May 20, 2023 
Printing solder paste:
First, fix the circuit board to be printed on the printing positioning table, and then use the front and rear scrapers of the printing machine to pass the solder paste or red glue through the stencil to miss-print the corresponding PCB pads, and input the evenly missed PCB to the next process through the transfer table. Solder paste and patch are both thixotropic and viscous. When the solder paste printing machine moves forward at a certain speed and angle, it will generate a certain pressure on the solder paste and push the solder paste to roll in front of the scraper, resulting in a The pressure required to inject solder paste into a mesh or leak. The viscous friction of the solder paste causes the solder paste to shear at the junction of the squeegee and the stencil of the solder paste printing machine, and the shear force reduces the viscosity of the solder paste, which is conducive to the smooth injection of the solder paste into the stencil opening and leakage.
SPI:
SPI plays a considerable role in the entire SMT placement process. It is a fully automatic non-contact measurement, which is used after the tin printing machine and before the placement machine. Relying on technical means such as structured light measurement and display (mainstream) or laser measurement (non-mainstream), 2D or 3D measurement (micron-level precision) of PCB printed solder. The principle of structured light measurement products: on the object (PCB and tin Sound) Set a high-speed CCD camera in the vertical direction, and use a projector to irradiate periodic fringe light or images to the object from obliquely above. When there are high components on the PCB, it will be photographed that the fringe moves relative to the base surface. Bit image. Using the triangulation principle, the offset value is converted into a degree value.
Pick and Place Machine
The placement machine is configured after the SPI, and it is a device that accurately places surface mount components on the PCB pads by moving the placement head. It is the equipment used to realize high-speed and high-precision placement of components, and it is the most critical and complex equipment in the entire SMT chip processing and production.
Reflow soldering
Reflow soldering is to remelt the solder paste solder pre-distributed on the PCB pad to realize the soldering of the mechanical and electrical connection between the solder end of the surface mount processing component or the pin and the PCB pad. The reflow soldering machine used in the reflow process is at the end of the SMT production line.
AOI
Using the reflection principle of light and the characteristics of different reflection capabilities of copper and substrates for light to form scanning images, the standard image and the actual layer image are compared, analyzed, and judged whether the detected object is OK.
X-ray
The X-ray inspection equipment penetrates the PCBA to be inspected through X-rays and then maps an X-ray image on the image detector. The image formation quality is mainly determined by resolution and contrast. This equipment is generally placed in a separate room in the SMT workshop.
Rework
It is to repair the PCB boards with bad solder joints detected by AOI. Tools used include soldering iron, heat gun, etc. Rework stations can be configured anywhere on the production line.
Cleaning
Cleaning is mainly to remove the flux slag on the processed PCBA board. The equipment used is a cleaning machine, which is fixed at the back end of the line or at the packaging.
Summary of SMT Process Flow
The above content is the process flow of the SMT patch shared by SZTech-SMT for you. I hope it will be helpful to you. To learn more about SMT patch processing, welcome to visit www.sztech-smt.com, https://smtnet.com/
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