PCBA Tech - The basic process composition of SMT patch processing

The basic process composition of SMT patch processing includes: silk screen (or glue), placement (curing), reflow soldering, cleaning, inspection, rework silk screen: its function is to leak solder paste or patch glue onto the PCB pads, To prepare for the welding of components. The equipment used is a screen printing machine (screen printing machine), located at the forefront of the SMT production line.

Dispensing: It is to drop the glue onto the fixed position of the PCB, and its main function is to fix the components on the PCB board. The equipment used is a glue dispenser, located at the forefront of the SMT production line or behind the testing equipment.

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

Mounting: Its role is to accurately mount surface mount components to a fixed position on the PCB. The equipment used is a placement machine, located behind the screen printing machine in the SMT line. Production

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

Cleaning: Its function is to remove the solder residues such as flux that are harmful to the human body on the assembled PCB board. The equipment used is a washing machine, and the location may not be fixed, it may be online or offline.

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 in a suitable place on the production line according to the needs of the inspection.

Rework: Its function is to rework the PCB boards that have failed to detect faults. The tools used are soldering irons, rework stations, etc. Configured at any position in the production line.

SMT process inspection:

1. Single-sided assembly:

Incoming material inspection => silk screen solder paste (point patch glue) => patch => drying (curing) => reflow soldering => cleaning => inspection => repair

2. Double-sided assembly:

A: Incoming inspection => PCB's A side silk screen solder paste (point patch glue) => SMD => drying (curing) => A side reflow soldering => cleaning => flipping board => PCB side B Silk screen solder paste (point patch glue) => patch => drying => reflow soldering (best only for side B => cleaning => inspection => repair)

This process is suitable when large SMDs such as PLCC are mounted on both sides of the PCB.

B: Incoming inspection => PCB's A side silk screen solder paste (point patch glue) => SMD => drying (curing) => A side reflow soldering => cleaning => flipping board => PCB side B Point patch glue => patch => curing => B surface wave soldering => cleaning => inspection => repair)

This process is suitable for reflow soldering on the A side of the PCB and wave soldering on the B side. In the SMD assembled on the B side of the PCB, this process should be used when there are only SOT or SOIC (28) pins or less.

3. Single-sided mixed packaging process:

Incoming inspection => PCB's A-side silkscreen solder paste (point patch glue) => SMD => drying (curing) => reflow soldering => cleaning => plug-in => wave soldering => cleaning => inspection = > Rework

4. Double-sided mixed packaging process:

A: Incoming inspection => PCB's B side patch glue => SMD => curing => flip board => PCB A side plug-in => wave soldering => cleaning => inspection => rework

Paste first and insert later, suitable for situations where there are more SMD components than separate components

B: Incoming inspection => PCB's A side plug-in (pin bending) => flip board => PCB's B side patch glue => patch => curing => flip board => wave soldering => cleaning => Inspection => Repair

Insert first, then paste, suitable for the situation where there are more separate components than SMD components

C: Incoming inspection => PCB's A side silk screen solder paste => SMD => Drying => Reflow soldering => Plug-in, pin bending => Turnover => PCB's B side point patch glue => Patch => Curing => Turnover => Wave soldering => Cleaning => Inspection => Rework

A side is mixed, B side is mounted.

D: Incoming inspection => PCB's B side spot patch glue => SMD => curing => flip board => PCB's A side silk screen solder paste => patch => A side reflow soldering => plug-in => B-side wave soldering => cleaning => inspection => repair

A side is mixed, B side is mounted. Paste SMD on both sides first, reflow soldering, then inserting, wave soldering

E: Incoming inspection => PCB's B-side silk screen solder paste (point patch glue) => SMD => drying (curing) => reflow soldering => flip board => PCB's A-side silk screen solder paste => Patch => Drying =>

Reflow soldering 1 (partial soldering can be used) => plug-in => wave soldering 2 (if there are few inserted components, manual soldering can be used) => cleaning => inspection => repair

A-side mounting, B-side mixed mounting.

Five, SMT process ------ double-sided assembly process

A: Incoming inspection, PCB A side silk screen solder paste (point patch glue), patch, drying (curing), A side reflow soldering, cleaning, flipping; PCB B side silk screen solder paste (point patch Glue), patch, drying, reflow soldering (preferably only for side B, cleaning, testing, and rework) This process is suitable for mounting large SMDs such as PLCC on both the PCB sides .

B: Incoming inspection, PCB A side silk screen solder paste (point patch glue), patch, drying (curing), A side reflow soldering, cleaning, flipping; PCB B side point patch glue, patch, Curing, B-side wave soldering, cleaning, inspection, rework)

This process is suitable for reflow soldering on the A side of the PCB and wave soldering on the B side. In the SMD assembled on the B side of the PCB, this process should be used when there are only SOT or SOIC (28) pins or less.