SMT Process

The SMT (Surface Mount Technology) assembly process, which is the initial stage of PCBA (Printed Circuit Board Assembly) production, involves several critical steps:

First, the solder paste is stirred to ensure its uniformity. This is followed by solder paste printing, where the paste is applied to the PCB surface pads according to a defined pattern. A preliminary check is then performed using an SPI (Solder Paste Inspection) device. Next is component placement, where electronic components are accurately mounted onto their corresponding positions on the PCB. This is succeeded by reflow soldering, which uses heat to create a robust connection between the solder paste and the components. Finally, a thorough and detailed inspection is conducted with an AOI (Automatic Optical Inspection) machine to verify the quality of the placement and soldering. Any defective products identified are then moved to the rework process for correction.

Solder Paste Handling and Printing

Before commencing the SMT process, the solder paste must first be taken out of the refrigerator and thawed. Once thawed, the paste is thoroughly stirred, either manually or with a dedicated mixer, to ensure it achieves the optimal viscosity and consistency for printing and soldering. The solder paste is then uniformly spread across a stencil, and a squeegee is used to gently wipe it across, allowing the paste to be precisely deposited (or "leaked") onto the PCB’s solder pads following the stencil's pattern. SPI (Solder Paste Inspection) equipment is widely used in the solder paste printing process to monitor the deposition in real-time, enabling precise control over the quality of the printed solder paste.

Placement and Reflow Soldering

After the solder paste printing stage, the pick-and-place machine precisely identifies and mounts the surface mount components, which are supplied from feeders, onto the solder paste-covered pads of the PCB. This step is essential for ensuring the assembly accuracy and electrical performance of the circuit board. Once placement is complete, the PCB is transferred into the reflow oven. Within this high-temperature environment, the paste-like solder paste melts, and then cools and solidifies, thereby completing the soldering process. This thermal profile is crucial for establishing strong, reliable solder joints and the overall quality of the circuit board.