What is solder paste inspection?

Solder paste inspection (SPI) is an automated optical inspection (AOI) technique used in printed circuit board (PCB) assembly to verify the volume, shape, and placement of solder paste deposited on the board before component placement. It helps to identify and correct printing defects such as insufficient paste, excessive paste, bridging, or misalignment, preventing downstream issues like shorts, opens, and poor solder joints. SPI systems use various optical techniques, including 2D and 3D imaging, to accurately measure the solder paste deposits.