCB A side (apply SMD glue) => SMD => Drying (curing) => Reflow soldering on A side => Cleaning => Flip board => Apply SMD glue on PCB B side => SMD => Curing => Wave soldering on B side => Cleaning => Inspection => Rework)

　　This process is suitable for reflow soldering on the A side of the PCB and wave soldering on the B side. This process is suitable for SMDs assembled on the B side of the PCB when there are only SOT or SOIC (28) pins or less.

　　3. Single-sided mixed loading process:

　　Incoming material inspection => PCB A-side screen printing solder paste (applying SMD glue) => SMD => drying (curing) => reflow soldering => cleaning => plug-in => wave soldering => cleaning => inspection => rework

　　4. Double-sided mixed loading process:

　　A: Incoming material inspection => PCB B side SMD glue => SMD => Curing => Flip board => PCB A side plug-in => Wave soldering => Cleaning => Inspection => Rework

　　Mount first and insert later, suitable for situations where there are more SMD components than discrete components

　　B: Incoming material inspection => PCB A side plug-in (pin bending) => flip board => PCB B side SMD glue => SMD => curing => flip board => wave soldering => cleaning => inspection => rework

　　Insert first and then mount, suitable for situations where there are more discrete components than SMD components

　　C: Incoming material inspection => Silk screen solder paste on PCB A side => SMT => Drying => Reflow soldering => Plug-in, pin bending => Flip board => Apply SMT glue on PCB B side => SMT => Curing => Flip board => Wave soldering => Cleaning => Inspection => Rework mixed assembly on A side and SMT on B side.

　　D: Incoming material inspection => Apply SMD glue to PCB B side => SMD => Curing => Turn over => Screen printing solder paste on PCB A side => SMD => Reflow soldering on A side => Plug-in => Wave soldering on B side => Cleaning => Inspection => Rework A side mixed assembly, B side mounting. First mount SMD on both sides, reflow soldering, then plug-in, wave solderingE: Incoming material inspection => Screen printing solder paste on PCB B side (apply SMD glue) => SMD => Drying (curing) => Reflow soldering => Turn over => Screen printing solder paste on PCB A side => SMD => Drying=Reflow soldering 1 (local soldering can be used) => Plug-in => Wave soldering 2 (if there are few plug-in components, manual soldering can be used) => Cleaning => Inspection => Rework A side mounting, B side mixed assembly.

　　5. Double-sided assembly process:

　　A: Incoming material inspection, screen printing solder paste (applying SMD glue) on the A side of PCB, SMD, drying (curing), reflow soldering on the A side, cleaning, and flipping; screen printing solder paste (applying SMD glue) on the B side of PCB, SMD, drying, reflow soldering (preferably only on the B side, cleaning, inspection, and rework)

　　This process is suitable for mounting larger SMDs such as PLCC on both sides of the PCB.

　　B: Incoming material inspection, screen printing solder paste on the A side of the PCB (applying SMD glue), SMD, drying (curing), reflow soldering on the A side, cleaning, flipping; applying SMD glue on the B side of the PCB, SMD, curing, wave soldering on the B side, cleaning, inspection, rework) This process is suitable for reflow soldering on the A side of the PCB and wave soldering on the B side. This process is suitable for SMDs assembled on the B side of the PCB when there are only SOT or SOIC (28) pins or less.