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The solder paste screen printer is the core equipment of an SMT (Surface Mount Technology) production line. It is responsible for precisely printing solder paste onto the PCB pads, laying the foundation for subsequent component placement and reflow soldering. The industry believes that more than 60% of the SMT soldering yield depends on the printing quality.

I. Core Functions and Significance

Precise Transfer of Solder: Through the stencil openings, quantitative solder paste is transferred to the pads to prevent defects such as insufficient solder (cold solder) and excessive solder (short circuit).

Patterned Printing: Ensure that the solder paste only covers the pad areas without contaminating other parts of the PCB.

Impact on Overall Yield: Printing defects are the main source of SMT failures, directly related to the reliability of electronic products.

II. Working Principle and Process

PCB Loading and Positioning: The conveyor system sends the PCB to the workbench, where it is fixed by a vacuum or mechanical fixture.

Visual Alignment: High-definition cameras identify the fiducial marks of the PCB and stencil, and automatically fine-tune the stencil to achieve precise alignment at the ±15~25μm level.

Solder Paste Printing: The squeegee pushes the solder paste at an angle of 30°~60° with constant pressure, making it fill the stencil openings and transfer to the pads.

Stencil Peeling and Output: The stencil peels vertically at a speed of 0.5~1mm/s, and the PCB is sent to the placement machine.

Stencil Cleaning: Automatic wiping + vacuum recovery is used to remove residual solder paste and avoid clogging of the openings.

III. Main Structural Components

Frame and Conveyor System: A high-precision base + guide rail ensures smooth PCB transportation and high repeated positioning accuracy.

Stencil System: Includes stencils (laser/electroformed/etched), clamping and cleaning mechanisms; the stencil openings determine the pattern and dosage of the solder paste.

Printing Head (Squeegee System): A servo-driven squeegee that can adjust the pressure (0~6kgf/cm²), speed and angle; divided into metal scrapers (durable) and polyurethane scrapers (good adaptability).

Visual Positioning System: High-resolution cameras + annular light sources + image processing units, supporting 2D/3D alignment and post-printing inspection (SPI).

Control System: PLC + touch screen, programmable to store multi-product parameters, and supports intelligent control of pressure, speed, cleaning cycle, etc.