Utilization of sensory feedback during SMT assembly

This paper investigates the insertion of inline sensors into Surface Mount Technology (SMT) production lines for the purpose of improving yield and reducing production costs by elevating the quality level of the product to the six sigma level. Each process step in the assembly process, starting with board loading, through deposition, part placement, and reflow will be discussed for monitoring in real time for deviations. When deviations are detected, feedback can be sent either to operators or the equipment for corrective action thus providing a closed loop SMT assembly process. A study of an SMT assembly line indicates that video surveillance at the beginning of the line can be used to inspect the quality of the Printed Wire Boards (PWBs) before additional processing actions are taken on them. Similar surveillance techniques employed in the deposition stage to ensure that only PWBs with proper solder paste deposition are allowed to continue will be discussed. The parts placement stage provides many opportunities for the placement of inline sensors ranging from inspection of the parts for defects and orientation errors before they are placed to determining their exact position on the PWB after they have been placed. The potential of similar placement monitoring techniques before and after reflow for monitoring this process are explored.